A new procedure for calculating periodic response factors based on frequency domain regression method

The radiant time series method (RTSM) takes advantages of the fact that design cooling load calculations are based on steady periodic excitations. The main difference between the RTSM and the other cooling load calculation methods is that the periodic response factors of the RTSM are restricted to calculating the conduction heat gain through building elements under periodic outdoor conditions, which simplifies the computational procedure significantly. It is vital to have a reliable method or procedure to accurately calculate the periodic response factors of various types of walls and roofs. In this study, a procedure, based on the frequency-domain regression (FDR) method, is developed to directly and accurately calculate the outside, across and inside periodic response factors of a multilayer wall or roof from its geometric and thermal properties. At first, a polynomial s-transfer function is established from the frequency characteristics of the wall or roof using the FDR method. The periodic response factors are then generated from the poles and residues of the polynomial s-transfer function. Computational tests show that the FDR method provides an accurate and hopefully better alternative procedure to calculate periodic response factors. Using this procedure, the periodic response factors of various representative wall and roof types are calculated and compared with those calculated by other conventional methods. Some results, particularly of the periodic response factors whose CTF coefficients tabulated in the ASHRAE Handbook are inaccurate, are presented and evaluated.