Russell Brown /
08.13.2010 11:01 AM
Cooling equipment Part 2

There are several things that can be done to ensure the health of your cooling system, and various components that can be checked when things start to heat up.

Keep it clean

As covered in the last tutorial, keep your filters clean, both on the AC unit and on the equipment itself. It’s all too easy to forget and let the dust build up until a piece of equipment, in a 68-degree room, overheats and quits working. In addition, whenever any construction work is performed in or near your equipment room, you should check or change the filters on the cooling system.

Monitor the temperature

Monitoring the temperature of the equipment room is of paramount importance, and placing digital thermometers in and around the room eliminates the guess work. An even better method is to plug a USB thermometer into a computer within the equipment room and allow it to monitor the temperature 24/7. The cost of these units ranges from less than $50 to more than $100, and they come with software that will e-mail you when a temperature limit has been reached. Some of these units also measure humidity.

While some USB thermometers work as stand-alone units, which can have their data downloaded later, the best system will have real-time temperature data and alarms. (See Figure 1.) As with all data logging, the true value of constantly monitoring the temperature of your equipment room is in how it can help you or the AC technician troubleshoot problems.

Another important place to monitor the temperature is at the air supply and return registers. In most systems, the difference between the air in and the air out should fall between 18 to 22 degrees. A change in this differential can indicate a problem. Because the supply and return are usually on opposite sides of the room, using two thermometers with wired probes will assist in keeping an eye on the differential. To get an accurate reading and remove any losses from long runs with poor duct insulation, AC techs will use one of those small thermometers with a needlelike probe that is inserted into the air duct at a seam to make a measurement right at the input and output of the air handler.

If you have the budget, there are more expensive sensor systems that can connect several temperature probes and set limits and alarms set for each one. Sensatronics has a number of models that can handle from four to 16 probes, and TempElert makes software to monitor these sensors. (See Figure 2.)

Airflow per ton

The amount of airflow will, of course, affect the amount of cooling in the equipment room. As a rule of thumb, there should be about 400cf/m (cubic feet per minute) per ton of AC; for example, a 5T unit should be pushing 2000cf/m. If there is more than one supply register, then the airflow would be split between them. British Thermal Units (Btu) are the standard for measuring anything that gets hot or cold. In AC, 12,000Btu equals 1T of cooling.

Troubleshooting

A common cooling system problem is reduced performance from the chiller coils when they get too cold. This may not seem to make sense at first, but it’s really quite simple. Under normal conditions, the return air flows over the evaporator coils, thus cooling it. As this happens, the warm air loses its moisture, and condensation, or water, forms on these coils. That condensation then drips down into a pan below that is attached to a drain. But if the airflow is reduced, the coils cannot absorb the heat from the return air fast enough and they get colder still. If coils reach 32 degrees Fahrenheit, then the moisture in the return air starts to freeze on the coils. This ice then blocks the airflow even more, and ice builds up until there is hardly any air flow and hardly any cooling. (See Figure 3.) The solution to this is to shut down the cooling but leave the fan on to help melt the ice. Once the ice melts, whatever was slowing the airflow can be fixed.

Another common problem is low refrigerant. With too little refrigerant in the system, the pressure within the evaporator coils becomes too low. Low pressure equals lower temperatures, and the coils’ temperature falls low enough to allow the formation of ice. In this case, the solution is to find the leak that caused the loss of refrigerant and recharge the system, which may require an AC tech.

There are, of course, many possible causes to the failure of a cooling system, but these are just two common problems.

What you can do

Today, with the advent of server rooms and farms, several new approaches to cooling have been adopted.

Equipment racks can be ordered with or fitted with chimneys that allow the hot air to be vented into the plenum above the drop ceiling. The ceiling tiles around these chimneys make sure that the hot air leaving them exits directly to the space above and does not mix with the cool air in the rest of the room. (See Figure 4.)Also, curtains can be installed in place of the chimneys just above the tops of the racks or surrounding them to help direct air flow.

Any empty rack spaces should be filled with blank panels. Any open space in the front of the rack will allow the colder air in front to mix with the hot air inside or behind the rack. Keeping the front of your racks sealed helps contain and control the flow of air. (See Figure 5.)

Also, don’t forget to keep your racks neat and clean. A rack that is overflowing with cables will only block the flow of air to the equipment. If you have under-floor plenums, make sure they are clean and not allowing dust and dirt to clog or collect on the equipment. If it’s been a few years, have the plenums cleaned, because these are the most likely areas to collect dirt and foreign objects.

Lastly, some racks now come with self-contained AC units. These racks are wider than normal (about 3ft) and only require power, a water drain line and a space to push the hot air into, such as the plenum. When installing new equipment, these racks can be quite economical. Their cost can be tied directly into the overall budget of the project, making sure that it won’t overtax the current cooling system.

Conclusion

Today’s broadcast facilities contain more equipment generating more heat than ever before. With the cost of energy increasing, it only makes sense to cool them as efficiently as possible. Keeping the present cooling systems running as cost-effectively and investing in improvements to make them even more efficient also makes sense. By monitoring and maintaining this essential part of the broadcast facility, you can help keep your station on the air.



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