Computer room cooling projects require collaboration between contractor and customer. Present and future loads must be considered, and the most applicable products selected.
According to research by Info-Tech Research Group, London, Ontario, Canada, 33% of North American companies with computer rooms or data center complexes completed a renovation of those areas in 2010. Among the cost considerations for those projects, cooling renovations cost an average of $87/sq. ft, with the median cost of cooling system renovations landing between $51,000 to $100,000. It can be money well spent, since cooling the data center can amount to about 50% of a data center’s operating costs, according to Info-Tech Research Group. (infotech.com)
Types of Computer Room Cooling Systems
For the largest applications, computer room air conditioners (CRACs) monitor and maintain the temperature, air distribution and humidity in a network room or data center. A CRAC delivers cool air to the servers, and pulls exhaust air from the room. One CRAC setup that has been successful is to cool the air and circulate it through an elevated floor. The air rises through the perforated sections, forming "cold aisles." The cold air flows through the racks where it picks up heat before exiting from the rear of the racks. The warm exiting air forms "hot aisles" behind the racks, and returns to the CRAC intakes, which are positioned above the floor.
Computer Room Air Handlers (CRAHs) are chilled water-based units installed on the data center floor and connected to an outside chiller plant. The CRAH circulates air throughout the data center through fans, delivers cool air to the servers, and returns exhaust air from the room.
Humidifiers are usually installed within CRAC and CRAH units. They replace water loss before the air exits the air conditioning units. Standalone humidifiers are also available.
Chillers produce chilled water and deliver it through pumps to the CRAH units.
Split systems can be used to cool multiple zones or rooms as wall mounts or ceiling-mounted cassette units.
Portable cooling units can be maneuvered to cool various areas, or can also be mounted
The distinction between computer room cooling and comfort HVAC can't be over-emphasized.
Because data centers are high-density, enclosed spaces that generate a significant amount of heat, traditional HVAC comfort cooling systems can't remove enough heat to protect the critical equipment.
"Precise temperature control in a data center is critical to maximizing availability and performance of essential equipment," says Marc Zipfel, director, product marketing, Mitsubishi Electric Cooling & Heating.
According to Zipfel, the Mitsubishi Electric R2- and Y-Series VRF systems are the best choices for data center applications because they can be used with Mitsubishi's low ambient cooling kit. Mitsubishi Electric's low ambient cooling kit provides 100% cooling at outdoor temperatures down to -10F, while still allowing full airflow at higher temperatures, and full heating capacity if necessary. The system hood moves its position automatically, and along with its INVERTER-driven technology, provides optimum airflow at lower temperatures.
Specially-designed wind deflectors block unwanted wind that could impede data center operation and, at the same time, allow airflow when required at higher temperatures.
Mitsubishi Electric's W-Series (Water-Source Series) can also be used in data centers. These systems are designed for buildings with closed loop boiler/water tower or geothermal loop systems and are extremely energy efficient. The W-Series systems use water as a heat exchange medium and are installed inside, rather than out. This innovation offers efficiencies that are independent of the outside temperatures and well-suited to cooler climates. Mitsubishi Electric's extensive CITY MULTI Controls Network (CMCN) is always expanding with updated controls to be more user-friendly and precise. The CMCN can manage up to 2,000 indoor units from a single networked PC. Every data center has its own unique characteristics and challenges, and the CMCN is designed to support most any temperature demand.
Zipfel says contractors need to realize that specifications are prone to change with the development of new technology housed in the data centers.
"Computer systems are becoming more compact, and data centers and server rooms are becoming smaller and smaller, resulting in more heat generated in a smaller space. When new computers or systems that might change the load requirements of the space are brought into a data center, the temperature settings can easily be adjusted with the CMCN to accommodate the new equipment's temperature needs," Zipfel says.
John Martin, marketing manager, Data Aire, Inc., Orange, CA, providers of precision air solutions, says new servers are faster and more powerful, but they also generate considerably more heat than older server models. Therefore, air flow management in the data center is of vital importance.
"Computer room cooling is definitely a specialized area. If you've never done it you can get into a lot of problems," Martin warns. He says a big trend on the cooling side has been to replace axial fans in CRAC units with plug fans (also known as backward-curved EC fans). Higher efficiency EC motors generate less heat, which must be taken into consideration when determining the net capacity of CRAC equipment. The less heat that's generated by the motor, the more net cooling capacity the CRAC produces, while using the same amount of power, Martin says.
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Chris Richardson, product manager, Daikin AC (Americas) commercial systems, says total heat load and load type should be the primary considerations when cooling a server room.
"The majority of the load is going to be sensible or equipment heat load," Richardson says. "Consequently, there won’t be a lot of cooling needed due to humidity. When sizing equipment, it has to be sized according to sensible load."
According to Richardson, some computer rooms have tight temperature and humidity requirements that must be considered. "If they go out of a certain temperature range, it can affect computer components; if the humidity drops too low, you can have static problems," he says. "Daikin systems are primarily designed for comfort cooling. However, if precise temperature and humidity are not required for your server room, our equipment can be a great solution.
"You don't want to send cooling through the floor. There are several alternative ways to get the air into the room — ducted systems, wall mount units, or ceiling cassettes. Choose accordingly based on the size of the room," Richardson adds, and offers another caution with ceiling-mount cassettes:
"If a ceiling-mount cassette is being used to cool the computer room, there may be regulations that prohibit placing it above the equipment. If there's a condensate overflow, equipment could be ruined. Local codes may require a secondary drain pan, ducted unit, or a wall unit," Richardson says.
Jared Murphy, president, Smith Mechanical, Ferndale, WA recently installed an 8-ton Daikin VRV system with two FXTQs on a server room.
"The variable refrigerant volume lets you match the load, so you don't overshoot your target setpoint. That's the key for computer room cooling: to maintain as tight a tolerance as possible to the set point. The Daikin VRV system's variable speed inverter driven compressors allow us to do that."
There are many options and requirements associated with computer room/data center cooling. Contractors must assess their capabilities, and acquire the training needed before attempting these projects.
Consider Loads, Operating Conditions
For the largest data centers, Donald Beaty, president, DLB Associates Consulting Engineers, and a past chairman of the ASHRAE TC9.9 committee, — writing in 7x24 Exchange Newslink magazine —says there are five steps to a properly-sized cooling system:
- Determine the actual maximum load. An ASHRAE thermal report for each piece of equipment is most effective.
- Determine the load profile. Since the cooling system is affected by computer load and climate, Beaty recommends annual load profile curves for the compute load, climate, and a composite of both.
- Determine the future load. Upgrades are guaranteed to happen. According to ASHRAE, IT equipment life is from two to five years, and there will be five generations of IT equipment in one lifetime of cooling equipment.
- Determine the operating conditions. These have an impact on the amount of cooling being provided by free cooling, pumping and fan horsepower, and the amount of humidification required and its associated energy.
- Correct equipment and system selection. Develop several cooling alternatives based on the current and projected capacity needs and operational load profiles. Optimize equipment selections based on operating ranges.http://www.7x24exchange.org/
Portable Units Meet Special 24/7 Needs
Though many facilities operate only during business hours, data rooms must remain online around-the-clock. It’s a waste of energy and money to run the entire central building air conditioning system 24/7 just to keep the data room cool, yet, this is sometimes what happens. Clark Michel, vice president, Atlas Sales & Rentals, Newark, CA, says a more efficient approach is to install a portable cooling unit that’s dedicated to the server room, and set to operate when the central system is shut down or on nighttime or weekend setback.
"A portable air conditioner installed for this purpose will pay for itself in HVAC energy savings in no time versus running the entire building central system," he says. Additionaly, spot coolers used in permanent applications can often be connected to a building's existing exhaust ductwork.
Another option is to use a ceiling-mounted spot air conditioner. Joe Dotson, service account manager for Scarborough Mechanical, Louisville, KY, recently used this method to cool an overheating 8-ft. x 12-ft. server room at the University of Louisville Health Care Outpatient Center.
In an energy-saving effort, the set points of the building's central HVAC system were adjusted to turn the system off at night. As a result, equipment in the server room became excessively hot and was shutting down at night, incapacitating the health-care center for hours.
Dotson installed a MovinCoolCM12 ceiling-mounted spot air conditioner. The self-contained unit requires no external refrigerant lines, outside condensing unit, or charging of refrigerant. It measures only15.5-in. high, so it fits easily into the space above a drop ceiling.
MovinCool has just released the CMW30 ceiling-mount, water cooled air conditioner. With a cooling capacity of 29,400 BTU/hour total and 22,000 BTU/hour sensible for computer rooms, the CMW30 can be used in server rooms and other applications with dense heat loads.
ASHRAE TC9.9: a Guide to Data Center Cooling Efficiency
"2011 Thermal Guidelines for Data Processing Environments – Expanded Data Center Classes and Usage Guidance," published by ASHRAE Technical Committee (TC) 9.9, presents a guide to increasing the operational hours during which economizer systems are able to be used, and to increase the opportunity for datacenters to become "chillerless."
The whitepaper can be obtained from tc99.ashraetcs.org.v