Heat flux dissipated by electronic equipment, such as microprocessors and power supplies, is again reaching levels that require cooling other than simple air cooling as a means of controlling component temperature. Liquid cooling (e.g., water cooling) is an attractive technology to manage these higher heat fluxes. The liquid absorbs the heat dissipated by the components/modules in an efficient manner, i.e., with minimal temperature rise from the liquid to the component being cooled. Typically, the heat is ultimately transferred from the liquid out into the outside environment. Otherwise, the liquid coolant would continuously rise in temperature.
From the 1970's through the early 1990's, International Business Machines Corporation accomplished this task by circulating cooling liquid via a coolant distribution unit 100 (FIG. 1). Coolant distribution unit 100 included a single, large computer room water conditioning unit (CRWCU) 110, which distributed conditioned chilled water to the various electronics racks 120 of a mainframe computer system to be cooled. Conventionally, the electronics racks of the mainframe computer included memory frames, processor frames, input/output frames, power frames, etc. Operationally, the CRWCU 110 received customer chilled water which was then used to supply conditioned cooled water to the individual electronics racks of the computer room.
As shown in FIG. 2, the CRWCU 110 included a primary cooling loop wherein building chilled water was supplied 210 and passed through a single control valve 220 driven by a motor 225. Valve 220 determined an amount of building chilled water to be passed through a heat exchanger 230, with a portion of the building chilled water possibly being returned directly to the return via a bypass orifice 235. The CRWCU further included a second cooling loop with a reservoir tank 240 from which water was pumped either by pump 1 or pump 2 into the heat exchanger 230 for conditioning and output therefrom as a conditioned water source to the electronics racks to be cooled within the computer room. The computer room water conditioning unit normally stood separate from the electronics frames, and again, would supply system water (typically maintained at about 22° C.) to all electronics frames of the computer room.
The coolant distribution unit, and more particularly, the computer room water conditioning unit (CRWCU) depicted in FIGS. 1 & 2, contains a single heat exchanger, a single reservoir, a single control valve, and redundant pumps. Thus, in the case of a failed pump, the CRWCU would automatically switch to the redundant pump, but any other malfunction in the coolant distribution unit would have brought down the whole mainframe system. For example, if the heat exchanger, or control valve, or building chilled water source failed, then the entire mainframe system in the computer room would also fail. Redundant mainframe computers would have been on the computer room floor to allow continuation of processing (in a degraded mode) until the downed mainframe could be repaired.
Today, a multi-frame mainframe system such as existed in the 1970's and 1980's has been replaced with a single frame or rack. Thus, multiple system frames, from high end, mid-range and low end could now be sourced from a single computer room water conditioning unit such as depicted in FIGS. 1 & 2. Therein lies a problem, however. A single facility coolant leak or loss of chilled water source could bring down the entire computer room floor.