simulation of a solar absorption cooling system€¦ · the solar absorption cooling. absorption is...

11872nd PALENC Conference and 28th AIVC Conference on Building Low Energy Cooling and Advanced Ventilation Technologies in the 21st Century, September 2007, Crete island, Greece

Simulation of a solar absorption cooling system

G. Zidianakis, Th. Tsoutsos Technical University of Crete, Greece

N. ZografakisRegional Energy Agency of Crete, Greece

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 spe-cial 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 con-ditioning of most buildings. This is true especially in southern European countries, since the cooling load is roughly in phase with SE availability. The cooling re-quirements 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 abso-lutely harmless working fluids such as water, or salt solu-tion. 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 emis-sions’’ technologies in order to reduce energy consump-tion 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 ab-sorption 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 experi-mental 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-absorp-tion air conditioning applications, and it will be the only

ABSTRACT

During the last years there is an increased conscious-ness 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 under-lines 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 cool-ing. For air-conditioning applications, absorption sys-tems commonly use the water/lithium bromide or wa-ter/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 me-teorological year file exploited the hourly weather data where produced by 30-year statistical process. The re-quired data were obtained by Hellenic National Mete-orological 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 in-creases the peak electric load, causing major problems in the national electric supply system. The energy short-age 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 cor-responds to an annual increase of electric energy con-sumption 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 7/9/2007 1:26:34 µµ

1188 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

combination examined here (Li and Sumathy, 2001) (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: collec-tor plate area, collector plate slope angle, volume of hot water storage tank, nominal power of absorption chiller, cooling tower and backup heat source.

2. METHODOLOGY METHODOLOGYMETHODOLOGY

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 compo-nents 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: Sim-Cad 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) programSACE (Solar Air Conditioning in Europe) program (Solar Air Conditioning in Europe) program(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 val-ues of a typical meteorological year (TMY) for Iraklion, Crete, obtained through the “Meteonorm” program. The TheThe 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 heat-ing and cooling energy demands of the building, for de-termining the technical characteristics of the system 3. Feasibility study of the solar assisted air conditioning study of the solar assisted air conditioningstudy of the solar assisted air conditioning of the solar assisted air conditioningof the solar assisted air conditioning the solar assisted air conditioningthe solar assisted air conditioning solar assisted air conditioningsolar assisted air conditioning assisted air conditioningassisted air conditioning air conditioningair conditioning conditioningconditioning 4. Case studies of the solar fraction with alternative studies of the solar fraction with alternativestudies of the solar fraction with alternative of the solar fraction with alternativeof the solar fraction with alternative the solar fraction with alternativethe solar fraction with alternative solar fraction with alternativesolar fraction with alternative fraction with alternativefraction with alternative technical characteristics 5. Economical evaluation of case studies 6. Optimization of the system and final remarks.

2.3 Meteorological dataThe National Meteorological Service provided the me-teorological data, covering a time span of at least 30 years. After their processing, the average monthly val-ues 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 figure 1 the variability of environmental temperaturefigure 1 the variability of environmental temperature the variability of environmental temperaturethe variability of environmental temperature variability of environmental temperaturevariability of environmental temperature of environmental temperatureof environmental temperature environmental temperatureenvironmental temperature temperaturetemperature and relative humidity are demonstrated, while in figure relative humidity are demonstrated, while in figurehumidity are demonstrated, while in figure are demonstrated, while in figureare demonstrated, while in figure demonstrated, while in figuredemonstrated, while in figure while in figurewhile in figure in figurein figure figurefigure 2 the monthly solar radiation on horizontal surface. the monthly solar radiation on horizontal surface.

Figure 1: Variability of environmental temperature and relative humidity

Figure 2: Monthly solar radiation on a surface

2.4 Building descriptionThe building studied is located in Heraklion, Crete. In particular, this building is in Peza village, of N. Kazant-zakis 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. materials are shown in table 1.materials are shown in table 1. are shown in table 1.are shown in table 1.table 1.1.Table 1: Construction materials of the building

Description thicknesscm

u-value-valuevalue W/mW/m/mm2K

Basement floorMarble , insulation 2cm,, insulation 2cm,insulation 2cm, 2cm,cm,, concrete 30 cm density 30 cm density cm density densitydensity

2000 kg/m kg/m/mm3,34 0,961

Ground floor floorfloor Marble, concrete 20 cm, concrete 20 cmconcrete 20 cm20 cm cm density 2000 kg/m 2000 kg/m kg/m/mm3, plasterplaster 22,2 2,199



Story floor floorfloor Marble, concrete 20 cm, concrete 20 cmconcrete 20 cm 20 cm cm density 2000 kg/m 2000 kg/m kg/m/mm3, plasterplaster 22,2 2,199

RoofPitch, insulationch, insulation insulationinsulation

2,5 cm, concrete 20 cm cm, concrete 20 cm, concrete 20 cmconcrete 20 cm20 cm cm density 2000 kg/m 2000 kg/m kg/m/mm3, plasterplaster

24 0,901

Exterior base-ment walls

Pitch , concrete 30 cm density

2000 kg/m3, plaster32,5 1,382

External walls wallswallsPlaster , Hollow block 10 , Hollow block 10Hollow block 10 block 10block 10 10

cm, insulation 2 cm, hollow, insulation 2 cm, hollowinsulation 2 cm, hollow 2 cm, hollowcm, hollow, hollowhollow block 10 cm, plaster 10 cm, plastercm, plaster, plaster

15 1,185

Internal wallsGypsum plaster – mineral

wool – gypsum plaster

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 materials4. activity 5. internal sources of heating 6. ventilation 7. infiltration 8. lighting9. desired values of indoor temperature and humidity, values of indoor temperature and humidity,values of indoor temperature and humidity, of indoor temperature and humidity,of indoor temperature and humidity, indoor temperature and humidity,indoor temperature and humidity, temperature and humidity,temperature and humidity, and humidity,and humidity, humidity,humidity,, during summer and winter summer and wintersummer and winter and winterand winter winterwinter 10. meteorological conditions

2.5 System description5 System description System descriptionSystem description The system incorporates a number of solar thermal col-lectors, 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 ab-sorber passes through a heat exchanger in order to pre-heat 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.

2.6 Economic evaluation Solar processes are generally characterised by high in-vestment and low operating cost. Thus the basic eco-nomic 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 in-stallation of the equipment, plus the operating expenses. It is vital to determine the primary energy savings and relevant costs for different SCS. Several economic cri-teria have been proposed for evaluating and optimiz-ing 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)(Tsoutsos et al, 2003) the Payback period.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 an-nual 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 op-eration, maintenance and insurance of solar system The installation of equipment involves costs for labour, foundations, supports, construction expenses and oth-er 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 con-ventional vapour compression chiller. Energy saving is the cost of the conventional energy minus the costs of SE.The basic assumptions made during the economic eval-uation 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-



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 ��ypeype Fr(τα)(τα) FrUL €/m²m²² €/kWkWθ=90°CC

A FPC 0,78 8,7 168 1285 (7m²)m²)²))B FPCselective 0,72 4,86 228 903 (3,47m²)²)C FPCselective 0,833 4,25 18080 466 (2,6m²)²))D VTC 0,58 1,8 402 1117 (2,78m²)²))

Table 3: Cost of equipment

Equipment Cost Absorption Chiller LiBr – H LiBr – HLiBr – H – HH2O (COP=0,7) (COP=0,7)COP=0,7)=0,7) 400 €/kW00 €/kW €/kW€/kW/kWConventional chiller (COP=2,5) (COP=2,5) (COP=2,5) 310 €/kW0 €/kW €/kW€/kW/kWBack up heat source (n=85%) (n=85%)(n=85%) 50 €/kW €/kW€/kW/kWCooling tower 50 €/kW €/kW€/kW/kWStorage tank 600 €/m³00 €/m³ €/m³€/m³/m³³

Initially the investment costs for the solar systems and for 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 bene-fits were calculated, as a function of the energy savings.

2.7 Alternative scenariosThe 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 envi-ronmental solution.

3. RESULTS AND RECOMMENDATIONSRESULTS AND RECOMMENDATIONS

A number of simulations were carried out in order to opti-mize the various factors affecting the performance of the system. The results are demonstrated immediately below.

3.1 Building simulationBuilding simulation simulationsimulation The building’s profile was developed through the building’s profile was developed through thebuilding’s profile was developed through the’s profile was developed through thes profile was developed through the profile was developed through theprofile was developed through the was developed through thewas developed through the developed through thedeveloped through the through thethrough the thethe Simcad program, while the thermal zones and the simu- program, while the thermal zones and the simu-program, while the thermal zones and the simu-lation parameters were defined, as shown in Figure 3.. In Figure 4 the heating and cooling loads are presented Figure 4 the heating and cooling loads are presentedFigure 4 the heating and cooling loads are presented the heating and cooling loads are presentedthe heating and cooling loads are presented heating and cooling loads are presentedheating and cooling loads are presented and cooling loads are presentedand cooling loads are presented cooling loads are presentedcooling loads are presented on an hourly basis throughout a year, while in Figure 5 Figure 5Figure 5 these loads are presented on a monthly basis. loads are presented on a monthly basis.loads are presented on a monthly basis. are presented on a monthly basis.are presented on a monthly basis. presented on a monthly basis.presented on a monthly basis.

Figure 3: Building profile and thermal zones definition

Figure 4: Heating and cooling loads on hourly base

Figure 5: Heating and cooling loads on monthly base

With design conditions of 1% the power of the cooling design conditions of 1% the power of the coolingdesign conditions of 1% the power of the cooling conditions of 1% the power of the coolingconditions of 1% the power of the cooling of 1% the power of the coolingof 1% the power of the cooling 1% the power of the coolingthe power of the cooling power of the coolingpower of the cooling of the coolingof the cooling the coolingthe cooling coolingcooling system was calculated to be 160 kW, while the power of was calculated to be 160 kW, while the power ofwas calculated to be 160 kW, while the power of calculated to be 160 kW, while the power ofcalculated to be 160 kW, while the power of to be 160 kW, while the power ofto be 160 kW, while the power of be 160 kW, while the power ofbe 160 kW, while the power of 160 kW, while the power ofkW, while the power of the heating system was found to be 130 kW.130 kW.kW..

3.2 System optimizationSystem optimization optimizationoptimization3.2.1 Type of Collector and slope angle optimization2.1 Type of Collector and slope angle optimization.1 Type of Collector and slope angle optimizationType of Collector and slope angle optimization of Collector and slope angle optimizationof Collector and slope angle optimization Collector and slope angle optimizationCollector and slope angle optimization and slope angle optimizationand slope angle optimization slope angle optimizationslope angle optimization angle optimizationangle optimization optimizationoptimization Based on the meteorological circumstances of the re-gion and the desired output temperature, the collector C (table 2) was selected. The optimum slope angle wasThe optimum slope angle was calculated to be 10 – 15 degrees with South orientation, as shown in Figure 6.



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

3.2.2 Working temperature optimizationWorking temperature optimization temperature optimizationtemperature optimization optimizationoptimizationThe optimum operation temperature of the absorption optimum operation temperature of the absorptionoptimum operation temperature of the absorption operation temperature of the absorptionoperation temperature of the absorption temperature of the absorptiontemperature of the absorption of the absorptionof the absorption the absorptionthe absorption absorptionabsorption chiller and the collector systems was calculated from and the collector systems was calculated fromand the collector systems was calculated from the collector systems was calculated fromthe collector systems was calculated from collector systems was calculated fromcollector systems was calculated from systems was calculated fromsystems was calculated from was calculated fromwas calculated from calculated fromcalculated from fromfrom their efficiency curves and was found to be equal to 90 efficiency curves and was found to be equal to 90efficiency curves and was found to be equal to 90 curves and was found to be equal to 90curves and was found to be equal to 90 and was found to be equal to 90and was found to be equal to 90 was found to be equal to 90was found to be equal to 90 °C as demonstrated in Figure 7. 7.

Figure 7: Effect of driving temperature on system efficiency

3.2.3 Collector area optimizationThe estimation of the optimal surface of solar collec-tors as well as the solar cooling fraction was performed through the SACE program. In Figure 8 appears the so-lar cooling fraction as well as the net efficiency of the collector, while in Figure 9 appears the solar heating Figure 9 appears the solar heatingFigure 9 appears the solar heating appears the solar heatingappears the solar heating fraction as well as the net efficiency of the collectors, both depending on the total surface. In Figure 10 the Figure 10 theFigure 10 the the above are combined and the solar total fraction as wellthe solar total fraction as well as the net efficiency of the collectors are demonstrated, depending on the total surface.

Figure 8: Effect of specific collector area on solar fraction cool-ing and net collector efficiency

Figure 9: Effect of specific collector area on solar fraction heat-ing and net collector efficiency

Figure 10: Effect of specific collector area on overall solar frac-tion and net collector efficiency

In order to calculate the collector’s surface, emphasis order to calculate the collector’s surface, emphasisorder to calculate the collector’s surface, emphasis to calculate the collector’s surface, emphasisto calculate the collector’s surface, emphasis calculate the collector’s surface, emphasiscalculate the collector’s surface, emphasis the collector’s surface, emphasisthe collector’s surface, emphasis collector’s surface, emphasiscollector’s surface, emphasis’s surface, emphasissurface, emphasis, emphasisemphasis was placed on the solar cooling, for two basic scenarios. placed on the solar cooling, for two basic scenarios.placed on the solar cooling, for two basic scenarios. on the solar cooling, for two basic scenarios.on the solar cooling, for two basic scenarios. the solar cooling, for two basic scenarios.the solar cooling, for two basic scenarios. solar cooling, for two basic scenarios.solar cooling, for two basic scenarios. cooling, for two basic scenarios.cooling, for two basic scenarios., for two basic scenarios.for two basic scenarios. two basic scenarios.two basic scenarios. scenarios.scenarios.. The first emerges from the intersection of the solar cool- first emerges from the intersection of the solar cool-first emerges from the intersection of the solar cool- emerges from the intersection of the solar cool-emerges from the intersection of the solar cool- from the intersection of the solar cool-from the intersection of the solar cool- the intersection of the solar cool-the intersection of the solar cool- intersection of the solar cool-intersection of the solar cool- of the solar cool-of the solar cool- the solar cool-the solar cool- solar cool-solar cool- cool-cool-ing fraction with the net efficiency of the solar collectors, fraction with the net efficiency of the solar collectors,fraction with the net efficiency of the solar collectors, with the net efficiency of the solar collectors,with the net efficiency of the solar collectors, the net efficiency of the solar collectors,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, de-pending on the collector surface, as shown in Figure 11.



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:Table 4: Alternative scenarios

Con

ven-

tiona

lSc

enar

io 1

Scen

ario

2

Scen

ario

3

Scen

ario

4

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

The final comparative results for each scenario are dem-onstrated in table 5 (Henning 2004). Table 5: Final results

Con

vent

iona

l

Scen

ario

1

Scen

ario

2

Scen

ario

3

Scen

ario

4

0. General datacollector type 0 FPCsel FPCsel FPCsel FPCsel

collector area (m²)m²)²) 0 100 100 300 300volume of heat

storage unit (m³) (m³) 0 7.5 7.5 20 20

volume of cold-side storage unit

(m³)- - - - -

airflow (m³/h)(m³/h)³/h)h)) - - - - -heat power back up heater (kW) 130 230 130 230 130

nominal chiller power, compres-sion 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

1. Results of annual energy balance for system designannual total elec-tricity consump-tion (including pumps, fans)

(kWh)

30,877,877877 3,000,000000 21,854,854854 3,500,500500 6,267,267267

annual electricity consuption, chiller

(kWh)30,877,877877 0 19,854,854854 0 3,767,767767

annual required heat for cooling/ dehumidification

(kWh)

0 110,276,276276 39,368,368368 110,276,276276 96,822,822822

annual required heat for heating/ humidification

(kWh)

40,311,311311 40,311,311311 40,311,311311 40,311,311311 40,311,311311

total annual heat (kWh) 40,311,311311 150,587,587587 79,679,679679 150,587,587587 137,133,133133

annual heat from 2nd heat source

(fossil fuel) (kWh)

40,311,311311 102,834,834834 31,926,926926 34,496,496496 21,042,042042

annual amount of fossil heat source (primary energy)

(kWh)

47,425,425425 120,981,981981 37,560,560560 40,584,584584 24,756,756756

annual radia-tion on collector

(kWh)0 156,500,500500 156,500,500500 469,500,500500 469,500,500500

annual heat produced by solar collector (kWh)

0 51,755,755755 51,755,755755 155,264,264264 155,264,264264

annual overall cold produc-tion (cooling,

dehumidification) (kWh)

77,193,193193 77,193,193193 77,193,193193 77,193,193193 77,193,193193

annual cold pro-duction by com-pression (kWh)

77,193,193193 0 49,635,635635 0 9,418,418418

maximum elec-tricity demand

(maximum hourly value) (kW)

64 3 47 3 14



total annual water consuption (m³) - - - - -

2. Energy - related evaluation (co�puted fro� design results)annual useful

solar heat (kWh)(kWh) 0 47,764,764764 47,764,764764 116,248,248248 116,248,248248

annual gross col-lector efficiency

(%)0.00 33.07 33.07 33.07 33.07

annual net collec-tor efficiency (%) 0.00 30.52 30.52 24.76 24.76

annual COP of compression

chiller2.5 0 2.5 0 2.5

annual COP of thermally driven cold production

0 0.7 0.7 0.7 0.7

annual primary energy consuption

(kWh)122,593,593593 96,179,179179 48,051,051051 40,789,789789

annual primary energy savings

(kWh)0 7,967,967967 34,381,381381 82,509,509509 89,771,771771

relative primary energy savings

(%)0.00 6.10 26.33 63.20 68.76

specific useful net collector output

(kWh/m²)/m²))0 478 478 387 387

specific primary energy saving

(kWh/m²)/m²))0 80 344 275 299

3. Investment costsolar collector

system including supporting struc-

ture (€) (€)

0 18,000,000000 18,000,000000 54,000,000000 54,000,000000

heat storage unit (€) 0 4,500,500500 4,500,500500 12,000,000000 12,000,000000

additional heat source (€) 6,500,500500 11,500,500500 6,500,500500 11,500,500500 6,500,500500

air - handling unit (€) - - - - -

compression chiller (€) 49,600,600600 0 36,580,580580 0 10,850,850850

thermally driven chiller (€) 0 64,000,000000 16,800,800800 64,000,000000 50,000,000000

cooling tower (€) 0 16,000,000000 4,200,200200 16,000,000000 12,500,500500cold storage unit

(€) 0 0 0 0 0

Pumps (€) - - - - -control system (€) - - - - -planning cost (€) - - - - -total equipment

cost (€) 56,100,100100 114,000,000000 86,580,580580 157,500,500500 145,850,850850

installation cost (€) 6,732,732732 13,680,680680 10,389,389389 18,900,900900 17,502,502502

total investment cost without fund-ing subsidies (€) (€)

62,832,832832 127,680,680680 96,969,969969 176,400,400400 163,352,352352

funding (invest-ment support) (€) - - - - -

funding related to solar collector (€) (€) - - - - -

final total invest-ment cost (€) 62,832,832832 127,680,680680 96,969,969969 176,400,400400 163,352,352352

4. Annual costsannuity factror, conventional

equipment (%) (%)- - - - -

annuity factor, solar system (%) (%) - - - - -

capital cost (€) - - - - -cost for mainte-nance, inpection

(€)1,257,257257 1,277,277277 970 1,764,764764 1,634,634634

annual electricity cost (consuption)

(€)5,558,558558 540 3,934,934934 630 1,128,128128

annual electricity cost (peak) (€) 256 12 189 12 56

annual heat cost (fossil fuel) (€) (€) 2,474,474474 6,312,312312 1,960,960960 2,117,117117 1,292,292292

annual water cost (€) - - - - -

total annual cost (€) 9,545,545545 8,141,141141 7,052,052052 4,523,523523 4,109,109109

total annual sav-ings (€) - 1,404,404404 2,493,493493 5,021,021021 5,436,436436

5. Comparative evaluationpayback time (yr)yr) 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 issuessaved electric energy (kWh) (kWh) 0 27,877,877877 9,023,023023 27,377,377377 24,610,610610

CO2 savings due to electricity sav-

ings (kg)0 29,620,620620 9,587,587587 29,088,088088 26,148,148148

saved electric power (kW) (kW) 0 61 17 61 50

saved fossil fuel energy for heat

(kWh)0 -73,556,556556 9,864,864864 6,841,841841 22,669,669669

CO2 savings due to heat savings

(kg)0 -20,081,081081 2,693,693693 1,868,868868 6,189,189189

water saving (m³) (m³)³) - - - - -overall primary energy savings

(kWh)0 637 35,422,422422 80,534,534534 87,944,944944

total CO2 saving (kg) 0 9,539,539539 12,280,280280 30,956,956956 32,337,337337

material pair solar system (refriger-

ant/sorbent)0 LiBr-

H2OLiBr-H2O

LiBr-H2O

LiBr-H2O

refrigerant refer-ence system R-407c



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 compres-sion 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 tem-perature 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, So-lar air conditioning in Europe—an Overview Renewable and Sustainable Energy Reviews, Volume 11, Issue 2, February 2007, Pages 299-314Delft 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.Kalogirou, S. A. Tassou, S. A. Wrobel, L. C.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 interna-tional development, in: Proceedings of Eurosun 98, Freiburg, 1998.Henning, H.M. Solar-Assisted Air-Conditioning in Buildings, New York, International Energy Agency 2004Li, Z.F. Sumathy, K. Simulation of a solar absorption air condition-ing system, Energy Conversion & Management 42 (2001) 313-327Peters, M.S. Timmerhaus, K.D. Plant Design and Economics forPlant 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) 1427–1439Tsoutsos, T. Karagiorgas M., The development of solar air con-ditioning in Greece, 8th national conference for renewable energy sources, Department of Mechanical Engineering, Aristotle Uni-versity of Thessaloniki, 2006 various, personal notes of the author, 2007


simulation of a solar absorption cooling system€¦ · the solar absorption cooling. absorption is...

Documents