In industry, electronic equipment is typically housed in an enclosure to protect it from harsh atmospheres laden with dust, oils, other byproducts of industrial processes, and from particulate that occurs naturally. The enclosed electronics produce heat, which must be dissipated to allow the equipment to operate at peak performance and to achieve the maximum life cycle.
When equipment is placed in a NEMA type or IP rated electrical enclosure, the heat must be transferred through the walls of the enclosure to the ambient air surrounding the enclosure. Because of the physical property of warmer air being less dense and rising, the warmest point is typically near the top of the enclosure. Electronic equipment located at or near the top is subject to the warmer air and is the most likely to experience operating difficulties or premature failure.
Many methods are used to eliminate this problem. Which method is best is determined by many factors such as equipment loading, cabinet design, ambient environmental conditions and available space.
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 thermoelectric, 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.
These closed-loop vapor compression cooling systems are of two general types, horizontal mount and vertical mount. Horizontal mount systems are typically mounted to the tops of enclosures where they induce the warm air from the top of the enclosure and deliver cold air at the top of the enclosure. These systems perform well and maintain fairly uniform enclosure temperatures in applications where enclosure top space is available, the enclosure is not so tall that the throw of cold air extends to equipment near the bottom of the enclosure, and there is no restriction to air flow from the cold air outlet of the air conditioner by equipment located inside the enclosure.
A potential problem with horizontal type air conditioners is the condensate that may be produced by these air conditioners. Manufacturers of these types of air conditioners typically provide condensate drain nipples on the bottoms or sides of their systems to which tubing is attached and the water is routed to a floor drain or condensate evaporator. Others offer either internal or external condensate evaporators. One thing which is inevitable, the drain will eventually clog without proper maintenance, or the condensate heater may fail, which can lead to condensate overflow into the enclosure. This can be a disaster.
To avoid this potential problem, most users of vapor compression cooling systems select vertical mount models. These air conditioners are mounted to the walls of the enclosure, inducing heated air and supplying cold air at the sides of the enclosure. These vertical mount systems still produce condensate, but it is less of a threat to enter the enclosure and damaging equipment. Many manufacturers offer these vertical mount air conditioners. However, there are differences in the theories for air circulation within the enclosures.
Some manufacturers supply cool air near the top of the enclosure and remove the warmer air nearer the bottom. This method supports the theory of the colder air being more dense, 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. Tests with an evenly distributed heat load within the enclosure, no major air flow restriction, a properly sized cooling system will maintain an approximate 7 degree Fahrenheit (4 °C) air temperature difference between thermocouples placed near the top and bottom of the enclosure.
Other manufacturer designs supply cold air near the bottom of the enclosure and induce the warm air at the top, supporting the theory of filling the enclosure with cold air from the bottom. As the heat warms the air from the equipment, it will rise to the top where it is removed by the cooling system. Tests have again indicated an approximate 7 degree Fahrenheit (4 °C) air temperature difference between thermocouples placed near the top and bottom of the enclosure.
Another method is to supply cold air and induce warm air near the top of the enclosure. This method combines the two theories above in that the supply of cold dense air at the top of the enclosure will fall over the heat producing equipment, absorb heat and rise to the top where it is again removed by the cooling system. With this method of air circulation, equipment positioning is critical. If equipment is placed directly in front of the cold air supply of the air conditioner, short cycling of the air conditioner will occur because of cold air being diverted directly back to the warm air return. However, when equipment is located to promote adequate air circulation, test results have shown an approximate 4 degree Fahrenheit (2.2 °C) difference between thermocouples placed near the top and bottom of the enclosure.
Many methods and theories of proper air circulation in an enclosure exist. The key to maintaining adequate heat removal and air circulation within the enclosure is air movement throughout the enclosure, eliminating any “dead spots” or air stagnation. Equipment internal fans can help with this but none of the above methods of air delivery can insure elimination of the “dead spots”, and there is no “perfect air conditioner” for every application.
ICEqube is taking steps toward providing that “perfect air conditioner” for your enclosure cooling application by offering a multitude of cooling systems, horizontal and vertical mount, top and bottom flow, with a variety of air flow configurations. Contact your ICEqube sales representative for a consultation regarding your Btuh cooling requirement and the models available to meet your enclosure cooling requirements.
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.
