By Judith Koetzsch
By Judith Koetzsch
Choosing the right air conditioners for enclosures can have a tremendous impact on the overall performance and efficiency of industrial operations. Proper and efficient air conditioner cooling can significantly prolong the life of installed equipment, save energy and utility costs, and protect against unscheduled downtime. Although cooling is sometimes an afterthought during the course of planning a project at the enclosure layout level, with careful consideration and the right information, it can truly become an asset for increased productivity and profitability.
This paper identifies different factors that should be considered when choosing air conditioners for industrial enclosures, including internal heat loads, the various methods used to rate the cooling capacity of enclosure air conditioners, the impact of humidity and other ambient conditions, and energy efficiency. Understanding air conditioner performance diagrams and sizing tools in relation to application requirements is also covered.
Factors to consider
Internal heat load: The internal heat load is the amount of heat energy produced by the electronics inside the enclosure, and it comes from the unused electricity running through the components. In order to specify the right air conditioner capacity for an application, it is critical to know the amount of heat energy (in BTU per hour or in Watts) that will be created by the equipment housed within the enclosure.
Determining the amount of heat energy to be removed: There are multiple ways to determine the heat load inside an enclosure. One way is to add up the heat loads of all of the installed electronic components as specified by the component manufacturers. Another approach is to add up the electricity consumed by the electronics and then multiply it by the efficiency of the system. The resulting number equals the need for cooling capacity. For example, if an electronics system is consuming 500 Watts of power and it is 20 percent efficient, the system is only using 100 Watts of electricity for its actual function. The remaining 400 Watts is dissipated in the form of heat energy.
Impacting cooling capacity: In the world of electronics, cooling capacity is the maximum amount of thermal energy that a climate control product can remove, and it is shown either in Watts or BTU per hour (if necessary, to convert Watts into BTU per hour, multiply by 3.413). The cooling capacity, or performance, of a specific enclosure air conditioner not only depends on its overall design, but also on various application-specific factors. These factors include the ambient temperature, the maximum allowable internal temperature, and the operating frequency (in Hz).
The ambient temperature (Ta) can significantly affect the cooling capacity of an air conditioner. If an air conditioner operates in high ambient temperatures, it provides less cooling capacity. This is because air conditioners work by pulling the hot air from inside the electrical enclosure and transferring the thermal energy away from the cabinet to the surrounding environment. The hotter the outside air is, the ability of the air conditioner to transfer the enclosure heat energy out through the condenser coil is diminished. As to be expected, the opposite is true when air conditioners are placed in areas with lower ambient temperatures, since the heat transfer through the condenser coil into the ambient air is quicker, consequently raising the cooling capacity of the air conditioner.
The maximum allowable internal temperature (Ti) is also relevant to the cooling capacity of an air conditioner because it determines how much thermal energy needs to be removed from an enclosure and can vary from application to application. Typically, air conditioners operate by maintaining temperatures that do not exceed a specified set point. A recommended set point for two enclosure air conditioners lies between 86 and 104 degrees F, depending on the electronics installed in the enclosure. Lower temperature set points can easily lead to excessive condensation and should be avoided.
The third factor that influences the cooling capacity of an air conditioner is the operating frequency. Here in North America, 60 Hz is the norm, but throughout much of the world, 50 Hz is used. This is why, for example, most Rittal TopTherm Plus air conditioner models are dual-rated, meaning that they can operate at both 50 and 60 Hz. A dual rating allows for the same air conditioner to be used all over the world, where different power systems supply different frequencies. When an air conditioner is operating at 60 Hz, the fans and compressor actually rotate faster than at 50 Hz, resulting in higher performance for the air conditioner at 60 Hz.
When evaluating an air conditioner stated to have a certain cooling capacity, it’s important to consider under what temperature conditions, and at which operating frequency, that cooling capacity is provided.
Why do some manufacturers determine cooling capacity differently than others? In North America, no formal standard for testing or publishing cooling capacity exists, so most manufacturers use the maximum temperatures at which the air conditioner is designed to operate as reference points (maximum internal and external temperatures). The maximum operating temperatures can differ between air conditioner models, as well as manufacturers.
Typically, a maximum operating temperature is at 131 degrees F. If indicated, the rating temperatures could be shown as L131/L131 or Ti 95/Ta 95 or 95° F/95° F. Traditionally, the first number stands for the internal temperature.
In Europe, a standard called DIN 3168/EN 814 part 500 (European standard for enclosure climate control) is used. This standard levels the playing field, and provides a more realistic measure of performance, by requiring all manufacturers to use the same temperature conditions to determine cooling capacity – allowing users to make true one-to-one comparisons.
Air conditioner performance diagrams: To determine the cooling capacity of an air conditioner, a performance diagram can be used. These charts show the cooling capacity of an air conditioner per the requirements of DIN 3168, as well as under different temperature scenarios – including maximum operating conditions. This will help users to determine how a particular air conditioner will perform in a specific application.
Air conditioner sizing: When selecting an air conditioner, the easiest way to figure out how an air conditioner will perform at given temperatures is to use sizing software. These convenient tools typically walk users through the various factors that impact an application, and then determine the need for cooling.
Calculating air conditioner efficiency: Reducing power consumption and increasing efficiency are vitally important to protecting the environment, and to saving money during the operation of air conditioners at the end-user level. The formula to determine the efficiency of an air conditioner is simple – it’s the ratio between useful cooling capacity and power consumption. The higher the cooling efficiency factor, the more efficient the air conditioner is.
Calculating the impact of humidity: An unavoidable side effect of using air conditioners is the dehumidification of the enclosure’s interior air. As it cools down, part of the humidity contained in the air condenses on the evaporator coil. The reliable discharge of this condensate from the enclosure is important to consider, and is achieved by using condensate hoses and collection bottles in conventional units, or via condensate evaporators in more advanced products. The amount of condensate that is created depends on relative humidity, the air temperature in the enclosure, the evaporator coil, and the air volume present in the enclosure. It’s always recommended that control panels be operated with enclosure doors closed, and that all sides of the enclosure are properly sealed and gasketed. In addition, it is advisable to use a door switch that interrupts the operation of the air conditioner while the enclosure door is open, and to set the internal temperature of the enclosure only as low as is actually needed.
Selecting the right air conditioner for an industrial enclosure application is crucial to maximizing efficiency, performance and overall return on investment. Knowing what factors to consider, and taking the time to properly evaluate the products available, can save money by reducing utility costs, drastically improve the life and reliability of installed equipment, and solidify operations as a whole through increased productivity and reduced unplanned downtime.
Judith Koetzsch has been with Rittal since 2001, first working for Rittal GmbH & Co. Kg. in Germany as a part of the international climate control product management team, and then joining Rittal Corporation in the U.S. as product manager for Climate Control Products in 2006.