Until recently, the most common use of reference year data has been related to energy calculation. Representative weather data for use in moisture design calculations is as critical as other parameters required for heat, air, moisture (HAM) simulations e.g., material data or indoor climate data. The objective of ASHRAE’s research project, RP-1325 (2010), was to develop a method for generating more representative design weather years for use in heat and moisture performance predictions of building enclosure systems. Existing methods for selecting moisture design reference years have been reviewed. A new method was developed that provides an improved approach for selecting the most critical years in terms of hygrothermal performance. During the development of the method, eight U.S. locations were investigated, with 30 years of hourly weather data for each location. Another four locations were used to validate the accuracy of the method. The new method was applied in selecting the hygrothermal weather year for European location.

The performance of six different building enclosure components, 4 walls and 2 roofs, was investigated using existing hygrothermal simulation models. The effect of weather data on the performance of building enclosure components was evaluated. The new method allows for selection of weather years that are among the most severe for the simulated structures. The results show that weather data is an essential component of design criteria.