Thermal performance test results are used by solar heating designers to compare the performance of competing products. Previous solar collector test methods required that testing be performed during a narrow range of environmental conditions, e.g., conditions of high solar irradiance level and restricted air temperature, etc. In many climates, atmo- spheric conditions differ from these standard test conditions for a significant percentage of the time. Consequently, existing thermal performance test data may be inappropriate to predict collector performance.

To investigate the effect of atmospheric conditions on the thermal performance of solar collectors, an analysis of the heat transfer mechanisms for a variety of collector types was conducted and performance equations that would account for varying atmo- spheric factors developed. To verify these effects and to obtain the coefficients for these equations, a series of solar collector thermal performance tests were conducted in the solar simulator facility at the Canadian National Solar Test Facility. These "characterization" tests were performed on a variety of solar collector types, including conventional flat plate, flat plate incorporating a boiling/condensing fluid and integral condenser, vacuum tube type, and vacuum tube with integral heat pipe.

Results of this study indicate that typical solar collector testing practices are not adequate to fully evaluate the performance of many types of solar collectors and that traditional representations of thermal performance are not adequate to predict the performance of solar collectors under the range of conditions experienced during normal operation. The results of this study do indicate that a wide range of solar collector types can be represented by a general performance equation based on the classical representation with the addition of higher order terms.

Finally, for some of the test samples, limited outdoor testing was conducted and monitored day long thermal performance results were compared to the performance pre- dicted from the characterizing equations.