A metal products processor installed a new 75-kW VSD controlled air-cooled compressor in its plant — located in a separate compressor room. The environment in the plant is full of aerosols produced by the process machinery cutting and milling process, so the ventilation system is the compressor room was updated to bring in 100% outside air to cool the compressor. Use of this cleaner air will keep the compressor and its electronics clean, preventing contamination problems.
The plant is located in a part of the country where temperatures reach below freezing temperatures for six months of the year. Because bringing in very cold air would cause the compressor coolers to freeze up, something had to be done to temper the air.
A heating contractor was called, and after some calculations based on the compressor cooling air flow, the contractor installed a large, 90-kW electric heater to condition the inlet cooling air.
A compressed air auditor was called to do efficiency measurements to verify the operation of the new compressor and found that even with inlet temperatures hovering about 32° F, the inlet heater was consuming more than twice the power as the air compressor, calculating to about $1,300 per month in electricity costs!
The heating contractor was unaware that the waste compressor heat could be used to help condition the inlet air temperature and saving substantial heating costs (see Figure 2). In the arrangement at left, only the small amount of air brought in from outdoors needs to be heated, the rest of the heat is provided by the air compressor.
Modifications are underway to correct the situation, and to send the compressor into the plant to supplement building heaters.