Solar Engineering of Thermal Processes, 4th Edition

22.4 Unutilizability Design Method: Collector-Storage Walls

The unutilizability concept developed for direct-gain systems has been applied, with modifications, to collector-storage wall systems (Monsen et al., 1982). The presence of the wall introduces significant differences in the manner in which the energy balances on the building are written, in the definition of the critical radiation level and SLR, and in the form of the correlations for solar contribution. As with the direct-gain system, the double-U method establishes the limiting cases of zero- and infinite-capacitance buildings; where a real building performance lies between the limits and is determined by correlations based on simulations. The calculations are again done monthly, with the significant final result being the annual amount of auxiliary energy needed for the passively heated structure.

The monthly energy flows in a collector-storage wall building are shown schematically in Figure 22.4.1. The heating loads are shown in two parts. Load is that which would be experienced if the collector-storage wall were replaced by an adiabatic wall. It is the same as the net reference load in the SLR method and can be calculated by conventional means such as the degree-day method (Equation 22.4.1a). The load is the monthly ...