dissertation

ANALYSIS OF THE INFLUENCES OF SOLAR

RADIATION AND FAADE GLAZING AREAS

ON THE THERMAL PERFORMANCE OF

MULTI-FAMILY BUILDINGS

Dipl.-Ing. Gnter Haese Hannover

Thesis submitted in partial fulfillment of the requirements of the Technical University of Bialystok

for the degree of Doctor of Technical Sciences

Doctoral adviser : Dr. hab. Ing. Miroslaw Zukowski Prof. PB Reviewer : Prof. Dr. hab. Ing. Wladyslaw Szaflik : Prof. Dr. hab. Ing. Jerzy Andrzej Pogorzelski Defense of doctors thesis : December 6th 2010

Faculty of Building and Environmental Engineering

Technical University of Bialystok

2010

Abstract

Modern, urban multi-family buildings are characterized by large faade glazing areas. Under the perspective of ecology and the duty to design energy-efficient buildings, these market requirements are contributing to a technical conflict of goals. It is well known that large glazing openings are not only responsible for a large part of heat loss in cold periods, but can also help to collect a lot of energy for living rooms through the passive effect of solar radiation. The question is which opening sizes, which technical glazing properties and which directions support an optimal situation between thermal comfort and the use of primary energy. A qualified answer can only be found in an integrated approach with the application of modern and complex computer simulation programs which include all parameters of building geometry, building materials used and the interaction between all installed heating, cooling and ventilation systems. The aim of this work is to show new ways of designing modern, energy-efficient dwelling-houses taking solar radiation into special consideration. Three co-operative apartment houses, which are being built in Hannover in 2009, are the object of this dissertation.

The detailed simulation method was chosen for the current work. The use of the EnergyPlus V3-0 simulation tool helped to combine heat and mass transfers, to simulate multi-zone airflow and to operate heating, cooling and ventilation systems for long periods. Special attention was focused on the heat transfer through windows. Twelve cases of fenestration products with different types of low-e-coatings and different configurations of optical filters on glass surfaces were examined. All relevant parameters of the developed glazing systems were determined with the help of the WINDOWS 5.2 computer program. Based on the above analysis, a general procedural method was presented to determine an optimal window-to-wall ratio (WWR) for any dwelling house. As it turned out in the investigated case, the annual heating energy consumption could be reduced by over 30 % when using the considered WWR optimization. The simulations were conducted with different weather profiles for several locations in Germany. Additionally, experimental investigations were carried out to determine the thermal performance of a considered external wall in solid construction and then to calibrate the building simulation software. Furthermore, the analysis of the influence of the glazing system area on the buildings energy demand showed that there is an approximate linear correlation between energy consumption for space heating and the WWR. Another aspect of the investigations was to determine the relationship between the energy demand for space heating and the windows height above ground level in different seasons. Simulation results indicated that the difference between the first and the last floor is high and equal to 31 % for balcony-windows and up to 66 % for windows in winter. Large fenestration areas can generate overheating problems for living spaces during intensive solar radiation. Coupled with external shading devices, cooling through the use of ambient air driven by ventilation systems is an effective and energy-efficient solution if the ambient temperature is lower

than the inner air temperature. It was found that the amplitude between day and night internal air temperatures is significantly higher for apartments with variable air volume systems in comparison to constant air volume systems. The difference between the mean operative temperature reaches up to 4.4C. Window shades with the highest reflective surface mounted outside and near the fenestration guarantee the best protection of gains from solar radiation. In order to compile the energy balance of the analyzed building, the operation of a solar domestic hot water system (SDHW) was investigated. Several tilt angles were tested for the solar collectors, whereas the simulation showed that an angle of 35 is optimal in summer time and an angle of 70C is optimal for the cold period. If a fixed tilt angle of 45 is used throughout the year the absorbed solar energy varies only about 10 % maximum. It turned out that the solar conversion process is about ten times lower in winter than those during the summer time. Another important question in the design of a SDHW system is the optimal value of a stratified storage tank. Based on the analysis of the influence of the volume of accumulated water on the thermal performance of the SDHW system, it can be concluded that the recommended volume of the storage tank for the developed case is 4 m3. Results of the calculations showed that the temperature of storage water increased by over 50C between April and September. Hereby it could be shown that the total designed area of solar collectors is too small to be an effective support of the heating system during the whole year.

Table of contents

ABSTRACT ..... 2 TABLE OF CONTENTS ... 4 NOMENCLATURE .... 6

1 SCIENTIFIC FRAMEWORK .............................................................................................................. 8

1.1 INTRODUCTION .................................................................................................................................... 8 1.2 BACKGROUND AND LITERATURE REVIEW .......................................................................................... 10

1.2.1 Method for modelling and simulation of building thermal behaviour ..................................... 10 1.2.2 Solar heat gain through windows ............................................................................................ 18 1.2.3 Influence of envelope features on energy consumption and potential savings ........................ 23 1.2.4 Modelling and designing solar domestic hot water systems .................................................... 26 1.2.5 Summary of literature review .................................................................................................. 39

1.3 RESEARCH GOALS AND HYPOTHESIS .................................................................................................. 40 1.3.1 Scientific goals ......................................................................................................................... 40 1.3.2 Hyphothesis ............................................................................................................................. 40

2 RESEARCH METHODS .................................................................................................................... 41

2.1 BUILDING ENERGY SIMULATION SOFTWARE ...................................................................................... 41 2.2 EXPERIMENTAL RESEARCH METHODS ................................................................................................ 47

2.2.1 Experimental apparatus .......................................................................................................... 47 2.2.2 Experimental methods ............................................................................................................. 48

3 RESULTS AND DISCUSSION .......................................................................................................... 51

3.1 BUILDING DESCRIPTION ..................................................................................................................... 52 3.1.1 Description of building substructures and HVAC systems ...................................................... 52 3.1.2 Weather conditions for the simulation analysis ....................................................................... 66

3.2 SELECTION OF THE OPTIMAL GLAZING SYSTEM .................................................................................. 68 3.3 ESTIMATION OF THERMAL ENERGY GAIN AND LOSS THROUGH BUILDING FENESTRATION .................. 70

3.3.1 Characterization of heat gain and loss through glazing .......................................................... 70 3.3.2 Analysis of the energy balance for windows ............................................................................ 71 3.3.3 Definition of an optimal value of window-to-wall ratio .......................................................... 76

3.4 TESTING OF A BUILDING INDOOR ENVIRONMENT DURING THE WARM PERIOD .................................... 79 3.5 OPTIMIZATION OF A SOLAR DOMESTIC HOT WATER SYSTEM .............................................................. 90

3.5.1 Description of the solar collectors........................................................................................... 90 3.5.2 Solar heating systems control .................................................................................................. 91 3.5.3 Assumed parameters of domestic hot water systems ............................................................... 91 3.5.4 Results of computational analysis ........................................................................................... 92

4 SUMMARY AND CONCLUSIONS .................................................................................................. 99

4.1 SUMMARY .......................................................................................................................................... 99 4.2 COMMENTS AND CONCLUSIONS ....................................................................................................... 101 4.3 FUTURE RESEARCH .......................................................................................................................... 103

REFERENCES .... 104 APPENDICES .. 112 APPENDIX 1 PLANS OF BUILDING SUBSTRUCTURES AND THE FRONT/BACK/SIDE ELEVATION VIEWS .. 112 APPENDIX 2 LISTING OF THE BUILDING AND HVAC SYSTEM MODEL ... 122

Nomenclature

Roman Letter Symbols

a1 thermal transmittance coefficient simple, W/m2K a2 thermal transmittance coefficient square, W/m2K2 A area, m2 c specific heat, J/kgK C correction factor, C heat capacitance, J/C

DD degree-day, Cd E energy, J or kWh f fraction of time,

F angle factor, G solar irradiation, W/m2 G& mass flow rate, kg/s h convective heat transfer coefficient, W/m2K I intensity of solar radiation, W/m2 k thermal conductivity, W/mK

nl number of heat loads, ns number of heat transfer surfaces, nz number of adjacent zones, N number of hours, o operative temperature, C P power, W P energy per building area, kWh/m2

q heat flux, W/m2 r frame to glass ratio for a window, R thermal resistance, mK/W t time, s

U heat transfer coefficient, W/m2K WWR window-to-wall ratio,

V& volume flow rate, m3/s Xj, Yj, Zj outside, cross and inside CTF coefficients. W/m2K

Greek symbols

solar absorption of the surface, layer thickness, m surface emissivity, efficiency,

Stefan-Boltzmann constant, W m2K4 temperature, K density, kg/m3 solar azimuth angle, degree flux CTF coefficient.

Subscripts

a air, A ambient, b brick,

BR beam radiation c cold side, c cooling,

CON conduction, CONV convection,

eq equivalent, E external, G ground, h hot side, h heating, I internal,

in inlet boundary, in inflow,

INF infiltration, l loss,

LWR long wave radiation, m mortar, M mean,

MD mean daily, MR mean radiant, out outlet boundary, out outflow,

S surface, SDR sky diffuse radiation, SWR short wave radiation,

sf surface, SUP supply,

w wall, steady-state conditions.

1.1 Introduction 8

1 Scientific Framework

1.1 Introduction

It is estimated that the building sector consumes nearly 40 % of the total energy used in European countries. The potential for saving energy needed for heating, cooling, lighting and other services is still significant.

Modelling and simulation techniques can help to predict the environmental performance of building and HVAC systems in the future. Both of these methods are very important in the early stages of designing, as well as during the operation and management processes. Modern buildings should be characterized by a low level of primary energy demands and also provide an optimal thermal comfort environment and indoor air quality for occupants. Only computer-based predictions can reconcile these other contradictory and conflicting requirements. Moreover, energy simulations help to understand the interactions between occupants, building construction, HVAC systems, indoor and outdoor climate conditions. A sharp rise in energy prices and continuous development in the building industry demand a new design methodology. Traditional methods of calculation for steady-state conditions cannot be used in solving the problems of solar gain, passive and active thermal energy storage, night cooling ventilation and the optimal strategy in automatic control of HVAC systems. Solar radiation, as an energy source, is very time-dependent. In addition to variable character, absorption and reflection phenomena make it difficult to estimate its potential for space heating during the winter and to define its influence on the internal thermal environment during warm periods. Internal and external shading devices, building overhangs, wing walls and window performance can play a significant role in assessing solar gain. Modern buildings are characterized by large glazed areas. It provides the improvement of a visual environment. But on the other hand, large window sizes lead to overheating problems during the summer and may result in increasing the energy demand for heating in the winter. Only computer-aid modelling can help designers find the optimal solution to these complex problems. Also, installing large domestic hot water (DHW) systems operating with solar panels should be preceded by a simulation analysis. Among other things, detailed calculations can answer the following questions:

What kind of system connection diagram should be applied? What is the optimal number and thermal capacity of storage tanks? How does the tilt angle of solar collectors influence the thermal performance of the

DHW system and the effectiveness of energy conversion? What is the optimal and maximum power of an auxiliary heater?

1.1 Introduction 9

Another problem, which cannot be analyzed by traditional analytical methods, is the energy storage process. This phenomenon is clearly observed when solar energy transfers significantly change, for example during the day and night. Simulation of the thermal energy storage mechanism can be a precondition before sizing large free and mechanical night cooling ventilation, passive and active solar-supported heating systems.

Recapitulating above digressions, one should say that modelling and simulation techniques are necessary tools in the energy-efficient design of buildings. The current research is carried out as a multi-layered and detailed case study analysis of modern dwelling houses from the energy consumption point of view. The main goals of this complex investigation are the reduction of space heating demands and the minimization of the environmental effects on the auxiliary energy sources.

1.2 Background and literature review 10

1.2 Background and literature review

The duty of environmental protection and its sustainable development requires the design of energy efficient buildings. Computer-based simulations play a very important role in this process. Additionally, this type of analysis can be useful in achieving thermal comfort in occupied spaces. First a survey of problems concerned with the subject of the current dissertation was carried out in order to perform a more detailed and complex analysis of the thermal behavior of buildings and to determine the most important factors, especially solar radiation affecting energy consumption. A strong development of modelling techniques is observed and there are a lot of analytical and experimental works related to energy simulation in buildings. For these reasons, the literature review is limited mainly to scientific investigations that have been performed during the last decade. The current bibliographic survey and a short description of the elaborated problems are shared in the following sections and are presented below:

modelling and simulation of building thermal behavior, analysis of solar heat gain through windows, influence of building envelope construction on energy consumption, modelling and designing solar domestic hot water (SDHW) systems.

1.2.1 Method for modelling and simulation of building thermal behaviour

Building energy simulation methods can be divided into two basic levels: simplified and detailed analysis techniques. We find in the paper written by Al-Homoud (Al-Homoud, 2001) a complex review of both building energy simulation approaches. It is possible to distinguish between the four basic simplified methods of estimating energy consumption that are summarized below.

SIMPIFIED METHODS

Degree-Day (DD) method

The Degree-Day method assumes that heat loss and gain are proportional to the equivalent heat-loss coefficient of the building envelope. This steady-state procedure is very popular and widely used to estimate heating and cooling energy demands mainly in small buildings. The calculating procedure is based on the assumption that the average energy gain during a long-term counterbalance heat loss for the mean daily inside temperature F equals to 18.3C (65F), also called a balance point temperature. Therefore, energy consumption will be proportional to the difference between F and the mean daily temperature MD.


We can estimate the heating degree-day DDh using the following equation:

( )==

+mDd

dMDF

1 . (1.1)

Sign + means that we can only take the positive values. Analogically, Eq. (1.2) is used to determine the cooling degree-day DDc.

( )==

+mDd

dFMD

1 . (1.2)

Based on degree-day DDh it is possible to calculate the energy required for central heating systems.

E ( ) fhEIhL

VDDq

24 , (1.3)

where:

qL design heat loss of the buildings, I internal air temperature of the house, E external air temperature (ambient), h efficiency of the heating system, Vf heating value of fuel.

Modified Degree-Day method

In order to reduce the inaccuracy of the DD procedure, an empirical correction factor CD (ASHRAE Systems Handbook, 1976) that is a function of outdoor design temperature, is introduced.

( ) fhEIDhL

VCDDq 24 , (1.4)

where CD is a correction factor for the heating effect versus degree days.


Variable Base Degree-Day (VBDD) method

The VBDD procedure first calculates the balance point temperature B Eq. (1.5) that is the estimate for the whole building.

UAQg

I , (1.5)

where:

Qg a solar and internal heat gain, U an overall coefficient of heat loss, A an area of building elements.

Then the heating and cooling degree hours are calculated based on B. This approach takes into account different building conditions and requires an hourly weather database. Eq. (1.6) is used to calculate degree-days for heating in month m and period t out of 24 hours.

( )==

+mDd

dMDiB

1, . (1.6)

Consistently, the energy required for heating the building can be calculated as follows:

( )

h

ni

ihiUADDf

=

=124 , (1.7)

where:

n a number of operating periods, fi a fraction of time for the period t.

In a similar way, we can estimate the energy required for cooling the building.

( )==

+mDd

diBMD

1, . (1.8)


( )

c

ni

iciUADDf

=

=124 , (1.9)

Eq. (1.9) takes into account only heat transfers by conductance. Energy demands for ventilation and infiltration have to be calculated separately.

Bin method and Bin modified method

This method evolves from the VBDD procedure. It is used to calculate the annual building heating and cooling loads for a set of temperature samples called bins. The space-heating energy demand is determined based on the following relation:

( )==

+ni

iiMDiBiBIN

h

NUA1

,,, , (1.10)

where:

n a number of bins, NBIN,i a number of hours for i bin.

The Bin procedure is recommended for buildings where the magnitude of internal gains is dominated. The Bin modified method accounts for the impact of solar and wind effects on energy consumption and is useful for buildings which do not exceed 2,500 m2 of floor area.

DETAILED DYNAMIC SIMULATION METHODS

The simulation models are detailed and satisfactorily accurate tools that can be very useful both for energy-efficient design and for the cost-effective retrofitting of buildings. The flow chart of computer software for the use in determining the thermal behavior of buildings is presented in Fig. 1.1.


Fig. 1.1: The overall structure of the building energy simulation software by ASHRAE Handbook - Fundamentals (2005)

Large amounts of energy simulation software have been released during the last half century. Two tendencies in the simulation of the energy transfer processes in buildings can be distinguished. First, the conception consists of performing heat balance in isothermal zones that are component parts of the building. Depending on the requirements, the analysis can be performed over a very long period with different time intervals. We can find a comparison of the features of twenty major building energy simulation programs with a heat balance engine in a detailed and complex report prepared by Crawley (Crawley, et al., 2008) (Crawley, et al., 2005).

Very often the agreement between theoretical calculations and experimental values do not work well for large spaces and structures. The second conception is a compilation of

BUILDING DESCRIPTION Location Design data Construction data Thermal zones Internal loads Usage profiles Infiltration

WEATHER LIBRARYDry-bulb temperature Wet-bulb temperature Cloud factor Wind speed Pressure

SYSTEM DESCRIPTION System types and sizes Supply and return fans Control and schedules Outside air requirements

PLANT DESCRIPTION Equipment types and sizes Performance characteristics Auxiliary equipment Load assignment Fuel types

ECONOMIC DATA Economic factors Project life First cost Maintenance cost

LOADS ANALYSIS

SYSTEM ANALYSIS

PLANT ANALYSIS

ECONOMIC ANALYSIS

Peak heating and cooling loads

Hourly equipment loads by system

Fuel demand and consumption

Life-cycle cost


traditional balancing methods and Computational Fluid Dynamics (CFD) algorithms. Accuracy and agreement between the results of theoretical modelling and physical reality are the best advantages of this procedure. Simulations are usually performed for not very long periods of time in respect to complicated 3-D models, short-time calculating steps and long-time computer work. Often, this hybrid method is used to do steady-state analysis.

The overview of computer software for testing energy transfer in the built environment is also presented by Addison and Nall (Addison, et al., 2001). The authors concluded that the best energy analysis tools for the complex and atypical geometry of living spaces should apply hybrid algorithms. (Rees, et al., 1999) (Maliska, 2001) (Broderick, et al., 2001) (Beausoleil-Morrison, 2001) They came to similar conclusions about modelling strategy.

Available literature concerning advanced techniques and algorithms, which are used in whole-building energy performance simulations, is wide-ranging. An overview of the most important scientific projects is presented below.

Treeck and Rank (Treeck, et al., 2007) developed an algorithm for transforming building geometry which can be applied to energy simulation codes. The approach is based on a graph theory. The following graph is selected from a building model: a structural component, room faces, whole room and relational objects that represent the geometrical structure in a hierarchical manner. In order to demonstrate the capabilities of developed algorithms, the authors showed a practical example of the decomposition model based on a three-storey building with an integrated inner courtyard.

The building shape significantly influences its thermal performance. Ourghi and co-workers (Ourghi, et al., 2007) developed a simplified calculation method concerning this problem. A detailed simulation procedure was carried out with specialized software DOE-2 for several locations around the world. The authors analyzed several building configurations with different shapes, relative compactness, and various glazing types with different solar heat gain coefficient and window sizes. Estimates showed a strong influence of the building shape, the type and the percent of glazing on energy consumption.

A meteorological and a sociological (attitude and culture) influence on thermal load and energy consumption in buildings was investigated by Pedersen (Pedersen, 2007). The following different representations of weather data were analyzed: The test reference year (TRY), design reference year (DRY), typical meteorological year (TMY) and weather year for energy calculations (WYEC). The current work has presented a summary of different methodologies for the energy load and its estimations such as: neural networks (NN), engineering method (EM) conditional and demand analysis (CDA).

Detailed building thermal performance is possible to estimate when we apply both computational fluid dynamic algorithms and building energy simulation tools. The hard problem of an integration of the two different calculation techniques, which provide complementary information, was intensely developed and widely applied by Zhai and


Chen (Zhai, et al., 2002) (Zhai, et al., 2003) (Zhai, et al., 2005) (Zhai, et al., 2006). They proposed different static, dynamic and bin coupling strategies to decrease the computing time. A new coupling building energy simulation tool was developed and validated with experimental data available in literature. It was found that the best efficient coupling method is a transfer of surface temperatures from the energy simulation code to a CFD preprocessor. After calculation, heat transfer coefficients and gradients of air temperature are returned in the opposite direction. In order to reduce CPU-time demands, Zhai and Chen proposed the optimal staged coupling strategy.

The European JouleThermie OFFICE project concerned with labeling buildings checked the compliance of a building with regulations and evaluated the efficiency of the retrofit. Within this research project framework Roulet with colleagues (Roulet, et al., 2002) developed multi-criteria procedures based on a principle component analysis and on the ELECTRE family partial aggregation method. The proposed methodology can be used both before and after the retrofit.

Energy management and control units can monitor and optimize the work of various HVAC components during operation. Salsbury and Diamond (Salsbury, et al., 2000) created the concept of using simulation in the validation and energy analysis of HVAC systems in buildings. In this conception, a complex system is composed of a number of several linked subsystem models. The potential of using a simulation, which represents virtual and real parallel operating systems, was seen in a dual-duct air-handling unit located in an office building in San Francisco. Calculations were performed in the MATLAB programming environment. It was indicated that the use of simplified models can decrease the number of configuration parameters in a simulation.

Building energy performance can be predicted based on an artificial neural networks (ANN) method. Yezioro and co-workers (Yezioro, et al., 2008) developed and tested ANN using data from one week of an experimental period. The Pittsburgh Synergy Solar House was selected as the reference building. The experimental database consisted of the following electricity consumption: total, lighting, HVAC and electricity generated in the photovoltaic system. The MATLAB environment was used to implement the considered model of ANN. Calculation results from four building performance simulation tools: Energy_10, Green Building Studio, eQuest and EnergyPlus were used for the comparison of ANN purposes. It presented a good correlation (mean absolute error equal to 0.9 %) between the predictions and the results from the mathematical model.

Reducing the number of tests for complex systems can be done by the use of a lattice method for global optimization (LMGO) which was developed by Saporito (Saporito, et al., 2001). The influence of different design parameters of building energy consumption was investigated. In order to identify the main energy saving features, simulations of thermal behavior in simple office buildings located in Kew (London) with help of APACHE code were performed. The authors concluded that LMGO can be successfully


used in both sensitivity studies of dynamic systems and in building optimization problems with a large number of combination tests.

Building structures and environments are modeled by a system of differential algebraic equations. Required smoothness assumptions that can be applied in the solution of these types of equation sets have been proposed by Wetter (Wetter, 2005). A new multi-zone building energy simulation program called BuildOpt, which differs from other software because of the inclusion of various smoothing algorithms, was presented. The numerical experiments indicated a reduction in the computation time and a high precision of smoothing techniques proposed by the author.

Multi-objective genetic algorithm (MOGA) was used by Wright (Wright, et al., 2002) to estimate the optimum pay-off characteristic between daily energy costs and the quality of the thermal environment in the building. An example of a single zone HVAC system composed of cooling and heating coils, a regenerative heat exchanger and a supply fan was used to show the benefits of the multi-criterion optimization genetic algorithm. Estimates indicated that MOGA search methods can be successfully used in the thermal design of buildings in respect to occupant comfort.

Genetic algorithms were used by Xu and Wang (Xu, et al., 2007) in the thermal modelling of the building envelope. They developed a method to optimize the parameters of the simplified dynamic model based on frequency domain regression. Validation of the optimization method and its effectiveness were conducted by comparing the predictions with the results from the theoretical model. It was found that the frequency domain analysis greatly simplified the search for optimal parameters.

Earth-contact heat transfers in built environments were investigated by Davies and colleagues (Davies, et al., 2001). They improved the efficiency of the numerical technique by adopting some elements from the response factor method. The results of calculations based on the new model showed a dramatic decrease in the computing time of the simulations compared to the traditional finite volume technique in keeping with accuracy and flexibility.

The accuracy of the building energy simulations strongly depends on the estimate of solar irradiance on external facades. Loutzenhiser, along with co-workers (Loutzenhiser, et al., 2007), validated short-wave radiation in solar gain models applied in energy simulation software. In the experiment, a database of solar radiation from two 25-day measurements performed on the EMPA campus located in Duebendorf (Switzerland) was used. Calculations were made using four building energy simulation programs: EnergyPlus, DOE-2.1e, ESP-r and TRNSYS-TUD and seven solar radiation models. Using the mean absolute differences method, it verified that the uncertainties of the models are as follows: 14.9 % for the isotropic sky, 9.1 % for the HayDavies, 9.4 % for the Reindl, 7.6 % for the Muneer, 13.2 % for the Klucher, 9.0 % for the modified Perez and 7.9 % for Perez.


Wurtz and co-workers (Wurtz, et al., 2006) developed energy simulation tools which implemented a zonal method. The first program was created in an object-oriented SPARK environment in order to develop and test new algorithms and simulation models. The second tool, called SIM_ZONAL integrated definite models to quickly estimate the quality of the indoor thermal environment. These applications integrated single-node models with computational fluid dynamics algorithms. The authors concluded that the zonal method implemented in their computer programs can be used to indicate room temperature and environment quality with adequate accuracy.

The integration of the CFD environment with building simulation techniques was the main goal of the European Commission project number ERB IC15 CT98 0511, which was realized by Bartak (Bartak, et al., 2002). The approach taken within the ESP-r computer code was created. The empirical validation of the new module was carried out at the Technical University in Prague (Czech Republic). It was also compared with simulation results supported by measurements realized in a multi-storey block of flats in Gliwice (Poland). (The authors obtained good agreement between predictions and the results of measurements as the relative error did not exceed 14 %.)

Yan, along with colleagues (Yan, et al., 2008), carried out a method to simultaneously estimate thermal performance and indoor air quality in buildings. The new integrated simulation tool is characterized by applying the following: flexible system control strategy, multi-parameters analysis, flexible equipment selection and a new zonal model based on room air age. Computer programs can be used to estimate the energy demands and predict different indoor parameters (e.g., temperature, humidity, CO2, volatile organic compounds, particular matter) under different HVAC systems and automatic control strategies. A detailed analysis of the dynamic performance of a hypothetical health care building in Miami (USA) was carried out to show all the capabilities of the developed simulation tool.

1.2.2 Solar heat gain through windows Glazed openings are very important elements in building design. Windows provide natural daylight into rooms to reduce the use of electric light and allow heat gain from solar radiation. But large areas of glazing in each facade may result both in increased heat losses in winter and in deteriorating thermal comfort conditions for occupants by overheating in summer. The optimal value of the window-to-wall area ratio can be properly estimated only by energy balancing for a typical year of weather data with the use of simulation methods.

A good statement used to reduce energy consumption in buildings in cold climates is the application of low-emissivity window glass coverings. This film layer on the internal side of the window may significantly reduce heat transmission by long-wave radiation.


Different energy performance of glazed openings is needed in warm climates. Spectrally selective coatings should reflect the infra-red and ultra-violet spectrums and simultaneously transmit visible solar radiation.

Shading devices such as screens, blinds, shutters, drapes, pull-down shades, overhangs and wing walls can both reduce overheating in summer as well as energy consumption in cold periods. Simulation tools should allow setting a different location of these devices, as shown in Fig. 1.2.

Fig. 1.2: Location options of shading devices.

Electrochromic glazing technology is the best solution for buildings in moderate climates on account of its dynamically varied energy performance. Depending on the voltage generated by a photovoltaic layer, the window film coating adapts to actual environmental conditions. It is a very promising future technology but many challenging problems will need to be resolved such as the control and time change of the spectral properties in electrochromic layers. The newest shading devices consist of external horizontal louvers with spectrally selective holographic optical elements (HOE) that redirect sunlight.

A short description of the most important scientific research connected with the analysis of solar gain entering a building is presented below.

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Yohanis and Norton (Yohanis, et al., 2000) revealed that the investigation of direct solar gain utilization in buildings can be properly carried out based on a zone-by-zone analysis. The base-case building (located Hemel Hempstead, England) was divided into fourteen volume subjects, called zones. The SERI-RES computer program was chosen for simulation tests. The usefulness of heating buildings is a function of the ratio. The calculation of solar gain as a function of the ratio of total solar to total loss (TS/TL) on a base of whole-building analysis can only lead to rough results.

The absorption of solar radiation in buildings depends on the orientation and thermal mass of the building. This problem was investigated by the same authors (Yohanis, et al., 2002) based on a single-storey building with glazing areas equal to 42 % of the east and west elevations and located in London (latitude of 52). A model of the base-case building was created in the thermal simulation code SERI-RES. Estimates indicated that for large thermal mass and for smaller values of the total solar to total loss, the impact of orientation is not significant. But for the small mass of the considered buildings, the percentage differences increase to 8 % for east, 10 % for west and 12 % for north orientations.

Florides, with co-workers (Florides, et al., 2002), carried out a thermal response of modern houses taking into consideration ventilation, solar shading and the type of glazing, as well as the shape, orientation and thermal mass of the buildings. The heating and cooling loads were calculated with use of computer software TRNSYS and a typical meteorological year (TMY) for Nicosia, Cyprus. The considered modern house had a floor area of 196 m2 and consisted of four external walls with a low conductance and low transmittance window glazing with area equal to 5.2 m2. The simulation results for the warm period indicated that night ventilation can reduce peak internal temperatures by 2C, 3C and 7C for one, two and eleven air changes per hour, respectively. Moreover, nine air changes per hour can lead to a 7.7 % reduction (maximum value) in annual cooling load.

The problem of controlling the solar heat gains in order to reduce the capacity of an air conditioning system was studied by Saleh (Saleh, et al., 2004). They proposed a horizontal rotation of glass windowpanes. The computer program was developed to determine the sun declination and limits of sunlight hours. It was found that the percentage of direct solar heat gain changes achievable by a rotation-angle magnitude of 300 and for east wall orientation equals to -11 % and 42 % for summer and winter solstice time, respectively.

A novel glazing system with a rotatable frame for buildings located in climates where heating and cooling are required, was investigated by Etzion and Erell (Etzion, et al., 2000). Frame holds have transparent glazing and absorptive glazing with a low shading coefficient. Before a heating season, the glazing system rotates and the absorbing part is on the interior side. The experimental investigations for warm periods showed that the interior radiation for the reversible new glazing system and reference standard 3 mm transparent glazing were reduced to approximately 5 % and 37 % of exterior levels, respectively. For


winter conditions, the solar radiation through the tested windows was identical to the standard window.

Fissore and Fonseca (Fissore, et al., 2007) investigated the thermal behavior of an enclosed space with fenestration for temperate winter climates. Experiments were carried out for heating season conditions and during summer periods. An uncertainly analysis indicated that the most significant errors are generated from measurements of surfaces and air temperature. Errors connected with thermocouples and voltage measurement can be significant. The same authors (Fissore, et al., 2007) analyzed the thermal balance of a window in an office in climate conditions typical for Concepcion (Chile). One-year measurements of ambient and indoor parameters under simulation of various operation conditions showed that heat consumption for uncovered windows during clear winter days could be smaller about 50 % compared to a cloudy period. For autumn conditions, this value was reduced to 26.6 %.

The Task 34/Annex 43 project of the International Energy Agency (IEA) included six experiments in an outdoor test cell in order to provide the necessary data for the validation of building energy simulation models and computer software (Manza, et al., 2006). The experimental facility was assembled with two identical cuboid shape test cells with removable faade elements. An air-water heat exchanger was used to control the air temperature inside guarded zones. DOE-2.1E, EnergyPlus, ESP-r and HELIOS building energy simulation computer programs were used for modelling the thermal behavior of the tested spaces. Experimental data, which are available on the Internet from www.empa.ch/ieatask34, can be a good base to investigate solar gains through transparent elements and can also be used to validate existing software for the energy analysis of buildings.

The beam solar radiation incident on building fenestration can be controlled with holographic optical elements. This system was tested by James and Bahaj (James, et al., 2005) in modern, highly glazed office extensions with a low thermal mass at Southampton University (UK). The possible solutions of the solar control problem were tested based on the transient thermal simulation of the building structure with help of the computer code TRNSYS. The authors assumed that the HOE systems function at a 100 % diffraction efficiency but required alignment between incident direct radiation and the angle of the hologram. Moreover, the effects of glare and spectral dispersion may cause the unsuitable functioning of holographic elements.

Coating with a spectrally selective layer on external walls can affect heat transfer. Prager and co-workers (Prager, et al., 2006) analyzed the influence of solar radiation and convection on the energy balance of a building based on test facilities in Freiburg (Germany). It was found that the considered IR radiative component reduces the heat demand to between 5 % and 15 % during the winter season. However, in summer time, the


cooling energy demand increases to between 10 % and 50 % depending on the thermal resistance of the wall.

One of the factors that influence the building energy balance is ground reflectivity. Thevenard and Haddad (Thevenard, et al., 2006) developed two snow albedo models. The first simple approach can be operated together with a typical year and uses the monthly snow cover. The second advanced model assumes daily or hourly records of snow depth.

Two objects were tested: a passive solar house located in a rural setting in Canada and a photovoltaic system in order to evaluate both models considered. ESP-r was used as a simulation tool. The authors indicated that the ground albedo value depends on the surface and may range from 0.07 to 0.6 in the absence of snow. For snow cover age, this value ranges from 0.2 to 0.7.

The glazed openings percentage (GOP) may strongly affect a thermal comfort in the building. A dynamic thermal-circuit zone method to study a type of glazing and the area of fenestration influence on the maximum and minimum indoor air temperatures was used by Kontoleon and Bikas (Kontoleon, et al., 2002). The solution procedure assumed the combined heat transfer by conduction, convection and radiation in the space for changing internal and external environmental behaviors. The simulation results showed that overheating is observed in buildings with double-glazing and interior insulation when the GOP exceeds 70 % during the winter season. For the summer period, overheating disappears if the glazed openings percentage is less than 60 % and exterior insulation is placed on the horizontal surfaces.

Alvarez with co-workers (Alvarez, et al., 2005) tested the solar heat gain coefficient (SHGC) for commercial sheet glasses with the following solar control coatings: ZnS (40 nm) CuS (150 nm) and ZnS (40 nm) Bi2S3 (75 nm) CuS (150 nm) at exterior temperatures of 15C and 32C. This work presented the thermal performance of the different types of laminated glazings as a function of indoor and outdoor convective heat transfer coefficients. A reduction in SHGC that depends on exterior conditions was changed from 12 % to 20 % for single glazing with SnO2-based transparent conductive oxide film.

Double-glazing with vacuum or inert gas is characterized by low heat loss. This type of window with soft and hard emittance coatings was investigated by Fang (Fang, et al., 2007). A three-dimensional finite volume model was developed for obtaining vacuum glazing thermal performance. Experiments with the use of a guarded hot box calorimeter were carried out as well. It was found that vacuum glazing with a single low emittance has excellent performance. But the use of two low emittance coatings provides limited improvement.


1.2.3 Influence of envelope features on energy consumption and potential savings

Envelope features play an essential role in absorbing solar and internal gains. The storing of heat has a positive influence on less temperature fluctuations in living spaces and improves the quality of the thermal environment. Building structural elements, such as walls and floors, should be made with materials that have a high heat capacity and density in passive solar houses. Many complex problems are connected with the natural store of heat such as the location of thermal masses, wall configuration, insulation thickness, colour and structure of elevation. Moreover, it is necessary to estimate the optimal value of the solar heat gain coefficient (SHGC), which depends on climate factors, in passive heating design. The current part of the literature review is dedicated to highlighting these kinds of issues.

Lindberg with colleagues (Lindberg, et al., 2004) presented the thermal performance of six different exterior walls which were determined based on a detailed experiment. The construction of the tested walls were as follows: polyurethane insulated wooden frame wall, insulated cavity brick wall, insulated log wall, plastered massive brick wall, autoclaved aerated concrete (AAC) block wall and log wall. The dimensions of each test building were as follows: width and length equal to 2.4 m and height equal to 2.6 m. A 1500 W electric radiator was used as a heat source. Measurements were very detailed and included: horizontal global solar radiation, wind speed and direction, infiltration, air tightness, relative humidity, inside-outside air temperatures and temperatures at various depths within each side of the exterior wall facades. The authors concluded that the thermal mass of the walls reduces temperature fluctuations and absorbs energy surpluses from solar and internal gains. As it turned out, the thermal performance of the AAC block wall is better than that of the massive brick wall. The results of the calculation showed that one steady-state method leads to an overestimate of the heating or cooling energy transfer through the building envelope by 40 %.

A method to assess the cost-effectiveness of residential building exterior walls for cold climate conditions was proposed by Wang (Wang, et al., 2007). Among other things, the cost/benefit difference is calculated by comparing insulated exterior walls with typical for Chinese non-insulated solid clay brick exterior walls. An application of the proposed method was presented by the authors. A seven-storey residential building constructed with three types of different exterior walls and located in Northern China was chosen as the object of the cost-efficiency analysis. The calculation results indicated that the economical evaluation of the insulated exterior walls is a proper and easy way thanks to applying the proposed methodology. Future work on this project will include the integration of cooling aspects and other difficulties in construction and environmental impacts.

Smeds and Wall (Smeds, et al., 2007) compared a multi-family apartment building and a single-family detached house, designed according to the Nordic Building Code, with high performance houses using the best available technology, which fulfills the target


requirements of IEATask 28 (2003). Simulations of the buildings for cold climate data in Stockholm were carried out with computer code DEROB-LTH (2005). This dynamic simulation tool was built based on a ray tracing model. The results of the calculation revealed that the space-heating demand can be reduced by up to 83 % for single-family houses and by up to 85 % for apartment buildings. The authors conclusion was that we should take into consideration the following design features: tightness of the building envelope, air ventilation balancing and heat recovery systems in order to obtain demand space-heating requirements equaling less than 15 25 kWh/m2.

Experimental investigations of three Danish single-family houses constructed according to the new building energy requirements introduced in Denmark in 2006, were carried out by Tommerup and co-authors (Tommerup, et al., 2007). This project assumed a complex measure of energy consumption for space heating, domestic hot water and electricity consumption, solar radiation, outdoor and indoor temperatures and temperatures in HVAC systems. Findings of the experiment indicated that the energy consumption of all investigated houses can be classified as low-energy house class 2. It means that energy consumption is 75 % of the required maximum value. Furthermore, applying existing low-energy products in analyzed buildings can reduce consumption of electricity by about 40 %. The authors hope that the results of the current project will be a good basis for the development of energy-saving buildings in the future.

Turkish Standard Number 825 (TS 825) introduces four different degree-day (DD) regions namely: Izmir (DD: 1450), Bursa (DD: 2203), Eskis-ehir (DD: 3215) and Erzurum (DD: 4856). For these provinces Sisman and co-workers (Sisman, et al., 2007) determined an optimum insulation thickness for a lifetime of N years. Optimization calculations assumed exterior air temperature, length of the heating period, operating time of the system, economical lifetime and properties of the insulation material. The optimum value of insulation thickness, which is the result of the current analysis, is equal to 0.033 m for Izmir, 0.047 m for Bursa, 0.061 m for Eskis-ehir and 0.08 m for Erzurum.

Bakos (Bakos, 2000) analyzed the thermal insulation in residential and tertiary sector, which was built before the enactment of the Greek Thermal Insulation Code. Various insulation protection approaches for buildings situated in Kavala (Northern Greece) were investigated. The economical analysis took into account the costs of insulation material, labour and insurance. Bakos concluded that the correct combination of insulation materials can make substantial energy savings.

The analysis of heat transfer through composite roofs consisting of different positions of insulation materials was realized by Ozel and Pihtili (2007). They applied numerical models based on an implicit finite difference scheme and MATLAB environment in their simulations. Twelve different roof constructions were investigated for both winter and summer periods. Ozel and Pihtili (Ozel, et al., 2007) states that the best load leveling was achieved in the case where three pieces of insulation of equal thickness were placed one at the outdoor surface of the roof, the second piece of insulation was placed in the middle of the roof and the third piece of insulation was placed on the indoor surface of the roof.


Fig. 1.3 presents the best location of insulation inside a roof.

Fig. 1.3: Configuration of insulation selected by Ozel and Pihtili (2007) as the best solution.

Dombayci and co-workers (Dombayci, et al., 2006) investigated the optimization of external wall insulation thickness for Denizli (southwestern Turkey) weather conditions. The effects of the energy source types (coal, natural gas, LPG, fuel oil, electricity) on energy savings and the use of different insulation materials (expanded polystyrene, rock wool) were analyzed. The difference between the buildings heating costs, with and without the insulation of external walls, was used in a life-cycle cost analysis (LCCA). Results of the calculations revealed that the life cycle savings are $ 14.09 per square metre of wall surface area and a very short payback period of 1.43 years for the optimum insulation-thickness. These results were obtained with coal as the energy source and expanded polystyrene as the insulating material.

Khaled (Khaled, 2003) comprised two types of roof insulation (polystyrene and fiberglass) for warm and cold climate conditions. Energy analysis was carried out for a 108 m2 house in two USA locations: College Station (Texas) and Minneapolis (Minnesota). The RENCON simulation program (Degelman, et al., 1991) was used to determine annual heating and cooling energy consumption. Six different insulation resistance levels of the roof (R5, R10, R15, R20, R25, R30) were examined. In Khaleds opinion, the most cost-effective thermal resistance for polystyrene is R5 and for fiberglass is R10. Besides this, the author remarked that the payback time of using insulation in a cold climate is shorter than that of a warm climate and that the best solution for thermal insulation design is the use of a life-cycle cost analysis rather than the construction budget limitation.

The problem concerning the best insulation level of the envelope of new residential buildings in 6 Italian climatic zones was studied by Lollini (Lollini, et al., 2006). Economical analysis was based on two main parameters of investment efficiency: the net present value (NPV) and the payback rate (PBR). The methodology used in this project included the following factors: calculation of the optimal insulation thickness, analyses of market and cost, energy calculation of the reference buildings, calculation for different

glass wool concrete block

glass wool concrete block

glass wool


configurations of insulation levels and evaluation of the environmental impact. The EC501 computer code was used to determine the energy consumption for many configurations, which assumed climatic conditions, selected building characteristics and the insulation levels. The Lollini at al. study revealed that the better insulated buildings can strongly reduce the heating energy demand. Moreover, PBR is always shorter than 5 years for the tower building, and the payback rate is shorter than 8 years for the single-family house.

Persson, with colleagues (Persson, et al., 2006), analyzed the influence of decreasing the window size facing south and increasing the window size facing north on the energy consumption of 20 terraced passive houses, which were built outside Gothenburg in Spring, 2001. DEROB-LTH software (DEROB-LTH, 2005) was used to simulate the energy demand dynamic conditions over a whole year. Calculations considered different orientations of buildings and window types. The findings of the simulation showed that it is possible to enlarge north window areas in order to obtain better conditions in natural lighting. There is also an optimal south window area, which is smaller than the designed size of the existing terraced passive houses.

1.2.4 Modelling and designing solar domestic hot water systems Solar radiation can be converted into thermal and electric energy. In the last two decades a large-scale development of solar domestic hot water systems has been observed, even in cold climates. These applications may provide between 40 % to 70 % annual DHW demand and even 100 % during summer months. A typical SDHW heater is made up of solar panels, storage tanks and supplemental heat sources.

There are two alternative types of solar collectors for heating water. The most popular in Europe are flat plate panels which unfortunately have a low efficiency performance and high energy losses during winter. A typical conversion device is made up of metal or plastic casing, insulation, a glass or plastic cover and an absorber plate. The collector heats up a circulating fluid. Tube solar water heaters have a quite different structure. They are constructed of a series of annealed glass tubes with an integrated metal absorber plate. There is a vacuum between the inner and outer glass tubes.

European Standard (EN12975-2, 2007) introduced a simple calculation method for the estimation of solar collector efficiency SC. The value of SC depends on six parameters and is defined by:

( )

Ga

Ga AMAM

2

210 , (1.11)

where:

0 zero-loss collector efficiency (conversion factor),


a1, a2 thermal transmittance (loss) coefficients, G solar irradiation,

M collector mean temperature, A ambient air temperature.

Consequently, the solar collector power PSC is obtained by the following relation:

AGSC , (1.12)

where A is an area of the solar collector absorber.

The value of solar radiation strongly depends on the time of day and the year. For this reason, it is necessary to use storage tanks and auxiliary heating units. Photothermal conversion of solar energy can be carried out as an active or a passive solution. The basic schemes of SDHW systems are presented in Fig. 1.4 Fig. 1.7.

Fig. 1.4: Connection diagram of thermosyphon SDHW with two separate loops.

solarcollector

Stor

age

tank

DHW supply

cold water


Fig. 1.5: Connection diagram of thermosyphon SDHW with open water loop.

The passive systems do not include any mechanical devices, but are used mostly in moderate and hot climate regions.

Fig. 1.6: Connection diagram of active SDHW system that is coupled with supplementary heater.

solarcollector

Stor

age

tank

Aux

iliar

y he

at so

urce

DHW supply

cold water

solarcollector

Stor

age

tank

cold water

DHW supply


Fig. 1.7: Connection diagram of active SDHW system with separate supplementary heater.

The closed-loop active systems are recommended in colder climates because they have high efficiency and can operate throughout the year.

The complexity of the energy conversion effect and the dependence of the solar radiation rate currently often cause problems in designing large-scale applications. Computer simulations carried out for the full annual operating period may help to optimize the area of solar collectors and the volume of storage tanks. Additionally, this type of analysis is used to estimate energy production by photothermal conversion. The review of the newest research projects that has focused on the modelling and experimental testing of DHW systems integrated with solar panels is presented below.

A complex overview of the main tendency in modelling and designing in simulation of the solar heating process was carried out by Nafey (Nafey, 2005). In order to systematize this problem, the author classified methods, algorithms, techniques and computer programs. Two main types of simulation programs were distinguished: special purpose (on-off programs) and general-purpose (modular programs). The author created a simplified flow diagram for the simulation of the solar heating process performance as shown in Fig. 1.8. Each block represents a separate processing unit and the arrow lines represent possible unit connections with a pipe system.

Fig. 1.8: Flow chart of Nafey (2005), which shows the sequence of actions within the simulation of the solar heating process.

FEED 1 UNIT A UNIT B UNIT C

FEED 2

solarcollector

Stor

age

tank

DHW supply

cold water

Auxiliary heat source

~


The exergy concept and the use of a new feature of the visual programming with comfortable interfaces were mentioned as developments in the simulation of solar heating processes in the future.

Kulkarni, with co-workers (Kulkarni, et al., 2007), presented a methodology in the design space approach for the synthesis, analysis and optimization of solar water heating systems. The design space in this concept is obtained by tracing constant solar fraction lines on a collector area versus the storage volume diagram. Results of the calculation showed that a minimum and maximum storage volume for a given solar fraction and an area of collector exists. Apart from that, it can be observed that a minimum and maximum collector area for a fixed solar fraction and storage volume exists. Benefits of the energy savings of the SDHW system were determined using the economical objective function based on annual life cycle costs. The methodology proposed by Kulkarni and co-workers can be used in many different solar thermal configurations, as well as in retrofit cases.

Furbo and Shah (Furbo, et al., 2003) examined the influence of a glass cover with antireflection surfaces on the thermal performance of solar heating systems and the efficiency of solar panels. Two glass plates were compared. One of them was covered by an antireflection layer. Measurement of surface transmittances was performed for different incidence angles. The dependence of the incidence angle on the transmittance of the antireflection surfaces was increased by 59 %. The influences in increasing solar collector efficiency by 46 % are due to the antireflection. The yearly simulation of the thermal performance of solar systems revealed that the energy produced by a solar collector increased by about 12 % using antireflection surfaces, if the mean solar collector fluid temperature is 60C. We can obtain a 20 % savings for fluid temperature equal to 100C.

A discharge process from different levels in solar storage tanks was investigated by Furbo (Furbo a, et al., 2005) (Furbo b, et al., 2005). They tested two identical small low-flow SDHW systems which contained standard mantle tanks. The difference between the tanks lay in that first one was equipped with a PEX pipe for hot water draw-off from the very top of the tank and the second had an additional PEX pipe placed in the middle of the device. Auxiliary energy sources were used as electric heating elements in both cases. The experiment was carried out during a 6-week-period with a draw-off temperature of 50C and for 7 weeks with a draw-off temperature of 47C. The Mantlsim model, which was developed at the Technical University of Denmark by Furbo and Knudsen (Furbo, et al., 2004), was used to analyze two low-flow storage systems. Simulations were carried out with the use of weather data from the Danish Test Reference Year. The findings of the study indicated that the best level of the second draw-off is in the middle of the tank and that the increase in the thermal performance by the second draw-off level is about 6 %.

The application of the transparent insulation material (TIM) in minimizing top heat losses of solar water heaters was proposed by Chaurasia and Twidell (Chaurasia, et al., 2001). Two identical solar water heaters were tested in order to determine the role of transparent


insulation. The TIM cover was placed on the absorbing surface of one unit to prevent heat losses during the night period. The insulation was made of polycarbonate material consisting of a honeycomb construction with a square section of 3 mm on 3 mm tubes and 100 mm long. The TIM glazing was found to be quite effective as compared to glass glazing SWH. Experiments showed water at higher temperatures of 8.5C to 9.5C by the next morning thanks to the use of transparent insulation materials. Also, it was found that the efficiency of solar storage water heaters was 39.8 % with TIM glazing compared to 15.1 % without this insulation.

A method for determining the performance of solar water heating systems was developed by Yohanis and co-authors (Yohanis, et al., 2006). If the solar-heated rate is at a set-temperature, this approach can be used to determine the number of days each month that solar heating alone satisfies the needs. The authors maintained that their method is easy to understand by users without knowledge of solar systems which is different from the solar fractions approach. The computer analysis tool TRNSYS was used to simulate a domestic-scale solar hot water system (Fig. 1.9), which consisted of a solar collector, storage tank, auxiliary heater and controller.

Fig. 1.9: SDHW system, which was analyzed by Yohanis at al. (2006).

solarcollector

insu

late

d st

orag

e ta

nk

DHW supply

cold water supply

Auxiliary heater

controller

~


In calculations, typical meteorological years (TMY) for Belfast (Northern Ireland) were applied. Finally, it was concluded that for a lower normalized number of days, solar fraction is less defined than for a higher number of days and high solar fraction does not necessarily mean that the storage tank water temperature reached a set temperature.

Norton and Lo (Norton, et al., 2006) discussed technical developments in solar thermal applications. They presented the taxonomy of principle generic tracking and stationary solar thermal collectors. It is stated that a thermal characteristic of solar collectors can be seen, shown in Fig. 1.10, and that it is impossible to select the universally best solar panel. The authors quoted the following example in low temperature applications in areas with high insulation, an unglazed collector with a plastic absorber resistant to ultra-violet radiation may be the optimal choice. On the other hand, under high insulation conditions, solar thermal electricity generation requires the use of evacuated tubes located at the focus of line-axis tracking parabolic reflectors; direct steam generation takes place in the absorber tube which is coated with a high temperature solar selective absorber.

Fig. 1.10: Hottel-Whillier-Bliss performance characteristic of low and medium temperature solar collectors.

An alternative way to solve problems concerning the simulation of solar energy conversion systems is the Artificial Neural Networks (ANN) technology.

Kalogirou and co-workers (Kalogirou, et al., 1999) tested an ANN in order to evaluate the performance characteristics of solar domestic water heating systems. The ANN test database included 30 known cases varying from collector areas between 1.81 m2 and 4.38 m2. Apart from that, open and closed systems, horizontal and vertical storage tanks, which operate in variety of weather conditions, were investigated. The energy extracted from the SDHW system and the rises in temperature in the storage tank were the results of calculations based on an ANN algorithm. The ANN method can be successfully used even

0,00,10,20,30,40,50,60,70,80,91,0

0,00 0,02 0,04 0,06 0,08 0,10 0,12 0,14 0,16 0,18 0,20( M - A )/G [Km2/W]

SC

Plastic absorberAir collectorPlat plate collectorEvacuated tube collector

SC


in the simulation of completely unknown systems because the authors obtained predictions within 7.1 % and 9.7 %.

The results of computer simulations of solar domestic hot water systems, based on the time marching model, were obtained by Bojic (Bojic, et al., 2002). The analyzed system, which was used for a typical Yugoslavian family, consisted of a flat-plate solar panel having an area of 3 m2, a storage tank (volume ranged from 60 l to 400 l), an auxiliary heater and a mixing device. A computer tool called TEMP was created which can be used to design and operate SDHW systems. Estimates showed, among other things, that when the volume of a storage tank is larger, the fraction of solar radiation is less sensitive to a variation in the operation parameters of the system.

Furbo and co-workers (Furbo a, et al., 2005) investigated small systems in which domestic water may be heated by solar collectors or by an auxiliary electric heat source. Three different tanks (one traditional and two smart), shown in Fig. 1.11, were experimentally and theoretically examined in the same operating conditions.

Fig. 1.11: Three solar tanks investigated by Furbo at. al (2005).

to solarcollector

cold water hot water

from solar collector to solar

collector


from solar collector

to solarcollector


from solar collector

electricheatingelement

electricheatingelement

side arm

electricheatingelement electric

heating elementplastic

pipe


The experimental systems were supplied by 3 m2 solar collectors and by horizontal and vertical electric heating elements. Investigations revealed that the thermal performance of SDHW systems based on smart solar tanks is 5 % 35 % higher compared to traditional systems.

An analysis of heat transfer in a vertical mantle tank, as illustrated in Fig. 1.12, was the main goal of the Shah, L.J. project (Shah, 2000). The main advantages of the mantle tank are a large heat transfer area and an effective fluid distribution over the tank wall.

Fig. 1.12: Sketch of a solar domestic hot water system analyzed by Shah L.J. (2000), which is typical in Denmark and Holland.

The CFD technique was used for the three-dimensional flow simulation in a mantle tank. The results of the calculations were validated by comparing the measurements and good agreement was reached. Based on the CFD simulations, Shah L.J. (Shah, 2000) introduced heat transfer correlations for the analyzed systems.

Investigations of the SDHW systems are mainly based on energy balance. But there are not many works which utilize exergetic analysis. Gunerhan and Hepbasli (Gunerhan, et al., 2007) used the exergy approach to model a system, which consisted of a flat solar collector (2 m2 aperture area), a storage tank as a heat exchanger and a circulation pump. A characteristic performance of the system was evaluated based on the measurements of mass flow rates, water temperatures, solar flux, wind velocity and ambient atmospheric pressure. The experiment was made at the Ege University (Turkey). Estimates indicated that the exergy efficiency varied in the following ranges: 2,02 % 3,37 % for the solar panel, 10,0 % 16,67 % for the circulation pump and 16 % 51,72 % for the heat exchanger at a reference state fluid temperature equal to 32.77C.

cold water supply

electric heating element

DHW supply

solarcollector St

orag

e ta

nk


Strategies (costs and feasibility) of solar energy conversion based on open loop, flat-plate solar collector systems were studied by Badescu (Badescu, 2008). The optimization problem was solved by using a direct shooting approach - trajectory optimization by mathematical programming (TOMP) developed by Kraft (Kraft, 1994). A registry-type, flat-plate solar collector and meteorological database for Bucharest were used in this study. Simulations were performed during a one-year operating period and good agreement was observed in calculations with the measurements available in literature. Estimates obtained for the considered system indicated that the maximum exergetic efficiency was usually less than 3 %.

The next study of Badescu (Badescu, 2008) was also conducted to determine the optimal flow control in a closed loop flat plate solar collector, which cooperated with a water storage tank. The following design configurations were analyzed: a tank with one serpentine and a tank with two serpentines. In both cases, a fully mixed regime in the storage tanks was considered. In the present project, the author implemented an indirect optimal control technique based on Pontryagins maximum principle. As it turned out, the first considered system performed better than the second configuration. There is one limitation in the storage system with one serpentine. It should not operate during the winter period in regions with higher latitudes. Badescu (Badescu, 2008) stated that the optimal operation strategy consists of two jump steps up and two jump steps down between zero and the maximum rate of fluid flow in the primary circuit of the storage tank.

Biaou and Bernier (Biaou, et al., 2008) carried out research in the various ways of domestic hot water production for two climate conditions: Montreal and Los Angeles. The following renewable energy sources were examined:

conventional electric hot water tank, ground-source heat pump (GSHP) desuperheater (refrigerant-to-water heat

exchanger) combined with a regular electric hot water tank, SDHW system composed of flat plate solar collectors, an external heat exchanger, a

solar water storage tank and a regular auxiliary electric water tank, two circulators and a temperature controller (Fig. 1.13),

heat pump water heater (HPWH) indirectly coupled to a space conditioning ground-source heat pump.

Four alternative systems were applied in zero-net energy homes (ZNEH), consisting of a well-insulated two-storey 156 m2 residence with an unheated half-basement.


Fig. 1.13: SDHW system studied by Biaou and Bernier (2008).

The main examined components were modeled using a TRSNYS and IISIBAT interface. The results of the simulations explicitly indicated that the system with solar collectors was the best solution for the production of DHW in zero-net energy homes.

The main goal of the Cardinale and co-workers (Cardinale, et al., 2003) study was an economical optimization of low-flow solar domestic hot water plants. Domestic hot-water production was 500 litres a day for a four-person Italian family. The analyzed system, as shown in Fig. 1.14, consisted of a solar collector (1.9 m2 surface area), a 2.16 m height storage tank, two pumps powered by photovoltaic panels and an auxiliary heater. The TRNSYS code was used to estimate the thermoenergetic performances of the solar plant.

Fig. 1.14: Schematic sketch of the system studied by Cardinale at al. (2003).

from main

to load

solarcollector

Stor

age

tank

heat exchanger

PV pump PV pump

auxiliary heater

solarcollector

stor

age

tank

DHW supply

cold water

back

up ta

nk

elec

tric

heat

ers

controller

external heatexchanger


Simulations indicated that there are many advantages for the considered solar system in comparison with the utilization of electric energy. Moreover, the authors concluded that the tested plant can be clearly justified when fossil fuel consumption is dramatically reduced.

The Dahm, with co-workers (Dahm, et al., 1998), tested system, which consisted of an electrical auxiliary storage heater with a volume of 750 litres, internal heat exchangers and tempering valves. Fig. 1.15 presents four different storage considered systems. Investigations were carried out on a statistically generated six-day test sequence and a solar collector simulator under conditions similar to those in Sweden.

Fig. 1.15: The schematic layout of the four configurations considered in the Dahm (1998) experiments.

An acceptable accuracy rate (relative and absolute difference) between the measured and calculated energy transfer for solar and load heat exchangers was obtained. The authors concluded that when using a real weather database, the solar fraction is about 10 % lower than the measured value based on the considered six-day test system for the summer period.

Configuration 1

1

2 2

1

1

3

1

1

3

1

1

Configuration 2

Configuration 3 Configuration 4


Mather, with co-workers (Mather, et al., 2002), investigated a SDHW system, shown in Fig. 1.16, with a multi-tank configuration and a total volume of water larger than 2000 l. The authors have proposed an arrangement of small tanks that are serially connected by immersed-coil heat exchangers. Experimental tests demonstrated a thermodynamically advantageous thermal diode effect that the examined system can achieve. A model for a considered tank configuration based on a reversion-elimination algorithm of Marshall and Li (Marshall, et al., 1991) and Newton (Newton, et al., 1995) was developed. Experimental and analytical modelling proved to be an economical advantage of the thermal energy storage based on multi-tank systems over a single circulating tank system. The authors listed the reduction of installation and engineering costs as the main advantages of the developed configuration.

Fig. 1.16: A schematic view of a multi-tank thermal storage system investigated by Mather at al. (2002).

A control strategy of the solar domestic hot water system with a mantle exchanger manufactured in Switzerland was investigated by Prud'homme and Gillet (Prud'homme, et al., 2001). Three smaller electrical elements with different lengths as an auxiliary heater were used in the storage tank under consideration. A principle of a developed optimization algorithm is explained in Fig. 1.17.

Fig. 1.17: A scheme illustrating a control principle introduced by Prud'homme and Gillet (2001).

Weather forcasts: - solar radiation, - ambient temperature.

Users needs: - tapped water.

ESTIMATIONS

MODEL-BASED OPTYMIZER

Flow rate in the collector loop Power supplies of the auxiliary heaters

OPTIMAL INPUTS

solarcollector

tank 1 tank 2 tank 3 tank 4

heat load

cold fluid to collector

hot fluid to load

hottest tank

coldest tank


The authors stated that an advanced control strategy (structural and control level), coupled with a considered storage tank, can lead to a significant increase in the solar fraction and a higher degree of comfort. However, an on/off control system can be more suitable from a computational point of view.

1.2.5 Summary of literature review The literature review shows that the impact of solar radiation on the thermal behavior of buildings is very complicated and still under investigation by scientists. The last decade has brought a large amount of research on particular aspects of this problem. But according to the authors knowledge, there is still not a comprehensive study which includes the wide scope of the current dissertation research. According to bibliographic searches, one can say that using detailed analysis techniques, i.e. the energy simulation method, may certainly lead to an accurate estimation of the dependence of building performance on solar radiation. The newest simulation software includes: annual weather data-bases that contain solar radiation, wind speed and direction, humidity and air temperature. This option enables one to model weather conditions throughout the year as well as during a particular period with very short time steps. It is especially important due to the strong dependence of solar radiation on time. There are some works that have applied simplified methods, but these types of steady-state procedures only give approximate results that may be seen in preliminary studies. Therefore, in order to prove the thesis of this dissertation, it was decided to apply the detailed simulation method based on the dynamic heat balance of isothermal zones. As scientific literature shows, it is necessary to integrate balancing techniques with CFD algorithms to improve the accuracy of the calculation results. Mainly, this coupled method is recommended for analyzing large spaces and structures with more complicated ventilation air-paths. Considering a small volume of isothermal zones, the author has decided to not take the CFD analysis into account. In the current work, it is assumed that a single apartment is a base energy balance cell. Furthermore, the detailed simulation method was chosen, as recommended in the literature, as the best tool for the research of active solar domestic hot water, heating, ventilation and air conditioning systems. Simultaneous modelling of building thermal behavior and the operation of plant and HVAC systems was employed by the author in order to achieve simulation results with physical reality.

1.3 Research goals and hypothesis 40

1.3 Research goals and hypothesis

The current thesis framework and scope was formulated based on knowledge and experiences gathered during the design time of high-end apartment buildings in Hannover. The project, called VASATI 2.0, has been realized by Wohnungsgenossenschaft Gartenheim eG, architecture office Peter Lassen, engineering office Udo Sprengel and Wienerberger in cooperation with the Technical University of Bialystok.

1.3.1 Scientific goals The main objectives pursued in this thesis are the following:

determination of an optimal value of a window-to-wall ratio that leads to minimum energy consumption for space heating,

testing the influence of thermal and optical properties of glazing systems on the thermal performance of buildings,

analyzing how a type of glazing systems may influence the thermal comfort in the considered houses,

optimization of a solar domestic hot water system, experimental determination of the thermal performance of a POROTON-T9-30,0

brick in order to calibrate an energy-simulation tool for buildings.

1.3.2 Hyphothesis Based on literature review and preliminary analysis, the following hypothesis is proposed:

Through the analysis of the influence of the solar radiation in the energy balance of a multifamily building it is possible to determine an optimal value of window-to-wall ratio that leads to a minimum of energy consumption for space heating.

2.1 Building energy simulation software 41

2 Research methods

In order to prove the hypothesis, three basic research methods were chosen. Firstly, detailed literature searches were conducted to identify current published knowledge concerning the impact of solar radiation on thermal behavior in buildings. Computer simulation techniques, which grow in popularity each year, were selected as the next step in our investigation. Additionally, experimental investigations were carried out for the determination of the thermal performance of the considered external wall and then for calibrating building simulation software.

2.1 Building energy simulation software

The main goal of this project was to determine the thermal performance of the dwelling house. The most popular and advanced simulation software that can be used for this type of analysis for residential and office buildings are the following: BLAST, BSim, DeST, DOE-2.1E, ECOTECT, Ener-Win, Energy Express, Energy-10, EnergyPlus, eQUEST, ESP-r, IDA ICE, IES/VES, HAP, HEED, PowerDomus, SUNREL, Tas, TRACE and TRNSYS.

The EnergyPlus V3-0, as a verified and fully-validated tool, was chosen from a wide variety of simulation programs. This software contains structured, modular code models combining heat and mass transfer, simulating multizone airflow and operating conditions of heating, cooling and ventilation systems in all kinds of buildings for long periods. The modularity structure of EnergyPlus and links to other programming elements are shown in Fig. 2.1.


Fig. 2.1: Network structure of EnergyPlus by getting started with EnergyPlus (2007)

EnergyPlus integrates all the following aspects of the simulation process: loads, systems and plants. Fig. 2.2 depicts connections and relations between these essential parts of energy modelling for buildings.

Fig. 2.2: Basic overview of the integration of internal elements structure by getting started with EnergyPlus (2007)

ENERGYPLUS INTEGRATED SOLUTION MANAGER

SURFACE HEAT BALANCE MANAGER

SKY MODEL MODULE

AIR HEAT BALANCE MANAGER

BUILDING SYSTEMS SIMULATION MANAGER

SHADING MODULE

DAY- LIGHTING MODULE

WINDOW GLASS MODULE

CTF CAL-CULATION MODULE

ZONE EQUIP. MODULE

AIR LOOP MODULE

PLANT LOOP MODULE

CONDEN-SER LOOP MODULE

PHOTO- VOLTAIC MODULE

AIRFLOW NETWORK MODULE

BUILDING DESCRIPTION

ENERGYPLUS SIMULATION MANAGER

HEAT AND MASS BALANCE SIMULATION

BUILDING SYSTEMS SIMULATION

SPARK POLLUTION MODELS ON-SIDE POWER FUTURE MODULES

WINDOW 5 AIRFLOW NETWORK GROUND HEAT TRANSFER FUTURE MODULES

CALCULATION RESULTS

DATA

DATA

ZONE CONDITIONS

DATA

DATA

DATA

DATA

UPDATE FEEDBACK

DESCRIBE BUILDING THIRD-PARTY USER INTERFACES

DISPLAY RESULTS


In EnergyPlus, the scheme of calculations, shown in Fig. 2.3, is based on a series of elements connected by air or water loops. Each fluid circuit has supply and demand sides. The Gauss-Seidell scheme is used to integrate, control and solve mass and energy balance equations for all loops.

Fig. 2.3: Simultaneous solution scheme used in EnergyPlus

A concept of heat and mass transfer modelling in EnergyPlus is based on the following balancing equation for each analyzed zone.

dissertation

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