The radiant time series method (RTSM) is a cooling load calculation procedure developed by ASHRAE as a simplified companion to the rigorous heat balance procedure. The RTSM was initially verified for a large parametric set of zone configurations by comparing cooling loads predicted by the RTSM with cooling loads predicted by the heat balance method. The experimental results reported in this paper demonstrate the validity of the previous parametric studies and confirm the significance of the so-called “adiabatic zone assumption,” which results in underprediction of conduction losses by the RTSM for highly glazed spaces. The investigation also demonstrated the importance of calculating the reflected solar radiation incident on the interior surfaces of the windows. The expected error in the RTSM for highly glazed spaces can be reduced up to 80% by accounting for reflected visible radiation leaving the space. Including a reflected solar radiation calculation in the RTSM resulted in predicted cooling loads within 15% of measured data for passive sun spaces with well-defined zone configuration parameters. Consequently, the study not only demonstrates the validity of the RTSM for standard zone configurations, but it also suggests that the RTSM can be used to obtain a first order estimate of cooling loads for solar heat gain dominated spaces.

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