Solar energy and heat pumps: evaluation of combined systems for heating and cooling of buildings

An analysis of a broad range of solar assisted heat pump systems was carried out. Systems were divided into three categories on the basis of whether ground coupling was included in the system and, if so, whether solar energy was stored in the ground or used in some other way. In the category of non-ground-coupled systems, an advanced air-source heat pump concept designed to improve capacity and coefficient of performance at low source temperatures was used as the basis for a dual source heat pump. For ground coupled systems which do not store solar heat in the ground, three options were considered: use of simple passive techniques to reduce the effective heating load; use of photovoltaics to drive the heat pump compressor; and use of active solar components as a source to the heat pump, for direct space heating, or for domestic hot water only. For systems which do store solar energy in the ground, the minimum size for efficient thermal carryover from summer to winter was determined to be a system capable of serving approx. 100 houses. Use of a fuel-fired heat pump is also an advantage in these larger systems. Economic analyses were based on a maximum allowable payback of 8 years for residential systems. For the large-scale system, a simplified 10-year life-cycle costing was employed.