4/23/2009 6:00 AM
introduced you to the cooling requirements of some broadcast spaces. Now we’ll look at the most important television space — the machine room. This is the heart of all content production centers. If this room goes down, so does all production and transmission.
Machine room basics
When configuring a machine room, there are some basic guidelines. First, don’t try to put every piece of production gear into one room. If possible, locate only rack-mountable devices there. Adding standalone devices like printers, monitor stations, UPS systems and power supplies merely complicates the room’s cooling requirements. Once you move a heat source outside of the rack, it adds new variables into the cooling calculations and makes it more difficult to control airflow.
Photo: Note the hot-aisle/cold-aisle construction in this typical broadcast equipment room.
Second, put like devices in close-proximity racks. This allows similar heating/cooling techniques to be applied to like spaces. For instance, a rack of servers is designed to operate in similar temperatures. Locating them near each other helps create a uniform cooling load. If, for instance, an intercom chassis or UPS system is located in the same rack as a bank of servers, their different cooling needs can complicate solutions. Also, some newer servers rely on water cooling techniques. Mixing water-cooled gear with more common air-cooled gear will greatly complicate design factors.
Be sure to use the hot-aisle/cold-aisle technique. If you only need a couple of racks, this probably isn’t important. However, any larger production or broadcast center will have 15 or more racks, and a dual row of seven is more efficient to cool than one long row of 15.
Third, plan for scalability. In other words, build enough space to serve the facility’s needs for a targeted number of years. Plan now for the future. Depending on management’s goals, that might require double or triple the amount of equipment room space you now need. Also, it is no longer necessary to plan a facility to last 20 years. The life of today’s equipment may be as little as three years and perhaps as long as seven.
Instead, design for a device’s remaining useful life, not just on required square feet to house the machine. Equipment will continue to shrink in size and increase in individual power consumption. It’s wise to slightly overbuild, but don’t plan on this facility being your “last great hurrah.” Technology moves too fast for anyone to think they can see what is needed tomorrow.
Fourth, calculate the amount of heat that would be generated in the machine room if it were full. Then, recalculate the amount of heat predicted to be generated in the space on day one. Then, install an AC system based on near terms, not long-term needs.
While it sounds logical to use a larger air-conditioner than needed to allow for growth, that can actually result in less efficiency (higher operating costs) and improper humidity control. An air-conditioner needs to run near its maximum to be efficient. This saves power and better controls humidity. (See Figure 1.)
Figure 1. When an air-conditioner is run at its full load, it is most efficient.
When considering the long-term goals, plan for a second air-conditioner. Today’s solution may be as simple as allowing extra pad space for an air handler and extra duct space. This may be much less expensive than installing a two-stage air-conditioning system.
Fifth, don’t fill the racks from top to bottom with gear. Spread the equipment out. Not only does this improve the cooling efficiency, it also provides easier servicing and allows better access from the back, which is often cramped. Of course, there are instances when gear must be located together, like patch bays and signal processing gear, but look for opportunities to add a few blank spacer panels between devices.
Also, once you’ve decided to use the hot-aisle/cold-aisle cooling technique, don’t ruin it. Sometimes engineers will be concerned that the hot aisle seems “too hot.” Rely on the equipment manufacturer to tell you what temperature is best for the device. Adjust the system to that temperature and tell your people to “live with it.”
Do not defeat the air-conditioning system by leaving the rear doors of racks open. One open door can cause the rest of the racks in that row to receive insufficient cooling. Also, do not install extra deep equipment in a hot-aisle/cold-aisle configuration. This will disrupt the airflow because the rack door won’t close. (See Figure 2.)
Figure 2. The efficiency of an air-conditioner as a percentage of its cooling load
This illustrates the efficiency of an air-conditioner as a percentage of its cooling load. A too lightly loaded cooling system can suffer from high head pressures and short-cycling of compressors, both of which reduces compressor life. Note also the number of years that this facility’s air-conditioner was underloaded. This represents a huge waste of electricity — and a costly mistake.
Sixth, design for modularity. Carefully consider the size of your racks. Will a standard 24in-deep rack be sufficient? With much of today’s IT-centric equipment, probably not. Broadcasters are often unfamiliar with the deeper racks normally used in data and telco environments. Much of today’s video servers and other IT equipment require deeper racks, and the gear won’t fit in smaller ones. Deeper racks require more floor space. If there’s one place to plan ahead, it would be to use extra deep racks. Tomorrow’s equipment will grow into those spaces.
Finally, calculate the weight of the gear what will be located in the machine room. Buildings have specified load limits, usually specified as weight per square foot. These loads must not be exceeded. Your architect can calculate those factors for you, but you will need to specify the type of equipment and approximate weight you’ll be placing on the floors. Don’t forget to include the weight of the wiring. A modern television plant can have hundreds of miles of heavy cabling, which adds tons of additional weight to a floor.
Don’t forget to verify that your raised flooring will carry the needed weight. Include ramps and the floor grid in the calculations.
We will discuss raised flooring considerations and begin an examination of creating clean power in the next column.
Virtualization: Optimized power and cooling to maximize benefits
Fundamentals of data center power and cooling efficiency zones