How do I size an air conditioner for a VFD enclosure based on BTU/h requirements?
In certain environments, a drive enclosure may require an A/C unit to properly manage heat generated by a VFD. This article will help the user determine the cooling requirements for PowerFlex drives based off information provided in the PowerFlex drives technical manual.
To determine the cooling requirements for a PowerFlex drive panel, the following steps should be taken:
1. Determine the PowerFlex drive's heat dissipation or "Total Watts Loss."
-Using the appropriate PowerFlex technical manual, locate the "Total Watts Loss" information for the associated drive catalog part number. Links to the PowerFlex 520 and 750 series drives can be found below:
2. Convert Watts to BTU/h (British Thermal Units per hour)
-Take the Total Watts Loss of the PowerFlex drive and multiply it by the constant value of 3.412 to convert Watts to BTU/h.
- Energy Equivalency: 1 watt equals 1 Joule per second. One BTU is approximately 1,055 Joules.
- Time Conversion: When you convert 1 Joule per second into Joules per hour (3,600 seconds) and divide by the Joules in a BTU (1,055), you get the constant 3.412.
-It is recommended to factor in a safety margin of 15% to 20% when calculating air conditioning requirements for PowerFlex drives to account for ambient temperature spikes and component aging.
Ex:
PowerFlex 753 156A 125HP Normal Duty = 1,593 Total Watts Loss
1,593 Watts x 1 (drive per enclosure) x 3.412 (W to BTU/h constant) x 1.15-1.2 (Safety Factor) = 6,251 - 6,523 BTU/h.
- Ambient Temperature: If your enclosure operates above 40°C (104°F), you must derate the drive and increase the cooling capacity by 10–15%.
- Altitude: Drives used above 1,000 meters (3,300 ft) require additional cooling due to thinner air density.
- Enclosure Rating: Ensure the cooling unit maintains the NEMA rating (e.g., NEMA 12 or 4X) of your cabinet.