Trane RT-SVX10C-EN Limited Modulating Gas Furnace, Unit Start-UpContinued, Figure, Heat Exchanger

10.If the measured carbon dioxide level is below the rec- ommended values for low heat, return the burner to 90% fire rate and repeat steps 6 and 7, to achieve optimum combustion.

11.Program the burner for 100% operation and recheck the CO2 or O2 value.

12.Check the flue gas values at several intermediate out- put levels. If corrections are necessary;

-Adjust the pressure ratio screw 1 at high fire operation only.

-Adjust the bias screw 2 at low fire operation only.

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

Limited Modulating Gas Furnace

Unit Start-Up (Continued)

2.Follow the checkout procedures discussed in the previ- ous 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.

Figure 4-9

Modulating Gas Regulator

Limited Modulating gas heaters are available for the 500, 850 and 1000 MBH heater sizes. These heaters are avail- able 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 head- ers utilities the same materials as the standard two stage furnace.

Unit control

The unit is controlled by a supply air temperature sensor lo- cated 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 sig- nal 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 ac- tuator motor. The position of the air damper in turn controls the combustion air pressure that is sensed by the modulat- ing 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 Modu- lating 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 4-1 to program the limited modulating heat system components for 90% operation by scrolling through the Human Interface displays.

Modulating Gas Regulator Legend

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.

6.Stroke indication.

Note: There are no serviceable parts on the SKP70 actuator. Should it become inoperative, replace the actuator.

98