Installation With Ductwork - Modine Manufacturing PTX Installation And Service Manual

INSTALLATION WITH DUCTWORK

Figure 19.1- 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
IMPOR T ANT
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 19.1.
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 19.1).
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 27.
Additional Requirements for Installation of Blower
Models (model BTX)
Determining Blower Speed
The drive assembly and motor on gas-fired blower unit heaters
with motors 2HP and below are factory assembled. 3HP and
larger motors are shipped loose to prevent shipping damage.
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 26 and the temperature rise range shown on
the unit's rating plate.
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
To determine the proper blower speed and motor sheave turns
open, the conditions under which the unit is to operate must be
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 22
and 23. As an example, a model BTX 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 23). See "Blower Adjustments" on page 20 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 21. 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 BTX 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 22 for a
BTX 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.
6-534.1
Dimension "B" Should Never
Be Less than 1/2 of "A"
C
12"
B
MIN.
TURNING
A
VANES
BAFFLE
TOP VIEW
F
12"
MIN.
TURNING
VANES
TOP VIEW
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