Keep cool! Portable air conditioners offer flexible solutions

06/21/2013


Cooling non-manufacturing areas

Even in the most temperate climate, a production plant with no need for central air conditioning is still likely to require cooling for non-manufacturing areas such as server and equipment rooms, office suites and conference rooms.

Sometimes this is accomplished through permanently installed air handling equipment, but portables often play a role in these applications. They can offer a faster, easier and/or more cost-effective solution than mini-splits or other unitary a/c systems.

The term “portable” need not be synonymous with “temporary”. Portable equipment is often installed on a permanent basis to provide primary cooling to offices and server rooms, or to deliver supplemental cooling to growing facilities where the primary HVAC system is no longer adequate or hot spots are a problem.

This situation is especially prevalent with server rooms, which can present challenges as they become densely packed with more heat-generating electronics. A typical cost comparison might reveal that a portable 5-ton cooler can deliver supplemental cooling to a server room for under $10,000, where a permanently installed solution might cost 4-5 times as much to cool the same space. 

Selecting Portable Cooling Equipment

There are many things to consider when selecting portable cooling equipment. Table 1 summarizes the selection factors to review with your supplier.

Every model of portable air conditioner is designed for use with a particular type of electric circuitry. So it’s a good idea to start by looking at the available power supply, which will often dictate equipment selection.

Fortunately, with recent product advances, the choices are better than they were in the past. There are now portables on the market that will run on convenient 460-volt 3-phase power and deliver 5 tons of cooling or more, allowing a single unit to do the job where two or three used to be needed – if there is adequate floor space for the larger unit.

Sizing

Equipment sizing, defined as cooling capacity in Btu/hr or tonnage (12,000 Btu/hr = 1 ton of cooling), is also critical. A general rule of thumb is to plan on 3.413 Btu per watt when calculating equipment size. That translates to around 1 ton of air conditioning for a “typical” 400 sq. ft. room with an 8-ft ceiling and no additional loads other than lighting, or 3200 cu. ft. if the space must be cooled all the way up to a higher ceiling. From there, heat load factors unique to the application must be added into the equation.

If you are cooling a non-manufacturing space such as an office or conference room, you will need to consider:

  • Does the room have windows or other openings, and what is the exposure?
  • What power is available?
  • What kind of equipment is in the room and how much load is being generated?
  • What is the occupant level and activity within the space?
  • How much cooling is already coming in via a central air handling system or other source?
  • How many portable units will be needed to achieve even cooling distribution?

All of this should be considered when determining the proper a/c unit(s) for the application.

On the manufacturing floor, the same factors as above will come into play, but other things will impact equipment sizing as well. How much heat is being generated by the process? What temperature are you trying to maintain at the given location? How hot is the product? A plastic part will be hotter than a cookie. How dense is the product? A metal part will require more energy to cool than that same cookie. How fast should it be cooled?

For server and equipment rooms, similar calculations apply, but the loads can be very heavy due to the high heat generated by such equipment. If the room uses a UPS backup battery, you can actually take the battery wattage (i.e., 6000 watts) and multiply by 3.413 to arrive at the amount of Btu/hr or cooling needed for a “worst-case” scenario. It might result in overkill, but server rooms are one of the few applications in which over-specification actually tends not to be a problem.

After installation, if sizing turns out to be less than perfect, all is not lost. Remember, a big advantage of portable cooling equipment is – to state the obvious – its portability. A rented unit can be readily swapped out with a larger or smaller model to ensure optimum cooling performance. 

Installation considerations

Will the unit be located inside or outside the space to be cooled? If the portable unit is inside the space and a spot cooling effect is desired, you might want to select a model equipped with cold air nozzles or chutes that allow you to direct the air at hot spots on the assembly line or other location. If you are using a portable cooler with a grill-front design, there are kits available to retrofit most units with nozzles.

Another spot cooling strategy is to use Plexiglas or heavy curtains to create a booth or enclosure to contain the cooling, if space allows. If portables are used on a crowded production floor, you will probably want to position the unit(s) off to the side and run overhead ducting to the process to avoid tripping hazards.

If the portable cooling must be located outside the room due to floor space constraints, safety, heat rejection or other concerns, you will need to find a way to duct the evaporator return and cold air supply in and out of the room to be cooled. This might involve cutting openings in the dry wall to insert ductwork or, for temporary solutions, ducting the cold air in and out over the wall by removing ceiling tiles.

Often a portable unit will be used to cool an office, server room, clean room or other small enclosed space within a warehouse. If it is a large facility with high ceilings, the hot air can usually be discharged up towards the warehouse ceiling with minimal effect on the rest of the building since cold air drops to the floor level. Similarly, in a manufacturing space, the hot air from the spot cooler can be discharged by running a single rigid plastic or flexible duct above workers’ heads to the ceiling, where there is often an exhaust fan to help remove the heat being generated by the a/c unit from the space.

If the entire space is to be cooled, a two-duct system can be devised using a condenser plenum on the portable unit with an additional duct, so there will now be two ducts going to the ceiling, window or door. This creates a closed-loop system that no longer creates a negative pressure. With doors shut, the space can be cooled very efficiently. The a/c unit can also be placed outside and the cold air ducted in and out through a doorway or windows. 

Getting the water out

The cooling process creates condensate water, so you will need to determine how to dispose of this water. If you plan to collect it in the standard condensate tank or bucket that comes with the portable cooler, it simply needs to be emptied when full. Buckets are more common with smaller units that do not generate a lot of condensate. Pumps or gravity drains are more common with larger units.

In some applications, especially server rooms, it will be necessary to run a condensate line out of the room to an external drain of some sort – in a janitorial closet, bathroom floor drain, or perhaps out a window to an outdoor drain. A condensate pump for this purpose can be obtained from your portable cooling equipment supplier.

Rent or buy?

A final consideration is whether to rent or purchase portable cooling equipment. The answer to this question will often be self-evident; but when in doubt, your equipment supplier can help perform a quick cost analysis to determine the best approach.

Even if the equipment is going to be used long-term, renting might make more sense if you want to avoid capital expenditures or if you anticipate a change in cooling requirements down the road. Rentals also offer greater flexibility for plants who lease space or who renovate frequently. 

Buddy Phillips is a regional manager with Atlas Sales & Rentals, Inc. He holds a mechanical engineering degree from Purdue University and has 29 years’ experience in the HVAC industry. www.atlassales.com.


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