# How to Design Enclosures for Heat Dissipation

by Jan Benschop

When you design an enclosure for electronic equipment, for every drop of 10 degrees Celsius or 18 degrees Fahrenheit you can expect double the life expectancy before failure. The size and material of the cabinet and whether you have cooling fins for heat dissipation and heat-conductive material between heat-producing components and the outside of the cabinet are all critical factors. How crowded the cabinet is, how many objects impede airflow and whether you are using fans to cool the cabinet all help or hinder the design object of lower temperature. Heat dissipation depends on outside surface area, not cabinet volume.

1

Add together the total heat dissipation of all components to be mounted in the enclosure, in watts at maximum power. If a manufacturer provides only a British Thermal Unit (BTU) per hour figure, calculate the watt equivalent by dividing the BTU value by 3.414.

2

Lay out the positions of high-heat components at the top of the circuit so that their heat output does not raise the temperature of other components.

3

Calculate enclosure dissipation area in feet as follows: For all six sides, multiply length times width in inches. Add all figures together. Divide by 144 to get area in square feet.

4

Calculate watts per square foot by dividing the total watts from Step 1 by the total square foot surface area from Step 3.

5

Use a temperature rise graph to plot how many degrees the ambient temperature will rise with your equipment/enclosure combination. Experiment with enclosure sizes to aim for an ambient temperature of as close to 25 degrees Celsius or 77 degrees Fahrenheit as possible. If using a cabinet made of aluminum or stainless steel, multiply times 1.5 for efficient heat transfer. Allow a safety factor of an additional 25 percent of surface area.

6

Add fans at the bottom of an enclosure, blowing inward. Positive pressure aids natural tendency for hot air to rise. Provide open venting at the top of the cabinet.