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Maritime Geothermal Ltd.
12-Feb-00
Horizontal Loop Fields
The successful application of a DX heat pump
depends on sizing the machine correctly for the
home or area to condition and providing enough
land area or volume of earth from which to extract
or reject heat.
DX heat pumps react with the earth much like
a
conventional reversing heat pump
and
closed
loop plastic earth heat exchanger.
Heat that is
available to the unit must travel through the earth
and therefore the conduction capability of the earth
in the location of the heat exchanger is very impor-
tant. A unit used entirely or primarily for heating
will have no problem with conduction and heat
transfer since it will be cooling the loop during
heating mode which draws moisture towards the
coils because they are colder than the surrounding
ground. Horizontal loop fields should be laid out so
that the copper coils have good cross-sectional in-
fluence on the minimum areas listed above. As a
general rule, wider spacing between the loops so
that they do not influence one another, will result in
improved performance of the heat pump.
Unless you are sure there will be sufficient
moisture present in the loop field area during the
summer, a
soaker hose
is recommended in all hori-
zontal trench systems which will used for air condi-
tioning purposes.
Vertical Bore Systems
Vertical bores (3” x 100 ft. holes) provide an
alternate method of installing a DX unit. A high
water table in the borehole area (20 to 30 ft.) will
insure that there is adequate conduction with the
earth and although the loop length per ton is shorter
than the horizontal design, the vertical orientation
and moisture in the boreholes provides very uni-
form conduction both winter and summer.
Air Flow
The charts above and below are general guide-
lines in selecting a DX-to-Air heat pump for resi-
dential application. A detailed heat loss analysis
should be performed to determine the actual loads
on the building and to assist in sizing ductwork for
NORDIC® DX Heat Pump System Prerequisites
There are four specific parts or sub-systems to a DX heat pump installation:
1. The source of energy ............................................................... Solar & Geothermal
2. The storage media ................................................................... The Earth’s mass
3. Converting the energy to a useable form ................................... Heat Pump
4. Distributing the heat .................................................................. Ductwork / radiant slab
Model
# of
Loops
Area
Req’d
Trench
Layout
Nordic DX-45 (3) x 350’ 8,000 ft²
4’x 175’
Nordic DX-55 (4) x 350’ 10,000 ft²
4’ x 175’
Nordic DX-65 (5) x 350’ 12,500 ft²
4’ x 175’
Note: These are minimum loop field requirements
based on an earth temperature of 45° F.
Nordic® DX-45 models 1600 cfm
Nordic® DX-55 models 1900 cfm
Nordic® DX-65 models 2100 cfm
@ 80°F DB / 67°F WB and static pres of .2” H
2
0
Air Flow Available from each heat pump
Nordic® DX-45 will heat up to 1500 sq.ft.
Nordic® DX-55 will heat up to 2000 sq.ft.
Nordic® DX-65 will heat up to 2500 sq.ft.
Assuming at least R-20 walls and R-40 ceiling
Nordic® DX-45 could have up to 16 hot air grills.
Nordic® DX-55 could have up to 19 hot air grills.
Nordic® DX-65 could have up to 21 hot air grills.
