Some Like It Hot…Your Compressor Room Doesn’t

By: Neil Mehltretter

Many facilities have issues with compressor room temperature regulation. This is due in large part to poor planning. Too often the compressor room is the last part of the facility considered when building a new plant or retrofitting an old one. As a result, the compressed air system is installed wherever there is room left—cramped spaces, alongside boilers or other equipment. Most compressed air systems have standard temperature ratings between 40 oF and 115 oF. However, considering that refrigerated dryers and heated desiccant dryers have correction factors when inlet temperatures rise above or fall below 100 oF, careful consideration should be taken into account for ambient conditions for both summer and winter.

Ventilation has a huge impact on the ambient temperature in the compressor room and is often the missing link to temperature regulation issues. Here are four factors to consider when designing the ventilation for your compressor room.

Some_Like_It_Hot1. Inlet Air: The compressor room needs a sufficient source of inlet air. The recommended size of the opening can often be found in the equipment manual. If you have multiple pieces of equipment, you can either have one large opening or, better still, separate openings for each piece of equipment. The inlet air opening should have thermostatically controlled louvers/dampers to automatically open and close based on the temperature.

2. Recirculating Ductwork: Compressors produce a lot of heat (approximately 2550 Btu/hp). This heat needs to be removed otherwise the ambient and operating temperatures will increase, reducing the system efficiency, and in extreme cases, cause equipment shutdown. Again, it’s best to have thermostatically controlled louvers/dampers on the ductwork. In the winter, the warm air can be recovered and recirculated to the compressor room or an adjoining room to provide space heating. In the summer, the warm air can be ducted outdoors.

3. Exhaust Fan: Ancillary equipment in a compressed air system, such as refrigerated dryers, can require significant amounts of cooling air. If this is the case, an exhaust fan may be required to provide additional airflow.

4. Cooling Air Flow: Be careful of recirculation when planning where each piece of equipment and ducting will be placed. This picture below shows hot air inadvertently recirculating to the cooling air inlet:


This image shows the ductwork corrected so the exhaust is now directed towards the roof and the cooling air inlet can no longer inadvertently ingest the warm air:


There are a number of factors to consider when planning the ventilation for your compressor room, these are just a few of the major components. The best advice is to talk with an HVAC specialist as well as the compressed air equipment manufacturer to make sure you will have the proper supply of cooling air for your equipment. Taking the time to plan the compressor room will help eliminate temperature swings, equipment downtime, and keep your system as efficient as possible.

4 thoughts on “Some Like It Hot…Your Compressor Room Doesn’t

  1. I need to calculate the savings of a not ventilated compressor operating system against a well ventilaated system. Can you help me with the logic for savings calcualtion

    1. Calculating the savings would be three-fold:

      1) Off-setting Costs: You would need to look at the cost savings potential by using the space heating in your facility rather heating up the space with an alternative means (such as heating oil). This would be assuming that the hot cooling air is sent out to the general atmosphere rather than repurposed. If the compressor is oil-flooded, then there are also options to use the hot compressor oil to heat water for a process or as a pre-heater for a boiler. If the compressor is oil-free then there are also other options available to heat process water. You would have to check with your manufacturer for such an option with a new compressor purchase or as a retrofit.
      2) Lost Productivity Costs: Compressors are very effective heaters. 96% of electrical energy input to the compressor is available as heat recovery. If all this heat is then discharged to the compressor room, it can be recirculated to the inlet. The hotter the cooling air inlet to the compressor, the hotter the cooling air outlet. If the compressor cannot properly cool itself, it will shut down on high temperature. This can cause a full plant outage for your facility, and if there is not a sufficient back-up compressor this can be very costly to your facility.
      3) Maintenance Costs: In addition to the potential of repeated shut downs affecting production, the hotter cooling air inlet temperatures and ambient temperatures can affect the operational components of the compressor. In effect increasing maintenance intervals, which will also increase the costs.

      The Off-Setting Costs can be calculated—here is an example for a 60 hp, air-cooled compressor at 110 psig (note that the calculation would be for a specific time frame per year):
      Heating period: 125 days
      Airend load period: 8 hours/day
      Price of heating oil: $2/gallon
      Specific heat value of the oil: 9.87 kWh/l = 37.4 kWh/gallon
      Heating efficiency: 0.9
      Total electrical power consumption: 51.4 kW

      Usable energy in hot air (assumes new compressor):
      =96% of total power consumption
      =0.96 * 51.54 kW = 49.34 kW

      Usable energy * time under load * heating oil price / heat value of the oil * heating efficiency
      =49.34 kW * 1,000 h * $2/gallon / 37.4 kWh/gallon *0.9
      =$2,931.67 at 1,000 hours under load per year

      You would also have to consider the cost of installing ductwork, and or running piping in the case of pre-heating water. The Lost Productivity Costs can also be calculated, if you know that any plant outages are due to overheating issues (or a secondary result of overheating issues). An increase to Maintenance Costs is variable; you may see an increase in the intervals of minor services per year as well as major services per year. You could also see a reduction in compressor lifetime, which means that you will be purchasing a new compressor sooner rather than later.

      When considering the purchase of a new compressor or a new compressed air system, the overall environment is key. Simply replacing an unreliable and inefficient compressor by purchasing a more efficient compressor or compressed air system doesn’t always solve your problems; especially if you are putting the new system in the same poor environment. This lends to premature failure and unmet expectations.

  2. We have a air compressor right next to a dock door and. We are using the heat from the compressor to heat this are up. Couple of time the compressor has gone off and the dignostic alarm said ( off back pressure )
    Bit after the compressor trips off on high tempe.
    We had the compressor checked about 3 or 4 time for the same issue and the technician keep telling me that the issue is the cold weather. The area has not gone lower then 65 or may be 60 degrees.
    I dont think that’s the issue.
    I think we have a problem with the unloader valve or may be the minimum pressure check valve.
    What do you think ?

    1. It’s difficult to say for sure without knowing the particulars about your installation. In cases like this, it’s always best to check your service manual or check with your manufacturer. Here’s some general guidance.

      In general even though the temperature in the area can be 60 to 65 F, that doesn’t mean that the cooling air temperature into the compressor is 60 to 65 F. If the cooling air inlet is taken from outside directly (i.e. not from the room), it could be closer to 40 F (or lower) during colder days. In these cases, the temperature would be too cold and most newer PLC controlled compressors may shutdown due to ambient temperature too cold. In the same scenario with inlet temperatures 60 to 65 F, if the ducting is too restrictive and the pressure drop the cooling fan has to overcome is too high, then this can cause a high discharge temperature. Other contributing factors to a high discharge temperature are general maintenance issues such as cleaning the oil and aftercoolers regularly. We’d recommend that you check the compressor service manual for the specific messages and address accordingly.

      The “off back pressure” alarm could refer to the discharge pressure of the compressor, meaning the compressor reaches its discharge pressure too quickly and even exceeds it. This typically means that there is an issue with a restriction in the discharge piping (may times the discharge valve is closed), or that there could be an internal issue with the compressor. Again, we’d recommend that you check the compressor service manual for the specific messages and address accordingly.

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