CROSS REFERENCE TO RELATED APPLICATIONS
This application is related to co-pending U.S. patent application Ser. No. 12/758,674 (attorney docket number 080077) filed by William H. Scofield and entitled “Electronic System Cooler”, commonly assigned with this application and incorporated herein by reference in its entirety.
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This application is directed, in general, to cooling of electronic systems.
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An electronic system dissipates heat that, unless removed, increases the temperature of components within the system. If allowed to rise too high, the temperature may reduce the operating life of some components, and in some cases may result in loss of a service provided by the electronic system. A cooling system may thus be used to reduce the temperature of the electronic system.
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One embodiment provides a cooling system. The cooling system includes an electronic enclosure and a liquid-cooled heat exchanger configured to receive heated air from within the enclosure. A geothermal loop is connected to the heat exchanger to form a closed-loop path. The closed-loop path is suitable for circulating a pressurized liquid refrigerant between the geothermal loop and the heat exchanger to transfer heat from the heated air to the geothermal loop without the liquid refrigerant undergoing a phase change.
Another embodiment provides a method. The method includes configuring a liquid-cooled heat exchanger to receive heated air from an electronic enclosure. The heat exchanger is connected to a geothermal loop to form a closed-loop path. The closed-loop path is suitable for circulating a pressurized liquid refrigerant between the geothermal loop and the heat exchanger to transfer heat from the heated air to the geothermal loop without the liquid refrigerant undergoing a phase change.
Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
FIG. 1 illustrates an embodiment of a system including an electronic enclosure and a cooling system having a closed-loop path;
FIG. 2 illustrates a vapor pressure curve representative of a refrigerant that may be used as a liquid refrigerant within the cooling system of FIG. 1; and
FIGS. 3A and 3B present a method that may be used to fabricate a cooling system, e.g., the cooling system of FIG. 1.
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Some electronic system installations are located at a site that is difficult to reach, is off the electric grid, or both. An example of such a system is a remote cellular tower transceiver system. In some conventional installations, the electronic system is cooled by a refrigeration system, including a compressor, evaporator and condenser, and a refrigerant that is compressed and expanded in a refrigeration cycle. The power required to operate such a conventional system may be substantial. For example, a refrigeration system that dissipates 10 kW may be needed to remove 9 KW of heat dissipated by the electronic system. Thus, the site may require electrical infrastructure sufficient to provide 19-20 kW to the combined electronic and refrigeration systems.
The electronic system may be situated in a relatively inaccessible location, so the cost of repairing the electronic system may be quite expensive, and the loss of service supported by the electronic system, such as a cell phone tower, may result in lost revenues and customer goodwill. Moreover, the conventional refrigeration system typically includes various components that must be serviced, and may fail unpredictably, adding potential sources of failure and expense. Repairing and maintaining the refrigeration system may involve expensive or difficult travel and access by a service provider.
In other conventional installations, a geothermal cooling system using water or a water/glycol solution has been used. However, in such systems the coolant poses a significant risk to electronics being cooled. If a leak develops near these components, aqueous coolant may spill onto electronic assemblies or power supplies. An aqueous coolant may have a low enough resistivity, e.g. from dissolved solids (salts), to conduct a significant current. The current may cause immediate failure of electronic components due to shorting or arcing. Even if no immediate failure results, ionic contaminants may react with various parts of the electronic, such as tin-based solder connections, causing corrosion that may eventually lead to failure.
The inventor has recognized that the deficiencies of conventional practice may be reduced or overcome by a cooling system based on geothermal cooling using a liquid refrigerant that is circulated substantially without a phase change. The liquid refrigerant is expected to substantially reduce or eliminate the aforementioned risks of shorting and corrosion. Moreover, the geothermal cooling system is expected to have an inherently greater reliability than a cooling system that relies on refrigeration, e.g. a compression-expansion cycle. Furthermore, the power required to operate the geothermal cooling system is expected to be significantly lower than that needed for a refrigeration system. Thus, expenses associated with the equipment site may be significantly reduced, and reliability of the electronic system increased.
Turning to FIG. 1, illustrated is an embodiment of a system 100. The system 100 includes an electronic system 105 and a cooling system 110 configured to circulate a liquid refrigerant as a coolant. Herein the terms “liquid refrigerant” and “coolant” may be used interchangeably. Aspects of the refrigerant are described further below. The electronic system 105 includes an enclosure 115 that includes electrical components 120 that dissipate heat when operating. A fan 123 may circulate air within the enclosure through a liquid-cooled heat exchanger 125 having an inlet 126 and an outlet 127. Herein, a “liquid-cooled heat exchanger” is a heat exchanger configured to transfer heat from a warmer source to a cooler liquid coolant. The heat exchanger 125 is configured to receive heated air circulating within the enclosure 115, and to transfer heat from the heated air to a liquid coolant flowing in a closed-loop path that includes the heat exchanger 125. In various embodiments the heat exchanger 125 is a micro-channel heat exchanger.
The cooling system 110 includes the heat exchanger 125 and various components configured to transport heat therefrom. A first coolant line 130 connects a pump 135 to the heat exchanger 125. The pump has an inlet 136 and an outlet 137. A second coolant line 140 connects the heat exchanger 125 to a geothermal loop 145 having an inlet 146 and an outlet 147. A third coolant line 150 connects the geothermal loop 145 to the pump 135. The heat exchanger 125, pump 135, geothermal loop 145, first line 130, second line 140, and third line 150 form a closed-loop path configured to circulate the liquid refrigerant.
Herein and in the claims, the term “closed-loop path” refers to an assembly of components configured to circulate a liquid refrigerant between the heat exchanger 125 and the geothermal loop 145 without a compression-expansion cycle and having no breaks in the path that would allow the liquid refrigerant to collect or escape under normal operating conditions. In various embodiments the refrigerant is under pressure to maintain a liquid phase.
The geothermal loop 145 is distinguished from a conventional geothermal loop configured for an aqueous coolant by being configured to maintain the pressure of the liquid refrigerant therein. Thus, the geothermal loop may include components sometimes used in refrigeration systems, including high-pressure tubing and fittings and/or pressure seals.
The geothermal loop 145 is illustrated as including a first vertical loop 145a and a second vertical loop 145b. The geothermal loop 145 is not limited to any particular number of loops, however. In other embodiments, the geothermal loop 145 may be configured to transfer heat to a body of water. In such cases, the geothermal loop 145 may be any other appropriate orientation with respect to the water surface, including about parallel thereto.
In various embodiments, the geothermal loop 145 is located below a surface 160 of the earth. “Below a surface of the earth” encompasses embodiments in which the geothermal loop 145 is embedded in soil, e.g., buried in a shaft, and embodiments in which the geothermal loop 145 is underwater, e.g., submerged in a body of water such as a river, lake or pond. For brevity of discussion, for embodiments in which the geothermal loop 145 is located below a surface of the earth, the geothermal loop 145 are referred to herein and in the claims as “buried.”
When the geothermal loop 145 is long enough, a portion of the geothermal loop 145 may be located in an isothermal region of the ground. Such a region may be characterized as having a temperature that is relatively insensitive to seasonal fluctuation. In some cases, it is believed that the isothermal region will have a relatively constant temperature of about 10-15° C. Thus the ground at a sufficient depth may provide an effective heat sink for the coolant.
The coolant circulates through the heat exchanger 125 where heat is transferred from warm air therein to the coolant, thereby cooling the air. The warmed coolant flows to the geothermal loop 145, in which the heat carried by the coolant is transferred to the relatively cool ground (or water). The coolant returns to the pump 135 via the inlet 136. The head pressure is sufficient to circulate the coolant. However, unlike a refrigeration compressor, the pump 135 is not configured to compress the refrigerant from the gas phase to the liquid phase.
The coolant flows to the geothermal loop 145 via the second line 140. While it is generally expected that the coolant will remain in the liquid phase within the second line 140, the presence of some vapor is within the scope of the disclosure. Such vapor, if present, is expected to be transient and occupy a negligible volume of the closed-loop path. Any such vapor is expected to condense before or within the geothermal loop 145.
The pressure differential between the outlet 137 and the inlet 136 of the pump 135 should be sufficient to overcome drag between the coolant and the various paths through which the coolant passes, and to lift the coolant through any vertical paths in the cooling system 110. For example, a height H between the bottom of the geothermal loop 145 and the inlet 136 may be 100 meters or greater.
An optional receiver 155 located inline between the geothermal loop 145 and the pump 135 may be used to trap any vapor mixed with the coolant to prevent loss of pumping action by the pump 135. In some embodiments a bubble detection system (not shown) may be used in lieu of or in addition to the receiver 155. Such a system may disable the pump 135 when bubbles are detected near the inlet 136 of the pump 135. The bubble detection system may then re-enable the pump 135 when the closed-loop path is determined to be free of bubbles.