Innovative server rack design with bottom located cooling unit

Abstract

One important motivation of data center mechanical system R&D is to improve the energy efficiency and reliability. Many new cooling solutions have been successfully used in production data centers, such as hybrid/liquid cooling systems and free cooling systems, and a better Power Usage Effectiveness (PUE) has been achieved when compared with traditional air cooling data centers. Liquid cooling can be assorted in different categories such as server liquid cooling, rack liquid cooling and pod liquid cooling. In terms of rack liquid cooling, there are several mature technologies such as a rear door heat exchanger, an in row cooler, an overhead heat exchanger, a water cooled cabinet and so on. The hybrid cooling solution can be understood as a rack liquid cooling solution operated in a hybrid environment with CRAH/CRAC units in either a raised or a non-raised floor data center. This paper proposes and investigates a new rack liquid cooling design which the cooling unit is located at the bottom of a customized server rack. The bottom cooling unit consists of an air duct and a heat exchanger. The rack is front door and back door contained, and air is moved by a fan wall installed on the back of the rack recirculating within the cabinet, passing through the cooling unit and cooling the IT. First of all, a description of the customized rack and the concept of the novel rack cooling solution is provided. Then, a thermal feasibility analysis of this proposed rack cooling solution is conducted using a combination of analytical and computational modeling. Several modeling cases are designed to characterize the sensitivities of some major design and operating parameters. The results and corresponding analyses will be used to guide the prototype development. The height of the rack cooling unit is one of the key design parameters: with a minimal height required by the cooling coil, the loss of node space on the rack can be reduced. Therefore the design and selection of the heat exchanger is of paramount importance. On one hand, the design should provide adequate cooling capacity and sufficient heat transfer area; on the other hand, the height should be minimized. The effects of the heat exchanger design on the cooling performance and air side pressure drop are modeled and analyzed quantitatively in this work. In addition, another two important design parameters namely the front door and back door containment sizes are parametrically modeled. Furthermore, the operating conditions including the chilled water supply temperature, water flow rate, fan operating duty circle are investigated and results are reported. An expected mechanical PUE of this novel rack design is proposed.