The Night Cooling Effect on a C-PVT Solar Collector
Abstract
Night cooling consists in running a fluid through a solar panel during the night in order to reduce the fluid temperature which can be used for cooling applications. Radiative heat losses can allow the fluid to reach temperatures below ambient while conduction and convection works to equalize the collector with the ambient temperature. This paper analyzes the possibility of using an asymmetric concentrating photovoltaic thermal solar collector (C-PVT) for cooling applications during the night by losing heat through convection, conduction and irradiation. The cooling performance of the C-PVT collector has been measured during the night at different inlet temperatures in the interval of 13 to 38°C which corresponded to a ∆T (between the collector average and the ambient) from 6 to 28°C. The performance of the tested C-PVT collector has been measured at different inlet temperatures in an interval of 13 to 38°C. During all performed measurements, the radiation losses did not drive the collector temperature below ambient temperature. With high ∆T (between the inlet and the ambient) of 300C, a 1,850C temperature decrease in the fluid was obtained. For ∆T of 140C, the temperature decrease was only 0,880C. The measurements showed a night U-value for the Solarus C-PVT of 4,2 W/m2K This correlates well with previous papers showing measurements taken during the day. Heat losses seem to be dominated by convection and conduction due to the existence of the glass in the collector. Despite this, a measurable relation between heat losses and cloudiness factor exists. This shows that the irradiance losses are not negligible. Only very specific applications can be suited for night cooling with this collector design, since it is not so common to have applications that require low grade cooling during the night time or justify storing this energy. However, if the C-PVT design was made without a glass cover, the results could potentially be very different for locations with many clear nights.
Keywords
Concentrating pvt, Cpc-collector, Asymmetric collector, Collector testing, Night cooling