TABLE OF CONTENTS At the time this article was written, Kevin Rafferty was a research associate at the Geo-Heat Center at the Oregon Institute of Technology, Klamath Falls. Reprinted from ASHRAE Transactions 1995, Vol. 101, Part 2.
Kevin Rafferty, P.E.
Commercial ground-source heat pump systems have been installed in a variety of configurations. Among the most common are groundwater, vertical ground-coupled, and hybrid ground-coupled (with cooling tower). This paper reports on a comparison of the capital costs associated with the installation of these three designs. Based on the assumption of equal building loop costs, a comparison is made of those costs associated with the ground-source portion of the system. Sensitivity of cost to a variety of factors including well depth, system capacity, and soil (or groundwater temperature) is evaluated. Results indicate that shallow (200ft 160 m]) groundwater systems are the least-cost alternative (ranging from 500 $/ton (142 $/ kW) at 50 tons (176 kW) to less than 200 $/ton (47 $/kW) at 500 tons (1760 kW) for capacity range evaluated in this report. When deeper (600ft to 800 ft 1180 m to 240 m]) groundwater wells are required, hybrid and ground-coupled systems are less expensive at system sizes less than about 150 tons (528 kW). Above 150 tons, ground-water systems are the lowest-cost approach. When injection wells are omitted, groundwater systems are the lowest-cost alternative down to 100 tons (352 kW), even when requiring two 800ft (240 m) production wells.
Unitary ground-source heat pump systems for commercial buildings can be...
