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  1. 1. Design of a Solar driven Absorption chiller forSchool of Energy - CFD laboratory in PSG College of Technology Anirudh Bhaskaran School of Energy PSG College of Technology Coimbatore, India krrbanirudh@gmail.comAbstract—Air conditioning is one of the primary systems which available solar collectors, solar assisted air conditioning can are responsible for greenhouse gas emissions, ozone lead to remarkable primary energy savings, if the systems are depletion and for energy guzzling. The use of solar properly designed [3,4]. energy in buildings is an important contribution to the Till 2007 there were 81 installed large scale SCS, environment by the reduction of fossil fuel consumption including systems which are currently not in operation. 73 and harmful emissions. This paper contributes to the design of solar absorption chiller for School of energy – installations are located in Europe, 7 in Asia, China in CFD laboratory in PSG college of Technology. Solar particular and 1 in America (Mexico). 60% of these absorption cooling systems have the advantage of using installations are dedicated to office buildings, 10% to absolutely harmless working fluids such as water or factories, 15% to laboratories and education centers, 6% to solutions of certain salts. The primary goal is to utilize hotels and the left percentage to buildings with different final zero emissions technologies to reduce energy use (hospitals, canteen, sport center, etc.). The overall cooling consumption and CO2 emissions. The objective of this capacity of the solar thermally driven chillers amounts to 9 study is to design the Solar absorption chiller based on MW; 31% of it is installed in Spain, 18% in Germany and the cooling load requirement and to evaluate the 12% in Greece [5]. techno-economics of the system to suggest the institution to make use of the potential of solar energy Wide-ranging studies of different aspects of absorption in air conditioning of buildings. system, such as performance simulations and experimental test results, have been reported. Amongst the various types of Keywords- fossil fuels; Solar absorption cooling system; CO2 continuous absorption SCS, LiBr–H2Oand H2O–NH3 are theemissions; techno-economics; Air conditioning major working pairs employed in these systems. It is reported that LiBr–H2O has a higher coefficient of performance (COP) I. INTRODUCTION than that of the other working fluids [6]. Solar energy cooling systems for buildings have received However, for these applications to be economicallymuch attention from the engineers in the past few years due to interesting, in terms of payback period, it would be importantthe world energy shortage. Especially, the solar driven to extend the system operation period as much as possibleabsorption cooling system appears to be one of the promising throughout the year. Solar thermal collectors can also be usedalternative methods for conventional air conditioning system. for water or indoor space heating, thus making it possible toThe blackout situations faced by the Tamil Nadu electricity use an integrated system for building cooling and heating [7].board due to power shortages can be partially overcome by the This study aims to evaluate the techno-economics of theutilization of solar energy in air conditioning of buildings. cooling system for building applications and make it The traditional refrigeration cycles are driven by economically feasible to incorporate in the educationalelectricity or heat, which strongly increases the consumption institutions.of electricity and fossil energy. The International Institute ofRefrigeration in Paris (IIF/IIR) has estimated that II. DESCRIPTION OF SOLAR ABSORPTION COOLING SYSTEMapproximately 15% of all the electricity produced in the whole Absorption is the process in which material transferred fromworld is employed for refrigeration and air-conditioning one phase to another, (e.g. liquid) interpenetrates the secondprocesses of various kinds, and the energy consumption for phase to form a solution. The principle of the single effectair-conditioning systems has recently been estimated to 45% system with water-LiBr as working pair is described belowof the whole households and commercial buildings[1,2]. [8]. Several thermally driven AC technologies are marketavailable by today, which enable the use of solar thermal  A pump brings the rich solution towards the high-energy for this application. Based on current technologies, i.e., pressure available thermally driven cooling devices and market
  2. 2.  The mixture is heated in the generator. A contribution iii) Auxiliary power of heat (hot water from solar flat plate collector) iv) water tank volume allows the separation of the refrigerant (H2O) from v) cooling tower type and power the absorbent (LiBr solution).  Economical evaluation of optimized solutions  The vapors of refrigerant are sent towards the traditional cycle of condenser, expansion valve and evaporator. Cold is produced by the evaporation of IV. ROOM DESCRIPTION AND ITS CHARACTERISTICS refrigerant in the evaporator at low pressures and the The room studied in this paper is the CFD laboratory which cool air is circulated in to the telecommunication is a part of School of Energy in PSG college of Technology. shelter. The lab is currently cooled by a vapour compression air-  The poor solution turns over in the absorber by conditioning system which is to be replaced by SAC. The lab passing by a pressure-relief valve. has a surface area of 36m2 with heat generating equipment’s  The vapors of refrigerant are absorbed by the poor such as LCD monitors, CPU, wall mounted racks for network solution of absorber coming from the generator. The connection, LCD projector, lightings, ceiling fan. The detailed cycle can start again. specification and heat generating capacity of the equipment’s are given in table II. The knowledge of materials of the room is necessary to conduct the cooling load calculation and is givenIII. METHODOLOGY OF THE WORK in table I. The methodology comprises of the following steps [9,10]: TABLE I. CONSTRUCTION MATERIALS OF THE ROOM  Collection of the required meteorological data of the Type Building material Total U value Thickness examined area for the last 30 years. (W/m2K) (mm) These data include the monthly solar irradiation, monthly dry bulb temperature, relative humidity. Ceiling RCC (400mm) and 404 2.75 tiles (4mm) on the  Study of the maximum, minimum and average exterior surface cooling energy demand of the building, for Floor RCC (400mm) and 404 2.75 determining the technical characteristics of the tiles (4mm) on the interior surface system. In order to maintain stable humidity and temperature Wall1 Plaster 300 2.033 conditions within the building, the cooling loads (100mm),Brick (100mm), should be calculated. These depend on a great Plaster(100mm) number of parameters, such as: Wall2 Plaster 300 2.033 i) size and geometrical characteristics of the (100mm),Brick building (100mm), ii) orientation Plaster(100mm) iii) construction materials Wall 3 Glass with 5 5.88 iv) activity aluminium frames v) internal sources of heating Wall 4 Glass with 5 5.88 vi) ventilation aluminium frames vii) infiltration viii) lighting ix) desired values of indoor temperature and The examined lab as shown in Fig.1&2 is in the first floor of a humidity, during summer and winter block and it is enclosed by 2 seminar halls (air conditioned x) meteorological conditions space) which is separated by the brick and plaster layers (wall 1 and 2) while the other 2 sides are enclosed by an internet lab with 5 computers and office room separated by aluminium  Selection of the solar cooling technology to be framed glass layers (wall 3 and 4). The space right below the applied. The procedure adopted to select the optimum lab floor is occupied by another department (un-air conditioned SAC technology depends on several building space) .The space above the lab ceiling is occupied by IT parameters. The selected technology is also chosen department (un-air conditioned space). There is no direct solar taken into account the type of the AC installation and heat gain in to the lab; therefore wall cooling load due to solar the climatic conditions. heat gain is neglected.  Sizing study of the solar assisted air-conditioning The lab has an automatic door of 2.16m2 area which is  Carryout studies on optimized solutions for the solar responsible for the infiltration of outside air in to the lab. The fraction by varying the technical characteristics that lab will be occupied by a maximum of 15 people. The mainly concern the: equipment’s operating time is from 8:30am to 5:00pm except i) solar collector surface the LCD projector. It is assumed that 20% of the cooling load ii) absorption chiller power
  3. 3. from lighting is directly absorbed in the return air stream Figure 2. 3D model of CFD lab (top cut section view)without becoming room load. V. COOLING LOAD CALCULATIONS TABLE II. EQUIPMENT SPECIFICATIONS The cooling loads are calculated on component basis usingEquipment Manufacturer Avg. heat No. of Operating the RTS method. The following parts illustrate cooling load with generating Equipments hours calculations for individual components of the CFD lab for a specifications capacity particular day of a month.Flouroscent 40W T5 lamp 40W 3 8:00am to A. Internal lighting cooling load using radiant time serieslamp with electronic 8:00pm ballast The primary source of heat from lighting comes fromCeiling fan 40W 5W 2 8:00am to light emitting elements, or lamps, although significant 5:00pm additional heat may be from associated appurtenances in theLCD BENQ 250W 1 1 hr per day light fixtures that house such lamps [11]. Instantaneous rate ofprojector corporation, M (avg) heat gain from electric lighting is given by [11], series with 210W light bulb ̇ (1)LCD 17” TFT 33W 18 8:00am to Here the lighting use factor is taken as 1 and lighting specialmonitors display HCL 5:00pm monitors allowance factor as 1.1. To determine the total sensible cooling load, the total heat gainCPU Intel corp., 60W 18 8:00am to Core 2 duo 5:00pm has to be split up in to convective and radiant cooling processor components. The convective and radiant percentages are taken E7200 to be 41% and 59% for fluorescent lamps recessed, vented to @2.53Ghz return air and supply air [11].Convective cooling load is givenWall 24 port Giga 30W 1 8:00am to by [11],mounted switch with a 8:00pmrack for cooling fannetwork ̇ ̇ (2)connection Radiant cooling load is given by [11], ̇ (3) Total lighting load is given by [11], ̇ ̇ ̇ (4) As assumed earlier, 20% of the lighting load is absorbed by the return air stream, net lighting load is given by [11], ̇ ̇ (5) Figure 1. 3D model of CFD lab (side cut section view) B. Wall,ceiling and floor cooling load The conditioned space is adjacent to a space with different temperature; therefore heat transfer through the separating physical section must be considered and given by [11], ̇ (6) C. Equipment cooling load The heat gain from the office and lab equipment can create a significant amount of heat gains, sometimes greater than all other gains combined. The individual equipment heat generation can calculated from the average heat generation capacity as specified by the manufacturer.
  4. 4. ̇ (10) Figure 3. Schematic of Solar absorption chiller plantD. Occupants load Latent heat gain corresponding to change in humidity ratio is The sensible and latent heat gains comprise a large given by [11],fraction of total load. Even for short term occupancy, the extra (11)heat gain brought in by people may be significant [11], Total heat gain is given by,Sensible heat gain is given by [11], ̇ ̇ ̇ (12) ̇ ̇ (7)Latent heat gain is given by [11], VI. SOLAR ABSORPTION COOLING MODEL The schematic model of the solar absorption cooling system is ̇ ̇ (8) shown in Fig.3. The thermal energy required by the absorption chiller to handle the cooling load is given by [12], ̇E. Infiltration load ̇ (13) Automatic doors are a major source of air leakage inbuildings. They are normally installed where a large number Where, is the coefficient of performance of theof people use the doors. They stay open longer with each use absorption chiller which varies with demand is given in a fourth order polynomial for partial load efficiency ofthan manual doors. Therefore, it is important to that designers absorption chiller [12],take in to account the airflow through automatic doors whencalculating the cooling loads in the space next to them [11]. (14)To calculate the average airflow rate through an automatic Where, is the ratio of the cooling load and the chillerdoor, the designer must take into account the area of the door, nominal capacity and given by [12],pressure difference across it, the discharge coefficient of the ̇door when it is open and the fraction of time it is open. (15) The infiltration rate through the automatic door is given Energy balance applied at the chiller can be given by,by [11], ̇ ̇ ̇ (16) (9) The water leaving the chiller can be let through a flow control valve to operate the chiller at partial load.Here the airflow coefficient is taken as 25 L/(s.m2.Pa0.5) and thepressure difference across the door is taken as 4 Pa0.5[11]. An Auxiliary heater is also provided at the inlet of the chiller in order to attain the desired temperature of the heating mediumSensible heat gain corresponding to change in dry bulb and also can be used in the absence of solar energy.temperature is given by [11],
  5. 5. Auxiliary heater 4000 Rs./kW Cooling tower 5000 Rs./kW Storage tank 4500 Rs./m3 The characteristics of the required solar absorption air conditioning system are given in table IV. TABLE IV. CHARACTERISTICS OF THE SOLAR ABSORPTION AIR CONDITIONING SYSTEM Equipment Type Specification chiller Absorption, LiBr-H2O 9.1kW Solar collector Flat plate 16m2 Storage tank Hot water 0.4m3 heater Auxiliary cum pre heat 7.2kW Cooling tower open 23kW Figure 4. Monthly variations of dry bulb temperature TABLE V. INVESTMENT, OPERATING COST AND PAYBACK PERIOD VII. THEORETICAL RESULTS OF THE COOLING SYSTEM Equipment Investment cost Rs.Based on the 30 years dry bulb temperature data as shown in Absorption chiller 3,20,000Fig 4, the monthly cooling load requirement is calculated and Solar flat plate collector 2,24,000shown in Fig. 5 Storage tank 1,800 Auxiliary heater 28,800 Cooling tower 1,15,000 Total installation cost 5,000 Annual O&M cost 5,000 Annual electricity cost 10,000 Total cost* 7,09,600 Total annual savings* 1,08,917 Payback period 6.51 years *cost of electricity =4.715 Rs./kWh TABLE VI. ENVIRONMENTAL BENEFITS Benefits Saving units Figure 5. Monthly variation of total cooling load requirement Annual Electricity savings 23,100 kWhThe monthly cooling load helps us to find out the peak load CO2 savings * 12,173 kgrequirement and accordingly we can select the required Working fluid in SAC LiBr-H2Otonnage of solar absorption chiller. From Fig. 5 it is evidentthat the peak load of 9.093kW occurs in the month of April and *CO2 emission factor = 0.527kg/kWhthe required tonnage of SAC is calculated for this cooling load The total annual savings is calculated by assuming theand found to be 2.6 tons. conventional air-conditioning system runs for 300 days a year VIII. ECONOMIC ANALYSIS and having a tonnage capacity of 5.5tons with 80% cooling load. The electrical energy consumed by a solar absorptionThe techno-economics of the cooling system is performed in chiller to pump the solution and water is also taken in tothis section. The financial data for all the equipment’s is given consideration for calculating the annual table III. The payback period is calculated by, TABLE III. FINANCIAL DATAEquipment cost (17)Absorption chiller 32000 Rs./kW From the environmental aspect, the annual electricity savingsCompression system 25000 Rs./kW can lead to reduction in CO2 emission as shown in table VI.Solar collector 14000 Rs./m2
  6. 6. IX. CONCLUSIONThe design of solar absorption chiller for CFD laboratory has sa Special allowancebeen carried out as per the ASHRAE standards and the cooling inf Infiltrationload was found to be 9.093kW for which a 3ton SAC can ch Chillerhandle the cooling load. The required cooling load needs a h Hotthermal input from solar flat plate collector of area 16m2 which Abbreviationmeans a total of 6 flat plate collectors are needed to provide thedesired amount of hot water to the chiller. The economic CFD Computational Fluid Dynamicsanalysis carried out in section VIII shows that in order to SCS Solar cooling systemimplement this system, a total investment of 7 lakhs (approx.) SAC Solar absorption chillerhas to be invested. The replacement of vapour compression COP Coefficient of performancesystem with the solar absorption system will provide a LCD Liquid crystal display CLF Cooling load factorsignificant annual electrical energy savings of 23,100kWh and RCC Reinforced cement concretetotal annual savings of Rs.1,08,917. The payback period forthis renewable cooling system is found to be 6.5 years(approx.). Apart from the energy cost savings, it also has some REFERENCESmajor environmental benefits like CO2 emission reduction of [1] Wimolsiri P. Solar cooling and sustainable refrigeration,12.17 tons per year. / ARHPT Sustain Refrig 2005WP.pdfSFrom overall perspective, the SAC system has many [2] Santamouris M, Argiriou A. Renewable energies and energyadvantages compared to the conventional system and therefore conservation technologies for buildings in southern Europe. Int J Solthe application of such systems should dominate the future Energy 1994;15:69– [3] H.M. Henning, Solar assisted air conditioning of buildings – an overview, Applied Thermal Engineering 27 (10) (2007) 1734–1749If the SAC system is installed for the entire institution, the [4] A. Argiriou, C.A. Balaras, S. Kontoyiannidis, E. Michel, Numericalannual savings will be enormously high with additional simulation and performance assessment of a low capacity solar assisted absorption heat pump coupled with a sub-floor system, Solar Energy 79environmental benefits. (3) (2005) 290–30 [5] W. Sparber, A. Napolitano, P. Melograno, Overview on worldwide installed solar cooling systems, in: Proceedings of 2nd Solar Cooling NOMENCLATURE Conference, Tarragona Costa Dorada, Spain, 2007 [6] C.A. Balaras, G. Grossman, H.M. Henning, C.A. Infante Ferreira, E. Podesser, W. Lei, E. Wiemken, Solar air conditioning in Europe – an A Area, m2 overview, Renewable and Sustainable Energy Reviews 11 (2) (2007) a,b,c,d,e Coefficients of COP 299–31 CA Air flow Coefficient, [7] Tiago Mateus, Armando C. Oliveira, Energy and economic analysis of L/(s.m2.Pa0.5) an integrated solar absorption cooling and heating system in different Ful Lighting utilization factor building types and climates, Applied Energy 86 (2009) 949–957 Fsa Lighting special allowance [8] Y. Fan, L. Luo, Review of solar sorption refrigeration technologies factor Development and applications, Renewable and Sustainable Energy fch Chiller cooling load ratio Reviews 11 (2007) 1758–1775 𝑚̇ Mass flow rate hot water, kg/s [9] G. Zidianakis, T. Tsoutsos, N. Zografakis, Simulation of a solar Np Payback period, years absorption cooling system, in: Proceedings of 2nd PALENC N No. of person Conference, Crete, Greece, 2007. Q Air flow rate, m3/s [10] T. Tsoutsos, M. Karagiorgas, G. Zidianakis, V. Drosou, A. Aidonis, Z. 𝑄̇ , 𝑞̇ Heat gain rate Gouskos, C. Moeses, Development of the applications of solar thermal tb Avg. air temp. in adjacent cooling systems in Greece and Cyprus, Fresenius Environmental space, o C Bulletin, June 2009. ti Conditioned air temp, o C [11] ASHRAE Handbook fundamentals -2005 Th1 Hot water inlet temp to the [12] N. Fumo, V. Bortone, J. C. Zambrano, Solar Thermal Driven Cooling chiller, o C System for a Data Center in Albuquerque New Mexico, Journal of Solar Th2 Hot water outlet temp from the Energy Engineering, nov 2011, Vol. 133 chiller, o C W Lighting wattage, W Greek symbols θ Time, hours Subscripts c,θ Covective r,θ Radiant l Latent s Sensible ul Utilization