One thing is certain, optimal data center design is a complex puzzle to solve. With all the options available, no one environmental control system can fit all situations. One must consider all the solutions and technology available to best manage assets and adapt to the evolving data center.
There is a precision cooling system for whatever scenario best fits one's current strategy or future goals. The question only remains, has one considered each of the options with the design engineer and the environmental control manufacturer? The two need to be in synch to help maximize the return on investment.
In most instances, if one wants an environmental control system that scales with your needs, provide the lowest energy costs, and provides the most reliable airflow throughout the data center, a variable-speed system is the best solution. Nevertheless, one may be curious about what other options may suit the current application.
Precise Modulated Cooling
Companies need to decide on their strategy and design for it. When one knows they have swings in the load – seasonal, day to day, or even from one corner of the data center or electrical room to the other, one should consider variable speed technology. A system with variable speed technology and accurate control design modulates to match the current cooling load
A system with variable speed technology and accurate control design modulates to precisely match the current cooling load. This precision gives the variable speed the highest efficiency at part-load, which equates to a greater return on investment. In other words, when the data center is not running at maximum cooling load a variable speed system will use less energy and save money.
If one thinks of the cooling output of the environmental control system as the accelerator of a car — one can press the pedal to almost infinite positions to exactly match the speed one wants to travel. One is not wasting energy overshooting the desired speed. A well-designed control system also ensures a smooth response to a change in load. Further efficiency is gained by accelerating at an efficient rate for the system.
Advanced Staged Cooling
Looking for something that offers a portion of the benefits of a variable speed system but at a reduced first cost, a multi-stage cooling system can be a good compromise. A multi-stage system will manage some applications well and can reduce overcooling space — as-built today. If one needs greater turndown than what a fixed speed system offers, then this is a good choice.
If one finds this to be the right-now solution, one is in good hands. The system is more advanced than a fixed speed unit; it is developed with a level of design optimization to transition its small steps. Unlike digital scroll, this accurate solution, with two-stage compressors, has high part-load efficiency.
Example
Think about the car accelerator example again; there are many positions to move the accelerator to with a multi-speed system. With two-stage compressors the positions are precise and repeatable, meaning one can smartly change positions to prevent overshoot, and one is more likely to have a position that matches the speed that is desired.
Although the return on investment is better with a multi-stage than a fixed-speed system; the benefits are less than with a variable speed system.
Fixed-Speed Systems
Some consider the entry point for precision cooling based on their current budget constraints Some consider the entry point for precision cooling based on their current budget constraints. So, if one is on a tight budget and needs a lower first cost, then a fixed-speed, single-stage precision cooling system may get the job done. However, this can be short-sighted as energy consumption and costs are higher when the data center is operating at less than the maximum designed cooling load. With experience, this seems to happen quite frequently based on what the mechanical engineer has been asked to design vs. the actual heat load of the space.
If a fixed system is applied to the car accelerator example, one can see how only applying 100% throttle or 0% throttle would prevent from getting close to a precise speed. This is clearly not as efficient as the other examples unless one wants to go at the car’s maximum speed all the time.
Ramping Up Data Center
The needs and goals of a data center can change over time. While the initial objective may only require getting the space in running order, customers may reassess based on changing scenarios. If the data center needs to scale, one may be challenged if haven’t planned ahead with the design engineer for phased buildouts, or perhaps even varying IT load considerations that are seasonal or shift from day to day or even hour to hour.
Likewise, one may need to consider the difference between design and actual usage – whether it be too little or too much. Perhaps the IT team says they need two megawatts, or one is going to be running at 16 kW per rack. The cooling system designed may underserve the needs or may be overkill for the current state of usage. In addition, pushing your system to do more than it is engineered for can potentially accelerate the aging of the infrastructure.
Again, depending on your application, goals, and business strategy, one of these three systems is right. The best course of action is to evaluate where one is today and then future-proof the data center with technology that can grow.
