A highly-efficient heat pump system with solar thermal and sky radiation cooling

摘要

A unique heat pump system with high Coefficient of Performance (COP) using solar thermal/sky radiation cooling is introduced in this article. The proposed system has a solar collector for collection of heat for space heating and sky radiator for space cooling. This heat pump is operated with nighttime electricity to heat and cool the main tank water. The system has four operational modes: The first is the sky radiation (SR) cooling mode that is a typical mode in summer. In this mode, the main tank water is cooled using the heat pump connected with the sky radiator. The second is the rainwater tank (RT) mode that cools the main tank water with rainwater as a low temperature source. The third is the subtank (ST) mode that is used in spring to cool the main tank water and heat the auxiliary tank water at the same time. The fourth is the winter (WIN) mode, in which the main tank water is heated by the heat pump connected with the auxiliary tank water heated by the solar collector. The experimental COP of the present solar thermal/sky radiation cooling heat pump system will be shown in detail. The total COP exceeds 7.0 for the SR cooling mode. The proposed heat pump system will be very promising especially in large cities like Tokyo in order to mitigate the heat island effects.