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or W RN R W ISS

Solar Heating Systems for HousesDESIGN H NDBOOK FOR SOL R COMBISYSTEMS

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Published by James James (Science Publishers) Ltd8-12 Camden High Street, London, NW1 OJH, UK

003 Solar Heating and Cooling Executive Committeeof the International Energy Agency (IEA)The moral right of the author has been asserted.

All rights reserved. No part of this book may be reproduced in any form orby any means electronic or mechanical, including photocopying, recording or byany information storage and retrieval system without permission in writing fromthe copyright holder and the publisher.

A catalogue record for this book is available from the British Library.ISBN 1 902916 6 8

Typeset by Saxon Graphics Ltd, DerbyPrinted in the UK by The Cromwell Press

Cover photos courtesy ofSolarNor, Norway (top)AEE INTEC Austria (left, centre left and right)Wagner Co. Germany (centre right)This book was prepared as an account of work done within Task 26 SolarCombisystems of the IEA Solar Heating and Cooling Programme.Neither the International Energy Agency, nor any of their employees, nor anyof their contractors, subcontractors or their employees, make any warranty,expressed or implied, or assumes any legal liability or responsibility for theaccuracy and completeness of any information, apparatus, product or processdisclosed, or represents that its use would not infringe privately owned rights.

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Contents

PrefaceW e r n e r W e i r s

xi

1 Solar combisystems and the global energy challenge 11.1 Towards a sustainable energy future 1

demand in Europe 3

heating systems 51.3 Solar combisystems- a promising solution 6References 9

W e r n e r W e i s s

1.2 The contribution of solar thermal energy to the overall heat1.2.11.2.2 Collector area in operation in the year 2000 in EuropeCurrent and medium-term energy supply from solar

3

2 The solar resourceWolfgang S t r e i c k e r2.1 Solar radiation and ambient temperature2.2 Availability of climatic data2.2.1 Test Reference Years2.2.2 Weather data generatorsReferencesInternet sites for climatic data

3 Heat demand of buildingsWolfgang S t v e i c k e r3.1 Thermal quality of buildings3.23.3 Space heating demand3.4 Hot water consumption

The reference buildings ofTask 26

U l v i k e o r d a n a d Klaus jen3.4.1 DHW load profiles on a 1 minute timescale3.4.2 DHW load profiles on a 6 minute timescale3.4.3 DHW load profiles on an hourly timescale3.4.4 Final remarksReferences

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v i CONTENTS

4 Generic solar combisystems 384.1

4.24.34.4

Basic features of solar combisystems - a short summary4.1.2 Stratification in water storage devices 39

The generic solar combisystems considered

38Jean-Marc utev4.1.1 Comparison of combisystems with solar water heaters 38Classification of solar combisystems 41Jean-Mavc utev 43Jean-Mavc SiiterTechnical description of the generic systems 48Thomas Letz andjean-Mavc utev4.4.1 General remarks 484.4.3 System 1: basic direct solar floor (France) 514.4.4 System 2: heat exchanger between collector loop and4.4.2 The symbols used 49

space heating loop (Denmark) 534.4.5 System 3a: advanced direct solar floor (France) 55(Denmark and the Netherlands) 57with drainback capability (the Netherlands)

4.4.6 System 4: DHW tank as a space heating storage device4.4.7 System 5: DHW tank as space heating storage device 594.4.8 System 6: heat storage in D H W tank and in collectordrainback tank (the Netherlands) 614.4.9 System 7: space heating store with a single load-side heatexchanger for DH W (Finland) 624.4.10 System 8: space heating store with double load-side heatexchanger for DHW (Switzerland) 644.4.11 System 9: small D H W tank in space heating tank(Switzerland, Austria and Norway) 664.4.12 System lo: advanced small DH W tank in spaceheating tank (Switzerland) 694.4.13 System 11: space heating store with D H W load-side heatexchanger(s) and external auxiliary boiler (Finland andSweden) 71

heat exchanger(s) and external auxiliary boiler (advanced4.4.14 System 12: space heating store with DHW load-sideversion) (Sweden) 734.4.15 System 13: two stores (series) (Austria)4.4.16 System 14: two stores (parallel) (Austria)

75774.4.17 System 15: two stratifiers in a space heating storagetank with an external load-side heat exchanger for DH W(Germany) 794.4.18 System 16: conical stratifer in space heating store with

4.4.19 System 17: tank open to the atmosphere with three heatload-side heat exchanger for D H W (Germany) 81exchangers (Germany) 83
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CONTENTS vii^ X I I1

4.4.20 System 18: finned-tube load-side D H W heat exchangerin stratifier (Germany)4.4.21 System 19: centralized heat production, distributed heatload, stratified storage (Austria)4.4.22 Large systems for seasonal heat storage

ReferenceBuilding related aspects of solar combisystems5.1 Space requirements

Peter Kovdcs and Werner Weiss5.1.1 Is a low space requirement always desirable?5.1.2 How to achieve a low space requirement?5.1.3 Space requirements of the 20 generic combisystemsArchitectural integration of collector arraysIrene Bergmann, Michaela MeiqJohn Rekstad and Werner Weiss5.2.1 Roof integration5.2.2 FaGade integration5.2.3 Aesthetic aspects5.2.4 Project planning and boiler room

ReferencesFurther reading

5.2

6 Performance of solar combisystemsUlvike]ordan , Klaus K jen and Wolfgang Streicher6.1 Reference conditions6.1.1 Boiler parameters

6.1.2 Collector parameters6.1.3 Pipe parameters6.1.4 Storage parameters6.1.56.1.6 Combined total energy consumption

6.2 Fractional energy savings6.2.1 Target functions6.2.2 Penalty functions

6.3 Combisystems characterizationThomas Letz6.3.1 FSC method6.3.2 Cost analysis

Electricity consumption of system components

ReferencesDurability and reliability of solar combisystemsJean-Marc Suter and Peter Kovdcs7.1 General considerations

7.1.1 Durable materials

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7.1.2 Reliable components and systems7.1.3 Quantitative assessment of system reliabilityPeter Kovdcs7.2 Stagnation behaviour

Jean-Marc Suter7.2.1 Stagnation in solar combisystems7.2.2 Stagnation in pressurized collector loops withexpansion vesselsRobert Hausner7.2.3 Drainback technologyHuib Vissev and Markus PeterReferences

8 Dimensioning of solar combisystemsChris Bales, Wol ang Streichev, Thomas Letz and Bengt Pevers8.1 Dimensioning guidelines

Wokatg Streichev, Chris Bales and Thomas Letz8.1.1 Collector slope and orientation8.1.2 Collector and store size8.1.3 Climate and load8.1.4 The boiler and the annual energy balance8.1.5 Design of the heat store8.1.6 Design of the collector circuitChris Bales, Thomas Letz and Bengt Perers8.2.1 The Task 26 nomogram8.2.2 The Task 26 design tool8.3 Simulation of system performanceChris Bales8.3.1 TRNSY simulations8.3.2 Simulation ofTask 26 systemsNumerical models for solar combisystemsChris Bales and Bengt Perers8.4.18.4.2 Parameter identification and verificationReferencesSimulation programs

8.2 Planning and design tools

8.4Models used in Task 26

9 Built examples9.1 Single-family house, Wildon, Austria9.29.3 Single-family house, Koege, Denmark9.4 Multi-family house, Evessen, Germany9.59.6 Single-family house, Colbe, Germany

The Gneis-Moos Housing Estate, Salzburg, Austria

Multi-family house with office, Frankfurt/Main, Germany

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9.79.89.99.10 Single-family house, Falun, Sweden9.1 1 Single-family house, Orebro, Sweden9.12 Single-family house, Dombresson, Switzerland9.13 Single-family house, Buus, Switzerland9.14 Single-family house, Oslo, Norway9.15 Klosterenga Ecological Dwellings: multi-family house,References

Factory-made systems, Dordrecht, the NetherlandsSingle-family house, Saint Baldoph, FranceSingle-family house, Saint Alban Leysse, France

Oslo, Norway

1 Testing and certification of solar combisystemsHarald Driick and Huib Visser10.1 European standards10.1.1 Classification of solar heating systems10.1.2 Current status of the European standards

10.2.1 Collectors10.2.2 Testing of hot water stores10.3 Testing of solar heating systems10.3.1 The CSTG test method10.3.2 The DST method10.3.3 The CTSS method10.3.4 The D C and the CCT methods

10.2 Testing of solar thermal components

10.4 Certification of solar heating systemsReferences

Appendix 1 Reference libraryCompiled by Peter KovdcsAl.l Contents of the reference library sorted by authorAppendix 2 Vocabulary

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27727827928028028 1282283283284284286287289

289296

Jean-Marc Sutev, UlrikeJordan a n d DagmarjaehriigA2.1 Terms and definitions 296A2.2 Symbols and abbreviations 30 1A2.3 Terms and definitions specific to Chapters 6 and 8 302References 303

Appendix 3 IEA Solar Heating and Cooling Programme 3 4Wernev WeirsA3.1 Completed Tasks 305A3.2 Completed Working Groups 305A3.3 Current Tasks 305A3.4 Current Working Group 306
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x SOLAR HEATING SYSTEMS FOR HOUSES A DESIGN HANDBOOK FOR SOLAR COMBISYSTEMS

Appendix 4 Task 26Werner WeissA4.1 ParticipantsA4.2 Industry participants

Index

307308309

311
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Preface

Since the beginning of the 1980s, the rate of growth in the use of solar collectorsfor domestic hot water preparation has shown that solar heating systems are bothmature and technically reliable. However, for several years, solar thermal systemsseemed to be restricted to this application.

When the first systems for combined domestic hot water preparation and spaceheating, called solar combisystems, appeared on the market, complex andindividually designed systems were the rule.

The combination of thermally well insulated buildings and low-temperature heatsupply systems offered a wealth of new possibilities for solar space heating systemswith short-term storage. In addition, the growing environmental awareness andsubsidies in some countries supported an increase in the market share of this systemtype in many European countries.

From 1990 onwards the industry offered new, simpler and cheaper systemtechnologies, but basic scientific knowledge was laclung in certain areas and on somemethods. The designs were mainly the result of field experience and had not beencarefully optimized. A first international survey in 1997 revealed more than 20 differentdesigns that did not simply reflect local climate and practical conditions. Collaborativework in analysing and optimizing combisystems was seen as a proactive action thatcould favour high-quality systems that would be appropriate for a more global market.However, there were no common definitions of terms or standard test procedures forthis type of system. This meant that it was difficult to determine a meaningfulperformance rating, and even more difficult to compare the systems.

While a great effort was made in Task 4 of the Solar Heating and CoolingProgramme SHC) of the International Energy Agency IEA) dvunced ctiveSoluv Enevgy Systems to assess and compare the performance of different designsof domestic hot water systems, in 1997 there was no available method for findingthe best solution for a combisystem in a given situation.

International co-operation was therefore needed to analyse and review moredesigns and ideas than one country alone could cover. It was felt that an IEAactivity was the best way to deal with solar combisystems in a scientific and co-ordinated manner. Since it was also considered that combisystems needed furtherdevelopment in terms of performance and standardization, the IEA SHC launchedTask 26 Solar Combisystems in 1998.

From autumn 1998 to December 2002,35 experts from nine European countriesand the USA and from 16 solar industries worked together to further develop and

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x SOL R HE TING SYSTEMS FOR HOUSES DESIGN H NDBOOK FOR SOL R COMBISYSTEMSX

optimize solar combisystems for detached one-family houses groups of one-familyhouses and multi-family houses. Furthermore standardized classification andevaluation processes and design tools were developed for these systems. Anothermajor outcome ofTask 26 has been proposals for the international standardizationof combisystem test procedures.The further development and optimization of system technologies and designsby the Task 26 participants has resulted in innovative systems with betterperformance-cost ratings. The architectural integration of the collector arrays andthe durability and reliability of solar conibisystems were also investigated. This willlead to greater confidence amongst the end-users of this technology.

Both the solar industry and builders were involved in all activities in order toaccelerate the dissemination of results on as broad a scale as possible.This design handbook for solar combisysteins summarizes the results of Task 26and is also a contribution to the dissemination of the collaborative work. We hopethat it will contribute to the large-scale use of solar energy for hot water and spaceheating.Th e work on Task 26 and on the design handbook proceeded a t a very high levelthanks to the excellent co-operation of all the experts involved for which I am verygrateful. In particular my heartfelt gratitude is extended to Jean-ChistopheHadorn who originally initiated the task and to Jean-Marc Suter Huib Visser andWolfgang Streicher who acted as the leaders of the three subtasks:

Subtask A: Solar combisystems survey and dissemination of task resultsSubtask B: Development of performance test methods and numerical modelsfor combisystems and their componentsSubtask C: Optimization of combisystems for the market.

I also very much appreciate the co-operation of all of the authors of this book thehelp of Dagmar Jaehnig and Michaela Meir who assisted me in compiling andediting it and the contributions of William A. Beckman Chris Bales Jill GertzCnand Jean-Marc Suter in proofreading.

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Solar com bisystem s and theglobal energy challengeWevrzer Weirs

The increase of greenhouse gases in the atmosphere, and the global warming andclimatic change associated with it, represent one of the greatest environmentalthreats of our time and, in the future, also one of the greatest social dangers. Theanthropogenic reasons for this impending change in the climate can for the greaterpart be put down to the use of energy and the combustion of fossil primary sourcesof energy, and the emission of CO, associated with this.

To set the course towards a sustainable energy future it is necessary to look forsolutions that are based on renewable energy.

1 . I TOWARDS A SUSTAINABLE ENERGY FUTUREToday, the worlds energy supply is based on the non-renewable sources of energy:oil, coal, natural gas and uranium, which together cover about 82 of the globalprimary energy requirements. The remaining 18 is divided into approximatelytwo thirds biomass and one third hydropower.

According to many experts, the effective protection of the climate for futuregenerations will demand a t least a 50 reduction in the worldwide anthropogenicemission of greenhouse gases in the next 50 to 100 years. With due considerationof common population growth scenarios and with the assumption of a simultaneitycriterion for CO, emissions from fossil fuels, an average per capita reduction in theyield in industriai countries of approximately 90 will be required. This means areduction to one tenth of the current per capita yield of CO, (Figure 1.1).

A reduction of CO, emissions on the scale presented will, however, demandconversion to a sustainable supply of energy, which is based on the use of renewableenergy with a high proportion of direct solar energy use.

There is no doubt that it would be possible to supply technologically advancedcountries exclusively with renewable sources of energy in the next 50 to 100 years.For example, the overall solar energy incident on the earths surface exceeds bymore than 10,000 times the worlds current primary energy requirement.

There are numerous studies based on socio-economic, technological andinstitutional-structural models of global and national energy supply scenarios,showing shares of renewable sources of energy of 50 up to almost 100 in thenext 50 to 100 years.A reliable, favourably priced and environmentally sensitive supply of energy is animportant prerequisite for the development of modern societies and for upholdingand further improving the standard and the quality of life.

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Figure 1 1 Per capita emissionso f carbon into the atmosphererequired to mee t climatestabil ization agreements with adoubl ing o f the w orl d populat ionlevels Source: Lang et al. 1999

Beginning with the Final Report ur Common Future of the World Commissionon Environment and Development (Brundtland Committee),which was publishedin 1987, and the Conference of the United Nations for the Environment andDevelopment (UNCED), which took place in 1992 in Rio de Janeiro, the termsust in ble development became a central idea in the 1990s and the overridinggoal of global environmental and development policy.

Essential elements for the implementation of the concept of sustainabledevelopment in the field of energy are the orientation towards energy services, theefficient use of energy and the greater use of renewable energy sources, especiallythe direct or indirect use of solar energy.

The Brundtland Report (1987) and the discussion about sustainabledevelopment, as well as the climate and environment conferences held in Kyoto(1997) and Johannesburg (2002), have resulted in most countries having developedprogrammes and mechanisms to implement renewable energies as part of theexisting energy system and to extend their use. New legal and institutionalframeworks have had to be, and still have to be, developed to reach the goals set.Aswell as the environmental concerns, factors such as security of supply and socio-economic development play an important role in most national programmes.

The European Commission has laid down its goals with respect to futuredevelopment in the field of renewable sources of energy in the White Paper Enevgyfor the Future : Renewable Souvces of Eizevgy (European Commission, 1997). In theCommissions White Paper the following is mentioned as a strategic goal: . . toincrease the market share of renewable sources of energy to 12 by the year 2010.The yearly increase in the installed solar collector area in the Member States asgiven in the White Paper is estimated at 20 . Thus, solar heating systems inoperation in the year 2010 would correspond to an overall installed collector areaof 100 million m2.

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SOLAR COMBISYSTEMS AND THE GLOBAL ENERGY CHALLENGE 3x x x X I

If the direct use of solar energy for heating purposes via solar collectors is tomake a significant contribution to the energy supply in future, it is necessary that avariety of different types of systems are developed and established in the market, inaddition to those supplying only domestic hot water. One very promising sector forsolar thermal applications is space heating.1.2 THE CONTRIBUTION OF SOLAR THERMAL ENERGY TOTHE OVERALL HEAT DEMAND IN EUROPEIn 1998,energy consumption in the building sector totalled 16,077 PJ in EuropeanUnion Member States, or around 40 of overall energy consumption in theEuropean Union. Requirements for hot water and space heating amounted to12,200 PJ, or 75 , of consumption in buildings. O f this, 9200 PJ was accounted forby residential buildings (Figures 1.2 and 1.3).Figure 7.2. Breakdown o fenergy consumption inresidential b uildings in the EU,1998 European Com mission,2000)

Figure 7.3.Breakdown oenergy consumption incomm ercial and publ icbuildings in the EU, 1998European Com mission,2000

Since the heat needed in the building sector is low-temperature heat, this shows thelarge potential for solar thermal systems to provide space heating as well as domestichot water for the inhabitants of the building.1 2 1 Col lector area in operat ion in the year 2000 in Europ eSince the beginning of the 1990s the European solar market has undergoneconsiderable development. s the figures from the IEA Solar Heating and CoolingProgramme (Weiss and Faninger, 2002) and the German Solar Energy Association(Stryi-Hipp, 2001) confirm, sales of flat-plate collectors recorded a yearly average

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4 SOLAR HEATING SYSTEMS FOR HOUSES: A DESIGN HANDBOOK FOR SOLAR COMBISYSTEMS

growth of 17 between 1994 and 2000. This meant that while 480,000 m2 ofcollector area was installed across Europe during 1994, by 2000 the annual rate ofinstallations was around 1.17 million mz of collector area, meaning that the rate hadmore than doubled within a period of six years.

The installed collector area in Europe was around 11.4 million m2 at the end of2000 (Table 1.1). Of this, 1.7 million m2 was accounted for by unglazed collectors,which are used in the main to heat swimming pools, and 9.7 million m2 by flat-plate and evacuated tube collectors used to prepare hot water and for space heating.Table I I Total collec tor area in o per ation in th e year 2000 in EU countries in rn2

Water collectorsCount ry Unglazed Glazed Evacuated tube TotalAustriaBelgiumDenmarkFinlandFranceGermanyGreeceItalyThe NetherlandsNonvayPortugalSpainSwedenSwitzerlandU KTotal

571,80621,87515,56384,500615,00020,000100,305500100030,000221,200

1,681,749

1,581,18519,400243,16910,200470,0002,399,0002,815,000300,000176,5807000238,000399,922175,045250,800149,0009,234,301

26,2191700100

392,00020,000

100500300015,0002000

460,619

2,179,21042,975258,73210,300554,5003,406,0002,815,000340,000276,8857600239,500399,922208,045487,000151,000

11,376,669

If the installed flat-plate and evacuated tube collectors up to the end of 2000 areconsidered, then Greece and Austria are in the lead with 264 m2 and 198 m2respectively per 1000 inhabitants. They are followed by Denmark with 46 mz per1000 inhabitants, Switzerland with 37 m2 per 1000 inhabitants and Germany with34 m2 per 1000 inhabitants (Figure 1.4).The markets that underwent the greatest growth in the time period mentionedabove included Spain, the Netherlands and Germany. In the main, this can beattributed to the fact that the dissemination of solar heating systems had been verylow in these countries, compared with Greece and Austria. In addition to this,deliberate state programmes of financial incentives contributed to high growthrates.As mentioned above, in the White Paper on renewable energy, the EuropeanCommission set the goal of installing 100 million m2 of collector area in EuropeanUnion Member States. To achieve this ambitious goal, a yearly rate of increase of38 is required up to 2010, meaning that the present growth rate would have tobe a little more than doubled. Such a rate of increase can, however, only be reachedif the Member States and the Union support this with corresponding measures forspeedy market introduction and for research and development.

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SOLAR COMBISYSTEMS AND THE GLOBAL ENERGY CHALLENGE 5

300

-2 250Cm- 150

100

z00

50

Figure 1.4.Total installed flat-plate and evacu ated tube collector area per 1000 inhabitants inthe year 2000

1 2 2 Current and medium term energy supply from solarheating systemsAround 11.4 million m2 of flat-plate and evacuated tube collectors were installedin Europe by the end of 2000.The calculated annual collector yield of all recordedsystems in Europe is approx. 4600 GWh (17 PJ). This is annually saving theequivalent of 704 million litres of oil, thus avoiding the emission of 1.9 milliontonnes of CO, into the atmosphere (Weiss and Faninger, 2002).

If it is assumed that the final energy consumption for hot water and space heating inthe EU has not risen much since 1998, then around 0.14 of the overall requirementsfor hot water and space heating were covered by solar heating systems in 2000 acrossthe EU. If the ECs goal for 100 d o n m2of collectors by 2010 is met, then the totalarea installed will generate 144 PJ of heat per annum. If this is compared with theoverall hot water and space heating requirements for residential, commercial andpublic buildmgs n 1998, then 1.18 could be covered by solar energy (Table 1.2).Table 1.2.Current and m edium -term energy supply from thermal col lectors in Europe

Energy (PJ) Solar share ( )12,171urope Requirements for hot water and space heating - EU (1998)Solar heat 2000 - EU 17 0.14Solar heat 2010 EU 144 1.18

Developments in the building sector (low-energy and passive-energy houses) showthat it is possible to reduce the specific heating requirements of new buildings

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quickly. As studies illustrate, existing buildings have medium-term potential for areduction of 20 in the energy required for heating (European Commission, 2000).If such a reduction in heating requirements can be achieved in the medium term(i.e. up to 2010), then solar energy could provide around 2 of the energy neededby residential buildings for hot water and space heating in Europe.At this point it should also be remembered that, until now, solar heatingapplications have concentrated almost entirely on the supply of hot water to single-family homes, whether individually or in small groups. In countries such asGermany, Switzerland and Austria, there has been a marked trend towards solarspace heating systems for some years, and in this respect significant increases areanticipated in the years to come.Results from Austria show that the targets for Europe are realistic and theyillustrate the medium-term potential in a country where the solar heating marketis already widely developed compared with other European countries.If both the contribution solar energy currently makes to the supply of heat inAustria and its potential up to 2010 are analysed (Table 1.3), t becomes clear that,in the medium term, solar collectors will be able to supply significant amounts ofthermal energy to meet heat requirements.Table 1.3. Current and med ium-term energy supply from solar col lectors in Austria

Energy (PJ) Solar share ( )Austria Requirements for hot water and space heating (1998) 303Solar heat 2000 3.22 1.06Solar heat 2010 12.87 4.25

Figures for Austria in 2000 indicate that the solar contribution to hot water andspace heating requirements is 3.22 PJ or 1.06 ; this means Austria has alreadyreached the amount which all Member States of the EU are striving for in themedium term. If it is assumed that the average growth rates in Austria up to 2010will be below the European average at 20 , because the market is already highlydeveloped, then the collector area can be quadrupled in the next ten years.Thiscorresponds to an overall collector area installed in Austria of approximately 8million m2.Thps n 2010, around 4.25 of the countrys overall hot water and spaceheating requirements can be covered by solar energy, provided that theserequirements remain the same.

1.3 SOLAR COMB ISYSTEMS - A PROMISING SOLUTIONThe demand for solar heating systems for combined domestic hot water preparationand space heating, so called solar combisystems is rapidly growing in severalcountries. In Sweden the share of the collector area installed for solar combisystemsin 2001 was already sipficantly larger than the collector area installed for solardomestic hot water systems. In Austria, Switzerland, Denmark and Norway thecollector area installed for solar combisystems and for solar domestic hot water

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SOLAR COMBISYSTEMS AND THE GLOBAL ENERGY CHALLENGE 7

systems was almost the same. In Germany, which installed 900,000 m2 of collectorarea in 2001, the share of the collector area installed for combisystems was 25 .Figure 1.5 shows that in some countries, such as Germany, Austria, Switzerland,Sweden and Denmark, solar combisystems already have a noteworthy share of themarket. The primary energy sources of these solar combisystems are solar energywith auxiliary sources such as biomass, gas, oil and electricity, either directly or witha heat pump.

g 900,000; 800 0005 700 000600,000u 500 000

400 000.- 300 000-g g

200 00000 000-

Figure 1.5.Share of c ollector area used for solar do mes tic hot wate r systems and for solarcom bisystems in selected countries

A realistic approach would be to assume that, in the next ten years, a minimum of20 of the collector area installed annually a t middle and northern latitudes will beused for solar combisystems. This means that around 120,000 solar combisystemswith 1.9 million m2 of collectors need to be installed per year in the countries ofthe European Union, if the goals set in the European Commissions White Paperare to be met (Figure 1.6). Increasing the installed collector area by a factor of 10

100up 80

70I

p 60Qa 5040

100 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Figure 7.6. bjectives for the installed collector area and ma rket share o f solar com bisystemsup to 2010 in the me mb er countr ies of the European Union

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8 SOLAR HEATING SYSTEMS FOR HOUSES A DESIGN HAND BO OK FOR SOLAR COMBISYSTEMS- x _ _ _ ~ _ L

over 10 years is a major challenge, but this can be achieved if there is massive andcontinuous support, both political and financial, from the member countries.Solar combisystems are more complex than solar domestic hot water systems, asthere are more interactions with extra subsystems. The intrinsic complexity ofimplementing a solar combisystem working in conjunction with auxiliary heatinghas led to a large number of widely differing system designs. The most promisinggeneric system designs are introduced in Chapter 4.

The solar contribution, which is the part of the heating demand met by solarenergy, varies from 10 for some systems to up to 100 for others, depending onthe size of the solar collector, the storage volume, the hot water consumption, theheat load of the building and the climate.The different system concepts can partly be attributed to the different conditionsprevailing in the individual countries. Thus, for example, the 'smallest systems' interms of collector area and storage volume are located in those countries in whichgas or electrical energy are primarily used as auxiliary energy. In the Netherlands,for example, a typical solar combisystem consists of 4-6 m2 of solar collector and a300 litre storage tank. The share of the heating demand met by solar energy is,therefore, correspondingly small.

Figure 7.7.A Dutch house witha solar com bisystem Source:ATAG, The Netherland s)In countries such as Switzerland, Austria and Sweden, where solar combisystems aretypically coupled with an oil or biomass boiler, larger systems with high fractionalenergy savings (the term is defined in the appendix) are encountered. typicalsystem for a single-family house in these countries consists of up to 15-30 m2 ofcollector area and 1-3 m3 of storage tank volume (Figure 1.8).The share of theheating demand met by solar energy is between 20 and 60 . In some cases ofextremely well insulated houses and low-flow mechanical ventilation, the solarcontribution can even reach 100 .

Apart from collector types and storage tank details, the layout of the system, thatis the connections between components, is one of the most differentiating itemsamong the various system concepts analysed in Task 26. Based on the experienceof Task experts, the requirements for the hydraulic layout of solar combisystems canbe summarized s follows (Streicher, 2000):

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SOLAR COMBISYSTEMS AND THE GLOBAL ENERGY CHALLENGE 9 X x x X I I

Fgu re 1.8.Solar combisystemfor a single-family house inSweden Source: K. Lorenz,SERC, Sweden)

the delivery of solar energy to heat store(s) and heat consumers with as low aheat loss as possiblethe production and delivery of auxiliary heat to consumers with as low a heatloss as possiblethe distribution of all the heat needed to meet hot water and space heatingdemandsthe reservation of sufficient storage volume for auxiliary heating, with theminimum running time for the specific heater taken into accountlow investment costslow space demandeasy and fail-safe installationreliable operation and low maintenance cost.

These conditions require simple systems in terms of connections, compared to thesystems designed and constructed in the 1980s.

REFERENCESEuropean Commission, 1997, Ei ie yy or the Future: Reriewable Sources o f Ei ieyy - W i t e Paper fo r

Commuriity Strategy and Actiori Plan COM. (97) 599 of 6.11.1997.European Comnussion, 2000, Green Paper - owards European Strategy fo r the Security of Ei9eyy

Supply Technical document, Brussels.Lang R W,Jud T and Paula M, 1999, Impulsprogramm Nachhaltig Wirtschaften Bundesministerium

fur Wissenschafi und Verkehr,Vienna.Stryi-Hipp G, 2001, Der Europaische Solarthermiemarkt Proceedingr 11 Symp osium ThermischeSolareneyie StafelsteiH Ostbayerisches Technologie-Transfer-Institut e.V., Regensburg,

Germany.Weiss W and Faninger G, 2002, Collector Market in IEA-Member Countries 2000 EA Solar

Heating rid Coolirlg Programme Gleisdorf, Austria, http: //www.iea-shc.orgStreicher W, 2000, Solar combisystems - from small niche market to standardised application,

Proceedings Eurosun 2000 Conference Copenhagen ISES-Europe, http://www.ises.orgWorld Commission on Environment and Development (UNCED), 1987, Our Comm on Future

Oxford University Press, Oxford.

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The solar resourceWo fgang Streickev

The Sun is the central energy producer of our solar system. It is a 1,390,000 kmdiameter sphere with nuclear fusion taking place continuously in its centre. A smallfraction of the energy produced in the Sun hits the Earth and makes life possibleon our planet. Solar radiation drives all natural cycles and processes such as rain,wind, photosynthesis, ocean currents and several others which are important forlife. The world s energy need has been based from the very beginning on solarenergy. All fossil fuels (oil, gas, coal) are converted solar energy.The solar radiation is emitted by the Sun s corona a t an effective blackbodytemperature of approximately 5800 K with an irr di nce (terms are defined in theAppendix) of 70 000-80 OOOW/m . Our planet receives only a very small portionof this energy. In spite of this, the incoming solar radiation energy in a year is some1.5x10 x kWh; this is about 15,000 times the yearly energy need of the wholeworld in 2000

The duration of the sunshine as well as the solar irradance is dependent on the timeof the year, weather conltions and naturally also on the geographical location. Theamount of yearly global radiation (on a horizontal surface) in the sunbelt regions mayexceed 2200 kWh/m . In northern Europe, the maximum value is about 1100kWh/m .

kWh/a; BPAmoco, 2002).

2 1 SOLAR RADIATION A ND A MB IENT TEMPERATUREThe climate is one of the key factors influencing the energy yield of a solarcombisystem. This interaction takes place on several levels:

Solar collector:collector.collector absorber and the ambient.

The absorber temperature is dependent on the solar radiation on the solarLosses to the ambient are driven by the temperature difference between the

Heat demand of the building:Heat losses to the ambient are driven by the temperature difference between

Solar radiation through the windows can be seen as inner heat gains in theDomestic hot water (DHW) demand

The cold water temperature from the mains varies over the year.This

the house and the ambient (air and ground).period of the year when space heating is effectively needed (heating season).

variation is mainly dependent on the average monthly ambient temperatures.

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THE SOLAR RESOURCE

Climate varies from location to location and from year to year. Figures 2.1 and 2.2show the world s yearly average global irralation and the Earth s surfacetemperature. In Figure 2.3 the average values of solar irradiation and outdoor

f igure 2 World map of yearly average globa l irradiation on a horizontal surface) in kW h/ m BSource METEOTESj: Berne, Switzerland, http Nwwwmeteo norm c om ) See also colour plateMREONORM 4

Figure 2.2. Wo rld map of yearly average amb ient temperature in C. Source: METEOTESTBerne, Switzerland, http://www.meteonorm.com).See also colour plate 2

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12 SOLAR HEATING SYSTEMS FOR HOUSES A DESIGN HANDBOOK FOR SOLAR COMBISYSTEMS

Month ly va lues of ambient tem perature 1991 200025.020.0

15.0

6 10.0

5.0

0 0

Monthly values of g lob al i r radiat ion 1991 2000250

200

150

100

50

-19911992

99319941995

996- 1997

99819992000

-Average

1991

1992993

19941995

996I997

19981999

- 2000=- Average

Figure 2.3 . Ten-year mo nthly average am bient tempe rature and horizontal) glob al irradiation fora cen tral European location ZAMG,2001)

temperature for one location over 10 years are shown. Despite the obvious seasonaltrend, a wide range of fluctuations between the months can be seen. In order tocompare the performance of different combisystems under different climateconditions on the same basis, average data for each location are needed.

The orientation of the absorbers window, collector) is also significant. Figure 2 4shows the monthly hemispherical irradiation on differently orientated surfacesfor a central European climate. It can be seen that horizontal surfaces and surfacesfacing south with a tilt angle of 45 have much higher summer than winter

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THE SOLAR RESOURCE 13

250

g 2003 150

0JAN FEE MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

f igu re 2.4. Hem ispherica l irradiation on surfaces of differen t orientations for a central Europeanclimate Streicher; 2002

irradiation. The winter incident radiation on the south-facing 45 tilted surface ismuch higher than that for the horizontal surface. Vertical surfaces facing south dohave a nearly constant irradiation from March to September, and nearly as muchirradiation in winter as surfaces facing south with a 45 tilt angle.Two-axis trackmgmainly increases the solar yield in summer, while in winter the irradiance is similarto a 45 slope facing south.

In order to cover the geographical range for the main markets of solarcombisystems, t was decided to choose a northern, a central and a southern Europeanclimate for ll further investigations and simulations. Respectively, these were:

Stockholm, SwedenZurich, SwitzerlandCarpentras, France.

Table 2.1 shows the characteristics of the locations with respect to geographicaldata, design temperatures (for space heating) and yearly global irradiation (on ahorizontal surface).Table 2.1. Characteristics of the locations Streicher et al., 2001Location Latitude Longitude Height above Ambient design Yearly globalNorth East sea level temperature for irradiation

m space heating kWh/m aO CCarpentras (F) 44.05 5.05 105 -6 1502Zurich (CH) 47.37 8.543 413 -10 1088Stockholm (S) 59.31 11.938 44 17 981

Figure 2.5 shows the global solar irradiation and ambient temperature on a long-term average monthly basis for the chosen climates. The differences between the

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T

months Stockholm A Zur ich C Caroentras

25

a Stockholm A Zurich arpentrasFigure 2 5 Mo nthly globa l irradiation on a horizontal surface) and am bien t temp erature o theclima tes cho sen in Task 26

three climates are obvious. In the heating season, Stockholm has the lowestirradiation coupled with the highest heat demand, due to the lowest ambienttemperatures.The opposite is the case for Carpentras in France. Only minor partof the solar irradiation is available during the heating period for all locations.

For simulations it is necessary to use hourly values of irradiance and ambienttemperature see Section 2.2).The hourly values of climate data forTask 26 globaland direct irradiance, ambient temperature, wind speed, relative humidity and dry-bulb temperature) were calculated with the Swiss climate data generatorMETEONORM 1999) using long-term monthly averages of global irradiationand ambient temperature. Figure 2.6 shows the daily fluctuations for a summerweek in Zurich with cloudy weather t the beginning and sunny weather t theend.

The irradiance on the collector and on the windows has to be calculatedseparately and split into direct and diffuse sky- and ground-reflected) radiationbecause of its different angles of incidence. This has been done in Task 26 using theTRNSYS Klein t a l . 1998) radiation processor.

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THE SOLAR RESOURCE 1 5

1000900800700600500400300200100

04441 4465 4489 4513 4537 4561 4585

Hour of the year

35

30 at-25

20

1510

f igure 2.6. Hourly average values of global irradiance and am bient tem perature for a summ erwe ek in Zurich, generated wit h METEONORM 1999)

2.2 AVAILABILITY OF CLIMATIC DATAClimatic data for ambient temperature and global solar irradiance (on a horizontalsurface) is available for a wide range of locations. In Figure 2.3 it was shown thatboth irradiation and temperature differ from place to place over a wide range on amonthly basis and less on a yearly basis. If different locations are to be compared, itis therefore necessary to use average climate data.For simulating solar combisystems with one to three days of water storage, a t leasthourly climatic data is necessary to calculate correctly the behaviour of the storage.The same type of data is needed if the effect of the thermal active mass of thebuilding (the storage of excess energy during the day for use at night to reduce theheat demand) is taken into consideration. One of the problems is to find hourly datathat match long-term averages as well as standard fluctuations (sunny and cloudyweather situations in a realistic statistical distribution, where irradiance,temperature, humidity, wind speed etc. correspond with each other). Two methodsare described in the literature.2 2 1 Test Reference YearsTest Referenceyears are generated by selecting time spans (typically one month) ofmeasured climatic data from a number of measured years for one location in sucha way that the long-term monthly averages of all climatic data for this location arematched. Using measured data ensures that the weather fluctuations of the regionare correctly represented. Of course, the links between the time spans have to besmoothed. However, generating Test Reference Years (TRY) is very timeconsuming. Consequently, they are often very expensive (as for example the 1 2available Test Reference Years for Germany). However, they are sometimes availablefree of charge, as for example the Typical MeteorologicalYears (TMY) for the USA

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16 SOLAR HEATING SYSTEMS FOR HOUSES A DESIGN HANDBOOK FOR SOLAR COMBISYSTEMSI _ I I _ - 1 r--for 234 sites (see http://rredc.nrel.gov/solar/old~data/nsrdb/tmy2/ .n order tohave data available for a whole country, it has to be divided into typical weatherzones, for which Test Reference Years have to be developed.2 2 2 Weather d ata generatorsThe second option is the use of weather data generators.These programs use long-term average monthly data of some key values (normally monthly average dailyglobal irradiation and ambient temperature) and generate hourly data, using physicaland statistical approaches. Well known are the weather data generators of thesimulation tool TRNSYS (Klein t af. 1998) and of the Swiss tool METEONOM(1999) The latter was used in Task 26 Long-term monthly average temperatures canbe found at http://www.top-wetter.de/klimadiagramme/welt.htm.Worldwideirradiation data can be found a t http://wrdc-mgo.nrel.gov/html/get-data-ap.htd.All of the combisystem simulations performed within Task 26 needed evensmaller time steps (down to one minute) to model the behaviour of the systemscorrectly. Therefore the hourly values were linearly interpolated, ensuring that noirradiance occurs before or after sunset.

The simulations were set up in such a way that other locations can be easilyincluded if hourly weather data are available in the proper format.REFERENCESBPAmoco, 2002, BPAmoco Statistical Rev iew ofworld Energy 2001 BPAmoco, London.M E T E O N O M , 1999,Weather Data Generator. METEOTEST, Fabrikstrasse 14, CH 3012

Bern, Switzerland; ww w.me teonorm .com.Streich er W, 2002 Lecture book Sonnenenergienutzuq Institute of Thermal Engineering, GrazUniversity of Technology.

Klein, SA, Beckmann WA, M itchell JW, Duffie JA, Duffie N A, Freeman TL, M itchell JC , BraunJE, Evans BL, Kumm er JP, Urban RE iksel A, T ho rn to n JW, Blair N J, 1998, TRNSYS ATransient Sys tem Simula tion Program Version 14 2 (as used in p roject), Solar Energy Laboratory,University o fW isconsin, Madison, USA.ZA MG , Zentralanstalt fur M eteorologie and G eodynamik,Vienna, Austria, 2002.

INTERNET SITES FOR CLIMATE DATAhttp://rredc.nrel.gov/solar/old~data/nsrdb/tmy2/:ree T M Y data sets for the USA.http://www.top-wetter.de/klimadiagramme/welt.htm:ong-term worldwide monthly averagehttp://wrdc-mgo.nrel.gov/html/get-data-ap.htd: orldwide irradiation data.

temperatures.

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Heat demand of buildingsWolfgang Streicker UlrikeJordan and Klaus k j e n

In this chapter, the building models used for annual system simulations in Task 26are described and the requirements for the definition of the thermal quality ofbuildings are discussed. In order to fulfil the thermal requirements of a building, theroom temperature, the indoor humidity and the air quality need to be adjusted byan active heating system within the building. Devices for active cooling have notbeen taken into account. Assumptions made concerning the effect of climateconditions during the year, as well as internal gains such as heat emitted by people,electrical appliances and lighting, are presented.Finally, the load profiles for domestic hot water used for the annual systemsimulations are described. The profiles were generated with statistical methods inorder to take into account fairly realistic conditions. The assumptions madeconcerning the probability distributions of draw-offs during the year and flow ratesare shown.3.1 THERMAL QUALITY OF BUILDINGSThe thermal quality of buildings can be viewed, on one hand, as the energy demandof the building and, on the other hand, as the indoor air quality, which is definedby temperature (air and surface of inner walls), humidity, air velocity and pollutants(CO,, CO, NOx,odours).A major factor is the insulation level of the building envelope, which affects thethermal quality of a building in several ways:

The space heating energy demand is directly related to the thermal quality ofthe envelope of the buildmg.When the thermal quality of the building increases, the heat distributionsystem can be operated either with lower temperatures or with a smallerheating surface. This allows either integration of highly efficient heating devicesthat need low temperatures (e.g. condensing gas boiler, heat pump, solarcombisystem) or a decreased investment cost for the heat distribution system.The indoor air quality of buildings is also related to the thermal quality of theenvelope. The better insulated the building is, the smaller is the differencebetween the temperatures of the inner surface of the envelope (wall, ceiling,windows, floor) and the room air temperature. Figure 3.1 shows therecommended range of room air and surface temperatures that lead to

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comfortable and still acceptable indoor temperature conditions. These valuescan also be used to determine the influence of the heat distribution system onindoor comfort (if wall or floor heating is used).

32

2 282624

00 30

.cQI 22

20181614

tJ 12m 10

12 14 16 18 20 22 24 26 28Room air temperature [ C]

Figure 3.1. Recommended room air temperature as a function of w all temperatureAdditional factors influencing the thermal quality of a building are the glazing area,the amount of thermally active mass, the ventilation rate and the indoor humiditylevel. Windows allow the use of daylight and permit solar energy to pass throughand be absorbed inside the building (passive solar energy use). Passive solar gainsreduce the space heating demand and connect the user inside the building to acertain extent with the ambient climate conditions. In order to avoid overheatingin summer, the window area should mainly face south (see Figure 2.4). A secondmeasure to avoid overheating and to damp the daily temperature swing within abuilding is the use of active thermal mass.

282 27a- 26

25J .O 241 23E mL

E 220a 2120

18 19 20 21 22 23 24 25 26 27 28 29 30 31 32Outdoor temperature [ 'C]

Figure 3.2. Recommended room air temperature for air conditioning in buildings DIN 1946,part 21

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HEAT DEMAND OF BUILDINGS 1911 1, _ x

According to the German standard DIN 1946 the recommended room airtemperature is 20C in the case of space heating. For air conditioning, Figure 3.2shows the recommended indoor air temperature range as a function of the outdoorambient temperature according to the German standard VDI 2067: 22-25OC forambient temperatures up to 27OC.

The indoor humidity should be kept within the ranges shown in Figure 3.3.Thiscan be achieved either with air conditioning systems with humidification in winterand dehumidification in summer or with wall layers that can absorb and evaporatemoisture in a manner analogous to energy in thermal active mass.90807060z=O40- 30Wm.-22010

12 14 16 18 20 22 24 26 28Room air temperature [ C]

Figure 3.3. Recomm ended room air temperature as a function o f relative hum idityHalozan, 7 998)

The thermal insulation of buildings has increased significantly in the past 25 years.The specific space heating energy demand of buildings was about 200 kWh/m'afor Central Europe in the mid-1970s. New building codes in Germany,Austria andother European countries have reduced specific space heating energy demandsbelow 70 kWh/m2a. Low-energy buildings with a space heating demand of lessthan 50 kWh/m2a can be built in Central Europe without increasing theinvestment costs compared to conventional buildings. Without air heat recovery ofventilation air the specific space heating energy demand can be decreased to about30 kWh/m'a. So-called passive houses use fan-assisted balanced ventilation with airheat recovery. The resulting specific heat demand (without the electricity demandof the ventilation system) is below 15 kWh/m2a. Several thousand of these passivehouses as single- and multi-family houses or as office buildings) have been built inEurope so far. Of course, all of these buildings meet the indoor air quality criteriamentioned above.

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The shape of such buildings can vary widely, because insulation can be put on allsurfaces and in all kinds of shapes (see Figure 3.4). Most of these buildings have acompact form, in order to reduce the surface area exposed to the ambient, and havemore window area facing south compared to the other directions to achieve highsolar passive gains.

Figure 3.4. Examples of a low -en ergy mu lti-family terraced house Source: Okoplan, Rankweil,Austria) and a single-fam ily house Source: SOLVIS, Brau nschw eig, G ermany) wit h solarcombisystems

3.2 THE REFERENCE BUILDINGS OF TASK 26Three single-family houses (SFH) with the same geometry but different buildingphysics data were defined in such a way that the specific annual space heatingdemand for the Zurich climate amounts to 30,60 and 100 kWh/m2a.Additionally,a multi-family house (MFH) with five apartments and a specific annual spaceheating demand for Zurich of 45 kWh/m'a was defined. Figures 3.5 and 3.6 showthe principal design of these buildings. Table 3.1 shows the reference space heatingload (according to the ambient design temperature ofTable 2.1) and the layoutcharacteristics of the radiator heat distribution system.

Table 3.2 shows heat transfer coefficients (U-values) of typical buildings from thepast 30 years and the respective data for the reference buildings. SFH 100 representsTable 3.1. Heat load for the buildings according to DIN 4701 and design temperatures for theheat distribution svstem

L > r / r r < l , r , l l l lC of Design flowheat distribution temperaturedistributionSpace heating system of heatdemand* Stockholm Zurich Carpentras system

kWh/m?a kW kW kW K O CHeat load

SFH 100 9.05 7.29 6.32 10 5 t ) 60 4 5 t )SFH 60 6.16 4.95 4.26 5 40SFH 30 3.48 2.83 2.46 5 35MFH 45t 17.35 13.97 12.06 5 40* Gross area, Zurich conditionst Recommended for the French solar heating floor system (generic System #3 , Chapter 5): Multi-family house with flats of 100 m2 gross area

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HEAT DEMAND OF BUILDINGS 21

Figure 3.5: Sketch of the single-family house SFH) used in Task26

Figure 3.6: Sketch of the multi-family house MFH) used in Task 26

a typical building that is about 10 years old, SFH 60 represents a buillng to thecurrent standard and SFH 30 represents a highly insulated building.

Table 3.2. G- and U-values for historical buildings and the reference buildings in Task 26Historical Task 26 reference buildings

U-values Units 1970 1980 2000 SFH 100 SF H6 0 SFH 30 MFH 45Wall W/m2K 1.50 0.80 0.50 0.51 0.34 0 .14 0.37roof W/m2K 1.00 0.50 0.30 0.49 0.23 0.11 0.22ground floor W/m2K 1.00 0.60 0.40 0.55 0.20 0.12 0.23window W/m'K 5.00 3.00 1.40 2.80 1.40 0.40 1.40Gvalues of window - 0.90 0.75 0.50 0.76 0.49 0.41 0.49

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Table 3.3 shows typical U-values of different European regions and, for comparison,for Mexico.These values were evaluated in Task 25 (Solar Assisted Air Conditioningof Buildings) and Task 27 (Performance, Durability and Sustainability of AdvancedWindows and Solar Components for Building Envelopes) of the ImplementingAgreement on Solar Heating and Cooling of the IEA. It can be concluded that therange of the buildings chosen in Task 26 covers the wide range of buildings presentlybuilt in Europe.Table 3.3. G- and U-values common in different countries and chosen in IEA Solar Heating andCooling Task 27 Task 25. 2002)

Freiburg Perpignan Madrid Palermo Athens Merida Task 27U-values Units Copenhagenexternal wall W /m ZK 0.35 0.32 0.59 1.26 0.60 0.70 0.38roof W /m 2K 0.17 0.33 0.32 0.48 0.50 0.36 0.30ground floor W /m 2K 0.35 0.42 0.36 0.85 1.50 1.50 0.26floor W /m 2K 0.36 0 .23 0 .74 0 .59 1 .50 1 .50 0 .85internal wall W /m2K 0.29 1 .57 1 .25 1 .50 1 .50 0 .42window W / m 2 K 1.10 1.40 3.90 4.13 3.70 5.32 1.56frame W /m 2K 2.00 2.27 2.26 2.00 2.26 3.00 2.40frame share m2/m2 0.20 0.20 0.20 0.15 0.20 0.20 0.20of window

G v a l u e s ofwindow - 0.60 0.59 0.77 0.80 0.80 0.80 0.53

3.3 SPACE HEATING DEM A NDThe space heating demand is dependent on the following factors:

conduction/convection losses through the envelopeventilation losses to provide good indoor air quality (keep humidity, CO,, CO,odours, etc. below specified values)infiltration due to incomplete tightness of the buildingpassive solar gains through windowsthermal gains from people inside the building, electricity demand of devicesand artificial lightingthe thermal mass (because of its ability to dampen daily indoor temperaturefluctuations)user behaviour (in terms of indoor air temperature, which is often above 2OoC,manual ventilation, and active shading in summer and winter).

Figure 3.7 shows the main energy flows between a building and the environmentand within a building. If a room or group of rooms within a building acquiressignificantly different temperatures because of user behaviour or from passive solargains, then this group has to be treated as a separate zone in the calculation of theenergy demand. For Task 26, the SFH building was assumed to be a single zone.The MFH was first calculated as a two-zone model (one zone for the middle

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Figure 3.7.Schematic energy flows in a building Heimrath, 1998)

apartments and one zone for the outer), but the differences turned out to be verysmall, so that finally the MFH was also assumed to be a single zone.The space heating demand is strongly dependent on the user behaviour,especially for low-energy buildings. Figure 3.8 shows this dependency calculatedfor a low-energy building as a function of indoor air temperature and ventilationrate. Increasing the indoor temperature from 20-24OC doubles the space heatingenergy demand in this case, because the period where the space heating demandcannot be covered by the internal gains will be much longer.Also, the ventilationrate (Figure 3.8, right), which is user-dependent if no automatic ventilation systemexists, has a high impact on the annual space heating demand. Even the presence of

20 21 24Indoo r air temperature ['C]

0.1 0.2 0.28 0.4 0.6 0.8Vent i la t ion ra te [llh]

Figure 3.8, Influence of the indoor air temperature and the ventilation rate on the space heatingdemand of a low-energy building Lari, 1999)

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24 SOLAR HEATING SYSTEMS FOR HOUSES. A DESIGN HANDBOOK FOR SOLAR COMBISYSTEMS_ _ _ _ _ L I ~ ~~~~~~~

people in the building can have a significant impact on the space heating demandas shown in Figure 3.9. Consequently, user behaviour has to be clearly defined,when the space heating demand of buildings is to be calculated.

No people Two people Two people Two peopleat night half day + full day

nightf igure 3.9. Influence of people on the space heating demand of a low-energy building Lari, 7999)The annual heat demand is normally calculated with standards that use either theannual heating degree days (i.e. the GermanVDI 2067) or monthly average climatevalues (i.e.EN832). Both methods take into account the above-mentioned itemsbut are restricted to the building itself and provide only the annual (VDI 2067) ormonthly (EN832) energy demand.To evaluate solar combisystems it is necessary toknow a t least the hourly values of the heat demand of the building because the heatstorage volumes are normally sized for the heat demand of one to three days.

In Task 26 it was decided to simulate the building in parallel with thecombisystem to model the dependencies between the two systems correctly. Allcalculations were performed with the simulation tool TRNSYS.

The following assumptions for the thermal requirements and the user behaviourwere chosen for all buildings:

Room temperuture:The controls on the heating system were set in such a waythat the room temperature is kept around tR = 20 ? 0.5 C and never dropsbelow 19.5OC during heating season. For buildings with a floor heating systemthat use the thermal mass of the floor as a heat storage, the room temperaturewas allowed to range between 19.5 and 24'C.Temperatures above 24OC wereexcluded from the analysis because solar combisystems for heating purposesand not the buildings (with their specific overheating characteristic) were to becompared.I/entilution:The air change rate of ventilation is assumed to be 0.4 h-' based onthe gross volume of the buildmg. This rate is assumed in most Europeanstandards.No air heat recovery system was used.Shading:There was no internal or external shading device used, because onlythe heating period was analysed and shading is mainly used a t times whenoverheating occurs and no space heating is needed.

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* Internal gains:The user behaviour in terms of people present in the buildingswas assumed to be the same for alI buildings. The following internal thermalgains were taken into account:- According to I S 0 7730:1994, internal thermal gains of 2.5 kWh/day were

assumed, caused by one person at rest for 24 hours/day, and one person for14.5 houdday.etc. were taken into account for single-family houses and constant thermalgains of 550 kJ/h for multi-family houses

- Constant thermal gains of 700 kJ/h, caused by lighting, electrical devices,

The hydraullc layout of the reference space heating system is shown in Figure 3.10.Thespace heating is simulated with radiators and thermostatic valves, which adjust the massflow controlled with a PID controller (non-standard TFWSYS Types 162 and 120).Floor heating systems are simulated with transfer functions (non-StandardTRNSYSType100).The design flow temperatures of the space heating systems are shown inTable 3.1.

Ambienttemperaturesensor

Boi ler with Flow temperature Thermos tat icvar iab le power ad justment accord ing va lves

Figure 3.10. Schematic of the space heating distribution system of the reference buildingsto ambient temperature

Figure 3.11 shows the control characteristics of the radiator heating system for atime period of three weeks in spring. In the first and third weeks, there is spaceheating demand, while in the second week the room air temperature rises above20.5 C because of passive gains and the finite thermal mass of the building,resulting in no additional heat demand.The outdoor temperature in the secondweek remains below 20OC for most of the day. Therefore the flow temperature tothe radiators is kept above 20.5 C. The flow temperature to the heating system isdirectly dependent on the outdoor temperature.When the sun is shining during theday or when other internal gains occur, the room air temperature rises and the massflow rate of the heating system is reduced by the thermostatic valves. Thesefluctuations of the mass flow rate can be clearly seen in Figure 3.11.

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35 35030 300

25-2 20f 15aaE 10c

5

250 K200 &I

150 '100

2500 0

-51680 1840 2016

Time [h]50

2184

Figure 3.7 7 Heat demand, mass flow rate and temperatures of the reference heating systemfor a time period of three weeks in spring, with radiators and PID controller thermostaticvalve), using DIN 4701 heating load for the reference SFH 60 in Zurich as the design heatingrate Streicher; Heimrath, 2003)Figure 3.12 shows the specific energy demand of the four reference buildings in thethree climates.The expected high dependency of the space heating demand on thelocation, as a result of different ambient temperatures and lengths of the heatingseason, can be seen (see also Figure 2.5).This high dependency has to be taken intoaccount when solar combisystems are optimized for different regions or when solarcombisystems optimized for l fferent regions are compared.

160-0 140sE 120-0

10080604020

SFH 30 SFH 6 SFH 100 MFH 45Figure 3.12. Specific space heating demand for the reference buildings

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In Figure 3.13, the monthly sums of space heating and domestic hot waterdemand for the different buildings are plotted, as well as the solar energy incidenton different collector areas facing south with a slope of 45' for the climates ofCarpentras and Stockholm. The different annual characteristics of incident solarenergy and heat demand of the building can be seen clearly. The annual solarfluctuation is much higher for Stockholm than for Carpentras. O n a monthlyaverage basis, a solar plant with a 10 m2 collector area is sufficient to cover the totalload of the SFH 30 building and 20 m2is sufficient for the SFH 100 for Carpentras.With the efficiency of the solar collector, and the real weather with its daily andhourly fluctuations in solar irradiance and ambient air temperature (which partlydrives the space heating demand of the building), taken into consideration, 100fkactional savings are not possible, of course. For Stockholm in winter, even with thelargest collector, the incident solar energy is much smaller than the heat demand.

870006000

p 500025 4000300020001000

CW

Carpentras

1 2 3 4 5 6 7 8 9 1 0 1 1 1 2Month

Stockholm8760005000i

F 32

4000CW

SFH 30SFH 60SFH 100MFH 455 mz10 mz15 mz20 m2

SFH 30SFH 60SFH 100MFH 455 m210 m215 ma20 m2

10000

1 2 3 4 5 6 7 8 9 1 0 1 1 1 2Month

f igu re 3.13. Mon thly space heating and dome stic hot water dem and for the referencebuildings and incide nt solar energy o n different collector areas [facing south, slope of 45O) forCarpentras and Stockholm climates

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3 4 HOT WATER CONSUMPTIONSeveral research projects in the past have shown that the domestic hot water(DHW) consumption of different households can vary broadly (e.g. Dittrich et al.1972; Loose, 1991; Dichter, 1999; Nipkow 1999). In VDI 2067, Part 4, values ofDHW consumption between 15 and 120 litres per day per person, at a temperatureof 45OC, are given. According to that, the demand for the Task 26 simulation studieshas also been fixed at the specific value of 50 litres per day per person a t atemperature of 45OC.Different concepts are used for DHW preparation in the various combisystemsanalysed inTask 26. In some systems, separate DHW stores are used, while in others,instantaneous D H W heat exchangers are used. For the various designs, the thermalstratification in the storage tank and therefore the fractional energy savings of thesystem (the values of the target functions FS,,,Fl,v,extnd Fsl; ee Chapter 6) can bequite differently dependent on the number and duration of draw-offs. In addition,fluctuations in the D H W temperature a t the beginning of a draw-off can occur.These temperature fluctuations have an additional effect on the Fslarget function.The generated DHW draw-off profiles are presented in the following.Each profile consists of a value of the DHW flow rate for every time step of theyear. Profiles were generated for three different timescales. In order to take intoaccount fairly realistic conditions, a time step of 1 minute was chosen. In orderto carry out system simulations with time steps higher than 1 minute, profiles weregenerated on a minute timescale. The reference conditions concerning thedistribution of the draw-offs were chosen similar to those of the 1 minute profiles.Finally, a third set of profiles with hourly mean values of the 6 minute profiles wasproduced. The third set of profiles is necessary in order to simulate large solarheating systems with a simulation time step higher than 6 minutes. Because the flowrates become very small when mean values are calculated, the flow rates of theprofiles on an hourly scale may not be regarded as realistic for small and medium-sized solar heating systems.The values of the flow rate and the time of occurrence of every incidence wereselected by statistical means. The basic load in each set of DHW profiles is 100litredday at a temperature of 45OC. For higher demands, the profiles were generatedwith the demand doubled a t each step (100, 200, 400, 800, 1600, 3200 litredday),with different initial random values. In this way, it is possible to produce a loadprofile for multi-family houses (for demands that are a multiple of 100 litredday)very easily by superposition.

In addition to the flow rates, a function representing the temperature of coldwater from the mains during the year needs to be defined. The cold watertemperature can be described as a sinusoidal function given by Equation 3.1:)time+(273.75-do,) 248760Tnv,, T,+ ATS, . sin(360 .

with Tfn\%[he cold-water temperature in C, T,. the yearly average cold watertemperature in OC, ATsh he average amplitude for seasonal variation in K, 'time' the

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hour of the year a TRNSYS internal value) and do the time-shift parameter (dayof the year with maximum temperature).The amplitude of the seasonal variations ATshand the time offset do differsignificantly for different locations. For the reference locations chosen for thesimulation studies, the values for ATsh nd dOrare given in Table 3.4.Table 3.4. Temperature shift of the cold water for the different climates adapted from EN12976-2:2000, 2000)

doffdocation OC KCarpentras 13.5 4.5 19Stockholm 8.5 6.4 80Zur ich 9.7 6.3 60

T, AT$,

3.4.1 DHW l oad profiles on a 1 minute t imescaleFor the simulation studies, a mean load volume of 200 litres per day was chosen fora single-family house. As an example, a three-day sequence of the profile is shownin Figure 3.14.

12001000g 800600o' 4

= 200

L3

I

g00 6 12 18 24 30 36 42 48 54 60 66 72time I h

Figure 3.74. Load profile for 72 hours, 1-3 January 200 litres/daK 1 minute timescale) createdaccording to the procedure described below

3.4.4.1 Basic assumptionsFour categories of loads are defined. Each category profile is generated separatelyand they are superposed afterwards. The actual values of the flow rates are spreadaround the mean value according to a Gaussian distribution, as described byEquation 3.2:

1 -( V-VmeJprob(V) = exp2TU 2u2The probability functions are shown in Figure 3.15.

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30 SOLAR HEATING SYSTEMS FOR HOUSES: A DESIGN HANDBOOK FOR SOLAR COMBISYSTEMS_ ~ ~

~~~~~ ---------800.

kg 700g 600

500400E8 300

ZF

g 2.-

Figure 3.15. Total dura tion o fdraw-offs d uring a year as afunction o f flo w rate. Theduration o f draw-offs was f ixed.For example, 702 showers duringthe year w ere taken into accou ntwith a duration of 5 minuteseach. The flow rates aredistribu ted as a Gaussianfunction. Discretization of flo wrates: 0.2 l i tredminute

0 0 5 10 15 20flow rate / (Ilmln)

Four categories to describe the different types of loads are defined:Category A: short load (washing hands, etc.)Category B: m el u m load (dishwasher, etc.)Category C: bathCategory D: shower.

Assumptions were made for each category for:the mean flow rate Wthe duration of one loadthe number of incidences (loads) per day, inc/daythe standard deviation of different flow rates, 0

From these assumptions, the corresponding values for the following can be derived:the mean volume of each draw-offthe total volume per daythe water volume share of each category.

The values for a load profile, with a mean load of 200 litredday, are listed in Table3 . 5 .The maximum energy of one draw-off is:

14 litredminute x 10 minutes x 1.16 Wh/(kgK) x 35 K = 5680 Wh.The suggested maximum heat demand according to DIN 4708 is:

= 5820 Wh.

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Table 3.5. Assumptions and derived quantities for the load profi le with a minim um draw-of fduration of minuteCategory A: Category B: Category C: Category D:short load medium load bath shower Sum

V in (litres/minute) 1 6 14 8Duration (minutes) 1 1 10 5Number of incidences per day 28 12 0.143 2Standard deviation, u 2 2 2 2Derived assumptions:Water volume per load (litres) 1 6 140 40

(once a week)

Water volume per day (litres) 28 72 20 80 200Average water volume share 0.14 0.36 0.10 0.40 1

The chosen reference conditions are based on a few research studies about DHWconsumption patterns in Switzerland and Germany. In these investigations,measurements of the power of electrical DHW heating elements, measurements oftemperatures or flow rates, and a representative phone research study were, forexample, taken into account (e.g. Dittrich et af. 1972; Loose, 1991; Nipkow, 1999;Real et al. 1999, Dichter, 1999).3.4.1.2 Probability functionWith the assumptions described above, the number of draw-offs and the flow rateof each load are fixed. As a final step, the incidences need to be distributedthroughout the year.A probability function describing variations of the load profileduring the year (also taking into account European daylight saving time), theweekday and the day is defined for each category. The cumulative frequencymethod is used to hstribute the incidences described by the probability function.

prob(year) = prob(season) x prob(weekday) x prob(day) x prob(ho1iday).The following assumptions are made for the terms of the probability function:

The course of probabilities during the seasons is described by a sinusoidalfunction with an amplitude of 10 of the average daily discharge volume (seeMack et al. 1998).The assumptions for the daily distribution used, are shown in Figure 3.16.The probability function of hfferent weekdays for takmg a bath and the meandistribution for the total volume per day are shown in Figure 3.17. ForCategories A , B and D, the probability distributions are identical for all days ofthe week, although not for Category C.This approach was taken based on theresults of research studies (e.g. Dichter 1999).account between 1 June and 30 September for each load of 100 litredday. Thebeginning of the holiday period is given by a random number. Theinitialization of the random number generator is set in such a way that theholidays for a single-family household with a load of 100 litredday start on

Holidays:a period of two weeks of no DHW consumption is taken into

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32 SOLAR HEATING SYSTEMS FOR HOUSES: A DESIGN HAND BOOK FOR SOLAR COMBISYSTEMS- - ~ ~ _ ~ ~~-0 30 252 0 2

gBd 0.15

0.1

Figure 3.16. Probability distribution of theDHW load during the course of the day;prob day). For short and medium draw-offs the probability distributions for a loadare distributed uniformly between 5:OOand 23:OO h

0.050

0 4 8 12 16 20 24t ime h2 5

2

U Figure 3.17. Probability functionprob weekday) for Category 3 bath) and themean value of the weekly distribution of all0.50 Mon Tue Wed Thu Fri Sat Sun categories

1August. For a profile with a mean daily load of 200 litredday (single-familyhouse in Task 26) the D H W load is reduced by 100 litredday in two periods.The duration of both periods is also two weeks, starting o n 14 July and 8August, respectively. In multi-family houses the number of reduced DHW loadperiods is given by the average daily load volume divided by 100 litredday.Therefore, for the multi-family house modelled with an average load of 1000litredday, 10 periods are taken into account.For the overall lstribution of the energy necessary for the DHW supply during theyear, Mack et a l (1998) found a variation of 25 in the form of a sinusoidalfunction. These variations were found to be due to variations of the cold watertemperature by 5K (14 of the energy supply), due to the holidays (3.8 of theenergy supply), and due to the consumption patterns during the different seasons ofthe year. These variations are taken into account by the hnctions prob(season) andprob(ho1idays).Distributions of draw-off volume per day over the course of the year, with a meandaily draw-off volume of 200 litredday, are shown in Figure 3.18 for a single-familyhouse and in Figure 3.19 for a multi-family house.The sinusoidal function, used tocalculate the probability during the course of the year with an amplitude of 20litredday (lo ), s shown by a solid line.

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HEAT DEMAND OF BUILDINGS 33~ - - _ - ~ - - ~ ~~

Figure 3.78. Single-family hous ehold:daily draw-off volume over the course ofthe year mean value: 200 litreslday)700

P 6.00*8 4300

gL

f 200- 1000 0 100 200 300

day of the year3000280026002400

m

*& 22000 2000- 1800g 16005 14001 1200e= 1000draw-off volume over the course of the 0 30 60 90 120 150 180 210 240 270 300 330 360Figure 3.19. Mu lti-family house : dailyyear mean value: 2000 litreslday) Day of th e year

Investigations of the influence of the DHW profile showed that the profile detailsare important when combisystems are compared, especially if the duration and flowrate of a DHW draw-off have a major influence on the temperature stratificationin the storage tank (Jordan andVajen, 2000). Further investigations of the influenceof the presented DHW profiles on a 1 minute scale have been carried out, forexample by Frei et a l (2000) and Knudsen (2001).3.4.2 DHW load prof i les o n a 6 m inu te t imesca leFor the 6 minute profiles only draw-offs with a minimum duration of 6 minutesare taken into account.This means that only one category of loads is defined forthe 6 minute profiles, representing all types of draw-offs (small and medium draw-offs, shower and bath-tub filling).As an example, a sequence of the profile of oneweek is shown in Figure 3.20.The assumptions made for the 200 litredday profile are given in Table 3.6. Thevalues of the flow rates are distributed around the mean value with a Gaussiandistribution as shown in Figure 3.21 A probability function describing variations ofthe load profile during the year (also taking into account European daylight savingtime), the weekday and the daily distribution is defined in the same way as for the1 minute profile. In addition, the probability distribution (Figure 3.22) is based on

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0 Figure 3.20. One-week0 1 2 3 4 5 6 7 sequence o fa DHW pro f il etime I days on a 6 minute timescale

Table 3.6. Assumptions and de rived quantities for the load profile with draw-off durations of6 minutes)One categoryTotal load volume 73,000.2* litredannumMean flow rate 8 litres/minuteMinimum flow rate 1 litredminuteMaximum flow rate (single draw-off) 15 litres/minutesMaximum flow rate (superposition) 23.9 litres/minute=> maximum energy demand of one draw-off 5,822t W hDiscretization of flow rates 0.1 litres/minuteDuration of each load 6 minStandard deviation, u 4Total number of draw-offs 1,521 per annum

=> mean load =200 litredday

* Due to the discretization of flow rates of 0.1 l/min, only multiple values of 0.6 1 are possible for theyearly volume.t The maximum energy of one draw-off is 23.9 litres/minute x 1 kg/litre x 6 minutes x 1.16 Wh/(kgK)X 35 K =,5822 Wh (the suggested maximum heat demand according to DIN 4708 (1994) is Q = 5820Wh, => Vnlax=3.9 litres/minute).

2520

.c0 105

2

0 -0 5 10flow rate / (Vmin)

Figure 3.21.DHW prof i l e on a6 minute t imescale: Numberof draw -offs as a function offlo w rate. The deviations fro mthe Gaussian function are du e15 to the discretization of thef low rate

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0 140 12

0 0.1.- 0 08L)Qg 0 06

0 040 02

0Figure 3.22. DH W profi le on a six minute t ime 0 2 4 8 8 10 12 14 16 1820 22 24scale: Distribution of probab ilities during the day time of the day I hour

the relations that were chosen for the 1 minute profile.The functions are multipliedby the volume share of each category defined for the one-minute profile.Variationsof the probability of draw-offs per day at different weekdays are given in Table 3.7.Table 3.7. Me an probabil i ty distribution o f DH W loads among days of the weekDay ProbabilityMonday to Thursday 0.9Friday 1Saturday, Sunday 1.2

3.4.3 DHW load pro f i les on an ho ur ly tim escaleThe DHW load profiles on a timescale of one hour are produced by taking hourlymean values of the 6 minute profiles.This is done only for the purpose of simulatinglarge solar heating systems with a time step of one hour. Because the flow ratesbecome very small when mean values are calculated, they may not be regarded asrealistic flow rates. However, the effect of smearing out the DHW draw-offsbecomes smaller for an increasing total load.

3.4.4 Final rem arksThe influence of the DHW profile on the annual system performance of a solarcombisystem depends on the system design.The thermal performance tends to beoverestimated if simplified load profiles with either a fixed number of draw-offsevery day or with relatively long draw-off durations are used. However, thedifferences in performance can be neglected for a large number of system designs.For example, combisystems with conventional internal-coil heat exchangers fordomestic hot water preparation show only small differences in systemperformance when the 1 mi

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