Ground-Loop Heat Pump Applications - Rheem RPVS Series Installation, Operation & Maintenance Instructions Manual

R e s i d e n t i a l S p l i t
R e v. : 1 3 M a r c h , 2 0 1 5

Ground-Loop Heat Pump Applications

CAUTION! The following instructions represent industry
accepted installation practices for closed loop earth
coupled heat pump systems. Instructions are provided
to assist the contractor in installing trouble free ground
loops. These instructions are recommendations only.
State/provincial and local codes MUST be followed and
installation MUST conform to ALL applicable codes. It is
the responsibility of the installing contractor to determine
and comply with ALL applicable codes and regulations.
Pre-Installation
Prior to installation, locate and mark all existing underground
utilities, piping, etc. Install loops for new construction before
sidewalks, patios, driveways, and other construction has
begun. During construction, accurately mark all ground loop
piping on the plot plan as an aid in avoiding potential future
damage to the installation.
Piping Installation
The typical closed loop ground source system is shown in
Figure 5. All earth loop piping materials should be limited
to polyethylene fusion only for in-ground sections of the
loop. Galvanized or steel fi ttings should not be used at any
time due to their tendency to corrode. All plastic to metal
threaded fi ttings should be avoided due to their potential to
leak in earth coupled applications. A fl anged fi tting should
be substituted. P/T plugs should be used so that fl ow
can be measured using the pressure drop of the unit heat
exchanger.
Earth loop temperatures can range between 25 and
110°F [-4 to 43°C]. Flow rates between 2.25 and 3 gpm
per ton [2.41 to 3.23 l/m per kW] of cooling capacity is
recommended in these applications.
Test individual horizontal loop circuits before backfi lling.
Test vertical U-bends and pond loop assemblies prior to
installation. Pressures of at least 100 psi [689 kPa] should be
used when testing. Do not exceed the pipe pressure rating.
Test entire system when all loops are assembled.
Flushing the Earth Loop
Once piping is completed between the unit, Flow Controller
and the ground loop (Figure 5), the loop is ready for fi nal
purging and charging. A fl ush cart with at least a 1.5 hp
[1.1 kW] pump is required to achieve enough fl uid velocity
in the loop piping system to purge air and dirt particles. An
antifreeze solution is used in most areas to prevent freezing.
All air and debris must be removed from the earth loop
piping before operation. Flush the loop with a high volume
of water at a minimum velocity of 2 fps (0.6 m/s) in all piping.
The steps below must be followed for proper fl ushing.
1. Fill loop with water from a garden hose through the
fl ush cart before using the fl ush cart pump to insure an
even fi ll.
10
CAUTION!
2. Once full, the fl ushing process can begin. Do not allow
the water level in the fl ush cart tank to drop below the
pump inlet line to avoid air being pumped back out to
the earth loop.
3. Try to maintain a fl uid level in the tank above the return
tee so that air cannot be continuously mixed back into
the fl uid. Surges of 50 psi (345 kPa) can be used to help
purge air pockets by simply shutting off the return valve
going into the fl ush cart reservoir. This "dead heads"
the pump to 50 psi (345 kPa). To purge, dead head the
pump until maximum pumping pressure is reached.
Open the return valve and a pressure surge will be sent
through the loop to help purge air pockets from the
piping system.
4. Notice the drop in fl uid level in the fl ush cart tank when
the return valve is shut off . If air is adequately purged
from the system, the level will drop only 1-2 inches (2.5 -
5 cm) in a 10" (25 cm) diameter PVC fl ush tank (about a
half gallon [2.3 liters]), since liquids are incompressible. If
the level drops more than this, fl ushing should continue
since air is still being compressed in the loop fl uid.
Perform the "dead head" procedure a number of times.
Note: This fl uid level drop is your only indication of air in
the loop.
Antifreeze may be added before, during or after the fl ushing
procedure. However, depending upon which time is chosen,
antifreeze could be wasted when emptying the fl ush cart
tank. See antifreeze section for more details.
Loop static pressure will fl uctuate with the seasons.
Pressures will be higher in the winter months than during
the cooling season. This fl uctuation is normal and should
be considered when charging the system initially. Run the
unit in either heating or cooling for a number of minutes to
condition the loop to a homogenous temperature. This is
a good time for tool cleanup, piping insulation, etc. Then,
perform fi nal fl ush and pressurize the loop to a static
pressure of 50-75 psi [345-517 kPa] (winter) or 35-40 psi
[241-276 kPa] (summer). After pressurization, be sure to
loosen the plug at the end of the Grundfos loop pump
motor(s) to allow trapped air to be discharged and to insure
the motor housing has been fl ooded. This is not required
for Taco circulators. Insure that the Flow Controller provides
adequate fl ow through the unit by checking pressure drop
across the heat exchanger and compare to the pressure
drop tables at the back of the manual.
Antifreeze
In areas where minimum entering loop temperatures drop
below 40°F [5°C] or where piping will be routed through
areas subject to freezing, antifreeze is required. Alcohols
and glycols are commonly used as antifreeze; however your
local sales manager should be consulted for the antifreeze
best suited to your area. Low temperature protection
should be maintained to 15°F [9°C] below the lowest
expected entering loop temperature. For example, if 30°F
[-1°C] is the minimum expected entering loop temperature,
the leaving loop temperature would be 25 to 22°F [-4 to