A response-factor method for calculating coupled heat and moisture transfer in building

Analytical solutions for coupled diffusion of heat and moisture through a material are used to develop a generalisation of the wellknown 2 x 2 matrix method for describing heat flow only. A new 4 x 4 matrix is derived which relates temperatures, humidities, heat flows and moisture flows at one surface of a slab with those at the other. Multilayer slabs and surface boundary conditions, including moisture-impermeable surfaces, are easily handled by multiplication of matrices. The method is well suited for implementation in an existing program, CHEETAH, which was designed to calculate hourly temperatures and sensible air?conditioning loads in small buildings, using real weather data. The new version calculates hourly absolute humidities and latent air?conditioning loads in addition to temperatures and sensible loads, taking into account the effects of outdoor air temperature and humidity, solar radiation, ventilation, internal sources of heat and moisture, and the presence of adsorbing materials. This paper briefly outlines the theoretical basis of the method, and presents some results showing the effects of adsorbing materials on temperatures and humidities in a simple building.