Ductwork - Modine Manufacturing PTC Installation And Service Manual

InsTAllATIon WITH duCTWorK
figure 18.1- 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 18.1.
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 18.1).
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 BTC)
determining Blower speed
The drive assembly and motor on gas-fired blower unit heaters
below 3 HP are are factory assembled, motors 3 HP and above
ship 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 24 and the
temperature rise range shown on the unit's rating plate.
To determine the proper blower speed and motor sheave turns
18
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
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 page 21.
As an example, a model BTC310 unit, operating with no
external static pressure, that is, no duct work, filters, etc., and is
to deliver an air volume of 6674 cfm (cfm = cubic feet of air per
minute) requires that the unit be supplied with a 5 hp motor, a
-260 drive, and the drive sheave must be set at 3.0 turns open
to achieve a blower speed of 809 rpm (see performance table
for units with or without blower enclosure, page 21). See
"Blower Adjustments" on page 19 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 BTC310 is to be used with a Modine supplied
blower enclosure and Modine supplied filters attached to
ductwork. The unit is to move 6674 cfm of air flow against an
external static pressure of 0.2" W.C. Also, 0.1" W.C. must be
added for the filter pressure drop for a total of 0.3" W.C. total
pressure drop. Entering the performance table on page 21 for a
BTC310, at 6674 cfm and 0.3" W.C. static pressure, it is seen
that the unit will require a 5 hp motor using a -260 drive, and
the motor sheave should be set at 2.0 turns open to achieve a
blower speed of 866 rpm. 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.
6-563.7
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