How to Select an Enclosure Air Conditioner with the Right Cooling Capacity
The selection of the right size enclosure air conditioner should be based on a careful assessment of the total heat load, ambient temperature variation, and the required enclosure temperature. If the air conditioner is larger than required, energy usage will increase and the unit will cycle excessively. Conversely, an air conditioner that’s too small will run continuously and not control the temperature properly. A number of factors need to be considered when choosing an air conditioner. Here is how to select an enclosure air conditioner with the right cooling capacity:
1. Calculate the Total Heat Load
The most important step is to calculate the total heat load in the electrical enclosure. This is a vital step and entails consulting manufacturers’ catalogues to ascertain the power loss for each piece of equipment.
To establish heat losses for coil-operated equipment, such as relays and contactors, use the electrical rating of the coils. For high power equipment such as variable speed drives and servo drives, use the efficiency of the device at the appropriate power point to calculate internal heat generation. Efficiencies may vary from 85 percent to 98 percent, so make sure you obtain the right information.
Consider the transfer of heat into the enclosure from the environment. If the ambient temperature is higher than the enclosure temperature, there will be a heat gain. Identify any equipment in the vicinity of the enclosure that is hot. Also take into account solar radiation if the electrical enclosure is exposed to the sun. The impact of external heat gain may be significant.
2. Assess the Required Enclosure Temperature
Carefully assess the required enclosure temperature. Although much modern equipment can run very hot, doing this affects service life and reliability. Usually you will find a wide variation in the maximum operating temperatures of the equipment in the enclosure, so identify the lowest temperature and choose a temperature that is somewhat lower to provide a measure of safety.
3. Identify the Effect of Ambient Temperature
It’s necessary to accurately identify the ambient temperature range. The capacity of an air conditioner is adversely affected by high ambient temperature and this must be allowed for. Consult product brochures to calculate the actual cooling capacity at the highest ambient temperature expected. Also consider the lowest ambient temperature; it may be wise to install internal heaters to prevent condensation.
4. Use a BTUH Calculator
The calculation of the cooling capacity requirements for the air conditioner can be performed manually or using an online Enclosure BTUH calculator. Unless you’re experienced and make the calculations frequently, it’s more accurate to use such a calculator because it takes into account the effect of the enclosure heat transfer characteristics.
5. Don’t Go Too Big
Avoid the temptation to go too big. An enclosure air conditioner that is too large will quickly reach the set temperature and cycle frequently, potentially leading to shortened compressor life. Excessive temperature variation will also occur.
6. Avoid Temptation to Go Too Small
If the enclosure air conditioner is too small, it will run most of the time and could eventually result in premature failure. There will be insufficient capacity to control the internal temperature, especially during hot weather, and this will lead to excessively internal high enclosure temperatures that could affect the electrical equipment in the enclosure.
7. If You’re Not Sure, Speak To a Specialist
The selection of the correct size enclosure air conditioner, while apparently relatively straightforward, requires detailed knowledge of the heat load, accurate information regarding the climate, and experience to understand the factors that may affect correct sizing.