Carrier 50YX - Manual (Page 6)

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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.................. 30,000 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............ ... 0.40 in. wg
Field-Supplied Filter Pressure Drop . . .0.15 in. wg
Electrical Characteristics (V-Ph-Hz) ....... 230-1-60
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 50YX030 unit
will provide a total cooling capacity of 31,000 Btuh and
a sensible heat capacity of 24,400 Btuh.
For indoor-air temperature other than 80 F edb (en­
tering dry bulb), calculate sensible heat capacity cor­
rection, as required, using the formula found in Note 3
following the cooling capacities tables.
NOTE: Unit ratings are net capacities.
Ill Select electric heat.
Enter the Heating Capacities table at 1125 cfm. At
70 F return indoor air and 20 F air entering outdoor
coil, the integrated heating capacity is 16,200 Btuh. (Se­
lect 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 30,000 Btuh. There­
fore, 13,800 Btuh (30,000 — 16,200) additional elec­
tric heat is required.
Determine additional electric heat capacity in kW
13,800 Btuh
3414 Btuh/kW
= 4.0 kW of heat required
Enter the Electric Heater Packages table for 50YX030
unit. The 5-kW heater at 240 v most closely satisfies
the heating required. To calculate kW at 230 v.
5 kW X .92 = 4 6 kW
5 kW X .92 X 3414 = 15,704 Btuh
To calculate kW at 208 v, see note below Electric Heater
Packages table on page 13.
Total unit heating capacity is 31,904 Btuh (16,200 -f
15,704).
IV Determine fan speed and power requirements at
design conditions.
Before entering Air Delivery tables, calculate the total
static pressure required. From the given and the Elec­
tric Heat Accessory Pressure Drop table, find-
External static pressure
Filter
Electric heat
Total static pressure
0.40 in. wg
0.15 in. wg
0.04 in. wg
0.59 in. wg
Enter the Air Delivery table, page 12, at 1125 cfm and
230-v high speed for wet coil. By interpolation, the stan­
dard motor will deliver 0.65 in. wg static pressure. This
will adequately handle job requirements.