9
50ZH
Selection Procedure
I DETERMINE COOLING AND HEATING
REQUIREMENTS AT DESIGN CONDITIONS:
Given:
Required Cooling Capacity (TC) . . . . . . . . . . 28,000 Btuh
Sensible Heat Capacity (SHC) . . . . . . . . . . . . 20,500 Btuh
Required Heating Capacity. . . . . . . . . . . . . . . 28,550 Btuh
Outdoor Entering-Air Temperature . . . . . . . . . . . . . . 95° F
Outdoor-Air Winter Design Temperature . . . . . . . . 20° F
Indoor-Air Winter Design Temperature. . . . . . . . . . . 70° F
Indoor Entering-Air Temperature. . . . . . . . . . . . 80° F edb,
67° F ewb
Indoor-Air Quantity . . . . . . . . . . . . . . . . . . . . . . .1125 cfm
External Static Pressure . . . . . . . . . . . . . . . . . . 0.20 in. wg
Electrical Characteristics (V-Ph-Hz) . . . . . . 208/230-3-60
edb — entering dry bulb
ewb — entering wet bulb
II SELECT UNIT BASED ON REQUIRED COOLING
CAPACITY.
Enter Cooling Capacities table at condenser entering
temperature of 95° F, indoor air entering at 1125 cfm and
67° F ewb (entering wet bulb). The 50ZH030 unit will
provide a total cooling capacity of 28,800 Btuh and a
sensible heat capacity of 21,700 Btuh.
For indoor-air temperature other than 80° F edb (entering
dry bulb), calcualte sensible heat capacity correction, as
required, using the formula found in Note 3 following the
cooling capacities tables.
NOTE: Unit ratings are net capacities.
III SELECT ELECTRIC HEAT.
Enter the 50ZH030 Heating Capacities table at 1125 cfm.
At 70° F return indoor air and 20° F air entering outdoor
coil, the inegrated heating capacity is 15,500 Btuh. (Select
integrated heating capacity value since deductions for
outdoor-coil frost and defrosting have already been made.
No correction is required.)
The required heating capacity is 28,550 Btuh. Therefore,
13,050 Btuh (28,550 – 15,500) additional electric heat is
required.
Determine additional electric heat capacity in kW.
13,050 Btuh
3414 Btuh/kW
Enter the Accessory Electric Heater Usage table on page 4
for 208/240 v. three-phase, 50ZH030 unit. The 5-kW heater
at 240 v most closely satisfies the heating required. To
calculate kW at 230 v, multiply the heater kW by
multiplication factor 0.92 found in the Multiplication
Factors table on page 5.
5 kW x 0.92 = 4.6 kW
4.6 x 3414 = 15,704 Btuh
To calculate kW at 208 v, see Multiplication Factors table
on page 5.
Total unit heating capacity is 31,204 Btuh (15,500 +
15,704).
IV DETERMINE FAN SPEED AND POWER
REQUIREMENTS AT DESIGN CONDITIONS.
Before entering the air delivery tables, calculate the total
static pressure required. From the given, the Accessory
Electric Heat Pressure Drop table, Wet Coil Pressure Drop
table, and the Filter Pressure Drop table, find:
External static pressure 0.20 in. wg
Filter 0.09 in. wg
Electric heat 0.11 in. wg
Wet coil 0.07 in. wg
Total static pressure 0.47 in. wg
Enter the table for Dry Coil Air Delivery — Horizontal
Discharge at 1125 cfm and 230-v high speed. By
interpolation, the standard motor will deliver 0.48 in. wg
static pressure. This will adequately handle job
requirements.
= 3.8 kW of heat required
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