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1、Energy 32 (2007) 1749–1760Energy consumption analysis on a dedicated outdoor air system with rotary desiccant wheelWeiwei Liua, Zhiwei Liana,?, Reinhard Radermacherb, Ye YaoaaInstitute of Refrigeration and Cryogenics, Sh
2、anghai Jiao Tong University, 800 Road Dongchuan, Shanghai 200240, China bDepartment of Mechanical Engineering, University of Maryland, College Park, MD 20742-3035, USAReceived 18 October 2005AbstractA dedicated outdoor a
3、ir system (DOAS) with rotary desiccant wheel is the combination of a desiccant dehumidification system and a vapor compression refrigeration system. An energy consumption model of this hybrid DOAS is established for its
4、analysis. Coefficient of performance, COP, is appropriately defined for evaluation on performance of the hybrid DOAS. The results indicate that, compared with a conventional DOAS, energy savings are possible for the sugg
5、ested DOAS, when solar energy or natural gas is used for regeneration. Ventilation air flow rate, temperature or humidity of outdoor air, as well as regeneration-to-process air ratio, influence the energy consumption and
6、 the COP of the hybrid DOAS, greatly. r 2006 Elsevier Ltd. All rights reserved.Keywords: Dedicated outdoor air system; Energy consumption; Rotary desiccant wheel; Hydrid1. IntroductionThe severe acute respiratory syndrom
7、e (SARS) has made people attach importance to the possibility of disease transmission by air. So, as the most important air-handling unit, air conditioning systems become the focus of attention. Aiming at the challenges
8、by the SARS calamity for air conditioning systems, it is required that the air conditioning systems should not only maintain the thermal and humidity environment for comfort and the indoor air quality for health, but als
9、o reduce humidified surfaces and the possibility of internal air circulation between different zones [1]. A dedicated outdoor air system (DOAS) is a good choice to meet these new requirements. In this system, outdoor air
10、, the ventilation makeup air, is separately conditioned without first being mixed with indoor air, with the entire humidity load and part of sensible load handled in the process (other part of sensible load is handled by
11、 the indoor air conditioning unit) [2,3]. Because indoor air doesnot recirculate among different zones, the possibility of disease transmission by it is greatly reduced. A conventional DOAS uses cooling coils to accompli
12、sh dehumidification. On the one hand, higher the humidity load, lower is the dew-point temperature required. But, the evaporator temperature of the chiller must not go below 0 1C, the freezing point, which means that the
13、 conventional DOAS cannot be applied when the required dew-point temperature is lower than 0 1C. Therefore, solving the problem of the limitation on the dew-point temperature is the crux to employ DOAS widely. On the oth
14、er hand, there is condensation water during the cooling dehumidification process, which is a breeding ground for mildew. Desiccant technology is a promising alternative for dehumidification. Compared with cooling dehumid
15、ifica- tion, it has lots of advantages, three of which are that no limitation on the dew-point temperature, no condensation water, and having greater energy saving potential. So, a DOAS using desiccant dehumidification w
16、ill be an ideal system without the problems existing in the conventional DOAS. In this paper, a DOAS with rotary desiccant wheel is suggested.ARTICLE IN PRESSwww.elsevier.com/locate/energy0360-5442/$ - see front matter r
17、 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2006.11.012?Corresponding author. Tel.: +86 21 34204263; fax: +86 21 34206814. E-mail address: zwlian@sjtu.edu.cn (Z. Lian).effects of these factors on the hy
18、brid DOAS are also studied here.2. DOAS with rotary desiccant wheelIn a conventional DOAS (as shown in Fig. 1), outdoor air is first dehumidified by cooling below its dew-point temperature (the entire humidity load and p
19、art of sensible load are handled in the process), and then reheated to a proper temperature (when required) via a heater, before entering the room. The indoor sensible cooling unit handles other part of the sensible load
20、. The corresponding psychrometric process is indicated in Fig. 3(a). As shown in Fig. 3(a), delivered into the room, the ventilation air absorbs excess heat and moisture in the room, with both its temperature and humidit
21、y increasing to the same with indoor air (from point ‘‘O’’ to point ‘‘N’’). As depicted in Fig. 2, the suggested DOAS with rotary desiccant wheel is the combination of a desiccant dehumi- dification system (DDS) and a va
22、por compression refrig- eration system (chillers). It is the same in the two DOAS that outdoor air must remove the whole humidity load and part of the sensible load, and the indoor sensible cooling unit handles the other
23、 part of the sensible load. But the means of dehumidification is different. In the hybridDOAS, outdoor air, the process air, is dehumidified when passing through the desiccant wheel. In this process, its temperature incr
24、eases, which is the result of the dehumi- dification effect and the heat transfer from the regeneration airstream via the desiccant wheel. As the process air flows through the heat recovery wheel, the heating effect is p
25、artially offset by transferring heat from the process air to the cooler incoming regeneration air. The process air is further cooled to the required temperature in the chiller 1, and then enters the room. The whole psych
26、rometric process is shown in Fig. 3(b), and it can be seen that there is truly no limitation on the dew-point temperature in the suggested hybrid DOAS. In the DDS, the regeneration air is heated to a sufficiently high te
27、mperature to bring out the moisture extracted by the sorbent in the desiccant wheel. Before entering the heater, the regeneration air is preheated by the heat recovery wheel, which leads to less energy consump- tion. The
28、 regeneration air can be outdoor or indoor air or a mixture of both. In order to avoid the pollution of the process air by the regeneration air, because of the leakage between the process area and the regeneration area,
29、outdoor air is a better choice. In the two DOAS, heat recovery of the exhaust air from the room is not considered here.ARTICLE IN PRESSDESICCANT WHEELHEAT RECOVERY WHEELHEATEROAExhaust r4OA Exhaust CHILLER1INDOOR SENSIBL
30、E COOLING UNITCHILLER2ROOM DDSP1 P2 P3 O Nr3 r2 r1Fig. 2. Schematic of a suggested DOAS with rotary desiccant wheel.CHILLER1 HEATERROOMExhaust OACHILLER2INDOOR SENSIBLE COOLING UNITW O N LFig. 1. Schematic of a conventio
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