Catalogue

UH-PRC001-EN 13
Selection Procedure
Example 2:
Problem: A Trane Model S Horizontal
Unit Heater is desired to deliver
200,000 Btu per hour in a garage
where ventilation is required.
Entering air temperature is 40 F.
Steam at 30 lbs. pressure is available.
Temperature to be maintained is 70 F.
Solution: Under 40 F and across from
30 lbs. in Table 2, find the factor 1.51.
Equivalent capacity of required unit
at 2 lbs. steam 60 F entering air is
Required Btu per hour/F=200,000/
1.51=132,500 Btu
From Tabl e 7, select a Number 132S
Unit Heater with a capacity of
132,000 Btu per hour with standard
coil, and at 2 lbs. steam and 60 F
entering air.
The capacity of this unit at 30 lbs.
steam and 40 F entering air is:
1.51 x 132,000 = 199,300 Btu per hour.
Surplus Capacity
While the ventilation load is being
handled, any air entering the space
over the desired room temperature
should be considered in the heating
calculations. This surplus capacity
can be found by multiplying the
difference between the final
temperature leaving the heater and
the room temperature to be
maintained by 1.085 and that by the
cfm. That amount of heat can be
used to offset heat losses.
Model S
Maximum mounting heights for
Model S Unit Heaters are given in
Ta bl e 1. When equipped with
standard vertical Louvers, direction
of air flow can be adjusted both
horizontally and vertically.
Mounting the unit at or below
maximum mounting height will
insure that heated air reaches the
living zone.
Model P
Maximum mounting heights for
Model P Unit Heaters are given in
Ta bl e 4. These distances are figured
from the floor line to the bottom
plate of the unit heater.
Where ceilings are unusually low, a
nearly horizontal flow of air can be
obtained by equipping these units
with Louver Cone Diffusers. The
individually adjustable blades of the
Louver Cone permit an infinite
variety of adjustments to meet any
on-the-job problems. By setting the
blades vertically to straighten the
airstream, as much as 45% increase
in throw can be obtained.
Hot Water Selection Example
Selection Procedure
Select the proper size of unit heater
for whatever application desired, as
illustrated by the following
examples.
Select a Model S horizontal unit
heater to deliver 95 MBH with 220°F
entering water temperature (EWT),
70°F entering air temperature (EAT)
and a 30°F water temperature drop
(WTD).
1. Determine GPM: GPM=Btu/hr/
(485) WTD=95000/485x30=6.53
2. Refer to Table 17 to select the
conversion factor at 220° EWT
and 70° EAT. Factor is 1.06.
3. Determine equivalent MBH at
standard conditions (200° EWT,
60° EAT). Equiv. MBH=MBH/
Factor=95/1.06=89.6.
Table 2. Factors for Determining Steam Capacity of Model S Horizontal Unit
Heaters at Various Pressures and Temperatures (Table based on 2 psig and 60F
entering Air)
Steam Pressure PSIG Temperature of Entering Air (F)
30 40 50 60 70 80 90 100
Blow
Through
Type
0 1.19 1.11 1.03 0.96 0.88 0.81 0.74 0.67
2 1.24 1.16 1.08 1.00 0.93 0.85 0.78 0.71
5 1.29 1.21 1.13 1.05 0.97 0.90 0.83 0.76
10 1.38 1.29 1.21 1.13 1.06 0.98 0.91 0.84
15 1.44 1.34 1.28 1.19 1.12 1.04 0.97 0.89
20 1.50 1.42 1.33 1.25 1.17 1.10 1.02 0.95
30 1.60 1.51 1.43 1.35 1.27 1.19 1.12 1.04
40 1.68 1.60 1.51 1.43 1.35 1.27 1.19 1.12
50 1.70 1.60 1.58 1.50 1.42 1.34 1.26 1.19
60 1.81 1.73 1.64 1.56 1.47 1.39 1.31 1.24
70 1.87 1.78 1.70 1.61 1.53 1.45 1.37 1.29
75 1.90 1.81 1.72 1.64 1.55 1.47 1.39 1.32
100 2.02 1.93 1.84 1.75 1.66 1.58 1.50 1.42
125 2.11 2.02 1.93 1.84 1.76 1.68 1.59 1.51
150 2.20 2.11 2.02 1.93 1.84 1.76 1.67 1.59
To determine the Btu per hour capacity of a Model S Horizontal Unit Heater at any steam pres-
sure and entering air temperature multiply rated capacity at 2 psig steam 60 F entering air
(Table 7) by factor from above table.
4. Select unit size from Tab le 13.
Select the unit which will provide
89.6 MBH In this example, the
selection indicates a Model S 132
unit heater.
To determine the actual capacity of
this Model S 132 at operating
conditions (220° EWT and 70° EAT)
proceed as follows:
1. Determine the MBH at 6.53 GPM
by applying factor from Ta b l e 20.
Multiply this MBH by the water
flow factor (95.8 MBH X .95=91.0
MBH)
2. Multiply this MBH by the
conversion factor 91.0 X 1.06 =
96,500.
3. The GPM remains constant =
6.53 GPM.
4. Calculate the water temperature
drop WTD=Btu/hr/GPM x 485 =
96,500/(6.53)(485) = 30.5