Unit Heater Sequence of Operation

How Water Unit Heater in a mechanical room

Unit Heater Sequence of Operation – Mechanical rooms have very important equipment that needs to be protected. Often mechanical rooms are not conditioned and subject to outside temperatures and freezing conditions that can freeze piping inside the mechanical. For that reason, mechanical rooms often have unit heaters located there to protect piping and other things that cannot be frozen or subject to freezing conditions. The components and sequence of operation are fairly simple. The main components in a hot water unit heater include a fan, a valve, and of course the piping and coils along with the cabinet. Unit heater sequence of operation can also rely on an automatic control system but it can also be stand-alone.

Unit Heater Mechanical Room - Hot Water Unit Heater Sequence of Operation

Each Hot Water Unit Heater shall be controlled by a unit-mounted thermostat. Sometimes this will refer to as a wall-mounted thermostat. Upon a drop-in space temperature below the heating setpoint of 55° F the fan shall start and the hot water valve shall open. When the temperature rises above the setpoint, the fan shall stop and the valve shall close.

The location of the thermostat is dependent upon the design engineer’s specifications.  Typically it is located on the wall next to the door of the mechanical room especially if the door has access to the outdoors.

The valve is usually located on the piping near the unit heater and is controlled by a thermostat and monitored by the building automation system. Sometimes the unit heater is controlled and monitored by the building automation system so any alarms from the unit heater by the BAS especially in freezing conditions should not be ignored.

Unit Heater Sequence of Operation | Conclusion

Unit heaters can be either electric, gas, infrared, hydronic hot water, or steam depending on the availability of resources and power. The bottom line, is that unit heaters are needed to protect mechanical rooms from freezing conditions. Everything from boilers to water heaters to other piping systems such as fire sprinkler piping and controls is protected with unit heaters.

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Unit Heater Sequence of Operation