The Humid Threshold:  Cooling hot, humid climates via membrane dehumidification

The Humid Threshold: Cooling hot, humid climates via membrane dehumidification

By Pamela Cabrera (MDes ’19); advised by Jonathan Grinham

The thesis centers on the design of a membrane screen for cooling hot, humid climates via dehumidification. Humidity drives the cooling load in humid climates, where it is estimated that up to 80% of the work of a typical HVAC is solely on dehumidification.[1] Membranes have the potential to separate substances through diffusion, a passive process that is isothermal, and therefore selecting water vapor molecules out of air through membranes can be less energy intensive than condensing the water vapor with typical vapor compression systems.[2],[3],[4]While membrane selectivity is a well-known field of study, found throughout nature and applied across industries, architecture has only regarded membranes as barriers. This thesis investigates the possibility of using membranes as a building screen material to dehumidify incoming air as it is drawn into a building. This application could lower the latent heat that drives air conditioning demand in humid climates, and thus increase natural ventilation potential and other passive dry-bulb cooling strategies.

In comparison with desiccants and condensation processes, membrane dehumidification extracts water vapor as a gas, without a phase change, meaning that there is no heat byproduct from the process. Through a mixed-method study that included experimentation, design prototyping, and simulation, the thesis proposes a Miura geometry membrane arrangement to deploy as a building screen. The geometry increases surface area and induce flow turbulence for higher air-membrane contact. Two membrane materials are tested under different form configurations, a dry membrane (PVA with LiCl) and a supported liquid membrane (PTFE and CA with PEG400). The results show that the proposed design has a higher impact on the performance than the difference in material properties. This application could reduce the need for vapor compression mechanical systems, reduce the operational energy of buildings and create more resilient and healthier spaces by allowing natural ventilation in humid climates.

 

[1] Bui, D. T., Ja, M. K., Gordon, J. M., Ng, K. C., & Chua, K. J. (2017). A thermodynamic perspective to study energy performance of vacuum-based membrane dehumidification. Energy, 132, 106-115.

[2] Yang, B., Yuan, W., Gao, F., & Guo, B. (2015). A review of membrane-based air dehumidification. Indoor and Built Environment, 24(1), 11-26.

[3] Woods, J. (2014). Membrane processes for heating, ventilation, and air conditioning. Renewable and Sustainable Energy Reviews, 33, 290-304.

[4] Mahmud, K., Mahmood, G. I., Simonson, C. J., & Besant, R. W. (2010). Performance testing of a counter-cross-flow run-around membrane energy exchanger (RAMEE) system for HVAC applications. Energy and Buildings, 42(7), 1139-1147.