23
IOM, WD Models
Enertech Global
Heating
Cooling
LWT = EST - HE
GPM x 500*
LWT = EST + HR
GPM x 500*
HE = 500* x GPM x (EWT - LWT)
HR = 500* x GPM x (LWT - EWT)
*500 = Constant factor for pure water. Brine should be 485.
Heating & Cooling Calculations Table
Notes:
1. Desuperheater Capacity is based upon 0.4 GPM Flow per nominal ton at 90°F entering hot water temperature.
2. Extrapolation data down to 25°F for heating and interpolation between EST & GPM data is permissible.
3. EWT (Entering Water Temperature) is also called EST (Entering Source Temperature).
4. Load flow rate is the same as the nominal source flow rate, approximately 3 GPM per ton.
Application Notes for Performance Data
Source Water Flow Selection
Proper flow rate is crucial for reliable operation of geothermal
heat pumps. The performance data shows three flow rates for
each entering water temperature (EST column). The general
“rule of thumb” when selecting flow rates is the following:
Top flow rate: Open loop systems (1.5 to 2.0 gpm per ton)
Middle flow rate: Minimum closed loop system flow rate
(2.25 to 2.50 gpm/ton)
Bottom flow rate: Nominal (optimum) closed loop system flow
rate
(3.0 gpm/ton)
Although the “rule of thumb” is adequate in most areas of
North America, it is important to consider the application type
before applying this “rule of thumb.” Antifreeze is generally
required for all closed loop (geothermal) applications.
Extreme Southern U.S. locations are the only exception. Open
loop (well water) systems cannot use antifreeze, and must
have enough flow rate in order to avoid freezing conditions at
the Leaving Source Water Temperature (LWT) connection.
Calculations must be made for all systems without antifreeze
to determine if the top flow rate is adequate to prevent LWT at
or near freezing conditions. The following steps should taken
in making this calculation:
Determine minimum EST based upon your geographical area.
Go to the performance data table for the heat pump model
selected and look up the the Heat of Extraction (HE) at the
“rule of thumb” water flow rate (GPM) and at the design
Entering Load Temperature (ELT).
Calculate the temperature difference (TD) based upon the HE
and GPM of the model.
TD = HE / (GPM x 500).
Calculate the LWT.
LWT = EST - TD.
If the LWT is below 35-38°F, there is potential for freezing
conditions if the flow rate or water temperature is less than
ideal conditions, and the flow rate must be increased.
Example 1:
EST = 50°F, ELT = 95°F.
Model 036 Full Load, heating. Flow rate = 5 GPM. HE = 33,600
Btuh.
TD = 33,600 / (5 x 500) = 13.4°F
LWT = 50 - 13.4 = 36.6°F
Water flow rate should be adequate under these conditions.
Example 2:
EST = 40°F, ELT = 95°F.
Model 036 Full Load, heating. Flow rate = 5 GPM. HE = 28,700
Btuh.
TD = 28,700 / (5 x 500) = 11.5°F
LWT = 40 - 11.5 = 28.5°F
Water flow rate must be increased.
Section 9: Equipment Start-Up Procedures