1、408 2010 ASHRAEABSTRACTSolar thermal heating for sanitary hot water and spaceheating has grown considerably over the years and is wellestablished in several countries, while solar cooling is anemerging market with a huge growth potential. A combinationof solar heating and cooling systems is an ideal
2、 solution thathas the potential to lead to both high solar fractions andeconomical systems due to the continuous (annual) exploita-tion of the solar collector field and other system components.This paper reviews the various options for exploiting solarthermal systems for sanitary hot water and space
3、 heating(solar combi systems), solar cooling, and combined solarspace heating-cooling and sanitary hot water) systems(combi-plus) in Europe, summarizing their main design, oper-ational and performance characteristics, in order to derivesome practical guidelines. The paper also includes an over-view
4、of high combi-plus solar systems that aim to developsolar thermal heating and cooling systems with high solarfraction, combining different technologies and components tooptimize performance, as a result of an ongoing Europeanresearch and demonstration project.INTRODUCTIONThe existing building stock
5、in European countriesaccounts for about 39% of final energy consumption in theEuropean Union (EU) member states, of which residential userepresents 67% of total energy consumption in the buildingssector. In 2006, the gross inland consumption in the EU-27member states was 1825.2 million ton of oil eq
6、uivalent(Mtoe), of which 129.7 Mtoe or 7.1% from renewables largelymade of biomass (69%), hydro (20.5%), wind (5.5%),geothermal (4.3%) and only 0.8% for solar. The final energyconsumption reached 1177.4 Mtoe, of which 59.7 Mtoe or5.1% from renewables excluding consumption for electricityand delivere
7、d heat, and 9.2% including consumption of theenergy branch for electricity and heat generation and distribu-tion losses (EC 2009). Consequently, efforts to reduce energyconsumption in the building sector can constitute an importantinstrument in the efforts to alleviate the EU energy importdependency
8、 (currently at about 53.8% and may reach two-thirds by 2030 (Capros et al. 2008) unless some urgent addi-tional measures and policies are adopted) and comply with theKyoto Protocol that came into effect on February 16, 2004 toreduce carbon dioxide emissions by an overall 8% in the EUcompared with 19
9、90 values, by 2012. This is also in accor-dance with the European Directive on the Energy Performanceof BuildingsEPBD (2002/91/EC). Finally, the EuropeanDirective on energy end-use efficiency and energy services(2006/32/EC amending Directive 93/76/EEC) to limit carbondioxide emissions mandates that
10、EU member states shalladopt and aim to achieve an overall national indicative energysavings target of 9% by 2017, to be reached by way of energyservices and other energy efficiency improvement measures.Details on all European Directives and EU law is availablefrom the gateway to Community legislatio
11、n online (EUR-Lex).Along the same lines, the European Parliament adopted inDecember 2008 a proposal for a new European Directive onthe promotion of the use of energy from renewable sources.Accordingly, each member state should increase its use ofrenewable energy sources (RES)such as solar, wind orhy
12、droin an effort to reach an ambitious 20% share of energyfrom renewable sources by 2020. Each EU member state willbe required to increase its share of RES by 5.5% from 2005High Solar Combi Systems in EuropeConstantinos A. Balaras, PhD, PE Elena G. Dascalaki, PhDMember ASHRAEPanagiotis Tsekouras, PE
13、Aristotelis Aidonis, PhDC.A. Balaras is a mechanical engineer, research director and E. Dascalaki is a physicist, senior research scientist, in the Institute for Envi-ronmental Research and Sustainable Development, NOA, Athens, Greece. P. Tsekouras is a mechanical engineer and a Ph.D. candidate in t
14、heDepartment of Mechanical Engineering, National Technical University of Athens, Greece. A. Aidonis is a physicist, researcher in the SolarThermal Department, Centre for Renewable Energy Sources, Athens, Greece.OR-10-044 2010, American Society of Heating, Refrigerating and Air-Conditioning Engineers
15、, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. ASHRAE Transactions 409levels, with the remaining
16、 increase calculated on the basis ofper capita gross domestic product, for example, to reach by2020 a share of 10% in Malta up to 49% in Sweden. While thefocus of the Directive is on the promotion of large scale renew-able energy installations, member states are neverthelessrequested to use “minimum
17、 levels for the use of energy fromrenewable sources in buildings”. Architects, engineers andplanners are also to benefit from member state “guidance”when planning new construction projects, while local andregional administrative bodies should be recommended to“ensure equipment and systems are instal
18、led for the use ofheating, cooling and electricity from RES, and for districtheating and cooling when planning, designing, building andrefurbishing industrial or residential areas”. Under the newDirective, EU member states must stipulate the “use of mini-mum levels of energy from renewable sources i
19、n new build-ings and in existing buildings that are subject to majorrenovation”. The city of Barcelona, Spain has pioneered themandatory use of renewables in building through its “SolarOrdinance”. The “Barcelona Model” accelerates the penetra-tion of solar thermal in the construction sector and seve
20、ral EUmember states have already enacted such renewables obliga-tions, while even more regions and municipalities are adoptingsimilar support measures.The EU final energy consumption for 2006 in the build-ings sector (EC 2009) amounted to 455.2 Mtoe (38.7% of thetotal EU-27 final energy use), of whi
21、ch 304.9 Mtoe in residen-tial (25.9%) and 150.3 Mtoe in non-residential (NR) buildings(12.8%). Residential energy demand is expected to rise by12% between 2005 and 2030, mainly as a result of the increas-ing number of residencies (+14% up to 2030), the growingdegree of indoor comfort conditions and
22、the important prolif-eration of electrical appliances and services (Capros et al.2008). Energy demand in NR buildings is projected to grow atan annual rate of 0.9% in the period 2005-2030.Final energy consumed for residential space heatingaccounts for 66% of total energy used in the sector, cooling
23、forless than 1%, but is projected to grow at a fast pace in thefuture, water heating and cooking for 22%, electrical appli-ances for 6%, and lighting for 5%. For NR buildings, spaceheating accounts for 50.5% and other heat uses (sanitary hotwater and cooking) for 22.5%, electrical appliances for 16.
24、5%,lighting for 4% and cooling for 6.5%. On the other hand, moreenergy efficient building design, better materials andconstruction practices, and more energy efficient equipmentand appliances (e.g., in 2004 the sales of certain high energyefficiency white appliances accounted for more than 70% oftot
25、al sales), which are progressively being introduced to themarket, help alleviate some of the escalating trends for higherenergy consumption.In this paper, system characteristics, benefits and obsta-cles from combined solar heating and cooling systems toachieve both high solar fractions and better fi
26、nancial perfor-mance are discussed. Existing solar combi (space heating andsanitary hot water), solar cooling and solar combi-plus (spaceheating and cooling, and sanitary hot water) systems in Europeare reviewed, providing a compilation of their main design,operational and performance characteristic
27、s. Finally, an over-view of the ongoing work of a european research and demon-stration project on high combi-plus systems identifiesdifferent technologies and components to optimize perfor-mance and reach high solar fractions.SOLAR HEATING energywaste of solar energy is as unacceptable as any other
28、energysource. Implementing proper building and plant design,construction and operation following well established princi-ples, reducing heat losses in winter and heat gains in summerthrough the building envelope, using energy efficient equip-ment and technologies, is a practical and mandatory proces
29、sfor any high performance building project (Swift 2006).Solar Combi SystemsThe most common solar energy thermal application is forsanitary hot water (SHW) production. However, the samesolar collectors can be used to deliver thermal energy for spaceheating. A typical installation for the combined pro
30、duction ofSHW and space heating (solar combi systems) includes thesolar collectors, the heat storage tank and a boiler used as anauxiliary heater. Apparently, a combi system will require alarger collector area than a SHW system to meet the higherloads. It is possible to use a heat storage tank and a
31、 SHW stor-age vessel, but it may also be suitable to combine them in asingle storage tank with a high vertical stratification, to meetthe different operating temperatures for space heating andSHW.Europe has the most well developed market for differentsolar thermal applications. Small systems for SHW
32、 produc-tion using natural flow systems (thermosyphon) without anyneed for pumps or control stations are widely used in southernEurope, with an electric heat resistance in the SHW storagetank as a back-up. More complex forced circulation systemsthat are necessary for solar combi systems are more com
33、monin central and northern Europe (ESTIF 2007).The European market share of combi systems in 2006 wasabout 5% of the total solar thermal market (Weiss et al. 2008).In Austria, the total capacity of glazed and evacuated tubesolar collectors for solar combi-systems already have a marketshare of almost
34、 40%, about 35% in Switzerland, 20% in TheNetherlands, 15% in Denmark and 5% in France (ESTIF2007), while according to the German Solar Industry Associ-ation (BSW) the German market share of combi-systemsreached 45% of newly installed solar systems in 2007 (Kolde-hoff 2008). The future is even more
35、promising in Germany,given that as of January 2009, all new homes will be requiredto install renewable energy heating systems under a newnational law (EEWrmeG 2008). Homeowners will have touse RES to meet 14% of residential total energy consumptionfor heating and sanitary hot water using solar colle
36、ctors, woodpellet stoves and boilers. This effort will be supported byfederal grants of about 350 million Euros ($455 million) eachyear. For existing houses undergoing major refurbishmentafter 2010, 10% of the heating and SHW energy needs willhave to be covered by renewables.Solar collector efficien
37、cy (delivered heat to incident solarradiation) depends on the type of the collector, the hot waterstorage and back-up systems, averaging on an annual basis 40to 55% for SHW, while annual average solar utilisation(accounting for storage heat losses and waste heat) of 20 to25% have been obtained in co
38、mbi systems (Philibert 2006).Depending on the size of the solar collector field, hot waterstorage, local climatic conditions and building loads, solarcombi systems may cover 10 to 60% of the combined SHWand space heating demand at central and northern Europeanlocations (Philibert 2006). For example,
39、 in Austria, the collec-tor area of solar combi systems for SHW and space heating isbetween 12 to 20 m2(129 to 215 ft2) for a single family house(Weiss and Faninger 2008). In a well insulated house thesesystems cover about 40% of the total heat demand. However,installations with larger collector are
40、as and heat storage capac-ity could cover 50 to 70% of the total heat demand or evenachieve 100% load coverage when they are coupled withseasonal thermal energy storage.To assess and compare performances of different designsfor solar combi systems, the International Energy Agency(IEA) launched Task
41、26 to address issues in this area (IEA2002). Standardized classification and evaluation processesand design tools were developed for these systems, along withproposals for the international standardization of combisystem test procedures. A follow-up European project (Elle-hauge 2003) converted the f
42、indings of the IEA Task 26 toinformation usable for the public, and collected practicalinformation on installed combi systems. Typically, solar combi systems need a specific design inorder to avoid operating problems during summer, due to theoversize of the solar system compared to the low thermalde
43、mand, resulting to overheating. To handle this problem, it ispossible to use a specific solar collector field configurationand connection with an expansion vessel, collector drainback,cooling devices in the collector loop, and a heat discharge loop(Ellehauge, Thr, and Jhnig 2003). To reach a high so
44、larcollector efficiency, a low return temperature from the spaceheating loop is desirable. For example, an average increase of10 K in the return temperature from radiators will require a 25to 40% larger solar collector area in order to reach the sameperformance. Special care should also be exercised
45、 for properthermal insulation of the large water storage tanks.Figure 1 illustrates the range of gross solar collector areaand storage volume (including the heat storage and SHWvolume) of various combi system installations in seven Euro-pean countries for primarily residential buildings (Thr 2003).T
46、he storage volume per unit gross solar collector area dependson design weather conditions (expressed with Heating DegreeDays HDD) and averages 75.9 lt/m2(0.25 ft3/ft2) in Austria(HDD = 3838), 42.8 lt/m2(0.14 ft3/ft2) in Denmark (HDD = 2010, American Society of Heating, Refrigerating and Air-Conditio
47、ning Engineers, Inc. (www.ashrae.org). Published in ASHRAE Transactions 2010, Vol. 116, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission. ASHRAE Transactions 4113000), 26.8
48、lt/m2(0.09 ft3/ft2) in France (HDD = 3170),65.3 lt/m2(0.21 ft3/ft2) in Germany (HDD = 3576), 69.9 lt/m2(0.23 ft3/ft2) in Italy (HDD = 2623), 66.8 lt/m2(0.22 ft3/ft2) inThe Netherlands (HDD = 3504), 116.7 lt/m2(0.38 ft3/ft2) inSweden (HDD = 4521). The average cost of these systems is765 Euro per m2gr
49、oss collector area ($92 per ft2), althoughthere are large national deviations, depending on systemdesign and cost components (e.g., whether installation isincluded in the cost, and/or auxiliary systems etc).A simple method to characterize and compare thesedifferent combi systems (taking into account their differentclimatic conditions, collector areas and loads) is the FractionalSolar Consumption (FSC) procedure (Letz 2002). FSC is adimensionless parameter defined as the ratio of the solar heatdelivered from a system (usable solar energy from a specificcollector area) to the total
