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InsTAllATIon WITH duCTWorK
figure 13.1- Typical duct & Airflow Installation
recommended Installations
A
TURNING
VANES
3" MIN.
A
3" MAX.
B
12" MIN.
sIde vIeW
d
B
A
BAFFLE
sIde vIeW
ImpORTANT
Do not attempt to attach ductwork of any kind to propeller
models.
When installing the heater, always follow good duct design
practices for even distribution of the air across the heat
exchanger. Recommended layouts are shown in Figure 13.1.
When installing blower units with ductwork the following must be
done.
1. Provide uniform air distribution over the heat exchanger.
Use turning vanes where required. See Figure 13.1.
2. Provide removable access panels in the ductwork on the
downstream side of the unit heater. These openings should
be large enough to view smoke or reflect light inside the
casing to indicate leaks in the heat exchanger and to check
for hot spots on exchanger due to poor air distribution or lack
of sufficient air.
3. If ductwork is connected to the rear of the unit use Modine
blower enclosure kit or if using field designed enclosure
maintain dimensions of blower enclosure as shown on
page 23.
Additional requirements for Installation of Blower
models (model BTs)
determining Blower speed
The drive assembly and motor on all gas-fired blower unit
heaters are factory assembled. The adjustable motor sheave
has been pre-set to permit operation of this unit under average
conditions of air flow and without any external static pressure.
The motor sheave should be adjusted as required when the unit
is to be operated at other than average air flows and/or with
external static pressures. Adjustment must always be within the
performance range shown on page 20 and the temperature rise
range shown on the unit's rating plate.
To determine the proper blower speed and motor sheave turns
open, the conditions under which the unit is to operate must be
B
3" MAX.
12"
MIN.
3" MIN.
B
12"
A
TURNING
VANES
BAFFLE
sIde vIeW
e
12"
MIN.
B
TURNING
A
VANES
BAFFLE
sIde vIeW
known. If the blower unit is to be used without duct work or
filters, the only criteria for determining the motor sheave turns
open and blower speed is the amount of air to be delivered. The
performance tables for blower models are shown on pages 16
and 17. As an example, a model BTS 350 unit, operating with
no external static pressure, that is, no duct work, filters, etc.,
and is to deliver an air volume of 6481 cfm (cfm = cubic feet of
air per minute) requires that the unit be supplied with a 5 hp
motor, a -207 drive, and the drive sheave must be set at 2.5
turns open to achieve a blower speed of 960 rpm (see
performance table for units with or without blower enclosure,
page 17). See "Blower Adjustments" on page 14 for setting of
drive pulley turns open.
If a blower unit is to be used with ductwork or filters, etc., the
total external static pressure under which the unit is to operate,
and the required air flow must be known before the unit can be
properly adjusted.
If Modine filters are used, the expected pressure loss through
the filters is included in the performance data on page 15. If
filters or ductwork are to be used with the unit, and they are not
supplied by Modine, the design engineer or installing contractor
must determine the pressure loss for the externally added
devices or ductwork to arrive at the total external static pressure
under which the unit is to operate.
Once the total static pressure and the required air flow are
known, the operating speed of the blower can be determined
and the correct motor sheave adjustments made. As an
example, a model BTS 350 is to be used with a Modine
supplied blower enclosure and Modine supplied filters attached
to ductwork. The unit is to move 6481 cfm of air flow against an
external static pressure of 0.2" W.C. Also, 0.2" W.C. must be
added for the filter pressure drop for a total of 0.4" W.C. total
pressure drop. Entering the performance table on page 17 for a
BTS 350, at 6481 cfm and 0.4" W.C. static pressure, it is seen
that the unit will require a 5 hp motor using a -207 drive, and
the motor sheave should be set at .5 turns open to achieve a
blower speed of 1050 rpm. You can see this example differs
from similar conditions in paragraph 2 by the number of turns
open and a higher rpm, which is needed to overcome the added
external static pressure from the filters.
6-561
Dimension "B" Should Never
Be Less than 1/2 of "A"
C
12"
B
MIN.
A
ToP vIeW
f
12"
MIN.
TURNING
VANES
ToP vIeW
13
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