Catalogue
12 UH-PRC001-EN
Selection Procedure
Formula
The following formula is used to
arrive at final air temperature volume
when 70 F (Standard Air Basis) is
known or vice versa:
Cfm at final temp. =
Cfm at 70 F =
Determining Special Steam
Capacities
Where capacity of the unit under
standard conditions is known – 2 lbs.
steam, 60 F entering air – and it is
desired to know the capacity of this
same unit under different steam and
air conditions, follow instructions
given in Example 1.
Where a set of conditions is given –
Btu, temperature rise, final
temperature, cfm, steam pressure
available, etc. Refer to Example 2.
Useful Data
Btu/240=Sq. Ft. of radiation (EDR)
Sq. ft. of radiation/4=Lbs. of
condensate per hour
Btu/Latent heat=Lbs. of water per
hour
Cfm x Temp. Rise x 1.085 = Btu.
Specific heat of air (70 F) = .241
Specific weight of one cubic foot of
air (70 F) =.075.
Cfm x 60 = cfh.
Therefore, .241 x .075 x 60 = 1.085
Example 1
Given: Model 60S Horizontal
Propeller Unit Heater with a rated
capacity of 60,000 Btu at 2 lbs. steam
with 60 F entering air.
Desired: Capacity of this unit using 15
lbs. steam and 40 F entering air.
Under 40 F and across from 15 lbs. in
Ta bl e 2, we find the factor 1.34.
60,000 x 1.34 = 80,400 Btu per hour.
Cfm at 70F
460 Final temp+
460 70+
--------------------------------------------------
×
Cfm final air
460 70+
460 Final temp+
--------------------------------------------------
×
Determining Amount of
Condensate
To determine the amount of
condensate, divide the capacity in
BTU by the latent heat of steam:
80,400/945=85 lbs per hour.
945=Latent Heat of Steam at 15 psi.
(See Table 12 )
Table 1. Max. Mounting Heights and Distance of throw for Model S Units (based on
2 lbs Steam Pressure 60F entering Air)
Unit
Outlet
Velocity CFM
Final Temp
(F)
Mounting
Height Max Throw
A08* 250 245 91 8 20
A18* 500 500 94 8 25
A25* 590 580 102 9 29
A36* 550 850 99 9 29
018 395 395 102 8 20
024 450 450 109 8 24
036 550 550 119 9 28
048 550 750 119 9 30
060 650 900 121 10 30
072 800 1100 120 10 29
084 900 1400 115 10 30
096 930 1400 123 11 38
108 1000 1800 115 11 40
120 900 1900 118 12 40
132 950 2000 121 13 54
144 1000 2200 120 13 55
156 1150 2600 115 13 55
180 800 2200 135 13 53
204 1000 2900 124 13 55
240 900 3500 123 14 57
280 980 4200 121 14 57
300 700 5000 117 15 58
360 1000 5500 120 15 60
H
MAXIMUM DISTANCE OF THROW = T
Determining Final Temperature
Final temperature of air leaving Trane
Unit Heaters may be determined as
follows:
Inlet Air Temp. + Btu rating/Cfm X
1.085=Final Temp
Inlet Air Temp. 40F + 80,400/900
(from Tab le 7) X 1.085=Final Temp