The Reference Period for Predicting Long-Term Thermal Performance of Thermal Insulating Foams

With the advent of thermal insulating foams manufactured with alternative blowing agents, the need for estimating their long-term thermal performance became evident. Two predictive techniques (slicing and scaling [1,2] or slicing and modelling [3,41]) are now considered for different foam products. However, the selection of the reference period for which the thermal performance is evaluated has not received sufficient attention. In this paper, the limit of economic considerations for aging processes is assumed to be fifteen to twenty years. The analysis indicates that for a wide range of thermal insulation products and thickness, the same reference time can be used. The reference time denotes the period of aging when the measured thermal resistivity (inverse of thermal conductivity) represents the timeaveraged thermal resistivity over the considered service life. This paper postulates that the five year reference period should be used for all thermal insulations with thermal performance varying during the service time. This estimate is based on economic analysis and modelling techniques applied to five different cellular plastic insulations and analyzed in three Canadian climates using two heating fuels for comparison. The cost of construction of the wall assemblies and the cost of insulation alternatives, as well as all economic assumptions such as future interest rates, inflation rate and fuel escalation rate, were the same as provided by the provincial authorities for development of the 1995 Canadian Energy Code.