A prototype computer equipment rack-level cooling device with two heat exchangers was demonstrated to illustrate an energy efficient cooling capability. This unique device was designed and constructed by APC by Schneider Electric to operate with higher-temperature cooling water, so that it can support many more hours of free cooling compared to traditional systems that utilize chilled water. The cooling system contained two separate air-to-water heat exchangers, rather than one usually found in similar devices that operate using chilled water. In this design, one heat exchanger was configured to use higher temperature water produced by a cooling tower alone. The other coil was configured and controlled to allow chilled water flow, should supplemental cooling be required. The device also contained three fans, which were used to pull warm air from the computer equipment exhaust area through the two heat exchangers and return the cooled air to the air intake area of the computer equipment. A model of the heat exchangers performance was developed and used with an industry standard energy-efficiency metric to explore the device's capabilities and efficiency The device effectively cooled the warm air from the exhaust of the computer equipment and had favorable energy use efficiency and capability when compared to other similar equipment. In this analysis, the concept of using two heat exchangers in the intended configuration is more energy efficient, compared to typical designs using a single heat exchanger. The high cooling performance of this device is able to meet cooling requirements while using higher-temperature water, thereby reducing energy needed for compressor-based cooling. Results suggest that the development of a production version be continued using the design concepts of this prototype.

A large cluster of High-Performance Computing (HPC) equipment at the Lawrence Livermore National Laboratory in California was retrofitted with an Asetek cooling system. The Asetek system is a hybrid scheme with water-cooled cold plates on high-heat-producing components in the information technology (IT) equipment, and with the remainder of the heat being removed by conventional air-cooling systems. In order to determine energy savings of the Asetek system, data were gathered and analyzed two ways: using top-down statistical models, and bottom-up engineering models. The cluster, “Cabernet”, rejected its heat into a facilities cooling water loop which in turn rejected the heat into the same chilled water system serving the computer-room air handlers (CRAHs) that provided the air-based cooling for the room. Because the “before” and “after” cases both reject their heat into the chilled water system, the only savings is due to reduction in CRAH fan power. The top-down analysis showed a 4% overall energy savings for the data center (power usage effectiveness (PUE) —the ratio of total data center energy to IT energy— dropped from 1.60 to 1.53, lower is better); the bottom-up analysis showed a 3% overall energy savings (PUE from 1.70 to 1.66) and an 11% savings for the Cabernet system by itself (partial PUE of 1.51). Greater savings, on the order of 15-20%, would be possible if the chilled water system was not used for rejecting the heat from the Asetek system. About 37% of the heat from the Cab system was rejected to the cooling water, lower than at other installations.