Good things come in small packages. And for colocation data center operators looking to reduce costs, energy savings of up to 30% can be delivered via a new generation of shoebox-sized variable speed drives (VSD). These devices save energy compared to traditional fixed speed models. When a fan is controlled directly by a fixed speed motor the airflow is higher than it really needs to be; a fan connected to a VSD however is programmed to respond to a set of pre-defined conditions. Therefore, the fan speed adjusts to the environmental need, slowing down or speeding up only when required. This reduces the energy consumption and drives up efficiency. The same concept can be extended to compressors, which adapt the cooling capacity to the actual thermal demand; or to water pumps, which allow continuous adaptation to pressure changes and enable constant tuning of the entire water circuit.
In recent years, it has become generally accepted that data centers can be run at higher temperatures without risking increased incidences of downtime; however, maintaining higher operating temperatures requires technological changes if efficiencies are to remain high. The ASHRAE TC 9.9, “Thermal Guidelines for Data Processing Environments” discusses recommended and allowable temperature ranges for IT equipment. Precision air conditioning units with imbedded variable capacity compressor solutions are well suited to accommodate these new standards and to exploit the associated energy efficiency gains.
The variable speed compressors within the precision cooling units are linked to brushless motors and specially designed high efficiency composite fans. For colos, the high efficiency means lower energy bills. These systems are particularly efficient when the load over time is not constant and always changing (which is characteristic of colo data centers today).
Potential worldwide energy savings from using CRACs with variable speed drives versus fixed speed drives.
Benefits of VSD compressors
Schneider Electric has developed a complete portfolio of cooling units based on this VSD compressor technology.
Below are some of the benefit highlights:
- Energy efficiency – VSD compressors allow extremely low power consumption levels by leveraging the motor technology and the partial load efficiency. The diagram below illustrates a comparison between VSD and non-VSD compressors. While the efficiency (EER) at 100% capacity is pretty similar, when the required thermal load is between 50 to 70%, the difference is significant. Since part-load conditions occur frequently, the efficiency improvements help to greatly reduce total power consumption during the year.
- Cooling infrastructure cost savings – More efficient compressors, with optimized amperage and the ability to “trim” the cooling also reduces capital expense (CAPEX). The new design provides additional cooling capacity in the same footprint, meaning that the new units provide more cooling capacity per square foot of floor space.
- Trim cooling – Higher chilled water temperatures, adiabatic cooling and air economizers reduce dependency on mechanical cooling, moving to a “trim” cooling concept. In “trim” cooling, compressors are used to cover the capacity not dissipated by the economization system. VSD compressors, in particular, are well suited to fulfill this need for matching the exact required supplemental capacity.
Variable speed on hydraulic systems
VSD pumps are available as onboard primary circulation pumps on chillers. This solution allows for more efficient management when water pressure and water flow requirements fluctuate. During chiller operation, VSD pumps allow the water flow rate to be modified by varying the pump rotation speed.
This could be a good solution when the pressure drop value of the system is not completely known or an expansion is planned. Once the chiller is installed, the pressure drop and the water flow is set on the control board according to the local environmental conditions and the required deltaT of the inlet/water temperatures. In the event of any new modifications to the site, the operating parameters can be changed in order to adjust the correct operation of the unit.
Inverter-driven pumps can be useful when the pressure drop of the system varies during chiller operation (e.g., installations where the cooling units are equipped with 2-way valves or when there are separate water circuits). The required available head pressure settings can be input directly on the local display interface. Then the unit can operate with a variable water flow and constant available head pressure in all different pressure drop conditions, improving efficiency and circuit optimization.
Be ready for the next evolution
Schneider Electric representatives and partners play an important role in helping colo data center stakeholders understand the nuances of data center cooling and energy efficiency best practices. Visit http://www.schneider-electric.com/en/product-range/62220-uniflair-le/ to learn more about how the latest generation of Schneider Electric cooling products can help reduce energy consumption by 20-30%
Contributor: Maurizio Frizziero
Maurizio Frizziero has been working in the cooling business for more than 10 years, specializing in mission critical applications and IT data center solutions, moving in 2003 from nuclear fusion applications and controls. He has experience in R&D and product management, thermodynamic solutions for continuous cooling, high temperature operations and noise impacts.
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