Optimum position and distribution of insulation layers for exterior walls of a building conditioned by earth-air heat exchanger

Abstract

In this paper, the optimum thermal insulation configuration in buildings with earth-air heat exchanger has been calculated based on time lag and decrement factor theory. In previous studies which all focused on buildings with conventional air-conditioning systems, the indoor air temperature has been assumed constant, while it is not valid for buildings conditioned by earth-air heat exchanger. Thereby, optimal insulation configuration in these buildings seems to be different from what previously reported. In this study, transient heat conduction equation is solved numerically for different multilayered wall configurations. Results showed that three-layer insulation, which is the optimal layout for buildings with conventional air-conditioning systems, is not desirable for buildings with earth-air heat exchanger. In such buildings, a wall with single-layer insulation at the outside and a wall with two layers of insulation (middle and outside) have the best performance, respectively. In these configurations, the decrement factor is 35% smaller, and the time lag is an hour longer than those of three-layer layout. Furthermore, results indicated that the optimum insulation configuration is independent of the system design characteristics and building wall materials.