Recovering latent and sensible energy from building exhaust with membrane-based energy recovery ventilation

Abstract

Energy can be recovered from building exhaust via water vapor transport and heat transfer across gas permeation membranes, thereby reducing latent and sensible loads during both heating and cooling seasons. The process known as membrane-based energy recovery ventilation (ERV) has been commercialized by several HVAC manufacturers, but so far has mostly been offered in flat sheet membrane configurations. In this study, we investigate the use of polydimethyl siloxane membranes packaged into hollow fiber modules, which offer the advantage of high packing density, but which have so far not been commercially adopted due to concerns about parasitic pressure loss. We evaluate here the work required to overcome friction of circulating air through membrane fibers, and we assess the net energy savings that account for these losses relative to the energy saved by water vapor and heat transfer. The concept of normalized net energy savings is introduced to provide a useful metric for comparing performance independent of flow volume and membrane size, and we observe up to 2.75 W/m2 of net latent energy savings. Case studies are used to illustrate the potential of this technology, and energy savings of 1.15 and 1.03 kWh/yr/lpm are demonstrated for Detroit, MI, and Houston, TX, respectively.