development of the applications of solar thermal ...

© by PSP Volume 18 – No 7b 2009

Fresenius Environmental Bulletin

DEVELOPMENT OF THE APPLICATIONS OF SOLAR THERMAL COOLING SYSTEMS IN GREECE AND CYPRUS Theocharis Tsoutsos1,*, Michaelis Karagiorgas2, George Zidianakis1, Vassiliki Drosou2, Aris Aidonis2, Zacharias Gouskos1,and Costas Moeses3 1

Environmental Engineering Department, Technical University of Crete, Kounoupidiana Campus, 73100 Chania, Greece 2 Centre for Renewable Energy Sources (CRES), 19th km Marathonos Avenue, 19009 Pikermi, Greece 3 Cyprus Institute of Energy, 2 Agapinoros st. 1070, Nicosia, Cyprus

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].

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.

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:

KEYWORDS: solar cooling, solar energy analysis, absorption, adsorption, heating, ventilating and air conditioning (HVAC)

• 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);

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].

• 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.

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TABLE 1 - The most common SAC systems (various, 2004) Method Refrigerant cycle Principle Phase of sorbent Typical material pairs Available technology Typical cooling capacity (kW) Typical COP Driving temperature (°C) Solar collectors

Closed Cycle Closed refrigerant cycle Water as refrigerant solid water /silica gel

Open cycle

Adsorption chiller

liquid Water/LiBr NH3/water Absorption chiller

50 – 430

15 kW – 5.000

Chilled water Dehumidification of air and evaporative cooling solid liquid Water/silica gel, Water/CaCl2 Water/LiBr water /LiBr Desiccant cooling Close to the market introduction 20 – 350

0.5 – 0.7 60 – 90

0.6 – 0.75 (single effect) 80 – 110

0.5 >1.0 45 – 95

> 1.0 45 – 70

Vacuum tubes, high efficiency flat plate

Vacuum tubes, high efficiency flat plate

Flat plate

High efficiency flat plate

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.

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.

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.

POTENTIAL SAC APPLICATIONS IN THE MEDITERRANEAN The following application sectors are promising for SACs [4]:

Public buildings, hospitals, athletic centers have also potential for applications of SAC systems.

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.

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.

Office buildings

This application is well-known since almost 60 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.

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 22,000 m2 (130,000 m3). A park of 2,700 m2 selective flat plate solar collectors was manufactured in Greece by Sole SA. The total annual cooling load of the building was estimated to be 2,700 MWh.

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

The solar collectors supply two adsorption chillers with hot water of temperature 70-75 °C, and they operate with a coefficient of performance (COP) of about 60%.

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TABLE 2 - Existing SAC applications in Greece and Cyprus. Owner

Location

Type of building

Cooling capacity (kWc)

“Photonio” (Sarantis SA)

Oinofyta, Viotia, Greece

Warehouse

700

Adsorption

168

7

American College Reporting period: 1year

Athens, Greece

Athens, Greece

Lentzakis S.A.

Rethimno, Hotel Crete, Greece Rethimno, Hotel Crete, Greece

Sol Energy Hellas A.E.

Lavrio, Athens, Greece

Educational building/ Solar 35,2 Laboratory

Gross collector area (m2)

In operation since

Annual Solar Energy Load Energy Output

kg CO2 reduction/year

Selective flat plate 2 .700 solar collectors

1999

1,283 MWh 49% coverage

2,614 MWh

5. 124. 596 *

Absorption

Evacuated tube

(net) 615

1984

------

------

Vapor Thermal Compression

Evacuated tube

(net) 30

1988

------

-------

------

------

Absorption

Flat plate selective 160

2003

105

Absorption

Flat plate solar collectors-selective 448 surfaces

2002

105

Absorption

Flat plate solar collectors-selective 450 surfaces

2000

Open cycle desiccant evaporative cooling system

Flat plate solar collectors

10

Absorption

Flat plate solar collectors

78.6

Research Centre

Palaio Faliro, Office BuildAttiki, ing Greece

L’Amor Nicosia, Rouge Bakers Cyprus

Collector type

Educational building

Demokritos Research Centre

Koutroulis Bros. SA (Rethmno Village) Centre for Renewable Energy Sources (CRES)

Technology

Bakery

35.1 70

Absorption

Evacuated tube

170

2.4 toe per heating season 5,400 kWh per season of net electricity 4,860 kWhel and 1,2 toe (July 1988- July 1990) Not elaborated yet.

576 MWh 1,100 MWh

1,070.361*2

651 MWh Solar coverage: 61%

1,067 MWh

1,094.972 *3

2007

------

------

------

2007

------

------

------

2006

123.54 kWh Solar coverage: 58%

213.65 kWh

------

Solar coverage: 57.5%

50% funded by Operational Programme for Energy (Greek Ministry of Development) The use of flat plate solar collectors (this cost is less than 50% compared with vacuum tube collectors) in combination with adsorption chillers is considered as important innovation.

The two adsorption coolers (350 kW each, 700 kW in total) use the hot water as source and produce cool water of temperature 8-10 °C. The cooling medium is also water (instead of CFCs, NH3). 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 350 kW each have been installed. Also two oil boilers, 1,200 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.

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 CO2 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 150 beds. This is a commercial application in a highly promising sector (hotels). The absorption chiller is driven by relatively low temperatures (70-75 0C). 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 m2 for central AC and also 152 m2 polypropylene collectors providing hot water for the heating of the swimming pool. The flat plate solar collectors’ plant also feed a 5,000-L sanitary hot water boiler. The design, supply and installation of this system were done by Sole SA.

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 €

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Total air conditioned area: 2,175 m2. The solar collectors supply an absorption chiller with hot water of temperature 70-75 °C, which operates with a COP = 0.6. The absorption chiller uses the hot water as source and produces cool water of temperature 8-10 °C. The cooling medium is also water (instead of CFCs or NH3). 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 (0.5 kW). The useful power is 105 kW. For the coverage of the peak load, one conventional electric chiller of 80 kW has been installed. Also a gas boiler of 600 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.

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: 1,067 MWh Solar coverage: 61% Financial aspects

Total cost of investment: 264,000 € 50 % subsidized by National Operational Programme for Energy (of the Greek Ministry of Development) Environmental Benefits

Primary Energy Savings: 651 MWh/year Environmental Savings: Emissions 1,094 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 320 m2 and its volume 1,250 m3. 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 85,000 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: 10 RT (35.2 kW) • Working fluid: LiBr (absorbent)/ Water (refrigerant) solution • Outlet chilled water: 7 oC • Heat medium: water 88 oC (optimum)/Range: 70-95 oC • 80 flat-plate solar collectors (selective absorbing surface)


Solar Energy contribution: 576 MWh Total Energy load: 1,001 MWh Solar coverage: 57.5% Financial aspects

Total cost of investment: 264,000 € 50% subsidized by National Operational Programme for Energy (Greek Ministry of Development) Environmental benefits

Primary Energy Savings: 576 MWh/year Environmental Savings: Emission 1,070 tons/year Rethimno Village Hotel, Rethimno, Crete

The Rethimno Village hotel caters mainly for tourism; with a bed capacity of 170. This installation is similar to those of the Hotel Lentzakis SA; 450 m2 flat plate collectors are used for central AC and also 199 m2 polypropylene collectors providing hot water for the heating of the swimming pool. The flat plate solar collectors’ plant also feed a 5,000 L sanitary hot water boiler Total air conditioned area: 3.000 m2. The solar collectors supply an absorption chiller with hot water of temperature 70-75 °C, which operates with a COP of 60%. The absorption chiller uses the hot water as source and produces cool water of temperature 8-10 °C. The cooling medium is also water. The useful power is 105 kW. Also a gas boiler, 600 kW, substitutes the collectors’ field when it beclouds or whenever there is need for AC during the night.

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

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of the tanks are 5 m3 and 2 m3 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 (120 L) having an internal electrical resistance of 50 kW is used as a back-up heating system to meet the loads at night or during cloudy days.

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 0C required for their nominal capacity (COP = 0.70). However, the temperature was allowed to go down to 80 0C. The storage tanks for the DHW had a total volume of 9,000 L. The storage volume for other uses (space heating and cooling) was only 9,000 L since the design philosophy of this plant was to deliver directly to the load the collected solar energy.

The solar field

Technical results

The FOCO Ikarus A3 type was selected for the construction of the solar field. The solar panel field consists of 80 flat-plate solar collectors, facing south and inclined at 300 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 0.7 and the average collector efficiency 55%. The project was subsidized by the European Commission (DESHC/nne5/104/1999) and national funds of the participating organizations.

The solar plant of the Deree College has been designed to cover the air conditioning loads by 30%. The COP of the absorption machine was about 0.7. Financial aspects

The cost of the complete installation was 700,000 $. The American Government has covered 100% of the cost. Environment

The reported data for the energy savings are: • 2.4 tons of emission (toe) per heating season • 5,400 kWh per season of electricity Experimental VTC cooling in the American College, Athens

Solar-assisted air-conditioning 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 90-95 oC. 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-120) and inclined at 300 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

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 1,200 m2 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 540 m2. The desired indoor temperature in summer is 25 0C and in winter 22 0C. The peak-cooling load is 120 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 m2 while the net area is 615 m2. The evacuated tube collectors were manufactured by General Electric (type Solartron TC-120) and inclined at 300 facing south.

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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.

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 2006. This installation uses vacuum tube solar collectors for central AC at the facilities of the company. The conditioned space is 276 m2. The absorption area of the solar collectors (TEC Solar) is 120 m2, while the total area of the collectors is 1,70 m2. The solar collectors supply an absorption chiller with hot water of temperature 83-88 °C. The absorption chiller (Yazaki, 70kW) produces cool water of temperature 7.0-12.5 °C. The working pair fluid of the chiller is LiBr / H2O. The rest of the equipment consists of the cooling tower (KING SUN, model KST-N 60) rolls of hot water, 7 m3 (ELBI model P-3000, SE-TS1), and a gas atmospheric boiler, 60 kW (SIME RX55). The system has been designed only for daylight operation, 10:00 am to 3:00 pm. There is no provision for night cooling, as the backup boiler is too small - only 60 kW whereas heat input required to the chiller is 100 kW.

Technical results

During the research and experimental work, the COP of the VTC chiller has been increased from its initial value of 0.2 to 0.45, and it has been found that it is possible to arrive up to 0.55 with further improvements. Financial aspects

The cost of the installation was 38,000 $1988 35% of the total cost has been subsidized. Environment

Only the expected savings have been reported. These are 4,860 kWhel and 1.2 toe over the demonstration period (July 1988- July 1990). 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 m2. 10-m2 flat plate solar collectors manufactured in Greece by CALPAK are used. Solar collectors supply the system with hot water of temperature 60 °C. The nominal air volume flow-rate is 1,100m3/h, and the desiccant type is lithium chloride.


Total Solar Energy contribution to cooling and heating: 123.54 kWh Total actual Energy Load: 213.65 kWh Solar coverage: 58% Financial aspects

Total cost of the investment: 134,560 € 40% 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.

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 360 m2 (1,800 m3). 78.6 m2 flat plate solar collectors supply an absorption chiller with hot water of temperature 83 °C which operates with a COP about 70%. The absorption cooler (35.1 kW) uses the hot water as source and produces cool water. The cooling medium is also water.

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

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CRES HVAC HX RT SAC SACE SE TMY TRNSYS VTC $1988

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 4th scenario is more attractive because it provides an economically and environmentally optimum technical solution. The suggested system consists of a 300m² flat plate selective collector titled 15° from the horizontal, 20 m³ hot water storage tank, 125 kW nominal power of absorption chiller, 35 kW nominal power of compression chiller, 130 kW oil back up heat source, and 250 kW nominal power of a cooling tower.

Centre for Renewable Energy Sources Heating Ventilation Air Conditioning Heat Exchanger Refrigerating Tone Solar assisted Air Conditioning Solar Air Conditioning in Europe Solar Energy Typical Meteorological Year Transient System Simulation Program Vapor Thermal Compression $ prices of 1988

REFERENCES

• 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.

[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. (2003) Solar Cooling Technologies in Greece. Applied Thermal Engineering 23(11), 1427-1439.

[3]

Henning, H.M. (2007) Solar assisted air conditioning of buildings - an overview. Applied Thermal Engineering 27 (10), 1734-1749.

[4]

various (2004) CLIMASOL. ALTENER Programme. Available at : www.raee.org/climasol. Accessed in August 2008.

[5]

Balaras, C.A., Argiriou, A.A., Michel, E., Henning H.M. (2003) Recent activities on Solar Air-Conditioning. ASHRAE Transactions 109 (1), 251-260.

[6]

Karagiorgas, M., Tsoutsos, T., Drosou, V., Pouffary, S., Pagano, T., Lopez Lara, G., Melim Mendes, J.M. (2006) HOTRES: Renewable energies in the hotels, an extensive technical support project for the hotel industry. Renewable and Sustainable Energy Reviews 10 (3), 198-224.

[7]

various (2003) The HOTRES project, European Commission, DG Energy and Transport, contract 2000/Z/133.

[8]

various (2007). SOLAIR. ALTENER Programme. Available in: www.solair-project.eu. Accessed in August 2008.

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 4.1030/Z/02-121/20020)

[9]

• 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/06/116)

Tsihftes, K. (2006) Solar cooling and new applications. Solar cooling seminar and New Applications, Technical Chamber of Cyprus.

[10] Zidianakis, G., Tsoutsos, T., Zografakis, N. (2007) Simulation of a solar absorption cooling system. In: 2nd PALENC Conference, Crete, Greece.

ABBREVIATIONS

[11] Peters, M.S., Timmerhaus, K.D. (1994) Plant Design and Economics for Chemical Engineers, McGraw-Hill International Editions.

AC ACG COP

[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.

Air Conditioning American College of Greece Coefficient of Performance

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Field Code Changed



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.

[13] various (2003) SACE- Solar air conditioning in Europe, Delft University of Technology, NNE5- 2001-00025. Energy's Programme (1998-2002).

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 [10]: 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

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 2,500 m². The construction materials are presented in Table 3 [10]. 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 30 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.

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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].

TABLE 3 - Construction materials of the building 1 CO2 SO2 CO NOX HC Particulars

Basement floor Ground floor Story floor Roof

2 5,124,596 kg/year 89.268 kg/year 1,076 kg/year 201,216 kg/year 302 kg/year 4,606 kg/year

1,070k,361 CO2 kg/year SO2 17,872 kg/year CO2 183 kg/year NOX 1,444 kg/year HC 52 kg/year Particulars 920 kg/year Description

Marble , insulation 2cm, concrete 30 cm density 2,000 kg/m3, Marble, concrete 20 cm density 2,000 kg/m3, plaster Marble, concrete 20 cm density 2,000 kg/m3, plaster Pitch, insulation 2,5 cm, concrete 20 cm density 2,000 kg/m3,

9

Comment [u1]: PLS avoid to break the Table, if this is possible

3 CO2 SO2 CO2 NOX HC Particulars thickness cm

1,094,972 kg/year 17,919 kg/year 187 kg/year 1,463 kg/year 53 kg/year 923 kg/year u-value W/m2K

34

0.961

22.2

2.199

22.2

2.199

24

0.901


Exterior basement walls External walls Internal walls


plaster Pitch , concrete 30 cm density 2,000 kg/m3, plaster Plaster , Hollow block 10 cm, insulation 2 cm, hollow block 10 cm, plaster Gypsum plaster – mineral wool – gypsum plaster

32.5

1.382

15

1.185

12

0.991

FIGURE 2 - Building profile and thermal zones definition.

FIGURE 3 - Variability of environmental temperature, relative humidity and solar radiation on a surface.

200

25000

heating loads

180

cooling loads

Energy demands for cooling

Energy (kWh)

140 Power (kW)

Energy demands for heating

20000

160

15000

120 100

10000

80 60

5000

40

0

20

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

0 0

2000

4000 Time (hr)

6000

8000

Time (months)

FIGURE 4 - Heating and cooling loads on hourly basis.

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.

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• 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.

Economic evaluation

The basic assumptions made during the economic evaluation are: • Maintenance costs: conventional 2%, solar: 1% of investment costs.

TABLE 4 - Technical features and cost of collectors and equipment. a. Collector A

Τype

Fr(τα)

FrUL

€/m²

€/kWθ=90°C

FPC

0.78

8.7

168

1285 (7m²) 903 (3,47m²)

B

FPCselective

0.72

4.86

228

C

FPCselective

0.833

4.25

180

466 (2,6m²)

D

VTC

0.58

1.8

402

1117 (2,78m²)

b. Rest of equipment Cost Absorption Chiller LiBr – H2O (COP=0,7)

400 €/kW

Conventional chiller (COP=2,5)

310 €/kW

Back up heat source (n=85%)

50 €/kW

• Installation costs: 12% of the equipment cost [11]

Solar heat gains for the summer period (kWh/m²)

490

• The energy inflation is taken to be 2% [12] • Energy prices: electricity: 0.18 €/kWh, oil 600 €/t (2007) 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.

485 480 475 470 465 460 0

5

10

15 20 25 Collector slope (degrees)

30

35

FIGURE 6 - Effect of collector slope angle on solar energy gain.

With design conditions of 1% the power of the cooling system was calculated to be 160 kW, while the power of the heating system was found to be 130 kW.

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 90 °C as demonstrated in Fig. 7.

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 10–15 degrees with South orientation, as shown in Fig. 6.

0.9 absorption chiller efficiency collector efficiency system efficiency

0.8 Efficiency (%)

0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 60

70

80

90

100

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


100

75

80

60

60

45

40

30

20

15

0 0,2

0,3

0,4

0,5

0,6

0,7

0,8

2

0,9

SFC / 1 h eta / 1 h

80

60

60

45

40

30

20

15

0

0

Overall solar fraction, %

40

30

20

15 0 0,2

0,3

0,4

0,5

0,6

0,7

SFC / 1 h eta / 1 h

SFC / 3 h eta / 3 h

0,8

0,2

0,3

0,4

0,5

0,6

0,7 2

0,8

0,9

Net collector efficiency, %

SFC / 12 h eta / 12 h

solar cooling fraction first derivative

160

second derivative

S olar cooling fraction (%)

Solar fraction heating, %

1

SFC / 6 h eta / 6 h

180

0,1

0,9

2

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.

FIGURE 8 - Effect of specific collector area on solar fraction cooling and net collector efficiency. 75

45

FIGURE 10 - Effect of specific collector area on overall solar fraction and net collector efficiency.

SFC / 12 h eta / 12 h

100

60

Specific collector area, m /m

1

SFC / 6 h eta / 6 h

60

SFC / 0 h eta / 0 h

2

SFC / 3 h eta / 3 h

80

2

Specific collector area, m /m SFC / 0 h eta / 0 h

75

0,1

0 0,1

100

0


Solar fraction cooling, %

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. 10, 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.



1

140 120 100 80 60 40 20

2

Specific collector area, m /m

0

SFC / 0 h eta / 0 h

SFC / 1 h eta / 1 h

SFC / 3 h eta / 3 h

SFC / 6 h eta / 6 h

SFC / 12 h eta / 12 h

0

100

200

300

400

500

600

collector surface (m²)

FIGURE 9 - Effect of specific collector area on solar fraction heating and net collector efficiency.

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].

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TABLE 5 - Alternative scenarios. Conventional

Scenario 1

Scenario 2

Scenario 3

Total collectors area (m²)

0

100

100

300

300

Solar fraction for cooling (%)

0

35.7

35.7

87.8

87.8 12.2

Electrical fraction for cooling (%)

Scenario 4

100

0

64.3

0

Oil fraction for cooling (%)

0

64.3

0

12.2

0

Solar fraction for heating (%)

0

20.8

20.8

47.8

47.8

Electrical fraction for heating (%) Oil fraction for heating (%)

0

0

0

0

0

100

79.2

79.2

52.2

52.2

Conventional

Scenario 1

Scenario 2

Scenario 3

Scenario 4

TABLE 6 - Final results

collector type

0

FPCsel

FPCsel

FPCsel

FPCsel

collector area (m²)

0

100

100

300

300

volume of heat storage unit (m³)

0

7.5

7.5

20

20

volume of cold-side storage unit (m³)

-

-

-

-

-

airflow (m³/h)

-

-

-

-

-

heat power back up heater (kW)

130

230

130

230

130

nominal chiller power, compression chiller (kW)

160

0

118

0

35

nominal chiller power, thermally driven chiller (kW)

0

160

42

160

125

nominal power of cooling tower (kW)

0

320

84

320

250

annual total electricity consumption (including pumps, fans) (kWh)

30,877

3,000

21,854

3,500

6,267

annual electricity consumption, chiller (kWh)

30,877

0

19,854

0

3.767

0

110,276

39,368

110,276

96,822

0. General data

1. Results of annual energy balance for system design

annual required heat for cooling/ dehumidification (kWh) annual required heat for heating/ humidification (kWh)

40,311

40,311

40,311

40,311

40,311

total annual heat (kWh)

40,311

150,587

79,679

150,587

137,133

annual heat from 2nd heat source (fossil fuel) (kWh)

40,311

102,834

31,926

34,496

21,042

annual amount of fossil heat source (primary energy) (kWh)

47,425

120,981

37,560

40,584

24,756

annual radiation on collector (kWh)

0

156,500

156,500

469,500

469,500

annual heat produced by solar collector (kWh)

0

51,755

51,755

155,264

155,264

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

0

49,635

0

9,418

64

3

47

3

14

-

-

-

-

-

maximum electricity demand (maximum hourly value) (kW) total annual water consumption (m³) 2. Energy - related evaluation (computed from design results) annual useful solar heat (kWh)

0

47,764

47,764

116,248

116,248

annual gross collector efficiency (%)

0.00

33.07

33.07

33.07

33.07

annual net collector efficiency (%)

0.00

30,52

30,52

24,76

24,76

annual COP of compression chiller

2.5

0

2.5

0

2.5

0

0.7

0.7

0.7

0.7

130,560

122,593

96,179

48,051

40,789

annual COP of thermally driven cold production annual primary energy consumption (kWh) annual primary energy savings (kWh)

0

7,967

34,381

82,509

89,771

0.00

6.10

26.33

63.20

68.76

specific useful net collector output (kWh/m²)

0

478

478

387

387

specific primary energy saving (kWh/m²)

0

80

344

275

299

solar collector system including supporting structure (€)

0

18,000

18,000

54,000

54,000

heat storage unit (€)

0

4,500

4,500

12,000

12,000

relative primary energy savings (%)

3. Investment cost

13



additional heat source (€)

6,500

11,500

6,500

11,500

-

-

-

-

-

49,600

0

36,580

0

10,850

thermally driven chiller (€)

0

64,000

16,800

64,000

50,000

cooling tower (€)

0

16,000

4,200

16,000

12,500

cold storage unit (€)

0

0

0

0

0

Pumps (€)

-

-

-

-

-

control system (€)

-

-

-

-

-

air - handling unit (€) compression chiller (€)

planning cost (€) total equipment cost (€)

6,500

-

-

-

-

-

56,100

114,000

86,580

157,500

145,850

installation cost (€)

6,732

13,680

10,389

18,900

17,502

total investment cost without funding subsidies (€)

62,832

127,680

96,969

176,400

163,352

funding (investment support) (€)

-

-

-

-

-

funding related to solar collector (€)

-

-

-

-

-

62,832

127,680

96,969

176,00

163,352

annuity factor, conventional equipment (%)

-

-

-

-

-

annuity factor, solar system (%)

-

-

-

-

-

final total investment cost (€) 4. Annual costs

capital cost (€)

-

-

-

-

-

cost for maintenance, inspection (€)

1,257

1,277

970

1,764

1,634

annual electricity cost (consumption) (€)

1,128

5,558

540

3,934

630

annual electricity cost (peak) (€)

256

12

189

12

56

annual heat cost (fossil fuel) (€)

2,474

6,312

1,960

2,117

1,292

annual water cost (€)

-

-

-

-

-

total annual cost (€)

9,545

8,141

7,052

4,523

4,109

-

1,404

2,493

5,021

5,436

total annual savings (€) 5. Comparative evaluation payback time (years)

0

46

13.7

22.6

18.5

cost of saved primary energy (€/kWh)

0

0.203

0.072

0.061

0.060

6. Environmental issues saved electric energy (kWh)

0

27,877

9,023

27,377

24,610

CO2 savings due to electricity savings (kg)

0

29,620

9,587

29,088

26,148

saved electric power (kW)

0

61

17

61

50

saved fossil fuel energy for heat (kWh)

0

-73,556

9,864

6,841

22,669

CO2 savings due to heat savings (kg)

0

-20,081

2,693

1,868

6,189

water saving (m³)

-

-

-

-

-

overall primary energy savings (kWh)

0

637

35,422

80,534

87,944

total CO2 saving (kg)

0

9,539

12,280

30,956

32,337

material pair solar system (refrigerant/sorbent)

0

LiBr-H2O

LiBr-H2O

LiBr-H2O

LiBr-H2O

refrigerant reference system

R-407c

CORRESPONDING AUTHOR Theocharis Tsoutsos Environmental Engineering Department Technical University of Crete Kounoupidiana Campus 73100 Chania GREECE Phone: +30 28210 37825 Fax: +30 28210 37846 E-mail: [email protected] Received: November 13, 2008 Accepted: Februarya 03, 2009

FEB/ Vol 18/ No 7b/ 2009 – pages

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