Thermal Performance of PNIPAm as an Evaporative Cooling Medium within a Ventilated Wall Cavity

Learning from the anatomy of leaves, a new approach to bio-inspired passive evaporative cooling is presented that utilizes the temperature-responsive properties of PNIPAm hydrogels. Specifically, an experimental evaporation rate from the polymer, PNIPAm, is determined within an environmental chamber, which is programmed to simulate temperature and humidity conditions common in Phoenix, Arizona in the summer. This evaporation rate is then used to determine the theoretical heat transfer through a layer of PNIPAm that is attached to an exterior wall of a building within a ventilated cavity in Phoenix. The evaporation of water to the air gap from the polymer layer absorbs heat that could otherwise be conducted to the interior space of the building and then dispels it as a vapor away from the building. The results indicate that the addition of the PNIPAm layer removes all heat radiated from the exterior cladding, indicating that it could significantly reduce the demand for air conditioning at the interior side of the wall to which it is attached.