DEVELOPMENT OF THE APPLICATIONS OF SOLAR THERMAL COOLING SYSTEMS IN GREECE AND CYPRUS

Transcription

1 DEVELOPMENT OF THE APPLICATIONS OF SOLAR THERMAL COOLING SYSTEMS IN GREECE AND CYPRUS Theocharis Tsoutsos 1,*, Michaelis Karagiorgas 2, George Zidianakis 1, Vassiliki Drosou 2, Aris Aidonis 2, Zacharias Gouskos 1,and Costas Moeses 3 1 Environmental Engineering Department, Technical University of Crete, Kounoupidiana Campus, 731 Chania, Greece 2 Centre for Renewable Energy Sources (CRES), 19 th km Marathonos Avenue, 199 Pikermi, Greece 3 Cyprus Institute of Energy, 2 Agapinoros st. 17, Nicosia, Cyprus ABSTRACT During the past several years, the demand for air conditioning has continuously increased not only due to the increasing trend for comfort in the built environment, but also due to the high ambient temperatures. The large use of electrically driven cooling equipment is mainly accountable for high peak electricity demand in the summer, which often reaches the capacity limit, increasing at the same time the greenhouse gases emissions. The use of solar energy to drive cooling cycles for space conditioning of most buildings is an attractive concept, especially in Southern Europe, since the cooling requirements are roughly in phase with the solar radiation. This paper presents the development of solar thermal cooling systems in Greece and Cyprus. In the beginning, all the existing operating installations are presented for the different locations, use and applied techniques. Furthermore, a new promising project in the municipal building of Nikos Kazantzakis municipality in Crete is designed and presented. KEYWORDS: solar cooling, solar energy analysis, absorption, adsorption, heating, ventilating and air conditioning (HVAC) INTRODUCTION The interest in air conditioning (AC), especially in the domestic and service sectors, is constantly growing not only due to the continuously increasing trend of improved comfort, but also due to the high ambient temperatures during the recent years. In parallel, passive techniques, used traditionally in the past to keep comfortable indoor conditions, seem to have been neglected in many new buildings, and even in the cases that have been taken in account for the construction of the building, usually are insufficient to provide the required indoor conditions without supplementary cooling or heating [1]. In the summertime, the electricity demand raises due to the wide use of heating ventilation air conditioning (HVAC) systems, which increase the peak of electric load, causing major troubles in the electric supply system. At the same time, the greenhouse gases emissions are increased, by the energy production, or by the leakage of the cooling fluids, intensifying the vicious circle of the climate change [2, 3]. In the solar-assisted air conditioning cooling (SAC) systems, solar heat is required to drive the cooling process. During the last decade, the SAC technologies have proved their efficiency and reliability. SAC systems use harmless water-based cooling fluids, and much less primary energy than the conventional systems. SAC systems can be used, either as stand-alone systems or with conventional AC, to improve the indoor air quality [4]. Additionally, they cooperate with already existing conventional indoor installations. The use of solar energy to drive cooling cycles for space conditioning of most buildings is especially promising in Southern Europe, since the cooling requirements of a building are roughly in phase with the solar radiation [5]. The most common technologies used in combination with solar heat are presented in the Table 1 [4]. Thus, SAC systems installed so far may be classified into: Closed systems: thermally driven chillers, which provide chilled water, that is either used in air handling units to supply conditioned air (cooled, dehumidified) or is distributed via a chilled water network to the designated rooms to operate decentralized room installations, e.g. fan coils. Technically mature machines for this purpose are absorption chillers (most common) and adsorption chillers (a few hundred machines worldwide, but of rising interest in SAC); Open systems: allowing complete air conditioning by supplying cooled and dehumidified air according to the comfort conditions. The refrigerant is spray water, which is in direct contact with the atmosphere. Most common systems are desiccant cooling systems using a rotating dehumidification wheel with solid sorbent. 1

2 TABLE 1 - The most common SAC systems (various, 24) Method Closed Cycle Open cycle Refrigerant cycle Closed refrigerant cycle Chilled water Principle Water as refrigerant Dehumidification of air and evaporative cooling Phase of sorbent solid liquid solid liquid Typical material pairs water /silica gel Water/LiBr NH 3/water Water/silica gel, water /LiBr Water/CaCl 2 Water/LiBr Available technology Adsorption chiller Absorption chiller Desiccant cooling Close to the market introduction Typical cooling kw capacity (kw) Typical COP (single effect).5 >1. > 1. Driving temperature ( C) Solar collectors Vacuum tubes, high efficiency flat plate Vacuum tubes, high efficiency flat plate Flat plate High efficiency flat plate In the beginning, all the existing operating installations in Greece and Cyprus are presented. Furthermore, a potential new project in the new installations of a municipal building in N. Kazantzakis municipality in Crete is displayed. POTENTIAL SAC APPLICATIONS IN THE MEDITERRANEAN The following application sectors are promising for SACs [4]: Factories-warehouses Solar cooling is highly compatible with the environmental profile of the companies. In a first approach, the administration offices could become the principal target for solar cooling systems. Of course, the solar fraction will not be very high in all cases, due to the large areas required for solar collectors installation. But if the AC load is important throughout the year, the solar cooling system will be operational uninterruptedly. Office buildings This application is well-known since almost 6 solar cooling systems have been installed in Europe so far. In the demonstration project phase, public office buildings could benefit from high grants. The cooling load (with important internal loads due to computers) corresponds quite well to the solar production, however planners consider seriously the closure of the summer holiday during July or/ and August, making the project economically less attractive. In the future, these buildings will provide potential applications where, also, passive architecture techniques combined with solar cooling could be used. Hotels In the Mediterranean area, the energy consumption of HVAC systems in the hotels accounts for 45-55% of the total electricity consumption, and is depending on the building size and construction type [6, 7]. The high consumption of energy for AC purposes in hotels and the high level of solar radiation in the Mediterranean countries are considered as essential favorable conditions for the penetration of Solar Cooling Technologies in the tourism sector. As it is obvious, the peak of the load occurred at the same time of the peak of solar radiation. Additionally, after SAC installation hotels became more attractive to the rising share of environmentally conscious tourists. A further advantage is that existing systems of medium cooling capacity can be employed. Public buildings, hospitals, athletic centers have also potential for applications of SAC systems. SAC INSTALLATIONS IN GREECE AND CYPRUS Table 2 shows all plants in operation (factories, offices, hotels, R&D installations) as they have been identified in Greece and Cyprus. The authors covered every solar cooling plant in Greece and Cyprus up today. A short description follows. In the last two years, two additional installations are operating in Greece; limited information is yet available. Sarantis SA, Viotia This project is called Photonio and is related with the installation of central SAC system of the buildings and warehouses of the cosmetic company Sarantis SA. This installation uses high efficiency flat plate solar collectors for central AC at the facilities of the company. The conditioned space is 22, m 2 (13, m 3 ). A park of 2,7 m 2 selective flat plate solar collectors was manufactured in Greece by Sole SA. The total annual cooling load of the building was estimated to be 2,7 MWh. The solar collectors supply two adsorption chillers with hot water of temperature 7-75 C, and they operate with a coefficient of performance (COP) of about 6%. 2

3 Owner Photonio (Sarantis SA) American College Reporting period: 1year Demokritos Research Centre Location Oinofyta, Viotia, Greece Athens, Greece Athens, Greece Type of building Cooling capacity (kwc) TABLE 2 - Existing SAC applications in Greece and Cyprus. Technology Warehouse 7 Adsorption Educational building Collector type Selective flat plate solar collectors Gross collector area (m 2 ) In operation since Annual Solar Energy Output 1,283 MWh 49% coverage 168 Absorption Evacuated tube (net) Vapor Thermal Compression Evacuated tube (net) Educational building/ Solar 35,2 Absorption Flat plate selective Laboratory Lentzakis S.A. Rethimno, Flat plate solar Crete, Greece Hotel 15 Absorption collectors-selective surfaces Koutroulis Bros. SA (Rethmno Village) Centre for Renewable Energy Sources (CRES) Sol Energy Hellas A.E. Flat plate solar Rethimno, Crete, Greece Hotel 15 Absorption collectors-selective 45 2 surfaces Lavrio, Athens, Greece Palaio Faliro, Attiki, Greece L Amor Nicosia, Rouge Bakers Cyprus Research Centre Office Building Open cycle desiccant evaporative cooling system 35.1 Absorption Flat plate solar collectors Flat plate solar collectors Bakery 7 Absorption Evacuated tube MWh Solar coverage: 57.5% 651 MWh Solar coverage: 61% Energy Load kg CO2 reduction/year 2,614 MWh * 2.4 toe per heating season 5,4 kwh per season of net electricity 4,86 kwh el and 1,2 toe (July July 199) Not elaborated yet. 1,1 MWh 1,7.361* 2 1,67 MWh 1, * kwh Solar coverage: 58% kwh The two adsorption coolers (35 kw each, 7 kw in total) use the hot water as source and produce cool water of temperature 8-1 C. The cooling medium is also water (instead of CFCs, NH 3 ). This is achieved within the condensation and evaporation of the coolant (water) in vacuum. The adsorption chillers do not consist of movable parts and use minimum electric energy for the operation of the vacuum pumps (1.5 kw). For the coverage of the peak load, three conventional electric coolers of 35 kw each have been installed. Also two oil boilers, 1,2 kw each, substitute the collectors field when there is cloudiness or whenever there is need for AC overnight. The oil boilers are going to be replaced by natural gas ones in future. During the winter, the solar collectors often produce hot water about 55 C, which is circulated directly to the fan coil units in the building. The same boilers replace the collector field in case of overcast. The cold water (in summer) and the hot water (in winter) are directed to the local AC units where they cool or heat, respectively, the ambient air as needed. Technical results (annually) Solar Energy contribution to cooling: 654 MWh Solar Energy contribution to heating: 629 MWh Total actual Energy Load: 2,614 MWh Solar coverage: 49% Financial aspects Total cost of the investment: 1.3 million 5% funded by Operational Programme for Energy (Greek Ministry of Development) The use of flat plate solar collectors (this cost is less than 5% compared with vacuum tube collectors) in combination with adsorption chillers is considered as important innovation. Environmental benefits The amount of energy saved by the solar system would otherwise have to be produced by electricity (in summer) and oil (in winter). Reduction of CO 2 emissions: 5,125 tons/year Hotel Lentzakis SA, Rethimno, Crete The Lentzakis SA hotel is located in Rethimno, island of Crete, which caters mainly for tourism with a capacity of 15 beds. This is a commercial application in a highly promising sector (hotels). The absorption chiller is driven by relatively low temperatures (7-75 C). This is an important advantage that permits the solar collectors to operate with high efficiency rates. This installation uses high efficiency flat plate collectors, 448 m 2 for central AC and also 152 m 2 polypropylene collectors providing hot water for the heating of the swimming pool. The flat plate solar collectors plant also feed a 5,-L sanitary hot water boiler. The design, supply and installation of this system were done by Sole SA. 3

4 Total air conditioned area: 2,175 m 2. The solar collectors supply an absorption chiller with hot water of temperature 7-75 C, which operates with a COP =.6. The absorption chiller uses the hot water as source and produces cool water of temperature 8-1 C. The cooling medium is also water (instead of CFCs or NH 3 ). This is achieved within the condensation and evaporation of the coolant (water) in vacuum. The absorption chiller does not consist of movable parts and uses minimum electric energy for the operation of the vacuum pump (.5 kw). The useful power is 15 kw. For the coverage of the peak load, one conventional electric chiller of 8 kw has been installed. Also a gas boiler of 6 kw substitutes the collectors field when there is cloudiness or whenever there is need for AC during the night. In the winter, the solar collectors produce hot water of about 55 C, which is circulated directly to the fan coil units in the building. The auxiliary boiler replaces the collectors field in case of overcast. The cold water (in summer) and the hot water (in winter) are directed to the local AC units where they cool or heat, respectively, the ambient air as needed. Technical results (annually) Solar Energy contribution: 576 MWh Total Energy load: 1,1 MWh Solar coverage: 57.5% Financial aspects Total cost of investment: 264, 5% subsidized by National Operational Programme for Energy (Greek Ministry of Development) Environmental benefits Primary Energy Savings: 576 MWh/year Environmental Savings: Emission 1,7 tons/year Rethimno Village Hotel, Rethimno, Crete The Rethimno Village hotel caters mainly for tourism; with a bed capacity of 17. This installation is similar to those of the Hotel Lentzakis SA; 45 m 2 flat plate collectors are used for central AC and also 199 m 2 polypropylene collectors providing hot water for the heating of the swimming pool. The flat plate solar collectors plant also feed a 5, L sanitary hot water boiler Total air conditioned area: 3. m 2. The solar collectors supply an absorption chiller with hot water of temperature 7-75 C, which operates with a COP of 6%. The absorption chiller uses the hot water as source and produces cool water of temperature 8-1 C. The cooling medium is also water. The useful power is 15 kw. Also a gas boiler, 6 kw, substitutes the collectors field when it beclouds or whenever there is need for AC during the night. In winter, the solar collectors produce hot water of about 55 C, which is circulated directly to the fan coil units in the building. The same boiler replaces the collectors field in case of overcast. The cold water (during summer) or the hot water (during winter) is directed to the local AC units where they cool or heat, respectively, the ambient air within physical procedures. Technical results (annually) Solar Energy contribution: 651 MWh Total Energy load: 1,67 MWh Solar coverage: 61% Financial aspects Total cost of investment: 264, 5 % subsidized by National Operational Programme for Energy (of the Greek Ministry of Development) Environmental Benefits Primary Energy Savings: 651 MWh/year Environmental Savings: Emissions 1,94 tons/year Solar cooling at Demokritos Research Center, Athens The National Technical University of Athens has developed a Solar Heating and Cooling Plant at the premises of the National Center for Scientific Research Demokritos. With the existing experience it has been seen that SAC can be an efficient and reliable solution, even at a small scale. The system has been integrated to the building of the Solar and Energy Systems Lab, used both for laboratory and office purposes. The whole building construction is placed underground for temperature stability reasons. Its floor area is 32 m 2 and its volume 1,25 m 3. Two roofing elements made of concrete on a steel frame are placed over a transparent glazing structure in order to permit the sun penetration during the winter and shading during the summer. The existing conventional cooling and heating plant consists of two separate AC units of 85, Btu/h. The solar plant supplies the existing Heat Exchanger (HX) of the liquid-air type with cold water. Maximum cooling load was estimated to be 48 kw. The main technical characteristics of the plant are: Cooling power: 1 RT (35.2 kw) Working fluid: LiBr (absorbent)/ Water (refrigerant) solution Outlet chilled water: 7 o C Heat medium: water 88 o C (optimum)/range: 7-95 o C 8 flat-plate solar collectors (selective absorbing surface) Description of components A single-stage hot water-driven absorption chiller is used to cover the cooling loads. A cooling tower is combined with the chiller, to reject the heat produced during operation. Two isolated steel tanks are used for the storage of the hot water provided from the solar field. The capacities 4

5 of the tanks are 5 m 3 and 2 m 3 and they are placed vertically. In order to prevent corrosion, the tanks are internally coated with a Teflon layer. A plate heat exchanger is used to transfer the heat from the primary circuit of the solar collector field to the fluid used for the chiller. The heat transfer fluid is a mixture of water with 15 % ethylene glycol for both circuits. A small horizontal storage tank (12 L) having an internal electrical resistance of 5 kw is used as a back-up heating system to meet the loads at night or during cloudy days. The solar field The FOCO Ikarus A3 type was selected for the construction of the solar field. The solar panel field consists of 8 flat-plate solar collectors, facing south and inclined at 3 of the abovementioned type, integrating two independent systems. It has been decided to design the hydraulic system following two different ways, due to the fact that the series and the parallel connection of the solar collectors offer different advantages and disadvantages. The thermal COP is.7 and the average collector efficiency 55%. The project was subsidized by the European Commission (DESHC/nne5/14/1999) and national funds of the participating organizations. Solar-assisted air-conditioning in the American College, Athens Two solar cooling plants have been installed at the premises of the American College of Greece (ACG), Athens. The first plant has been installed in the Deree College and was planned to meet part of the heating and cooling demand of the Deree library, a building with a total of 1,2 m 2 of conditioned space. The second installation was designed to comply with the heating and cooling load of the Pierce Library, a building having a net conditioned space of 54 m 2. The desired indoor temperature in summer is 25 C and in winter 22 C. The peak-cooling load is 12 RT. This plant has been the first at such a scale, and it is positive that it had a successful operation for 8 years. At that time, evacuated tube collectors were necessary to achieve the high temperatures required. Since there have been improvements in both the absorption machines and the solar collectors, it now becomes feasible to use flat plate collectors for similar applications. Air conditioning system description The two solar plants installed were similar. The total gross area of the solar collectors is 728 m 2 while the net area is 615 m 2. The evacuated tube collectors were manufactured by General Electric (type Solartron TC-12) and inclined at 3 facing south. Two absorption chillers of 12 RT each have been used for each solar plant (total of 2x2x12 = 48 RT). The technology was that of LiBr, single effect chillers with an input of 95 C required for their nominal capacity (COP =.7). However, the temperature was allowed to go down to 8 C. The storage tanks for the DHW had a total volume of 9, L. The storage volume for other uses (space heating and cooling) was only 9, L since the design philosophy of this plant was to deliver directly to the load the collected solar energy. Technical results The solar plant of the Deree College has been designed to cover the air conditioning loads by 3%. The COP of the absorption machine was about.7. Financial aspects The cost of the complete installation was 7, $. The American Government has covered 1% of the cost. Environment The reported data for the energy savings are: 2.4 tons of emission (toe) per heating season 5,4 kwh per season of electricity Experimental VTC cooling in the American College, Athens The installation has been used for the AC of the Office of the Technical Direction of ACG through the use of solar heat and of a vapor thermal compression (VTC) chiller. A part of the existing solar field of the solar applications in the Deree and Pierce Library (see chapter 3.5) has been used to supply the heat in the 2 RT VTC-chiller. The project consisted mainly of an existing array of solar collectors, a new VTC-chiller combined with a cooling tower and an all-air AC system for the air treatment of the rooms. The solar heat is delivered at 9-95 o C. The VTC-chiller used R114 as the motive refrigerant. During the cooling season, the collected solar heat was used to generate the thermal compression of the VTCchiller, and the transfer of the cooling to the all air system was obtained through direct expansion. During the heating season, the solar heat was bypassing the all-air system and used to meet the heat demand directly. The evacuated tube collectors were manufactured by General Electric (Solartron TC-12) and inclined at 3 facing south. The most encouraging fact is that the COP of the machine has been increased enormously. There are two main research findings: o There is a strong relation between the jet compressors overall efficiency and the corresponding compression ratio. This relation has been expressed for each ejector 5

6 by a distinct curve, the peak of which is at the design conditions. The shape of the curve depends on the geometry of the ejector. o When the compression ratio increases, the efficiency factor under variable load increases up to a maximum value. Beyond this value, the efficiency factor drops. This could explain why the ejectors brake when operating at different than the design conditions. Technical results During the research and experimental work, the COP of the VTC chiller has been increased from its initial value of.2 to.45, and it has been found that it is possible to arrive up to.55 with further improvements. Financial aspects The cost of the installation was 38, $ % of the total cost has been subsidized. Environment Only the expected savings have been reported. These are 4,86 kwh el and 1.2 toe over the demonstration period (July July 199). Center for Renewable Energy Sources (CRES), Athens [8] The system is used for demonstration and research purposes. It is used to heat and cool the solar thermal building at the demonstration site of CRES, Lavrio, Greece. The system technology is an open cycle desiccant evaporative cooling system. Heat is provided by a solar thermal system and a back-up electric heater installed directly inside the hot water storage tank. In winter, the solar thermal system supplies a water-air heat exchanger installed in the DEC system in order to heat the room. This installation uses flat plate solar collectors for central AC. The conditioned space is 84 m 2. 1-m 2 flat plate solar collectors manufactured in Greece by CALPAK are used. Solar collectors supply the system with hot water of temperature 6 C. The nominal air volume flow-rate is 1,1m 3 /h, and the desiccant type is lithium chloride. Promitheus Building, Sol Energy Offices, Athens [8] The system is used to heat and cool the offices of the Sol Energy Company in Palaio Faliro, Attiki. The system technology is a closed cycle absorption cooling system. Heat is provided by a solar thermal system and is backedup by a ground source heat pump. This installation uses flat plate solar collectors for central AC at the Sol Energy Offices. The conditioned space is 36 m 2 (1,8 m 3 ) m 2 flat plate solar collectors supply an absorption chiller with hot water of temperature 83 C which operates with a COP about 7%. The absorption cooler (35.1 kw) uses the hot water as source and produces cool water. The cooling medium is also water. L Amor Rouge Bakers, Nicosia, Cyprus [9] Only one installation of solar cooling exists in Cyprus for the time being in Nicosia. This project is related to a cottage industry with bakery and confectionery items located in the Industrial Area in Nicosia. It consists of the bakery, the patisserie, offices and places of service. The project is in full operation since May 26. This installation uses vacuum tube solar collectors for central AC at the facilities of the company. The conditioned space is 276 m 2. The absorption area of the solar collectors (TEC Solar) is 12 m 2, while the total area of the collectors is 1,7 m 2. The solar collectors supply an absorption chiller with hot water of temperature C. The absorption chiller (Yazaki, 7kW) produces cool water of temperature C. The working pair fluid of the chiller is LiBr / H 2 O. The rest of the equipment consists of the cooling tower (KING SUN, model KST-N 6) rolls of hot water, 7 m 3 (ELBI model P-3, SE-TS1), and a gas atmospheric boiler, 6 kw (SIME RX55). The system has been designed only for daylight operation, 1: am to 3: pm. There is no provision for night cooling, as the backup boiler is too small - only 6 kw - whereas heat input required to the chiller is 1 kw. Technical results (annually) Total Solar Energy contribution to cooling and heating: kwh Total actual Energy Load: kwh Solar coverage: 58% Financial aspects Total cost of the investment: 134,56 4% of the total cost has been subsidized. Payback time: < 8 years The design, supply and installation of this system were done by Zenith mechanical consulting office. CONCLUSIONS From this study the following topics were obvious: The public buildings are an excellent case for SAC application, since they combine the social character, the pedagogical profile for the citizens, the increased operational energy cost, and, usually, the daily operation; for this reason, a new application has been designed as first one, in a public building on the island of Crete. Its operation will encourage the future new applications on this island, but also on Cyprus and the rest of Mediterranean islands The use of solar energy to drive cooling cycles for space conditioning of most buildings is especially promising 6

7 in Southern Europe, since the cooling requirements of a building are roughly in phase with the solar radiation SACs are promising for Public buildings, hospitals, athletic centers, office buildings, hotels, factories-warehouses, Due to the increasing energy crisis, the payback period is attractive, even for private investors As concerns the new forthcoming SAC application in Crete (see Appendix): The 4 th scenario is more attractive because it provides an economically and environmentally optimum technical solution. The suggested system consists of a 3- m² flat plate selective collector titled 15 from the horizontal, 2 m³ hot water storage tank, 125 kw nominal power of absorption chiller, 35 kw nominal power of compression chiller, 13 kw oil back up heat source, and 25 kw nominal power of a cooling tower. The critical parameters which were studied are type, slope angle and surface of the collector, driving temperature and the solar cooling fraction; afterwards, the sizing of absorption chiller, storage tank volume, back up heat source and cooling tower were carried out. The final results were compatible with the existing ones from the international experience. ACKNOWLEDGEMENTS The sole responsibility for the content of this publication lies with the authors. It does not necessarily reflect the opinion of the European Communities. The European Commission is not responsible for any use that may be made of the information therein. This study has been supported by: the ALTENER Programme of the European Commission (Directorate - General for Energy and Transport) through the project Promoting Solar Air Conditioning (CLIMASOL, contract 4.13/Z/2-121/22) the IEE Programme of the European Commission, Directorate General TREN, through the project Removal of non technological barriers to Solar Cooling technology across Southern European Islands (SOLCO, contract N : EIE/6/116) ABBREVIATIONS CRES Centre for Renewable Energy Sources HVAC Heating Ventilation Air Conditioning HX Heat Exchanger RT Refrigerating Tone SAC Solar assisted Air Conditioning SACE Solar Air Conditioning in Europe SE Solar Energy TMY Typical Meteorological Year TRNSYS Transient System Simulation Program VTC Vapor Thermal Compression $ 1988 $ prices of 1988 REFERENCES [1] various (1994) Natural and Low Energy Cooling in Buildings. CRES, Thermie Programme, for the European Commission, Directorate-General XVII for Energy. [2] Tsoutsos, T., Anagnostou, J., Pritchard, C., Karagiorgas, M., Agoris, D. (23) Solar Cooling Technologies in Greece. Applied Thermal Engineering 23(11), [3] Henning, H.M. (27) Solar assisted air conditioning of buildings - an overview. Applied Thermal Engineering 27 (1), [4] various (24) CLIMASOL. ALTENER Programme. Available at : Accessed in August 28. [5] Balaras, C.A., Argiriou, A.A., Michel, E., Henning H.M. (23) Recent activities on Solar Air-Conditioning. ASHRAE Transactions 19 (1), [6] Karagiorgas, M., Tsoutsos, T., Drosou, V., Pouffary, S., Pagano, T., Lopez Lara, G., Melim Mendes, J.M. (26) HO- TRES: Renewable energies in the hotels, an extensive technical support project for the hotel industry. Renewable and Sustainable Energy Reviews 1 (3), [7] various (23) The HOTRES project, European Commission, DG Energy and Transport, contract 2/Z/133. [8] various (27). SOLAIR. ALTENER Programme. Available in: Accessed in August 28. [9] Tsihftes, K. (26) Solar cooling and new applications. Solar cooling seminar and New Applications, Technical Chamber of Cyprus. [1] Zidianakis, G., Tsoutsos, T., Zografakis, N. (27) Simulation of a solar absorption cooling system. In: 2 nd PALENC Conference, Crete, Greece. [11] Peters, M.S., Timmerhaus, K.D. (1994) Plant Design and Economics for Chemical Engineers, McGraw-Hill International Editions. Field Code Changed AC ACG COP Air Conditioning American College of Greece Coefficient of Performance [12] Henning, H.M., Erpenbeck, T., Hindenburgh, C., Paulussen, C. (1998) Solar cooling of buildings- possible techniques, potential and international development. In: Proceedings of Eurosun 98, Freiburg. 7

8 [13] various (23) SACE- Solar air conditioning in Europe, Delft University of Technology, NNE Energy's Programme ( ). APPENDIX - APPLICATION IN THE MUNICIPAL BUILDING OF N. KAZANTZAKIS Methodology applied Transient System Simulation Program (TRNSYS) was used to simulate the building, in order to calculate its demand in terms of cooling and heating energy required. TRNSYS v.15 requires two smaller programs: SimCad and Prebid. SimCad depicts the building digitally as a file, which is then processed by Prebid that defines the relevant parameters of the simulation. Solar Air Conditioning in Europe (SACE) program was used for the feasibility study of the solar-assisted airconditioning system. Both programs require the weather values of a typical meteorological year obtained through the Meteonorm software. In brief, the steps for the estimation of the solar cooling system definition are described next [1]: a. Collection of the required meteorological data of the examined area. These data concern the solar radiation, the relative humidity and both the strength and the direction of wind. Average monthly weather values of a Typical Meteorological Year (TMY) were obtained through the Meteonorm program. b. Study of the maximum, minimum and average heating and cooling energy demands of the building, for determining the technical characteristics of the system. In order to maintain stable humidity and temperature conditions within the building, the heating and cooling loads should be calculated. These depend on a great number of parameters, such as size and geometrical characteristics of the building, orientation, construction materials, activity, internal sources of heating, ventilation, infiltration, lighting, desired values of indoor temperature and humidity during summer and winter, and meteorological conditions. c. Selection of the solar cooling technology to be applied. Fig. 1 shows the procedure to be followed to select the appropriate SAC technology depending on the characteristics of the building [11]. d. Feasibility study of the solar assisted air-conditioning. The results of TRNSYS are inserted in SACE, and the process of the output shows the feasibility or not of the system`s application in a specific building. e. Case studies of the solar fraction with alternative technical characteristics that mainly concern the solar collector surface, the absorption chiller power, the boiler power, the water tank volume, the cooling tower type and power. f. Economical evaluation of case studies. Solar processes are generally characterized by high investment and low operating cost. Thus, the basic economic problem is one of comparing an initial known investment with estimated future operating savings. The cost of any energy delivery process includes all the items of hardware and labour involved in the installation of the equipment, plus the operating expenses. It is vital to determine the primary energy savings and relevant costs for different solar cooling systems. Several economic criteria have been proposed for evaluating and optimizing SE systems, and there is no universal agreement which of them should be used [2]. The installation of equipment involves costs for labor, foundations, supports, construction expenses and other factors directly related to the erection of purchased equipment [11]. To be considered effective, a solar system must be able, under sustained conditions, to match the cooling output of a conventional system, while using less electricity or fossil fuel. This saving can be estimated only, if a basis for comparison is defined. The appropriate basis is the conventional vapor compression chiller. Energy saving is the cost of the conventional energy minus the costs of solar energy (SE). g. Optimization of the system and final remarks. Finally is selected the scenario, which optimizes both environmental and economic benefits. Introduction The building studied is located in Heraklion, Crete. In particular, this building is in Peza village, of N. Kazantzakis municipality. It is a public building that will serve as a town hall. It is comprised of a basement, a ground floor and one story with total surface of 2,5 m². The construction materials are presented in Table 3 [1]. The building s profile was developed through the Simcad program, while the thermal zones and the simulation parameters were defined, as shown in Fig. 2. The National Meteorological Service provided the meteorological data, covering a time span of at least 3 years. After their processing, the average monthly values were calculated as well as the maximum and minimum values, where it was considered to be necessary. From these average values, assisted by the Meteonorm program, the TMY was created. In Fig. 3, the variability of environmental temperature, relative humidity and the monthly solar radiation on horizontal surface are demonstrated. In Fig. 4, the heating and cooling loads are presented on an hourly basis throughout a year, while in Fig. 5 these loads are presented on a monthly basis. System description The system incorporates a number of solar thermal collectors, a thermally controlled storage tank, an absorption chiller, a cooling tower, heat exchangers, a conventional boiler, a building to be conditioned, and interconnecting piping. The process is divided into the following steps: a) The solar energy is gained through the collector and accumulated in the storage tank. 8

9 b) Then, the hot water in the storage tank is supplied to the generator to boil off water vapor from a solution of lithium bromide and water. c) The water vapor is cooled in the condenser and then passed to the evaporator, where it again gets evaporated at low pressure, thereby providing cooling to the space to be cooled. FIGURE 1 - Procedure to be followed to select the appropriate SAC technology [4]. CO2 5,124,596 kg/year TABLE 3 - Construction materials of the building ,7k,361 CO2 kg/year CO2 1,94,972 kg/year SO kg/year SO2 17,872 kg/year SO2 17,919 kg/year CO 1,76 kg/year CO2 183 kg/year CO2 187 kg/year NOX 21,216 kg/year NOX 1,444 kg/year NOX 1,463 kg/year HC 32 kg/year HC 52 kg/year HC 53 kg/year Particulars 4,66 kg/year Particulars 92 kg/year Particulars 923 kg/year Description thickness cm u-value W/m 2 K Basement floor Marble, insulation 2cm, concrete 3 cm density 2, kg/m 3, Ground floor Marble, concrete 2 cm density 2, kg/m 3, plaster Story floor Marble, concrete 2 cm density 2, kg/m 3, plaster Roof Pitch, insulation 2,5 cm, concrete 2 cm density 2, kg/m 3, Comment [u1]: PLS avoid to break the Table, if this is possible 9

10 plaster Exterior basement walls Pitch, concrete 3 cm density 2, kg/m 3, plaster External walls Plaster, Hollow block 1 cm, insulation 2 cm, hollow block 1 cm, plaster Internal walls Gypsum plaster mineral wool gypsum plaster FIGURE 2 - Building profile and thermal zones definition. FIGURE 3 - Variability of environmental temperature, relative humidity and solar radiation on a surface. Power (kw) 2 heating loads 18 cooling loads Time (hr) FIGURE 4 - Heating and cooling loads on hourly basis. 25 Energy demands for heating Energy demands for cooling 2 Energy (kwh) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Time (months) FIGURE 5 - Heating and cooling loads on monthly basis. d) The strong solution leaving the generator for the absorber passes through a heat exchanger in order to preheat the weak solution entering the generator. e) In the absorber, the strong solution absorbs the water vapor leaving the evaporator. Cooling water from the cooling tower removes the heat of mixing and condensation. An auxiliary energy source is provided so that hot water is supplied to the generator when solar energy is not sufficient to heat the water to the required temperature level needed by the generator. 1

11 Economic evaluation The basic assumptions made during the economic evaluation are: Maintenance costs: conventional 2%, solar: 1% of investment costs. a. Collector b. Rest of equipment TABLE 4 - Technical features and cost of collectors and equipment. Operating costs associated with a solar process include the cost of electricity for operation of pumps, interest charges on funds borrowed to purchase the equipment and others. The operation cost is connected to the specific characteristics of the system. Τype Fr(τα) FrUL /m² /kwθ=9 C A FPC (7m²) B FPCselective (3,47m²) C FPCselective (2,6m²) D VTC (2,78m²) Absorption Chiller LiBr H2O (COP=,7) Conventional chiller (COP=2,5) Back up heat source (n=85%) Cost 4 /kw 31 /kw 5 /kw Installation costs: 12% of the equipment cost [11] The energy inflation is taken to be 2% [12] Energy prices: electricity:.18 /kwh, oil 6 /t (27) The technical feature and cost of collector are shown in Table 4a, while in Table 4b the cost of the rest equipment [13]. Initially, the investment costs for the solar systems and for electric driven chiller were determined and further adjusted to the desired capacity. Then, the yearly benefits were calculated, as a function of the energy savings. With design conditions of 1% the power of the cooling system was calculated to be 16 kw, while the power of the heating system was found to be 13 kw. System optimization Type of collector and slope angle optimization Based on the meteorological circumstances of the region and the desired output temperature, the collector C (Table 4) was selected. The optimum slope angle was calculated to be 1 15 degrees with South orientation, as shown in Fig. 6. Solar heat gains for the summer period (kwh/m²) Collector slope (degrees) FIGURE 6 - Effect of collector slope angle on solar energy gain. Working temperature optimization The optimum operation temperature of the absorption chiller and the collector systems was calculated from their efficiency curves and was found to be equal to 9 C as demonstrated in Fig. 7. Efficiency (%).9 absorption chiller efficiency.8 collector efficiency system efficiency Temperature ( C) FIGURE 7 - Effect of driving temperature on system efficiency. Collector area optimization The estimation of the optimal surface of solar collectors as well as the solar cooling fraction was performed through 11

12 the SACE program. In Fig. 8 appears the solar cooling fraction as well as the net efficiency of the collector; while in Fig. 9 appears the solar heating fraction as well as the net efficiency of the collectors, both depending on the total surface. In Fig. 1, the above are combined and the solar total fraction as well as the net efficiency of the collectors are demonstrated, depending on the total surface. Overall solar fraction, % Net collector efficiency, % Solar fraction cooling, % Solar fraction heating, % ,1,2,3,4,5,6,7,8,9 1 Specific collector area, m 2 /m 2 SFC / h SFC / 1 h SFC / 3 h SFC / 6 h SFC / 12 h eta / h eta / 1 h eta / 3 h eta / 6 h eta / 12 h FIGURE 8 - Effect of specific collector area on solar fraction cooling and net collector efficiency.,1,2,3,4,5,6,7,8,9 1 Specific collector area, m 2 /m 2 SFC / h SFC / 1 h SFC / 3 h SFC / 6 h SFC / 12 h eta / h eta / 1 h eta / 3 h eta / 6 h eta / 12 h FIGURE 9 - Effect of specific collector area on solar fraction heating and net collector efficiency Net collector efficiency, % Net collector efficiency, %,1,2,3,4,5,6,7,8,9 1 Specific collector area, m 2 /m 2 SFC / h SFC / 1 h SFC / 3 h SFC / 6 h SFC / 12 h eta / h eta / 1 h eta / 3 h eta / 6 h eta / 12 h FIGURE 1 - Effect of specific collector area on overall solar fraction and net collector efficiency. In order to calculate the collector s surface, emphasis was placed on the solar cooling, for two basic scenarios. The first emerges from the intersection of the solar cooling fraction with the net efficiency of the solar collectors, with 6-h heat storage. The second scenario comes from the maximization point of the second derivative of the function calculating the solar cooling fraction, depending on the collector surface, as shown in Fig. 11. Solar cooling fraction (%) solar cooling fraction first derivative second derivative collector surface (m²) FIGURE 11 - Defining the optimum collector area. Sizing of the remaining equipment The capacity of the remaining equipment (absorption chiller, cooling tower, storage tank and back up heat source) emerges from the optimization results above. Alternative scenarios and economical evaluation Finally, four scenarios were studied to become aware of the most advantageous one as shown in Table 5. The final comparative results for each scenario are demonstrated in Table 6 [3]. 12

13 TABLE 5 - Alternative scenarios. Conventional Scenario 1 Scenario 2 Scenario 3 Scenario 4 Total collectors area (m²) Solar fraction for cooling (%) Electrical fraction for cooling (%) Oil fraction for cooling (%) Solar fraction for heating (%) Electrical fraction for heating (%) Oil fraction for heating (%) TABLE 6 - Final results Conventional Scenario 1 Scenario 2 Scenario 3 Scenario 4. General data collector type FPCsel FPCsel FPCsel FPCsel collector area (m²) volume of heat storage unit (m³) volume of cold-side storage unit (m³) airflow (m³/h) heat power back up heater (kw) nominal chiller power, compression chiller (kw) nominal chiller power, thermally driven chiller (kw) nominal power of cooling tower (kw) Results of annual energy balance for system design annual total electricity consumption (including pumps, fans) (kwh) 3,877 3, 21,854 3,5 6,267 annual electricity consumption, chiller (kwh) 3,877 19, annual required heat for cooling/ dehumidification (kwh) 11,276 39,368 11,276 96,822 annual required heat for heating/ humidification (kwh) 4,311 4,311 4,311 4,311 4,311 total annual heat (kwh) 4,311 15,587 79,679 15, ,133 annual heat from 2nd heat source (fossil fuel) (kwh) 4,311 12,834 31,926 34,496 21,42 annual amount of fossil heat source (primary energy) (kwh) 47,425 12,981 37,56 4,584 24,756 annual radiation on collector (kwh) 156,5 156,5 469,5 469,5 annual heat produced by solar collector (kwh) 51,755 51, , ,264 annual overall cold production (cooling, dehumidification) (kwh) 77,193 77,193 77,193 77,193 77,193 annual cold production by compression (kwh) 77,193 49,635 9,418 maximum electricity demand (maximum hourly value) (kw) total annual water consumption (m³) Energy - related evaluation (computed from design results) annual useful solar heat (kwh) 47,764 47, , ,248 annual gross collector efficiency (%) annual net collector efficiency (%). 3,52 3,52 24,76 24,76 annual COP of compression chiller annual COP of thermally driven cold production annual primary energy consumption (kwh) 13,56 122,593 96,179 48,51 4,789 annual primary energy savings (kwh) 7,967 34,381 82,59 89,771 relative primary energy savings (%) specific useful net collector output (kwh/m²) specific primary energy saving (kwh/m²) Investment cost solar collector system including supporting structure ( ) 18, 18, 54, 54, heat storage unit ( ) 4,5 4,5 12, 12, 13

14 additional heat source ( ) 6,5 11,5 6,5 11,5 6,5 air - handling unit ( ) compression chiller ( ) 49,6 36,58 1,85 thermally driven chiller ( ) 64, 16,8 64, 5, cooling tower ( ) 16, 4,2 16, 12,5 cold storage unit ( ) Pumps ( ) control system ( ) planning cost ( ) total equipment cost ( ) 56,1 114, 86,58 157,5 145,85 installation cost ( ) 6,732 13,68 1,389 18,9 17,52 total investment cost without funding subsidies ( ) 62, ,68 96, ,4 163,352 funding (investment support) ( ) funding related to solar collector ( ) final total investment cost ( ) 62, ,68 96, , 163, Annual costs annuity factor, conventional equipment (%) annuity factor, solar system (%) capital cost ( ) cost for maintenance, inspection ( ) 1,257 1, ,764 1,634 annual electricity cost (consumption) ( ) 5, , ,128 annual electricity cost (peak) ( ) annual heat cost (fossil fuel) ( ) 2,474 6,312 1,96 2,117 1,292 annual water cost ( ) total annual cost ( ) 9,545 8,141 7,52 4,523 4,19 total annual savings ( ) - 1,44 2,493 5,21 5, Comparative evaluation payback time (years) cost of saved primary energy ( /kwh) Environmental issues saved electric energy (kwh) 27,877 9,23 27,377 24,61 CO2 savings due to electricity savings (kg) 29,62 9,587 29,88 26,148 saved electric power (kw) saved fossil fuel energy for heat (kwh) -73,556 9,864 6,841 22,669 CO2 savings due to heat savings (kg) -2,81 2,693 1,868 6,189 water saving (m³) overall primary energy savings (kwh) ,422 8,534 87,944 total CO2 saving (kg) 9,539 12,28 3,956 32,337 material pair solar system (refrigerant/sorbent) LiBr-H2O LiBr-H2O LiBr-H2O LiBr-H2O refrigerant reference system R-47c CORRESPONDING AUTHOR Theocharis Tsoutsos Environmental Engineering Department Technical University of Crete Kounoupidiana Campus 731 Chania GREECE Received: November 13, 28 Accepted: Februarya 3, 29 Phone: Fax: theocharis.tsoutsos@enveng.tuc.gr FEB/ Vol 18/ No 7b/ 29 pages 14

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