RT-PRC007-EN
16
Selection
Procedure
50 Hz
1
Winter outdoor design conditions –
0°F (17.7°C).
2
Total return air temperature – 72°F
(22.2°C).
3
Winter outside air minimum ventilation
load and cfm – 1,000 cfm and
87.2 MBh.
4
Peak heating load 150 MBh.
Utilizing unit selection in the cooling
capacity procedure.
Mixed air temperature = RADB +
% O.A. (OADB - RADB) = 72
+ (0.10) (0-72) = 64.8°F.
Supply air fan motor heat temperature
rise = 20,600 Btu ÷ (1.085 x 10,000) cfm
= 1.9°F.
Mixed air temperature entering heat
module = 64.8 + 1.9 = 66.7°F.
Total winter heating load = peak heating
+ ventilation load - total fan motor heat =
150 + 87.2 - 15 =
222.2 MBh.
Electric Heating System
Unit operating on 415 power supply.
From Table PD-22, kW may be selected
for TC*305 unit to satisfy the winter
heating load. The 67 kW module will do
the job.
Table PD-22 also shows an air
temperature rise of 21.2°F for 10,000 cfm
through the 67 kW heat module.
Unit supply temperature at design
heating conditions = mixed air
tempe air temperature rise = 66.7
+ 21.2 = 87.9°F.
Natural Gas Heating System
Assume natural gas supply – 1000
Btu/ft
3
. From Table PD-24, select the low
heat module (243 MBh output) to satisfy
222 at unit cfm.
Table PD-25 also shows air temperature
rise of 37.3°F for 10,000 cfm through
heating module.
Unit supply temperature design heating
conditions = mixed air tempe air
temperature rise = 66.7 + 37.3 = 104.0°F.
Air Delivery Procedure
Supply air fan bhp and rpm selection.
Unit supply air fan performance shown
in Table PD-25 includes pressure drops for
dampers and casing losses. Static
pressure drops of accessory
components such as heating systems,
and filters if used, must be added to
external unit static pressure for total
static pressure determination.
The supply air fan motor selected in the
previous cooling capacity determination
example was 5.35 bhp with 616 rpm.
Thus, the supply fan motor selected is
7.5 hp.
To select the drive, enter Table PD-28 for a
305 unit. Select the appropriate drive for
the applicable rpm range. Drive selection
letter E with a range of 625 rpm, is
required for 616 rpm. Where altitude is
significantly above sea level, use Table
PD-2 and PD-3, and Figure
PD-1 for applicable correction factors.
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 using the
model number nomenclature page.
