外文原文-在炎热潮湿的气候条件下采用液体循环辐射供冷的干燥剂除湿系统的性能.pdf

Energy and Buildings 51 2012 1 5 Contents lists available at SciVerse ScienceDirect Energy and Buildings j ourna l ho me p age Performance of desiccant dehumidifi cation with hydronic radiant cooling system in hot humid climates A S Binghooth Z A Zainal School of Mechanical Engineering Universiti Sains Malaysia Engineering Campus 14300 Nibong Tebal Penang Malaysia a r t i c l e i n f o Article history Received 21 December 2011 Received in revised form 20 January 2012 Accepted 29 January 2012 Keywords Desiccant dehumidifi er Chilled ceiling panels Hydronic Thermal comfort Relative humidity a b s t r a c t Experimental investigations were carried out to determine the performance of a rotating desiccant wheel with chilled ceiling panels for humid climates in Malaysia Dehumidifi cation capacity was in the range of 0 89 2 673 kg h Relative humidity reduction to 40 with high dehumidifi cation capacity of 2 673 kg h was achieved within 10 min with air fl ow rate of 243 kg h Chilled ceiling surface temperature between 14 and 18 C was achieved by varying the chilled water inlet temperature from 6 C to 10 C at steady state Condensation was absent on the chilled ceiling surface panels below 70 relative humidity Thermal comfort room temperature for this investigation was 24 24 5 C for chilled ceiling height of 2 m 2012 Elsevier B V All rights reserved 1 Introduction Humidity is indeed a problem to be addressed in all air con ditioning cases Desiccants are materials which have an ability to absorb and or adsorb water vapor from the surroundings The common types of desiccants used in dehumidifi er are silica gel and calcium chloride The most common solid desiccant is silica gel for removing moisture in an enclosed area Desiccants have been used to improve indoor air quality and reduce energy con sumption In attaining an acceptable thermal comfort controlling indoor air quality temperature relative humidity and ventilation are essential The humidity of an air condition can be reduced by removing the moisture via desiccant dehumidifi cation 1 2 Desiccant dehumidifi ers normally comprise of a singular desic cant however compound desiccant have also been used 3 5 Hot humid climates in the tropics have relative humidity in the range of about 70 80 and require signifi cant refrigeration capacity to reduce the temperature to the dew point to remove the moisture in the air Using desiccant dehumidifi cation in these climatic locations will reduce the electrical power consumption In general the advantageous of employing desiccant have encouraged many researches to extend their investigations exper imentally and numerically on the performance of the desiccant and improving indoor air quality 6 7 More advance dehumid ifi cation system integrated with a membrane based total heat Corresponding author Tel 60 4 5937788 fax 60 4 5941025 E mail address mezainal Z A Zainal exchanger would enhance the performance of the air conditioning system 8 Adequate amount of fresh air into an air conditioned space depends on the ventilation system in particular the location and either natural or forced convection 9 10 High fresh air compo sition is required for example in hospitals where contaminated air is removed and also to replenish oxygen supply However this requires a much higher refrigeration capacity to cool the higher amount of incoming hot and humid air especially for conventional air conditional system that uses a cooling coil with an air blower A different air conditioning system has to be considered with high fresh air composition and one of the candidates is hydronic radi ant cooling 11 Hydronic radiant cooling HRC system refers to the use of chilled water as a refrigerant medium via cooper tubes embedded into aluminum panels Since its introduction in the European countries HRC has attracted a lot of attention with displacement ventilation systems 12 Behaviors of indoor humid ity and the effect on condensation is an important consideration in hydronic chilled ceiling air conditioning 13 Integrating chilled ceiling with dehumidifi ed ventilated air presents many advanta geous related to thermal comfort absence of condensation and energy saving 14 16 In the desiccant dehumidifi er incoming humid air passes through a rotating wheel of desiccant When the desiccant wheel is saturated with moisture the desiccant wheel must be reactivated for continuous operating with heat energy sup plied via electrical heater Therefore to determine the required time for the desiccant to be saturated it is necessary to control relative humidity and reduce energy consumption Undesirable conden sation on chilled ceiling panels surfaces normally occurs in hot 0378 7788 see front matter 2012 Elsevier B V All rights reserved doi 10 1016 j enbuild 2012 01 031 2 A S Binghooth Z A Zainal Energy and Buildings 51 2012 1 5 Fig 2 1 Main process of the dehumidifi er humid climates like Malaysia and can be prevented by controlling the chilled ceiling surface temperature and relative humidity of the incoming air or ventilated air Investigation on controlling the desiccant operation time at various air fl ow rates to reduce power consumption whilst maintaining the RH and the dehumidifi cation capacity is proposed and has never been investigated There is no study yet on the appropriate position of the chilled ceiling panel height with respect to the chilled ceiling temperature and relative humidity 2 Methodology Bry Air compact dehumidifi er Fluted Flat Bed model FFB 600 with high performance metal silicate fl uted and desiccant syn thesized rotor was used in the present study Fig 2 1 shows the main processes of the desiccant dehumidifi er while the desic cant specifi cation is shown in Table 1 Hydronic radiant cooling system consists of three main components chilled ceiling panel water circulation system and environmental chamber Chilled ceiling panel is made from aluminum sheet and has a size of 1 70 m 0 5 m 0 02 m It removes heat gain inside the chamber Chilled water from a chiller passes through copper tubes of 0 01 m diameter embedded into the panel as shown in Fig 2 2 There are 12 chilled ceiling panels installed below the ceiling of the envi ronmental chamber The environmental chamber wall thickness is 100 mm constructed with demountable clip lock type insulated panels The insulated panels are made of galvanized steel sheets laminated with insulation core of polyurethane with dimension of 4 25 m 3 75 m 3 m An inlet into the chamber is located at the bottom right and exit at the left top directly opposite the air inlet These air vents are of the same diameter of 11 cm Fig 2 3 shows the geometry of the chamber that can accommodate four occupants The room temperature measurement TR is taken 1 m above the fl oor The performance of the desiccant dehumidifi cation 1 7m Copper tub e CC Water inle t Water outlet 0 5 m Fig 2 2 Schematic of chilled ceiling panels with copper tubes Table 1 Specifi cation of compact dehumidifi er FFB 600 Model Unit dimension data mm Process duct connection mm Reactivation duct connection mm Dia hose AB C Inlet connection Outlet connection mm Inlet connection Outlet connection DE F G H I J JJ J1 K K1 L L1 w O P Q R S S1 T T1 U U1 x V FFB 600 886 630 494 195 135 300 275 264 240 226 0 160 170 225 98 128 0 142 85 300 218 182 145 170 225 98 128 0 150 A S Binghooth Z A Zainal Energy and Buildings 51 2012 1 5 3 Fig 2 3 Model geometry in Gambit software of environmental chamber was evaluated by determining the minimum relative humidity the saturation time for dehumidifi cation and the dehumidifi cation capacity Two experiments were conducted on the desiccant dehumidifi er The fi rst experiment was conducted by switching off the electrical heater then running the desiccant with different air fl ow rates of 81 162 and 243 L h 1as soon as the desiccant reaches its active temperatures The dehumidifi cation capacity was determined by using the following equation Dc mair win wout 1 where mairis the mass fl ow rate of air kg s and win wout is the difference in the humidity ratio g water g dry air The relative humidity was measured at the air inlet and outlet by a relative humidity meter model BSU102 Psychometric probe sensor was connected to a data acquisition model BABUC A The relative humidity of the inlet air process was 86 Whilst in the reactivation sector the second experiment was done by running the desiccant for 60 min with and without electrical heater to con trol the relative humidity The desiccant was run with electrical heater and air fl ow rates of 81 162 243 L h 1for about 30 20 15 min respectively to maintain minimum relative then the elec trical heater thereafter switched off for the next 30 40 and 45 min respectively Chilled ceiling chamber was subjected to three experiments The fi rst experiment was carried out by measuring the chilled water inlet temperature TC W I chilled water outlet temperature TC W O chilled ceiling temperature TCC and room temperature TR at steady state The second experiment was carried out by vary ing the height of chilled ceiling panels HCC of 2 2 5 and 3 m and the chilled ceiling temperature TCCof 14 18 C The third experiment was carried out by varying the relative humidity in the desiccant dehumidifi er whilst observing condensation on the chilled panel s surfaces The dew point temperature of occupied zone was mea sured using Data acquisition instrument BABUC version 5 07 LSI 3 Result and discussion 3 1 Desiccant dehumidifi er Performances of the desiccant dehumidifi er are its ability to reduce relative humidity within a period of time the saturation time and its dehumidifi cation capacity Figs 3 1 and 3 2 show the minimum relative humidity and saturation state of the desiccant 30 35 40 45 50 55 60 65 246235224213202191180169158147136125114103928170 Mass flow rate kg h Relative humidity 50 C140C170C Fig 3 1 Minimum relative humidity 30 40 50 60 70 80 90 100 246235224213202191180169158147136125114103928170 Mass air flow rate kg h TIME min 50C 140C170C Fig 3 2 Saturation time for desiccant dehumidifi er dehumidifi er with varying air mass fl ow rates at different desiccant active temperatures The desiccant is able to reduce the relative humidity to 40 45 and 50 with respect to the air fl ow rates Fig 3 3 shows the dehumidifi cation capacity of the desiccant wheel with varying air mass fl ow rates of air The dehumidifi cation capac ity is almost linearly proportional with air fl ow rates since mass fl ow rate is always a dominant factor The maximum dehumidifi cation capacity was 2 673 kg h at air mass fl ow rate of 243 L h 1 0 0 5 1 1 5 2 2 5 3 2612312011711411118151 Mass air flow rate kg h Dehumidification capacity kg h Fig 3 3 Dehumidifi cation capacity 4 A S Binghooth Z A Zainal Energy and Buildings 51 2012 1 5 0 5 10 15 20 25 30 1110987654 Tc w i Temperature C TccTRTc w o Fig 3 4 The response of TCC TRand TC W O 3 2 Hydronic radiant cooling system Fig 3 4 shows the response of TCC 3 m above the fl oor TR and TC W O with varying TC W I The minimum temperature of TC W I was 6 C provided via a chiller The TCC TRand TC W O are linearly pro portional with TC W I TRis high because TC W I affects the air room temperature due to heat gain inside the room and the position of the chilled ceiling It was observed that when TC W I stabilized at 6 C the difference in TCC TRand TC W O were 14 C 24 C and 10 C respectively Thus the following equations 2 a 2 c at steady state condition are derived TCC TC W I 8 2 a TR TC W I 18 2 b CC W O TC W I 4 2 c When TC W I increases by 1 degree above the minimum value of steady state the TCC TRand TC W O increased by 1 0 5 and 1 degree respectively Thus the following equations 3 a 3 c at steady state condition are derived TCC 1 TC W I 1 3 a TR 1 TC W I 0 5 3 b CC W O 1 TC W I 1 3 c where TCC 1 TR 1and CC W O 1are the difference values related to the TC W I beyond 6 C steady state Thermal comfort condition can be evaluated by determining the comfortable room temperature TC Optimization was carried out based on lower power consump tion for economical reason Fig 3 5 shows the effect of varying TCCat different HCCon TR TRof 24 24 5 C can be provided at different TCC and HCC Points 1 2 3 4 and 5 are within the thermal comfortable condition Minimum HCCof 2 m is the most economical with low power consumption of 2 kWh However for higher HCCof 3 m the power consumption were 3 and 3 5 kWh at TCCof 14 C and 15 C respectively Dew point temperature is an important factor to be considered in order to avoid condensation on the chilled panel sur face The effect of increasing relative humidity on the chilled panel surface was observed by the occurrence of condensation on the panel s surface Figs 3 6 3 8 show the effect of increasing relative humidity on room dew point temperature at different HCCposi tions of 3 2 5 and 2 m above the fl oor with varying the TCC It was observed that at 50 RH condensation does not occur at all HCCand TRdue to the room dew point temperatures being lower than the TCC Thus the chilled ceiling is safe to operate without condensation at 50 RH Condensation occurred signifi cantly at all room tem peratures at all HCCwhen relative humidity ranges between 70 21 5 22 22 5 23 23 5 24 24 5 25 25 5 26 26 5 1918171615141312 CC surface temperatur C Room temperature C TR 3 m T R 2 5 mT R 2 m Fig 3 5 Thermal comfort temperatures condition 10 12 14 16 18 20 22 24 40 45 50 55 60 65 70 75 80 85 90 Relativr humidit y Dew point temperature C CC T 14 CCC T 15 C CC T 16 CCC T 17 CCC T 18 C Fig 3 6 The effect of RH on room dew point temperature within HCCof 3 m and 80 Therefore to operate chilled ceiling for the hydronic radi ant cooling in Malaysian climate it is preferred to control relative humidity to be about 50 or below with TCCof 14 18 C regardless of chilled ceiling height However for 60 relative humidity only HCCof 2 m at all TCCis possible 10 12 14 16 18 20 22 24 40 45 50 55 60 65 70 75 80 85 90 Relati ve hum idity Dew point temperature C CC 14 CCC 15 CCC 16 CCC 17 CCC 18 C Fig 3 7 The effect of RH on room dew point temperature within HCCof 2 5 m A S Binghooth Z A Zainal Energy and Buildings 51 2012 1 5 5 10 12 14 16 18 20 22 24 85 80 75 70 65 60 55 50 45 40 Relative humidit Dew point temperature C CC 14 C CC 15 C CC 16 C CC 17 C CC 18 C Fig 3 8 The effect of RH on room dew point temperature within HCCof 2 m 4 Conclusion Desiccant dehumidifi cation shows good performance by reduc ing the relative humidity to about 40 with mass fl ow rate of air 243 L h 1without heating for 10 min with dehumidifi cation capac ity of 2 673 kg h Chilled water temperature of 6 10 C was able to maintain the chilled ceiling panel and room temperatures within the thermal comfort requirements Chilled panels present its capa bility to operate at low temperature of 14 C with relative humidity of 50 without condensation occurring The desired thermal com fort condition for this investigation was ranged between 24 C and 24 5 C at HCCof 2 m above the fl oor when TCCof 18 C HCCof 2 5 m above the fl oor when TCCof 15 C and HCCof 3 m above the fl oor when TCCof 14 C Minimum HCCof 2 m provided the best value with low energy consumption Acknowledgment The authors would like to thank the Universiti Sains Malaysia Fellowship scheme for the fi nancial support References 1 N Subramanyam M P Maiya S S Murthy Application of desiccant wheel to control humidity in air conditioning system Applied Thermal Engineering 24 17 18 2004 2777 2788 2 D G Waugaman A Kini C F Kettleborough A review of desiccant cooling sys tem ASME Energy Resource Technology 115 1 1993 1 8 3 C S K Ahmed P Gandhidasan A A Al Farayedhi Simulation of a hybrid liquid desiccant based air conditioning system Applied Thermal Engineering 17 2 1997 125 134 4 Z Q Xiong Y J Dai R Z Wang Development of a novel two stage liquid desic cant dehumidifi cation system assisted by CaCl2solution using exergy analysis method Applied Energy 87 2010 1495 1504 5 R Narayanan W Y S Saman D White M Goldsworthy Comparative study of different desiccan