Selection Procedure
Heating capacity selection:
1
Winter outdoor design
2
Total return air temperature — 72 F.
3
Winter outside air minimum ventilation load and cfm — 1,200 cfm and 87.2 MBh.
4
Peak heating load 225 MBh.
Utilizing unit selection in the cooling capacity procedure.
Mixed air temperature = RADB + %O.A. (OADB - RADB) = 72
+ (0.10)
Supply air fan motor heat temperature rise = 20,600 BTU ÷ (1.085 x 12,000) cfm = 1.6 F.
Mixed air temperature entering heat module = 64.8 + 1.6 = 66.4 F.
Total winter heating load = peak heating
+ventilation load - total fan motor heat = 225 + 87.2 - 20.6 = 291.6 MBh.
Electric Heating System
Unit operating on 480/60/3 power supply. FromTable
Table
Unit supply temperature at design heating conditions = mixed air temperature + air temperature rise = 66.4 + 23.6 = 90 F.
Natural Gas Heating System
Assume natural gas supply — 1000 Btu/ ft3. FromTable
Table
Unit supply temperature design heating conditions = mixed air temperature + air temperature rise = 66.4 + 37.3 = 103.7 F.
Air Delivery Procedure
Supply air fan bhp and rpm selection. Unit supply air fan performance shown inTable
The supply air fan motor selected in the previous cooling capacity determination example was 7.27 bhp with 652 rpm.
Thus, the supply fan motor selected is 7.5 hp.
To select the drive, enterTable
Unit Electrical Requirements
Selection procedures for electrical requirements for wire sizing amps, maximum fuse sizing and dual element fuses are given in the electrical service selection of this catalog.
Unit Designation
After determining specific unit characteristics utilizing the selection procedure and additional job information, the complete unit model number can be developed. Use the model number nomenclature on page 14.
heating load of 291.6 MBh.
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| STANDARD MOTOR |
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| HIGH EFFICIENCY MOTOR |
| 120 |
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| 110 |
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MBH | 100 |
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90 |
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HEAT | 80 |
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70 |
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MOTOR | 60 |
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50 |
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FAN | 40 |
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30 |
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| 20 |
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| 0 | 5 | 10 | 15 | 20 | 25 | 30 | 35 | 40 |
MOTOR BRAKE HORSE POWER
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