System information

Carrier Geothermal Heat Pump Systems
41
Residential Products Technical Guide
Options
Carrier Geothermal residential geothermal heat pumps have a
number of options to customize the installation to the customer’s
individual needs.
ECM Fan
The ECM (Electrically-Commutated Motor) or variable speed
fan motor is standard on GT-PX, GT-PB and GT-PC series units.
For GT-PG Series water-to-air units, a PSC (Permanent Split
Capacitor) fan motor is standard, and the ECM motor is available
as an option. The ECM motor has a number of features such
as soft start, constant CFM [l/s], dehumidifi cation mode and
numerous airfl ow settings (4 heating airfl ow choices, 4 cooling
airfl ow choices, 3 dehumidifi cation mode airfl ow choices, 4
auxiliary heat airfl ow choices, and 1 constant fan airfl ow).
Hot Water Generator
The HWG (Hot Water Generator) or desuperheater option
provides considerable operating cost savings by utilizing excess
heat energy from the heat pump to help satisfy domestic hot
water requirements. The HWG is active throughout the year (any
time the heat pump is operating), providing virtually free hot water
when the heat pump operates in the cooling mode, or hot water
at the COP of the heat pump during operation in the heating
mode. Actual HWG water heating capacities are provided in the
appropriate heat pump performance data. All Carrier Geothermal
heat pumps (except outdoor splits) equipped with the HWG
option include a built-in water to refrigerant heat exchanger that
eliminates the need to tie into the heat pump refrigerant circuit
in the fi eld. The control circuit and pump are also built in for
residential equipment.
Figure 21 shows a typical example of HWG water piping
connections on a unit with built-in pump. Electric water heaters
are recommended. If a gas, propane, or oil water heater is used,
a second preheat tank must be installed. If the electric water
heater has only a single center element, the dual tank system is
recommended to insure a usable entering water temperature for
the HWG.
Typically a single tank of at least 52 gallons [235 liters] is used to
limit installation costs and space. However, a dual tank, is the most
effi cient system, providing the maximum storage and temperate
source water to the HWG.
It is always advisable to use water softening equipment on
domestic water systems to reduce the scaling potential and
lengthen equipment life. In extreme water conditions, it may be
necessary to avoid the use of the HWG option since the potential
cost of frequent maintenance may offset or exceed any savings.
Whole House Dehumidifi cation Overview
Indoor Air Quality (IAQ) and Relative Humidity (RH) are
increasingly becoming design issues that must be addressed by
selecting heating and cooling equipment with advanced capabilities.
The Carrier Geothermal Whole House Dehumidifi cation reheat
option (patent pending) offers unique features unlike anything
currently available today.
Carrier Geothermal’s Whole House Dehumidifi cation reheat
option is an innovative means of providing modulating reheat
without the complication of refrigeration controls. Whole House
Dehumidifi cation is Hot Gas Generated Reheat, which utilizes
one of the biggest advantages of a water source heat pump
(WSHP), the transfer of energy through the loop piping system.
Whole House Dehumidifi cation simply diverts condenser water
through a water-to-air coil that is placed after the evaporator coil.
If condenser water is not warm enough, the internal “run-around”
loop increases the water temperature with each pass through the
condenser coil.
Whole House Dehumidifi cation Benefi ts
Whole House Dehumidifi cation is like no other reheat option on
the market. Proportional reheat is controlled to the desired leaving
air temperature set point (factory set point of 72°F, [22°C}), no
matter what the loop temperature is. Since dehumidifi cation
operation will occur under less than full load cooling conditions
a good percentage of the time, it is important to have a reheat
function that provides 100% reheat in the spring and fall
when the loop is cool. Supply air temperature is fi eld adjustable to
+/- 3°F [+/- 1.7°C] for even greater fl exibility with an
optional potentiometer.
Competitors without Whole House Dehumidifi cation typically
use an on/off (non-modulating) refrigeration based reheat circuit,
typically referred to as “Hot gas reheat” (HGR). HGR needs
higher condensing temperatures to work well, typically 85°F
[29°C] entering water temperature (EWT). With HGR, cooler
water temperatures produce cooler supply air temperatures,
which could overcool the space, requiring additional space heating
from another source or a special auto-change-over relay to allow
the unit to switch back and forth between reheat and heating.
Figure 21: Typical HWG Installation
HWG Connections
Electric
Water
Heater
Options - Whole House Dehumidification