heat pump, membrane, low global warming potential, dehumidification
Membrane based heat pumps systems have attracted the attention of many research groups as a potentially more environmentally friendly alternative to conventional vapor compression systems that are being used for space cooling in 90% of the buildings in the United States. A membrane heat pump essentially combines an indirect evaporative cooler with a vacuum dehumidification process to provide sensible and latent cooling to a conditioned space. Membrane heat pumps potentially consume significantly less energy during the dehumidification process and do not use any refrigerant other than water, thereby eliminating the need of refrigerant compressor and the need for high global warming potential working fluids. Furthermore, membrane based systems effectively decouple latent and sensible cooling functions; allowing a possible novel control strategy to maintain thermal comfort as a function of dry bulb and relative humidity versus controlling to a fixed dry bulb temperature only. These features can lead to significant energy savings and increase in the system energy performance. Several prototypes systems have been developed, with reported claims of EER of 26. However, no detailed analysis is publically available which demonstrates the capability of these systems in different climate zones. Thus, the objective of this paper is to simulate seasonal performance in different climate regions within the United States. This is accomplished by developing a full thermodynamic cycle model of a representative membrane heat pump system, and then sizing the heat and mass transfer components to provide 5 tons of cooling at nominal rating conditions. Then, using the designed system, the seasonal performance of the system in different climate zones in the United States will be investigated. Energy performance ratings such as COP and EER as a function of time of year and location, as well as other utility parameters such as energy cost savings and annual water consumption will be evaluated. Finally, performance will be compared to conventional vapor compression systems.