In northern climates, when the ambient temperature drops, air source heat pumps become inefficient and cannot provide the required heat load. Multiple source heat pumps are attractive when considering the efficiency and capacity problems of northern climate heat pumps.

The university which the author is associated with has been involved in heat pump development since 1977. This development has produced four generations of multiple-source heat pump systems. The first three generations had serious drawbacks. In each, the charge requirements varied because two physically separate evaporators were needed and the system cost was high. The design and testing of the fourth generation, the Single Unit Dual Source (SUDS) evaporator, is the subject of this paper.

The SUDS combines two separate evaporators into a single evaporator, resulting in a less costly and more efficient northern climate heat pump system. Initial test results show that the evaporator performs as expected, resulting in an improvement in efficiency of northern climate heat pumps.

Units: Dual