Utilization of heat gains from transparently insulated collector-storage walls

Transparently insulated massive walls reduce heating loads to an impressive degree. The heating season of a building can be shortened by several months. Good transparent insulation materials (TIM's) have transmittances of up to 70% for diffuse irradiation and U-values in the range from 0.5 to 1.5 Wm E-2 K E-1. The combined effect of thermal insulation and collecting solar radiation allows the use of these materials not only for southern, but also for other orientations. Steady-state theory gives upper limits for the potential of this passive component to reverse the heat flow towards the interior. Experimental data indicate that it may be applied for periods greater than the time constant of the wall. Apart from overheating in summer, which makes some shading device necessary in most cases, there is always some mismatch between solar heat gains and heating demand. This leads to a non-utilizable fraction of the solar gains. Simulations allow the inclusion of dynamical, non-linear effect s and non-utilizability depending on the storage capacity of the system, but easy and rapid design methods are desirable. The Solar-Savings-Fraction method of Heidt (1985) and the method of Monsen (1982) shall be compared with simulation results. Results show that the most relevant parameters can be incorporated in the steady-state theory. Corrections are due to the storage capacity of the house, which influences utilizability especially in spring and autumn. (ISE)