Don't overlook how important it is to consider all contributing factors that will adversely affect equipment operation. One of the chief enemies of a successful enclosure installation is heat, which is a by-product of electrical and electronic components that are contained within and possibly the air surrounding the installation. If not dissipated, this heat has the potential to cause early failures and malfunctions. The components commonly packaged in electrical enclosures, computer server racks, and other product compartments are the vital controls for drives and displays used in many industries, such as:
- Telecommunications • Food and Beverage Manufacturing Equipment
- Industrial Automation • Machine Tools
- Medical Instrumentation • Wastewater Treatment
- Transportation • Water Purification
- Retail Kiosks • Security Imaging and Detection Equipment
- Petrochemical • Robotics
- Steel Manufacturing and Forming • Paper Manufacturing
- HVAC • Elevator Controls
The Sources of Heat
For example, nearly all of the power of electronics or microprocessors is converted into heat, and devices that transmit power have voltage drops or efficiency losses that are also converted into heat. This internal heat load is one source that will cause the enclosure temperature to rise to an unacceptable level. To help estimate heat generation, spreadsheets or calculators are available from enclosure cooling manufacturers. Heat gain or loss is expressed in watts or BTU’s (British Thermal Units); these units of heat are converted with the following formulas: Watts = BTU /hr. ÷ 3.414 and BTU/hr. = Watts x 3.414.
Ambient air, the air outside the enclosure, can also be a potential source of heat gain. In some environments, the ambient air may be cool enough to allow the enclosure to dissipate heat; however, ambient air in warmer climates may be so hot that it adds to the heat load.
When enclosures are located outdoors, heat from the sun is transferred to the sensitive components inside the cabinet. This is known as solar load or solar gain, and the effects can be significant. A prime example of this is a car parked outside on a sunny day; the temperature quickly rises in the passenger compartment as the solar rays travel through the exposed glass and metal and the heat becomes trapped within the confines of the vehicle. To help offset solar load in an electrical enclosure, thermal insulation, white or light colored reflective paint finishes and a roof or sunshield can be used. Enclosures can also be constructed with a double wall to help protect against solar load, however this tends to be a costly solution.
Humidity and Air Infiltration
Outside air entering an electrical enclosure carries both heat and humidity, and high relative humidity in the air potentially increases the heat content. Additionally, condensing water vapor or the formation of dew from high humidity (particularly in outdoor enclosures) will damage the electrical and electronic contents within the enclosure. Therefore, it is best to seal up enclosures and feeding conduits completely to avoid this type of heat gain and the harsh effects humidity can have on the components.
Removing the Heat
There are many ways to successfully manage unwanted heat. Addressing the requirement and including a thermal management solution to the system from the onset is always preferable. If needed, a sizing program will help guide you to the best choice for your application. Factors such as heat load that must be removed, operating voltage, and NEMA (National Electrical Manufacturers Association) style required will also help narrow your choices. Based on the environmental conditions, a fan, blower, heat exchanger or air conditioner may be necessary.
If you plan ahead and consider all the factors that may have a negative effect on your equipment, costly field retrofits and downtime can be avoided.