Electronic International Standard Serial Number (EISSN)
The efficiency of a solar collector is a key factor for the performance of thermal facilities. As the weather conditions vary continuously during the day, the instant collector efficiency depends not only on the components employed in its construction but also on the actual environmental conditions, the hot water temperature and aging. An experimental research was performed to describe the transient behavior of a flat plate collector field under outdoor working conditions. A transient collector model was assembled using thermal resistances and capacitances. Three thermocouples were added to measure the center point temperature of the glass cover, box back surface and absorber plate of one of the collectors. Using this information, the parameters of a detailed thermal network model were determined. The model useful heat and thermal losses are calculated by applying a dynamic energy balance under the transient regime. The facility is based on a nine-year-old on-campus field with 50 m(2) flat plate solar collectors, which operated for a domestic hot water (DHW) application. The working parameters were recorded during an entire year for periods of 10 min. The model was experimentally validated by comparing its results to the instant collector temperatures and heat fluxes that were obtained from the experimental database. Both of the experimental and model results were compared to the direct application of the collector efficiency normalization curve (ENC) that was obtained from the EN-12975:2006 test as a reference. Being the operating conditions unlike, differences throughout the day became evident. The influence of several factors is fully described in Part II of this paper.
solar energy; flat plate collector; transient model; collector thermal efficiency; collector performance; solar domestic hot water