Get comfortable with an adiabatic cooling system in the data center

Is your data center in a hot climate? Rather than fight the environment with CRACs, take advantage of it with an adiabatic cooling system.

Adiabatic cooling saves hot climate data centers from massive energy bills. With end-user latency and data sovereignty gaining importance, adiabatic cooling is heating up.

TechWatch

Data centers and hot temperatures don't mix, but heat is relative. Data center temperatures will stay around 25 to 30 degrees C (77 to 86 degrees F) for the foreseeable future, and even data centers operating in the higher range of ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) guideline temperatures -- as high as 35 degrees C (95 degrees F) -- waste energy on CRACs (computer room air conditioners) and moving large volumes of air around the data center.

There are plenty of data centers in high-temperature climates where free cooling regularly exceeds ASHRAE temperature guidelines. But are CRAC units the only answer? Before pouring more money and facility maintenance into a CRAC, consider adiabatic cooling.

Data centers in temperate or colder climes operating solely with free air cooling can also implement adiabatic cooling for times when temperatures spike. A low-maintenance and low-energy adiabatic cooling system tops up free cooling better than a CRAC system.

How adiabatic cooling systems work

Adiabatic cooling, often called evaporative cooling or swamp cooling, uses high temperatures against themselves. The change in gas volume cools the temperature: As a gas expands, it takes in heat. At the best levels, the conversion from a liquid to a gas involves moving large amounts of temperature; this is where data center adiabatic cooling systems come in.

Imagine a thin glass beaker containing an amount of chloroform, placed in a small puddle of tap water. By blowing through a straw into the chloroform, a person can make the volatile chloroform evaporate, taking in heat from its surroundings -- in this case, the water. If the rate of evaporation is high enough (fast air through the straw), the water will freeze.

Even licking your finger then blowing on it demonstrates adiabatic cooling: The finger feels colder when it is wet than if you blew on it while it was dry.

Adiabatic cooling in the data center

Essentially, CRAC is a form of adiabatic cooling system: It compresses a gas into a liquid form with a mechanical pump, expelling the heat created, and then lets the liquid expand again, cooling a controlled mass of air. However, the compression stage in CRAC cooling requires relatively high energy input, making CRACs expensive.

A much cheaper adiabatic cooling system design exists. People in hot climates soak a sheet in water and hang it over a line within a room. As the water evaporates, it takes in enough heat to keep a residential room cool. This is the principal design for a data center adiabatic cooling system.

The basic approach for adiabatic cooling
Figure 1. To cool a data center without CRAC systems, adiabatic cooling systems rely on wet filters and air flow.

To cool a data center, a low-energy pump or gravity-fed system constantly drizzles water over a set of high surface area fibrous mats. A low-power fan with ducting forces air through these mats. The air evaporates some of the water on its way through, and the resulting air on the other side of the mats will be much colder than the inlet air (see Figure 1).

With an adiabatic system in certain climates, humidity may increase above ASHRAE's 80% guideline. A quick treatment -- secondary drying filters or low- or no-energy dehumidification -- ensures that the data center meets humidity guidelines.

By carefully targeting the cooling air directly onto IT equipment via ducting and low-energy air pumps, data centers can use a low volume of adiabatically cooled air, keeping the cooling equipment a manageable size.

There are many vendors in the field, including Munters, EcoCooling, Excool, Vent-tech, Coolerado and United Metal Products. As energy costs rise, more data center operators will be looking to replace expensive CRAC and other active cooling systems. This could push large cooling and energy management companies, such as Schneider, Emerson, GE and others to develop their own systems or acquire smaller vendors.

This was first published in May 2014

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