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IEA Task 21

APPLICATION GUIDEFOR DAYLIGHTRESPONSIVE LIGHTINGCONTROL

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D a y l i g h t i n B u i l d i n g s Solar Heating & Cooling Programme

Daylighting in buildingsIEA

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International Energy AgencyTask 21, Subtask BFebruary 2001

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Application guide for daylight responsive lighting control

PREFACE PREFACE

International Energy Agency

The International Energy Agency (IEA) wasestablished in 1974 within the framework of theOrganisation for Economic Co-operation andDevelopment (OECD) to implement anInternational Energy Programme. A basic aim ofthe IEA is to foster co-operation among thetwenty-one IEA Participating Countries toincrease energy security through energyconservation, development of alternative energysources and energy research development anddemonstration (RD&D).

IEA Solar Heating and Cooling Programme

An important part of the Agency’s programinvolves collaboration in the research,development and demonstration of new energytechnologies to reduce excessive reliance onimported oil, increase long-term energy securityand reduce greenhouse gas emissions. TheIEA’s R&D activities are headed by theCommittee on Energy Research and Technology(CERT) and supported by a small Secretariatstaff, headquartered in Paris. In addition, threeWorking Parties are charged with monitoring thevarious collaborative energy agreements,

identifying new areas for cooperation and advising theCERT on policy matters.

Collaborative programs in the various energytechnology areas are conducted under ImplementingAgreements, which are signed by contracting parties(government agencies or entities designated by them).There are currently 40 Implementing Agreementscovering fossil fuel technologies, renewable energytechnologies, efficient energy end-use technologies,nuclear fusion science and technology, and energytechnology information centers.

The Solar Heating and Cooling Programme was one ofthe first IEA Implementing Agreements to beestablished. Since 1977, its 20 members have beencollaborating to advance active solar, passive solar andphotovoltaic technologies and their application inbuildings.

Australia Finland NorwayAustria France SpainBelgium Italy SwedenCanada Japan SwitzerlandDenmark Mexico United KingdomEuropean Netherlands United States CommissionGermany New Zealand

A total of 26 Tasks have been initiated, 19 of whichhave been completed. Each Task is managed by anOperating Agent from one of the participating countries.Overall control of the program rests with an ExecutiveCommittee comprised of one representative from each

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contracting party to the Implementing Agreement.In addition, a number of special ad hoc activities—working groups, conferences and workshops—havebeen organized.

The Tasks of the IEA Solar Heating and CoolingProgramme, both completed and current, are asfollows:

Completed Tasks:Task 1 Investigation of the Performance of Solar

Heating and Cooling SystemsTask 2 Coordination of Solar Heating and Cooling

R&DTask 3 Performance Testing of Solar CollectorsTask 4 Development of an Insolation Handbook

and Instrument PackageTask 5 Use of Existing Meteorological Information

for Solar Energy ApplicationTask 6 Performance of Solar Systems Using

Evacuated CollectorsTask 7 Central Solar Heating Plants with Seasonal

StorageTask 8 Passive and Hybrid Solar Low Energy

BuildingsTask 9 Solar Radiation and Pyranometry StudiesTask 10 Solar Materials R&DTask 11 Passive and Hybrid Solar Commercial

BuildingsTask 12 Building Energy Analysis and Design Tools

for Solar ApplicationsTask 13 Advance Solar Low Energy BuildingsTask 14 Advance Active Solar Energy SystemsTask 16 Photovoltaics in BuildingsTask 17 Measuring and Modeling Spectral RadiationTask 18 Advanced Glazing and Associated

Materials for Solar and Building Applications

Task 19 Solar Air SystemsTask 20 Solar Energy in Building Renovation

Completed Working Groups:CSHPSSISOLDEMaterials in Solar Thermal Collectors

Current Tasks:Task 22 Building Energy Analysis ToolsTask 23 Optimization of Solar Energy Use in Large

BuildingsTask 24 Solar ProcurementTask 25 Solar Assisted Air Conditioning of BuildingsTask 26 Solar CombisystemsTask 27 Performance of Solar Facade ComponentsTask 28 Solar Sustainable HousingTask 29 Solar Crop DryingTask 30 Solar City (Task Definition Phase)

Current Working Groups:Evaluation of Task 13 HousesPV/Thermal Systems (Definition Phase)

To receive a publications catalogue or learn moreabout the IEA Solar Heating and Cooling Programmevisit our Internet site at http://www.iea-shc.org orcontact the SHC Executive Secretary, PamelaMurphy, Morse Associates Inc., 1808 CorcoranStreet, NW, Washington, DC 20009, USA, Tel: +1/202/483-2393, Fax: +1/202/265-2248, E-mail:[email protected].

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Energy Conservation in Buildings andCommunity Systems (ECBCS)

The IEA sponsors research and development ina number of areas related to energy. In one ofthese areas, energy conservation in buildings,the IEA is sponsoring various exercises to predictmore accurately the energy use of buildings,including comparison of existing computerprograms, building monitoring, comparison ofcalculation methods, as well as air quality andstudies of occupancy.The Executive CommitteeOverall control of the programme is maintainedby an Executive Committee, which not onlymonitors existing projects but also identifies newareas where collaborative effort may be beneficial.To date the following have been initiated by theExecutive Committee (completed projects areidentified by *):

1 Load Energy Determination of Buildings*2 Ekistics and Advanced Community

Energy Systems *3 Energy Conservation in Residential

Buildings *4 Glasgow Commercial Building

Monitoring*5 Air Infiltration and Ventilation Centre6 Energy Systems and Design of

Communities *7 Local Government Energy Planning *8 Inhabitant Behaviour with Regard to

Ventilation *9 Minimum Ventilation Rates *

10 Building HVAC Systems Simulation *11 Energy Auditing *12 Windows and Fenestration *13 Energy Management in Hospitals *14 Condensation *15 Energy Efficiency in Schools *16 BEMS - 1: Energy Management Procedures *17 BEMS - 2: Evaluation and Emulation

Techniques *18 Demand Controlled Ventilating Systems *19 Low Slope Roof Systems *20 Air Flow Patterns within Buildings *21 Thermal Modelling *22 Energy Efficient Communities *23 Multi-zone Air Flow Modelling (COMIS) *24 Heat Air and Moisture Transfer in Envelopes *25 Real Time HEVAC Simulation *26 Energy Efficient Ventilation of Large

Enclosures*27 Evaluation and Demonstration of Domestic

Ventilation Systems28 Low Energy Cooling Systems*29 Daylight in Buildings30 Bringing Simulation to Application31 Energy Related Environmental Impact of

Buildings32 Integral Building Envelope Performance

Assessment33 Advanced Local Energy Planning34 Computer-aided Evaluation of HVAC System

Performance35 Design of Energy Efficient Hybrid Ventilation

(HYBVENT)

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TNO-TUECentre for Building ResearchP O Box 5135600 MB Eindhoven, The Netherlands

Philips Lighting BVP O Box 800205600 JM Eindhoven, The Netherlands

Etap Lighting N.V.Antwerpsesteenweg 130B-2390 Malle, Belgium

Technische Universität BerlinInstitut für Elektronik und LichttechnikFG Lichttechnik, Sekr. E6Einsteinufer 1910587 Berlin, Germany

Delft University of TechnologyFaculty of ArchitectureP O Box 50432600 GA Delft, The Netherlands

ENEA, SIRESystems and Components for Energy SavingsCasaccia00060 S.M. di Galeria, Roma, Italy

ENTPE/DGCBRue Maurice Audin69518 Vaulx-en-Velin, Cedex, France

SEFAS7491 Trondheim, Norway

Helsinki University of TechnologyOtakaari 5 A02150 Espoo, Finland

Contributors to this application guide:

Laurens Zonneveldt TNO-TU EindhovenHeiko Belendorf TU BerlinBjørn Brekke SEFASCatherine Laurentin ENTPEShauna Mallory-Hill TNO-TU EindhovenFerdinando Raponi ENEAFrans Taeymans Etap LightingAriadne Tenner Philips LightingMartine Velds TU Delft

Participating institutions, IEA Task 21, Subtask B

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TABLE OF CONTENTS TABLE OF CONTENTS

EXECUTIVE SUMMARY .................................................................................................. 5

GENERAL INTRODUCTION ............................................................................................ 7

CONTROL SYSTEMS ..................................................................................................... 11

2.1 Introduction .............................................................................................................. 112.2 Properties of daylight. .............................................................................................. 11

2.2.1 Thermal aspects of daylighting ...................................................................... 112.2.2 Psycho-physiological aspects of daylighting.................................................. 11

2.3 Daylight control systems .......................................................................................... 122.3.1 Manual control systems for daylight control .................................................... 122.3.2 Automatic systems for daylight control .......................................................... 12

2.4 Objectives to use daylight responsive artificial lighting control systems..................... 132.4.1 Energy savings and durability. ....................................................................... 142.4.2 Economics ................................................................................................... 142.4.3 Comfort ........................................................................................................ 15

2.5 Control strategies .................................................................................................... 152.5.1 Control principles. ........................................................................................ 152.5.2 Level of control ............................................................................................. 16

2.6 Daylight responsive control systems for artificial lighting .......................................... 172.6.1 Working principle .......................................................................................... 17

DECISION SUPPORT IN THE SELECTION OF CONTROL SYSTEMS ......................... 19

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3.1 Introduction .............................................................................................................. 193.2 Is daylight responsive control feasible? .................................................................... 19

3.2.1 Lighting demands ......................................................................................... 203.2.2 Daylight availability ....................................................................................... 203.2.3 Electric Lighting System ............................................................................... 22

3.3 Which control system? ............................................................................................. 223.3.1 Control requirements .................................................................................... 223.3.2 Economics ................................................................................................... 233.3.3 Ergonomics .................................................................................................. 253.3.4 Decision table .............................................................................................. 26

PREDICTION OF ENERGY SAVINGS AND COSTS ....................................................... 29

4.1 Introduction .............................................................................................................. 294.2 Frequency method to predict direct savings from daylight responsive controls ......... 32

4.2.1 Reference situation for energy use ................................................................ 344.2.2 Electric lighting ............................................................................................. 34

4.3 Calculating the energy saving potential .................................................................... 364.3.1 TU Berlin method for describing and predicting the energy saving potential ... 36

4.3.1.1 Room potential ................................................................ 364.3.2 Availability of daylight .................................................................................... 37

4.3.2.1 Relative usable light exposure ........................................ 374.3.2.2 System potential ............................................................. 38

4.3.4 The average sky condition ............................................................................ 384.4 A simplified method to characterise the efficiency of daylight systems ..................... 38

4.4.1 Introduction ................................................................................................... 384.4.2 Calculation method ....................................................................................... 404.4.3 Explanation of the calculation ........................................................................ 404.4.4 Examples ..................................................................................................... 414.4.5 Results and conclusions................................................................................ 41

4.5 Laboratory Test Methods - Daylighting Box .............................................................. 44

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4.5.1 Experimental set-up ...................................................................................... 444.5.2 What is recorded? ........................................................................................ 454.5.3 Evaluations ................................................................................................... 454.5.4 Application ................................................................................................... 45

4.6 Scale model testing of daylight responsive lighting control systems.......................... 45

USER REACTIONS TO DAYLIGHT RESPONSIVE CONTROLLED LIGHTING ............ 47

5.1 Introduction .............................................................................................................. 475.2 User awareness ...................................................................................................... 475.3 Acceptance ............................................................................................................. 485.4 Things to remember ................................................................................................ 48

INSTALLATION PROCEDURES...................................................................................... 51

6.1 Introduction .............................................................................................................. 516.2 Installing sensors for closed loop systems ................................................................ 516.3 Installing sensors for open loop systems .................................................................. 516.4 Installing Luminaires with built-in sensors ................................................................. 526.5 Installing room-based systems ................................................................................. 536.6 Installing building-based systems............................................................................. 546.7 System awareness .................................................................................................. 556.8 Selecting a consultant .............................................................................................. 55

MAINTENANCE AND FLEXIBILITY ................................................................................ 57

7.1 Introduction .............................................................................................................. 577.2 The first stage: evaluation of initial performance ....................................................... 587.3 Changes in the required lighting conditions .............................................................. 587.4 Ageing of components............................................................................................. 59

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7.5 Malfunctioning of components.................................................................................. 607.6 Maintenance program ............................................................................................. 60

DESIGN EVALUATION..................................................................................................... 63

8.1 Introduction .............................................................................................................. 638.2 Evaluation of the design........................................................................................... 63

8.2.1. Technical evaluation ...................................................................................... 638.2.2 Maintained illuminance level ......................................................................... 638.2.3 Energy savings ............................................................................................. 63

8.3 User acceptance evaluation .................................................................................... 64

OUTLOOK ........................................................................................................................ 65

FURTHER READING ....................................................................................................... 67

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EXECUTIVE SUMMARY EXECUTIVE SUMMARY

Daylight responsive control of lightingapplies both to the control of the artificiallight and dynamic control of the distributionand amount of daylight. Objectives for usingdaylight responsive controls are energysavings, visual comfort and reduction ofcost. It is a prerequisite that windows areused as a light source, not just for a view.Also proper integration of daylight andartificial lighting is important. The eventualsavings depend very much on the behaviorof the user.

Finding the right solution

The best approach to come at a goodsolution is to first optimize daylight in termsof levels and distribution in the space. Thisdoes not mean that daylight will supplysufficient light for illuminating the room andthe visual task(s) all the time and thuseliminating the need for artificial light. Itmeans to look for a solution that gives asignificant contribution of daylight, with littleannoyance for the user. Typically a daylightfactor of 1-3% up to two times the roomheight from the façade is a suitable target.

Daylight systems will in general not improve theamount of daylight but are often needed toimprove the distribution of the light and avoidglare.

Control of daylight is mostly manual. Automaticcontrol is often based on illuminance/irradianceof the façade. This criterion is used to avoid directsunlight entering the space. Only very few stillexperimental systems exist that really intent tocontrol daylight conditions in the interior and arebased on criteria related to visual comfort otherthan avoiding direct sunlight.

Electric lighting and daylight have to cooperatein order to achieve the goals of energy efficiencyand good visual comfort. Therefore the layout ofthe electric lighting has to be designed in such away that suitable zones are created and daylightis supplemented in each zone. The daylightresponsive control system of the electric lightinghas to take care of this. There is quite a varietyof daylight responsive control systems forartificial lighting on the market. The main objectiveof this guide is to support the user in selection,installation and maintenance of such a system.

What are the benefits?

Daylight responsive controls systems may giveyou significant savings on electricity for lightingat an unaffected visual comfort level. In a number

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of practical demonstrations energy andcomfort aspects are evaluated. In theconclusions of this book it is shown that theactual savings from different types of systemsdo not differ much: almost all systems save asignificant amount of energy. More essentialdifferences between systems are in the userinterface and adaptability to user demands.

Once the step is taken to install daylightresponsive lighting at little more cost otheradvanced controls may be available. Not onlycontrols for lighting but, in the case of buildingbased systems, control over shading mayalso be made available to individual users.Also when the users are absent (e.g. at night)the controls may be used for climatic controlof the building.

What will be the future?

As can be seen in this guide thedevelopments in electric lighting controls haveled to a vast number of satisfactory performingsystems. The actual savings from thesesystems strongly depend on the use ofshading. Future developments therefore willbe more in the direction of improved daylightsystems that are adjustable, or automaticallyadjusting to daylight availability. This willincrease the benefits of daylight responsive

lighting even further and will also lead to optimizeworking conditions with respect to visualcomfort and thermal environment. Currentdevelopments aim at more distributed logicreplacing the centrally controlled systems. Thecentral computer is then mostly used forissuing building wide commands, inputs andmonitoring performance.

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CHAPTER1 GENERAL INTRODUCTION

Daylight is generally preferred above electriclighting. It is free and has perfect colour renderingand a positive effect on human well-being.Daylight is associated with a view on the weatherand the exterior. Moreover daylight is a dynamicin many ways. A lighting designer, who intendsto illuminate demanding visual tasks, such asfound in office work, with daylight, should takespecial care.Daylight consists of three components. The firstdaylight component is the direct beam from thesun. The second is the daylight scattered in theatmosphere (including clouds) resulting in thediffuse sky component. Thirdly some daylightcomes from reflections on the ground and objectsin the exterior environment. Daylight is by itsnature a source that varies constantly in intensity,colour and luminance distribution. Thesevariations of daylight are characterised in timeby periodical and random variations on sometypical time scales (see insert).Using daylight as a source for illuminating tasksin the working environment demands specialmeans to handle this dynamically changingsource. Generally the continuous variations indaylight availability require adaptable shadingdevices and electric lighting systems to keepluminance ratios and variations in the interiorwithin the acceptable bounds.Often daylighting systems are used. Adaylighting system is an adaptation of a plane

clear daylight opening in order to distribute daylight ina space and/or reduce the luminance of that daylightopening. Even if the most ideal daylighting system isinstalled, it is always necessary to provide electriclighting. At night, or on dark winter days, electriclighting must be able to provide all necessary lighting.During the day whenever daylighting provides aninsufficient or incorrect distribution for a particular task,electric lighting will be used as additional source oflight. Daylight responsive lighting controls are aninvaluable tool to supply the right amount of electriclight there and when it is needed.The use of automatic daylighting or electric lightingcontrols will have influence on the energy balance of abuilding. Daylight responsive controls will provide ameans to optimally benefit of the natural light source,and thus energy will be saved. On the other hand, thecontrol electronics and sensors also use energy. Thisenergy use for the controls can be significant (up to10% of all energy for lighting) in cases where complexbuilding management systems with additional controlssuch as occupancy sensors are used in combinationwith highly efficient lighting. Also the use of daylightlinked lighting control will have an influence on theenergy used for heating and cooling of the building.The balance between these factors should be carefullyestimated.

Objectives of this application guide

The purpose of this book is to guide designers inselecting, installing, and using daylight responsive

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devices for daylight as well as for electric lighting.As these systems are relatively new and manyaspects of their implementation and use areunknown, this guide also addresses thecommissioning and maintenance of these systems.Everyone involved in the design of buildinginstallations can benefit from the informationcontained in this guide. Practical aspects andexperiences are shown in cases describing whathas been learned from the use of daylight responsivecontrols in real buildings.This application guide for daylight responsive lightingcontrols is the key product of the work in SubtaskB of International Energy Agency (IEA) Task 21.

Contents of the Application Guide

The flowchart shown in figure 1 illustrates the designprocess for integrated daylight and electric lighting.It focuses on lighting that is controlled on the basisof daylight availability. It also gives the relationshipwith the IEA task 21 Subtask A Source Book ondaylighting systems.This scheme illustrates that in order to save energyfor electric lighting a proper daylighting design mustbe made. Guidance for this daylighting design canbe found in the subtask A Source Book.This design task starts with laying down the‘Boundary Conditions’ together with the client. Inthe next stage the ‘Daylighting Design’, consistingof windows and shading, is made meeting theseboundary conditions.The established daylighting design is analysedcarefully in ‘Analysis Daylighting Design’, which is

part of the Subtask B and is described in the secondchapter of this guide. When the results of theanalysis match the criteria that were set for both thequantity and quality of the daylight in the interior ofthe building the process is continued with the‘Artificial Lighting Design’, which will not be discussedin this guide. If the results do not meet the criteriathe designer can either try to improve the ‘DaylightingDesign’ or decide to make the design for the artificiallighting without daylight responsive lighting control.In the next stage controls for daylighting and theelectric lighting are added in ‘Control System Design’.The aspects involved in this stage are discussed inthe chapters 2, 3, and 4 of this guide. Installationrelated topics are dealt with in chapter 6.Maintenance schemes form an important product ofthe design: good maintenance will help to optimisesavings and is discussed in chapter 7.It is important to have feedback on the performanceof the total lighting installation. Therefore a chapteron evaluation of the design is included (chapter 8).

Time scales in daylightThe first period is the twenty-four hour variation between dayand night that is caused by therotation of the earth.The other typical frequenciesin the variations of daylight aredetermined by the weather.Depending on the climatesome types of weather can lastfrom a few days, to a week, orsometimes a whole season.The type of clouds involved inthe weather type mainlycauses the variations indaylight. Clouds have aninhomogeneous density andoften several layers of cloudsare moving with differentspeeds. So also if there is anovercast sky, there is acontinuous variation in thedaylight contribution, althoughhuman beings often do notnotice it. These variations incloud density cause variationsin illuminance distribution ofapproximately 25-40% on atime scale of 5-10 minutes;slow enough for the eye toadapt to it.

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Overcast skyAn even more complex situationarises when the cloud layers arenot continuous i.e. when the skyis partly clouded. Then there isnot only the variation in density,but also the effect of the sun thatis sometimes visible andsometimes not. An additionalcomplication is that the sunlightreflects on the separate clouds.The brightness of those cloudsthat reflect the sunlight cancause problems of visualdiscomfort, and also increasesuddenly the intensity of thedaylighting. During partly cloudydays variations on a small timescale (5 seconds to 5 minutes)and with large dynamics (200-300%) will be too disturbing formost people in workingenvironments.

Clear skyMost constant is the situationwith a clear sky. In the course ofthe day the amount of daylightchanges gradually with the sun’sposition in the sky on a timescale of hours.

Table 1:

Relation between the activitiesin IEA task 21, Subtask A andSubtask B, and theircontributions to improvementof lighting design.

Daylighting Design • windows• shading

Boundary Conditions

establish lighting design requirements

Artificial Lighting Design

Outside the scope of this book

Control System Design

Chapter 2,3,4

SUBTASK A

SUBTASK B

Analysis Daylighting Design

Chapter 2,5 Satisfactory? NoYes

Installation/Commissioning/Management

Chapter 6,7,8

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CHAPTER2 CONTROL SYSTEMS

2.1 Introduction

This chapter introduces the reader to daylightresponsive control of lighting. In most cases onlythe electric lighting is controlled as this has themost obvious impact. Although daylight is anunpredictable and constantly changing source,the control of daylight through moving shuttersor blinds or through other forms of adaptivedaylight openings can be desirable.This chapter discusses the control systemsthemselves, introduces a number of practicaldesign and installation issues and gives theprinciples behind the electric lighting controlsystems.

2.2 Properties of daylight.

Daylight can be characterized as a highly efficientlight source with full-spectrum light, giving aperfect colour rendering, large variations in colourappearance and intensity, and a variable directionof the major light incidence. The availability andthe characteristics of the daylight are dependingon latitude, climate, weather, time of the yearand time of the day. In some climates the daylightcan be predictable in other climates veryunpredictable.Daylight is an interesting light source, but it

should be controlled ( through solar shading, dosingand/or redirecting of the natural light) in order to makeit useful for lighting the working environment. Even inthe best daylit buildings, a need remains forcomplementary- or substituting artificial lighting.With a daylight responsive control system daylight canbe used to reduce the energy consumption for electriclighting.

2.2.1 Thermal aspects of daylighting

Windows and daylighting systems influence thedistribution of daylight and the thermal load of a building.A daylighting system can help to reduce the heat gainsin the building due to the favourable lumen per wattratio of daylight and save on energy for cooling. Thisimplies a careful dosage and distribution of the daylightalong with a properly working artificial lighting control.Daylight responsive control of lighting is often combinedwith thermal control. When no occupants are presentthermal control will reduce heat gains in summer byclosing the shades in daytime to keep out the heatand opening the shades during the night to cool byradiation. In winter this may be reversed.

2.2.2 Psycho-physiological aspects ofdaylighting

It is widely recognised that the composition, quantityand variation of the natural light is experienced byhuman beings as pleasant and stimulating. It can evenprevent or cure sickness; e.g. the light treatment ofSAD (Seasonal Affective Disorder).

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A very important psycho-emotional factor is thevisual contact with the exterior.Today some manufacturers of artificial lightingsystems produce artificial dynamic lightsurroundings and special desk-luminaires fortreatment, curative as well as preventive, of varioussymptoms concerning the circadian rhythm, suchas sleeping problems, fatigue, lowered mood etc.Although the Task 21’s major objective is energysaving through promoting daylight use, one has toconsider that perhaps the indirect savings, throughgood daylight application, leading to a more pleasantsurrounding of an higher quality, are even moreimportant than the direct energy savings. Thereforeit is extremely important that the daylight on theworkplaces is applied in a comfortable andergonomic way, assuring that the users accept theapplied daylighting and the various daylightingrelated control systems, also in combination withthe tasks they have to perform (daylight can causeconsiderable glare).

2.3 Daylight control systems

There are several ways to control the amount anddistribution of daylight entering a space (seeSubtask A). Firstly window size and position in thefaçade determine most of the potential to utilisedaylight. Secondly the transmission characteristicsof the glazing determine the maximal flux of daylight.Based on window size and transmittance adaylighting system is selected and dimensioned.A daylighting system is an adaptation of the windowaimed at improving the amount and distribution of

daylight in the space. The selection depends onfactors such as external obstructions, climate andthe desired interior lighting conditions.Daylighting systems can consist of fixed and/ormovable elements (see figure 1). Fixed daylightsystems are for instance overhangs, fixed lightshelves or other light redirecting elements.In case of movable elements these may be controlledmanually or automatically. The automatic control canbe based on daylight availability.

2.3.1 Manual control systems for daylightcontrol

These are the systems enabling the user manualcontrol over the quantity and quality (i.e. avoidingglare) of daylight in the rooms. They can range fromvery simple widely-used diffusing curtains or venetianblinds to very sophisticated light re-directing systemsaiming to optimise the quantity and quality of thenatural light incidence.

2.3.2 Automatic systems for daylight control

Automatic systems can perform a wide range ofactions. They will tilt or turn horizontal/verticallamellae, lower or rise curtains, rotate sun-trackingsystems etc.Many of these systems are not responding to overalldaylight availability. Their actions may also dependon the direct sunlight or solar position only. Examplesare shading controlled on the basis of direct sunlight,which use a roof-based sensor measuring total

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radiation on a tilted surface, controls for tiltingblinds based on astronomical data for solarposition and controls of heliostats based on solarposition.Daylight responsive daylight control systemsconsist of a sensor, measuring incident flux, andcontrol system acting according to the sensor’ssignal.For all control systems yields that the bestfunctioning systems are preferably unnoticeableto the users

2.4 Objectives to use daylight responsiveartificial lighting control systems.

There are several reasons to apply daylightresponsive artificial lighting control systems,

such as:

Energy saving.A number of lamp types can be dimmed usingelectronics. Dimming will lead to a reduction of energyconsumption; however, the electronics added to enabledimming (or other forms of electronic control) requireenergy to operate. Most of the popular fluorescent lamps(T8, T5 and compact lamp types) are easily dimmablewith a significant reduction in energy use. But thereduction of light output and energy consumption arenot equal: a fully dimmed fluorescent tube may have alight output of 2% of the maximal light flux and will stillrequire 20% of the energy consumption at 100% lightoutput. This is because of the energy consumption ofthe ballast and the lower efficacy of the dimmed lamp.Reducing the energy consumption for the lighting alsoreduces the cooling costs because less heat isproduced by the lighting.

Economics - reducing the running costs of the building.An initial investment in energy efficient dimmablelighting may seem expensive at first but can havesignificant benefits over the years. One has to look atlighting costs in terms of cost of ownership, not justas an investment separated from using and maintainingthe installation.

Occupant’s comfort.People are the main capital of most organisations.Taking care of them is a key factor in success. Thebenefits of good lighting are often underestimated.Recent research shows more and more how importantlighting is in the total working environment. A lighting

Figure 1 Overview of types of shading systems

Daylight System

Fixed System Movable System

Daylight Responsive Control

Automatic Control Manual control

Other Control

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control system can improve the comfort bybalancing the brightness ratios in the room.Furthermore lighting control systems can offeradditional features such as automatic and remotecontrol.In the following paragraphs these issues will bediscussed.

2.4.1 Energy savings and durability.

Electric energy is generally created throughconversion of primary energy sources (such as coal,natural gas or nuclear energy). It is inevitable thatenergy is lost in this conversion process. Alsotransport losses of electric power along wires maybe considerable. Saving electric energy is thereforean important means to reduce CO

2 and other

wastes.Daylight is freely available and renewable. The maindrawbacks are the thermal load that may come fromwindows and (in most climates) the unpredictabilityof the daylight. The total possible energy saving ina building by using daylight is a combination of“direct” energy savings on the artificial lighting bydimming when there is enough daylight availableand the dimming of new lighting installations whichalways are “over-dimensioned”. New equipment istypically over-dimensioned by 10-25% anticipatingthe normal depreciation; so even without theutilisation of daylight linked dimming a considerableenergy saving can be achieved. Also the coolingload will be reduced, resulting in energy saving oncooling (if building is quipped with a cooling system)

2.4.2 Economics

Initial cost, cost of ownership and energy costs etc,.are other issues. With the current (1999) low energyprices the payback time may seem long, but thereare other arguments to invest in expensiveinstallations, like flexibility, comfort and prestige.The major economical arguments are presented here.Peak electricity consumption reduction is animportant “direct” economical argument; a typicalenergy consumption pattern shows a coincidence oflow artificial lighting demands with high coolingdemands; daylight responsive control systems cantherefore result in a considerable lower peak demand.Cheap and simple systems with only daylightresponsive control of the lighting exist and offer areasonable payback period.The acceptance of the system by the user is perhapsthe most important indirect economical aspect. If acontrol system is not-accepted by the user it willprobably be sabotaged and the productivity of theworkers might be reduced. A slightly reducedproductivity of dissatisfied workers can spoil allexpected savings. Current (1999) annual electricityconsumption for artificial lighting in modern officescosts per person barely as much as one-houremployee’s wage.Subsidising policies and/or tax advantages for energysaving measures are offered by some governments.Both for retrofit and new buildings it is always worthchecking the local policies; in most cases, electricitysuppliers are the intermediaries.With the high-ranking bus-systems the lightingequipment can be easily adapted for other tasks or

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users. They also give the possibility toreconfigure switched- or controlled groups in caseof layout changes. For big buildings with a highre-conversion rate this can be of economicalinterest.

2.4.3 Comfort

User comfort can be enhanced by offeringappropriate lighting conditions; remote control,scenario possibilities and dynamic lighting forthe more complex systems.It is generally accepted that there is a correlationbetween user comfort and productivity, whichmakes comfort and acceptance also importanteconomical items. Lighting design is always acompromise and not everybody will like it. Addingremote control possibilities gives the users afeeling of control over their environment.It is also possible to install higher lighting levels,up to 700-800 lux, while the installation is normallyrunning at levels around 500 lux, but offers thepossibility to have the higher levels when required.

2.5 Control strategies

The concept ”lighting control” covers a numberof different methods that are used in lightingsystems to change the lighting in a space.A control system may be manual (like an ordinary

switch or a remote controller) or automatic (based onmonitoring by a sensor system or a clock), and it mayoperate on different parameters of the lightinginstallation, like:- The light level (illuminance / luminance)(amount

of light, dimming)- The light distribution (directional control)- The spectral distribution (the colour) (like in

theatre lighting)The control systems that control the light level are themost common systems to use.The automatic lighting control may be based on oneor more of the following control criteria· Daylight access (The electric light is controlled

by the amount of daylight available)· Absence of persons (The light is automatically

turned off in unoccupied rooms)· Time (like automatic on/off switching of the light

at fixed hours)Control systems based on daylight access are calleddaylight responsive control systems.

2.5.1 Control principles.

Control of the light level can be achieved by continuousdimming, step dimming or on/off switching.The dimming systems may be divided into 2 categoriesaccording to the position of the sensor:

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· A so-called ‘open loop’ control system; apredetermined control system, measuringthe appropriate daylighting level (i.e.illuminance on the roof or façade) or adaylight-related luminosity (i.e. luminanceof solar shading devices or window-view) andcontrolling the artificial lighting using somepredetermined algorithms.

· a so-called ‘closed-loop’ control system; afeed-back control system, measuring theworkplace’s entire luminosity level (sum ofthe daylight plus artificial light); mostly atseveral places in the room.

According to the dimming behaviour two types ofsystems can be distinguished:- Proportional systems, where the dimming

is performed proportionally to the measureddaylight level or total light level in the room.

· Constant holder systems, where thedimming is performed in such a way thatthe sum of daylight levels and artificial lightlevel is constant. In practice, since thedynamic range of the daylight level often ismuch higher than the dynamic range of theartificial light level, the “constant holding” isonly possible within a limited range of lightlevels. Constant holder systems are always“closed-loop” systems.

2.5.2 Level of control

An electric lighting installation ( as well as thedaylight systems) may be controlled on severallevels:

· individual control; the electric lighting is thencontrolled by a so-called luminaire-basedcontrol system (Each luminaire has its owncontrol system, like individual workplaceluminaires or luminaires for general officelighting equipped with an individual sensor anddimming- or switching system).

· room control; (All luminaires on the samecircuit are controlled by one control unit. Allluminaires can be dimmed in the same wayor with master-slave principle the lamps inthe interior of the room can have an offset,leading to less dimming. If the control isapplied to all luminaires in one room; this iscalled a room-based control system)

· building control (Luminaires with more or lessidentical positions are controlledsimultaneously, like a window row ofluminaires). Several groups from an entirebuilding linked together in a network or to acentral control system is sometimes calledbuilding-based control system.

Control systems vary widely in complexity andcapabilities. The simplest systems consist of astandalone control system which just dims the lampsaccording to the luminaire’s surroundings luminance.On the other end of the range complex bus-basedbuilding management systems exist, which controlnot only the lighting but also equipment like the solarshading and HVAC and offer the possibility of remotecontrol, pre-set scenarios, switching/dimmingaccording to occupancy, etc.

Total sun’s irradiation (visibleradiation + IR + UV) can bemore the 1000 W/m2.

A part of the sun’s radiationconsists of visible radiation(light). It is impossible to bringin high light quantities withoutsignificant increase of theheatload; also by absorptionlight is transformed in heat.

Good dosed natural light canhelp reducing the internalheatload because of the highlumen per watt ratio..

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2.6 Daylight responsive control systemsfor artificial lighting

Daylight responsive control systems for artificiallighting are automatically acting systems thatwill control the artificial lighting as a function ofthe natural light available in the space. A daylightresponsive control system is expected tomaintain the designed lighting level or a userselected level in all circumstances, all the timeon the whole designated work surface, withoutannoying the user, preferably unnoticeable tohim. Depending on the amount of daylight asignificant amount of electric energy for lightingcan be saved.

2.6.1 Working principle

These systems consist of two main units:· The sensor unit. This is a photosensitiveelement (photodiode, phototransistor, LightDependent Resistor) with an optical unit, whichdetermines the “visual field” of the sensor. It mayalso have a spectral filtering device in order tomatch the spectral sensitivity of the sensor tothe sensitivity of the human eye. The sensor unitmay be designed to be mounted on the luminaire,at the ceiling, on the inside wall or on the outsidewall or even on the roof. In many cases the sensorunit must be tuned to the required illuminancelevel or range of levels (sometimes this has beendone in the factory).· The operative unit. This contains anelectronic part which can be adjusted to the

individual room. The unit also contains the dimming orswitching element, which is positioned either centrally(for circuit or group control) or within the luminaire (forindividual control).The dimming systems are dominating the lightingcontrol market. This is mainly due to a higher savingpotential than the others.The control system interprets the sensor’s signal(s)and switches or dims the artificial lighting accordingto the daylight conditions. The algorithms used in thisprocess can be various; ranging from maintaining asimple pre-set switching level to computer-controlled,fuzzy-logic inspired algorithms. As already mentionedbefore, the bus-based systems or buildingmanagement systems generally can do more than onlydaylight responsive control of the electric lighting.Generally closed loop systems need simpler controlalgorithms than open loop systems. Many room-basedand building-based control systems are open loopsystems; in order to avoid user’s dissatisfaction theyneed to have a delayed action.Luminaire-based control systems are always closed-loop systems and may be quick responding.The actual energy saving potential through daylightresponsive control systems is rather restricted becausetypical modern office lighting equipment ’sconsumption, even without controls, is less than 10-15 W/m2.In relative terms, a good functioning daylight responsivecontrol system can save 20 to 50% on lighting energy(see, for example, part B of the Application Guide).Actual available combinations with presence detectors,can strongly enhance these savings.

The worker’s capability toinfluence his surrounding(self-decision latitude) is veryimportant.

Colour temperature (Tc) ofdaylight variations > 3000K;between warm-white andhigher than 7000 K coolwhite.

Iluminance levels vary from 0to100.000 lux (100.000 lm/m2). During variable weatherconditions, illuminance canchange in a few seconds from20.000 to 100.000 lux.

Total power irradiation (incl.UV and IR) up to more than1000 W/m2.

Light efficiency of daylight isup to more than 120 lm/W;in comparison efficiency ofbest fluorescent lamps (incl.control gear) is +/- 90 lm/

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CHAPTER3 DECISION SUPPORT IN THESELECTION OF CONTROLSYSTEMS

3.1 Introduction

This chapter discusses whether a daylightresponsive control system is useful in a givenapplication. When it is concluded that a systemis useful the next question is which system tochoose. A decision table is presented that willguide the reader through this selection process.Only generic types of control systems arediscussed here, because brand names andtechnical details of daylight responsive controlsystems change constantly with time due tocontinuous improvements and developments.The decision to install a control system has tobe based on the overall lighting demands, theavailability of daylight and energy constraints.This approach follows closely the normal designprocess. An important issue (but difficult tospecify) in the design process is lighting quality.To most designers lighting quality means not justmeeting the demands for visual performance(enabling the user to read text) but also creatingan atmosphere (ambiance).

Most codes and standards present minimumrequirements for lighting. These minimumrequirements are based on safety and visual

performance. This could be a demand on the presenceand dimensions of windows offering the occupants aview on the outside world or the specification of aminimum horizontal illuminance.The preference of the users however might differconsiderably from the minimum requirements. Theusers might prefer a room with windows not just forthe view but also for the daylight that contributes tothe illumination of the room. Moreover additionaldemands might be posed on the luminous environmentsuch as higher preferred illuminances for the worksurface, lighting of the walls, specific luminance ratios,colour rendering, etc. Furthermore users prefer to havecontrol over the lighting of their working place.The constraints on energy use and the available budgetput a limit to what is achievable. Many countriesnowadays have Compulsory Energy PerformanceStandards that place an upper limit on energyconsumption.This means we have to look for a solution that meetsthe user preferences, satisfies the relevant codes andis energy efficient. Daylight responsive control systemscan help to achieve the energy efficiency but they alsorequire an investment.

3.2 Is daylight responsive control feasible?

Whether there is any benefit in installing a daylightresponsive control system depends on the lightingdemands for a space and the daylighting conditions inthat space. A number of economic aspects play a role.When a space is only used occasionally or the daylightavailability is limited the costs for an automatic systemhave to be low to make it feasible. When the tasks to

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be performed in that space are crucial anddemanding then good lighting is essential.Sometimes the price of a control system mightbecome less relevant. It is obvious that in any casethe approach should be based on total cost ofownership.Most countries have Compulsory EnergyPerformance Standards for buildings that placelimits on installed power or on the efficiency of thelighting installation. A control system can help tomeet these standards.

3.2.1 Lighting demands

The demands for the lighting from different partiesinvolved, such as the building owner, facilitymanagement and the users of the lighted spacescan be different and sometimes even conflicting.The required lighting conditions for a givenapplication can be found in the local codes andstandards applicable for the building.The codes and standards generally offer minimumillumination values for the visual task(s) and concernonly electric lighting. Daylighting is in most caseshardly discussed. In some countries a minimumdaylight factor is specified, in other countries onlythe availability of an outside view is required.Additional criteria may be given for colour rendering,glare protection, etc. Other demands may deal withflexibility, which may mean that the lighting mustbe adaptable to different tasks and different users(for instance in a multiple user environment suchas a sports hall) or it may mean that it allowsadaptation of the space (moving partitions or

rearrangement of furniture).The user preferences are mostly too subtle todescribe in standards but are not less important.Sometimes codes or standards will give preferredconditions in addition to minimum requirements. Inmany places research is ongoing trying to establishpreferred conditions.With a lighting control system it is possible to adaptthe electric light levels to the user’s preferences (i.e.depending upon the actual visual task, preferably onindividual basis).Another aspect of functional flexibility of a controlsystem is the ability of the system to react not onlyto external influences (weather…) but also to internalinfluences; i.e. local manipulation of the sun-shading,changes in furniture or decoration, ageing orbreakdown of lamps/luminaires etc.

3.2.2 Daylight availability

The daylight availability primarily defines the building’spotential to utilise daylight for energy savings (seeChapter 4). In an existing building (retrofit) theevaluation of the daylight availability can be done bymeasuring daylight conditions. In a building in thedesign stage there are several ways to predictdaylight availability [ref.: Daylight tools]. Thesemethods range from simple prediction of DaylightFactors (DF) by means of graphs to complexcalculations and even photo-realistic visualisationsoftware (e.g. Radiance).

Here are two rules of the thumb for the daylightcondition in the room at overcast sky:

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· If in the overcast sky condition half of thedesign illuminance is met by the daylight,a control system may be profitable.

· When there is too much daylight in theroom, generally the demand for shadingis so high that the system looses a bigpart of its efficiency.

Only when there is a significant daylightcontribution one should explore the possibilitiesto use daylight responsive controls for the lighting.After the analysis of the daylight conditions acareful design of the electric lighting has to bemade and an appropriate control strategy has tobe selected.The selection of a system is primarily based oneconomical criteria (investments and paybacktimes). Sustainability is in many projects anotherimportant criterion. The easiest way to convincebuilding-owners to invest in a particular systemis to present an attractive payback period for theirinvestment. There are two main sources forpayback: reduction in energy costs andimprovement in productivity of the workers in thebuilding.

Factors influencing daylight availability in thebuilding are listed below.The building site defines the daylight availabilityat daylight openings, such as whether thebuilding is free-standing or not, and whether thereare external reflections of surfaces of ground andwhether there is an influence of other buildingsand the landscaping (high trees etc.).The orientation of the facade is an importantfactor in the design of the daylight system. This

will determine the need for, or the influence of (venetian)blinds, screens and control (manual or automatic) formovable systems.The building height is another factor. Strongshadowing by adjacent buildings, trees etc. occursmore often in the lower part of the building. So it canbe interesting to install control systems only in thehigher stories.Glazing and presence of daylight-handlingsystems have an effect on the potential energy savings.The use of low transmittance glazing reduces theamount of daylight entering the room and as aconsequence the energy saving potential. But the lowtransmittance glazing keeps the heat outside, whichis sometimes considered more important for the energysavings than the effect on the lighting.The room-depth is an important factor. In rooms thatextend deep into the building one can install daylightresponsive artificial lighting control systems that handlejust the peripheral zones.It is clear that only a fully integrated daylight responsivecontrol system will offer optimal energy savings anduser’s satisfaction.Daylight through a clear window results in too highlevels near the window and too low at a few metersdistance; good daylight systems are expected toimprove the distribution by reducing levels near thefaçade and raising levels further away.After all, it is not necessary, nor possible in the conceptphase of the building, to strive for very accuratecalculations, because there are too many uncertaintiesin this phase. A simple approach can be sufficient forthe decision to use daylight responsive control systemsor not, while an advanced visualisation can be very

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helpful for prediction of some comfort shortcomingswith considered daylighting systems under well-defined daylighting conditions.

3.2.3 Electric Lighting System

Proper operation of daylight responsive control ofelectric lighting asks for a suitable lay-out andselection of lamps and luminaires. For dimmablecontrol systems the lamps have to be dimmable.This is not the case for all lamp types. The widelyused (compact) fluorescent lamps (with appropriatehigh frequency ballasts) are dimmable. Other typesof discharge lamps that are sometimes used in up-lighters cannot be dimmed (at present).Incandescent (also halogen) lamps are dimmable,but not recommended in combination with daylightlinked control systems, because of their high energyconsumption. New future halogen lamps maychange this situation.Lamp colours and colour rendering must fit; i.e. incase of a quick transition from predominantly naturallight to electric light “colour perception shocks” haveto be avoided, too low colour temperature of theelectric lamps (i.e. incandescent) doesn’t fit wellwith daylight.High Intensity Discharge lamps are becoming morecommon in uplighters, sometimes also indownlights in office applications where theaesthetical effects, such as object- and accentlighting, are considered important. It is clear that inthis case it is not a problem that the lamps cannotbe dimmed, because daylight responsive dimmingcould destroy the desired effects.

In some applications it is not desirable that theartificial lighting varies under influence of a controlsystem, i.e. accent lighting of exposed goods inwarehouses or display-cases, blackboards inclassrooms etc. In addition, in some industrialapplications where the artificial lighting is used asan inspection tool (i.e. surface examining) automaticvariations of this artificial lighting component mustbe avoided.

3.3 Which control system?

3.3.1 Control requirements

Since natural light can show very large and quickvariations, i.e. in the case of cumulus clouds; theresponse time of the control system must be capableto follow these variations without becoming tooagitated. In general a sharp decrease of daylightshould be supplemented immediately by an increaseof artificial lighting, whereas dimming of the artificiallighting (and switching off) should be done moresmoothly. For switching systems the problem is todefine the on-off hysteresis: too high hysteresismeans illumination gaps or poor saving and too smallhysteresis means agitated lighting.The user acceptance of an on/off switching systemis strongly dependent upon the climate, i.e. in regionswith predominantly blue sky (Arizona…) where thereis no risk for frequent disturbing switching. A typicalunstable English weather condition can cause manyproblems. Even the orientation of the window can be

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decisive when choosing for a switching or dimmingsystem; i.e. the non-sunny side (North side inEurope) is much less varying than the sunny-sides and will offer far less problems in case ofswitching.Constant-holder systems are designed tomaintain the illuminance chosen, which shouldbe conforming the indoor lighting standard.A control system that is not linked to daylight isoccupancy sensing. This may be especiallyenergy effective in rooms with a low occupancyrate. One has to be very careful by usingoccupancy sensors; for safety reasons it shouldbe ensured that the field of detection of thesensors covers the necessary space.Furthermore sudden on/off switching in the vicinityof workers can be very annoying to them (flashingeffect). The use of more sophisticated occupancysensors, switching on or off after a smoothdimming cycle, can be more convenient in anoccupied environment. These systems are moreexpensive than the simple ones mainly becausethey need the use of dimmable lamps (ballasts).It is important to control both the natural and theartificial lighting, but in many cases the controlof the daylight is done manually.The possibility for the user to overrule theautomatic control and the user interface areimportant for the general acceptance by the user.Good acceptance can even lead to enhancedenergy saving; i.e. when the user uses thepossibilities like manually overrule the lightinglevels downward, or switching off the lighting etc.In case of very high natural light levels in parts of

buildings, i.e. atrium, good balanced and comfortablelighting asks for relative high levels in the adjacentzones. Users tend to prefer higher indoor light levelswhen there is more natural light entering the space,the use of so-called light level constant-holders maylead to a rather gloomy interior impression and toohigh contrasts with the window parts.

3.3.2 Economics

Reduction of energy cost is roughly predictable whenthere is enough information available about the selecteddaylight systems, the artificial lighting system, theapplied control systems and the concerned building(see chapter 4). Reducing energy with daylightresponsive controls is achieved by dimming of lightsources based on the amount of available daylight. Inthis way also the energy load is reduced, resulting inreduced cooling energy costs and increased thermalcomfort.Installations can range from simple fixed group on/offswitching or individual luminaire-based dimmingsystems to bus-like building management systemswherein the aspect “daylight responsive control” is justone of the many objectives, besides aspects likecomfort, flexibility and prestige. Of course also thenecessary investment as well as the operating costswill vary accordingly, but for the more sophisticatedsystems, it is hard to estimate which part of the costscan be attributed to the daylight responsive controlfunction. In the case of the simple switching- orluminaire-based dimming systems, the daylightresponsive system related costs are easy to estimate.One should be aware of the energy consumption of

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some permanently operating control systems; thismay cancel a part of the possible energy savings.For instance, a simple switching relay can consumea few watts.Maintenance counts for an important part of theoperating costs. In some (large) buildings thepresence of skilled technical people can play adecisive role in the decision to choose for moresophisticated systems; they can keep theinstallations in optimum working condition.Based purely on economics, in many cases, surelyin smaller buildings, a very simple closed loopluminaire-based control system is a good choice;functional and simple to install and tune. In largerbuildings a more complex group system or bussystem can be considered. And also combinationsof bus-based control systems with autonomousfunctioning luminaire-based controls are possibleto apply.The payback period depends on the energy savingand the cost of energy. Since the saving potentialof a building is the sum of the saving-potentials ofthe different spaces in the building it can beinteresting to choose different systems for differentspaces in one building. For specific spaces of abuilding, for instance spaces with very limiteddaylight incidence (some internal corridors, cellarsetc) and/or spaces with a limited occupancy-timeit is not necessary to install a daylight-linkedsystem. In those cases occupancy-linked controlcan be a good choice, in case of a low occupancyrate such a system will save energy and enhancecomfort (no need to search for the light switch).The climate and the presence of a cooling installation

can be a decisive factor in the use of a system.Lowering the peak- and average heat load of a buildingusing a daylight responsive control system for theartificial lighting can lead to the choice of smallercooling units and will decrease cooling energy costs.The importance of the cooling load reduction isstrongly dependent of the type of building, the usedcooling system and the climate.The aesthetics or corporate image can ask for specialsystems or effects that have an impact on the costof the system.Some governments encourage energy savings bygiving subsidies or tax-advantages for energy savingmeasures; of course, this reduces the payback-timefor the investments. In general the electricity suppliersare able to give information about the subsidisingpossibilities and -procedures.The approach of defining whether or not a system isfeasible (as well as the question which system) canbe different for new or existing (retrofit) buildings.For new buildings a simulation method by existingsoftware can be used to predict the daylightavailability by the calculation of daylight factors (DF)in the rooms as well at the peripheral zones as wellas in the deeper parts of the building.Existing buildings offer the possibility to define thesaving-potential by measuring the daylight factor insome representative daylight situations.As a rule of thumb one can say that a system canbe useful if, measured during an overcast period DF>= 1%. Unlike for new constructions, it is possibleto measure the existing conditions and use the resultto support the decision-making.Some maintenance programs and facility

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management policies tend to interfere with theeffectiveness of daylight systems. For examplethere is a policy to close the blinds every night.In practice it is noted that closed blinds are leftclosed during the daytime after the occupantsreturn.The choice of a certain daylight responsive controlsystem, supposed that al considered controlsystems give satisfaction on ergonomic- andlegal demands, is mainly based on economicalreasoning. This means the highest benefit / totalcost ratio will probably be the best choice.However, as already mentioned above, certainextra possibilities, as there are in some casesfor remote control, scene pre-set possibilities,group configuring possibilities, integratingfacilities for control HVAC or integration inexisting BUS systems can influence the choice.Also the possibility of retrofitting the existingluminaires can influence the choice.

note:Although the “relative” energy saving potentialfigures through daylight application, combinedwith daylight responsive controls for the electriclighting, can look attractive on the first sight onehas to consider that generally (expressed inabsolute amounts) the saving potentials on actualoptimised artificial lighting installations are rathersmall. This due to the fact that these actualinstallations, i.e. in offices, consume generallyno more than 10-12 W per square meter. Withouttax-advantages and/or subsidising the paybacktime of some more complex controls can be too

long. Of course, as already mentioned above, energysaving is not always the only goal.

3.3.3 Ergonomics

As a general rule one can state that, whatever systemis used, it will only be accepted when the functioningof it is understandable, or even better, unnoticeable forthe user. If not accepted by the user systems will besabotaged and not lead to increased comfort andenergy savings.The acceptance by the users is influenced by the taskthey have to perform. For the more demanding tasks,that require concentration, less distraction from thelighting (switching lights, clicking relays or noisy blindmovements) will be tolerated.The need for constant adjustment of the lighting tocustomise it to a particular task or user seems tonegate the need for daylight responsive controlsystems. But the more complex systems can offervarious user interface possibilities; i.e. over-rulepossibilities for dimming/switching the artificial light orthe sunshading/daylight system. It is extremelyimportant that these functions are clear and simple tothe user. The same counts for reconfiguration andadaptation of the more complex systems, at least in(smaller) buildings where there is not a skilledtechnician permanently present.The simple luminaire-based daylight responsive controlsystems generally ask no special trained people,because user interface mostly is limited to the controlof the luminaire’s dimming threshold.Improvement of productivity in a better-lighted and moreagreeable working environment, although generally

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accepted, is difficult to measure. Other issues,beyond the scope of this application guide, includeuser comfort and corporate image.

It is important to understand the interrelationshipbetween the preferences of users and energysavings. Experience has shown that user comfortand acceptance are critical for generating energy-savings. For instance, a free-standing highly glazedbuilding can potentially have a lot of daylight.However, without appropriate glare control as partof the daylighting system, occupants will keep theshading closed and potential energy savings fromthe use of daylighting controls will be lost.Distraction caused by noisy motors or dramaticswitching on and off of lights can also lead theoccupants to disable systems.It is good to realise that energy-costs in professionalworking environments are just a very small portionof the total cost or even of the total labour cost. Anon-happy worker who’s productivity decreases fora few percent can neutralise quickly a lot of effortsmade on energy-saving on lighting; this in additionto the above already mentioned possible systemsdisabling actions. On the other hand a good lightingdesign with the appropriate lighting controls canhelp to create a pleasant working environment inwhich the productivity is enhanced.Offering a good comfortable and ergonomicenvironment, adapted at the specific function of thebuilding (or space) therefore offers the largestbenefit.The user’s tolerance for variations in artificial lighting,i.e. sudden variations of intensity or colour, glare,

contrasts etc. is rather small compared by the user’stolerance for the natural light. Therefore control ofthe electric lighting must function in such a way thatit ensures maximum energy saving and at the sametime guarantees a “good lighting” (level anddistribution) under all circumstances of daylightincidence, no matter whether this incidence isinfluenced by external- or internal parameters.

3.3.4 Decision table

From the previous discussion it is clear that theselection f a control systems will be based on multiplecriteria. Some of these criteria may be quantified.Other criteria however (such as sustainability) areless easy to specify or even subjective (such as‘image’ added to a building).Here the focus will be on those criteria that can beevaluated.The selection is summarised in a so-called DecisionTable (table 3.1) that should guide the decisionprocess. This table is based on the results of thetest conducted by the Subtask B participants. Theselection follows more or less the line of thediscussion in this chapter. It is based on seven criteria.The first three conditions ‘Daylight availability’,‘Suitable shading device’, and ‘Suitable electriclighting system’ are the main exclusive conditions.Their values should all be ‘Yes’. The fourth condition‘Building management system for lighting’ checkswhether a BUS-system is available in the building tocontrol the lighting conditions centrally. If the answeris ‘yes’ open loop control systems are probably thebest (cheapest etc.) choice; although it is also

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possible to have autonomous operating luminaireor room based closed loop systems operating“under” a bus system. With an open loop controlsystem it is also possible to integrate the lightingcontrol with other indoor climate functions. If theanswer is ‘no’ the following conditions determinethe ‘Number of people’ in the room, the average‘Time of occupancy’ of these people, and the‘Required illuminance’. The answers to thesequestions determine which control systems canbe selected. What is not taken into account inthis table are the comfort needs of the people.These also will influence the choice of the controlsystem.

Design Level: The desiredilluminance on the worksurface (e.g. 500 lux, 750lux, 10000 lux…) willinfluence the amount ofenergy needed and thereforethe cost. As a rule of thumbone can say that applicationof daylight responsive controlsystems are not interestingfor design levels below 300lux, unless there ’s animportant subsidy policy(see below).

Rules of thumb can be used;i.e. if DF >=3% for the mostefficient zone (daylight zone)and DF > 1% for theintermediate zone the use ofa daylight responsive controlsystem for artificial lightingcan economically-based beconsidered (taken in accountthe energy-cost).

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Daylightavailability

yesno

Suitable shadingdevices

yes no -

Suitable electriclighting system

yes no - -

Buildingmanagementsystem for lighting

no yes - - -

Number ofpeople

1 2 or more - - - -

Time ofoccupancy

short longirreg-ular

short longirreg-ular

- - - -

Requiredilluminance

<400

>=400

<400

>=400

-<

400>=400

<400

>=400

- - - - -

Closed loop,room based,

x x x x

Closed loop,luminaire based

x x x x x x x

Open loop,building based

x

Open loop, roombased

x

Occupancy on/off x x x

Occupancydimming

x x x x x x

Possibility tointegrate withother functions

x

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CHAPTER4 PREDICTION OF ENERGYSAVINGS AND COSTS

This chapter will explain the reader how toestimate the benefits from daylight responsivecontrol in terms of possible energy savings andcosts. The objective is to explain how thereduction of energy use for electric lighting bymeans of daylight responsive control can beestimated/calculated.First a general introduction to this topic will bepresented. Then some methods will be describedin detail. In these technical sections the advancedtopics are:· TU Berlin method for estimating potential

energy savings:- Estimating the amount of available

daylight in a given room: the roompotential

- Estimating the amount of energy that canbe saved by a given type of controlsystem: system potential

· The characterisation of the performanceof daylight systems. The amount ofdaylight that is brought into a room withoutreduction of visual comfort is an importantfactor in the possible energy savings

· Statistical method of energy savingprediction based on measured daylightfrequencies

· Characterisation of control systems in alaboratory test facility

· Evaluating control systems in a scalemodel test facility

4.1 Introduction

When talking about the saving of energy, first one hasto define what kind of energy can be saved whenimplementing a daylight responsive lighting controlsystem. The energy consumed in a building can beclassified into different types, see figure 4.1. Theelectric energy expended for artificial lighting can besaved with intelligent control systems. But there issome interaction between these different forms ofenergy, e.g. saved energy for lighting has an impacton the necessary cooling or heating energy in thebuilding, see figure 4.2. This can signify that the coolingloads can be reduced when the lighting is controlledor on the contrary that the necessary heating energyis increased. Therefore the prediction of energy savingsby utilisation of daylight through control systemsshould not be treated isolated from the thermalenvironment. The thermal aspects of lighting canpositively or negatively affect the entire resulting energysaving potential.

Although an overall energy reconsideration isnecessary when making an exact prediction orcalculation of the (overall) energy savings created bycontrol systems, there exist some simplified methodsto assess the saving potential. In this chapter some ofthe most important procedures to make estimationsof the possible energy savings by daylight responsivelighting control use are presented and explained. Mostof them consider the direct energy saving potentialneglecting the thermal aspects.

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In the discussion of control systems and theirexpected energy savings the aspect of time has tobe considered too. With increasing time in which alighting control system is in use, the absoluteamount of saved energy and therewith the savedcosts for electric lighting will increase.

The question that comes up now is, at what timethe regarded control system will have been paidback by the energy savings, because a short payback time means a monetary advantage to thebuilding owner, who decides whether to install a

control system for artificial lighting or not. To assessthe monetary savings of a control system not onlyits effectiveness has to be considered, also theinvestment cost, the installation cost and theoperating cost are relevant criteria, see figure 4.3.

In order to compare systems with regard to theireffectiveness, the most important thing to consideris the building, e.g. the room in which a controlsystem will be installed. The regarded control systemin combination with the building in which it should beapplied has to be treated as a unit, in which besides

Figure 4.1. Rough classification of the energy used in buildings. Three major parts are the energy flows neededfor lighting, heating and cooling. The amount and kind of ‘other energy’ depends on the use of the building.

otherenergy

coolingenergy

electricenergy for

lighting

ENERGY

heatingenergy

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the system’s property the amount of usabledaylight influences the effectiveness.

As shown in this introduction, the topic of theenergy saving potential is multi-dimensional, butthe following techniques will help to facilitate theanalysis and the decision process.

Figure 4.2 Energy flow into the building and energy saving potential

heatDEMAND ON

ENERGY

SOLARENERGY

light, heat, ...

Energy saving potentialElectrical energy

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4.2 Frequency method to predict directsavings from daylight responsivecontrols

This method is meant to give a quick estimate ofthe energy savings from daylight responsive controlsystems. As this is a simplified method complexfactors such as the reduction of cooling load(depending on heat storage in the building) cannotbe taken into account.To estimate the possible energy savings from

daylight responsive controls a number of steps haveto be made. The actual calculation depends on thesystem(s) used. The ideal system will maximise theamount of daylight in the room (within the acceptableluminance ratios) by adjusting the daylight systemand supplement just enough electric light to meetthe requirements. In order to see how an actualsystem performs a calculation has to show thetheoretical maximum savings, so the energy the realsystem uses can be compared with this result.In the simplified method the control characteristics

Figure 4. 3 Time as a relevant factor determining the relationship between the costs and the saved costs byenergy savings.

Saved costs for electric energy for lighting

Operating Costs + Acquisition Costs

TIME

33


of the system are evaluated under a number ofsky conditions. Most actual sky conditions canbe described sufficiently accurate for this purposeas a linear combination of a limited number oftheoretical skies. The results of this evaluationare then to be extrapolated to estimate the annualsavings. This extrapolation (site dependent) hasto be based on climatic data (for instance IDMPdata). The validity of the extrapolation dependsstrongly on the type of control.In a given room different solutions for the

daylighting system and the electric lighting systemare possible. The most important requirement ofdaylighting systems in a working environment is thatthey must enable the user to exclude any directsunlight (shading).Often the shading is controlled manually, soassumptions have to be made about the way theshading is set by the occupant. This can be very trickyas the behaviour of users can differ enormously.Generally speaking, people tend to close the shadingto get rid of disturbing luminances and forget to reopen

Figure 4.4 Sample frequency distribution of the illuminance on a North oriented facade in the Netherlands.

Illumination on North fa ade

0

2

4

6

8

10

12

14

25 40 63 100

158

251

398

631

1000

1585

2512

3981

6310

1000

0

1584

9

2511

9

3981

1

6309

6

1000

00

Lux

% o

f w

ork

ing

ho

urs

34


21

it after the cause of the disturbance has vanished.It is clear that the selection of the shading and itscontrol are the key factors in actual energy savings.In rooms without direct sunlight (North/South facing- depending on the hemisphere or any obstruction)often no shading system is necessary, butbrightness control remains important. To give someinsight in the factors influencing the energyconsumption the calculation is split into severalfactors and can be performed by the aid of acomputer.

4.2.1 Reference situation for energy use

In order to make comparisons the considered roomwith the same lighting installation but without anydaylight responsive lighting control is taken as areference case. It gives the energy used when noform of lighting control is installed. Furthermore itsis assumed that the electric lighting is used duringworking hours with 100 % light output. In manyoffices without any daylight responsive controlsystem for the artificial lighting, normally the lightis switched on in the morning and remains switchedon during the whole working day regardless ofavailable daylight. Of course manual switching(preferable in zones related to the daylightdistribution in the room) can be a profitable strategyto start saving energy.

4.2.2 Electric lighting

In this paragraph only the electric lighting isdiscussed. The effect of the daylighting system willbe calculated separately.

In most cases for daylight responsive electric lightingcontrol the sensor is ceiling or luminaire mountedand looking downward to the working plane. In alimited number of systems the light sensor is locatedoutside the room, either in a reference room orelsewhere in the building or mounted on the roof oron the facade.In the case of a ceiling mounted sensor the sensormeasures the luminance within its field of view. Basedon the sensor position and the opening angle of thesensor the area “seen” by the sensor can bedetermined Then it is necessary to know what(il)luminances occur on this area in practice (seefigure 4.5). This can be determined sufficientlyaccurate by using a daylighting computer programsuch as SUPERLITE which is part of the Adeline3.0 package also developed within IEA task 21. Thecalculation has to be performed for a CIE overcastsky and a uniform sky. For rooms with possible directsunlight the effect of a shading system has to becalculated separately (see below).From the calculated illuminances and thecharacteristics of the system the relation betweenthe daylight levels in the room and the energy use ofthe system is known and can be used to estimateyearly values.

35


Figure 4.5 Step 1, Estimate of the average luminance/ illuminance registered by the sensor (red circle). Theaverage daylight factor is 6%. At 10000lux exterior illuminance and with a reflection of 30% the luminance willbe 58 cd/m2

0.25 0.74 1.23 1.72 2.21 2.7 3.19 3.68 4.17 4.66 5.151.54

1.03

0.51

0

-0.51

-1.03

-1.54

18-19

17-18

16-17

15-16

14-15

13-14

12-13

11-12

10-11

9-10

8-9

7-8

6-7

5-6

4-5

3-4

2-3

1-2

0-1

1.54 1.03 0.51 0 -0.51 -1.03 -1.54 0.25 1.34 6.22 14.48 18.28 14.48 6.22 1.34 0.74 3.72 8.46 14.29 14.94 14.3 8.46 3.72 1.23 3.79 5.97 8.22 9.53 8.22 5.97 3.79 1.72 3.02 3.98 5.1 5.5 5.1 3.98 3.02 2.21 2.29 2.83 3.27 3.44 3.27 2.83 2.29

2.7 1.93 2.28 2.53 2.63 2.53 2.28 1.93 3.19 1.55 1.71 1.84 1.89 1.84 1.71 1.55 3.68 1.02 1.09 1.15 1.17 1.15 1.09 1.02 4.17 0.87 0.93 0.98 0.99 0.98 0.93 0.87 4.66 0.87 0.93 0.98 0.99 0.98 0.93 0.87 5.15 0.83 0.88 0.92 0.93 0.92 0.88 0.83

36


21

Step 1 see figure 4.5

Step 2 Calculate optimal energy savings from anideal control systemBased on the “ideal” control system. This is ahypothetical control system controlling the sameinstallation that will always supplement with artificiallight up to the minimum desired lighting level andswitches the electric lighting off when there isenough light from daylight only. Such a system isnot (yet) available on the market. The calculation isbased on the same daylight data as used in step1.The switching of electric lighting can be a verydisturbing effect.

Step 3 Calculate savings from a real controlsystemIn this case the control characteristics of thesystem have to be known. These characteristicscan then be used to calculate the estimated energysavings as described.

4.3 Calculating the energy saving potential

4.3.1 TU Berlin method for describing andpredicting the energy saving potential

At the Institute of Electronics and LightingTechnology, Technical University of Berlin, a methodhas been developed to calculate the possible energysavings by the use of daylight responsive lightingcontrol systems in buildings. The effective use of

the given daylight in buildings in combination withdaylight dependent lighting control systems meansa possibility for saving electrical energy, i.e. theminimisation of energy consumption of the artificiallighting. The energy saving potential is the maximumamount of energy that can be saved when installinga daylight responsive control system in a particularroom with a certain electric lighting system. Itscalculation can be divided into two parts: the roompotential and the system potential /6,7,8,9/. Theprocedure works with the concept of the average skycondition model as a basis in order to characterisethe daylight availability in the room /1,2/.

4.3.1.1 Room potential

The room potential in general describes the availabilityof daylight in the room. It is assumed that the lightingdesign is done properly. The room potential isinfluenced by the following parameters:· geographical latitude· local daylight availability (referring to the

meteorological data and the average skycondition)

· daylight system (if installed)· building, room and window properties

(reflectance of the walls, the ceiling and thefloor, geometry, window size and orientationof the glazed area, obstruction, etc.)

· the working time· the design illuminance E

S

The calculation of the room potential considering allaspects and referring to the average sky is relativelycomplex, therefore it can be calculated with acomputer programme, for instance Easydays

energy saving potential =room potential x systempotential

37


(available at PRC, Berlin Germany). The roompotential is based on the relative usable lightexposure, describing the daylight availability,which will be discussed in the next paragraphs.

4.3.2 Availability of daylight

The amount of usable daylight in the buildinginterior mainly depends on:- The sun position (angles of azimuth and

elevation), that can be derived from theinformation about the geographicallatitude of the building and the exact timeand date.

- The sky condition (e.g. cloudiness, directsunshine or not, type of clouds etc.)

- The turbidity of the atmosphere, whichdepends on the height of the place abovesea level and the aerosol and vapourcontent of the atmosphere.

- Obstruction and its properties(dimensions, reflectance)

- Ground reflectanceThe sky condition is important for theassessment of daylight in interiors. Obviously,the momentary sky condition is not very usefulfor the estimation of the energy-saving potentialfor a long period of time. In this case, the longterm average of daylight data is needed.Therefore the German standard introduced theaverage sky type /1/.

4.3.2.1 Relative usable light exposure

If the electric lighting level can be adjusted by

dimming, the economical benefits by using the availabledaylight depend on the annual relative usable lightexposure Huse,A,rel . The annual relative usable lightexposure is the ratio of the total annual daylightexposure in the room and the required total lightexposure, which can be calculated with /3,4/:

Huse,A,rel

(%) = 100 . (∑ Ni . (∫ E

p .dt)) / ( E

s . t

w . N

A )

withN

i: Number of working days per month

NA

: Annual number of working daystW

= TE - T

B: hours of daily working time

TB

: Begin of the working time (e.g. 900

LCT, Local Clock Time)T

E: End of the working time (e.g. 1800

LCT)E

P: daylight illuminance at a point in the

i nteriorE

S: the design illuminance

The equation holds only for values of EP (daylight

illuminance) ≤ ES only. For E

P > E

S one has to calculate

with EP = E

S. The usable light exposure can be used

to describe the part of the artificial lighting that canthen be replaced by the available daylight. The roompotential is the mean annual relative usable lightexposure over the room area A.

Huse,A,rel , average

= ( ∫∫ Huse,A,rel

dA ) / A

For more details see /1,2/.

38


21

4.3.2.2 System potential

The system potential has to be assessed bymeasurements or derived from data supplied by themanufacturer. The system potential is mainlyinfluenced by the way of the daylight dependentcontrol of the artificial lighting:· daylight dependent switching· daylight dependent dimming· daylight dependent dimming with respect to

the room depth· open or closed loop control strategyAt the Institute for Electronics and LightingTechnology the system potential of a daylightdependent lighting control system can be measuredin combination with daylight systems under varioussky conditions. The measurements take place intest rooms that are equipped with some controlsystems.

4.3.4 The average sky condition

The CIE described standard sky types for overcastand clear sky and gives formulae how to calculatethe data. But most of the time these sky types donot occur in their pure form, often the sky is partlyclouded. The average sky can be calculated fromthe daylight data for overcast and clear sky. Thelocal sunshine probability P

sun has to be taken into

consideration. Psun

is the ratio of the actual longterm sunshine duration and the possible sunshineduration.

In working areas direct sunshine is usually not veryuseful because of glare, heat and too high contrasts.Because of the large differences between direct sunlight and diffuse sky light, the components of theresulting light (the illuminance of the average sky)have to be calculated separately. Therefore the diffuseand the direct components of the solar radiation andthe daylight data on average sky conditions must becalculated separately according to the local sunshineprobability, i.e. one calculates the part for the timeinterval with sunshine and for the time interval withoutdirect sun according to P

sun . In /1/ a detailed

description of the German average sky is given. In /1/ and /2/ the calculation of the relative usable lightexposure on the working area in dwellings accordingto the average sky is explained.

4.4 A simplified method to characterise theefficiency of daylight systems

4.4.1 Introduction

The actual savings on electric energy that can beachieved by the use of daylight responsive control ofelectric lighting are determined by the amount ofdaylight in the room. This amount of daylight isstrongly dependent on the properties of the shadingand/or glare protection system. Some opaque typesof shading may fully block the daylight while othersystems (even in a closed position) will bring someof the daylight in the room through deflection and ordiffusion. An essential criterion to observe is the visual

39


comfort of the user. So in this method we comparesystems under several sky conditions in order to seehow efficient they are in bringing daylight into the roomwithout glare for the user.The efficiency of a daylighting system may be definedas the amount (total flux) of daylight entering the roomwithout causing glare or annoyance for the user(s) ofthe room. As this involves many parameters a completedescription is too complex to give in the context ofthis guide. More information on this can be found inthe Source Book of Subtask A /see Further Reading/. What can be demonstrated here is a simplified methodfor the comparison of daylighting systems that can beused to estimate the energy performance of the overalllighting system.This simplified method may be used to compare theinfluence of passive daylight control such as curtains,venetian blinds in fixed positions and other daylightingor shading systems. The comparison is dependent onthe sky conditions (sunny, overcast, etc). It showsthe effect of the daylight system on the total amountof daylight entering a room. The method does not lookat the spatial distribution of daylight. When moredaylight is entering a room the possible energy savingswill increase (if the visual comfort is good).Furthermore the method described here is based onthe most relevant comfort parameter. This is the averageluminance seen in the direction of the window. It doesnot take other factors into account. Other luminancesresulting from incident daylight and reflections (suchas ceiling luminance) sometimes play a role.This method offers a simple first order check that needsto be extended for complex systems. This is necessaryfor those systems using one or more specular

The flow diagram gives an overview about thesteps how to calculate the annual relative usablelight exposure related to a reference point in theoffice with side windows /2/.

40


21

reflections of direct sunlight. Sunlight cast towardsthe walls or ceiling may give rise to unacceptablehigh luminances.It is important to note that the criterion given hereis just a measure for the amount of daylight. If thedaylight creates an uncomfortable or otherwisewrong luminance distribution, or if the room surfacesare so dark that no light is reflected, the daylightwill not contribute to energy savings.

4.4.2 Calculation method

The approach followed here is based on thecondition of the maximum luminance of shadingand on the acceptable contrast ratio between thetask luminance and the (background) luminance ofthe shading. Given a certain background luminance,it may be measured against the amount of daylightthe system brings into the room.For instance for VDU work the typical taskluminance is in the order of 100 to 200 cd/m2. Thiskind of task therefore permits a backgroundluminance in the order of 1000-2000 cd/m2. Severalshading systems exist that are able to control thewindow luminance within this range. The amount ofdaylight that is entering the room however may differconsiderably between these systems.The criterion proposed here to describe thosedifferences is the ratio of the average windowluminance and the total luminance of all surfacesof the room.

4.4.3 Explanation of the calculation

To be able to compare a large number of elementsthe geometry is kept very simple. Thecharacterisation process of a the daylight systemsis done as follows:Given a black room (no surface reflections, so nointerreflections) with only one vertical window throughwhich the daylight can enter the room

The total flux of daylight entering the room is equalto the sum of all the illuminances on all the surfacesin the room. This can be expressed in the form of anequation as:

Φ = ∑ Εi ∆σi

This is the sum over all surface elements of theilluminance times the area of the element.

When a perfectly diffusing screen covers the windowemitting daylight in all directions, the flux from thewindow into the room can be calculated as:

Φ = ∑ Εi ∆σi

dA = area of screen (window) surfaceL = average luminance of the surfaceFor a box of unit dimensions (1m x 1m x 1m), with awindow on one side (of 1m x 1m) the equations maybe simplified to:

∑ Εi,average = π ∗ L

41


If we define the Daylight Efficiency of the daylightsystem as

DE = ∑ Ei,average / (π * L) =sum of average surface illuminance / window

illuminance

Then, in the case of a perfect diffuse emittingwindow surface:

DE = ∑ Ei,average / (π * L) = (π * L)/ (π * L) = 1

For surfaces with other transmission types otherratios will be found. Generally when the ratio isgreater than 1 the system will bring more daylightinto the room than the diffuse screen. When theratio is less than 1 the situation is worse.The given correlation can be verified bycalculation. A preliminary test with Radiance (fora diffuse screen) showed good agreementbetween the results.The calculation of this factor allows for thecomparison of different daylight systems. Othertests are currently being developed to determinehow to apply light-shelves, venetian blinds anddaylight redirecting systems. This method canbe used both in theoretical calculations usingsimulation models like Radiance as well as inlaboratory measurements. In the latter case datafrom for instance integrating spheremeasurements have to be used.

4.4.4 Examples

In the examples (table 4.1) a number of sampleRadiance calculations are given. As the result for thesystems that change the direction of the daylight as afunction is dependent on the sky conditions calculationshave been made both for overcast and clear conditions.

4.4.5 Results and conclusions

The results presented in the two graphs show that thismethod can be used to characterise the performanceof daylighting systems. It is clear from the results thatthe performance is dependent on the sky conditions.As most problems in the visual environment occur forclear skies with direct sunlight this is the most relevantevaluation.Some examples (light shelves, open window) are notrealistic for clear sky with direct sunlight as the directsunlight can enter the box and give rise to highluminances.A general conclusion is that vertical elements performbetter for overcast conditions while the horizontalsystems are more suitable for sunny skies. This isbecause the direct sunlight is directed out of the lineof view (towards the ceiling) while the luminance of theblinds in the horizontal line of sight is acceptable.For the vertical blinds with 20% transmission the ratioof luminance versus transmitted flux is less favourable.The method presented here can be used to give a roughcomparison between daylighting systems that cover awhole window. It does not give useful results forelements that often form part of a shading strategysuch as light-shelves.

42


21

Table 4.1 and figures, Overview of example calculations

Name Description

Clear window Window without shadingDiffuse window Perfect diffuse surface, e.g. screenLightshelf Interior lightshelf with diffuse surfaceHor. - Dark – 0 deg. Venetian blinds dark surface - horizontal positionHor. - Dark – 15 deg. Venetian blinds dark surface - tilted 15 degrees towards outsideHor. - Dark – 30 deg. Venetian blinds dark surface - tilted 30 degrees towards outsideHor. - Dark - 45 deg. Venetian blinds dark surface - tilted 45 degrees towards outsideHor. - Dark - 60 deg. Venetian blinds dark surface - tilted 60 degrees towards outsideHor. - Dark - 75 deg. Venetian blinds dark surface - tilted 75 degrees towards outsideHor. - Light - 0 deg. Venetian blinds light surface - horizontal positionHor. - Light - 15 deg. Venetian blinds light surface - tilted 15 degrees towards outsideHor. - Light - 30 deg. Venetian blinds light surface - tilted 30 degrees towards outsideHor. - Light - 45 deg. Venetian blinds light surface - tilted 45 degrees towards outsideHor. - Light - 60 deg. Venetian blinds light surface - tilted 60 degrees towards outsideHor. - Light - 75 deg. Venetian blinds light surface - tilted 75 degrees towards outsidevert. 20% trans - 0 degr Vertical blinds with 20% transmission - closedvert. 20% trans – 15 degr. Vertical blinds with 20% transmission - opened 15 degreesvert. 20% trans – 30 degr. Vertical blinds with 20% transmission - opened 30 degreesvert. 20% trans – 45 degr. Vertical blinds with 20% transmission - opened 45 degreesvert. 20% trans – 60 degr. Vertical blinds with 20% transmission - opened 60 degreesvert. 20% trans – 75 degr. Vertical blinds with 20% transmission - opened 75 degrees

43


CIE Clear Sky

0

1

2

3

4

5

6

Clear w

indow

Diffuse

wind

ow

Light

shelf

Hor. -

Dar

k - 0

deg

.

Hor. -

Dar

k - 1

5 de

g.

Hor. -

Dar

k - 3

0 de

g.

Hor. -

Dar

k - 4

5 de

g.

Hor. -

Dar

k - 6

0 de

g.

Hor. -

Dar

k - 7

5 de

g.

Hor. -

Ligh

t - 0

deg

.

Hor. -

Ligh

t - 1

5 de

g.

Hor. -

Ligh

t - 3

0 de

g.

Hor. -

Ligh

t - 4

5 de

g.

Hor. -

Ligh

t - 6

0 de

g.

Hor. -

Ligh

t - 7

5 de

g.

vert.

20%

tran

s - 0

deg

r

vert.

20%

tran

s - 1

5 de

gr.

vert.

20%

tran

s - 3

0 de

gr.

vert.

20%

tran

s - 4

5 de

gr.

vert.

20%

tran

s - 6

0 de

gr.

vert.

20%

tran

s - 7

5 de

gr.

To

tal f

lux

/Lw

ind

ow

CIE Overcast Sky

0

1

2

3

4

5

6

Clear w

indow

Diffuse

wind

ow

Light

shelf

Hor. -

Dar

k - 0

deg

.

Hor. -

Dar

k - 1

5 de

g.

Hor. -

Dar

k - 3

0 de

g.

Hor. -

Dar

k - 4

5 de

g.

Hor. -

Dar

k - 6

0 de

g.

Hor. -

Dar

k - 7

5 de

g.

Hor. -

Ligh

t - 0

deg

.

Hor. -

Ligh

t - 1

5 de

g.

Hor. -

Ligh

t - 3

0 de

g.

Hor. -

Ligh

t - 4

5 de

g.

Hor. -

Ligh

t - 6

0 de

g.

Hor. -

Ligh

t - 7

5 de

g.

vert.

20%

tran

s - 0

deg

r

vert.

20%

tran

s - 1

5 de

gr.

vert.

20%

tran

s - 3

0 de

gr.

vert.

20%

tran

s - 4

5 de

gr.

vert.

20%

tran

s - 6

0 de

gr.

vert.

20%

tran

s - 7

5 de

gr.

To

tal f

lux/

Lw

ind

ow

44


21

The results can be based on calculations but alsoon laboratory experiments using an integratingsphere for the flux measurement and a luminancemeter to determine the average luminance of theelement.

4.5 Laboratory Test Methods - DaylightingBox

The daylighting box is an experimental set-up tomeasure the performance of various sensor-controlled luminaires. Its results should bereproducible anywhere in the world. The set-upmeasures three items:(1) Characteristic of control. When daylight is

increased how much does the controlleradjust the artificial light? When daylight isincreased what is the reduction of energyuse (in watts) by the luminaire?

(2) Range of control. What is the range ormaximum and minimum setting of thecontroller (in lux)? Is the adjustmentcontinuous or stepped through the range(e.g. 300, 500 and 750 lux)?

(3) Responsiveness. What is the time delaybetween daylight changes and changes toartificial light levels?

4.5.1 Experimental set-up

The set-up consists of 2m x 2m x 2m cube thatrepresents the space above a typical office deskthat is lit by a single luminaire. The test luminaireis centred in the top plane of the cube (the ceiling).

An illuminance sensor is placed in the centre of thelower plane of the cube (the work surface). The verticalplanes of the cube represent the wall surfaces. Allinterior surfaces in the cube are painted a mattemedium grey colour (reflectance factor of 0.38).One wall has an opening representing a window thatextends from floor (worksurface level) of the cube toapproximately 10 centimetres below the ceiling.Attached to this opening is a daylight simulator. Thedaylight simulator is designed to reproduce a rangeof daylight levels found in an overcast sky. Thesimulator consists of a bank of 27 daylight lampsarranged parallel to one another. The lamps do notshine directly into the room. Instead, they are directedat a surface that bounces light back into the room ata 45 degree angle. This helps to distribute the lightevenly.A computer controls the testing. This is importantbecause the temperature of the lamps must bestabilised first before lighting measurements aremade. If the temperature is not stable the output ofthe lamps will vary. The computer records thetemperature of all the lamps in the experiment onone-minute intervals. When the difference betweentemperature measures is small enough the computertakes a lighting measurement.The temperature of the testing environment iscontrolled. The daylighting box and simulator arelocated inside a laboratory room. The temperatureinside the daylighting box generally matches that ofthe laboratory room in which it is located. Within thedaylight simulator ventilation is provided across thesurface of the lamps to prevent the introduction ofheat into the test cube. Since the ventilation for the

45


daylight simulator exhausts into the laboratoryroom, the overall temperature in the laboratoryroom can rise a few degrees during testing (whenthe daylight lamps are on). To compensate forthis, the laboratory room is mechanically cooledas necessary to maintain a constanttemperature.

4.5.2 What is recorded?

During a typical test cycle “daylight” is graduallyincreased from zero to a maximum of 4000 lux.During this test cycle the following issimultaneously recorded: energy use by theballast, illuminance level at the controller, lightoutput of the daylight lamps, light output of theluminaire, and illuminance at the worksurface.

4.5.3 Evaluations

The artificial light versus the daylight and thepower of the ballasts (watts) versus the daylight(energy use) are evaluated.

4.5.4 Application

This test method is appropriate for establishingthe physical performance of various daylightsensor-controlled lighting systems, the resultscan be used to calculating potential energysavings. It is not appropriate for predicting user

acceptance, maintenance, or durability of systems.

4.6 Scale model testing of daylight responsivelighting control systems

The testing of lighting control systems generallyrequires a complex and large measuring system,including a 1:1 realistic test room with dimensions ofan average office room. Performing tests in 1:1 testfacilities can have some disadvantages. Therefore someinstitutions are performing measurements on lightingcontrol systems using miniaturised test-rooms (scalemodel testing). This has some advantages. The roomparameter of miniaturised test-rooms (reflection factorsof the room surfaces, relative dimensions, room-orientation, window sizes and orientations, etc.) caneasily be changed compared to large 1:1 test rooms.The possibility to change the orientation of the room(correspondingly the window orientation) is a bigadvantage of such scale model testing, also theflexibility and mobility of small-scale model rooms,which allow testing in different climatic regions.Although the scale model testing is a useful tool, thedisadvantages of such procedures have to be named.Normally the measuring of the illuminances can be aproblem if one wants to transfer the results directly toa 1:1 room because of the fact that the roomdimensions are scaled down, but the measuring deviceis not. The relative detection area of the photometer-heads compared to the room size is therefore different(in the scale model averaging over a larger area takesplace).

46


21

At the institute for Electronics and LightingTechnology of the Technical University Berlin a scalemodel testing facility is used to assess additionalinformation on control systems and also daylightsystems in order to compare them to results of the1:1 test-room results. The scale model room is a1:4 scale model of the realistic 1:1 test rooms fordaylight responsive lighting control systems. Theroom has the dimensions B x H x T = 1m x 1.2m x 2m, its reflection factors and thewindow size corresponds to the 1:1 rooms. Theroom is mobile and weather-resistant (outdoor use)and can be used in different situations. For practicalreasons, the test room is located on the top of thebuilding of the faculty in order to create a buildingsituation without obstruction. A further feature ofthe facility is that the room can be rotatedhorizontally in different orientations via computercommands in order to simulate different azimuthangles. Testing cycles therefore in some cases canbe performed in a shorter time period. The room isequipped with a bus system and a complete artificiallighting installation, including dimmable electronicballasts, permitting the option to test different kindsof control systems, also bus-based solutions, e.g.EIB controller. Because of its geometry the roomis equipped with three rows of luminaires, which isuseful for testing of strategies for room depthdependent dimming (with an additional inner wall,one can change the room depth correspondingly).The room is equipped with 20 photometer-headsmeasuring the illuminance distribution in the room.Additionally the power consumption of theluminaires is measured. All the data is collected

over the measuring time with an automated dataacquisition system. The data acquisition softwarealso calculates the daylight contribution on themeasured illuminances, i.e. the measuredinformation corresponds to the 1:1 testing. Finallyit can be said that scale model testing always haveto be combined with tests in realistic 1:1 test-rooms,in order to have the possibility to determine thelimitations of the scaled test-system.

47


CHAPTER5 USER REACTIONS TODAYLIGHT RESPONSIVECONTROLLED LIGHTING

5.1 Introduction

The purpose of this chapter is to discuss whyand how to introduce a lighting control systemto the occupants of the building.Experiences with complex control systems showthat problems may occur when the users do notknow what the purpose of the control system isand how it works. These problems can vary fromcomplaints to completely overruling of the systemthrough sabotage, which may lead to reducedenergy savings.Understanding and acceptance of the controlsystem are important keywords for this chapter.They form the basis for achieving energy savingsand improved lighting comfort. In short: the userhas to know why the system has been installed,what it offers and how to use it.

5.2 User awareness

The user awareness is the understanding of thecontrol system by the users of the space, theawareness that and why the system is there andhow it works. In most cases the control systemis noticed, either by the observation of thedimming of the lamps or because the user has

to interact with the system (e.g. turning on lights thathave been switched off automatically). To enhance theacceptance of the system it should be introduced tothe users (see also chapter 6). This can be done bybuilding or facility managers who explain briefly thepurpose of the system, (e.g. the energy saving) andwhat the users can expect in terms of automaticcontrol. They also have to explain how to use theswitches or the remote control. And when the buildingmanager is not always present, it is necessary tospecify to the users where they can find documentationor technical support. To ensure that the informationcan be retrieved later by the users or by new employeesit should be written down on paper or in electronic form.To explain the working of a control system properlythe working of the sensor must be made clear to theuser. In case of a system with the sensor on the ceilingfacing down the user can be told that the sensor “sees”the brightness of the (working) surface and that thelighting will be adjusted automatically if this brightnesschanges. This brightness changes not only when thedaylight contribution changes, but also when forexample an additional light source (desk lamp) is usedor if the desk is covered with a large piece of whitepaper. In both cases the lamps will be dimmed, whichmay be the contrary of what the user wants.In case of a sensor looking to the window the usershould be told what will happen when the blinds areclosed.

48


21

5.3 Acceptance

A daylight linked lighting control system will notfunction properly when it is not accepted. If thereare too many complaints from the occupants, thesystem will be forgotten or tampered with and thereis no chance to achieve energy savings. When theusers do not notice that the light is controlled in anautomatic way no problems with acceptance arelikely to occur, but otherwise user awareness, asdescribed above, will enhance the chance ofacceptance.As people like to control their environment thereshould be a possibility to overrule the system.Therefore the remote control or switches, that offerthis, will probably increase the user acceptance ofthe system, but the acceptance is influenced bythe complexity of this manual control. If the systemis too complex the user might get annoyed in hisattempts to master it.A lighting control system is better accepted if itreacts in an predictable way, for example when thesun shines on the façade and the electric lightinglevel is dimmed.Changes in illuminance are mostly accepted whenthe system is reacting fast when an action isneeded (e.g. sudden dark clouds) and slowly whenthe user should not notice it (e.g. increasing daylightin the morning).A number of common complaints and their possiblesources are mentioned in table 1. It should be keptin mind that the complaints can have other causesthen the control system, even causes that havenothing to do with the lighting (but the control system

is used as scapegoat). It is therefore necessary tostudy each situation separately.First of all, one should test whether the lighting controlsystem works according to the specifications. If thecomplaints cannot be dealt with, ask a consultant orthe manufacturer.Most people are not aware of the electric lighting ina building, but if the lighting is not adequate, itbecomes an important issue to them. Therefore it isnecessary to take complaints seriously and put thesituation right as soon as possible.Also to avoid complaints, it could be useful to askthe occupants, after the installation, how theyperceive the visual environment with the controlsystem, if the illuminance level is acceptable and ifno unwanted fluctuations occur. This can be donewith a simple questionnaire or an interview.

5.4 Things to remember

· Install the system as it is mentioned to install.Use it the way it is prescribed.

· Don’t set the illuminance too low. When theilluminance is too low people will bring theirown luminaires or cover the sensor.

· To increase the acceptance of lighting inrooms, one should avoid discomfort glare fromwindows.

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Table 1 Common complaints and their possible sources

Complaints Possible sources and remedies

Light switches on, although there is enough light, or

Light switches off, although there is not enough light

• Inappropriate strategy for application (closed loop when open loop is more appropriate or vice versa) or wrongly positioned sensors.

• Calibration inaccuracies. If possible, adjust the set point, if not: contact the manufacturer.

Too little light on the desk Several possibilities:

• The illuminance level is set too low. If possible, adjust the set point, if not: contact the manufacturer.

• The installed luminous flux is too low. Replace lamps, clean luminaires or change the total installation.

• Control system does not maintain the minimum illuminance level (see above).

• The plane that the sensor looks at has changed, for example as a result of movement or change of furniture.

• One sensor is used for several workplaces and illuminance of the plane that the sensor looks at, is changed by a user of the room, for example by lowering or opening blinds.

• Change of the situation characteristics (new furniture, other orientation of tasks, use of large white surfaces in the neighbourhood of a closed loop system)

Light switches on and off almost constantly, or

dimms up and down almost constantly

• The system reacts too fast on changes in the illumination of the room. Change the delay time or adjust the light output or contact the manufacturer.

• The sensor ’looks’ into the lamps it controls.

• The sensor is covered or the system is disturbed by extra lighting or blinds or by reflections of sunlight.

Areas too dark especially in the back of the room

• The system controls a group of luminaires and the sensor is mounted in the window zone. Use a master/slave connection with an offset for the lamps in the back of the room.

Noise • Relays or other mechanical parts or electromagnetical ballasts

Different lamp colours • Lamps which are dimmed an extreme very low level show a colour shift towards pink.

• Lamps have different colour temperatures.

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CHAPTER6 INSTALLATIONPROCEDURES

6.1 Introduction

In order to achieve user satisfaction andmaximum energy saving it is important that thecontrol system is installed correctly so that itwill function optimally. Malfunctioning of thesystem will lead to complaints of the users or toreduced energy saving or even no saving at all.This chapter deals with the most importantissues concerning the installation of the sensorsfor the different types of control systems. In orderto keep the system running correctly afterinstallation “system awareness” of maintenancepersonnel and occupants is necessary, thisaspect is discussed in 6.6.

6.2 Installing sensors for closed loopsystems

Most daylight linked closed loop control systemsmeasure the combination of the daylight and theartificial lighting with a ceiling mounted orluminaire mounted light sensor. This sensor“looks” downward to the working plane. Theoutput of the sensor is a measure of the lightthat reflects towards the ceiling and should be ameasure of the light reflected by the workingplane and the immediate surroundings. The

control system will not work properly if:1. there is a light source (e.g. an uplighter) shining

directly on the sensor or2. there is reflected light (e.g. from a car parked

outside or a shiny surface at a nearby building)or

3. the sensor “sees” a part of the window or4. the sensor is blocked by objects (e.g. message

panels, bookshelves, plants)In these cases the reading of the sensor is not directlyrelated to the luminance of the working plane and thecontrol system will not work properly.Therefore, the positioning of the sensor(s) should bedone carefully.All of the currently available sensors do not measureilluminance (lux values) on the workplane, but a kindof “average luminance” of it, which depends on thereflecting properties of the materials of the room andthe furniture. Therefore there is a need for adaptationof the system in order to adjust the wanted “threshold”of dimming for each specific case with specificreflectances and initial (night time) illuminance levels.

6.3 Installing sensors for open loop systems

Daylight linked open loop control systems determinethe contribution of the daylight to the lighting in a roomby measuring the daylighting level outside the buildingand/or from the inside of the room and control theartificial lighting using predetermined algorithms.The external sensor is placed on the roof or on thefaçade. In both cases care should be taken that thereading of the sensor is representative for the daylightcontribution on the total building. There should be no

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shading objects or highly reflective objects that are“seen” by the sensor, but are not influencing thedaylight contribution on all parts of the building.If the building is surrounded by large structures,which lead to a daylighting pattern on the façadesthat is not uniform, it should be considered to placemore than one external sensor.The internal sensor will have to “see” only thewindow, mostly it will be mounted near the ceiling“looking” to the window. Care should be taken thatthere are no obstructions or reflecting surfacesbetween the sensor and the window (except for theshading device), so that the reading will berepresentative for the luminance of the windowincluding shading device.

6.4 Installing Luminaires with built-insensors

The installation of luminaires with factory-installedsensors does not differ greatly from the installationof ordinary luminaires. Therefore this type of systemis suitable for retrofit. No extra control cabling isnecessary. After the luminaire is in place it isnecessary to measure the illuminance on the worksurface under each luminaire at night and duringthe daytime to see if the illuminance is at the desiredlevel.If the units have manufacturer pre-set installationsettings these are based on assumptions on theaverage reflection factors in a typical office room.Once the system has been installed it may benecessary to make some adjustments. This canbe checked by measuring light levels at different

locations to see what the actual performances are. Ifthe combined levels are too high this is because thereflectivity of surfaces below the sensors (desktop)or the height of the ceiling may differ from themanufacturer-assumed conditions. Adjust the sensorsetting until the desired lighting level is achieved.With some systems the location of the sensor onthe lamp itself can be readjusted to improveperformance. For example, a sensor that can “see”the wall leads to different control behaviour than whenit is located at the other end of the lamp and only“sees” the floor. Such fine-tuning processes maytake some trial and error to optimise the system fora particular context.Measuring and regulating based on luminance meansalso that, even in one specific room with a uniformlighting in terms of illuminance, there will be a non-uniform luminance distribution (due to different coloursof i.e. furniture), leading to different adjustments fordifferent luminaires.Therefore there is a need for a certain regulatingmargin; as a result all manufacturers offer this featureon their systems, but different systems offer differentpossibilities. Possible systems are:· changing of lenses with different optical

transmittance (colour filters); mostly 3(coloured) lenses giving the possibility toobtain 3 dimming thresholds. Manufacturersdocument it mostly as 3 illuminance levelsfor “normal” reflectances. These systems donot allow the possibility for continuous tuning,rather tune in steps of about 50%.

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· tuning with a potentiometer (analog) givesthe possibility to tune and adjustcontinuously thresholds of dimming levelseven for “abnormal or non-uniformreflectances”

· tuning via a mechanical light passingaperture- or acceptance angle regulation:gives also the above-mentionedcontinuous tuning possibility.

· via infrared remote control eliminating theneed to open the luminaire or manipulatethe luminaire after closing it. Avoids theproblem that the installer blocks thesensor when adjusting it.

The best way to tune an installation is:· start with all sensors with equal setting

in a representative room or room-partition(some manufacturers deliver sensors witha specified manufacturer setting)

· measure initial (night-time or coveredwindows, or on a not too bright day)illuminances on a few representativepoints (i.e. at the desk(s), conferencetable)

· tune the sensors; some manufacturersgive simple rules for it (i.e. 10 % variationof dimming-threshold per turn of aregulating-device)

· based on this experience, pre-tune allsensors.

It is important to note that the so-called “constant-holders” require a more precise tuning than thesystems which partly compensate (i.e. 50%)for incident daylight.

6.5 Installing room-based systems

The mounting position of the sensor is critical whenthere is one daylight sensor controlling multipleluminaires in a single zone or room. Most types ofsensors are located in the ceiling and look down. Othermore unusual wall or work surface sensor locationsare not considered here.The sensor:· should view a part of the room which is relevant

for the lighting to ensure that the lighting iscontrolled at the right place (e.g. placed over awork-surface and not over the floor)

· should have a surface in the field of view with arelatively large surface area, otherwise it willbe difficult to predict if the control system willwork.

· should not be able to “look outside”, becausethe extra signal from an uncontrolled area(outside, or from other lamps that are notcontrolled by the sensor) will lead to incorrectoperation of the closed loop control system.

· should be located where it will not receive directlight from upward directed lamps when indirect(uplighting or pendant) lighting is used, as thiscould lead to oscillating behaviour of thesystem.

Unlike the self-contained units (where the sensor isinstalled in each luminaire) it will be necessary toprovide additional cabling between the sensor and theluminaires. Power may be supplied to the controller ordirectly to the luminaires. If the wires for power andcontrol are located close to each other there my occurelectrical interference between them, so care shouldbe taken to separate the wires properly.Once the installation is complete, measurements of

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illuminance levels in the room should be taken atnight (or otherwise for rather low daylightcontribution) and during daytime in requiredlocations. If necessary the sensor should beadjusted to provide the desired levels.Some systems allow the user to choose theirpersonal illuminances within a certain range or evenstore preset values in the memory of the controller.

6.6 Installing building-based systems

In building based systems the daylight sensorcontrolling the electric lighting can be locatedoutside of or inside some or all the rooms of whichit controls the lighting.

Interior location:If a sensor is placed in every room the installationof the system is similar to the installation of a roombased system, except that the components areconnected to a “bus” system.If the sensor is placed in a representative roomcontrolling the lighting in other, similar rooms, aconsultant should be asked to determine theappropriate representative room. Care should betaken that the representative room has the samedaylight contribution as the other rooms, and thatno deviating shading patterns on the facade exist.If there are differences, corrections have to becalculated to assure the correct lighting in thedifferent rooms.

Exterior location:An exterior mounted sensor is normally located on

the building’s roof, although it is possible for sensorsto be located on building facade(s) as well. Thesesystems rely on algorithms that translate the exteriorluminance pattern or distribution (incl. sun’s position)into a certain amount of lighting for each interior room.The effect of adjacent buildings (e.g. reflection) andobstructions (e.g. shading) should be taken intoconsideration during the placement of the sensor orduring programming. The direction of view of thesensor is dependent on the type of system beinginstalled. Because these systems are outside ofthe rooms they control, the effect of the interiorshading devices is not taken into account unless anextra sensor is installed behind the blinds, or thecontrol system also controls the blinds . In almostevery situation professional assistance for the properlocation and calibration of the sensor is required.Another variation of building-based systems is whenthe lighting control system is connected to orintegrated with a Building Management System. Inthis case it is possible for the BMS computer tomonitor or overrule the lighting control or to couple itwith non-lighting building systems. This can be usefulwhen, for example, lights are turned off for holidayperiods or the performance of the heating and lightingsystems are adjusted to compliment each other. Interms of installation this means that all buildingsystems may need extra cabling to connect them tothe BMS. In other concepts the lighting controlsystem and the BMS share the same bus line.Building management systems require trainedpersonnel. These systems can take into accountshading devices and they offer the possibility tocontrol different building installations, for example,

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diminishing the cooling when less artificial lightis used.Automatic shading control is also a form ofbuilding-based control when exterior shades orawnings are adjusted automatically bycontrollers. Sometimes this type of automaticcontrol is also used for interior shading that islocated in an inconvenient location such as in askylight or high windows.

6.7 System awareness

An important, but often overlooked aspect ofinstallation is the training of maintenancepersonnel and building occupants in the operationand purpose of the daylight responsive controlsystems. Although most manufacturers willprovide technical support during and for a periodfollowing the installation of their system, it iseasier and likely more economical if mostproblems can be addressed by those managingand occupying the building themselves.Building and facility managers need to be awareof how to operate the system and to adjust itaccordingly. They must be trained to answerquestions that may come to them fromoccupants. They need to be aware of the normalperformance of the system and how to spottypical problems associated withcommissioning. For simple systems thisinformation is found in the operation manuals.For more complex systems special trainingsessions from the manufacturer are necessary.Most manufacturers will provide some technical

support.Building occupants should receive information aboutthe purpose of the system. One approach may be toplace such information in documents normally foundin each office such as the company telephone orpersonnel book. The following is an example of textused to explain the Philips TRIOS Multisenseluminaires:The light fittings in your area are fully intelligent andwill adjust themselves automatically according to thelevel of ambient light and switch on by movementdetection if the area is occupied. Some fittings mightlook brighter than others. This is quite normal, sinceambient light conditions might differ. Some fittings mayhave switched off completely since no one occupiesthe area or sufficient daylight is available.Any further questions relating to the lighting in yourarea should be referred to the person in charge of thefacility.

6.8 Selecting a consultant

In most cases the manufacturer of the daylightresponsive control system will be able to provide orsuggest a suitable lighting consultant to assist in theproper installation of their system. A special “systemintegrator”, a person who is trained for this job, isneeded for lighting control systems that are integratedwith building management systems.

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CHAPTER7 MAINTENANCE ANDFLEXIBILITY

7.1 Introduction

This chapter discusses the factors that influencetechnical performance of the lighting system afterinstallation.A special emphasis will be on the aspects relatedto the functioning of daylight responsive controlsystems in time.Modern lighting systems with electronic controlsare capable of creating a pleasant atmosphere.At the same time such systems may be energyefficient. Unfortunately the electronics may partlyfail - or more difficult to notice - malfunction.So, once the lighting installation is in use andthe controls are set up and tuned, maintenanceis required to keep it functioning as expected.Regular maintenance takes little effort and willensure years long service of the installationFor those daylight systems that have movingparts, this is more obvious than for artificiallighting. For the artificial lighting it is generallynot sufficient to simply replace broken lamps.Also luminaires have to be cleaned periodicallyand lamps have to be replaced after theireconomic life time because of their reduced lightoutput.Within the context of this Application Guide notall the issues related to maintenance can be

discussed in detail. Especially for artificial lightingstandard cleaning and relamping and the relation withcost and energy use is discussed in most books onelectric lighting [1].Here mainly remarks will be made with respect tomaintenance issues specific for daylight responsivecontrols.Another aspect of the use of installations over time isthe need to sometimes modify control parameters oreven adapt the layout to accommodate changes inthe demands from the user. This may be a change inthe type of work or the visual task, rearrangement offurniture or a different partitioning of spaces.Components will age and eventually fail. Proper regularmaintenance will compensate for the effects of ageingand failure. Daylight responsive lighting controlsystems demand additional care in comparison withsituations without control systems. It will be necessaryto be aware of:· Obstructed or dirty light sensors· Malfunctioning of components· Ageing and breaking down of componentsThe most common factors with respect to flexibilityare changes in:· the required lighting conditions within a space

- mostly due to changes in visual task(s) orchanges in occupancy

· the daylight availability; in most cases a resultof modification of the external obstructions (forexample new buildings and growing / changingtrees)

· the interior; such as relocating room partitions,new paint in a different colour, new furniture,etc.

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7.2 The first stage: evaluation of initialperformance

It is apparent that the lighting control system hasto perform as expected after installation. Therefore,it is useful to check and document the systemperformance directly after installation and repeatthese checks periodically. Suggestions for thisevaluation can be found in this guide in Chapter 8‘Design Evaluation’ and in Appendix A ‘MonitoringProtocol’.

During the installation and in the initial period ofuse often other people are in charge of the technicalinstallation than during normal service. Due to thesemutations in personnel, information anddocumentation may get lost.A example of what could happen in a large projectis the project of the ‘Palace of Justice’ in DenBosch, the Netherlands (see case ..). After oneyear of actual use of the building the occupantsidentified the solar shading system to be the causeof a number of complaints, but already then it wasdifficult to find out which company installed thissystem. During the building phase a number ofresponsible managers of the constructing companydid not see the need to pass on (as was apparentlater) critical system information to the end user.When good documentation and a description of thesystems and their performance are available it ispossible to compare real performance with thedesign expectations.

7.3 Changes in the required lightingconditions

Organisations nowadays change continuously whichleads to adjustments in use of spaces and tocombinations or new spaces. This may lead to theneed to adjust the lighting controls. This is especiallyimportant for daylight responsive controls of electriclighting. Systems with ceiling mounted sensors reactto the average luminance below the sensor. So aslong as these luminances are not seriously affectedthere is no need for re-adjustment.When partition walls are changed sometimes newarrangements have to be made in the more complexcontrol systems. In the case of bus based systemsthese changes may require special action. Often thesystem has to be re-programmed by trained personnelto ensure proper functioning. The reprogramming isneeded to define new groups of luminaires which arecontrolled according to the new spaces or users.Luminaire based systems might not need to bechanged.A special problem is a drastic change in averagework surface reflectance under ceiling mountedsensors. As explained in previous chapters thesesensors react on the average luminance of the worksurface. This means that changes in average reflectionwill influence the average illuminance from the lightingcontrol system. So the system needs to be re-calibrated in case of significant (>10%) change inthe average reflectance. This involves measurementof illuminance and adjustment of system parameters(in luminaire based systems often adjustment of thehardware, in other systems adjustment of software

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parameters in the control software).Ceiling mounted sensors will fail to work correctlyfor extremely low reflectances. This may occurfor instance in a space with a very dark floor.When too little daylight and or electric light isreflected no significant luminance can be seenby the sensor the system will compensate thiswith a maximum (full) output and no dimmingoccurs.Changes in the required lighting conditions canalso be required by changes in visual task(s).In recent practice complaints about the electriclighting in a workspace revealed the following.The workspace is a large drawing room. Originallythe lighting in this room was laid out toaccommodate the drawing on large drawingboards, typically a visual task which demandshigh vertical illuminance values in order to seesmall details on inclined surfaces. Recentlyhowever the drawing boards have been replacedby computer based drawing systems equippedwith computer screens. Of course this visualenvironment demands much lower verticalilluminances and luminaires that are sufficientlyshielded to avoid direct and reflected glare. Inthat situation the lighting installation of the‘drawing room’ has to be adapted for the newtask by replacing the luminaires (optics).Apart from such drastic changes, more subtleadaptations of the lighting may be necessary.In many cases the maintained lighting levelsneed adjustments. There is always a number ofpersons who prefer less or more light. Switchinggroups of luminaires or adding (task) lighting or

adapting the reference setting of the control systemare possible structural solutions. The complexity ofthe last adjustment is dependent on the type of systemand hence should be an issue in the initial selection ofthe system.Daylight responsive controls are often part of a moreextensive control system. However, already thesimplest lighting control systems have the possibilityto adjust the set point.Most computer-based systems require the adjustmentof a parameter in the control software. Other systems(some luminaire based systems) demand physicaladjustment of the sensor often in combination withilluminance measurements. This may be very timeconsuming.

7.4 Ageing of components

The ageing of the components of a daylight responsivelighting control system can be subdivided in two parts:the lighting installation (lamp, luminaire) and the controlsystem (sensor and controller).The most obvious component in the lighting installationis the lamp. The lamp life (time after which 50% of thelamps will probably fail) reflects the number of hoursthat a lamp is expected to burn. The use of a controlsystem might influence the lamp life negatively, as aresult of switching lamps on and off more than withoutthe use of the system. However – as a result of thisswitching – the burning hours per year for the lampsare less than for the case of lamps that are notcontrolled. Therefore the replacement time caneffectively be equal or even longer than without daylightlinked control.

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An additional benefit of the use of a control systemis that the effect of lamp ageing can becompensated by a control system. Because of theexpected lamp depreciation artificial lightinginstallations have to be over dimensioned. Due tothe control system the lamps are dimmed in thebeginning, thus compensating for the extra powerinstalled and gradually regulate to full output whenthe lamps depreciate over time. With this “constantlux” feature energy will be saved.

Besides by the ageing of the lighting installationcomponents, the efficacy of the system can beinfluenced by the ageing and degradation of thesensor. Little is known about ageing of the lightsensors, but some conclusions can be drawn uptill now:· It is well known that certain older types of

Light Dependent Resistors [LDR] degradeover time. In some cases a difference of morethan 50% in one year has been recorded.LDRs used in the individual lighting controlsystems today are regeneratingautomatically. This requires a sufficientamount of light. This means that if thesensor is used in a very dark environment(with little or no daylight and a low artificiallighting level), after some time problemsmay occur.

· Serious problems can be caused by thedegradation of certain types of plastic usedin the white diffusing covers of cells.

· Photo diodes are known to be very stableover time.

The life of the electronics used to drive the lamp andpossible the electronics of the control system play arole. In general it is assumed that the electronicslive longer than the lamps.

7.5 Malfunctioning of components

System failure can have multiple causes. Somefailures are difficult to notice especially when thevisual comfort is not affected. This is for instance thecase when the daylight responsive dimming functionof an electric lighting installation does not work: thelights will stay on and so there is sufficient light. Noenergy will be saved however.What may happen is that an electronic circuit breaksdown, or a light sensor is short circuited ordisconnected. If the failure in the electronics causesa constant voltage of 10V output at the sensor thelights will dim and eventually switch off. This will soonbe noticed. In case of short circuit the control systemwill respond with maximum light output, in case ofdisconnection the controller reacts according to thesystem type as if no sensor is present (generallyalso with maximum output). Then user complaintsare less likely.

7.6 Maintenance program

To prevent the system from degradation or loss infunctionality (from the viewpoint of visual comfort aswell as in energy savings) periodical inspection and

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maintenance are essential.In general it is advised to refer to the operation/maintenance manual of the manufacturer to findsuggestions for the maintenance of the system.When lamps are replaced or cleaned as part ofa normal maintenance program the sensorsshould be cleaned along with the luminaire.Whenever extensive re-lamping takes placeilluminance measurements should be conductedand sensors recalibrated in order to secure properfunctioning of the control system.Depending on the type of control system, thelight sensors might need some extra care.Sensors located on the outside of the buildingshould be regularly checked to be sure they areclear of debris and do not suffer from weatherdamage (corrosion, yellowing).

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CHAPTER8 DESIGN EVALUATION

8.1 Introduction

To guarantee an optimised use of a daylightresponsive lighting control system, it might benecessary to adjust the system some time afterit is installed. In most cases the building owner/facility manager will be responsible to checkwhether the system is working as it is supposedto do. This chapter will show how to evaluate thesystem in use, technically and on useracceptance, and include information on possiblemethods to deal with complaints, preferencesand technical problems.

8.2 Evaluation of the design

A daylight responsive lighting control system canbe chosen to save energy, to improve comfort orto realise a certain image. In order to assure thatthe system fulfils the demands, evaluation couldlead to improvement or adjustment of the systemto meet these demands.

8.2.1. Technical evaluation

The technical evaluation contains themeasurements of the maintained illuminancelevel and energy consumption.

8.2.2 Maintained illuminance level

An installed control system should at least maintain acertain (design) illuminance level and the lamp powerwhen the illuminance falls below this. Whether thesystem fulfils this task can be checked with a calibratedlight sensor, placed at the users’ work plane. For amore extensive monitoring or long term monitoring aMonitoring Protocol is drawn up (see Appendix …)

8.2.3 Energy savings

The reduction of energy consumption can be monitoredwith a kWh meter. To determine the energyconsumption of the room without control system, theprocedure is as follows:· install a kWh meter just before installation of

the control system and measure the energyconsumption of the artificial lighting, or

· measure the energy consumption when thecontrol system is installed, for 100% output ofthe artificial lighting, for example during the night

· use the installed power and the monitoring timeto determine the energy consumption of thereference situation

To get a reliable assessment of the energyconsumption with a control system, long termmonitoring of the energy consumption is necessary,while the energy consumption varies significantly underdifferent weather conditions. Therefore one shouldmeasure the energy consumption at least for twoweeks, including different weather conditions and fordifferent seasons. One whole year of monitoring ispreferable. Also the time the lighting would be used

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without the control system should be taken intoaccount. User behaviour can vary between leavinglights on all the time and switching them off alwayswhen leaving the office or when enough daylight ispresent.Total energy savings can be calculated accordingto:

Energy savings (%) =

100 . ( 1 - Qcontrol

/Qreference

) =

100 . ( 1 - Qcontrol

/ (P.T))

where:Q

controltotal measured energy consumption of

situation with control systemQ

referencetotal measured energy consumption of

situation without control systemP installed powerT total time over which the energyconsumption is measured

8.3 User acceptance evaluation

In order to realise energy savings it is necessarythat the user accepts the daylight responsive lightingcontrol system. Acceptance is an important issue,especially when the system is installed to enlargethe comfort of the users. Both acceptance andcomfort can be reviewed after installation of thecontrol system.An important aspect that can determine theacceptance of a system, is that one has to ensure

that the user understands how to work with and whatto expect from the installed daylight responsivelighting control system. Therefore it is necessary tointroduce the system and show the attributes thatthe system offer. More information can be found inthe chapter on ‘User Reaction to Daylight ResponsiveControlled Lighting’.There is no need for a specific questionnaire to beused to indicate problems coming with the daylightresponsive lighting control system. Users of thebuilding can be asked to write down whether theyare disturbed by the lighting and / or blinds, or informthe building owner when there are specific problems.Besides this, it can be useful to go through thebuilding, talk to the users and evaluate byobservation, focussing on signs of sabotage.When the user is disturbed, for example when thereis too little light for him at his work place, or theblinds should be opened while the system keepsthem closed, the user will mostly complain or try tosabotage the system.This means that the control system cannot performas it is supposed to do, or even not perform at allanymore. Intended energy savings will not be reachedin this case. Therefore it is necessary to take useracceptance into consideration (see chapter 5).

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CHAPTER9 OUTLOOK

The studies conducted within Subtask B of IEATask 21 showed that the vast majority of daylightresponsive control systems only control theartificial lighting. The control of the enteringdaylight is will be left to the user or to anotherbuilding system (mostly only sunscreening). Theexisting systems can be used with tradionalwindows with traditional sun or glare protection.For the combination with innovative daylightingsystems no guidelines could be given, exceptfor the general advices for installing sensors.Existing daylight responsive artificial lightingcontrol systems realise in practice an energysaving of 40 to 50% of the energy by dimmingand switching off (sometimes even more energycan be saved by replacing old installations bynew, high frequency lamps and ballasts in efficientoptical systems). There is no tendency to improvethese systems with respect to a higher precisionin the maintenance of the illuminance level atthe desk, since it might increase these energysavings only slightly. Only when energy costsincrease it will be useful to focus on the last smallpercentages of extra energy savings that can bereached.In some cases (e.g. single cell offices) presencedetection combined with the lighting control cansave around 50% energy because on averagethe office workplace will be occupied only 50%of the time. This type of lighting control has notbeen studied in this task, but many daylight

responsive conrol systems have presence detectionas an optional feature, which can be more effectivethan the daylight responsive dimming.It seems to be useful to focus on user acceptance anduser interface. The existing control systems maintaina minimum task illuminance (daylight responsiveartificial lighting control system).Nonetheless, the variety in individual preferences isshown in various research (for task illuminances e.g.Tregenza et al. 1974, Halonen and Lehtovaara 1995,Begemann et al. 1997, Tenner et al. 1997, for discomfortglare from windows e.g. Hopkinson 1970, Osterhaus1996, Velds 2000). The maximum and minimum setvalues might not be accepted by all users. Therefore,they should have the opportunity to overrule or influencethe blind control. The actual control that the user shouldhave over the lighting should be given consideration aswell. Control over the workplace lighting can lead to adecrease of performance and influence the user’s mood(Veitch and Gifford 1992). Stress and frustration canbe caused by having too many choices and therequirement to make frequent adjustments in theworkplace (Heerwagen et al. 1991). Additional researchis required to obtain information on the necessaryinfluence an user should have on a control system, torealise acceptable lighting conditions for each user.Within this research project, the performance of daylightresponsive artificial lighting control systems insituations with daylighting systems has not beenstudied. Whereas daylighting systems can influencethe illuminance and luminance distribution in the roomsignificantly, additional research with respect to thisaspect is necessary.

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FURTHER READING FURTHER READING

- N.C. Ruck, O. Aschehoug, J.Christoffersen, R. Jakobiak, K. Johnsen,E.S. Lee, S.E. Selkowitz, (Ed) 2001.Daylight in Buildings: A Source Book onDaylighting Systems and Components,Report of IEA SHC Task 21/ECBS Annex29. Lawrence Berkeley NationalLaboratory, CA.,USA (In Press).

- IES Lighting Handbook, IlluminatingEngineering Society of North America

- S.H.A. Begemann, M.P.J. Aarts, A.D.Tenner, Daylight, artificial light andpeople, Philips Lighting B.V., 1994, 8p.

- J.A. Love, Manual switching patterns inprvate offices, Lighting Research andTechnology, Vol. 30-1, 1998, pp.45-50.

- C. Laurentin, V. Berrutto, M. Fontoynont,Manual control of artificial lighting in adaylit space, EPIC’ 98, 1998, 6p.

- J.P. Bohrer, Evaluation of manual selectiveswitching as an office lighting controlstrategy, Master’s thesis, 1992.

- E. Vine, E. Lee, R. Clear, D. DiBartolomeo, S.Selkowitz, Office worker response to anautomated venitian blind and electric lightingsystem: a pilot study, Energy And Buildings,Volume 28, n°2, 1998, pp. 205-218.

- S. Escuyer, V. Berrutto, M. Fontoynont, Testingin real offices of daylight responsive lightingcontrol systems: a review of recent articles,EPIC’ 98, 1998, 6p.

Chapter 4/1/ Baker N, Fanchiotti A, Steemers K (editors),

various authors, Daylighting in architecture, AEuropean Reference Book, Published for thecommission of the European communities(directorate-general XII for science, researchand development) by James & James Ltd.,London 1993

/2/ Hunt D R G, Improved daylight data for predictingenergy savings from photoelectric controls,Lighting Research and Technology, Vol. 11 No.1 1979

/3/ Hunt D R G, Availability of Daylight, BuildingResearch Establishment, Garston, 1979

Chapter 4.3/1/ DIN 5034 Part 2, Tageslicht in Innenräumen,

German Standard, February 1985/2/ Aydinli S., Seidl M., Van Bergem-Jansen P.M.,

Keller B., Tageslichtanforderungen,Grundlagen, Berechnung, Messung,energetische Aspekte II-1.1, Innenbeleuchtung/Planung und Berechnung, Handbuch fürBeleuchtung, 5. Auflage, Landsberg 1992

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/3/ Aydinli S., Seidl M., Determination of theeconomic benefits of daylight in interiorsconcerned with the fulfilment of visual tasks,Proceedings I, International DaylightingConference, California U.S.A. November 4-7, 1986

/4/ Aydinli S., Krochmann J., Seidl M.Possibilities for energy saving for electricallight by daylighting of interiors inconsideration of the visual task.Proceedings, European Conference onArchitecture. Commission of the EuropeanCommunities. Munich, Germany, 6-10 April1987

/5/ Aydinli S, Hornoi O., Krochmann E.,Tageslichtabhängige Steuerung vonBeleuchtungsanlagen – Gewinn für alle ?,Tagungsberichte zur 10.Gemeinschaftstagung der LichttechnischenGesellschaften Deutschlands, derNiederlande, Österreichs und der Schweiz,Licht 92 in Saarbrücken, 1992

/6/ Ehling K., Knoop T., Aydinli S., Kaase H.,Energy efficient and ergonomic lighting byinnovative daylight systems and buildingmanagement systems. Proceedings, LUXEUROPA 1997, Amsterdam 11-14 May1997.

/7/ Knoop T., Ehling K., Aydinli S., Kaase H.,Investigation of daylight redirecting systemsand daylight responsive lighting controlsystems. Proceedings Right Light, 4thEuropean Conference on Energy-EfficientLighting, Copenhagen, Denmark, 19-21November, 1997

IllustrationsThe photographic illustrations in this application guideare reprinted from International Lighting Review,published by Philips Lighting Luminaire Group, withpermission of the publisher.

/8/ Belendorf H., Aydinli S., Kaase H., A practicalmethod for the assessment of daylightresponsive lighting control systems regardingenergy saving and lighting quality, EuroSun2000, Kopenhagen, 2000

/9/ Belendorf H., Aydinli S., Kaase H., Einpraxisorientiertes analytisches Verfahren zurenergetischen und lichttechnischenBewertung tageslichtabhängigerKontrollsysteme, Licht 2000, Goslar, 2000

/10 / Belendorf H., Aydinli S., Kaase H., Acomprehensive method for the prediction ofenergy-savings using daylight-systems anddaylight-responsivelighting control systems,Lux Europa 2001, Reykjavik, 2001

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