Selection Procedure - Carrier AQUAZONE 50PEC09-18 Product Data

Selection procedure (with 50PEC12 example)
I Determine the actual cooling and heating
loads at the desired dry bulb and wet bulb
conditions.
Given:
Total Cooling (TC). . . . . . . . . . . . . . .10,750 Btuh
Sensible Cooling (SC) . . . . . . . . . . . . .8,650 Btuh
Entering-Air Temperature db . . . . . . . . . . . . 80 F
Entering-Air Temperature wb . . . . . . . . . . . . .66 F
II Determine the following design parameters.
Determine entering water temperature, water flow
rate (gpm), airflow (cfm), water flow pressure drop
and design wet and dry bulb temperatures. Airflow
cfm should be between 300 and 450 cfm per ton.
For applications using multiple units, the water pres-
sure drop should be kept as close as possible across
units to make water balancing easier. Enter the
50PEC12 Performance Data tables and find the
proper indicated water flow and water temperature.
For example:
Entering Water Temp . . . . . . . . . . . . . . . . . 90 F
Water Flow (Based upon
10 F rise in temp) . . . . . . . . . . . . . . . . . . 3.0 gpm
Airflow Cfm . . . . . . . . . . . . . . . . . . . . . . 396 cfm
III Select a unit based on total cooling and total
sensible cooling conditions.
Enter tables at the design water flow and water
temperature. Read the total and sensible cooling
capacities.
NOTE: Interpolation is permissible, extrapolation is
not.
For example:
Enter the 50PEC12 Performance Table at design
water flow and water temperature. Read Total
Cooling, Sensible Cooling and Heat of Extraction
capacities:
Total Cooling . . . . . . . . . . . . . . . . . .11,000 Btuh
Sensible Cooling . . . . . . . . . . . . . . . . 9,200 Btuh
Heat of Extraction. . . . . . . . . . . . . . .13,600 Btuh
NOTE: 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. Heating capacity is selected based on
different entering water conditions than cooling
capacity.
IV Determine the correction factors associated
with the variable factors of dry bulb and wet
bulb using the Corrections Factor tables
found in this book.
Using the following formulas to determine the cor-
rection factors of dry bulb and wet bulb:
a) Corrected Total Cooling = tabulated total cooling
x wet bulb correction x airflow correction.
b) Corrected Sensible Cooling = tabulated sensible
cooling x wet/dry bulb correction x airflow
correction
V Determine entering air and airflow correction
using the Corrections Factor tables found in
this book.
The nominal airflow for 50PEC12 is 450 cfm. The
design parameter is 396 cfm.
396/450 = 88% of nominal airflow
Use the 89% row in the Correction Factors —
Airflow table.
The Entering Air Temperature wb is 66 F. Use the
66.2 F row in the Entering Air Correction table.
Using the following formulas to determine the cor-
rection factors of entering air and airflow correction:
Table
Corrected
Total Cooling = 11,000 x 0.990 x 0.974 = 10,607
Corrected
Sensible Cooling = 9,200 x 1.030 x 0.974 =
Corrected
Heat of Extraction = 13,600 x 0.992 x 0.981 = 13,235
Compare the corrected capacities to the load
requirements established in Step I. If the capacities
are within 10% of the load requirements, the equip-
ment is acceptable. It is better to undersize than
oversize as undersizing improves humidity control,
reduces sound levels and extends the life of the
equipment.
VI Water temperature
assessment.
Calculate the water temperature rise and assess the
selection using the following calculation:
Actual Temperature
=
Rise
For example, using the Corrected Heat of Extrac-
tion from the last step:
Actual Temperature
=
Rise
If the units selected are not within 10% of the load
calculations, review what effect changing the gpm,
water temperature and/or airflow will have on the
corrected capacities. If the desired capacity cannot
be achieved, select the next larger or smaller unit
and repeat Steps I through VI.
Ent Air Airflow Corrected
9,230
rise calculation and
Correction of Heat Extraction
gpm x 500
13,235
= 8.8 F
3.0 x 500
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