Solar load ratio design tool predictions compared to level B monitoring data

The authors generated solar load ratio (SLR) design tool auxiliary energy predictions and compared them with estimates obtained from level B monitoring program for 54 sites throughout the United States. On the average, over all houses monitored, the difference between the predicted and measured auxiliary energy values was relatively small. For a given house, however, the discrepancy between the predicted and measured auxiliary was relatively large on the average. The root mean square difference is approximately 30% of the mean measured auxiliary. Using historical data from weather records of nearby cities in place of measured weather data at the actual site introduced little additional discrepancy between the predicted and measured auxiliary energy values. Much of the discrepancy for individual houses appeared to be due to uncertainties in the measured heat loss coefficient values and measured solar radiation, and limitations in the SLR method. Perhaps this study's main lesson for designers is that on the average, over several buildings, SLR predictions will be relatively accurate compared to measurements of auxiliary. However, for a given passive solar building, the predictions can vary significantly from measurements.