The growing dependency on air conditioning for building occupants and equipment cooling has given rise to an entire new generation of cooling equipment that is portable. While building air conditioning systems are very dependable, there are times when they simply aren’t available. Failure of central air conditioning or distribution equipment can shut down systems for extended periods of time. Failures in the building electrical distribution system or the utility company’s system can also shut down large building central air conditioning systems for long periods of time. High levels of electrical demand can force shutdowns of air conditioning systems for several hours.
The problem that many facility executives face is that many of their building occupants cannot afford to be without air conditioning. Computer systems rapidly overheat without air conditioning, forcing system shutdowns that may cost tens of thousands of dollars per minute. Telecommunications equipment is equally sensitive to heat; operations throughout the facility can be disrupted if sufficient air conditioning is not available.
To help protect their operations from disruptions caused by air conditioning outages, many facilities have invested in portable air conditioning units that can be rapidly moved to the required area and installed easily. Units are available in a wide range of capacities and several different configurations, allowing them to be used in practically any application. Many simply plug into standard electrical outlets. Others with larger capacities may require special or dedicated electrical connections.
Applications for portable cooling systems go well beyond those caused by equipment failures. Maintenance operations use the systems to provide cool air to personnel working in confined spaces, such as boiler interiors during shutdowns for inspection or repair. Building occupants use portable units to provide after-hours air conditioning to personnel working in spaces where the central air conditioning system has been shut down to conserve energy. The units can be used to provide supplemental air conditioning to areas where the cooling loads may temporarily exceed the capacity of the central system. Portable air conditioning units are frequently used to provide conditioned air for special events, such as those held outdoors in tents during summer months.
There are two major categories of portable cooling systems: air-to-air systems and water- or refrigerant-based systems. Most portable air-to-air systems have a capacity of one ton or less. They are rolled to the required location and plugged into a standard electrical outlet; the conditioned air is directed where it is needed. Heat from the unit’s condenser is discharged through a window to outside the facility by means of a section of flexible duct. In cases where the unit cannot be located close to a window and the portable unit is to be used for only a short period of time, the heat from the unit’s condenser can be vented above the drop ceiling through ducts. Larger air-to-air systems, typically in the range of one to five tons, can be located outside the facility with the cool air ducted through a window or other building opening.
In cases where it is not easy to duct the portable unit’s condenser heat away from the conditioned space, or where larger capacity units are required, portable cooling systems using once-through water cooling can be used. Available in capacities of up to five tons, the units are fully mobile, requiring only electrical, water supply and drain connections.
The most appropriate applications for portable cooling systems are those that are temporary, either emergency or planned. But portable cooling systems should not be used as permanent fixes for building HVAC problems. While the systems are efficient and dependable, they cannot match the performance of a properly designed and installed building system. Permanent problems are better addressed through modifications of or additions to the existing building system.
