The Cabinet Cooling System Choice: How to Ensure Success
The best time to consider cabinet cooling system options is during the cabinet design stage. Crucial decisions that affect heat load and methods of cooling can then be made in conjunction with equipment selection and cabinet layout. It’s also the correct time to evaluate the implications of the cabinet’s location and to identify environmental constraints.
The careful evaluation of all these factors helps ensure the successful choice of the cabinet cooling system.
Cabinet Size and Shape Affects Cooling Design
The type of cooling solution has a bearing on equipment layout. With fan cooling, equipment that generates heat should be placed near the bottom where the air is cooler. But if a side-mounted cooling solution is used, hot equipment should be placed next to the cool air inlet.
Consequently a wide, short cabinet may be better for fan cooling, whereas a tall and narrow cabinet is more suited to side-mounted cooling. Also, take into consideration that the greater surface area of a large enclosure will have better heat conduction properties than a small enclosure.
Assess the Heat Load
Calculate the cabinet heat load by adding together the heat generated by each piece of equipment. To calculate the heat generated by power conversion equipment like variable frequency drives, inverters, rectifiers and transformers, subtract the device efficiency from one (1-Efficiency) and multiply this by the input current times the input voltage. You can reduce the total heat load considerably by choosing efficient power conversion equipment.
If the cabinet is outdoors, solar radiation will contribute towards the total heat load. Try to minimize this by shielding the cabinet.
Identify Ambient Conditions
Establish the ambient conditions at the location where the cabinet is to be installed. Key considerations include:
- Maximum ambient temperature: Establish the highest ambient temperature recorded for that location by consulting local climate data, if outdoors. If indoors, identify heat sources and, if possible, measure the air temperature.
- Dust and dirt: Is the location excessively dusty?
- Risk of corrosion: Are corrosive vapors, including salt spray, or chemicals present?
- Water: Will the enclosure be sprayed, washed down or subject to excessive splashing?
- Humidity and dew point: In humid locations, condensation may occur inside the enclosure when the temperature falls below the dew point; check to see if this is a possibility.
These factors will largely determine what cooling options are viable and help establish the required NEMA rating of the cabinet.
Select the Enclosure Temperature
Choose a maximum enclosure temperature that’s lower than that of the most sensitive equipment. It’s wise to adopt a conservative approach and increase the margin of safety by selecting an enclosure temperature that’s several degrees below the maximum temperature; 95 °F is a good choice for most electrical equipment.
Enclosure Temperature Management Calculation
It’s now possible to calculate the cabinet cooling system capacity using the information that’s been collected. Preferably use an online Enclosure Temperature Management (ETM) calculator as this method of calculation has proven to be simpler and more accurate than manual calculations. If you are unsure which is the best cooling method, repeat the calculation for all three cooling options; Air Conditioners, Heat Exchangers and Filtered Fans.
Cabinet Cooling System Choices
After identifying the viable cooling solutions, the next step is to decide between open loop and closed loop cooling:
Open loop cooling:
Open loop cooling draws outside air into the enclosure using filtered fans and is most suitable for NEMA Type 1 and Type 3 ventilated enclosures that are not subject to excessive dust, heavy splashing or water spray. An optional 3R Fan Shroud Kit can be specified for outdoor use. Always bear in mind that fans only remove heat and cannot cool the enclosure below the ambient air temperature.
Closed loop cooling:
With closed loop cooling, the enclosure cooling circuit is completely separate from the external air cooled circuit. The two options are air to air heat exchangers and enclosure air conditioners. An air to air heat exchanger is a good choice for moderate heat loads and its only limitation is that, like cooling fans, it cannot cool below the ambient air temperature. If the ambient temperature is higher than the required enclosure temperature or the heat load too large, an enclosure air conditioner is the best choice. Another benefit of an air conditioner is that it can be equipped with an optional heater package to prevent internal condensation in cool, damp weather. Air conditioners and air to air heat exchangers can be supplied for NEMA Type 12, 4 or 4X enclosures to suit all environmental requirements. Heavy-duty filters are also available to provide added protection to air conditioner condensers in extremely dusty conditions.
The Recipe for Success
Most enclosure cooling problems can be avoided by incorporating the cabinet cooling system design into the initial design phase. Benefits include the ability to select the best cooling option and the optimum internal layout; these can be drawn up before the detailed panel arrangement is completed to suit cooling airflow requirements and ensure a uniform internal temperature profile.
To find out more about electrical enclosure cooling packages that can fit your needs, contact the knowledgeable sales team at Thermal-Edge. Together we can plan a cooling system that fits your application.
