Operating instructions

5
hydronic loop and the open system is required when
corrosive fluid is used in the open loop; especially on
swimming pools where pH imbalance can damage the heat
pump.
Note: Expect the operating temperature of an
indirect coupled application to be 10
o
F below the LWT of
the heat pump.
Other forms of closed loop systems such as indoor
swimming pools, pretreated fresh air systems, snow melt
systems, and valance heating/cooling systems are also very
common with hydronic heat pumps. The sizing of the heat
pump to these systems is more precise, and information
from those system manufacturers is required.
IV. UNIT SIZING
Selecting the unit capacity of a hydronic geothermal heat
pump requires four things:
A) Building Heat Loss / Heat Gain.
B) Ground Sources and Design Water Temperatures.
C) Hydronic-Side Operating Temperatures.
D) Temperature Limitations
A. Building Heat Loss / Heat Gain
The space load must be estimated accurately for any
successful HVAC installation. There are many guides or
computer programs available for estimating heat loss and
gain, including the Enertech Geothermal Heat Pump
Handbook, Manual J, and others. After the heat loss and
gain analysis is completed, Entering Water Temperatures
(EWT’s) are established, and hydronic-side heating
conditions are determined. The heat pump can now be
selected using the hydronic heat pump data found in the
Engineering Specifications. Choose the capacity of the heat
pump based on both heating and cooling loads.
B. Ground-Sources and Design Water
Temperatures
ECONAR Engineering Specifications provide capacities at
different loop water temperatures and hydronic leaving
water temperatures. Note: Table 2 shows the water-flow
(GPM) requirements and water-flow pressure differential
(dP) for the heat exchanger, and Table 3 shows the dP
multiplier for various levels of freeze protection.
Table 2 – Ground-Side Flow Rate Requirements
Series
Flow
(gpm)
dP*
(psig)
GW240
60
5.6
GW360
78
6.0
* dP (psig) heat exchanger pressure drops are for pure water.
Note: dP values are for standard heat exchanger configurations.
Cupro Nickel heat exchanger configurations for Ground
Water applications have higher dP.
Table 3 – Heat Exchanger Pressure Differential (dP)
Correction Factors for Freeze Protection (Typical)
Anti-
Freeze
Percent
Volume
Freeze
Level
dP Multiplier
25
o
F
35
o
F
90
o
F
110
o
F
GTF
(1)
50% GTF
12
o
F
125%
123%
N/a
N/a
Propylene
Glycol
20%
18
o
F
136%
133%
118%
114%
25%
15
o
F
145%
142%
N/a
N/a
(1)
GTF = GeoThermal Transfer Fluid. 60% water, 40%
methanol.
1. Ground Loop Systems (see Figure 2)
Loop systems use high-density polyethylene pipe buried
underground to supply a tempered water solution back to
the heat pump. Loops operate at higher flow rates than
ground water systems because the loop Entering Water
Temperature (EWT) is lower. EWT affects the capacity of
the unit in the heating mode, and loops in cold climates
are normally sized to supply a wintertime EWT to the heat
pump down to 25
o
F.
C. Hydronic-Side Heat Exchangers
Hydronic-side heat exchangers discussed in section VI are
designed to operate at a specific fluid supply temperature.
This operating temperature will have to be supplied to the
selected space conditioning heat exchanger by the hydronic
heat pump. The manufacturers or suppliers of the hydronic-
side heat exchangers publish the capacity of their
equipment at different operating temperatures and fluid
flow rates, and these capacities and operating temperatures
are required to select the heat pump to be used in the
system.
When selecting the heat pump, choose a unit that will
supply the necessary heating or cooling capacity at the
minimum and maximum hydronic loop temperature
conditions, respectively. Example; if a fan coil system
requires 35000 Btu/hr to cool a space with 45
o
F water
temperature entering the water-to-air fan coil, a GW47x
Ultra heat pump is required to handle the cooling load.
If an intermediate heat exchanger is used between the
storage tanks as pictured in Figure 1, expect a 10
o
F
operating temperature difference between the two tanks.
For example, if the direct-coupled storage tank is at 110
o
F,
expect the maximum operating temperature of the indirect-
coupled tank connected through an intermediate heat
exchanger to be 100
o
F.
D. Temperature Limitations
Be aware of the operating range of the geothermal system
when sizing the particular heat pump to avoid premature
equipment failure. Operating outside of these limitations
may cause severe damage to the equipment and may void
warranty.
CAUTIONS: