Why Enclosure Cooling Is a Critical Component of Electrical Design Specifications

 

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Most maintenance engineers have experienced firsthand the problems of dealing with electrical enclosure overheating caused by excessive heat load, insufficient ventilation, and inadequate cooling.

Yet, it is interesting that a review of publicly available electrical design specifications shows very little thought is given to electrical enclosure cooling despite the frequent and often detailed references to allowable temperature rise limits for transformers, variable frequency drives, control panels, and power supplies. Perhaps there’s an assumption that electrical and electronic equipment can handle high temperatures, but this isn’t validated by manufacturers’ specifications that generally indicate the maximum allowable temperatures for electronic equipment is in the 35 to 40 ºC range.

Here are some reasons why you should include enclosure cooling in your electrical design specifications.

Maximum Advisable Temperature Limits

The life of electrical and electronic equipment is dictated to a large extent by the Arrhenius equation that predicts that a 10 ºC temperature rise will halve the life of the equipment.

Schneider, a manufacturer of electrical and electronic equipment, recommends the maximum temperature in an electrical enclosure containing such equipment should be 35 ºC (95 ºF). They give an example of how the life of an electrolytic capacitor decreases from 10 years at 40 ºC to 1 year at 72 ºC. Although there may be debates about the optimum temperature, it’s clear that manufacturers are uncomfortable with high temperatures and that equipment life is extended by ensuring electrical enclosures are operated at moderate temperatures.

Heat Load

Modern electronics generally dissipate a lot more heat than electro-mechanical devices. For example, a 15 HP variable frequency drive with an efficiency of over 95 percent will generate 375 Watts of heat.

As a general guide, the temperature rise of an average-size sealed cabinet (60 x 60 x 12 inches) with 375 Watts of heat load would be between 30ºF and 45ºF. As such a panel could contain several drives, the total heat load could be significant and may see the internal temperature soar without some form of enclosure cooling.

Heat Dissipation

Using the example above and assuming several drives and other equipment, it could be expected that the total heat load would be in the region of 2,000 Watts. This amount of heat cannot be dissipated by natural ventilation, and the electrical specification should make provision for some form of enclosure cooling.  The BTUH Calculator provided by Thermal Edge, shows that an air conditioner with a capacity of 8200 BTU/H would be required to maintain a 95°F enclosure temperature with an ambient temperature of 105°F.

Sealed Enclosures

Sealed enclosures are recommended in many circumstances. This may be to prevent contamination by chemical vapor, dust, or prevent water ingress in locations where the enclosure may be sprayed or drenched. Sealed enclosures should always be provided with closed-loop cooling except when the heat load is very low.

Taking cognizance of the enclosure’s heat load, the electrical specification should always make provision for enclosure air conditioning or cooling for sealed enclosures.

Don’t Neglect Enclosure Cooling

It’s wise to include a section on electrical enclosure cooling in electrical design specifications. Good design practices indicate the need to specify relatively moderate enclosure cooling temperatures for the following reasons:

  • Service life is drastically reduced at elevated temperatures.
  • Most equipment manufacturers specify maximum temperatures that are between 35 and 40 ºC
  • Others often derate equipment used at temperatures above 40 ºC.

Do you need help specifying the enclosure cooling system for your next project? Lean on the experts at Thermal Edge. Contact us today!