The Benefits of Portable A/C

July 10, 2006
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The 12-ton dual centrifugal cart-mounted air conditioner was designed for large-capacity requirements inside of commercial office space. It usually has a small footprint and it can fit into most freight elevators, through double doors, and down most hallways.
By now, nearly everyone has at least heard of portable air conditioners. Also referred to as "spot coolers," they serve as temporary cooling units when permanent a/c systems must be shut down or fail. Portables also serve as permanent-cooling systems for small- to medium-sized equipment centers, such as telephone systems or server rooms.

In the eyes of Garth Tagge, vice president of sales at Spot Coolers, they are called portable air conditioners for two reasons:

  • They are on wheels and easily movable.

  • They will fit through interior doorways, which allows placement inside any commercial building or space. This fact tends to limit their capacity and portables typically top out at 5-tons capacity, he said.

    "To make a distinction, portables are different from mobile air conditioners, which are also mounted on wheels but are often towed, trailered, or trucked to a job site," said Tagge. "In addition, mobile units are usually much larger in physical size and capacity, and must be set up outside."

    According to Tagge, the most familiar type of portable air conditioning is air-cooled. In his estimation, air-cooled units provide flexibility and make equipment set up and tear down fast and simple. It is his belief that air-cooled portables can fit the bill perfectly for seven out of 10 applications.

    "Today, a wide range of models and types of portable air conditioners are available for sale or rent," said Tagge. "Air-cooled portables still make up the bulk of the market. However, specialty units have grown in importance and represent the fastest growing segment of the market."

    TYPES AVAILABLE

    Some of the different types of portable air conditioners often used include water-cooled portables, water-to-air split-system portables, heat pump portables, and 12-ton dual centrifugal units. In regard to water-cooled portables, Tagge explained that there are some applications where the introduction of makeup or exhaust air - required of air-cooled units - just cannot occur.

    "Sometimes the application prevents the inflow or outflow of air into a space," he said. "Other times, it is the venue itself."

    One example of where air-cooled portables won't work is a surgery suite, he said. The air conditioning system for the surgery suite is always a dedicated, closed-loop system.

    "There can't be even the slightest amount of outside air allowed to penetrate the surgery suite in order to keep it germ free," he said. "In addition, all air that circulates through surgery must be HEPA-filtered to maintain the germ-free environment."

    The problem is how to add capacity to such an environment, he said. Most supplemental cooling schemes would use air outside of the existing cooling loop, making air-cooled equipment useless.

    "However, many hospitals have discovered that the addition of a water-cooled portable, set up and operating during a surgery, provides exactly the added capacity that they need to keep the surgical team cool and comfortable," said Tagge. "Surgery suites contain all of the elements needed to make water-cooled units operational, including a water source and a drain."

    TOUGH-TO-COOL APPLICATIONS

    Certain buildings - or parts of certain buildings - are not air conditioned, either due to age or construction issues. Many older buildings - like some in New York, Chicago, Philadelphia, or other older cities - were built before air conditioning was standard equipment. In Tagge's estimation, these are good examples of structures which have minimal or no provision for air conditioning or heat rejection. Many of these buildings have tenants with computers, server rooms, and telephone systems, creating localized heat loads, compounding the problem.

    "Even in buildings built with air conditioning there are numerous occupants or equipment rooms located in the basement or rooms that don't have access to the return air system," he said. "This makes using air-cooled equipment nearly impossible. For these, water- cooled portables are ideal."

    In regard to water-to-air split-system portables, Tagge called them "the perfect marriage between a water-cooled unit and an air-cooled unit."

    "Water-to-air split-systems can be an ideal way to solve problems for which neither is ideal," he said. "They utilize a water-cooled heat exchanger located in the air-handling unit to accept the heat. The air-handling unit is placed inside the space to be cooled and provides the cool evaporator air, as well. This unit creates no positive or negative air pressure condition as it circulates only interior air through the evaporator, just like a water-cooled unit."

    In this case, the heated water is then pumped through a triple hose line set to a remote fan coil condenser - much like a dry cooler or automotive radiator. The fan coil unit is placed somewhere outside the space to be cooled - and this could be outdoors or in the hallway.

    "Ambient air passes over the remote condenser and the heat is rejected," explained Tagge. "The cooled water is then pumped back through the line set to the unit and the process is repeated. The third hose on the line set handles the condensate created in the process."

    There is a need for water-cooled portables. There are just some applications where the introduction of makeup or exhaust air — required of air-cooled units — just cannot occur.

    LARGE A/C, HEAT APPLICATIONS

    Many of the temporary needs, as well as the commercial rental requirements, for portable air conditioning are generated by computer room air conditioning shutdowns or failures. Sometimes a 5-ton a/c unit services these computer rooms; sometimes 25 tons or more services them.

    When a dedicated 25-ton computer room a/c unit fails or is shut down for service, portables of 5-tons or less aren't adequate to compensate, according to Tagge.

    "Often, you can get by on reduced capacity, perhaps one half of the system capacity," he said. "But wheeling in a 1-, 2- or even 5-ton unit isn't going to handle the load when a 25-ton unit is shut down or fails. Multiple portables may make up the needed tonnage but each requires floor space and its own power source - neither of which may be available."

    Enter the 12-ton dual centrifugal cart-mounted air conditioner. This unit was designed for large-capacity requirements inside of commercial office space, said Tagge. With a small footprint (45 inches wide by 65 inches long and 50 inches high), it can fit into most freight elevators, through double doors, and down most hallways, he said. The size allows access to high-rise office buildings and commercial spaces.

    Sometimes, the problem that you are dealing with is a space that is not too hot, but is too cool. This happens for a number of reasons, including:

  • A severe cold snap in an otherwise temperate location such as Jacksonville, Fla., or Atlanta, where heating systems were not designed for extreme cold.

  • The boiler or heating system fails or shuts down.

  • The space is too close to ingress or egress (lobby, construction) and the space cannot maintain an adequate temperature.

    "Heat pump portables look exactly like their portable a/c counterparts. In fact, all heat pump portables are also portable air conditioners," said Tagge. "They are air-cooled units that look and set up in an identical manner to the portable a/c units."

    The difference is completely internal. From the outside, you can only tell the difference between a heat pump and its "cooling only" counterpart by a few extra buttons on the control panel.

    "Portable air conditioning has come a long way in the last 20 years," said Tagge. "And with continuous and rapid advances in computer technology and information processing, expect to find new and flexible products emerging from the portable cooling industry."

    Publication date: 07/10/2006

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