Octadecane filled bubble wrap as phase change material layers to smooth temperature variations of buildings during summer time. An experimental study

Phase change materials (PCM) have good potential to be used in passive thermal energy systems to mitigate the temperature variations of buildings. Octadecane wax, with a 28 °C solid/liquid transition temperature and high fusion/crystallization enthalpy of 240 J/g is a good PCM candidate to improve the thermal management of living spaces because the comfort temperature is typically between 25 °C and 30 °C. To validate experimentally the capacity of octadecane to smooth the temperature variations around the comfort temperature, polyethylene bubble wrap, a standard insulating layer found in building structures is used as octadecane container support. About 1.5 L of wax per square meter of bubble wrap can be retained in a single layer of this insulating film, giving about 260 kJ/m2 of latent energy. A true daily temperature cycle, corresponding to a typical summer day in Los Angeles, is used to study the temperature gaps and delays induced by the octadecane filled bubble wrap. Stacking several layers of this PCM wrap makes warming/cooling delays and temperature gaps to increase rapidly. Indeed, four layers give about 1000 kJ/m2 of latent energy and prevent the temperature on the back side of the stack to exceed the fusion temperature of octadecane for more than 10 h. When the « outside » temperature is at its maximum at midday, the temperature difference between the two faces of the stack reaches −2.8 °C. A comfortable 28 °C temperature is maintained during 12 h while, in the same time, the « outside » temperature moves from 30 °C to 22 °C with a peak over 32 °C. This work was performed using only bubble wrap layers, without considering a representative wall or roof structure. In this case, a lower amount of PCM wax would be needed for a similar impact because the other parts of the structure will also play an important role in the thermal dynamic of the building.