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Forecasts predict that power and cooling will continue to be an issue within the data center for the foreseeable future. Will the stress and strain on the power grid and the need to be green have data center managers look more closely at this option to reduce energy consumption? Many have and are looking into it. Lets take a quick look at what economizers are.
One method of energy savings is not new and can be implemented to most data center environments. Economizers can cut data center cooling costs by over 60% using standard and available low cost equipment.
The term “economizer” refers to methods of cooling that do not use mechanical or chiller cooling. The two most common are air-side and water-side economizers.
An air-side economizer assures that the large air handling units have adequate openings to allow them to run at 100% using outside air. That way, whenever the outside air is cool enough (generally, at least 5 degrees below the inside set point), outside air can be used directly to cool the space. Thus the only energy cost is for the fan power.
Datacenters in most climates can significantly benefit from an airside economizer. Datacenters can often be served by using outdoor air during cooler weather and particularly at night when, unlike most office buildings, datacenters still require significant cooling.
A water-side economizer provides cooling by evaporation. When the weather is cold enough, water is circulated through the cooling towers, which are, in effect, giant evaporative coolers. As the tower water is sprayed in the air, some of it evaporates, cooling the rest down. A large heat exchanger transfers the “cool” to the regular chilled water loop. The heat exchanger prevents cross-contamination of the chilled water loop with water that has been exposed to the air and air-borne dust, etc. in the towers. Here, the only energy cost is for the tower pumps. The advantage of the water-side economizer is that it can cool the water to lower temperatures, since it can go down to the wet bulb, or dew point temperature, not just the regular dry bulb, or air temperature. This makes it very valuable for meeting the cooling loads in the data centers, where cooling loads are high and air flow is limited, reducing effectiveness of air-side economizers.
Depending on the climate, the steady, 24-hour cooling load of a data center is well suited to take advantage of seasonal and nighttime temperature variations to cool the space.
A standard data center cooling system can remove heat from the data center it serves only by running compressor(s), a major electrical cost. With an economizer, when the outside air is cooler than the return air, hot return air is exhausted and replaced with cooler, filtered outside air – essentially ‘opening the windows’ for free cooling.
Economization must be engineered into the air handling system. Small data centers may be economically served by low cost, mass produced package units. Larger data centers typically justify a more efficient chilled water system with central air handlers.
In dry climates, controls should include redundant outdoor air humidity sensors to stop economization when the absolute humidity (or dew point) is too low to prevent causing an artificially expensive humidification load on very cold days. Dry climates can often realize excellent savings from an evaporative cooling or water-side economizer approach.
An outdoor economizing system is best implemented starting at the schematic design stage, where the required architectural accommodations can be made with little or no additional cost. There are other issues and coordination requirements that have not been covered in this article that should be reviewed with your engineer to determine if an economizer will benefit your data center.
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