Pay Dirt
Designing, selecting and
installing a residential ground-source
heat pump system.
by XIaObINg LIu, PaTRICk HugHEs and JEff MuNk
hudSon vaLLey cLean eneRgy
The cost of a ground-source heat pump system depends on many factors, includ-
ing the size of the heating/cooling/hot water loads being served, ground thermal
conductivity, conditions for drilling and trenching and whether a qualified gSHP
contractor is active in the installation area.
by XIaObINg LIu, PaTRICk HugHEs and JEff MuNk
It’s a compelling proposition: Use the near-constant-temperature heat underground to heat and cool your home and heat domestic water, slashing your energy bills. Yet despite studies demonstrating significant energy sav- ings from ground-source heat pump (GSHP) systems, their adoption has been hindered by high upfront costs. Fewer than 1 percent of U.S. homes use a GSHP system. However, compared to a minimum-code-compliant conventional space-conditioning system, when properly designed and installed, a GSHP retrofit at current market prices offers simple payback of 4. 3 years on national average, considering existing federal tax credits.
Most people understand how air-source heat pumps work: They
move heat from indoor air to outdoor air when cooling and from outdoor
air to indoor air when heating. The ground-source heat pump operates
on the same principle, except that it moves heat to or from the ground
source instead of outdoor air. The ground source is usually a vertical or
horizontal ground heat exchanger (see the figures on page 35). Because
the ground usually has a more favorable temperature than ambient air for
the heating and cooling operation of the vapor-compression refrigeration
cycle, GSHP systems can operate with much higher energy efficien-
cies than air-source heat pump systems when properly designed and
installed.
A GSHP system used in a residential building typically provides space
conditioning and hot water and comprises three major components: a
water-source heat pump unit designed to operate at a wider range of
entering fluid temperatures (typically from 30°F to 110°F, or 1°C to
43°C) than a conventional water-source heat pump unit; a ground heat
