David P. Graybill

Server liquid cooling with chiller-less data center design to enable significant energy savings

This paper summarizes the concept design and hardware build efforts as part of a US Department of Energy cost shared grant, two year project (2010-2012) that was undertaken to develop highly energy efficient, warm liquid cooled servers for use in chiller-less data centers. Significant savings are expected in data center energy, refrigerant and make up water use. The technologies being developed include liquid cooling hardware for high volume servers, advanced thermal interface materials, and dry air heat exchanger (chiller-less with all year “economizer”) based facility level cooling systems that reject the Information Technology (IT) equipment heat load directly to the outside ambient air. Substantial effort has also been devoted towards exploring the use of high volume manufacturable components and cost optimized cooling designs that address high volume market design points. Demonstration hardware for server liquid cooling and data center economizer based cooling has been built and is operational for a 15 kW rack fully populated with liquid cooled servers. This design allows the use of up to 45 °C liquid coolant to the rack. Data collection has commenced to document the system thermal performance and energy usage using sophisticated instrumentation and data collection software methodologies. The anticipated benefits of such energy-centric configurations are significant energy savings at the data center level of as much as 30% and energy-proportional cooling in real time based on IT load and ambient air temperatures. The objective of this project is to reduce the cooling energy to 5% or less of a comparable typical air cooled chiller based total data center energy. Additional energy savings can be realized by reducing the IT power itself through reduced server fan power and potentially less leakage power due to lower device temperatures on average for most locations. This paper focuses on the server liquid cooling, the rack enclosure with heat exchanger cooling and liquid distribution, and the data center level cooling infrastructure. A sample of recently collected energy-efficiency data is also presented to provide experimental validation of the concept demonstrating cooling energy use to be less than 3.5% of the IT power for a hot summer day in New York.

Open side car heat exchanger that removes entire server heat load without any added fan power

The heat dissipated by electronic equipment continues to increase at a alarming rate. This has occurred for products covering a wide range of applications. Manufacturers of this equipment require that the equipment be maintained within an environmental envelope in order to guarantee proper operation. Achievement of these environmental conditions are becoming increasingly difficult given the increases in rack heat loads and the desire for customers of such equipment to cluster racks in a small region for increased performance. And with the increased heat load of the racks and correspondingly increased air flowrate the chilled air flow supplied either through data center raised floor perforated tiles or diffusers for non raised floors is not sufficient to match the air flow required by the datacom racks. In this case some of the hot air exhausting the rear of a rack can return to the front of the rack and be ingested into the air intake thereby reducing the reliability of the electronic equipment. This paper describes a method to reduce the effect of the hot air recirculation with a water cooled heat exchanger attached to the side of a rack. This heat exchanger removes all of the heat load of a rack up to 35 kW(27° C ambient temperature and 15° C inlet water temperature) thereby having a netzero impact to the data center environmental. This paper describes the unique design of the open side car and presents the test results showing that it removes all the server heat load up to 35 kW and has minimal impact on the flow and resulting component temperatures within the server packages. This open side car design will show improvement in energy efficient heat load removal equipment compared to those currently being shipped in the marketplace.

Extreme energy efficiency using water cooled servers inside a chiller-less data center

The paper summarizes part of a project that was undertaken to develop highly energy efficient warm liquid cooled servers for use in chiller-less data centers that could save significant data center energy use and reduce data center refrigerant and make up water usage. One of the key concepts developed as part of this project is the Dual-Enclosure-Liquid-Cooling (DELC), which comprises of a 100% liquid cooled server cabinet and an outdoor dry cooler unit for heat rejection to the ambient and this configuration is used to reject the Information Technology (IT) equipment heat load directly to the outside ambient air without the use of a chiller. Demonstration hardware for server liquid cooling and a chiller-less data center was built and is operational for a 15 kW rack fully populated with liquid cooled servers which has been designed for use for up to 45°C liquid coolant to the rack. The anticipated benefits of such energy-centric configurations are significant energy savings of as much as 25% at the data center level. This paper builds on recent work that focused on the server liquid cooling, the rack enclosure with heat exchanger cooling and liquid distribution, and the data center level cooling infrastructure and which also presented sample data from experiments in support of the DELC concept. This paper presents experimental data related to the novel data center loop in a new manner, which is used to create a simplified thermodynamic model using curve-fit of surfaces of heat exchanger approach temperatures and power use of cooling devices. The model is validated using experimental data for a 22 hour test that was conducted in August of 2011. Subsequent to model validation, the simplified model is then used to make projections for DELC prototype performance (thermal and energy) under different conditions including different simple control schemes and weather conditions in the US. Weather data from nine different US cities is analyzed for a single day in August and realizable energy and energy cost savings over traditional chiller based data center cooling designs are presented. The results show that the new innovative data center cooling configuration presented could reduce cooling energy use to be less than 3.5% of the IT power for most US locations even in warm summer times of the year.