System information

28
Geothermal Applications
ClimateMaster: Smart. Responsible. Comfortable.
equipment sizing is still important, but some fl exibility may be
gained by including some of the latest technology.
Regardless of location, local codes and/or electric utility program
requirements always supersede any recommendations in this
manual. In general, the following guidelines may be used when
sizing geothermal water-to-air heat pumps:
• Heat pump sensible cooling capacity (shown as SC in the
equipment catalog data) should be within 5-10% of the design
cooling sensible load at the maximum loop EWT.
• In most areas of North America the heat pump total cooling
capacity at design conditions should not exceed 25% of the
total cooling load. In Northern climates where heat loss may be
more than twice the heat gain, this may not always be possible,
and consideration should be given to two-stage equipment
and/or additional dehumidifi cation methods.
• Depending upon climate, the heat pump may need some
amount of auxiliary heat to satisfy the heating load at design
conditions. In Southern climates, the heat pump may provide
100% of the heating, but for most installations, auxiliary heat will
allow the use of a smaller heat pump and avoid over sizing the
equipment for cooling. Due to the higher heating capacities of
geothermal heat pumps as compared to air source heat pumps,
very little auxiliary heat is normally required.
• As a general rule of thumb, an economical balance point
(outdoor temperature below which auxiliary heat or less
is required) may be achieved by sizing the equipment such
that approximately 10% of the kilo Watt hours per year are
used by auxiliary heat (an example GeoDesigner report is
shown below). Since electric auxiliary heat is only about 25%
as effi cient as the heat pump, excessive amounts of auxiliary
heat may contribute to high energy costs. In the example
below, the balance point was 20°F [-7°C], which means that
the heat pump can handle the entire heating load when the
outdoor temperature is above this temperature. Below the
balance point, the heat pump will still provide most of the
heating, but will require some auxiliary heat to meet the full
load requirement. For the location where this example was
calculated, only 510 hours per year on average fall below 20°F
[-7°C], which is a relatively small portion of the total annual
heating hours. This rule of thumb only applies if the sensible
cooling load is satisfi ed by the heat pump selection. If the
cooling load requires a larger heat pump than what the rule
of thumb would indicate for heating, the cooling load should
determine the heat pump size.
Figure 18: Geo A Summary Report From
GeoDesigner Software
Equipment Sizing