Specifications

30
ENVISION COMMERCIAL SPECIFICATION CATALOG
Selection Example
To achieve optimal performance, proper selection of each
heat pump is essential. A building load program should
be used to determine the heating and cooling load of each
zone. WFI Select computer software selection program
can then be used to develop an accurate and complete
heat pump schedule. WFI Select can be obtained from
your local WaterFurnace representative.
While WFI Select is the easiest and most accurate method
to size and select equipment, however, selection can still
be accomplished manually using this manual and the
following selection procedure. Sizing so that the actual
sensible capacity of the equipment will satisfy the sensible
capacity of the zone is the recommended method for best
results.
Boiler/Tower Application
Typical boiler/tower application will result in entering
water temperatures of 60-90°F with 70°F for heating
and 90°F for cooling. Water to refrigerant insulation
option would not be required. Flow rates are 2.5 to 3
gpm per ton with 2.5 gpm per ton often representing an
economical design point.
Geothermal Application
Typical geothermal application can result in a wide
entering water temperature range of 30-100°F. Typically
minimum heating entering water temperatures can
range from 30 to 50°F depending upon loop type and
geographical location. Cooling performance should be
calculated using a maximum loop temperature of 100°F
in most loop applications. Water flow is typically 2.5 to
3 gpm per ton with 3 gpm per ton recommended with
the more extreme loop temperatures. PLEASE NOTE
THAT WATER COIL INSULATION OPTION SHOULD BE
SELECTED WHEN ENTERING WATER TEMPERATURES
ARE EXPECTED TO BE BELOW 45-50°F.
Geothermal Selection Example
Step 1: Determine the actual heating and cooling loads at
the desired dry bulb and wet bulb conditions.
Step 2: Obtain the following de sign parameters: Entering
water temperature, water flow rate in GPM, air flow in
CFM, water flow pressure drop and design wet and dry
bulb temperatures. Air flow CFM should be between 300
and 450 CFM per ton. Unit water pressure drop should
be kept as close as possible to each other to make water
balancing easier. Go to the appropriate tables and find the
proper indicated water flow and water temperature.
Step 3: Select a unit based on total and sensible cooling
conditions. Select a unit which is closest to, but no larger
than, the actual cooling load.
Step 4: Enter tables at the design water flow and
water temperature. Read the total and sensible cooling
capacities (Note: interpolation is permissible, extrapolation
is not).
Step 5: Read the heating capacity. If it exceeds the design
criteria it is acceptable. It is quite normal for water source
heat pumps to be selected on cooling capacity only since
the heating output is usually greater than the cooling
capacity.
Step 6: Determine the correction factors associated with
the variable factors of dry bulb and wet bulb.
Corrected Total Cooling = tabulated total cooling x wet
bulb correction.
Corrected Sensible Cooling = tabulated sensible cooling x
wet/dry bulb correction.
Step 7: Compare the corrected capacities to the load
requirements. Normally if the capacities are within 10%
of the loads, the equipment is acceptable. It is better to
undersize than oversize, as undersizing improves humidity
control, reduces sound levels and extends the life of the
equipment.
Step 8: When complete, calculate water temperature
rise and assess the selection. If the units selected are
not within 10% of the load calculations, then review what
effect changing the GPM, water temperature and/or air
flow and air temperature would have on the corrected
capacities. If the desired capacity cannot be achieved,
select the next larger or smaller unit and repeat the
procedure. Remember, when in doubt, undersize slightly
for best performance.
Example Equipment Selection - Cooling
1. Load Determination:
Assume we have determined that the appropriate cooling
load at the desired dry bulb 80°F and wet bulb 65°F
conditions is as follows:
Total Cooling ................................................................21,200 BTUH
Sensible Cooling ......................................................... 15,700 BTUH
Entering Air Temp ................. 75°F Dry Bulb / 60°F Wet Bulb
2. Design Conditions:
Similarly, we have also obtained the following design
parameters:
Entering Water Temp.............................................................. 100°F
Water Flow (Based upon 10°F rise in temp.) 6.0 GPM
Air Flow Required ................................... 755 CFM @ 0.4 in. wg.