In industry, electronic equipment is typically housed in an enclosure to protect it from harsh atmospheres containing dust, oils, chemical byproducts, and naturally occurring particulates. The enclosed electronics generate heat, which must be dissipated to ensure optimal performance and maximum service life.
How Heat Builds Up Inside an Enclosure
When equipment is placed in a NEMA Type or IP-rated electrical enclosure, the heat must be transferred through the enclosure walls to the surrounding ambient air. Because warmer air is less dense and rises, the warmest point typically occurs near the top of the enclosure. Electronic equipment located at/or near the top is therefore exposed to the warmest air and is most susceptible to operating issues or premature failure.
Factors That Determine the Best Cooling Method
Several methods can be used to eliminate this problem. This optimal approach depends on factors such as:
- Equipment loading
- Ambient environmental conditions
- Available space
When Active Cooling Systems are Required
In situations where the ambient temperature exceeds the optimum operating temperature of the equipment, or the heat dissipated by the equipment is such that it cannot be dispersed with passive systems such as ventilation or air-to-air heat exchangers, active cooling systems such as thermoelectrics, vortex tubes, chilled water systems or a vapor compression air conditioning system must be used. The most common of the active systems being the vapor compression system.
Passive systems include:
- Ventilation
- Air-to-air heat exchangers
Active cooling systems such as the following must be used:
- Thermoelectric systems
- Vortex tubes
- Chilled water systems
- Vapor compression air conditioning systems
Types of Vapor Compression Cooling Systems
These closed-loop vapor compression cooling systems are of two general types:
- Horizontal mount
- Vertical mount
Horizontal Mount Cooling Systems
Horizontal mount systems are typically installed on the top of enclosures, where they draw warm air from the top and deliver cooled air back into the top of the enclosure. These systems perform well and maintain fairly uniform enclosure temperatures when sufficient space is available on top of the enclosure; the enclosure is not excessively tall, and internal equipment does not obstruct the cold air discharge.
However, a common concern with horizontal mount air conditioners is condensate management. Most manufacturers provide condensate drain nipples on the bottom or side of the unit, allowing tubing to route the water to a floor drain or condensate evaporator. Other manufacturers may offer models with built-in internal or external condensate evaporators. Without regular maintenance, drain lines can clog, or the condensate heater can fail, causing condensate to overflow into the enclosure and potentially causing serious damage to sensitive electronics.
Why Many Users Choose Vertical Mount Systems
To reduce the risk of condensate entering the enclosure, many users of vapor compression cooling systems choose vertical mount air conditioners. These units mount on the side walls of the enclosure, drawing warm air and supplying cooled air from the sides. While they still produce condensate, the risk of it reaching internal components is significantly lower. Many manufacturers offer these vertical mount air conditioners. However, there are differences in the theories for air circulation within the enclosures.
Air Circulation Method 1: Cold Air from the Top
Cold air is delivered near the top while warmer air is removed near the bottom. This method supports the theory that cold air being denser and supplied near the top will fall over heat-producing equipment. As the air absorbs the heat produced by the equipment, it will rise causing turbulent convection currents within the enclosure, which will result in a balanced enclosure temperature. With an evenly distributed heat load, properly sized cooling system, and no major obstructions, testing typically shows an air temperature difference of approximately 7°F (4 °C) between thermocouples placed near the top and bottom of the enclosure.
Air Circulation Method 2: Cold Air from the Bottom
Cool air is introduced near the bottom while warm air is extracted from the top. This method is based on the theory of filling the enclosure with cool air from the bottom upward. As the equipment generates heat, the warm air rises to the top, where it is removed by the cooling system. Test results have again shown an approximate 7°F (4 °C) air temperature difference between thermocouples placed near the top and bottom of the enclosure.
Air Circulation Method 3: Combined Top Airflow Strategy
Both the cold air supply and induced warm air occur near the top of the enclosure. This hybrid approach combines the two previous methods: cold, dense air is supplied at the top, falls over the heat-producing equipment, absorbs heat, and then rises back to the top where it is removed by the cooling system.
With this method, equipment positioning is critical. If equipment is placed directly in front of the cold air discharge, the cooled air can be pulled straight back into the return, causing the air conditioners to short cycle. However, when equipment is positioned to allow proper airflow, test results show an approximate 4°F (2.2 °C) difference between thermocouples placed near the top and bottom of the enclosure.
Key Considerations
- Equipment positioning is critical
- Improper placement can cause short cycling
When properly configured:
- Approximate 4°F (2.2 °C) temperature difference is achieved
The Importance of Air Movement and Eliminating Dead Spots
Effective enclosure cooling depends on consistent air movement throughout the entire enclosure to prevent stagnant air or “dead spots.” While internal equipment fans can assist with air circulation, no single air delivery method guarantees perfect results in every application. There is no universal “perfect air conditioner.” The best solution always depends on the specific enclosure, load, design, and environmental application requirements.
ICEqube’s Approach to Enclosure Cooling
ICEqube is committed to delivering the ideal air conditioner solution for enclosure cooling applications. The company provides flexible mounting and airflow options, including horizontal and vertical mounts as well as top and bottom flow configurations.
Contact your ICEqube sales representative today for a personalized consultation to determine the right Btu/h cooling capacity and the best model for your specific enclosure cooling needs.
Note: Above reported test results were obtained using a 67” high by 26” wide by 26” deep free-standing enclosure with an evenly distributed internal heat load. Results may vary pending enclosure dimensions and internal equipment loading.
