Calculating Heat Load

I’ve worked through some strange applications lately.  From an end user using our 2” Super Air Nozzle to distribute an even bead of hot silicone, to helping a helicopter manufacturer eliminate static when conveying and manipulating Kevlar.

Undoubtedly though, the majority of my calls lately have been centering around Cabinet Cooler systems and using EXAIR product to cool electrical enclosures.  At first glance, the calculations to determine heat load can seem overwhelming and a bit confusing.  But, in reality there are only 3 steps.

1.  Determine the surface area of the enclosure.  (Not volume!)  Length x Width for all six sides of the enclosure.

a. Since this method of heat load calculation involves surface area, it is noteworthy to mention that at least one side of the enclosure will be on the floor, against a wall, or mounted to an item with an alternate heat transfer rate.  The surface area of this side can be subtracted from the total, or left into the equation to simplify and provide a margin of safety.

2.  Determine the temperature differentials and the corresponding value in our Temperature Conversion Chart.

3.  Add the temperature conversion values, and multiply by the surface area.  This will give you the BTU/hr. heat load of the application.

Here is an example:

Step 1:  Determine the surface area

Cabinet dimensions:  2’ x 2’ x 1’

Total surface area = 16 ft²

Step 2: Determine the temperature differentials and corresponding conversion values

External Temperature Now:  90°F

Internal Temperature Now:  105°F

Temperature differential, ΔT = 15°F.  The EXAIR conversion table notes a value of 5.1 BTU/hr./ft² for this temperature differential.

Maximum External Temperature:  100°F

Maximum Internal Temperature Desired:  95°F

Temperature differential, ΔT= 5°F.  The EXAIR conversion table notes a value of 1.5 BTU/hr./ft² for this temperature differential.

Step 3: Add the conversion values and multiply by the surface area

(5.1 BTU/hr./ft²   +1.5 BTU/hr./ft²) * 16ft² =

6.6 BTU/hr./ft²  *  16 ft²  =

105 BTU/hr.

As you can see, the heat load of this application is relatively low.  However, the process is the same for any Cabinet Cooler system calculation.  If you have any questions regarding the proper unit for your application, call an application engineer.

Lee Evans
Application Engineer

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