building energy performance modelling and simulation...

1

2011/2012

© ČVUT v Praze, FSv K125 prof.Kabele

BUILDING ENERGY PERFORMANCE MODELLING AND SIMULATION 5

125BEPM,MEB,MEC prof.Karel Kabele 56

Climate data

Project site

Building geometry

Materials & Constructions

Lighting & equipment

internal gains

Occupancy

Lighting

Ventilation

Plant & Systems

IEA, 1994 Study the detail of input data

Input data categories

125BEPM,MEB,MEC 57 prof.Karel Kabele

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2011/2012


Input data

•Hourly weather data (in most cases for an entire year). Main climate parameters:

– Dry-bulb temperature

– RH

– Wind speed and wind direction

– Solar radiation (direct and diffuse)

Reference year (RY)

Should represent mean values of main climate parameters that are as close as possible to long-time mean values.

Main requirements for RY

• True frequencies, i.e., as near as possible to true mean values over a longer period,

e.g., a month, and a natural distribution of higher and lower values for single days.

• True sequences, i.e., the weather conditions must have a duration and follow each

other in a similar manner to often-recorded conditions for the location.

• True correlation between different parameters, i.e. temperature, solar radiation,

cloud cover and wind.

prof.Karel Kabele 58

Climate data

125BEPM,MEB,MEC

Dry and wet bulb temperature


Fan

Wet bulb

temperature Dry bulb

temperature

Wet

„sock“

Air

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2011/2012


Psychrometric chart


Dry bulb

temperature

Relative

humidity %

Absolute

humidity

Dew

point

Wet bulb

temperature

Enthalpy

TEMPERATURE

HUMIDITY

RATIO

g/kg

Fan Wet bulb

temperat

ure

Dry bulb

temperatu

re

Wet

„sock“

Air

Weather data formats

• *.epw – EnergyPlus weather files

• *.wea - Weather Data File

• *.dat - plain text file

• WYEC and WYEC2 data files

• Test Reference Year (TRY)

• Typical Meteorological Year (TMY)

• Design Summer Year (DSY)

Data Sources

• Simulation programs file libraries

• Energy plus website

• Meteonorm

• ESP-r embedded files

• ASHRAE

Conversion of data formats possible

• Weather Tool (Square One)

• Esp-r

• Weather manager

Climate data


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2011/2012


62

Climate data for energy calculations:

Multi-year datasets: they are fundamental and include a substantial amount of information for a number of years.

Typical years: a typical or reference year is a single year of hourly data selected to represent the range of weather patterns that would typically be found in a multi-year dataset. The definition of a typical year depends on how it satisfies a set of statistical tests relating it to the parent multi-year dataset.

Representative days: they are hourly data for some average days selected to represent typical climatic conditions. Representative days are economical for small-scale analysis and are often found in simplified simulation and design tools.

Selection of weather data format driven by the modelling objective. E.g.:

Sizing of cooling/heating plant => design weather year

Estimation of overheating risk for naturally ventilated spaces (percentage of hours over a

certain temperature) => near extreme summer and mid-season

Annual energy use prediction=> typical weather year

Climate data

125BEPM,MEB,MEC prof.Karel Kabele


PRG iwec

Climate data

125BEPM,MEB,MEC

5

2011/2012



Solar processes

• Solar constant 1360 W/m2

• Difusse and direct radiation • Real radiation max 1000 W/m2

• Solar altitude (Alt) (β) sometimes referred to as elevation, that is the angle between the object and the observer's local horizon.

• Solar azimuth (Az) (φ), that is the angle of the object around the horizon


sinsincoscoscossin LATHLAT

cos

sincossin

H

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2011/2012


Solar processes

Incident angle of solar rays to sloped surface


cossinsincoscoscos

θ the angle of incidence

between the direct

solar beam and the

normal to the surface

β Solar altitude

γ Surface-solar azimuth - the

angular difference between

the solar azimuth φ and

the surface azimuth ψ.

Σ surface tilt angle, measured from the horizontal

Project Site

Input data

• Location (e.g. latitude, longitude, altitude)

• Solar and wind exposure

• Ground reflectance and temperature

Data Sources

• Client

• Architect

• Photographic material

• Weather file

• Google Earth

• Topographic maps

• Site visit

• Inherent program database


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2011/2012


Building Geometry

Input data

• Single- or multi-zone simulation programs orientation, space volumes, opaque and

transparent surface areas

• Whole-building simulation programs orientation, full 3D geometry

Data Sources

• Drawings and specifications

• CAD geometry import

Zoning

• Increased complexity has a significant negative impact on calculation time (for program)

and on modeling time (for user) especially for large projects with the benefits in the

simulation output from this more “realistic” representation of the building being only

minimal.

• Spaces should be grouped into one zone when similarities exist in:

Free-running environmental performance

Conditioning (HVAC) characteristics

Internal and solar gains.

Zoning


http://www.doe2.com/download/equest/eQUESTv3-Overview.pdf







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2011/2012


Input data

• Material properties (conductivity, density, specific heat, short-wave absorptivity, long-wave emissivity, moisture diffusion resistance )

• Thickness of individual element layers

Data Sources

• Opaque building elements:

o Architect

o Inherent program library

o User personal database

o Published databases from recognized institutions and associations (e.g. ASHRAE, CIBSE)

• Transparent building elements:

• Facade specialist

o Manufacturer data

o Output from specific programs (e.g. WIS and WINDOW)

Materials & Constructions


Optical properties


Documentation Visible transmittance Solar absorptivity and

reflectivity U-value

Calculation Incident angle (0-80°) related values Direct transmittance Reflectivity Heat gain Absorptivity

125BEPM,MEB,MEC

9

2011/2012


Optical properties

The Solar Heat Gain Coefficient (SHGC) or g-factor consists of two components: – Solar radiation passed through the window (solar optical transmittance) – Solar radiation absorbed within the glazing system and redirected to the

indoor space by heat transfer (inward flowing fraction)

• The solar optical transmittance is a wavelength-dependent spatial distribution function. It is associated with the incident direction of the sun (bi-directional function) and depends on the type (material, coating, thickness) and geometry of the fenestration system. The considered solar spectrum is mainly visible and near infrared.

• The inward flowing fraction depends in addition on the inside/outside air temperatures and film coefficients and on the room characteristics, and relies on the combination of convection, conduction and radiation effects. It is mainly based on the far infrared spectrum.


Glazing


Clear float 76/71, 6mm, internal blind id: DCF7671_06i

Clear float 76/71, 6mm, no blind id: DCF7671_06nb

125BEPM,MEB,MEC

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2011/2012


WINDOW 5.2


http://windows.lbl.gov/

125BEPM,MEB,MEC

Sensible heat from lights

Heat transferred to the room from the lights can be calculated as

Hl = Pinst K1 K2

where

Hl = heat transferred from the lights (W)

Pinst = installed effect (W)

K1 = simultaneous coefficient

K2 = correction coefficient if lights are ventilated. (= 1 for no ventilation, = 0.3-0.6 if ventilated)

76 prof.Karel Kabele

Installed effect W/m2

125BEPM,MEB,MEC

11

2011/2012


Sensible heat from electric equipment

Heat transferred from electrical equipment can be calculated as

• Heq = Peq K1 K2

where

– Heq = heat transferred from electrical equipment (W)

– Peq = electrical power consumption (W)

– K1 = load coefficient

– K2 = running time coefficient

prof.Karel Kabele 125BEPM,MEB,MEC 77

Sensible heat from machines

When machines runs heat can be transferred to the room from the motor and/or the machine.

If the motor is in the room and the machine is outside Hm = Pm / hm - Pm

If the motor is belt driven and the motor and belt is in the

room and the machine is outside Hm = Pm / hm - Pm hb

If the motor and the machine is in the room Hm = Pm / hm • In this situation the total power is transferred as heat to

the room. • Note! If the machine is a pump or a fan, most of the

power is transferred as energy to the medium and may be transported out of the room.

If the motor is outside and the machine is in the room Hm = Pm

If the motor is belt driven and the motor and belt is outside

and the machine is in the room Hm = Pm hb


where Hm = heat transferred from the machine to the room (W) Pm = electrical motor power consumption (W) hm = motor efficiency hb = belt efficiency

125BEPM,MEB,MEC

12

2011/2012


Sensible and latent heat from persons

• Number

– Design values

– Models – static, stochastic

• Heat

• CO2 production


REF: J. Page, D. Robinson, N. Morel, J.-L. Scartezzini, A generalised stochastic model for the simulation of occupant presence Energy and Buildings (2007)

Metabolic rate

• The metabolic rate, or human heat production, is often measured in the unit "Met". The metabolic rate of a relaxed seated person is one Met, where

• 1 Met = 58 W/m2 • The mean surface area, the Du-Bois area, of the

human body is approximately 1.8 m2. The total metabolic heat for a mean body can be calculated by multiplying with the area. The total heat from a relaxed seated person with mean surface area would be

• 58 W/m2 x 1.8 m2 = 104 W


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2011/2012



Activity W/m2

Reclining 46

Seated relaxed 58

Standing relaxed 70

Sedentary activity (office, dwelling, school, laboratory) 70

Graphic profession - Book Binder 85

Standing, light activity (shopping, laboratory, light industry) 93

Teacher 95

Domestic work - shaving, washing and dressing 100

Standing, medium activity (shop assistant, domestic work) 116

Washing dishes standing 145

Domestic work - washing by hand and ironing (120-220 W) 170

Volleyball 232

Gymnastics 319

Aerobic Dancing, Basketball, Swimming 348

Sports - Ice skating, 18 km/h 360

Skiing on level, good snow, 9 km/h, Backpacking, Skating ice or roller, Tennis 405 1 Met = 58 W/m2 , 58 W/m2 x 1.8 m2 = 104 W

125BEPM,MEB,MEC

Occupants - sensible x latent heat

Specific Enthalpy of Dry Air = Sensible Heat

ha = cpa . t Specific Enthalpy of Water Vapor = Latent Heat

hw = cpw . t + hwe

Specific Enthalpy of Moist Air h = ha + x hw


where

h = specific enthalpy of moist air (kJ/kg)

ha = specific enthalpy of dry air (kJ/kg)

x = humidity ratio (kg/kg)

hw = specific enthalpy of water vapor (kJ/kg)

t = air temperature = water vapor temperature (oC)

cpa = specific heat capacity of air at constant pressure (kJ/kg.oC,

kWs/kg.K) =1.006 (kJ/kgoC)

cpw = specific heat capacity of water vapor at constant pressure

(kJ/kg.oC, kWs/kg.K) =1.84 (kJ/kg.oC)

hwe = evaporation heat of water at 0oC (kJ/kg) = 2,502 (kJ/kg)

Radiation Convection

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2011/2012


Heat load by persons

0

50

100

150

200

250

300

350W

Latent heat

Radiation

Convection


Operation profile

Cold water use in residential building

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

hod

Co

ld w

ate

r (

w/o

DH

W)

l/p

ers

/hr

Monday

Tuesday

Wednesday

Thursday

Friday

Saturday

Sunday

Mean


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2011/2012


CO2 production

• Carbon dioxide (CO2) concentration in "clean" air is 575 mg/m3.

• Huge concentrations can cause headaches and the concentration should be below 9000 mg/m3.

prof.Karel Kabele 125BEPM,MEB,MEC 86

Ventilation

Input data

• Mechanical ventilation rates

• Infiltration rates

• Mechanical ventilation schedules (hourly, daily, weekly, seasonal etc)

• Controls

• Characteristics of fans and ducts

• External pressure coefficients and characteristics of natural ventilation openings (size, operation schedule etc) and

• In case of CFD also define geometry, grid, boundary conditions and turbulence model.

Data Sources

o Building services engineer

o Published databases and guidelines from recognized institutions and associations (e.g. ASHRAE, SMACNA, AIVC)


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2011/2012


Plant & Systems

Input data

• System types (e.g. VAV, CAV) and specifications (e.g. efficiency, capacity)

• Plant specification for each system component (e.g part load performance curves, full load efficiency, stand-by losses etc )

• System and plant components control characteristics (e.g. thermostat set points, sensor types and locations, operational characteristics such as: On/Off, proportional only, etc)

Resources

o Building services engineer

o Inherent program library

o Published databases from recognized institutions and associations (e.g. ASHRAE, CIBSE)


http://www.designbuilder.co.uk/content/view/115/182/

Graphical definition of HVAC plant and components


http://www.designbuilder.co.uk/content/view/115/182/

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2011/2012


ESP-r background

• ESP-r (Environmental Systems Performance; r for „research“) • Dynamic, whole building simulation finite volume,

finite difference sw based on heat balance method. • Academic, research / non commercial • Developed at ESRU, Dept.of Mech. Eng. University of

Strathclyde, Glasgow, UK by prof. Joseph Clarke and his team since 1974

• ESP-r is released under the terms of the GNU General Public License. It can be used for commercial or non-commercial work subject to the terms of this open source licence agreement.

• UNIX, Cygwin, Windows


http://www.esru.strath.ac.uk/

125BEPM,MEB,MEC

ESP-r architecture


Project manager

Climate

Material

Construction

Plant components

Event profiles

Optical properties

Databases maintenace

Model editor

Zones

Networks •Plant •Vent/Hydro •Electrical •Contaminants

Controls

Simulation controler

Results analysis

•Timestep •Save level •From -To •Results file dir •Monitor •…

•Graphs •Timestep rep. •Enquire about •Plant results •IEQ •Electrical •CFD •Sensitivity •IPV

125BEPM,MEB,MEC

18

2011/2012


LOW-ENERGY BUILDING ENERGY SYSTEM MODELLING

Case study


Introduction

• Low Energy Buildings ? < 50 kWh/m2/a

– perfect thermal insulation of the building envelope

– design and control of heating systems

– warm-air heating systems.

– solar energy utilisation

– long-term energy accumulation

• How to design?


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2011/2012


Low Energy Building


Architectural concept Zoning

Greenhouse

Thermal insulation

Air tightness of the envelope

Energy system concept – Controlled ventilation

– Warm-air heating

– Solar energy utilisation


Principles of solar energy utilisation

Active solar water collectors

Passive solar gains via glazed balconies

Gains from greenhouse – midterm accumulation into the gravel accumulator below the building.

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2011/2012



Midterm solar energy accumulation

Greenhouse air warming up

Loading of the accumulator

Unloading of the accumulator

Additional heat source


Problem description

Boundary conditions

Geometry

Climate

Fresh air volume

Required output of the system

Optimisation criterions

Annual energy consumption

Output of the additional heat source

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2011/2012



Modelling of energy performance

Modelling tool selection criterions

Dynamic modelling

Heat transfer coefficients

ESP-r, TRNSYS

Model in ESP-r

Zonal model describing building and energy system … why 2 models?

Energy system

Building

+

Building model


Input:

10 zones, construction, shading elements, operational schedule

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2011/2012


Model of active solar system with mid-term heat

accumulation


ESP-r model •HVAC system divided into 5 thermal zones

•roof air solar collector •greenhouse air solar collector •gravel heat accumulator •heat exchanger •air heater


Simulation Climate database:

Test reference year Time period 1 year Time step of the output 1 hour Time step of the calculation 1 minute

Building: What?

Energy demand for heating How? 1x simulation loop Output: Heating output

Energy system What? Annual energy consumption How? Virtual experiments •Loading air variation •Accumulation mass of the gravel Output? Design of the elements

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2011/2012


Simulation results


Annual energy consumption

Heating energy consumptionimpact of accumulator

100%

56%

52%

53%

47%

47%

44%

0%

20%

40%

60%

80%

100%

120%

0 1 2 3 4 5 6

Virtual experiment Nr.

Virtual experiment

0 without accumulator

1-3 change of the loading air volume 100 to 2000 m3/h

4-6 change of gravel mass 50 to180 t

Energetický systém

Temperature in the accumulator

100% = 11,4MWh =410EUR/year

Conclusions

• Virtual experiments confirmed that use of preheating of fresh air supply in gravel accumulator, located below the building contributes positively into the energy balance.

• Use of simple preheating of fresh air supply in gravel accumulator decreases annual energy consumption for ventilation air to approx. 50%.

• Virtual experiments did not confirm significant influence of design parameters to the collecting and accumulating of solar energy in simulated configuration of collectors and accumulator size. The solar energy contribution is in this case very small and most of the accumulator energy gain is given by relative constant earth temperature below the building. In all of simulated virtual experiments was the accumulator mass temperature during the year in the range 12°C to 16°C


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