Desiccant-enhanced evaporative (DEVap) cooler system introduction and its comparison with direct expansion (DX) system

Transcription

1 Applied Science Reports E-ISSN: / P-ISSN: DOI: /PSCP.ASR App. Sci. Report. 11 (1), 2015: PSCI Publications Desiccant-enhanced evaporative (DEVap) cooler system introduction and its comparison with direct expansion (DX) system Ali Sohani 1*, Hoseyn Sayyaadi 2, Morteza Zandie 3 1. M.Sc. Student, Faculty of Mechanical Engineering-Energy Division, K.N. Toosi University of Technology. 2. Associate Professor, Faculty of Mechanical Engineering-Energy Division, K.N. Toosi University of Technology 3. M.Sc. Student, Faculty of Mechanical Engineering-Energy conversion, Shahid Rajaee Teacher Training University *Corresponding author alisohany@yahoo.com Paper Information Received: 11 March, 2015 Accepted: 27 June, 2015 Published: 20 July, 2015 Citation Sohani A, Sayyaadi H, Zandie M Desiccantenhanced evaporative (DEVap) cooler system introduction and its comparison with direct expansion (DX) system. Applied Science Reports, 11 (1), Retrieved from (DOI: /PSCP.ASR ) A B S T R A C T In this study, first desiccant-enhanced evaporative (DEVap) cooler system and its performance is described. Then, consideration of this system in comparison with a direct expansion (DX) system in a 6-stored apartment cooling is Azadshahr is evaluated. According to obtained results, both systems are in the same weight. Initial costs of desiccant- enhanced evaporative (DEVap) cooler system is 28 percent more than DX systems, but its monthly primary energy consumption is less. In accordance with comparisons, this result show that, for same cooling operations, DEVap cooler systems are a proper choice with less initial energy consumption to DX systems, particularly in areas facing problems in energy providing and if release to mass prochannelion, they may be more competitive PSCI Publisher All rights reserved. Key words: Desiccant-enhanced evaporative (DEVap) cooler system; comparison; Direct expansion (DX) system; initial costs; monthly primary energy consumption Introduction Desiccants are solid or liquid hygroscopics that are able to decrease the damp of moist air. Since the process of moist absorption is exothermic, if there is no cooling afterwards, this heat will be transferred to air and will cause more heat. For this cause, in applications which dry and cold air is needed, desiccant in combination with a cooling system is used. The combined system should act in a manner doesn't cause re-increase in air moisture. Indirect evaporative cooling system has this feature. In order to recover the operation of desiccant and indirect evaporative cooling systems, many works have done in recent years including operation recovery of heat exchangers, increasing in contact area of air and desiccant, decreasing in temperature rising and decreasing the amount of amended desiccant (Lowenstein, 2008). Desiccant-enhanced evaporative (DEV ap) cooler system was presented by Slayzak and Kozubal in 2009 and its ownership right is registered. In this modern and developed system, referred operation promotions are used to recover the system operation (Slayzak and Kozubal, 2009). Woods and Kozubal were to modeling and numerical solution of this system and its comparison with experimental results. Obtained results of numerical solution have maximum difference of 10 percent with experimental data and so, modeling accuracy and solution were approved (Woods and Kozubal, 2013). Gao and et al tested a sample Desiccant-enhanced evaporative (DEVap) cooler system. They studied effects of each one gradually by changing input parameters of system individually. According to results, operation of the system is optimized by increasing in concentration and desiccant's flow. Also by increasing in input air's absolute humidity the amount of moisture absorption is increased but temperature's fall is decreased. (Gao and et al. 2014) In this study, after presentation of operation of Desiccant-enhanced evaporative (DEVap) cooler system, its competitiveness with a typical direct expansion (DX) system in cooling of a 6-stored apartment in Azadshahr is evaluated.

2 Desiccant-enhanced evaporative (DEVap) cooler system Fig1 shows schematic of a desiccant-enhanced evaporative (DEVap) cooler system. This system includes two parts: Dehumidifier and dew-point indirect cooler. In dehumidifier part, input hot and humid air which can be totally outdoor air or a combination of outdoor and return air from the room enters in state 1 and its moisture is transferred to desiccant by mass transfer process during passing a channel which called "main channel ". In order to prevent useless of desiccant and its transferring to air, a one-way membrane is used in contact area of air and desiccant which allows air moisture to pass but blocks transfer of desiccant to air. Other channels of this part which are located vertically on main air channels are covered by a layer of water sprayed on it and the released heat by desiccant partially causes evaporation some of this water. The evaporated moisture is absorbed and leaves the dehumidifier by the air entered the channel in state 3. Therefore, less amount of heat is transferred in main channel and so, output main air will have less temperature rising in state 1.5. Afterwards, the air which moisture is decreased in the last part enters dew-point indirect evaporative cooler. This cooler is a counter-flow exchanger which in main air reaches state 2 in a channel called "dry channel ". Some of this air is sent into the room and the rest guided to the other channel which is covered by water and is called " wet channel". Heat transferring from main air in dry channel to water and available air in wet channel causes decreasing in temperature without increasing in moisture. Figure 1. Schematic of a Desiccant-enhanced evaporative (DEVap) cooler system (From Enteria et al., 2013). Comparison with direct expansion (DX) system 17

3 In this section, a 6-stored apartment with specifications in table 1 which its floor plan is corresponding to fig 2 and located in Azadshahr with climate specifications in table 2 is chosen and the cooling load calculation is done using Carrier HAP According to calculations, total load of the building is watt. Then, based on obtained load, proper desiccantenhanced evaporative (DEVap) cooler and direct expansion (DX) system is chosen and later, comparisons are made using base system data in table 3 and equations 1 and 2. Parameter Average ceiling height (m) Overall external walls heat-transfer coefficient (W.m -2.K -1 ) Overall portions heat-transfer coefficient (W.m -2.K -1 ) Overall windows heat-transfer coefficient (W.m -2.K -1 ) Average walls weight per area (kg.m -2 ) Number of windows Each window area (m 2 ) Maximum occupancy in each story (people) Table1. Building Specification Value Figure 2. Proposed Building; plan of the flat. 18

4 Parameter Value Table 2. Climate data for Azadshahr (from Management and Planning Organization of Iran) Longitude Latitude (degree) Elevation from Dry-bulb Wet-bulb (degree) sea level (m) temperature at 3 temperature at 3 pm, July ( C) pm, July ( C) Average daily range in summer ( C) 14.2 System DEVap DX Table 3. systems specification for calculation of comparison parameters (Kozubal, and Woods, 2009) Cooling capacity (W) Weight (kg) Initial cost (US $) W W C C ( ( ) 0.6 ) )1( )2( In equations 1 and 2, indices w, cc, c are weight, cooling capacity and initial costs respectively and the index is related to base system (Systems in table 3). Comparison based on weight In fig 3, weight of both systems is compared to each other. As this figure shows, both systems weights are the same and there is no special superiority in this case. So, transportation costs are equal for both systems. Comparison based on initial costs Figure 3. Comparison based on weight. 19

5 Desiccant-enhanced evaporative (DEVap) cooler system is more developed than direct expansion (DX ) system and has more components. On the other hand, these systems haven't released to mass production yet. d on these explanations and what is seen in fig 4, for the building considered, initial costs for desiccant-enhanced evaporative (DEVap) cooler system is 28 percent more than that for direct expansion (DX) system. Figure 4. Comparison based on initial costs Comparison based on monthly required primary energy Required primary energy is thermal energy required to supply the total energy of system before implementation of any energy conversion process. (For example convert to electricity). fig 5 is drawn with assumption of 30 percent efficiency for converting thermal energy to electrical energy and calculations are done for months of operations during a year. Regarding that exit entered moisture from air to desiccant is done by thermal energy and desiccant-enhanced evaporative (DEVap)cooler system has only some fans and pumps with relatively low electrical energy consumption, Required primary energy for this system is less than direct expansion (DX) system which has high level of electricity consumption. So, one of the advantages of this system is lower primary energy consumption relative to direct expansion (DX) system. 20

6 Figure 5. Comparison based on initial monthly required energy Results and discussion In this study, Desiccant-enhanced evaporative (DEVap) cooler system performance was described and then, comparison was made between this system and direct expansion (DX ) system for a 6-stored apartment in Azadshahr. According to comparisons, both systems have no difference in weight and transportation costs. Initial costs for desiccantenhanced evaporative (DEVap) cooler system is 28 percent more than that for direct expansion (DX) system due to technological issues and not releasing this technology to mass production. Therefore, desiccant-enhanced evaporative (DEVap) cooler system can be a competitive case in comparison with direct expansion (DX) systems, specially in countries facing problems in energy providing. References Enteria N, Hiroshi Y, Akashi M. "Review of the advances in open-cycle absorption air-conditioning systems." Renewable and Sustainable Energy Reviews, Vol. 28, 2013, pp Eric K, Woods J, Burch J, Boranian A, Merrigan T Desiccant enhanced evaporative air-conditioning (DEVap): Evaluation of a new concept in ultraefficient air conditioning, [Report], National Renewable Energy Laboratory, January Gao WZ, Cheng YP, Jiang AG, Liu T, Keith A "Experimental investigation on integrated liquid desiccant Indirect evaporative air cooling system utilizing the Maisotesenko-Cycle." Applied Thermal Engineering, (Article in press). Lowenstein, Andrew "Review of liquid desiccant technology for HVAC applications." HVAC&R Research, Vol. 14, No. 6, pp Management and Planning Organization of Iran, Issue no. 271, < Access on December 20, Slayzak SJ, Kozubal EJ Indirect evaporative cooler using membrane-contained, liquid desiccant for dehumidification, < Access on January 22, Woods J, Eric K. "A desiccant-enhanced evaporative air conditioner: Numerical model and experiments." Energy Conversion and Management Vol. 65, January,2013,pp