Once again, vendors are ramping up with new and advanced data center cooling technologies, in fact, I have received many calls just in the last 2 months. There is a common thread, they claim up to 80% reduction in energy costs. Wow, thats a big savings, is there a catch? Sort of… There are some technologies that can reduce electrical consumption, it’s not entirely a false statement, but there is a big catch – and its a not a “Green” technology by any means. I will explain.
Typical data center providers use Liebert cooling, basic DX (direct expansion). You have a floor unit that contains a compressor and evaporator coil, heat is rejected to an air cooled or glycol cooled condenser. These units use approximately 1.5KW per 1-ton of cooling. So a 40-ton data center installation, will have about 60KW of electrical usage just for the Liebert AC units. Can we get that down to say 10KW for 40-ton, YES. Here’s how….
Evaporative cooling has been around for years. In fact most large buildings use evaporative cooling instead of air-cooled dry coolers because an evaporative cooling tower takes up much less space. These cooling towers are fairly simple, big fans, lots of airflow, a really big heat-transfer coil (with glycol circulating) and a water source that sprays liquid onto the coil for it to evaporate off. Even in the summer, a 100-ton evaporative cooling tower can easily reduce circulating glycol temperatures from 100 degress F at inlet to 60 degrees F at the outlet.
The low-energy cooling technologies being advertised are basically a non-DX non-compressor solution. They tend to be rack based. So right next to the rack cabinet is a coil with glycol circulating from the evaporative cooling tower. The side cabinet sucks hot air from the rear of the cabinet, cools it across the coil, and supplies the cool air back to the front of cabinet. The coils is about 60 degrees or so, and with enough airflow, that will cool an average size rack. The heat rejected goes to the roof tower and is dissapated through evaporation.
So if this works, and uses less energy, why doesn’t everybody do it? Simple. One piece of information has been left out. Evaporative cooling towers use a HUGE amount of water to perform this kind of cooling. Instead of electricity and freon in a closed DX circuit, they use water and physics, but water is a resource and its not cheap. A 100-ton tower at max capacity (which is where it would be to get glycol outlet down to 60 degrees F) will use about 5,000 gallons of water a day. Not only is that a huge waste of water, but you are only shifting cost. Yes, your electric bill will be lower, but your water bill will be insane, somewhere around $2000/month.
Its common sense, if there were a better cooling solution, we’d have it. Data Center Providers are already using the most efficient system since cost is already a major concern. The fact is, cooling is already as efficient as it can be. These modified systems, may work for some people, for example, if you have a huge underground source of well water that is “unlimited” this may work for you. But most datacenters don’t have access to unlimited, free, clean, non-brackish water.