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Single-stage and double-stage photovoltaic driven regeneration for liquid desiccant cooling system

Single-stage and double-stage photovoltaic driven regeneration for liquid desiccant cooling system

Single-stage and double-stage photovoltaic driven regeneration for liquid desiccant cooling system

Single-stage and double-stage photovoltaic driven regeneration for liquid desiccant cooling system

Xiu-Wei Li a ,b ,⇑,Xiao-Song Zhang a ,Shuo Quan c

a

School of Energy and Environment,Southeast University,210096Nanjing,China

b

College of Power Engineering,Nanjing University of Science and Technology,210094Nanjing China c

China Wuzhou Engineering Corporation Ltd.,100053Beijing,China

a r t i c l e i n f o Article history:

Received 21September 2010

Received in revised form 16June 2011Accepted 22June 2011

Available online 31July 2011Keywords:

Liquid desiccant Regeneration Photovoltaic Electrodialysis

a b s t r a c t

Liquid desiccant cooling system (LDCS)is a novel air-conditioning system with good energy saving potential.However,the present LDCS has a poor performance,mainly because the conventional thermal regeneration method wastes too much energy during the regeneration process.To improve that,photovoltaic-electrodialysis (PV-ED)regeneration method is introduced:it has a higher performance by using solar photovoltaic panels to drive an electrodialysis regeneration process.To further explore the PV-ED method,both single-stage and double-stage photovoltaic-electrodialysis regeneration systems are presented in this paper.Analysis is made on these two systems and some influential factors are inves-tigated.It reveals that the concentration difference between the desiccant solution before and after regeneration has a strong impact on system performance.Moreover,comparison is conducted between the single-stage and the double-stage systems,the results show that the double-stage system is more energy-efficient and it can save more than 50%energy under optimized working conditions.

Ó2011Elsevier Ltd.All rights reserved.

1.Introduction

Energy conservation is a hot topic nowadays.As to buildings,it would be favorable to make air-conditioning system more energy efficient and less dependent on electric energy produced from fos-sil fuels.At present,the most widely used air-conditioning system is vapor compression system,but it consumes large amount of electric power and the refrigerant may cause some environmental problems.To replace vapor compression system,many alternative air-conditioning systems have been developed.Among them,liquid desiccant cooling system (LDCS)has attracted ever-increasing attention from both researchers and consumers as it can make good use of kinds of renewable energies and is energy conservative [1–3].

In general,the regeneration process of LDCS is always driven by thermal energy (TH)[1–4],and that is also the most researched regeneration pattern of LDCS [5–10].Nevertheless,this regenera-tion pattern has some disadvantages:For one thing,the regenera-tion process heavily depends on the condition of the surrounding atmosphere and can be unreliable if the weather is hot and humid.For another thing,the desiccant solution is ‘‘hot’’after regenera-tion,but this high temperature is no good for the following dehu-midification process.Thus,excessive cooling measures must be taken to remove the harmful heat,which inevitably causes a waste of energy.Moreover,this regeneration manner can bring in air pol-lution,because it proceeds in an open cycle and some droplets of the solution may sneak into the air of the environment.To make improvement,Al-Farayedhi et al.[11]proposed the RO (reverse osmosis)regeneration method by using membrane technology.And that work has been extended [12]with the analysis of a liquid desiccant based two-stage evaporative cooling system using MFI zeolite membrane,which shows this new method could be a fine alternative plan for liquid desiccant regeneration.RO method is applicable because the regeneration process can be treated as a desalination process.In the same principle,electrodialysis (ED)method is also a promising choice.

ED method is a technique based on the transport of ions through selective membranes under the influence of an electrical field [13–15].In a conventional ED stack,cation-and anion-ex-change membranes (CM and AM)are placed alternatively between the cathode and the anode.When a potential difference is applied between electrodes,the cations move towards the cathode,and an-ions move towards the anode.The cations go through the cation membrane,which have fixed groups with negative charges,and are retained by the anion-exchange membrane.On the other hand,the anions circulate through the anion-exchange membranes,which have fixed groups with positive charges,and are retained by the cation-exchange membranes.This movement produces a rise in the ions concentration in some compartments (concentrate compartments)and decrease in the adjacent ones (dilute compart-ments).So by this means,both the concentrated desiccant solution and pure water can be obtained.

0306-2619/$-see front matter Ó2011Elsevier Ltd.All rights reserved.doi:10.1016/j.apenergy.2011.06.052

⇑Corresponding author.Address:School of Energy and Environment,Southeast

University,210096Nanjing,China.Tel.:+8602583792722.

E-mail address:good2007best@http://doc.xuehai.net (X.-W.Li).

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