Variable Speed Technology for Datacom Efficiency
Cooling today’s data centers and other mission-critical environments is a complex endeavor. Data centers are not expected to be fully populated with data processing equipment on day one. They are virtually all built with space for additional Datacom equipment in the future. The cooling requirements of the space will continue to grow as heat producing servers and storage are added to the racks. The situation is the same as old servers and storage are replaced with new versions, which produce more heat than the ones being taken out of service.
The data room cooling system must be able to adapt to the load as it changes. The question becomes, “What is the most cost effective and energy efficient way to approach this challenge?”
The answer depends a great deal on whether those units use a central chilled water system for cooling (CRAH units) or have unit mounted compressors that do the cooling (CRAC units).
Control Strategies for CRAH Equipment
There are multiple control strategies for chilled water CRAH units that allow them to throttle down their cooling to match the amount of cooling needed in the room. The single biggest drawback to chilled water is that they are not extremely scalable. Meaning that if you only need 100 tons of cooling on day one and you think you may need 1000 tons of cooling five years from now, it doesn’t make sense to put in a 100 ton system and then scale it up as the load increases.
You could only by 100 tons of CRAH units on day one, but the CRAH unit itself is a small percentage of the installed cost of a chilled water system. The biggest expense is usually in the piping, the pumps, the cooling towers, and the chillers themselves. The piping in a building is only installed once so the initial building is normally built with the largest piping the data center is ever likely to need. Same goes for the pumps. The price per ton of the chillers and cooling towers declines significantly as they get bigger so you kind of need to buy at least 1/2 the number of chillers and towers that you think you may ever need — and probably more than 1/2. So if you only need 100 tons on day one you end up paying for 500 tons of equipment and a 1000 tons of pipe.
Variable Speed CRAC Unit Benefit #1: Data Room Scalability
- Customizable for flexible capacity ranges
- Units can scale up or down in capacity to meet demand
DX CRAC units on the other hand are almost infinitely scalable. If you need 5 tons of cooling on day one you buy a 5-ton unit. If you need 100 tons on day one you buy 3 or 4 thirty-ton units. From then on you just add units and the cooling requirements of the space increases. There is not much economy of scale in the first cost or installation cost of the equipment, so there isn’t much incentive to buy equipment until you need it.
Variable Speed CRAC Unit Benefit #2: Redefined Efficiency and Energy Savings
- Variable speed operation increases efficiency because when running at lower capacities, units use less energy and save money
- Achieves greater turn-down while saving energy when compared to standard unit capacity measures. Turn down ratio is 4:1
The biggest drawback of DX systems had been that they were much less efficient than chilled water systems (30% to 50% less). In the last few years however, DX system efficiencies have more than doubled and have closed the efficiency gap with chilled water. Today there is very little efficiency difference when you select the correct DX CRAC units. Emphasis on “correct”.
The fans in the CRAC unit must be able to change speed according the cooling needs of the room. Chilled water CRAH units have this capability and the fans can use up to ½ of the total energy consumed by the unit if they are unable to vary speed.
Variable Speed CRAC Unit Benefit #3: Increased Precision
- Variable capacity technology quickly adapts to required cooling demands and retains a precise set point
- Effectively manages humidity and regulates temperature to ensure protection of mission critical data and potentially extends the lifetime of your cooling equipment
- Precise operation and control of fluctuating loads
The compressors must be able to vary their capacity to match the cooling needs of the room. There are two types of variable capacity compressors and there are dramatic differences between the two. Some compressor use mechanical ‘unloaders’ to match the required cooling and others vary their speed with a variable frequency drive. Both do a good job of matching the required cooling capacity in the room and delivering precise control.
Variable Speed CRAC Unit Bonus Benefit: Smaller Backup Generators
- Slowly ramps up inrush to avoid surges
- Quieter operation
Controlling mission-critical environments in an energy-efficient manner is an even bigger challenge than just controlling it alone. Today, the CRAC equipment in use at most facilities rely on mechanically-modulating fixed speed or fixed capacity components. Although these units provide adequate climate control, they do so at a cost. To understand the inherent problem with mechanically-modulating compressors and other components, imagine if vehicles operated this way. What if in order to maintain speed you had to keep your foot on the gas, run your car engine flat out, but keep switching gears between neutral and drive? Not only would this waste a lot of fuel, it would also be extremely hard on the car. Watch this video for a visual representation of this concept.
You may be asking yourself, “How does variable speed compressor technology compare to other compressor options?” To learn more about the comparisons between standard fixed speed compressors, tandem compressor installation, hot gas bypass installation, mechanically-modulating compressors and variable speed compressors, please download this guide to learn more about gForce Ultra, the industry’s first CRAC system with variable speed technology.
Incorporate variable speed technology into your plans and realize substantial energy savings, precise cooling and greater capacity modulation.