Geothermal Heating and Cooling System
A geothermal heat pump is a central heating and/or cooling system that pumps heat to or from the ground. It uses
the earth as a heat source (in the winter) or a heat sink (in the summer). This design takes advantage of the
moderate temperatures in the ground (compared to variable open air temperatures) to boost efficiency and reduce the
operational costs of heating and cooling systems.
The U.S. Environmental Protection Agency (EPA) has called ground source heat pumps the most energy-efficient,
environmentally clean, and cost-effective space conditioning systems available. Heat pumps offer significant
emission reductions potential, particularly where they are used for both heating and cooling and where the
electricity is produced from renewable resources.
How Does It Work?
Heat pumps can transfer heat from a cool space to a warm space, against the natural direction of flow, or they
can enhance the natural flow of heat from a warm area to a cool one. The core of the heat pump is a loop of
refrigerant pumped through a vapor-compression refrigeration cycle that moves heat. Heat pumps are always more
efficient at heating than pure electric heaters, even when extracting heat from cold winter air. But unlike an
air-source heat pump, which transfers heat to or from the outside air, a ground source heat pump exchanges heat
with the ground. This is much more energy-efficient because underground temperatures are more stable than air
temperatures through the year. Seasonal variations drop off with depth and disappear below seven meters due to
Closed Loop Vertical System
The geothermal system being installed in the Southern Living Showcase Home at The Bluffs of Weiss is a closed
look vertical system.
Most installed systems have two loops on the ground side: the primary refrigerant loop is contained in the
appliance cabinet within the house where it exchanges heat with a secondary water loop that is buried underground.
The secondary loop is typically made of High-density polyethylene pipe and contains a mixture of water and
anti-freeze (propylene glycol, denatured alcohol or methanol). After leaving the internal heat exchanger, the water
flows through the secondary loop outside the building to exchange heat with the ground before returning. The
secondary loop is placed below the frost line where the temperature is more stable.
Closed loop tubing can be installed horizontally as a loop field in trenches or vertically as a series of long
U-shapes in wells. At the Southern Living Showcase Home we are using the vertical system. A vertical closed loop
field is composed of pipes that run vertically in the ground. A hole is bored in the ground, typically 75 to 500
feet (23–150 m) deep. Pipe pairs in the hole are joined with a U-shaped cross connector at the bottom of the hole.
The borehole is commonly filled with a bentonite grout surrounding the pipe to provide a thermal connection to the
surrounding soil or rock to improve the heat transfer. Thermally enhanced grouts are available to improve this heat
transfer. Grout also protects the ground water from contamination, and prevents artesian wells from flooding the
property. Vertical loop fields are typically used when there is a limited area of land available. Bore holes are
spaced at least 5–6 m apart and the depth depends on ground and building characteristics. For the Southern Living
Showcase Home, our system is engineered for a house needing 10 kW (3 ton) of heating capacity. We are using xxx
boreholes approximately xxx feet deep.
Ground source heat pumps are characterized by high capital costs and low operational costs compared to other
HVAC systems. The initial cost can be two to five times that of a conventional heating system in most residential
applications, new construction or existing. Their overall economic benefit depends primarily on the relative costs
of electricity and fuels. Based on recent prices, ground-source heat pumps currently have lower operational costs
than any other conventional heating source almost everywhere in the world. In general, a homeowner may save
anywhere from 20% to 60% annually on utilities by switching from an ordinary system to a ground-source system. At
the Southern Living Showcase Home we are estimating annual utility savings of approximately xx%.
Ground-source heat pumps have unsurpassed thermal efficiencies and produce zero emissions locally.
This article uses material from the Wikipedia article
Heat Pump", which is released under the Creative Commons
Attribution-Share-Alike License 3.0.