Engineering Design Guide
HBH SERIES
Heat Controller, Inc.
4
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 fl ow rate in GPM, air fl ow in CFM,
water fl ow pressure drop and design wet and dry bulb
temperatures. Air fl ow 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 ap pro pri ate tables and fi nd
the proper indicated water fl ow and water tem per a ture.
Step 3 Select a unit based on total and sensible cooling
conditions. Select a unit which is closest to the actual
cooling load.
Step 4 Use data from performance tables at the design water
fl ow and water temperature. Read the total and sensible
cooling capacities (Note: interpolation is per mis si ble,
ex trap o la tion 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 (page 14).
Corrected Total Cooling =
tabulated total cooling x wet bulb correction.
Corrected Sensible Cooling =
tabulated sensible cooling x wet/dry bulb correction.
Step 7 Determine the correction factor associated with antifreeze
in system loop. If heating EWT is 50°F or below you
may have to use antifreeze. Calculate leaving water
temperature per performance data selection notes (page
18). If antifreeze is required, use correction table for
correcting total and sensible capacities.
Step 8 Compare the corrected capacities to the load
re quire ments. Normally if the capacities are within 10%
of the loads, the equipment is ac cept able. It is better to
undersize than oversize, as undersizing improves humidity
control, reduces sound levels and extends the life of the
equip ment.
Step 9 When completed, calculate water temperature rise and
assess the selection. If the units selected are not within
10% of the load cal cu la tions, then review what effect
chang ing the GPM, water temperature and/or air fl ow and
air tem per a ture 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 For Cool ing
Step 1 Load Determination:
Assume you have determined that the appropriate cooling load
at the desired dry bulb 80°F and wet bulb 65°F con di tions is as
follows:
Total Cooling.................................................90,500 BTUH
Sensible Cooling...........................................73,300 BTUH
Entering Air Temp...........80°F Dry Bulb / 65°F Wet Bulb
Step 2 Design Conditions:
Similarly, you have also obtained the following design
pa ram e ters:
Entering Water Temp (Cooling).................................90°F
Entering Water Temp (Heating).................................60°F
Water Flow (Based upon 12°F rise in temp.)......18 GPM
Air Flow..............................................................2,800 CFM
Step 3, 4 & 5 HP Selection:
After making your preliminary selection (TCH096), we enter the
data from tables at design water fl ow and water tem per a ture and
read Total Cooling, Sens. Cooling and Heat of Rej. ca pac i ties:
Total Cooling....................................................93,200 BTUH
Sensible Cooling..............................................70,390 BTUH
Heat of Rejection...........................................120,100 BTUH
Airfl ow...................................................................3,200 CFM
Step 6, 7 & 8 Entering Air, Airfl ow and Antifreeze Corrections:
Next, we determine our correction factors.
Airfl ow 2800 ÷ 3200 = 88%
Antifreeze - None
Table
Ent Air Air Flow Cor rect ed
Corrected Total Cooling = 93,200 x .977 x .976 x 1 = 88,871
Corrected Sens Cooling = 70,390 x 1.088 x .933 x 1=71,453
Corrected Heat of Rej. = 120,100 x .998 x .976 =116,983
Step 9 Water Temperature Rise Calculation & As sess ment:
Rise = Heat of Reject ÷ (GPM x 500)
Actual Temperature Rise 116,983 ÷ 9,000 = 13.0°F
When we compare the Corrected Total Cooling and Corrected
Sensible Cooling fi gures with our load re quire ments stated in Step
1, we discover that our selection is /- 10% of our sensible
load requirement. Fur ther more, we see that our Cor rect ed Total
Cooling fi gure is slightly undersized as recommended, when
compared to the actual in di cat ed load.
Alternate Step 7: If your EWT for heating is 40°F then system
requires antifreeze. If a solution of 15% Propylene Glycol is
required, then:
Corrected Total Cooling = 88,871 x .986 = 87,626
Corrected Sens Cooling = 71,453 x .986 = 70,452
Selection Procedure
