Why BTU/H Calculations Are Essential in Enclosure AC Selection


With the increasing application of electronics in instrumentation and control systems, the onus is on the enclosure air conditioner to maintain the proper temperature for normal operation of the components. True to Moore’s prediction, the number of transistors per square inch in electronic boards has doubled each year, not just increasing their capacity but also the heat that has to be dissipated. For equipment such as transformers, variable frequency drives and switching power supplies, there exists a general operating temperature range as described by the manufacturer specifications over which the life of the component starts to deteriorate. Many electrical drives are rated for operation at about 35 °C; for every 10 °C increase in temperature, the life of the equipment halves in value. If you want to prolong the life of your valuable electrical equipment, it is critical that you choose an AC for your enclosure that can handle its total heat load.

Process Variants

Other than a scientific approach used to calculate the heat load inside your electrical enclosure, there is no defined method to specify the size and cooling capacity of your air conditioner. There are factors like the size of your enclosure, material, color and type of insulation, maximum ambient temperature at the site of installation and maximum allowable temperature inside the enclosure that make your setup unique. Therefore, there may be no precursors to your current setup that you can base the size of your air conditioner on.

Finding the exact heat load in the enclosure is important so that you can choose air conditioners that fit your cooling capacity requirement. Air conditioners with a larger cooling capacity are not just expensive but would also raise your utility bill with their wastefully high energy consumption while a smaller size air conditioner could spell slow damage to your equipment due to insufficient temperature control inside the enclosure.

Heat Load Calculations

Temperature control inside the electrical enclosure is crucial to the longevity and efficiency of components; therefore, it is imperative to understand the heat sources inside the enclosure. The total heat load in the enclosure is the sum of heat dissipation from the electrical equipment and heat transfer from the environment. Improper calculations or neglecting to factor in the solar heat gain could be detrimental to the electrical and electronic equipment in the enclosure. For instance, consider a 10 kW variable frequency drive inside a 48×60×16” painted steel housing with no insulation. The equipment has a heat dissipation of about 300 W. If your installation is located in a place with maximum ambient temperature of 105 °F and the desired internal temperature is 85 °F, the required cooling capacity for an air conditioner is 1314 BTU/H. With this information, you are now equipped to choose from among air conditioners with a cooling capacity of 1500 to 2000 BTU/hr.

Selecting Your Air Conditioner

Typically, you will find air conditioners with cooling capacities ranging from 1000 BTU/H to 20000 BTU/H. Without the proper calculations of the heat load in your system, selecting the right air conditioner is an expensive guessing game. The ETM calculator from Thermal Edge factors in all constants of your system and gives you an accurate idea of the active cooling solution your enclosure requires. This enables you to pick the most cost-effective and energy-efficient solution from air conditioners, air to air heat exchangers, filtered fans and heaters that meet your cooling requirements. Having zeroed in on the most crucial element of design, you can proceed with identifying the NEMA rating of the enclosure, the type of sealing you need, and condensate management solutions.

With a fleet of enclosure cooling solutions and technical expertise, Technical Edge has helped innumerable customers with their cooling requirements. Give us a call and get a quote for your cooling needs today.