Retrofitting infrared heaters helped reduce heat loss, speed heat recovery, and boost worker productivity at this school bus maintenance facility in Oklahoma.
For the first time in 20 years, Woodward Public Schools' bus mechanics aren't wearing heavy coveralls, gloves, and other productivity-reducing impediments during wintertime work on the Oklahoma district's 28-bus fleet.

The comfort level of the 800-sq-ft bus maintenance facility rose dramatically after Woodward's HVAC specialist, Doug Morrison, replaced conventional forced air unit heaters with infrared heaters. Previously, heat produced by the three 85,000-Btu forced air heaters was lost through convection in the upper reaches of the 16-ft-high ceiling. Plus heat recovery after opening the large overhead doors was slow. "Heating from the ceiling down to the floor didn't work so well and the forced air heaters seem to run continuously," said Morrison.

Learning from woodshop

With previous infrared heating successes in the district's woodshop classroom and another district maintenance facility, Morrison installed two Schwank Inc., 135,000-Btu, Model STSP infrared heaters. Each tube-style heater is 50 ft long and Morrison added 10 ft of tubing with Schwank's add-on kit to one heater for more radiant coverage. Tube heaters are fueled with either natural gas or propane, and typically have firing rates from 45,000 to 200,000 Btuh. An associated tube length from 10 to 70 ft is attached to the burner and the heated tube emits infrared radiant heat. Tube heaters can be directly vented to the outdoors, or interlocked to an exhaust fan to take away the products of combustion.

"For 20 years, that facility was never warm," said Morrison. "Now the mechanics wear regular work clothes and no longer use winter gloves. Also, the facility is probably getting better energy efficiency, because the unit heaters ran continuously whereas the infrared heaters cycle on and off because they've reached the 60° setpoint."

Unlike forced air unit heaters, which heat the air, infrared's methodology employs radiant heating similar to the sun where objects and surfaces in the space are heated. The difference is significant in employee comfort, and energy savings range from 40% to 60% between the two technologies, according to Richard Smith, product manager of HVAC distributor Washer Specialties, who also assisted Morrison with the sizing and design of the system application.

"There's some convection to radiant heating," Morrison noted, observing that "most of the heat radiates down and keeps it at the floor level where people are working."

Making a quick recovery

Additionally, Morrison has noticed a quicker heat recovery with infrared heating after the large overhead doors are opened. Because infrared heats objects as opposed to the air, the objects such as the buses, tools, and floor continue to radiate heat after closing the doors thus creating a quicker heat recovery. Infrared heating also reduces the likelihood of condensation, since indoor air temperatures are lower and closer to interior surface temperatures.

Morrison took approximately one day to hang pipe and vent each infrared heater. The heaters are suspended about 20 ft above the floor, with chains hung from the roof purlins. The heaters needed two exhaust vents cut in the ceiling, but for the makeup air, Morrison used existing holes from the disconnected ceiling-hung space heaters. ES