Heat Rejection for Critical Facilities – Balancing Availability (Uptime) vs. Operating Costs

• Post By: Greg Crumpton
• Date: November 20, 2013
• Category: Blog

Are you trying to figure out how to balance keeping the HVAC for data rooms, computer rooms and telecom locations working at maximum efficiency and performance, while reducing operating expenses? This is just one of several challenges we face as data centers and critical environments continue to evolve.

Not so many years ago it was fairly simple: You called on a local mechanical company to install a couple of Computer Room Air Conditioning (CRAC) units up against the wall of the data center; they’d connect the piping, controls and the electrical service; perform a routine startup of the new units, and unless you were sold a PM agreement the project was done.

At this time engineers and data center operators were working on the premise of “how many watts per square foot” the Information Technology (IT) equipment would consume and the resulting amount of waste heat that would be rejected into the space.

The calculations were simple enough; the conversion from watts to Btuh was made and the appropriate tonnage CRAC units were ordered and installed. This process worked pretty well for many years, and even though the CRAC unit placement was not ideal, usually there was enough tonnage to totally saturate the room with cold air. The mindset concerning electrical costs was, “They are what they are.”

Faster and Hotter

In most businesses, as in life, the rules change. Moore’s Law states, “Every 18 months, the computing capacity, meaning work done by a computer, will double.” Therefore, the amount of heat given off by the computing equipment will rise as well.

That law drives many decisions in the IT field. As a result of those decisions, the cooling of those very same data centers has taken on a whole new complexity. We can no longer work based on watts per square-foot calculations. Today it’s all about kW per rack of IT gear. The introduction of larger-capacity, faster, and therefore hotter computers (especially blade-style servers) has forced many engineers to analyze the physics of “cooling” the data room.

The focus now is “heat removal” and in particular capturing the heat as close to the source as possible. Today’s CRAC units do not sit on a wall at the perimeter of the data center; they are strategically located within the rows of IT equipment, positioned to ingest all of the hot air possible – the higher the return air temperature is, the more efficient the overall operation is.

The units themselves do not resemble air conditioners. More often than not they look just like a rack of IT equipment, with the same dimensions and the same name brand. The current mindset regarding electrical cost seems to be, “We must be as efficient as possible in order to pay as little as possible for power.”

Many existing data centers have an abundance of heat-removal capacity, read this as tons. The problem is the supply and return (as hot as you can get it) air distribution.

Think about this: It’s highly inefficient to mix the supply and return air of any mechanical system; you wind up only extracting a portion of the heat from the room into the airstream, where it can then be transferred into the chilled water or refrigerant and finally be expelled from the room.

Saving Money

So how do you, as a service or installation partner for your IT-savvy clients or as an IT manager, help the company save money? As always, start by asking questions. What kind of input may your client need from you? Could you possibly save the client operating dollars by studying the layout of the IT gear and making placement suggestions based upon heat load? Would it make sense to duct or reduct either the supply or return air in an existing facility? Is this the only site they have in operation or is there a Disaster Recovery (DR) site elsewhere?

Start looking around; what are you working on? What is the IT staff installing and working on? Are the rows of equipment placed in a hot aisle / cold aisle design? Do you have to really turn the setpoints down low to keep the cooling on for longer cycles? Are the CRAC units fighting each other, meaning some are cooling, some are reheating, and others are fighting the humidity setpoint?

All of these are signs of inefficiency and waste.

What happens if you lose a compressor due to short cycling of air due to poorly placed perforated tiles? Will you drop the critical load?

What are the expectations of up time? Is it 99.999 percent of the time? If so, that is still 5½ minutes a year of outage; is that OK? Can you commit to responding to those requirements?

What tier level does their company commit to with their customers – tier one, two, three, or maybe even four?

Be a Resource

HVAC is only a slice of the pie that critical facilities managers are responsible for. We need to make it easy for them to communicate their needs, and that applies to internal and external customers. When you learn what is driving their business you can figure out a way to help them stay online and view you as a resource, not just the facilities guy, the network guy or even the heating and air guy.

We at AirTight are very aware of issues associated with the green movement. In fact, many of the data centers we are involved with connect in some way to a LEED-certified building.

The green certification impacts every area of data center operations, from operating procedures to chemicals for coil cleaning to how the CRAC units drain their condensate (into a reservoir for irrigation water or cooling tower makeup water?).

These are just a few of the interwoven complexities of operating an efficient data center within a green building that must be managed, while meeting all the requirements imposed by an ever-growing list of certification agencies.

By showing our willingness to step outside of the normal HVAC contractor stereotype, we are typically brought in during the planning phase for future projects and are becoming an ever-more-important partner to our clients.

Isn’t that where we all want to be?

Quote:
“When you learn what is driving their business you can figure out a way to help them stay online and view you as a resource, not just the facilities guy, the network guy or even the heating and air guy.”