System information

Carrier Geothermal Heat Pump Systems
25
Residential Products Technical Guide
Figure 6: Typical Ground-Loop Application
Inside Piping
Polyethylene pipe provides an excellent no leak piping material inside
the building. Inside piping fi ttings and elbows should be limited to
prevent excessive pressure drop. Hose kits employing 1” rubber
hose should be limited in length to 10-15 feet [3 to 4.5 meters] per
run to reduce pressure drop problems. In general 2 feet of head [6
kPa] pressure drop is allowed for all earth loop fi ttings which would
include 10-12 elbows for inside piping to the Flow Controller. This
allows a generous amount of maneuvering to the Flow Controller
with the inside piping. Closed cell insulation (3/8” to 1/2” [9.5 to
12.7 mm] wall thickness) should be used on all inside piping where
loop temperatures below 50°F [10°C] are anticipated. All barbed
connections should be double clamped.
Flow Controller Selection
The pressure drop of the entire ground loop should be calculated
for the selection of the Flow Controller (a pressure drop
spreadsheet is downloadable from the web site). In general, if basic
loop design rules are followed, units of 3 tons [10.6 kW] or less will
require only 1 circulating pump (UP26-99). Units from 3.5 to 6 tons
[12.3 to 21.1 kW] will require a two pump system (2 - UP26-99).
Larger capacity units with propylene glycol as antifreeze may require
2 - UP26-116 pumps. However, the UP26-116 should be avoided
where possible, as power consumption of the 26-116 is signifi cantly
higher than the 26-99, which will affect heating and cooling operating
costs. In many cases, where pressure drop calcuations may call for 3
- UP26-99 pumps, try substituting 2 - UP26-116 pumps. This makes
the installation much easier and reduces cost. Chart 1 shows the
various pump combinations.
Models with an Internal Variable Flow Controller include a Magna
Geo 25-140 ECM pump.
Loop pressure drop calculation should be performed for accurate
fl ow estimation in any system including unit, hose kit, inside piping,
supply/return headers, circuit piping, and fi ttings. Use Tables 3a
through 3e for pressure drop calculations using antifreeze and PE/
rubber hose piping materials.
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 (see Site Survey
Sheet). This should be done before and after loop installation. Final
installation should be plotted from two fi xed points to triangulate the
header/manifold location.
Loop Piping Installation
The typical closed loop ground source system is shown in Figure 6.
All earth loop piping materials should be limited to only polyethylene
fusion in below ground (buried) sections of the loop. Galvanized or
steel fi ttings should not be used at any time due to the tendency to
corrode by galvanic action. All plastic to metal threaded fi ttings should
be avoided as well due to the 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 in lieu of other fl ow measurement means (e.g.
fl ow meter, which adds additional fi ttings and potential leaks). Earth
loop temperatures can range between 25-110°F [-4 to 43°C]. Flow
rates of 2.25 to 3 gpm per ton [2.41 to 3.23 l/m per kW] of cooling
capacity are recommended for all earth loop applications.
High and
Low Voltage
Knockouts
Vibration Isolation Pad
To Thermostat
Closed Loop Design/Installation Guidelines
Figure 6a: Typical Closed-Loop Application (with
Internal Flow Controller Shown)
High and
Low Voltage
Knockouts
Vibration Isolation Pad
To Thermostat
Internal Flow
Controller
Water In
Water Out