5
heating load
Heating design loads must be calculated using at least 99 %
design dry bulb temperature (as listed in the ACCA Manual J
Table 1A) for the desired geographic location. If a thermostat
temperature setting warmer than the typical 65° F to 70° F
design range is preferred, this must be taken into account
as the load will be increased. The system must always be
furnished with a back-up auxiliary heating system, such as
electric strip heat.
cooling load
• Cooling design loads must be calculated using at least 1%
design dry bulb temperature (in Air Conditioning Contractors
of America (ACCA) Manual J Table 1) criteria for the desired
geographic location. This means design temperatures should
not be exceeded more than 1% of the time in the cooling
mode. The system and wells must be sized with enough
capacity to handle 99% of the cooling loads encountered
throughout the year in any particular geographic location.
• If thermostat temperature settings cooler than 75° F range
is preferred, this must be taken into account as the load will
be increased.
• Short-cycling for a moderately oversized system does not
present the dehumidification problems that it does for an
air-source design, because of the cooler heat sink in a
geothermal heat pump.
Well Seal Valve
For 4 and 5 ton systems, the compressor section is equipped
with an earth loop seal valve assembly to keep most of the
refrigerant in the earth loop during the off cycle. The assembly
consists of a vapor line solenoid valve and a check valve for
cooling mode. The solenoid valve is opened during heating
mode operation.
The purpose of this assembly is to:
• Minimize the chance of refrigerant leaking indoors during
the off cycle.
• Minimize the chance of leaking a large amount of refrigerant.
system Design capacity load
Always calculate the system’s design load, for system sizing
purposes, to the maximum of the greater of the heating or
below.
EXaMPlE
If a house requires 36,000 BTUs in heating and 48,000 BTUs
in cooling. Select a 4 ton system (12,000 BTUs = 1 ton).
Vertical Elevation Differential Design
The vertical elevation differential between the bottom of the
earth loop and the top of the air handler
must not be greater
than 125 feet per ton, with a maximum well depth of 400
feet
. If the vertical elevation exceeds this design criteria, the
well depths can be shortened by adding an additional well.
seasonal transition
During the cooling to heating or heating to cooling transitional
seasons, the operating conditions of a direct geothermal
heat pump are quite different from a conventional air source
heat pump. Unlike an air source heat pump, the heat will not
immediately dissipate from the vicinity of the earth loop. During
cooling to heating or heating to cooling transition, the earth loop
may experience surround temperature conditions outside the
operation range of an air source heat pump. To make smooth
transition between the seasons, the compressor section is
equipped with components and control logics described in
the following sections.
Heating To Cooling Transition
• The compressor section includes a hot gas injection valve
to ensure smooth transition from heating to cooling mode
operations. See
.
• After heating mode operation, the earth loop temperature
may be below the normal underground temperature (around
58° F). As the refrigerant rises back from the well, the
system pressure drop is around 40 psig per 100 feet. As a
result, the refrigerant returning to the compressor section
is usually in two phases. In cooling mode after 3 minutes
of operation, if the suction pressure drops below 95 psig, a
hot gas solenoid valve opens momentarily.
• Discharge gas is injected into the inlet end of the evaporator
coil via the liquid line. This process will repeat until the
suction pressure is above 95 psig.
• If after 60 hot gas injections, the suction pressure is still
below 95 psig, the system will go into soft lock out mode
(
SL
) for 60 minutes for the well to recover. See
• After one hour, the system will restart in cooling mode. For a
properly designed well or a shallow well (200 feet or below)
the soft lock should rarely occur.
Cooling To Heating Transition
After cooling mode operation, the earth loop temperature may
be well above the normal underground temperature (around
58 °F). If abnormally high suction or discharge pressure is
detected in heating mode, the system will be turned off for 30
minutes for the well to recover. For a properly designed well,
the soft lock out should rarely occur.
locating the Equipment
• Survey the job site to determine the best location for setting
the unit. Choose an appropriate location that minimizes the
length of the refrigerant lines. See
unit dimensions. Consideration should be given to availability
of electric power, service access, and noise. If there is any
question concerning the power supply, contact the local
power company.
• Select a solid, level position, preferably on concrete.
• Sufficient clearance for unobstructed service to the control
access panel must be maintained. See
.
1. Locate the compressor unit in a carefully considered place
(i.e. usually in basement, attic, closet, utility room, garage,
or crawl space).
Installation within the actual living space
is not recommended
. Basement and attic installations
also require careful planning to avoid placement directly
above or below bedrooms, living rooms, etc., whenever
possible. Placing the unit on an appropriate mounting base
(rubber, corkboard, or the like) should always be done, as
this will assist in absorbing compressor vibration. If the unit
is mounted in an attic, it should preferably be hung from
rafters (to lessen ceiling vibration), and provisions made for
an extra condensation drip pan.
notE:
When placing the compressor unit into position,
remember there are screws in the side panels. It is
recommended that the side panels of the compressor unit
be placed far enough away from walls or other structures so
that there is sufficient room to access the screws for future
servicing.
