Abstract
Many practical methods for calculating unsteady-state heat conduction of multi-layer walls have been developed in the time-discrete domain. They have some similarities in the basic algorithm to each other and then it is necessary to make clear the structures, the characteristics and the mutual relationships of them. In this paper, we derived systematically a series of calculation formulas in the time-discrete domain by using the pulse transfer functions based on the isosceles triangle or trapezoid hold function. We carried out numerical calculations for the five kinds of multi-layer walls and compared the CPU time and the accuracy of different calculation methods. The conclusions were obtained as follows: (1) Practical formulas for calculating unsteady-state heat conduction are divided into the numerical convolution type and the successive transition type. (2) The response factors method and the transfer function method belong to the numerical convolution type. The first or second common ratio method is thought to be a simplified transfer function method. (3) The successive integral method and the multiple common ratio method belong to the successive transition type. They are caused by the difference of hold function and state variables. (4) The calculating time interval is changeable in the successive transition type and we can treat approximately the time-variable parameter and non-linear problems by the successive transition method. (5) The calculation method used in HASP/ACLD/8001 is a combined type of the numerical convolution type and the successive transition type. (6) CPU time of the successive transition type depends upon the number of index terms composing the characteristic function and it is generally smaller than that of the numerical convolution type.
