Simple thermal evaluation of building envelopes containing phase change materials using a modified admittance method

This paper extends the admittance method to predict the diurnal energy flux reduction Er associated with adding microencapsulated phase change materials (PCMs) to single and multilayer building envelopes. The effects of phase change on the thermal load through composite building walls were accounted for by modifying the decrement factor fAM and time lag ϕAM. The procedure was demonstrated for single and multilayer PCM-composite walls subjected to a constant indoor temperature and to (i) a sinusoidal sol-air outdoor temperature, (ii) a non-sinusoidal idealized sol-air temperature, or (iii) a sol-air temperature based on weather data for three different days in California climate zone 9 (Los Angeles, CA). In all cases, the analytical results for the daily thermal load passing through PCM-composite walls agreed very well with those predicted using detailed finite element simulations. The computational speed and simplicity of this procedure can enable straightforward evaluation of the energy benefits of PCM-composite walls via user-friendly design tools and platforms.