When you plan a new data center, maximizing the facility's power and cooling efficiency should be a top consideration. In part two of this series on data center cooling, we discussed ways to modify existing facilities to reduce the cost per ton of cooling production and thus to delay or eliminate the need to build new facilities.
But when you reach power capacity limits, building a new data center is often the only option. This tip outlines some considerations for the data center building process that keep capital requirements in line with facility growth without sacrificing energy efficiency. In particular, we'll discuss how pre-packaged chiller plants, which are customized for a specific facility's needs, can maximize data center cooling efficiency and reduce the costs of data center buildout.
Consider chiller plant design efficiency
First and foremost, make optimized plant energy performance a design goal. While this recommendation may sound obvious, experience shows that nearly all chiller plant designs ignore efficiency method. In other words, they weren't designed to be energy efficient in the first place -- their design goal was to make enough chilled water on the hottest day of the year.
While it may be hard to believe, this sad fact explains the wave of current investment in existing chiller plant optimization upgrades for facilities other than data centers. Take a lesson from these realities and apply it to your new plant. You can check out the last article, "Improving data center cooling capacity with chilled - plants," for more details, but here is a quick summary:
- Choose centrifugal chillers only , don't use air-cooled energy hogs.
- Maximize free cooling with chillers and heat exchangers in series, not in parallel .
- Primary/secondary pumping wastes energy; go with full variable flow only .
- Use adaptive control techniques for continuous optimization.
- Use high-performance rotary valves on cooling coils – -- no cheap globe valves.
Data center capacity and size matter
One of the most significant challenges in data center planning is the tug of war in determining capacity and size. No one wants to run out of capacity, but a larger facility means more up-front capital cost. The options are difficult to balance, especially when the supporting tenant revenue is not immediate or the planned internal requirement is too far down the road. When the final buildout size is set, everyone can plan around the hard numbers associated with it. But a serious challenge remains: determining the demand requirements and timing between initial commissioning and maximum facility capacity utilization.
The size and scale decision has two serious effects on chiller plant design and operating efficiency. Data centers obviously exist to process and store data, so any function that takes away raised-floor space detracts from the facility's basic mission. Thus, the goal should be to make the chiller plant footprint as small as possible. But a large final buildout requires a large space for the final chiller plant.
The size problem can be partly addressed by installing large chiller sets at the outset (two large tonnage chiller sets require less space than four or five smaller ones). But large chiller pumps and towers cost more than smaller models, and the initial cost may not fit with the initial capital budget.
Oversized chiller sets create another problem: low efficiency. A fundamental engineering principle is that the efficiency of equipment (like pumps and chillers) decreases as the load it serves approaches its minimum output -- the exact condition when a large chiller serves a relatively small load. In reality, a chiller's kW per ton at minimum load is more than twice the kW per ton at maximum load. The pump efficiency degradation is equally dramatic at low loads, so the total plant kW per ton suffers. Long-term scale decisions and usable space impact are not unique data center issues, nor are they new challenges. Experienced mechanical design engineers and property owners have dealt with these problems for a long time, and many have used packaged chiller plants as a solution.
As noted previously, pre-packaged chiller plants are designed for a specific property in accordance with the owner's and engineer's equipment preferences. The specified chillers, pumps, towers and controls are assembled and tested in a factory and shipped to the job site as a functional unit. They not only address the size, scalability and efficiency issues mentioned previously but also offer key financial and project management benefits as well. Pre-packaged plants offer the following benefits:
- They are single source. The commercial transaction involves only one purchase order for the packager. Because packaged plants use the exact equipment you want, you won't need to cross your fingers for a contractor to get a chiller or pump for the least amount of money and that meets your specifications.
- Growth options. While it's possible to put an entire chiller plant in one package, dividing the plant into modules will conserve capital and mitigate the energy-efficiency impact of mismatching capacity with actual demand. One proven approach starts with a base module that contains the piping, power connections and control system for the entire buildout, but is equipped with only one or two chiller sets. As cooling demand increases, more modules can be connected to the base module.
- Impact on raised-floor space. Packages can be built to fit in an unused corner of the property. They can also be built in a house and put on the roof or in the parking lot. There are many options available to help conserve raised-floor space.
In addition, competent package manufacturers can design and build modules to address space utilization as well. For example, modules can be stacked. The packager's services can also be valuable with other site constraints and limitations, including assistance with zoning regulation compliance.
- Construction schedule impact. Since packages are factory built, they are not subject to typical site delays like weather, labor and logistical problems. Their delivery is reasonably predictable, and the on-site installation is limited to piping and power wiring connections and to the connection of field-installed instrumentation. And since the packages are factory tested, on-site startup typically involves verification of the operating sequence and communications with the site building automation system.
In existing chiller plants, hydronic and control techniques can help recover previously unusable capacity, which can help you avoid having to build a new data center. But when considering a new data center design, these same techniques can keep production costs low, especially when integrated with the packaged chiller plant approach at the project outset.
Packaged chiller plant flexibility can provide significant benefits in utilizing raised-floor space, since the plants can be designed to fit the property and local building requirements. In addition, their scalability and modularity can be extremely helpful in matching cooling production capacity with actual demand. Improving the match makes for more efficient use of capital and improves production efficiency. All this, and you can deal with just one supplier to get the exact equipment you want for the space you need to put it in.
ABOUT THE AUTHOR: Mike Flaherty is general manager of tekWorx, a Cincinnati-based engineering and control firm that specializes in optimizing energy usage in chiller and boiler plants. Prior to founding tekWorx 2000, Mike had over 20 years experience in computer control and software technology for production machinery and industrial processes. He has served in executive positions at leading industrial automation companies including Allen-Bradley and Parker-Hannifin Corp.
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