Russell Brown /
07.30.2010
Originally featured on BroadcastEngineering.com
Cooling equipment Part 1

One can only imagine how a room full of vacuum tubes was kept cool enough to keep the paint from melting off the walls. Today’s problem in keeping a facility cool is the same as it was then, and with the amount of equipment and its sensitivity to heat, it’s even more critical. And with today’s around-the-clock, 24/7 work environment, it’s very important to have backup cooling systems as well. Today’s sophisticated, high-speed, densely packed electronic equipment’s main enemy is heat, and keeping it under control is oftentimes the engineer’s job. This tutorial will take a look at the way equipment rooms are cooled and what can be done to prevent a meltdown.

Cooling is required both at the studio and at the transmitter site to keep temperatures within a range that enables the equipment to operate efficiently. This is called a “process application” of air conditioning, because the point is to accommodate the equipment, not necessarily the people working there. Fortunately, both the equipment and people work best in about the same temperature range.

If you are fortunate, your station has a main and backup AC units and a service contract to maintain them, but many stations rely on their engineers to keep their AC units running. Following is some basic information to help you if you find yourself is this situation.

How air conditioning works

Here is a brief overview of how a typical AC unit works. Simply put, a coolant is used to transfer heat from one area to another — typically, this is an equipment room, studio or transmitter room that has its heat removed to the outside environment.

The most common coolant or refrigerant in use is called R22. When R22 is placed under high pressure (200psi), it releases its stored heat, and when it’s under low pressure (50psi), it absorbs heat. The AC system takes advantage of this by placing the refrigerant under high pressure and then running it through a set of heat exchanging coils called the condensing coils where the heat is transferred from the refrigerant to the air around the coils. A compressor is used to pressurize the refrigerant and pump it through these coils. All of these components are located on the roof or on the ground outside the building.

After the refrigerant has its heat removed, it is piped inside to the air handler. Here the liquid refrigerant enters a metering device that turns it into a spray, thus lowering its pressure. It’s then fed into another set of coils called the evaporator coils. The air to be cooled is passed through these coils, and the heat within that air is absorbed into the refrigerant, which then passes back up to the compressor outside. (See Figure 1.)

Airflow

Much has been learned about how air flows and the best ways to cool equipment in the last 10 years. Data centers with hundreds of racks full of servers have forced companies to explore new and better ways to address the problem of cooling equipment. Although broadcast facilities do not normally have hundreds of racks, the ones we do have require cooling as well.

One of the simplest ways cooling is carried out in data centers is with hot and cool aisles where cold air is dumped into a aisle between two rows of racks, each facing the other. The next aisle over, at the back of the rack, is the hot aisle; here there are two rows of racks, but the rear of the two rows face each other. In this aisle, the hot air is removed. Because most equipment is designed to pull air in from the front, this system has worked well. The problem comes from the mixing of air above the racks. The solution is to place dividers between the front and rear of the rack from its top to the ceiling.

Another popular method is to feed the cold air below the raised flooring and let it be sucked up from the bottom of the rack and then exit from the top. Once again, it is the air flow that causes problems. In this case, air from below leaks out around where cables enter and exit the rack, and the cables themselves tend to block the cold air flow. A filter to contain the air around the cables and paying attention to the routing of cables can fix these problems.

For most broadcasters, the situation is much simpler. Sometimes just rerouting the air registers can remove hot spots and improve cooing efficiencies. A very simple setup is with the cold air entering across the room from the equipment racks. This allows the cold air to flow across and enter the front of the equipment. The return air registers are placed above the equipment racks to catch the hot air as it rises up. (See Figure 2.)

Filters

Keeping air filters clean is the first line of defense to keep your equipment cool. I am not just talking about the filters in the AC system, but also the filters on the equipment itself. Many times, this small but important function is overlooked, especially because there can be quite a few filters. Many of these filters are located just behind the front panel. If you pull it off, you will see a very dusty filter pad. Even in the cleanest of rooms dust gets in. You should check and clean your equipment filters every quarter.

The AC filters should be checked at least once every month or two to ensure the efficiency of the cooling system. When air filters become clogged with dirt, they reduce airflow, which can lead to increased temperature and icing on the evaporator coils. You should always keep a supply of filters on hand and pay attention to the direction of airflow that is marked on the filter. (See Figure 3.)

Remember that whenever construction is going on within the building, it creates a great deal of dust that can quickly clog AC filters. So if you are building a new studio set or adding or removing walls, check your filters.

In case of emergency

Many facilities have more than one AC system. In the event that one fails, the other(s) can take over. But what if you only have one and it breaks down? For some that means opening doors and setting up fans to blow air around. A better solution, and one that works automatically, is to mount fans directly above the equipment racks with a thermostat set to turn the fans on when the temperature gets too high. If you have enough space above the drop ceiling, then the hot air can just be pushed into that space where it will dissipate. If there is not enough space above your ceiling, then install duct to the roof or out the side of the building; you just need to get the hot air away from the equipment. As the hot air is removed, cooler air will be drawn in from surrounding rooms. It won’t be cold, but it should keep your equipment from melting down. You can also use the thermostat to trip an alarm to let the operator know there’s a problem, if the noise of the fans does not let him know first. (See Figure 4.)

Another method, if the air handler’s fan is still working, is to disconnect the return air duct. If the air handler can pull cool air into its return port, then send cool air to your equipment. The hot air will just be pushed up into the space above the ceiling.

If you are planning a UPS or generator system, don’t forget to include the power requirements of your cooling system. If your equipment is on, it needs to be cooled.

Next time

The next tutorial will cover some of the causes and cures for common cooling problems.



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