IT Data Centers

In the spring 2005, a graduate student from UEP evaluated the energy consumption of data and telecom centers and closets at Tufts University Medford Campus.

A literature review was conducted in order to understand the engineering principles regarding the cooling of electronic equipment and data centers.

Major increases in efficiency are possible through evaluating and minimizing ventilation rates. Evaporative cooling in dry climates where data centers need humidification will also increase cooling efficiency.

Glycol cooling has a very significant advantage over other methods. In cold locations, the glycol within the fluid cooler can be cooled so much (below 50°F) that it can bypass the heat exchanger in the AC unit and flow directly to a specially installed “economizer coil”. If the outside air is cold enough, the refrigeration cycle is turned off and the air that flows through the economizer coil, filled with flowing glycol, cools the IT environment. This process is called “free cooling” and provides excellent operating cost reductions when used.

“Recirculation” (mixing of hot and cold air) results in a decrease in overall efficiency and cooling costs that are 10-25% higher. In order to prevent the mixing of hot and cold air in the data center, data racks should be aligned in rows where they have their fronts facing each other, with an empty aisle in between. The implementation of the ‘hot aisle – cold aisle principle’ can reduce costs by almost 20 percent. In addition, all unused space in the front of a rack should be covered with blanking panels to prevent mixing.

The following are the environmental requirements and a list of installed A/C equipment at the larges Data Center at the Tufts Medford Campus:

• Temperature range: 68-72 oF
• Relative Humidity: 40-55%.
• Cooling Requirement: 52 tons (626,484 BTU/h, 183.6 kW)

Equipment at the Tab Data Center:
• The glycol-cooled Liebert unit has a total cooling capacity of 265051.2 BTUs per hour(22 tons).
• There are two identical glycol-cooled Stulz Units (Model MRD522G), each with a total cooling capacity of 183,800 BTUs per hour.
• ‘Hot aisle – Cold aisle’ principle is starting to be implemented.
• The Telecommunications Department is considering an expansion of the AC System by 5 tons in late summer or early fall, 2005.

The annual CO2 emissions and costs resulting from A/C usage in the TAB Data Center:

The study also looked at possible ways of reducing the carbon emissions resulting from the operation of A/C systems used in Data Closets. The focus of the study was the data closet in the Ginn Library. This data closet utilizes a small, ductless, split / AC unit although the library has a central HVAC system in place. The closet has a cooling requirement of 2 kW which translates to 1 ton of CO2 emissions annually resulting from AC usage.

The following recommendations were made as a result of the study, regarding possible reductions in carbon emissions.

Replacement of AC Units in Data Closets with Fans:
The replacement of the AC unit with a fan would allow the Data Closets to utilize the cooling provided by the central HVAC system. This would also enable savings to be made from heating costs during winter.

Estimated Reduction in Annual CO2 Emissions: 0.5 tons per data closet.
Estimated Reduction in Annual Operating Cost: $440 per data closet.

Implementation of the ‘Hot Aisle – Cold Aisle Principle':
The full implementation of the ‘hot aisle - cold aisle’ principle would reduce operating costs and the resulting carbon emissions by 20 percent.

Estimated Reduction in Annual CO2 Emissions: 13.2 tons.
Estimated Reduction in Annual Operating Cost: $2470.

Future Installation of Glycol-cooled Systems:
Installing glycol-cooled AC systems is one of the most cost effective carbon reduction options. The Computer Services and Facilities Departments should choose to install glycol-cooled AC units whenever an expansion is needed. Compared to other conventional options the glycol-cooled units can provide the following reductions:

Estimated Reduction in Annual CO2 Emissions: 0.6 tons per ton of cooling added
Estimated Reduction in Annual Operating Cost: $114.6 per ton of cooling added

Documentation of Electricity Consumption in the Data Center:
Electricity consumption by the AC units in the Data Center should be observed and documented. Currently, there are no meters installed to show consumption by each individual unit, or the total consumption by the AC units. When such data is available, it will be easier to quantify the costs and benefits related to the different carbon-reduction options described above.

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