Keep cool! Portable air conditioners offer flexible solutions
Plant engineers can benefit from understanding the basics of how to choose and use portable cooling equipment for a range of applications.
As summer arrives, heat waves can wreak havoc with manufacturing processes while also causing miserable conditions for workers. Though plants with no air conditioning are particularly vulnerable, even climate-controlled facilities are subject to problems if an overworked HVAC system should fail or if supplemental cooling is needed to deal with excessive heat.
Portable air conditioners can often provide fast and effective solutions, and not just for hot weather emergencies. The applications for industrial plants are virtually unlimited but can be roughly divided into three categories:
- Improving manufacturing speed and/or quality through focused cooling of products or processes;
- Protecting the health and safety of production personnel; and
- Delivering cooling to non-manufacturing areas such as server rooms, equipment rooms, offices and conference rooms.
This article will investigate all three areas of application and will provide an overview of the different types of portable coolers to choose from and how to size and select this equipment properly.
Types of portable cooling equipment
There are three main categories of portable equipment in use today. Your HVAC contractor or portable cooling supplier can help you identify the best type for your application:
- Air-cooled portable air conditioners work by exhausting hot air out through duct work. Air-cooled portables are the most common system of choice because they can be installed almost anywhere, usually in minutes. One- to 5-ton units (one ton of cooling = 12,000 Btu/hr) are the most common, though in recent years the market has expanded to include 12-ton portables that are compact enough to fit through a standard door.
- Water-cooled portable air conditioners connect to an external water source. They are very efficient to operate but are best suited to use in facilities where it is possible to tap into a central cooling tower or chiller system, or in regions where the municipal water supply is plentiful and economical. Water-cooled systems need no exhaust ducts, so they are often specified when there is no convenient way to exhaust hot air out of the room.
- Evaporative coolers use an internal or external water source to lower temperatures and a fan to push the cooling vapor across the space. Though their performance is not comparable to portable air conditioners, when correctly set up in the right environment they can provide a simple, low-cost cooling option for large manufacturing areas, warehouses and loading docks — especially in situations where budget or power supply is limited. One important caveat is that the units add cool moisture to the air and can potentially interfere with any humidity-sensitive processes within the plant. Evaporative coolers perform better in low- humidity environments since dry air is not at saturation and has a strong affinity for the cooling moisture.
Improving manufacturing speed and/or quality
Portable cooling is most frequently employed in plants to speed up production processes, to protect heat-sensitive equipment on the manufacturing floor, or to preserve raw materials or finished products from heat degradation. Following are examples of each.
A manufacturer of plastic magnifying glasses used on solar panels needed to find a way to improve output. By using a portable air conditioner to inject cool air into a specific location in the assembly machine, they were able to increase production line speed and ramp up output without having the expense of adding a second line.
Although the plant was equipped with central air conditioning, this focused “spot cooling” approach was still needed to achieve production goals. Portable cooling is used in this way in many areas of plastics manufacturing to cool parts faster and speed up production.
Similarly, gluing or bonding of parts can often be a temperature-sensitive task. Portable cooling directed at this assembly process helps ensure more precise temperature control and allows adhesives to cure at the desired speed. The resulting benefits can be increased product output, lower product rejection rates or both.
Sometimes product needs to be cooled prior to bagging or packaging operations. In the fertilizer industry, pellets of fertilizer are spot-cooled using portable air conditioning before they go into a feeder that dispenses measured amounts into bags. If not properly cooled in this manner, pellets can gel and cause the feeder to jam, resulting in line shut-downs and maintenance headaches.
There are many similar applications in food and chemical processing. If powders become too warm, they tend to gel and clog machinery or cause the manufactured end-product to clump together. Portable cooling directed at conveyors, hoppers or at other points where finished product is being transported and collected at the end of the manufacturing process can help guard against these problems. Targeted cooling of bakery items and candies coming off the line is also common, allowing product to be packaged more quickly in order to speed production throughput.
Powder coating is another process that benefits from spot cooling. A manufacturer of metal air conditioner components has used portable air conditioning for years in the area where metal parts are being powder-coated, for the dual purpose of cooling the process and assembly line personnel.
Protecting equipment and product
Sometimes the role of portable air conditioning is not to cool a process but rather to protect equipment, raw materials or finished products from heat damage. For example, laser-cutting machines often depend on heat-sensitive electronics to control the process. If electronic controls overheat, they can malfunction and cause the machine to shut down, resulting in costly downtime. Similarly, printing presses are subject to jamming in hot and humid environments. By reducing humidity as well as temperature levels, portable cooling is an effective solution.
In the packaging industry, the shrink sleeves used to wrap a variety of food and beverage products come in enormous rolls of plastic sheeting. A packaging converter found that hot and humid conditions in the non-air conditioned storage room would cause the sheeting to deteriorate, resulting in costly loss of material and production slow-downs. Several large portable coolers installed in the storage room now keep the area cool during summer months to avoid further problems. Warehouses that store finished products such as chocolates are also common locations for portable cooling, to prevent inventory from melting before it leaves the plant.
Keeping workers cool
In addition to the obvious comfort factor, portable cooling directly impacts safety by reducing heat-related fatigue, illness and accidents. It can also improve productivity and morale. Portable units can be moved around to different locations and easily installed to deliver spot cooling to the most demanding production areas.
At a steel pipe and tube plant, the use of a 5-ton portable cooler in a galvanizing area succeeded in bringing ambient temperatures down by as much as 30 degrees F. Instead of being limited to 30 minutes, crews can now work for two hours in the galvanizing area before needing relief for ergonomic (not heat) fatigue. There have been no heat-related illness problems in the plant since installing the cooler. That is compared to four to five incidents per year over the previous two seasons, and twice that number in prior years. As a result, the manufacturer plans to bring in more portable coolers to handle additional processes in the galvanizing shop this summer.
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.
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.
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.