Diseño

Energy and Buildings 42 (2010) 2416–2423

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Energy and Buildings
journal homepage: www.elsevier.com/locate/enbuild

The effects of operational conditions of the desiccant wheel on the performance of desiccant cooling cycles
Ghassem Heidarinejad ∗ , Hadi Pasdarshahri
Tarbiat Modares University, PO Box 14115-143, Tehran, Iran

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a b s t r a c t
A desiccant cooling model is developed and applied to the ventilation, recirculation, makeup, and mix modes of the operating system. The mathematical model is based on the transient coupled heat and mass transfer and is used to predict the performance of the system under various design and operational conditions. The numerical results are validated using experimentalmeasurements. The effects of the regeneration temperature and rotational speed of the desiccant wheel on the COP and output cycle temperature are investigated. The results show the availability of an optimum regeneration temperature and rotational speed in which the output cycle temperature has a minimum value. The optimum regeneration temperature and rotational speed are detected and shown on thePsychrometric charts. Calculating these values has a significant effect on the energy use of these cycles. © 2010 Elsevier B.V. All rights reserved.

Article history: Received 26 April 2010 Accepted 14 August 2010 Keywords: Desiccant cooling Desiccant wheel Numerical simulation Air conditioning

1. Introduction Recently, evaporative and desiccant cooling technology systems are increasingly beingdeveloped as an alternative to the conventional vapor-compression systems. Desiccant cooling systems are heat driven cooling units. The basic component in the operation of the system is the use of a desiccant wheel in which air is dehumidified. Then, the resulting air is cooled in a heat exchanger and is further cooled by an evaporative cooler. Afterwards, the resulting cooled air is directed intothe room. A heat supply is needed in the system to regenerate the desiccant. Renewable energy such as solar and geothermal heat as well as waste heat from any conventional fossil fuels can be used because a low grade heat, at a temperature of about 60–95 ◦ C is needed. The major advantages of desiccant cooling are: • CFCs free; thus, the system is environmentally friendly. • The system causes muchelectrical power savings, mainly in places where the thermal energy sources are easily found. • Construction and maintenance are simple. Because of these advantages, much effort is devoted in the research and application of desiccant cooling components, espe-

∗ Corresponding author at: Tarbiat Modares University, Mechanical Engineering Department, PO Box 14115-143, Tehran, Iran. Tel.: +98 2182883361; fax: +98 21 88005040. E-mail addresses: gheidari@modares.ac.ir, gheidari@alum.mit.edu (G. Heidarinejad). 0378-7788/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2010.08.011

cially desiccant wheels [1–9]. Also, there are studies concentrated on the potential use of desiccant cooling systems in various locations in the USA and Europe [10–12]. Zhangand Niu [13] indicated that a chilled-ceiling combined with desiccant cooling could save up to 40% of primary energy consumption when compared to a conventional constant air volume system. Sand and Fischer [14] have shown that by designing a combined vapor-compression/active desiccant system in which the desiccant component is positioned after a conventional cooling coil, the dehumidificationeffectiveness of the desiccant is significantly enhanced. Dai et al. [15] conducted a comparative study of a standalone vapor-compression system (VCS), the desiccant associated VCS, and the desiccant and evaporative cooling associated VCS. They found an increase of the cooling load production by 38.8–76% and an increase of COP by 20–30%. Mazzei et al. [16] compared the operating costs of the desiccant...