Full Modulating Gas Furnace, Heat Exchanger

Full Modulating Gas Furnace

Full 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 the pilot rate of 125 MBH up to the nameplate rating of the unit. The turn down ratios, therefore, vary from 4:1 for the 500 MBH to 8:1 for the 1000 MBH heater.

Heat Exchanger

The heat exchanger drum, tubes and front and rear head- ers are constructed from AL-6XN or 25-6MO, two of the most corrosion resistant stainless steel alloys available.

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.Use Table 4-1 to program the following system compo- nents for operation by scrolling through the Human Inter- face displays;

Gas Heat

Supply Fan (On)

Inlet Guide Vanes (100% Open, if applicable) Variable Frequency Drive (100% Output, if applicable)

RTM Occ/Unocc Output (Unoccupied) High Fire (90%)

Turn the 115 volt control circuit switch 4S24 located in the heater control panel to the "On" position.

Open the manual gas valve, located in the gas heat section.

2.Once the configuration for the appropriate heating sys- tem is complete, press the NEXT key until the LCD dis- plays the “Start test in __Sec.” screen. Press the + key to designate the delay before the test is to start. This ser- vice test will begin after the TEST START key is pressed and the delay designated in this step has elapsed. Press the ENTER key to confirm this choice.

3.Press the TEST START key to start the test. Remember that the delay designated in step 2 must elapse before the system will begin to operate.

Unit Start-Up (Continued)

WARNING

Rotating Components!

During installation, testing, servicing and troubleshoot- ing of this product it may be necessary to measure the speed of rotating components. Have a qualified or li- censed service individual who has been properly trained in handling exposed rotating components, per- form these tasks. Failure to follow all safety precau- tions when exposed to rotating components could re- sult in death or serious injury.

4.Once the system has started, check the appearance of the flame through the sight glass provided on the front of the heat exchanger. In appearance, a normal flame has a clearly defined shape, and is primarily (75%) blue in color with an orange tip.

5.Check the inlet gas pressure at the modulating gas valve. The inlet pressure should be 6" to 8" w.c..

6.Use a carbon dioxide analyzer and measure the percent- age of carbon dioxide in the flue gas. Refer to the illus- tration in Figure 4-7. Take several samples to assure that an accurate reading is obtained. If the measured carbon dioxide level is between 8.0% and 9.5%, no adjustment

is necessary. If the CO2 is outside this range, it indicates incomplete combustion due to inadequate air or exces- sive gas.

The pressure ratio and bias adjustment screws are lo- cated on top of the regulator under a sealed plate. The actual settings can be seen through windows on each side of the regulator. Refer to the illustration in Figure 4-9.

Note: The burner capacity is controlled by the movement of the air damper. This has been preset at the factory and normally does not need field adjustment. The combustion quality (air/gas) is controlled by the settings on the regulator (the plus

(+)and minus (-) indications relate to the change in gas flow.

7.Set the air/gas ratio to the desired value using the #1 ad- justment screw until the optimum values between (8.0 and 9.5%) are obtained (course setting).

8.Use Table 4-1 to program the minimum (5%) firing rate. Allow the system to operate for approximately 10 min- utes.

9.Use a carbon dioxide analyzer and measure the percent- age of carbon dioxide in the flue gas. If the measured carbon dioxide level is between 6.0% and 8.0%, no ad- justment is necessary. If an adjustment is needed, turn the #2 adjustment screw on the regulator in the Plus (+)

direction to increase the CO2 and in the Minus (-) direc- tion to decrease the CO2. Refer to the illustration in Fig- ure 4-9 for the adjustment screw location.

Note: It is normal for the low fire CO2 to be lower than the high fire.