Polyurethane system optimization for energy efficiency

The standard conditions and equipment no longer adequately describe the insulation value of the products in the market place because of the elimination of CFCs from rigid polyurethane foam. As CFCs were replaced with more environmentally friendly HCFC, HFCs, carbon dioxide and hydrocarbons for foam expansion, the thermal efficiency of the insulation products produced with these blowing agents became confused and complex. This confusion arose due to the significantly differing boiling points of these blowing agents and the resulting dramatic changes of the partial pressure of the gases entrapped within the foam cell with respect to temperature. As a result, the k-factor of rigid polyurethane foams blown with HCFC-22 and KFC-134a are linear with respect to temperature, while foams blown with HCFC-141b, HFC-245fa and HFC-365mfc are not. The potential exists for one polyurethane foam system to provide a superior insulation material at an elevated temperature and not provide this at-a reduced temperature. To obtain a more accurate insulation value,which would reflect the energy efficiency of the final product measurement of the insulation value of the rigid polyurethane foam under actual use temperature is important. This paper describes the k-factor of rigid polyurethane foams over a mean temperature range from 17 degrees F to 75 degrees F (-8 degrees C to 24 degrees C). Blowing agents which are Liquid at room temperature, such as HCFC-141b, HFC-245fa, HFC-365mfc, n-pentane, c-pentane and isa-pentane, were evaluated. Gaseous blowing agents, such as HCFC-22 and HFC-134a, were also evaluated, as well as blends of Liquid and gaseous blowing agents. The use of this technique allows the end consumer of rigid polyurethane foam systems to evaluate the energy efficiency of various systems dependent upon the actual use temperatures of the specific application. A more informed consumer can then make the appropriate system choice.