Maintaining the proper climate inside industrial electrical enclosures is the key to trouble-free operation of the housed electrical components and, more importantly, the often delicate production processes they serve. Packaged air conditioners typically are used for this purpose. The conditioners mount directly to the enclosure and are selected based on the amount of heat gain and interior air temperature requirements. Since the heat from the interior is rejected by the condenser into the area adjacent to the enclosure, the ambient air conditions in the immediate vicinity also play a role in air conditioner selection.
Because industrial applications often involve harsh environments - including air laden with dust, grit and oil mist along with high ambient temperatures caused by heat generated from nearby process equipment - packaged air conditioners are not always easily applied. In some cases, a remote cooling solution might be more appropriate. Remote cooling moves the enclosure heat to a location away from its installation site, thereby allowing the control enclosure to be sealed against the operating environment.
Split SystemsOne option for remote cooling involves using an air conditioner with a remote condenser or “split” refrigeration system. In this case, the refrigerant compressor and evaporator remain packaged in the locally installed air conditioner, but the condenser, which rejects the heat to ambient, is located in a more environmentally favorable location.
Because the refrigerant gas from the compressor must be sent to the remote condenser and condensed refrigerant liquid must be returned to the conditioner’s evaporator, the piping between the local and remote components is an important part of the split system. If the piping size and geometry are not properly engineered, the cooling system will be under capacity, and the potential for problems with lubrication can cause premature compressor failure. Split systems of this type also require charging the cooling circuit with refrigerant in the field and require one remote condenser for each local conditioner.
Air-to-Water Heat ExchangersAnother option for remote cooling involves equipping the control enclosure with an air-to-water heat exchanger that uses chilled water and a fan to condition and recirculate the air within the cabinet. In this case, the entire refrigeration system is installed in a remote location, and chilled water (or a water/glycol combination) is circulated to the enclosure-mounted device to remove the heat. Circulating a single-phase fluid makes the connecting piping a less critical element of the system.
An air-to-water device can prove to be beneficial for many industrial applications. Because the air-to-water heat exchanger uses chilled water instead of vapor-compression refrigeration (compressor, evaporator, condenser, etc.), it provides a tremendous amount of cooling in a relatively small package. This economy with respect to installed footprint can provide real benefits for space-challenged installations. In some cases, a single air-to-water heat exchanger can take the place of two or more air conditioners.
The air-to-water remote cooling option also can offer increased energy efficiency compared to local air conditioners in environments where high ambient temperatures result in high refrigerant condensing pressures. As the refrigerant condensing pressure increases, the energy input for the compressor increases, which drives up operating costs. Contaminate-laden ambient air contributes to this situation by fouling the condenser coil and reducing its heat transfer efficiency. These problems are avoided by using a system where the refrigeration source is remote. In fact, if the chiller is located outdoors, additional efficiency gains can be achieved when seasonal changes in ambient air temperature allow even lower refrigerant condensing pressures - and lower operating costs.
Remote ChillersThe remote chiller-based system allows several enclosures to be cooled with a single chiller, which reduces equipment and installation costs. For this arrangement, the chiller is selected to circulate the water flow rate required by the total number of air-to-water heat exchangers, and it is programmed to maintain a certain water temperature. Each enclosure-mounted heat exchanger controls the amount of coolant that it receives from the common coolant loop based on its own local temperature controller. The controller can be programmed to maintain a fixed temperature or to maintain a variable temperature relative to the dewpoint temperature inside the enclosure to avoid condensation.
This coolant loop scenario also provides an easy method of increasing reliability through redundancy. Installing a second full-capacity chiller in parallel with the primary chiller will provide 100 percent backup for the cooling system. Simple controls are available to allow the backup chiller to be brought online automatically in the event of a cooling failure. These controls also can rotate the lead and lag chillers to provide even-duty cycles and ensure that the offline chiller is always ready.
Condenser cleaning, filter replacement and coolant additions can take place without affecting operations. Remote control panels are available to advise the operations area of any chiller alarms or warnings. The ease of service and warning enunciation can help reduce the mean time to repair (MTTR) following a failure as well as help increase the system’s “up time” or mean time before failure (MTBF).