The methods used to cool people, equipment, and processes in plant and manufacturing areas changed in 1984 when portable air conditioners for industrial high-ambient applications were introduced to the United States. Portable-air-conditioner designs had been tested outside of the United States for more than 10 years, prompting the development of ANSI/ASHRAE Standard 128, Method of Rating Unitary Spot Air Conditioners, which has become the standard for all spot- and direct-cooling applications.
Standard 128-compliant portable air conditioners allow people, equipment, and processes in high-ambient areas to be cooled without the generation of excessive cooling temperatures, airflow rates, or air volumes that could lead to heath issues. Various models can cool a single person, several people, or an entire assembly line. Larger units with 3 to 5 tons of cooling capacity can be rolled into place or hung from a ceiling and ducted over workers in an assembly or work area.
Providing a cooler and dryer workplace can lead to improved health and safety and increased productivity. For example, a cooling station can help workers cleaning out vessels or industrial storage tanks to avoid having to take "exhaustion breaks."
The design characteristics of portable air conditioners can improve the use and effectiveness of cooling in high-ambient areas inside or outside of a plant or in open areas in which traditional air conditioners are inadequate. Available in 115-v, 208-to-230-v, and 460-v models for normal industrial applications, portable air conditioners typically include wheels for portability, heavy-duty metal cabinetry, an internal refrigeration system, and moveable airflow nozzles for directing or ducting airflow.
Portable air conditioners protect employees, processes, and equipment from hot environments and can operate in temperatures as high as 115 F. Utilizing spot cooling for industrial processes can help protect products, such as small electronic chips, plastic-molded items, metal extrusions, rubber items, metal bars, and glass products, by increasing flow rates, curing products to specifications, removing unwanted moisture, and preserving product shapes and integrity. Products coming down a process line can be freed from deformity and produced 50 to 90 percent more quickly.
Relieving production equipment of excessive heat can lead to increased asset life and reliability. For example, electrical control panels affected by summer heat could receive additional help from portable air conditioners. Electric-furnace operations, nuclear-plant control areas, and process control rooms that lose cooling or need additional cooling for equipment and people can be candidates for spot cooling. Portable air conditioners also have improved the life and reliability of numeric-control (NC) machines.
Cooling industrial areas with portable units is not an exact science. Renting a portable air conditioner first can be an inexpensive method of proving a portable unit's ability to cool an application.
Standard 128-compliant Designs
Tested for cooling capacity at 95 F ambient temperature and 60-percent relative humidity at their condenser and evaporator coils, Standard 128-compliant portable air conditioners require a specific volume (270 cfm) and air velocity (33 fps) to produce a delta-T of 19.8 F. The delta-T is the actual temperature difference between the airflow into a portable unit's evaporator section and the air coming out of the unit's grilles or nozzles (Figure 1).
Utilizing Spot Cooling for People
Sizing methods for people, process, and equipment applications depend more on airflow volume and ambient temperature than unit capacities. Properly cooling people in industrial applications with temperatures of 85 F to 113 F is a function of ambient temperature, humidity, activity levels, air volume, velocity of airflow, and temperature difference. For example, a person with a high activity level in a 105 F ambient area with 60-percent relative humidity would require 260 to 290 cfm of airflow at a velocity of 26 to 30 fps and a temperature difference of 16 F to 20 F. Higher ambient temperatures and lower activity levels would change these developed standards and subsequently require more or less airflow.
Basic specifications can aid the sizing of portable air conditioners for high work activity levels and temperatures (Table 1). Five basic levels cover workers with low to high activity levels, temperatures of up to 113 F, and up to 60-percent relative humidity.
Utilizing Spot Cooling for Processes
Cooling industrial processes with portable air conditioners has become popular because of the low cost and high return for use in injection-mould and extrusion machines, edible and electronic products, and vessel-cooling applications. These applications use wind-chill physics and portable-air-conditioner parameters to achieve desired cooling objectives.
Objects lose heat from the inside out. The faster heat is removed from the outside of an object, the quicker it transfers from the core to outside layers, cooling the object to the required design temperature. This creates fewer rejects, faster rates of flow, and lower costs. Portable spot coolers can provide focused airflow between 270 to 1,680 cfm and a 13 to 20 F drop in supply temperatures to operate more effectively than industrial fans.
The size and desired flow rate of a processed object determine the size of a portable spot cooler. Increased airflow is required for larger objects. Increasing airflow can involve using multiple units or one larger unit over a bigger area of a moving line. The specific gravity of an object also influences the ability to cool an object quickly. This can include focused airflow over an object for more rapid cooling.
Utilizing Spot Cooling for Equipment
The type of spot cooling utilized for equipment applications is determined by the nature of the equipment being cooled. The equipment can include power panels, NC machines and control-room components, switching controls, testing devices, or computers in high-ambient or hostile environments.
Focusing the right amount of low-temperature airflow quickly can reduce the interior temperatures of equipment to desired levels. Directing airflow with an air conditioner's nozzles over and around an equipment cabinet can cool the cabinetry and flow cooler air into and out of the cabinet's air grilles.
Alternately, most equipment cabinets in these environments can be fitted with flanges on their outside panels. The flanges can attach flexible ducting from portable air conditioners with airflow volumes of 270 to 1,680 cfm. This method blows the heat generated inside of the cabinet out through openings in the cabinetry.
For example, if a transformer is overheating because of high ambient temperatures, airflow from a portable air conditioner quickly can remove heat from the cabinet via its convective-airflow cooling slits, or colder air from the air conditioner can be ducted in to increase the rate of cooling.
Portable air conditioners can be beneficial for cooling various types of hot spots for people, processes, or overheated equipment. Problem areas should be researched to determine the type of portable air conditioner needed.
Regional manager of U.S. field operations for Spot Coolers, a division of Carrier Rental Systems, Stan Speer has spent 17 years with the company in sales, installation, service, and support positions. Formerly a member of the U.S. Air Force's Strategic Air Command, he also has 20 years of experience in the information-technology field, working for such companies as Litton, Honeywell, Singer, and Prime Computer