Field performance measurements of a heat pump desiccant unit in dehumidification mode T.N. Aynur, Y.H. Hwang *, R. Radermacher Center for Environmental Energy Engineering, University of Maryland, 3163 Glenn L. Martin Hall, College Park, MD 20742, USA 1. Introduction In commercial buildings, indoor temperature control often receives far more attention than the indoor humidity control. Historically, mechanical HVAC systems have focused on control- ling the dry-bulb temperature, and space humidity has not been actively controlled and has often been described as coincidental [1]. However, especially in hot humid climates, moisture-related problems such as indoor air quality, building durability and operating costs of the air conditioning systems do occur. Good humidity control has the potential to reduce the operation and maintenance costs of buildings and to provide a comfortable working environment. For this reason, performance of desiccant based dehumidifiers and their interactions with the air conditioning systems [2–9], and the desiccant materials for these applications [10–12] have been widely studied. Since dehumidification is considered as a key feature of HVAC systems for indoor thermal comfort, it has been investigated [13], and an extensive review has been performed according to the mechanical and chemical dehumidification means [14]. Besides, a hybrid desiccant-assisted pre-conditioner and split cooling coil system, which combines the merits of moisture removal by desiccant and of sensible heat removal by cooling coil, has been investigated [15–19]. The hybrid system is considered as a potential alternative to a conventional vapor compression cooling system. There are also commercial products designed to function as a dedicated outdoor air unit in the market [20,21]. Basically, the desired quantity of outdoor air is drawn into the unit by a fan, and then passed through a filter and a cooling coil. A portion of this air stream is then passed through a desiccant wheel, where it is dehumidified. The remainder is bypassed around the desiccant wheel and mixed with the warmer air stream leaving the desiccant wheel to reach the desired supply air temperature before being delivered to the indoors. Meanwhile, a small outdoor air stream is heated by a heat source such as a gas burner and passed through the regeneration side of the desiccant wheel where it removes the adsorbed moisture and then exhausted outdoors. Despite that large number of studies, the work by Lazzarin and Castellotti [22] is found to be the only self-regenerating heat pump desiccant study. In that study, a liquid heat pump desiccant dehumidifier that can heat, cool and dehumidify the ambient air by an electric vapor compression heat pump system was introduced. The air to be treated, flows thorough a honeycomb cellulose media, where it enters in contact with the concentrated solution, which is previously cooled in the heat pump evaporator. After the process, the air is dehumidified and the solution is diluted. The thermal energy, which is used for the regeneration of the desiccant solution, is supplied to the solution in the heat pump condenser. The hot air enters in contact with hot diluted solution and removes water from it. The hot and wet air is exhausted and the concentrated solution moves towards dehumidification section. The performance of the desiccant unit was investigated Energy and Buildings 40 (2008) 2141–2147 ARTICLE INFO Article history: Received 3 December 2007 Received in revised form 3 April 2008 Accepted 2 June 2008 Keywords: Heat pump desiccant Self regeneration Dehumidification Thermal comfort VRV ABSTRACT The variable refrigerant volume (VRV) air conditioning system needs to be operated in conjunction with a ventilation system, because the VRV system cannot provide any fresh air. The common ventilation unit used with the VRV system is the heat recovery ventilation (HRV) unit. In this study, a new ventilation unit, a self-regenerating heat pump desiccant (HPD) unit, was introduced and the characteristics of the HPD unit was experimentally investigated over a wide range of operating conditions in a field performance test. In addition, the energy saving contribution of the HPD and HRV units to the VRV system was compared. It was found that the HPD unit maintained the target indoor humidity ratio of 10 g/kg throughout the cooling season resulting in a better indoor thermal comfort than the HRV unit. Besides, it was found that the outdoor unit of the VRV system consumed 26.3% less energy for the operation in conjunction with the HPD unit as compared to the operation in conjunction with the HRV unit. ß 2008 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +1 301 4055247; fax: +1 301 4052025. E-mail address: yhhwang@umd.edu (Y.H. Hwang). Contents lists available at ScienceDirect Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild 0378-7788/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2008.06.003