GoldStar GHD Dehumidifier Review

A typical dehumidifier wheel system is shown in Figure 1. In this system, there are two flow streams--supply air and regeneration air. As the dehumidifier wheel rotates, the water molecules are removed from the supply air and transferred to the regeneration air. Adjacent to this dehumidifying device is a heating device to heat the regenerator inlet air to a temperature much higher than the supply air. This elevated temperature is necessary to regenerate the desiccant coating on the wheel matrix for dehumidification of the supply air. The heating device can be an electric or gas heater, and it may be preheated upstream by a supply of waste or solar-heated air.

Dehumidifier wheels have very different operating conditions than energy wheels, although their construction is usually similar and in some cases they are identical. Just how each wheel matrix design and desiccant coating design impact dehumidifier wheel performance is not well explained in the literature. A comprehensive theory of how dehumidifier wheels can be expected to perform at various wheel speeds, face velocities, and fractions of the regenerator face area relative to the supply air face area would not only give the manufacturer of the wheels better design tools, it would give the HVAC system designer improved wheel selections and specification of operating conditions. The purpose of this research is to sort through this dearth of information.

In applications of desiccant dehumidifiers in HVAC systems, the coefficient of performance (COP) is often used for evaluating their performance. The COP is a dimensionless number and is defined as

COP = [latent energy exchange rate/net auxiliary energy input rate], (1)

Where the net energy input rate is taken to be the auxiliary heat energy necessary for regeneration (Harriman and Kiser 2004). Equation 1 uses the energy balance of the first law to analyze and design the dehumidifying system, as shown in Figure 1. It is clear that the waste heat utilization in the system design can reduce, and possibly eliminate, the purchase of thermal energy for regeneration. Due to external heat added, the performance of a dehumidifier wheel cannot be uniquely characterized by the COP unless, as is specified in ASHRAE Standard 139-1998 (ASHRAE 1998), the inlet air properties to the air heater are specified.

Prior to considering the capital cost and the cost effectiveness of this system, it is convenient to only consider this simple air dryer system without other HVAC equipment when evaluating the performance of dehumidifier wheels. The main objective of this system is to remove moisture from the supply air so that the bulk mean outlet air humidity, [[bar. W]. Sub. So], is significantly lower than the inlet humidity, [W.sub.si]. At the same time, the energy input rate to the regenerator auxiliary air heating device should be low, and the temperature rise in the supply air, [[bar. T]. Sub. So should be low. In general, both the operation of dehumidifier wheels and the heating device must be considered as a system when auxiliary heating is required. Unlike energy wheels with normally equal ventilation supply and exhaust mass flow rates and equal flow area regions of the wheel sector surface (i.e., 180[degrees]), the regenerator air mass flow rate, [m.sub.r], need not equal the supply air rate, [m.sub.s]. Also, the dehumidifier wheel angular segment for regeneration, [[theta]. sub's], does not have to equal the supply air segment, [[theta]. sub's].