A new dynamic test method for thermal performance of all-glass evacuated solar air collectors

A new study on testing thermal performance of all-glass evacuated solar collectors with the air as heat transfer fluid under dynamic conditions outdoors has been developed. The model of this dynamic method was established with the energy balance analysis on solar collectors of this type. Compared with the first order model under steady-state conditions, this model can characterize thermal efficiency of solar collectors under more extensive conditions, reducing considerable operating time spent in waiting for the right test conditions. Through the derivation of the proposed model, it proved a strong relationship existed between this model and the first order model mentioned above. The dynamic model projection for the outlet temperatures was in good agreement with the measured result.

► The new method offers more convenient and cheaper tests for thermal performance of solar air collectors.
► This method is suitable for unfavorable weather conditions and operational demands in the real service.
► The output temperature, the output power and thermal efficiency of solar air collectors can be predicted by this method.
► In the same test procedure, the time constant is obtained from experimental data.
► Minor errors between predicted and measured results show this method is reasonable and reliable.