LARGE SCALE SOLAR HEATING SYSTEMS FOR HOUSING DEVELOPMENTS

LARGE SCALE SOLAR HEATING SYSTEMS FOR HOUSING DEVELOPMENTS Boris Mahler and Manfred N. Fisch Steinbeis-Transferzentrum Energie-, Gebäude- und Solartechnik, Heßbrühlstr. 15, D-7565 Stuttgart, Germany, phone ++49 711 / 997-5, fax ++49 711 / 997-99, e-mail: boris.mahler@stz-egs.de Werner Weiß AEE Arbeitsgemeinschaft Erneuerbare Energie, Feldgasse 19, A-8 Gleisdorf, Austria, phone ++43 311 / 5886-17, fax ++43 311 / 5886-18, e-mail: w.weiss@aee.at Abstract In five European countries nine large scale solar heating systems will be realized within the period 1998 to 1. Aim of the project is to show the technical feasibility, the potential for CO - reduction and a cost reduction potential compared to small scale solar systems. A variety of system designs ranging from short term storage to seasonal storage systems are designed, realized and monitored. At the time this paper has been written, half of the projects are fully in operation. First results of the accompanying measurements and evaluations show, that the results correspond very well with the forecast in the design phase. 1. INTRODUCTION A target in all European countries is to reduce the consumption of fossil fuels and of CO -emissions. In some countries a fairly common mean to get to a reduction is the usage of thermal solar energy for domestic hot water preparation in single family households. Aim of the THERMIE A project "Large scale solar heating for housing developments" is, to realize solar thermal systems in a larger scale (collector area > 15m²). By increasing the systems in size an increase in system performance and a decrease in investment cost was anticipated. Measure for this behavior is the cost/benefit-ratio (investment cost/ energy savings per year). Fig. 1 shows the cost/benefit-ration for large solar systems compared to small systems. An improvement of up to 7% is feasible. Cost-Benefit ratio [EUR/kWh a] 4.5 4. 3.5 3..5. 1.5 1..5. 4..5.3 Small Systems A coll < 1 m² f sol < 15 % Range of cost/benefit ratio Fig. 1: Cost/benefit-ratio 1.4.9 Improvement of 6-7% Large Systems with Short-Term Storage A coll > 1 m² f sol < %. Improvement of - 4% Large Systems with Seasonal Storage A coll > 1 m² f sol = 5-7 % Prerequisite for this kind of solar systems is an area of houses connected to a district heating net. Five countries participate with nine locations in the EU-funded project.. GENERAL PROJECT DESCRIPTION Within the period from 1998 to 1 nine projects will be designed, realized and monitored. At the moment (spring ) about half of the projects are fully realized and the monitoring has started. Table 1 gives an overview of the projects. location type project size fsol storage Res. Units A coll m² V sto m³ GERMANY Neckarsulm - long-term +15 +.6 +45. >5% Amorbach Müllheim - short-term 11 446 5 14% Vögisheimer Weg Aalen - Weisse short-term 31+ 15 1 13% Steige office Esslingen Scharnhauser Park short-term 19 - <5% NETHERL. Vathorst- Amersfoort SWEDEN Anneberg- Danderyd decentral. short-term 36 8 61 6% long-term 5.4 6. 7% AUSTRIA Gleisdorf long-term 6+ 31 14 5% office Gneis Moos long-term 6 4 1 34% ITALY Melegnano short-term swim. pool SUM 7.417 1 7% DHW Tab. 1: Overview of the projects (fsol = solar fraction of total heat demand) There are two kinds of solar plants: a) Solar System with short-term storage b) Solar System with long-term storage.1 Solar Systems with short-term storage In Müllheim, Aalen, Esslingen, Stadtstuinen and Melegnano short-term storage systems are realized. The storage volume referred to the installed collector aperture area is in the range of 5-75 l/m². With this design a short period of a few days with little sunshine can be bridged. In doing so, the solar fraction of the systems is limited to

Heßbrühlstraße 15, 7565 Stuttgart, Tel. 711/997-5, Fax 711/997-99 muellh_d.skd a maximum of about 15%-% of the total heat demand (space heating, domestic hot water preparation and net losses).. Solar Systems with long-term storage In Neckarsulm and Anneberg systems with seasonal storage will be realized. The storage volume referred to the installed collector aperure area is about. l/m². With these large storages the solar heat produced in the summer months can be used for space heating in wintertime thus leading to a substantially higher solar fraction of 5% to 7%. The systems in Gneis Moos and Gleisdorf have a different approach. In Gleisdorf a high solar fraction is obtained by reducing the space heating demand as far as possible. Therefore the heat demand for domestic hot water is almost predominant. In Gneis Moos a system in between short-term and long-term storage is used. The idea is to reduce the cost of the expensive seasonal storage and get a relatively high solar fraction of about 34% by installing a big collector area. 3. EXAMPLE MUELLHEIM - short term storage 3.1 Project location The housing area "Ob dem Vögisheimer Weg" in Muellheim is situated in the Sout-West of Germany, close to the city of Freiburg. for about 18 residential units. During the realization, many multi-family houses have been replaced by terraced houses. All houses are equipped with low temperature radiator systems (7/4 C design temperatures or lower) and innovative low cost substations for the heat transfer from the heat distribution system into the houses. Most of the buildings comply with the requirements for low energy housing (less than 65 kwh/m²a heating energy demand related to the heated space area). All houses are connected to the district heating system. The regional utility Energieversorgung Oberbaden (EVO) owns and operates the solar assisted heating plant and supplies heat to the houses. 3. Technical Design The central heating station is housed in a new type of prefabricated container system. Two containers (one for the solar part, one for the conventional part) were delivered readily equipped. In between of the two containers two buffer storages with 1m³ volume each are located (fig. 3). The solar buffer storages serves also as buffer storage for the boiler thus enabling reasonable operating periods and low emission of NOx and CO (fig. 4). Fig. 3: Central heating station: solar container, buffer storages, gas-boiler container collector array 446 m² 1 m² heat transfer substation central heating station, comprising two containers 45 m² Heizzentrale M buffer store 1m³ gasboiler 895 kw district heating net (forward) solar forward return flow solar return buffer store 1m³ Fig. : Map of the residential area Muellheim The settlement comprises 7 terraced houses with about 11 apartments. The solar system was originally designed st w Steinbeis-Transferzentrum Energie-, Gebäude- und Solartechnik Fig. 4: Hydraulic scheme of the heating system The solar collectors are placed on the roofs of two blocks of houses nearby the central heating station to minimise piping cost and heat losses. The collectors cover the whole roof area, which was designed by the architect in a way to both allow for an optimal arrangement of the collectors and optimal lighting of the rooms in the building. A new type of Solar Roof collector, an element comprising beams, insulation and solar collector in one integrated building element was used (fig. 5). This system has great advantages with respect to installation,

reliability and cost. According to our experience the investment cost for a solar roof compared to a conventional collector integrated into the roof are about 1% - % less. Monitoring results: In fig. 7 the heat balance of the year 1999 is shown. The solar plant started operation in March. The total load is about 5% less than expected for the future, when all houses are connected to the net. About 16% of the heat demand was covered by the solar collectors. This is 4% higher than expected although the operation of the solar plant is without malfunction not before autumn 1999. The heat flow meter of the gas condensing unit is not working properly (measured volume flow too low). Therefore the heat balance (Q Load =Q Collector +Q Auxiliary ) is not correct in the months with high contribution of the gas burner (Oct- Apr). Fig. 5: Installation of the solar roof collector modules 18 16 14 QLoad QAuxiliary QCollector Heat in [kwh] 1 1 8 6 4 Fig. 6: Collector array of 45m² installed in two days 3.3 Experience during installation and operation Solar collectors and plant: Installation of the solar collector modules went without major problems in January 1999. Some adjustments had to be made concerning the volume flow through the two collector arrays. A temperature sensor used for turning the solar primary pump off was placed at a wrong position leading to a discharging of the buffer store during the evening hours. The sensor was moved from the lower buffer store to the pipe and from that time on the solar part works very well. Central heating plant: The central heating station works satisfyingly besides a quite high noise emission. Covering the boiler unit did not very much improve the situation so that an additional silencer had to be installed in the chimney. District heating net: Within the first months of operation only two houses were inhabited. Therefore the volume flow in the district heating net was very low leading to overheating of the pumps. Also the district heating net was not rinsed before set in operation and some of the house substations clogged. At the end of 1999 almost the whole load has been connected to the district heating station. Jan Feb Mrz Apr Mai Jun Jul Aug Sep Okt Nov Dez Fig. 7: Measured heat balance in Müllheim 1999 Investment cost: Component Investment cost solar collectors 13 keur... per m² collector area... 3 EUR/m² total solar system 41 keur... per m² collector area... 54 EUR/m² conventional heating plant 31 keur... per kw power... 336 EUR/kW district heating net 14 keur... per m trench length... 136 EUR/m house substations 14 keur... per residential unit....33 EUR/RU SUM 1.1 keur... per residential unit... 9.1 EUR Tab. : Investment cost Müllheim project excl. VAT 3.4 Result The solar plant works without major problems. Within the next year almost the whole area will be realized and therefore the ordinary performance of the system can be proofen. The investmentcost of the whole system realized lie within the expected level. Compared to small solar systems a substantial reduction in cost (reffered to the collector area) could be realized. 4. EXAMPLE GLEISDORF - medium term storage 4.1 Project location In Gleisdorf (close to Graz), Austria, six low energy terraced houses and one office building were erected within the framework of the project. As a result of the

, 4, 1, high heating insulation standard, thermal zoning and controlled air ventilation using ground heat exchangers it was possible to reduce the heating energy requirement of these buildings by 6% compared to the present new building standard. EG, OG, FB EG, OG, FB Kaltwasser Warmwasser Kaltwasser Warmwasser Drehzahlgeregelt nach dt primär! x MAG oder Druckhalteanlage EG, OG, FB Hackgut Kessel Kaltwasser Warmwasser Fig. 8: Office building + two attached houses in Gleisdorf Apart from optimising energy utilisation and cost efficiency, the development of an innovative and ecological wooden building concept forms an essential part of the project. As a result of a wall structure developed specially for this type of house, it was possible to attain the heat insulation demand (U =,11 resp.,17 [W/m²K]) in a cost efficient and space saving manner. Moreover, with this wooden building system a considerable amount of pre-fabrication was possible. Another advantage is offered by the wall and ceiling structure which is completely free of thermal bridges. 4. Technical Design Domestic hot water and space heating requirements are mainly supplied by thermal collectors. The collector arrays, which cover 31 m², were integrated in the roofs of the winter gardens (fig. 9). The remaining residual heating requirement is met by a wood pellets boiler. Thus the provision of heat for the building is met 1% by renewable sources of energy. Energy is stored in a 14 m³ steel tank. The individual houses are supplied by a central storage tank via a local heating network which is operated over hours a day at a low temperature level (4 C) (space heating operation). To prepare the hot water the same local heating network is operated during the night for two hours at a higher temperature level (65-7 C). In this time the heating is switched off and only the decentralised warm water storage tanks are loaded (fig. 1). Fixwertregler Fig. 1: Hydraulic scheme of the solar system 4.3 Experience during installation and operation Monitoring results: The operating results from construction part I (office building) for the first heating period (98/99) and the current heating season have exceeded expectations based on the simulation. The forecasted heating energy requirement - in relation to the heated net effective area was undercut in comparison to the simulation by 4%! The energy requirements for heating equalled kwh/m² in the first heating season (fig. 11). About 6% was covered by solar energy. The remaining residual energy requirement of 8 kwh/m² was covered by the automatic wood pellet boiler. The overall energy requirement, including electricity and electrical energy for pumps etc. equals by projection approximately 44 kwh/m²a. The solar yield for the whole project (including terraced houses) is lower than expected. But this is not a technical problem. It is determined by the very low energy consumption in the terraced houses. The reason for this is that the first occupants moved into the houses in October 1999 and up to now there are only two houses out of six inhabited. Both houses are inhabited by just one person. This causes a relatively low hot water consumption and corresponding low solar yields. When all terraced houses are occupied this should change according to the expected results shown in the simulation. 1 1 8 6 4 Okt 98Nov 98Dez 98Jan 99Feb 99Mrz 99Apr 99 Mai 99Jun 99 Jul 99 Aug 99Sep 99Okt 99Nov 99Dez 99 WW-Büro HZ-Büro Hilfsstrom Büro-Strom excl. PV Photovoltaik Fig. 11: Measured heat balance of the office building Fig. 9: Residential building with winter garden and solar collectors on top

Investment cost: Component Investment cost solar collectors 33,5 keur... per m² collector area... 145 EUR/m² total solar system 73 keur... per m² collector area... 316 EUR/m² conventional heating plant 14,8 keur Tab. 3: Investment cost Gleisdorf project excl. VAT 5. EXAMPLE NECKARSULM - long term storage 5.1 Project location Amorbach is a suburb of the city Neckarsulm in Germany. The housing estate will be developed in several steps (fig. 1, tab. 4). Step one is completed. Within the next two years step two will be realized. In the end a quite large area with about 74 resitential units will be connected to the central heating station with seasonal storage. shopping centre and a residence for elderly people. In the second step another 3.7m² collector area (.6m² are supported by the EU) will be installed on top of a parking lot and on attached houses. In the end a total size of 1.m² collector area will be realized. Surplus solar heat in summertime is stored in a seasonal duct storage (fig. 14). Vertical boreholes (3m in depth) are used to heat up the ground. In winter time the heat is drawn off and supplied to the buildings. For the first time a so called three-pipe district heating net is realized. Usually pipes for the heat distribution and another pipes for the collector net are required. In Neckarsulm one pipe is used either for the heat return (winter) or the collector return (summer) thus reducing the cost and heat losses for the district heating net. Central Heating Station Solar Collectors Buffer Store Gas Burner 1. Step. Step 1. Step Seasonal Storage Solar Substation Heat Substation Heat Forwar / Solar Return. Step 3. Final Charge Discharge Solar Forward Heat Return District Heating Net (3-pipe) Seasonal Storage Fig. 1: Neckarsulm-Amorbach Solar City Step I Step II Final Realization 1995-1999 - 3 ~1 Residential units 115 +school, + business +116 739 Power 93kW +96kW 4.83kW Heat demand Collector area Storage volume 977 MWh/a +1.87 MWh/a 8.754 MWh/a.637m² +3.7m² 1.m².m³ +43.m² 115.m³ Tab. 4: Overview of development in Neckarsulm 5. Technical Design The local authorities have decided that all houses in the settlement have to fulfill 5% better insulation standard as the building code requires. In Neckarsulm a high solar fraction of more than 5% is anticipated by combining reduced energy demand of the houses with solar heat and seasonal storage. In step one.64m² of collector area are installed on the roof of multi-family buildings, a school with sports hall, a Fig. 13: Hydraulic scheme in Neckarsulm i ef rti active depth 3m i v ti ( ground level distance (, m) ground refilled insulation refilling bentonite concrete-mixture borehole U-tube Charge Discharg e Fig. 14: Cross section of the duct storage. Source: ITW 5.3 Experience during installation and operation During realization of the first step, the building area of step two and three was modified. Because of the maket situation, larger multi-family blocks were replaced by terraced houses. During the modification the orientation of the buildings was changed from north-south to westeast thus enlarging the roof area usable for solar collector application. Originally the duct storage was designed for a depth of 5m. Because of an unexpexted ground water layer in

35m depth the U-tube heat exchangers are now limited to 3m. This leads to a sligtly lower performance of the storage. The storage is in operation since end of 1998. In the first years of operation the heat losses are higher than in the final, steady state status. Fig. 15 shows the calculated temperature distribution in the seasonal storage for steady state performance. Contrary to water storages a radial statification instead of a horizontal stratification takes place. Ducts in the centre of the store are hotter than ducts at the edge of the store. 65 6 55 5 45 4 35 artithmetic mean storage temperature duct outside temperature edge of store 3 73 146 19 9 365 438 511 584 657 73 83 876 time of the year duct outsidetemperature center of store Fig. 15: Simulated temperatures in the store, source: ITW In fig. 16 a forecast of the heat balance for the system including step two (6.3m² collector area, 63.m³ store) is given. The calculations were performed with the program TRNSYS at ITW, University of Stuttgart. The solar yield (used energy going into the district heating net) will be about 5 kwh/m²a respectively 5% of the total heat demand. 6 5 4 3 Gasboiler Solar, direkt use Duct store, discharge Duct store, charge 6. CONCLUSIONS Solar thermal energy can be used for replacing up to 7% of the fossil fuel requirement for space heating and warm water preparation in residential areas. Within this international cooperation a variety of systems and purposes have been tested. About half of the projects are in operation and measurements show that the results correspond well will the design values. Developments of larger areas take some time (up to several years). Within this time in many locations the type of buildings originally designed change. Solar systems in general, but especially with seasonal storage must fit to these changes. This has been proven to be difficult some times. All realized systems perform well after some time of improvement at the beginning. This behaviour is normal for "new" systems and show that the technique and knowlege in all participating countries is growing and more and more available. Several meetings of the participants have taken place thus leading to an exchange of experience which has been helpful for the countries not so experienced before. Although the investment cost for large scale solar systems are not negligible it is possible to get a reduction in specific cost compared to small systems. Compared to the total building cost, the share for the solar system lies in the range of 1 to 4% of the total cost. This seems to be a reasonable figure in regard of a CO -reduction of 15 to 7%. ACKNOWLEDGEMENT The authors acknowledge the support of the European Commission within the THERMIE program for realization of the projects. MWh/a 1-1 - -3 REFERENCES EU-Thermie B project REB 61/97: Large Scale Solar Heating Systems for Housing Developments; 1998 - -4 Jan Feb Mrz Apr Mai Jun Jul Aug Sep Okt Nov Dez Fig. 16: Heat balance Step I+II, source: ITW Investment cost: Component Investment cost solar collectors 956 keur... per m² collector area... 151 EUR/m² seasonal storage 1.398 keur... per m³ volume... EUR/m³ total solar system.917 keur... per m² aperture area... 46 EUR/m² conventional part heating station 35 keur... per kw power 186 EUR/kW district heating net 1.558 keur + house substations SUM 4.87 keur... per residential unit 16.1 EUR/RU Tab. 5: Investment cost STEP I+II excl. VAT and design Solare Nahwärme, ein Leitfaden für die Praxis: Hrsg. Fachinformationszentrum Karlsruhe, Gesamtleitung E. Hahne, TÜV-Verlag, Köln; 1998 ISBN 3-849-47-5 Mangold, D.: Technische Erfahrungen aus den solar unterstützen Nahwärmeanlagen des Förderprogramms "Solarthermie "; OTTI-Technologie-Kolleg, 1. Symposium Thermische Solarenergie; Fisch, M. N.: Solarstadt - Konzepte, Technologien, Projekte Kohlhammer-Verlag, Stuttgart; in print