TABLE OF CONTENTS At the time this article was written, Stephen P. Kavanaugh and Joey K. Parker were associate professors in the mechanical engineering department at the University of Alabama, Tuscaloosa. Robert S. Falls, a former graduate student, was with N.C. Morgan Construction Co., Tuscaloosa. Reprinted from ASHRAE Transactions 1994, Vol. 100, Part 1.
Stephen P. Kavanaugh, Ph.D
Member ASHRAE R.S. Falls
Student Member ASHRAE J.K. Parker, Ph.D.
Two of the most promising alternatives in the quest for higher efficiency in unitary heat pumps are ground-source heat pumps (GSHPs) and variable-speed air-source heat pumps. Ground-source systems can provide high efficiency, reduced demand, low maintenance, and high levels of comfort in heating and cooling. Variable-speed air heat pumps are available with outstanding part-load efficiencies and load-matching capabilities. A project has been undertaken to merge the two technologies to produce a very flexible and efficient heating, cooling, and water-heating system.
This paper reports on the test results of the first and second phases of development. The project began with the modification of a 3-ton (10.6 kW) variable-speed air heat pump. The compressor, indoor fun, air coil, and controls were retained. The outdoor coil was replaced with a coaxial water-to-ref -rigerant coil, and a vented water-heating coil was added. Tests were performed and EERs ranged from 12.8 to 27.6 Btu/W-h (COP = 3.8 to 8.1) in cooling. Heating COPs ranged from 3.1 to 6.0.
Further modifications to the systems were made to enhance capacity, efficiency, and water-hearing capability. These included improved thermostatic...
