Trane RT-PRC010-EN manual Selection Procedure, Motor Brake Horse Power, HotWater Heating

Selection Procedure

HEATING CAPACITY SELECTION

Step 1 — Determine AirTemperature Entering Heating Module

Mixed air temperature = RADB + % OA (OADB - RADB) = 70 + (0.10) (0 - 70) = 63

F

Supply air fan motor heat temperature rise = 46,000 Btu ÷ (1.085 x 17,500 cfm) = 2.42 F

Air temperature entering heating module = 63.0 + 2.42 = 65.4 F

Step 2 — DetermineTotalWinter Heating Load

Total winter heating load = peak heating load + ventilation load - supply fan motor heat = 475 + 133 - 46.0 = 562 MBh

Electric Heating System

Unit operating on 460/60/3 power supply.

FromTable PD-30, kw may be selected for a nominal 50 ton unit operating

460-volt power.The 170 kw heat module

(580.1 MBh) will satisfy the winter heating load of 563 MBh.

Table PD-28 shows an air temperature rise of 30.6 F for 17,500 cfm through the 170 kw heat module.

Chart SP-1 — Fan Motor Heat

STANDARD MOTOR

HIGH EFFICIENCY MOTOR

	120
	110
MBH	100
	90
-
HEAT	80
	70
MOTOR	60
	50
FAN	40
	30
	20
	10
	0
	0	5	10	15	20	25	30	35	40

MOTOR BRAKE HORSE POWER

Unit supply temperature at design heating conditions = mixed air temperature + air temperature rise = 65.4 F + 30.6 F = 96.0 F.

Gas Heating System (Natural Gas)

FromTable PD-24 select the high heat module (697 MBh output) to satisfy winter heating load of 563 MBh at unit cfm.

Table PD-26 also shows an air temperature rise of 36.0 F for 17,500 cfm through the heating module.

Unit supply temperature at design heating conditions = mixed air temperature + air temperature rise = 65.4 F + 36.0 F = 101.4 F.

HotWater Heating

Assume a hot water supply temperature of 190 F. Subtract the mixed air temperature from the hot water temperature to determine the ITD (initial temperature difference).

ITD = 190 F - 65.4 F = 125 F. Divide the winter heating load by ITD = 563 MBh ÷ 125 F = 4.50 Q/ITD.

FromTable PD-31, select the low heat module. By interpolation, a Q/ITD of 4.50 can be obtained at a gpm at 25.7.

Water pressure drop at 25.7 gpm is 0.57 ft. of water. Heat module temperature rise is determined by:

Total Btu		= ∆ T
1.085 x Supply cfm
563,000	= 29.7 F
(1.085 x 17,500)

Unit supply air temperature = mixed air temperature + air temperature rise = 65.4 + 29.7 = 95 F.

Steam Heating System

Assume a 15 psig steam supply.

FromTable PD-27, the saturated temperature steam is 250 F. Subtract mixed air temperature from the steam

temperature to determine ITD. ITD = 250 F - 65.4 F = 185 F.

Divide winter heating load by ITD = 563 MBh ÷ 185 F = 3.04 Q/ITD.

FromTable PD-26, select the high heat module.The high heat module at 17,500 cfm has a Q/ITD = 5.11.

Heat module capacity, Q = ITD x Q/ITD = 185 F x 5.11 Q/ITD = 945 MBh

Heat module air temperature rise

=Total Btu

1.085 x Supply cfm

945 Btu ÷ (1.085 x 17,500 cfm) = 49.8 F.

Unit supply temperature at design conditions = mixed air temperature + air temperature rise = 65.4 F + 49.8 F = 115 F.

RT-PRC010-EN 17