The Importance of Comparing Cooling Capacity Performance when Selecting Enclosure Air Conditioners
When selecting an enclosure air conditioner, it’s important to make adequate allowance for the effect temperature has on the cooling capacity performance of the unit. As the ambient temperature increases, the BTU/H capacity of an air conditioner decreases. This phenomenon, depending upon the design characteristics of the unit, is affected by the choice of refrigerant, compressor design, and the type of expansion device used. It also depends on the climatic and environmental conditions on site along with any special requirements that may exist.
Define Operating Parameters
As a first step, determine the maximum desired enclosure temperature taking into account the thermal sensitivity of the components inside the enclosure. It’s wise to adopt a conservative approach to ensure that electronic equipment such as PLCs and variable speed drives don’t exceed their design temperatures.
Then, calculate the heat load, allowing for the effect of solar radiation and other environmental influences that may exist where the enclosure is located. If necessary, use a BTU/H calculator to establish the required air conditioner capacity under those conditions.
High Ambient Temperature Performance
The ambient temperature at which an air conditioner’s nominal capacity is calculated is generally 105ºF. However, the ambient temperature around an electrical enclosure could be higher so it’s necessary to understand the effect temperature has on the performance and capacity of the unit.
For example, the actual capacity of an air conditioner at 125ºF may be less than half its capacity at 85ºF. Before selecting an enclosure air conditioner, it’s important to refer to the manufacturer’s specifications to establish the cooling capacity under actual operating conditions.
Benefit of Thermal Expansion Valves
All air conditioners have an expansion device that’s used to control the expansion of the refrigerant liquid into the evaporator. The simplest device is a capillary tube that’s great for limited temperature changes such as would be expected with a refrigerator, but is not well suited to the wide variations in temperature expected of an enclosure air conditioner. In fact, the performance loss of a capillary tube between the temperatures of 80ºF and 131ºF is as much as 85 percent.
A thermal expansion valve is better able to adapt to temperature and load changes and maintain an adequate supply of refrigerant to the evaporator. It’s twice as efficient as a capillary tube and is a far better solution for an enclosure air conditioner, offering better performance over a wider temperature range.
Review Performance Curves
It is crucial that an enclosure air conditioner controls the maximum temperature inside the electrical enclosure to within predefined limits to prevent the possibility of equipment failure or damage. For this reason, engineers selecting an enclosure air conditioner should ignore the nominal nameplate capacity of the air conditioner and review the air conditioner performance curves to establish the actual capacity of the unit under the actual conditions expected on site.
Clear Specifications Simplify Selection
A review of enclosure air conditioner supplier websites reveals a wide variation in the amount of information supplied on their different models, and at times it’s difficult to assess the debating factors that need to be applied at high ambient temperatures.
Before selecting an enclosure air conditioner, take time to verify the unit’s cooling capacity performance to make sure it has the capacity to keep the electrical enclosure cool at all times.
