In the past we shared tips for determining where to house your compressor. Once you’ve found the ideal home for your compressor, you need be mindful of a few key factors to ensure it continues working properly and efficiently.
Housing your compressor in a separate room saves space on the work floor and can reduce noise, but a few measures need to be taken to guarantee this room remains a safe space for your system. One of the most important issues is excess heat in compressor rooms.
We all know compressors generate heat. But how does that happen? Kinetic energy – the energy of movement – manifests as temperature. When the temperature of an object is lower than the ambient temperature, the difference is perceived as heat. This can be seen in many daily examples from the agitated water molecules that make your coffee hot to the warmth you feel from rubbing your hands together on a winter day.
In compressor rooms, heat can come from various sources such as sunshine, people, lights and motors, as well as any other particular sources of heat. Some of these sources, like sunshine, lights and motors, are described as sensible heat sources. Sensible heat is the heat associated with a change in temperature, while latent heat is usually associated with phase changes in water vapor. The heat load from people is part sensible and part latent.
Sensible heat sources make the biggest impact on compressor room heat. When deciding how much sensible heat to allow, each source must be considered. A temperature rise of 10 degrees is very common for compressor room environments. The sensible heat rise can be determined by the equation:
Hs = Qs x ρ x Cp x ΔT
where
Hs = sensible heat gain (BTU/hr)
Qs = volumetric flow for sensible heat (CFM)
ρ = density of air (lb/ft3)
Cp = specific heat of the air (BTU/lb-deg. F)
ΔT = change in temperature (degrees F)
To calculate the required general ventilation (also described as the required volumetric flow), the acceptable temperature or humidity rise must be determined. To do this, the volumetric flow required for dissipating the sensible heat and latent heat must be calculated. The necessary volumetric flow is usually the larger of the two numbers, and in compressor room applications that is always the sensible heat.
The type of compressor used can affect the amount of heat in the compressor room. Ventilation air from air-cooled compressors transmits almost 100 percent of motor energy in the form of heat, while water-cooled compressors only retain about 10 percent.
Proper compressor room ventilation is not just about keeping the room comfortable, it is a critical factor in protecting your equipment, maintaining compressed air quality, and ensuring the long-term reliability of your entire compressed air system. A well-designed ventilation system accomplishes three primary goals: it removes the heat generated by the compressor and other heat sources, it supplies a steady flow of fresh, cool intake air for the compression process, and it maintains ambient conditions within the safe operating range of all equipment in the room.
The starting point for designing compressor room ventilation is calculating the total heat load in the room, as described in the sensible heat formula above. Once the total heat load is known, the required ventilation airflow in CFM can be determined. This figure tells you how much air must be moved through the room per minute to keep the temperature rise within acceptable limits, typically no more than 10 degrees F above the ambient intake air temperature.
Intake and exhaust vents must be correctly sized and positioned to create an effective airflow path through the room. Intake vents should be located low on the wall to draw in cooler air from outside, while exhaust vents or fans should be positioned high on the opposite wall or in the ceiling to expel hot air that has risen to the top of the room. This arrangement takes advantage of natural convection and ensures that hot air does not recirculate back over the compressor.
For air-cooled compressors, some manufacturers offer ducted cooling configurations that allow the hot discharge air from the compressor's cooling system to be directed directly out of the room through a dedicated duct, rather than releasing it into the compressor room. This can significantly reduce the ventilation load on the room and is particularly effective in warmer climates or heavily loaded installations where managing heat buildup is a challenge.
In situations where natural ventilation is insufficient to handle the heat load, powered ventilation fans should be installed and sized to deliver the required CFM of airflow through the room. In hot climates or rooms with particularly high heat loads, supplementary cooling such as a dedicated air conditioning unit may also be necessary to maintain safe operating temperatures year-round.
But why go through all this trouble to cool off a room you probably won’t be in that often? While heat is a normal byproduct of kinetic energy, too much heat in a compressor room can cause problems.
Air-cooled compressors with high discharge temperatures can cause dryer inlet temperatures to exceed the 100 degrees F maximum and ambient temperatures of air-cooled dryers to exceed 100 degrees F. Both of these issues will reduce the rating of the dryer to a point that will impact the rated pressure dew point and possibly cause more moisture to condense. Higher inlet temperatures reduce the air density, which reduces the mass flow of the compressor.
High temperatures can also cause the lubricant in oil-injected compressors to varnish, and oil-injected rotary screw compressors will shut down when temperatures exceed about 230 degrees F. To avoid these risks, consult an expert to make sure your compressor environment is properly ventilated.