How a Cabinet Cooling Fan Can Cut Project Costs
Provided the conditions are right, the lowest cost method of cooling an enclosure is to use filtered fans. The reasons are simple: fans are cheap, cost very little to run, and are capable of moving a significant amount of air. Furthermore, there is not a lot that can go wrong with them. The basic requirements for the successful use of fans include:
- The ambient temperature must be lower than the enclosure temperature
- The heat load must not be excessive
- No environmental conditions exist that preclude the use of fans.
Ambient Temperature Differential
It’s essential there is a reasonable temperature difference between the ambient air temperature and the anticipated enclosure temperature as this, together with the volume of air, determines the amount of heat that can be removed. The first step is to determine the maximum enclosure temperature; this will depend on the temperature ratings of the equipment, and it’s generally accepted that the temperature should be somewhat lower than manufacturers’ maximum temperature ratings to ensure adequate service life. Secondly, establish the maximum ambient temperature expected in the enclosure’s location. The difference between these temperatures will be the working temperature differential.
Heat Removed by a Fan
The next step is to establish the enclosure heat load by adding up the heat dissipated by each piece of equipment. It may be necessary to consult the manufacturers’ data to obtain accurate information.
Once this exercise is complete, you can obtain a general idea of the size of the fans that would be required to remove this amount of heat with the given temperature differential. To calculate the fan capacity, multiply the heat load in watts by a factor of 3.16 and divide the result by the temperature differential (in degrees Fahrenheit). The result will be the approximate air flow that’s required in cubic feet per minute (CFM). This calculation can be used to verify that the required air flow is within the capacity of the available fans.
Although the calculation above gives a reasonable approximation of the required fan size, it does not take into account important factors such as the heat loss through the walls of the enclosure and the effects of solar radiation. Although these can be assessed, the calculations required are complex. This is because heat loss is affected by the enclosure material, the finish, any insulation, and natural heat transfer. The best method of including these factors is to use an online calculator to arrive at an accurate result.
Ventilation fans should always be used with filters to reduce the amount of dust and debris that can enter the electrical enclosure. Normally, one filter is placed at the air inlet and a second filter is placed at the air outlet. As a rule of thumb, each filter can reduce the airflow by about one third. Therefore, when selecting the fan size, the free flow CFM should be three times the required air flow rate calculated to provide sufficient cooling.
It’s important these filters are regularly maintained. If this is not done, the air flow will be further restricted and the enclosure temperature will increase. If there is a significant amount of dust around the enclosure, washable replacement filters are available that extend filter life. Shrouds may also be fitted over the fans and filters to prevent the ingress of falling water and dust.
Cooling Fans Cut Project Costs
The amount of heat that fans can remove is significant. For example, a 750 CFM fan operating with a temperature differential of 20 °F removes 1500 watts or 5000 BTU/H of heat. This is as much as an air conditioner. If the circumstances are right, a filtered fan solution is an economical solution that will substantially reduce project costs.