Data Center Energy Efficiency Strategies

By: Dan Fanning, LEED AP, DC CEP, HCC, Projects & Engineering Manager

Around the world, enterprise data centers are running into power and cooling limitations when they try to deploy new servers, storage, and blades, which, in addition to consuming more power than their predecessors, are often much more dense. Businesses continue to implement more powerful applications that in turn put more pressure on IT organizations to deploy the latest technology. As more powerful computing systems are deployed, they bring more heat to the data center, pushing the limits of cooling systems. If CIOs and IT managers cannot find better ways to take the heat out of data centers, they cannot take advantage of ongoing improvements in processor performance and system density.

Consider the financial side of the equation, as well. Energy costs are a significant operating expense. New computing systems require more power, and data center cooling systems are using more electricity. This all adds up to a higher total cost of ownership. The objective of our program at EDI, Ltd. is to enable data centers to utilize more efficient equipment and reduce their HVAC loads.

To achieve energy efficient computing, an enterprise must look at more than just processors or even the servers themselves. This challenge is best addressed from a holistic, systems and services perspective that considers all components of the overall problem - including the design of processors, racks, and the data center itself, as well as the management of resources. This multifaceted approach is key to delivering an energy efficient infrastructure that allows an organization to increase computing density, improve power utilization, and hold the line on soaring energy costs. Power and cooling are critical aspects of building an effective data center infrastructure. To build an energy efficient data center, power and cooling must be managed as an agile resource that enables the data center to scale as computing demands increase.

Retro-Commissioning & HVAC

Retro-commissioning is a methodical and thorough process to ensure that all systems are installed and operating correctly, including optimal efficiency. Hence, the importance of performing retro-commissioning is to verify that all systems are operating as designed.

Perform a Full Retro-Commissioning (RCx): Many older data centers have never been commissioned, and even if they have, performance degrades substantially over time. Implementing retro-commissioning and optimizing controls will result in substantial energy savings. An example would be control loops that have been overridden due to immediate operational concerns (such as locking out condenser water presets due to chiller instability). RCx requires more emphasis on building operations and operating staff than commissioning.
Recalibrate All Control Sensors: Sensor drift can contribute to control problems and substantial overuse of energy if they are not regularly recalibrated.
Where Appropriate, Install Efficiency Monitoring Equipment: As a rule, a thorough retro-commissioning will locate a number of low-cost or no-cost areas where energy efficient measures can be implemented. However, without a simple means of continuous monitoring, the persistence of the savings is likely to be low. A number of simple metrics (cooling plant kW/ton, economizer hours of operation, humidification/dehumidification operation, etc.) should be identified and continuously monitored and displayed to allow facilities’ personnel to recognize when system efficiency has been compromised.

The culmination of our approach is a comprehensive program that addresses all aspects of data centers, including virtualization, HVAC, lighting, and emerging technologies to optimize energy efficiency potential. Our programs are a proven model that captures substantial energy savings, transforms the market to new technologies and methods of operation, and produces demand and energy savings over current practices.

Following are brief descriptions of key innovations EDI has incorporated into our data center methodologies:

Air Management

Use of best-practices air management, such as strict hot aisle/cold aisle configuration, can double the computer server cooling capacity of a data center. Combined with an airside economizer, air management can reduce data center cooling costs by over 60 percent. Removing hot air immediately as it exits the equipment is a key function as it allows for higher capacity and much higher efficiency than mixing the hot exhaust air with the cooling air being drawn into the equipment.
Poor airflow management will reduce both the efficiency and capacity of computer room cooling equipment. Examples of common problems that can decrease a Computer Room Air Conditioner (CRAC) unit’s usable capacity by 50 percent or more are: leaking floor tiles/cable openings, poorly placed overhead supplies, under-floor plenum obstructions, and inappropriately oriented rack exhausts.
Using flexible, clear plastic barriers, “supermarket refrigeration style covers,” or other physical barriers, to seal the space between the tops of the rack and the ceiling, or air return location, can greatly improve hot aisle/cold aisle isolation while allowing flexibility in accessing, operating, and maintaining the computer equipment below.
Use of ventilated racks, where the ideal air management systems duct cooling air directly to the intake side of the rack and draw hot air from the exhaust side, without diffusing it through the data center room space at all.

Air-Side Economizer

An economizer can cut data center cooling costs by over 60 percent using standard, commonly available, low-cost equipment. Depending on the climate, the steady, 24-hour cooling load of a data center is well suited to take advantage of seasonal/ nighttime temperature variations to cool the space.
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.
In small data centers located in mixed-use buildings, some energy savings may be realized by maximizing the use of a house, office, or support area system that is equipped with an economizer.

Central Air Handling

A central system allows redundancy to be implemented in a manner that provides maximum reliability (a spinning reserve) and increases normal operating system efficiency. System maintenance is also simplified through centralization. In most warm climates, air handlers can be located on the roof (ideally in a central location not directly over the data center space), allowing significant cost savings compared to Computer Room Air Conditioners (CRACs) by reducing the data center floor space required by the air conditioning. In addition:
Fans and motors tend to be more efficient in larger systems.
Large air handlers equipped with variable air volume fans tend to have better efficiency when under-loaded, as opposed to CRAC units where efficiency suffers at partial loads. Data center systems are typically operated at partial-load to ensure maximum temperature and humidity control stability, reliability, and margin for future increases in load.
While data center loads tend to be constant, 24-hours a day, the loading across the data center floor can vary significantly. A central system can reduce fan power use and save energy by taking advantage of this variance. A low-pressure drop design (“oversized” ductwork or a generous under-floor) is essential to optimizing energy efficiency and long-term build out flexibility.
Piping for condensate, humidification, chilled or condenser water, and/or refrigerant is reduced or eliminated within the data center envelope.
Implementation of an airside economizer system is simplified with a central air handler system.

Cooling Plan Optimization

Setting the cooling plant for medium temperature chilled water (55°F) helps eliminate uncontrolled dehumidification and reduces plant operating costs.
Use aggressive chilled and condenser water temperature presets to maximize plant efficiency. Specify cooling towers for a 5-7°F approach in order to economically improve chiller performance.
Design hydronic loops to operate chillers near design temperature differential (or dT), typically achieved by using a variable flow evaporator design and staging controls.
Primary-only variable flow pumping systems have fewer single points of failure, have a lower first cost (half as many pumps are required), are more efficient, and are more suitable for modern chillers than primary-secondary configurations.
Thermal storage can peak electrical demand savings and improve chilled water system reliability. Thermal storage can be an economical alternative to additional mechanical cooling capacity.
Use efficient water-cooled chillers in a central chilled water plant. A high-efficiency VFD-equipped chiller with an appropriate condenser water preset is typically the most efficient cooling option for large facilities.
For peak efficiency and to allow for preventive maintenance, monitor chiller efficiency.

Direct Liquid Cooling

Water flow is a very efficient method of transporting heat. On a volume basis, it carries approximately 3,500 times as much heat as air.
Cooling racks of IT equipment reliably and economically is the main purpose of the data center cooling system; conditioning the data center room without the rack load is a minor task in both difficulty and importance.
Capturing heat at a high temperature directly from the racks allows for much greater use of water-side economizer free cooling, which can reduce cooling plant energy use by 70 percent or more when operating.
Transferring heat from a small volume of hot air directly off the equipment to a chilled water loop is more efficient than mixing hot air with a large volume of ambient air and removing heat from the entire mixed volume. A water-cooled rack is equivalent to an almost perfect hot aisle/cold aisle configuration, where recirculation of waste heat is eliminated and the “hot aisle” heat exhaust can be run at very high temperatures with no impact on workers or equipment in the data center room.

Free Cooling via Water-Side Economizer

While free cooling is operating, chilled water plant energy consumption costs are cut by up to 70 percent.
Data centers require cooling 24-hours a day every day of the year – even when it is cold outside. This makes data centers very well suited to water-side economization.
Free cooling utilizing a water-side economizer can usually be economically retrofitted to existing chilled water-cooled facilities.
Isolation between the space air and outside air is not impacted by water-side free cooling, making it an alternative to airside economization when this is a concern.
A flat plate heat exchanger is used to isolate the chilled water loop from the open tower condenser water to prevent fouling of coils.
A low approach temperature cooling tower plant is critical for best results.
A traditional chiller is used to provide cooling during hot periods and as an always-available emergency backup. For a portion of the year, free cooling increases reliability by offering a non-compressor based backup to the traditional chiller, particularly at night when plant monitoring and staffing are liable to be lower.

Humidification Controls

Humidification is very energy intensive. Dehumidification incurs even higher energy costs since the air is usually cooled to below 45°F to condense out water and then is reheated by an electric heater to ensure the supply air is not too cold.
Modern servers do not require extremely tight humidity control, and typical data centers cannot actually provide tight humidity control due to sensor drift.
Centralized humidity control can keep all units serving the same space in the same humidification mode.
Utilize adiabatic humidifiers and evaporative cooling for humidification whenever possible. Waste heat in the return air stream can be used to drive adiabatic humidification “for free” when the outside air is too cold for adiabatic systems.
Computers do not emit humidity, nor do they require “fresh” outdoor ventilation air, so a well-controlled data center should have minimal humidity loads. Ensure outside air economizers, if present, are properly controlled to prevent unnecessary humidification loads. Optimize pressurization controls to minimize humid or dry outside air (OSA) infiltration.

Power Supplies

Specify and utilize high efficiency power supplies in Information Technology (IT) computing equipment. High efficiency supplies are readily available and pay for themselves in very short timeframes when the total cost of ownership is evaluated.
For a modern, heavily loaded installation with 100 racks, use of high efficiency power supplies alone could save $270,000 to $570,000 per year and decrease the square footage required for the IT equipment by allowing more servers to be packed into a single rack footprint before encountering heat dissipation limits.
Cooling load and redundant power requirements related to IT equipment can be reduced by over 10 to 20 percent, allowing more computing equipment density without additional support equipment (UPS systems, cooling, generators, etc.).
In new construction, downsizing of the mechanical cooling equipment and/or electrical supply can significantly reduce first cost and lower the mechanical and electrical footprint.
When ordering servers, use power supplies that meet at least the minimum efficiency recommendations by the Server System Infrastructure Initiative (SSI Initiative).
When appropriate, limit power supply over-sizing to ensure higher and more efficient load factors.

Self-Generation

Self-generation can improve efficiency by allowing the capture and use of waste heat.
Waste heat can be used to supply cooling required by the data center through the use of absorption or adsorption chillers, reducing chilled water plant energy costs by well over 50 percent.
High-reliability generation systems can be sized and designed to be the primary power source while utilizing the grid for backup, thereby eliminating the need for emergency generators and, in some cases, even uninterruptible power supply (UPS) systems.

Uninterruptible Power Supply (UPS) Systems

Select the most efficient UPS system that meets the data center’s needs.
For battery-based UPS systems, use a design approach that keeps the UPS load factor as high as possible.
Evaluate the need for power conditioning.

Savings

By targeting data centers as a whole, we are able to bring incentives to several disciplines (virtualization, cooling, IT equipment efficiencies, and lighting) under a single program umbrella. Virtualization is one of the key innovative technologies that can provide the “hook” to implement other innovative technologies within data centers. Virtualization allows servers and other critical IT hardware infrastructure to be consolidated, delivering significant opportunities to reduce energy savings, particularly in reducing the need for cooling. This is an innovative yet simple concept – reduction of servers can reduce power usage and cooling needs for the facility housing the servers.

Further, EDI’s approach ensures cost-effective delivery of kW and kWh savings by assisting clients in taking a holistic approach towards data centers. Some of these long-term strategies, which we coordinate with our clients include:

Establish Metrics for Overall Data Center Energy Intensity

IT and infrastructure
Energy cost ($), source energy (Btu), and carbon emissions
Specified best-in-class targets for various types of data centers

Create Tools & Guidelines to Drive Continuous Improvement

Tools will include checklists to manage energy efficiency in data centers
Benchmarking data to provide constant input on performance

Using the energy/demand and other holistic strategies outlined above, EDI’s Energy Transformation Programs help our clients realize targeted energy savings from this high growth, high energy use sector, as well as demand savings and significant, measurable GHG reductions.

For more information regarding Energy Efficiency contact EDI, Ltd. at info@ediltd.com or via telephone (888) 334-5831 and ask to speak with a member of the Data Center Services Team.

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