Energy-efficient enclosure climate control

Rittal Pty Ltd
Wednesday, 19 October, 2011


Sophisticated, sensitive electronics and drives are the backbone of many industrial applications and this equipment is often placed inside enclosures to protect it from the rugged environments it is deployed in. Depending on the surrounding temperature and other ambient conditions, it is imperative that these enclosures be cooled to ensure the proper performance of installed components and avoid heat-related downtime.

According to the Rocky Mountain Institute, a non-profit, efficiency-focused research organisation, in industrial settings “there are abundant opportunities to save ... 60% of the energy and cost[s] in areas such as heating [and] cooling ...” This article discusses tips for cooling enclosures that can reduce energy consumption and save money.

The design phase

How much cooling is needed?

The question to ask when seeking to save on energy while cooling industrial enclosures is simple, “Does this application require cooling, and if so, how much?” It is important to determine the correct amount of cooling to prevent energy from being wasted by cooling components to lower than needed temperatures or even by cooling components that might not need it at all - the most energy-efficient cooling device is one that is not needed.

To figure out the appropriate climate control solution for a given application, three pieces of information are required:

  • How big is the enclosure?
  • How much heat will be created by installed equipment?
  • Where is the enclosure going to be located?

Once these things are known, it is possible to perform some calculations either manually or by using software tools. For the purposes of this article, a manual calculation will be used. The first step in selecting the right climate control solution is to consider the factors listed in the flowchart of Figure 1 to see what types of products may be applicable to a given situation.

In order to properly size climate control components, the surface area of the enclosure, the ambient temperature and the amount of (installed) heat in the enclosure need to be taken into account.

  


Figure 1: Factors determining cooling choices.

What does the surface area have to do with the climate control? Without expending any outside energy, heat flows in only one direction - from hot to cold. It must be determined whether the heat from the surrounding area is going to move into the enclosure or if the heat from the enclosure is going to be dissipated. The surface of the enclosure is where this interaction takes place, and the heat will flow from the sides, top and bottom.

Although it’s possible to calculate the surface area by adding up the area of all the sides of the enclosure, this may not be exactly where the heat is leaving. For example, if the rear of an enclosure is placed against a wall, the wall will heat up in that spot creating a smaller temperature difference between the wall and the enclosure, slowing down or preventing the heat from flowing out of the enclosure.

Installed heat

Once the surface area of the enclosure is found, it is possible to calculate the heat ‘contained’ within it by using the temperature difference between the interior of the enclosure and the surrounding, exterior environment (for a previously completed system), or by adding up the total heat loss from installed components utilising information found on their respective data sheets (primarily when configuring a new system).

The heat calculation for a previously completed system is:

Qe = Qv - A X k X ΔT

where:

Qv = the amount of heat produced by the components inside the enclosure
A = the effective surface area of the enclosure
k = heat transfer coefficient (5.5 W/m2 for sheet metal)
ΔT = the temperature difference Ta - Ti in °C

After this calculation is completed and the amount of heat installed inside the enclosure is determined, if a need for climate control exists, the process of selecting the correct solution can begin in earnest. There are a variety of common solutions to suit different requirements including filter fans, air-to-air heat exchangers, air conditioners or air-to-water heat exchangers - each with distinct strengths and benefits. From an energy-efficiency standpoint, filter fans and air-to-air heat exchangers will use less energy but require an ambient temperature below that of the desired internal enclosure temperature to be effective. If cooling to temperatures below ambient conditions is necessary, an air conditioner or air-to-water heat exchanger is required.

Proper selection of a climate control device is an important starting point for maximising the energy efficiency of an application, but other factors like its placement on the enclosure and relative to its surroundings (both internal and external) along with general maintenance, can also lead to a significant increase in efficiency.

Installation phase

Mounting components inside and outside enclosures

When mounting components, including climate control, on or inside enclosures, it is important to leave enough space for the climate control to work effectively.

For example, equipment cabinets should not be used to store books, manuals or spare parts, and cables should be arranged so as not to impede air flow. Insufficient free air flow can mean that equipment life spans could be shortened and the possibility of heat-related failures can be drastically increased. It is vitally important to allow components enough free space to encourage air movement.

In addition to lack of space for air to circulate within an enclosure, another common problem that can hamper efficiency is climate control that doesn’t have enough room to ‘breathe’. Generally speaking, to prevent this, installed components should be spaced no less than 20 cm away from the incoming air generated by climate control products and component fans should not blow against the fans of a cooling unit as this may cause a short circuit. To allow for optimum airflow for climate control units in relation to possible hindrances outside of the enclosure, it is best to keep at least 20-40 cm between surrounding objects and the climate control device to provide adequate airflow.

Installing climate control properly on the enclosure is important for effective operation. Unless otherwise required by the demands of an application, it is normally recommended that filter fans be placed at the bottom of an enclosure with the corresponding exhaust filter installed at the top of the opposite side. This way, the fan can draw in the cooler air located near the floor and cross-ventilation is created inside the enclosure for increased heat removal. Air conditioners and heat exchangers can be mounted either on the walls or roof of an enclosure and should be installed according to the manufacturer’s instructions for best results.

Another way to aid the performance of climate control equipment is in the planning stages of enclosure placement. Keeping the enclosure far enough away from any heat sources prevents excessive heating and possible damage.

Operation phase

Efficiency in operation - filter fans and air conditioners

Maintaining filter fans is relatively simple because it’s usually possible, with a glance, to determine if the filter media is clogged or dirty and needs to be changed. While this may sound rudimentary, this is an important step for the fan to work effectively. Regular maintenance is required for air conditioners as well, although the areas of concern may not be quite as apparent. In order to understand what general maintenance is required, we need to take a simplified look at how air conditioners operate.

There are two sides to an air conditioner - hot and cold. The ‘hot’ side is the outside of the air conditioner and the ‘cold’ side is the internal side. There are copper coils located on both sides, the condenser coil externally and the evaporator coil internally. Refrigerant moves back and forth inside these copper coils and transfers the heat from the inside of the enclosure to the outside. To circulate the air treated by the coils, fans blow across them, making it problematic if the coils become blocked or clogged up with contaminants, because the airflow is reduced and the air conditioner becomes less efficient - working harder and harder, using more energy, but producing less actual cooling output.

In order to prevent the condenser coil from becoming clogged, the coil itself can be treated with a protective substance that prevents dirt, oil and other contaminants from sticking to it, or a filter can be installed to catch environmental particulates before they reach the coil at all. If a filter is used, appropriate cleaning and replacement frequency will be dependent on the environment that the air conditioner operates in. There are three common types of filters and each is designed specifically for different environments. Metal filters excel in oily environments, lint filters (as the name implies) are intended for settings where there’s an abundance of lint in the air and lastly, foam filters are effective for applications in exceptionally dusty environments. As with most devices, air conditioners and filter fans may need general required maintenance to ensure consistently high levels of performance and efficiency.

Air-to-water heat exchangers and energy efficiency

Air-to-water heat exchangers can be used in harsher environments than filter fans and can cool the components inside an enclosure to temperatures below ambient conditions like air conditioners. Air-to-water heat exchangers operate in conjunction with a chilled water supply. The chilled water runs through a coil inside the heat exchanger and an internal fan blows air across the coil. Heat is transferred from inside the enclosure to the water, where it is absorbed and then carried away to the chiller where the water is cooled and then recirculated.

Air-to-water heat exchangers require very little energy to operate and are considered to be a low-maintenance, highly efficient climate control solution. Air-to-water heat exchangers require a chilled water supply to function, and fortunately, many industrial factories have this readily available for use in cooling industrial processes such as metal and plastic forming. Industrial chiller systems are generally large in scale and vital to plant operations. These large systems are intrinsically efficient because of the economy of scale principle, and generally speaking, the larger a system is, the more efficient it is.

To get the most effective and efficient cooling from a chilled water system, the pipes used in the piping system should be insulated and not allowed to be exposed too much to extremely hot areas. It is also important to install the chiller itself in a location that doesn’t expose it to excessive heat - such as near ovens or furnaces.

Air conditioners and the cooling coefficient

To precisely select an air conditioner of the correct size and optimum efficiency for an application, it is necessary to consider the amount of heat that must be removed from the enclosure and how much energy it takes to do it.

For residential air-conditioning systems, this determination is made using the SEER (seasonal energy efficiency ratio) rating. Unlike the units found in residential settings, industrial air conditioners typically operate year round and 24 hours a day since the components in an enclosure are producing heat whenever the equipment is running. In the case of industrial air conditioners, a similar measure of efficiency is the cooling coefficient, which is a ratio calculated by dividing the amount of cooling capacity by the amount of power consumption. This calculation is made at a particular internal and ambient temperature (typically 35°C internally and externally). The ratings will change at different temperatures and allow users to compare manufacturers of similar equipment by evaluating efficiency by the same standard.

Conclusion

Creating effective and energy-efficient climate control solutions for industrial applications consists of three key phases - design, installation and operation.

During the design phase, the overall panel layout, heat calculations and climate control selection should be completed. When laying out the panel, care should be taken to ensure adequate airflow within the enclosure. Determining the amount of cooling needed as well as what type of environment the enclosure will be deployed in are crucial factors in accurately selecting the type and size of cooling solution that will deliver the performance and efficiency required for the job.

The design phase will, in part, develop a large portion of the installation plan simply by virtue of its results. Attention to detail is crucial at this stage and care must be taken to properly install the components and climate control products in accordance with the design plan to achieve the project goals for efficiency and effectiveness. Checking for proper enclosure seals and other possible trouble spots that could jeopardise the success of the application is recommended at this point.

Once operational, climate control devices and other components should be monitored for performance. Regular maintenance should be performed to extend the life of integrated parts and keep energy efficiency as close to desired levels as possible.

By Mark Madden, Lead Applications Engineer for Climate Control Products, Rittal Corporation

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