Abstract:
Abstract: Solar heat pump using solar energy as the low temperature heat source, can improve the COP (coefficient of performance) of heat pump. Solar collector is the core component of solar heat pump. In this paper, an energy storage solar collector with oscillating heat pipe is designed, which can improve the overall performance of the system when used in energy storage solar heat pump system. In the collector, the evaporation section of the oscillating heat pipe heat exchanger is arranged in the vacuum tube in the form of U-tube, and energy storage material is filled between the evaporation section of the oscillating heat pipe and the vacuum tube, which can achieve the peak load shifting of solar energy by storing energy during the day for use at night or on continuous rainy days. The oscillating heat pipe heat exchanger with R134a, ethanol/water and acetone/water as working fluid is designed, manufactured and applied into the energy storage collector. The test bench for the thermal performance of the energy storage solar collector with oscillating heat pipe is built, and experimental studies are conducted on the heat collection performance of the collector in daytime and nighttime conditions, when the oscillating heat pipe is filled with different working fluids (R134a, ethanol/water, acetone/water) and the vacuum tube is filled with different materials (air and paraffin). The results show that when oscillating heat pipe is filled with R134a, the solar collector has the best performance. Under daytime condition, it has the highest heat collection efficiency, the average collection efficiency is above 0.45, and the maximum value is 0.90 when using paraffin for heat storage. It has the highest daily useful energy, and the minimum value is still 7.14 MJ/(m2·d). And no matter what kind of working fluid is filled in the oscillating heat pipe and what kind of material is filled in the vacuum tube, the variation law of instantaneous collection efficiency is contrary to that of solar radiation intensity. When the solar radiation intensity is relatively high, under the similar solar radiation intensity and ambient temperature, the collector using sensible heat of air for energy storage has better performance than that using latent heat of paraffin. When the solar radiation intensity is relatively low, under the similar solar radiation intensity and ambient temperature, the collector filled with paraffin has better performance than that filled with air. The collector using sensible heat of air for energy storage can't meet the demand of temperature for hot water at night, while the collector using latent heat of paraffin for energy storage can meet the demand at both day and night in daily life. This is because when the solar radiation intensity is high, a small amount of heat is absorbed by the air filled in collector, but most of heat is transferred to the heat exchanger with oscillating heat pipe, while paraffin stores more energy during solid-liquid phase transition and transfers less heat than air. On cloudy or rainy days, when the solar radiation is insufficient, the paraffin filled in collector undergoes a liquid-solid phase transition and releases the latent heat stored before, while the sensible heat stored by air is inadequate for heating water. Therefore, the collector filled with paraffin has better performance than that filled with air on cloudy or rainy days with low solar radiation intensity. The results can provide reference for the design, popularization and application of solar heat pump with energy storage.