Limited Modulating Gas Furnace - Trane IntelliPak WEHE Series Installation, Operation And Maintenance Manual

System Start-up
13. Press the STOP key at the Human Interface Module in
the unit control panel to stop the system operation.

Limited Modulating Gas Furnace

Limited Modulating gas heaters are available for the 500,
850 and 1000 MBH heater sizes. These heaters are
available in the same cabinet sizes as the current heaters.
The firing rate of the unit can vary from 33% rated MBH up
to the nameplate rating of the unit. The turn down ratios,
therefore, is limited to 3:1.
Heat Exchanger
The heat exchanger drum, tubes and front and rear
headers utilities the same materials as the standard two
stage furnace.
Unit Control
The unit is controlled by a supply air temperature sensor
located in the supply air stream for VAV units. CV units
have two sensors, one located in the supply air stream and
the zone sensor. The temperature sensor signal is sent to
the Heat module of the IntelliPak Unit Control. The control
signal from the Heat Module is an inverse proportional 5
-10V DC. The higher the voltage signal, the lower the call
for heat.
The 5 -10V DC. signal controls the angular position of the
combustion air damper through a direct coupled damper
actuator motor. The position of the air damper in turn
controls the combustion air pressure that is sensed by the
modulating gas valve. The greater the combustion air
pressure, the greater the call for gas and the higher the
firing rate of the heater. As the temperature setpoint is
reached, the Modulating Heat control will cause the
combustion air actuator to change the damper position to
a lower firing rate that matches the heat load of the space.
1. To verify and check system optimum combustion, use
Table 20, p. 75 to program the limited modulating heat
system components for 90% operation by scrolling
through the Human Interface displays.
2. Follow the checkout procedures discussed in the
previous steps.
Note: The minimum firing rate for a limited modulating
gas furnace in step 8 is 33%. Travel of the
combustion air damper is limited by a welded stop.
3. Press the STOP key at the Human Interface Module in
the unit control panel to stop the system operation.
98
Figure 53. Modulating gas regulator
1 1
3 3
4 4
Modulating Gas Regulator Legend
Figure 53
—
1. Adjustment and indication of the air to gas ratio.
2. Adjustment and indication of the bias.
3. Connection for the Ambient compensation line.
4. Connection for the gas pressure sensing line.
5. Connection for the air pressure sensing line.
Note: There are no serviceable parts on the SKP70
actuator. Should it become inoperative, replace the
actuator.
2 2
5 5
RT-SVX35H-EN