Simulation of a solar absorption cooling system - CiteSeerX

2nd PALENC Conference and 28th AIVC Conference on Building Low Energy Cooling and Advanced Ventilation Technologies in the 21st Century, September 2007, Crete island, Greece

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Simulation of a solar absorption cooling system G. Zidianakis, Th. Tsoutsos

Technical University of Crete, Greece

N. Zografakis

Regional Energy Agency of Crete, Greece

ABSTRACT During the last years there is an increased consciousness of the environmental problems, which are created by the use of fossil fuels for electrical power generation consumed by converting cooling systems. In addition, the use of common working fluids (refrigerants), with their ozone-depleting and global warming potential, has become a serious environmental problem. This underlines the need to implement advanced, new concepts in building air-conditioning. The most common, globally, type of thermally driven technology to produce chilled water is absorption cooling. For air-conditioning applications, absorption systems commonly use the water/lithium bromide or water/ammonia working pair. In this paper, the performance and economic evaluation of a solar heating and cooling system is studied using the transient simulation program (TRNSYS). The meteorological year file exploited the hourly weather data where produced by 30-year statistical process. The required data were obtained by Hellenic National Meteorological Service. The water heating, space heating, and the cooling load of a municipal building in N. Kazantzakis municipality in Crete were considered. The exploitation of the results of the simulation provided the optimum sizing of the system. 1. INTRODUCTION During the summer the demand for electricity increases dramatically because of the extensive use of heating ventilation air conditioning (HVAC) systems, which increases the peak electric load, causing major problems in the national electric supply system. The energy shortage is worse during dry years because of the incapability of the hydroelectric power stations to operate. The total energy demand increases by 3–4% per year, which corresponds to an annual increase of electric energy consumption about 1.000 GWh and implies the installation of a new thermal power generation plant of 300 MW every 18–24 months (Tsoutsos and Karagiorgas, 2006). The energy consumed for heating and cooling of domes-

PALENC 2007 - Vol 2.indd 1187

tic premises accounts for just 7% of the country’s total energy demand, but is responsible for 29% of the CO2 emissions. Sales of mini split units tripled during the period 1996/2000. In 1970 the CO2 emissions were 22 million t/y (tonnes/year) whilst by the end of 1990s they have reached 83 million t/y, almost four times higher. Crete and the Greek islands in general, constitute a special case due to both increased temperatures as well as their isolated power grids. Therefore, alternative energy solutions should be adopted in wide scale. The use of solar energy (SE) is an attractive concept that can be used to drive cooling cycles for space conditioning of most buildings. This is true especially in southern European countries, since the cooling load is roughly in phase with SE availability. The cooling requirements of a building are roughly in phase with the solar incidence. Solar cooling systems are a nice tool for the exploitation of solar energy. They have the advantage of using absolutely harmless working fluids such as water, or salt solution. They are energy efficient and environmentally safe. They can be used either as stand-alone systems or with conventional AC, to improve the indoor air quality of all types of buildings. The main goal is to utilize ‘‘zero emissions’’ technologies in order to reduce energy consumption as well as the CO2 emissions (Tsoutsos et al, 2003). One of the many categories of solar cooling systems is the solar absorption cooling. Absorption is the process of attracting and holding moisture by desiccants. During absorption the desiccant undergoes a chemical change it takes on moisture, for example, table salt, which changes from solid to a liquid as it absorbs moisture (Florides et al, 2002). Wide-ranging studies of different aspects of absorption system, such as performance simulations and experimental test results, have been reported. Of the various� continuous absorption solar air conditioning systems, LiBr-H2O and H2O-NH3 are the major working pairs employed in these systems. It is reported that LiBr-H2O has a higher Coefficient of Performance (COP) than that of the other working fluids (Balaras et al, 2007). For various reasons, the lithium bromide-water system is considered to be better suited for most solar-absorption air conditioning applications, and it will be the only

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combination examined here�� (Li and Sumathy, 2001) The objective of this work is to model a complete system comprised of a solar collector, a storage tank, a back up heat source, a water cooling tower and a LiBr – water absorption chiller. This system aims to cover a fraction of the total cooling and heating energy demands of a public building in Crete, throughout the year. During the process specialized software was used. The optimized parameters were the following: collector plate area, collector plate slope angle, volume of hot water storage tank, nominal power of absorption chiller, cooling tower and backup heat source.

2.3 Meteorological data 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 – minimum values, where it was considered necessary. From these average values, assisted by the “Meteonorm” program, the TMY was created. In�� figure �� 1�� the�� variability�� of�� environmental�� temperature� �� and�� relative �� humidity�� are�� demonstrated,�� while�� in�� figure �� 2�� the monthly solar radiation on horizontal surface.

2.�� METHODOLOGY �� 2.1 Software description The TRNSYS (‘Transient System Simulation Program’) program is a quasi-steady simulation model consisting of many subroutines that model subsystem components. The mathematical models for the subsystem components are given in terms of their ordinary differential or algebraic equations. This program was used to simulate the building, in order to calculate its demands in terms of cooling and heating energy required. In particular, the TRNSYS v.15 requires two smaller programs: SimCad and Prebid. The SimCad represents the building digitally as a file, which is then processed by Prebid that defines the relevant parameters of the simulation. The �� SACE�� (Solar Air Conditioning in Europe) program was used for the feasibility study of the solar assisted air conditioning system (Delft University of Technology, 2003). Both of these programs require the weather values of a typical meteorological year (TMY) for Iraklion, Crete, obtained through the “Meteonorm” program.�� The �� Meteonorm is software extracting hourly and monthly values of meteorological parameters. 2.2 Steps for the estimation of the solar cooling system definition In order to consider the potential of a building for applying solar assisted air conditioning in a specific area, a study is applied, which is comprised of the following steps:� 1. Study of the meteorological factors in the examined area 2. Study of the maximum, minimum and average heating and cooling energy demands of the building, for determining the technical characteristics of the system 3. Feasibility�� study�� of�� the�� solar�� assisted�� air�� conditioning� �� 4. Case�� studies�� of�� the�� solar�� fraction with alternative technical characteristics� 5. Economical evaluation of case studies 6. Optimization of the system and final remarks.


Figure 1: Variability of environmental temperature and relative humidity

Figure 2: Monthly solar radiation on a surface

2.4 Building description 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 shown in table �� 1. �� Table 1: Construction materials of the building Description Marble ,�� insulation �� 2�� cm��, Basement floor concrete �� 30�� cm�� density � �� 2000�� kg�� /� m3, Marble�� , �� concrete 20�� cm� Ground �� floor �� density �� 2000�� kg�� /� m3, �� plaster

thickness cm

u�� -�� value W�� /� m2K

34

0,961

22,2

2,199

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Marble�� , �� concrete�� 20�� cm� density �� 2000�� kg�� /� m3, �� plaster Pit�� ch, �� insulation �� Roof 2,5�� cm�� , �� concrete 20�� cm� density�� 2000�� kg�� /� m3, �� plaster Pitch , concrete 30 cm Exterior basedensity ment walls 2000 kg/m3, plaster Plaster�� , �� Hollow�� block�� 10 External �� walls cm�� , �� insulation�� 2 �� cm�� , �� hollow block�� 10 �� cm�� , plaster Gypsum plaster – mineral Internal walls wool – gypsum plaster Story �� floor ��

22,2

2,199

24

0,901

32,5

1,382

15

1,185

12

0,991

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�: 1. size and geometrical characteristics of the building 2. orientation 3. construction materials 4. activity 5. internal sources of heating 6. ventilation 7. infiltration 8. lighting 9. desired�� values�� of�� indoor�� temperature�� and�� humidity��, during�� summer�� and�� winter� 10. meteorological conditions 2.�� 5�� System description �� The system incorporates a number of solar thermal collectors, a thermally 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: 1. The solar energy is gained through the collector and is accumulated in the storage tank. 2. 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. 3. 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. 4. The strong solution leaving the generator for the absorber passes through a heat exchanger in order to preheat the weak solution entering the generator. 5. 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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2.6 Economic evaluation Solar processes are generally characterised 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 that are 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 SCS. Several economic criteria have been proposed for evaluating and optimizing SE systems, and there is no universal agreement on which should be used. For the needs of the current study, we used criteria, such as �� (Tsoutsos et al, 2003) the Payback �� period. The payback period is determined by the equation (1)�:

(1) where: PB: payback period (yr) C: capital cost of installed solar cooling equipment (€) i: energy inflation (the change of energy prices relative to general inflation) E: energy saving (€/yr). The yearly benefits represent an expression of the annual costs for both solar and non-solar systems to meet energy needs. Yearly benefits equal to cost of operation, maintenance and insurance of conventional system minus cost of operation, maintenance and insurance of solar system The installation of equipment involves costs for labour, foundations, supports, construction expenses and other factors directly related to the erection of purchased equipment (Peters and Timmerhaus, 1994). 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 vapour compression chiller. Energy saving is the cost of the conventional energy minus the costs of SE. The basic assumptions made during the economic evaluation are: • Maintenance costs: conventional 2%, of solar: 1% of investment costs (Delft University of Technology, 2003). • 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 spe-

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cific characteristics of the system. • Installation costs: 12% of the equipment cost (Peters and Timmerhaus, 1994). • The energy inflation is taken to be 2% (Henning et al, 1998) • Energy prices: electricity: 0.18€/kWh, oil 600€/t (various, 2007) The technical feature and cost of collector are shown in table 2 (various, 2007), while in table 3 the cost of the rest equipment (Delft University of Technology, 2003). Table 2: Technical feature and cost of collectors Collector Τ�� ype A FPC B FPCselective C FPCselective D VTC

Fr�� (τα) 0,78 0,72 0,833 0,58

FrUL 8,7 4,86 4,25 1,8

€/�� m�² €/�� kWθ=90°�C 168 1285 (7�� m�� ²�) 228 903 (3,47m�� ²) 1�� 80 466 (2,6m�� ²�) 402 1117 (2,78m�� ²�)

Table 3: Cost of equipment Equipment� Absorption Chiller�� LiBr�� –� H2O�� (�� COP�� =0,7) Conventional chiller �� (COP=2,5) Back up heat source�� (n=85%) �� Cooling tower� Storage tank �

Figure 3: Building profile and thermal zones definition

Cost� 4�� 00�� €�� /kW 31�� 0�� €�� /kW 50�� €�� /kW 50�� €�� /kW 6�� 00�� €�� /m�³

Initially�� the investment costs for the solar systems and for electric driven chiller were determined and were further adjusted to the desired capacity. Then the yearly benefits were calculated, as a function of the energy savings. 2.7 Alternative scenarios The scenarios were studied are a result of the alternative sizing of the system depending on the collector area and contribution of solar, electrical and oil energy fraction, in order to achieve an optimized economical and environmental solution. �

Figure 4: Heating and cooling loads on hourly base

3. �� RESULTS AND RECOMMENDATIONS A number of simulations were carried out in order to optimize the various factors affecting the performance of the system. The results are demonstrated immediately below. 3.1 �� Building�� simulation� �� The�� building�� ’�� s�� profile�� was�� developed�� through�� the� Simcad�� program, �� while the thermal zones and the simulation parameters were defined, as shown in Figure 3��. In�� Figure 4�� the�� heating�� and�� cooling loads are presented on an hourly basis throughout a year, while in�� Figure �� 5� these�� loads�� are�� presented �� on a monthly basis.


Figure 5: Heating and cooling loads on monthly base

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��. 3.2 �� System�� optimization 3.�� 2�� .1 �� Type�� of�� Collector�� and�� slope�� angle�� optimization� �� Based on the meteorological circumstances of the region and the desired output temperature, the collector C (table 2) was selected. The �� optimum slope angle was calculated to be 10 – 15 degrees with South orientation, as shown in Figure 6.

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Figure 6: Effect of collector slope angle on solar energy gain

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Figure 8: Effect of specific collector area on solar fraction cooling and net collector efficiency

3.2.2 �� 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 Figure�� 7.

Figure 9: Effect of specific collector area on solar fraction heating and net collector efficiency

Figure 7: Effect of driving temperature on system efficiency

3.2.3 Collector area optimization The estimation of the optimal surface of solar collectors as well as the solar cooling fraction was performed through the SACE program. In Figure 8 appears the solar cooling fraction as well as the net efficiency of the collector, while in�� Figure �� 9�� appears �� the solar heating fraction as well as the net efficiency of the collectors, both depending on the total surface. In�� Figure �� 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.


Figure 10: 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 six hours’ 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 Figure 11.

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Figure 11: Defining the optimum collector area

3.2.4 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. 3.3 Alternative scenarios and economical evaluation Four scenarios were studied finally due to become aware of the most advantageous as shown in table 4:

Total collectors area (m²) 0 100 100 300 Solar fraction for cooling (%) 0 35.7 35.7 87.8 Electrical fraction for cooling (%) 100 0 64.3 0 Oil fraction for cooling (%) 0 64.3 0 12.2 Solar fraction for heating (%) 0 20.8 20.8 47.8 Electrical fraction for heating (%) 0 0 0 0 Oil fraction for heating (%) 100 79.2 79.2 52.2

Scenario 4

Scenario 3

Scenario 2

Conventional Scenario 1

Table 4: Alternative scenarios

300 87.8 12.2 0 47.8 0 52.2

The final comparative results for each scenario are demonstrated in table 5 (Henning 2004).

0. General data collector type collector area (�� m�� ²) volume of heat storage unit�� (m³) volume of coldside storage unit� (m³)


0 0

Scenario 4

Scenario 3

Scenario 2

Scenario 1

Conventional

Table 5: Final results

FPCsel FPCsel FPCsel FPCsel 100 100 300 300

0

7.5

7.5

20

20

-

-

-

-

-

airflow �� (m�� ³/�� h�) heat power back 130 230 130 230 up heater (kW) nominal chiller power, compres- 160 0 118 0 sion chiller (kW) nominal chiller power, thermally 0 160 42 160 driven chiller (kW) nominal power of cooling tower 0 320 84 320 (kW) 1. Results of annual energy balance for system design annual total electricity consumption (including 30�� ,�� 877 3�� ,�� 000 21�� ,�� 854 3�� ,�� 500 pumps, fans) (kWh) annual electricity consuption, chiller 30�� ,�� 877 0 19�� ,�� 854 0 (kWh) annual required heat for cooling/ 0 110�� ,�� 276 39�� ,�� 368 110�� ,�� 276 dehumidification (kWh) annual required heat for heating/ 40�� ,�� 311 40�� ,�� 311 40�� ,�� 311 40�� ,�� 311 humidification (kWh) total annual heat� 40�� ,�� 311 150�� ,�� 587 79�� ,�� 679 150�� ,�� 587 (kWh) annual heat from 2nd heat source 40�� ,�� 311 102�� ,�� 834 31�� ,�� 926 34�� ,�� 496 (fossil fuel) (kWh) annual amount of fossil heat source 47�� ,�� 425 120�� ,�� 981 37�� ,�� 560 40�� ,�� 584 (primary energy) (kWh) annual radiation on collector 0 156�� ,�� 500 156�� ,�� 500 469�� ,�� 500 (kWh) annual heat produced by solar 0 51�� ,�� 755 51�� ,�� 755 155�� ,�� 264 collector (kWh) annual overall cold production (cooling, 77�� ,�� 193 77�� ,�� 193 77�� ,�� 193 77�� ,�� 193 dehumidification) (kWh) annual cold production by com- 77�� ,�� 193 0 49�� ,�� 635 0 pression (kWh) maximum electricity demand 64 3 47 3 (maximum hourly value) (kW)

130 35

125

250

6�� ,�� 267

3�� ,�� 767

96�� ,�� 822

40�� ,�� 311 137�� ,�� 133 21�� ,�� 042

24�� ,�� 756

469�� ,�� 500 155�� ,�� 264

77�� ,�� 193

9�� ,�� 418

14

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total annual water consuption (m³) 2. Energy - related evaluation (computed from design results) annual useful 0 47�� ,�� 764 47�� ,�� 764 116�� ,�� 248 116�� ,�� 248 solar heat (kWh) �� annual gross collector efficiency 0.00 33.07 33.07 33.07 33.07 (%) annual net collec0.00 30.52 30.52 24.76 24.76 tor efficiency (%) annual COP of compression 2.5 0 2.5 0 2.5 chiller annual COP of thermally driven 0 0.7 0.7 0.7 0.7 cold production annual primary energy consuption 122�� ,�� 593 96�� ,�� 179 48�� ,�� 051 40�� ,�� 789 (kWh) annual primary energy savings 0 7�� ,�� 967 34�� ,�� 381 82�� ,�� 509 89�� ,�� 771 (kWh) relative primary energy savings 0.00 6.10 26.33 63.20 68.76 (%) specific useful net collector output� 0 478 478 387 387 (kWh�� /m²�) specific primary energy saving 0 80 344 275 299 (kWh�� /m²�) 3. Investment cost solar collector system including 0 18�� ,�� 000 18�� ,�� 000 54�� ,�� 000 54�� ,�� 000 supporting structure�� (€) heat storage unit 0 4�� ,�� 500 4�� ,�� 500 12�� ,�� 000 12�� ,�� 000 (€) additional heat 6�� ,�� 500 11�� ,�� 500 6�� ,�� 500 11�� ,�� 500 6�� ,�� 500 source (€) air - handling unit (€) compression 49�� ,�� 600 0 36�� ,�� 580 0 10�� ,�� 850 chiller (€) thermally driven 0 64�� ,�� 000 16�� ,�� 800 64�� ,�� 000 50�� ,�� 000 chiller (€) cooling tower (€) 0 16�� ,�� 000 4�� ,�� 200 16�� ,�� 000 12�� ,�� 500 cold storage unit 0 0 0 0 0 (€) Pumps (€) control system (€) planning cost (€) total equipment 56�� ,�� 100 114�� ,�� 000 86�� ,�� 580 157�� ,�� 500 145�� ,�� 850 cost (€) installation cost 6�� ,�� 732 13�� ,�� 680 10�� ,�� 389 18�� ,�� 900 17�� ,�� 502 (€) total investment cost without fund- 62�� ,�� 832 127�� ,�� 680 96�� ,�� 969 176�� ,�� 400 163�� ,�� 352 ing subsidies�� (€)


funding (investment support) (€) funding related to solar collector�� (€) final total invest62�� ,�� 832 ment cost (€) 4. Annual costs annuity factror, conventional equipment�� (%) annuity factor, solar system�� (%) capital cost (€) cost for maintenance, inpection 1�� ,�� 257 (€) annual electricity cost (consuption) 5�� ,�� 558 (€) annual electricity 256 cost (peak) (€) annual heat cost 2�� ,�� 474 (fossil fuel)�� (€) annual water cost (€) total annual cost 9�� ,�� 545 (€) total annual savings (€) 5. Comparative evaluation payback time (�� yr) 0 cost of saved primary energy 0 (€/kWh) 6. Environmental issues saved electric 0 energy�� (kWh) CO2 savings due to electricity sav0 ings (kg) saved electric 0 power�� (kW) saved fossil fuel energy for heat 0 (kWh) CO2 savings due to heat savings 0 (kg) water saving�� (m�� ³) overall primary energy savings 0 (kWh) total CO2 saving� 0 (kg) material pair solar system (refriger0 ant/sorbent) refrigerant referR-407c ence system

1193

-

-

-

-

-

-

-

-

127�� ,�� 680 96�� ,�� 969 176�� ,�� 400 163�� ,�� 352

-

-

-

-

-

-

-

-

-

-

-

-

1�� ,�� 277

970

1�� ,�� 764

1�� ,�� 634

540

3�� ,�� 934

630

1�� ,�� 128

12

189

12

56

6�� ,�� 312

1�� ,�� 960

2�� ,�� 117

1�� ,�� 292

-

-

-

-

8�� ,�� 141

7�� ,�� 052

4�� ,�� 523

4�� ,�� 109

1�� ,�� 404

2�� ,�� 493

5�� ,�� 021

5�� ,�� 436

46

13.7

22.6

18.5

0.203

0.072

0.061

0.060

27�� ,�� 877

9�� ,�� 023

27�� ,�� 377 24�� ,�� 610

29�� ,�� 620

9�� ,�� 587

29�� ,�� 088 26�� ,�� 148

61

17

61

50

-73�� ,�� 556

9�� ,�� 864

6�� ,�� 841

22�� ,�� 669

-20�� ,�� 081

2�� ,�� 693

1�� ,�� 868

6�� ,�� 189

-

-

-

-

637

35�� ,�� 422 80�� ,�� 534 87�� ,�� 944

9�� ,�� 539

12�� ,�� 280 30�� ,�� 956 32�� ,�� 337

LiBrH2O

LiBrH 2O

LiBrH 2O

LiBrH2O

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4. CONCLUSION The 4th scenario is more attractive because it provides an economically and environmental optimum technical solution. The suggested system consists of a 300-m² 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. 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 carried out. The final results were compatible with the existing ones from the international experience. REFERENCES� Balaras, C. A. Grossman, G. Henning, H.M. Carlos A. Infante Ferreira, Erich Podesser, Lei Wang and Edo Wiemken, Solar air conditioning in Europe—an Overview Renewable and Sustainable Energy Reviews, Volume 11, Issue 2, February 2007, Pages 299-314 Delft University of Technology, SACE, Solar air conditioning in Europe, NNE5-2001-00025, Energy’s Programme (1998-2002), 30/09/2003 Florides, G. A. Kalogirou, �� S. A. Tassou, S. A. �� Wrobel, L. C. Modelling and simulation of an solar cooling system for Cyprus, Solar Energy Vol. 72, No. 1, pp. 43–51, 2002 Henning, H.M. Erpenbeck, T. Hindenburgh, C. Paulussen, C. Solar cooling of buildings––possible techniques, potential and international development, in: Proceedings of Eurosun 98, Freiburg, 1998. Henning, H.M. Solar-Assisted Air-Conditioning in Buildings, New York, International Energy Agency 2004 Li, Z.F. Sumathy, K. Simulation of a solar absorption air conditioning system, Energy Conversion & Management 42 (2001) 313-327 Peters, M.S. Timmerhaus, K.D. Plant �� Design and Economics for Chemical Engineers, McGraw-Hill International Editions, 1994.� Tsoutsos, T. Anagnostou, J. Pritchard, C. Karagiorgas, M. Agoris, D. Solar cooling technologies in Greece, An economic viability analysis, Applied Thermal Engineering 23 (2003) 1427–1439 Tsoutsos, T. Karagiorgas M., The development of solar air conditioning in Greece, 8th national conference for renewable energy sources, Department of Mechanical Engineering, Aristotle University of Thessaloniki, 2006 various, personal notes of the author, 2007


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