Industrial Air Make Up Gas-Fired Units

Northern Industrial Co. has developed many types of Industrial Make Up Air Units for larger industrial plants ventilation needs. An improvement in the at industrial facilities environment can produce substantial benefits in terms of increased production, reduced errors, and a decline in complaints and absenteeism among employees.

Air-Handling Units for Make-Up Air and Space Pressurization Applications have the following features:

- Outlet Temperature is usually monitored with a probe mounted near the outlet of the unit.

- Discharge Air Temperature is set at the control panel or using a remote control station.

- Gas input is “modulated” using a butterfly valve, actuator, and controller.

For Space Heating Applications, a room thermostat is used to control outlet temperature. On a call for heat, the unit will provide air heated to the maximum allowed temperature until the room thermostat is satisfied. Once satisfied, the unit will either turn off or will continue to operate at a reduced outlet temperature.

An override option may also be supplied. In this case a room thermostat is supplied in addition to the basic system. The unit is set to full-fire when room temperature falls too low.

Direct Spark units are supplied with an ignition transformer for the igniter.

Piloted Units are supplied with a solenoid-operated Automatic Pilot Valve and a small pressure regulator – around 20,000 BTU – as well as an ignition transformer for the pilot spark igniter.

Pre-purge of the system (by starting the blower for a specified time to provide a minimum air volume change) before ignition of main burner is not required by ANSI code, but is frequently specified by the user. This should be provided whenever a building contains flammable dusts or vapors that could potentially reach and collect within a direct gas-fired unit while it is idle.

To assure safe operation of a direct gas-fired heating system, a number of Safety Interlocks are commonly provided:

A. Damper Limit Switch – Dampers must be fully open before unit will operate.

B. Air Proving Switch – Located near outlet of unit to prove air flow before igniting burner.

C. Flame Supervision – Discussed above. Shuts down unit on flame failure.

D. High Temperature Limit – Signals unit to reduce gas supply when maximum allowable temperature is reached. If air temperature exceeds limit, the unit is shut down.

E. High Gas Pressure Switch – Shuts down unit to protect regulator against spikes in inlet gas pressure.

F. Low Gas Pressure Switch – Shuts down unit when low inlet pressure detected. Redundant safety device, since low flame would also shut down unit.

G. Safety Shut-off Valve – Responds to various inputs listed above – closes off gas supply.

Direct Gas-Fired Air Heating Systems are a class of equipment utilized primarily in industrial and commercial environments to provide for worker comfort. To a lesser extent, these systems are used to condition air for process and finishing applications such as material drying and paint curing.

Direct-fired pressurization units are approximately 93% efficient, with much of the available energy in the burned natural gas being delivered to the space in the form of heat. The supply airstream absorbs the heat that would be normally lost through a flue or vent pipe as in the indirect-fired configuration.