HK1095624B - Cooling system for high density heat load - Google Patents

Description

Cooling system for high density thermal loads

Technical Field

The present invention relates generally to cooling systems and, more particularly, to a cooling system for high density thermal loads.

Background

Electronic equipment in a critical location, such as a computer room or a communications room, requires accurate and reliable control of indoor temperature, humidity, and airflow. Overheating or overtemperature can damage or impair the operation of the computer system and other components. To this end, precision cooling systems are operated to cool at these locations. However, problems arise when such high density heat loads are cooled using a direct evaporative (DX) cooling system. Existing DX systems for high density loads monitor air temperature and other variables to control the cooling capacity of the system in response to load changes. Thus, existing DX systems require rather complex controls, temperature sensors, and other control elements. Therefore, there is a need for a cooling system that can be sensitive to thermal loads of varying densities and that requires less control valves and other system components. In addition, conventional computer room air conditioning systems require excessive floor area in order to manage high density thermal loads. The present disclosure is directed to overcoming, or at least reducing, the effects of, one or more of the problems set forth above.

Disclosure of Invention

A cooling system for transferring heat from a thermal load to the environment is disclosed. The cooling system has a working fluid, which in the exemplary embodiment is a volatile working fluid. The cooling system includes a first cooling cycle and a second cooling cycle thermally coupled to each other. The first cooling cycle includes a pump, a first heat exchanger, and a second heat exchanger.

The first heat exchanger is in fluid communication with the pump via a conduit and is in thermal communication with a thermal load, which may be a computer room, electronics enclosure, or other space. The first heat exchanger may be, for example, an air-to-fluid heat exchanger. In addition, a flow regulator may be disposed between the pump and the first heat exchanger.

The second heat exchanger includes a first fluid passage and a second fluid passage in thermal communication with each other. The second heat exchanger may be, for example, a fluid-to-fluid heat exchanger. A first fluid path for the working fluid of the cooling system connects the first heat exchanger with the pump. The second fluid passage forms a portion of a second cooling cycle.

In one embodiment of the disclosed cooling system, the second cooling cycle includes a chilled water system in thermal communication with the environment adapted to maintain the first cooling cycle above the dew point. In another embodiment of the disclosed cooling system, the second cooling cycle includes a refrigeration system in thermal communication with the environment. The refrigeration system may include a compressor, a condenser, and an expansion device. The compressor is in fluid communication with one end of the second fluid passage of the second heat exchanger. A condenser, which may be an air-to-fluid heat exchanger, is in fluid communication with the environment. The condenser has an inlet connected to the compressor and has an outlet connected to the other end of the second fluid path through the second heat exchanger. An expansion device is disposed between the outlet of the condenser and the other end of the second fluid path. Wherein the cooling system is controlled to prevent condensation.

The foregoing summary is not intended to summarize each potential embodiment or every aspect of the present disclosure.

Drawings

The foregoing summary, preferred embodiments, and other aspects of the subject matter of the present disclosure are best understood with reference to the following detailed description of specific embodiments when read in conjunction with the accompanying drawings, wherein:

FIG. 1 schematically illustrates one embodiment of a cooling system according to certain teachings of the present disclosure;

FIG. 2 schematically illustrates another embodiment of a cooling system according to certain teachings of the present disclosure;

FIG. 3 illustrates a cycle diagram of the disclosed cooling system;

fig. 4 shows a cycle diagram of a typical vapor compression refrigeration system.

While the disclosed cooling system is susceptible to many modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. The drawings and written description are not intended to limit the scope of the inventive concepts in any manner. Rather, the figures and written description will illustrate the inventive concept to those skilled in the art by referencing a specific embodiment.

Detailed Description

Referring to fig. 1 and 2, the disclosed cooling system 10 includes a first cooling cycle (i.e., a first cycle) 12 in thermal communication with a second cooling cycle (i.e., a second cycle) 14. The disclosed cooling system 10 also includes a control system 100. Both the first cycle 12 and the second cycle 14 contain independent working fluids. The working fluid in the first cycle is any volatile fluid suitable for use as a conventional refrigerant including, but not limited to, chlorofluorocarbons (CFCs), Hydrofluorocarbons (HFCs) or Hydrochlorofluorocarbons (HCFCs). The use of volatile fluids avoids the use of water above sensitive equipment that is sometimes used in conventional systems for cooling computer rooms. The first cycle 12 includes a pump 20, one or more first heat exchangers (evaporators) 30, a second heat exchanger 40, and piping interconnecting the various elements of the first cycle 12. The first cycle 12 is not a vapor compression refrigeration system. Instead, the first cycle 12 uses a pump 20 rather than a compressor to circulate the volatile working fluid to remove heat from the heat load. The pump 20 is preferably capable of pumping the volatile working fluid throughout the first cycle 12 and is preferably controlled by the control system 100.

The first heat exchanger 30 is an air-to-fluid heat exchanger that transfers heat from a thermal load (not shown) to the first working fluid as the first working fluid passes through a first fluid path within the first heat exchanger 30. For example, the first heat exchanger 30 may include a plurality of tubes for the working fluid disposed to allow hot air to pass therethrough. It should be understood that many air-to-fluid heat exchangers known in the art may be used with the disclosed cooling system 10. A flow regulator 32 may be connected between the conduit 22 and the inlet of the first heat exchanger 30 to regulate the flow of the working fluid into the first heat exchanger 30. The flow regulator 32 may be a solenoid valve or other type of device for regulating the flow within the cooling system 10. The flow regulator 32 preferably maintains a constant output flow rate independent of the inlet pressure over the operating pressure range of the system. In the embodiment of fig. 1 and 2, the first cycle 12 includes a plurality of first heat exchangers 30 and a flow regulator 32 connected to the conduit 22. However, the disclosed system may have one or more first heat exchangers 30 and flow regulators 32 connected to the conduit 22.

The second heat exchanger 40 is a fluid-to-fluid heat exchanger that transfers heat from the first working fluid to the second cycle 14. It should be understood that many fluid-to-fluid heat exchangers known in the art may be used with the disclosed cooling system 10. For example, the second heat exchanger 40 may include a plurality of tubes for one fluid disposed within a chamber or housing containing a second fluid. Coaxial ("tube-in-tube") exchangers are also suitable. In some embodiments, plate heat exchangers are preferably used. The first circuit 12 also comprises a receiver 50 connected to the outlet conduit 46 of the second heat exchanger 40 by a bypass line 52. The receiver 50 may store and accumulate the working fluid within the first cycle 12 to account for temperature and thermal load changes.

In one embodiment, the first heat exchanger 30 may be used to cool a room in which the computer equipment is stored. For example, the fan 34 may draw air from the room (heat load) through the first heat exchanger 30, where the first working fluid absorbs heat from the air. In another embodiment, by mounting the first heat exchanger 30 on or near a heat-generating electronic device (thermal load), the first heat exchanger 30 can be used to directly remove heat from the electronic device. For example, the electronic device is typically housed within an enclosure (not shown). The first heat exchanger 30 may be mounted on the enclosure and the fan 34 may draw air from the enclosure through the first heat exchanger 30. Alternatively, the first heat exchanger 30 may be in direct thermal contact with a heat source (e.g., a cold plate). Those skilled in the art will appreciate that the heat transfer rates, dimensions, and other design variables of the elements of the disclosed cooling system 10 depend on the size of the disclosed cooling system 10, the amount of thermal load to be managed, and other details of the specific implementation.

In the disclosed embodiment of the cooling system 10 shown in fig. 1, the second cycle 14 includes a cold water cycle 60 connected to the second heat exchanger 40 of the first cycle 12. Specifically, the second heat exchanger 40 has a first portion or fluid passage 42 and a second portion or fluid passage 44 in thermal communication with each other. A first fluid path 42 for the volatile working fluid is connected between the first heat exchanger 30 and the pump. The second fluid passage 44 is connected to a cold water circuit 60. The cold water cycle 60 may be similar to those known in the art. The cold water cycle 60 includes a second working fluid that absorbs heat from the first working fluid passing through the second heat exchanger 40. The second working fluid is cooled by techniques known in the art for conventional cold water circulation. Generally, the second working fluid may be volatile or non-volatile. For example, in the embodiment of fig. 1, the second working fluid may be water, ethylene glycol, or a mixture thereof. Thus, the embodiment of the first cycle 12 in fig. 1 may be configured as a stand-alone unit housing the pump 20, the first heat exchanger 30 and the second heat exchanger 40, and may be connected to an existing supply of cold water available, for example, in a building housing the equipment to be cooled.

In the embodiment of the disclosed cooling system 10 shown in FIG. 2, the first cycle 12 is substantially the same as described above. However, the second cycle 14 includes a vapor compression refrigeration system 70 connected to the second portion or fluid path 44 of the second heat exchanger 40 of the first cycle 12. Rather than using cold water to remove heat from the first cycle 12 as in the embodiment of fig. 1, the vapor compression refrigeration system 70 in fig. 2 is directly connected to the second heat exchanger 40 or the "other half" of the heat exchanger. The vapor compression refrigeration system 70 may be substantially the same as those known in the art. The exemplary vapor compression refrigeration system 70 includes a compressor 74, a condenser 76, and an expansion device 78. Tubing 72 interconnects these elements and connects to the second fluid passageway 44 of the second heat exchanger 40.

The vapor compression refrigeration system 70 removes heat from the first working fluid flowing through the second heat exchanger 40 by absorbing heat from the second heat exchanger 40 using the second working fluid and rejecting this heat to the environment (not shown). The second working fluid may be volatile or non-volatile. For example, in the embodiment of FIG. 2, the second working fluid may be any conventional chemical refrigerant, including but not limited to a chlorofluorocarbon (CFC), a Hydrofluorocarbon (HFC), or a Hydrochlorofluorocarbon (HCFC). The expansion device 78 may be a valve, orifice, or other device known to those skilled in the art that creates a pressure drop in the working fluid passing therethrough. The compressor 74 may be any type of compressor known in the art suitable for providing refrigeration services, such as a reciprocating compressor, a scroll compressor, or the like. In the embodiment shown in fig. 2, the cooling system 10 is self-contained. For example, the vapor compression refrigeration system 70 may be part of a single unit that also houses the pump 20 and the first heat exchanger 30.

During operation of the disclosed system, the pump 20 moves the working fluid into the first heat exchanger 30 via the conduit 22. Pumping increases the pressure of the working fluid while the enthalpy of the working fluid remains substantially unchanged. (see line segment 80 of the cycle chart in FIG. 3). The pumped working fluid then enters the first heat exchanger 30 of the first cycle 12. The fan 34 may draw air from the heat load through the first heat exchanger 30. When hot air from a heat load (not shown) enters the first heat exchanger 30, the volatile working fluid absorbs heat. As the fluid heats up through the heat exchanger, a portion of the volatile working fluid will evaporate. (see line segment 82 of the cycle chart in FIG. 3). In a fully loaded system 10, the fluid exiting the first heat exchanger 30 will be saturated vapor. Vapor flows from first heat exchanger 30 through conduit 36 to second heat exchanger 40. Within the conduit or return line 36, the working fluid is in a vapor state and the pressure of the fluid is reduced while the enthalpy remains substantially constant. (see line segment 84 of the cycle chart in FIG. 3). In the second heat exchanger 40, the vapor in the first fluid passage 42 condenses by transferring heat to the cooler second fluid of the second cycle 14 in the second fluid passage 44. (see line 86 of the loop diagram in FIG. 3). The condensed working fluid exits the second heat exchanger 40 via conduit 44 and enters the pump 20, whereby the first cycle 12 may be repeated.

The second cycle 14 operates in conjunction with the first cycle 12 to remove heat from the first cycle 12 by absorbing heat from the first working fluid into the second working fluid and rejecting heat into the environment (not shown). As noted above, the second cycle 14 may include a chilled water system 60, as shown in fig. 1, or a vapor compression refrigeration system 70, as shown in fig. 2. For example, during operation of the cold water system 60 in fig. 1, the second working fluid may flow through the second fluid passage 44 of the second heat exchanger 40 and may be cooled within a water tower (not shown). For example, during operation of the refrigeration system 70 in fig. 2, the second working fluid passes through the second portion of the second heat exchanger 40 and absorbs heat from the volatile fluid in the first cycle 12. The working fluid evaporates within the process. (see line segment 92 of a typical vapor compression refrigeration cycle in fig. 4). The vapor travels to a compressor 74 where the working fluid is compressed. (see line segment 90 of the refrigeration cycle in FIG. 4). The compressor 74 may be a reciprocating, screw, or other type of compressor known in the art. After compression, the working fluid travels through a discharge line to a condenser 76 where the heat of the working fluid is dissipated to an external radiator, such as an outdoor environment. (see line segment 96 of the refrigeration cycle in FIG. 4). Upon exiting the condenser 76, the refrigerant flows through a liquid line to an expansion device 75. The second working fluid creates a pressure drop as the refrigerant passes through the expansion device 75. (see line segment 94 of the refrigeration cycle in fig. 4). Upon exiting the expansion device 75, the working fluid flows through the second fluid path of the second heat exchanger 40, which functions as an evaporator of the vapor compression refrigeration system 70.

Conventional cooling systems for computer rooms and the like take up valuable floor space. However, the cooling system 10 of the present invention can cool high density heat loads without consuming valuable floor space. Furthermore, the cooling system 10 saves energy as less energy is required to pump volatile fluids than to pump non-volatile fluids such as water, as compared to conventional types of cooling schemes for high density loads such as computer rooms. In addition, pumping volatile fluids can reduce the size of the pumps required, as well as the overall size and cost of the piping that interconnects the system components.

The disclosed cooling system 10 advantageously uses the phase change of a volatile fluid to increase the cooling capacity per square foot of space or room. In addition, the disclosed cooling system 10 also eliminates the need for water within the cooling equipment mounted above the computing equipment, which would risk damaging the computing equipment in the event of a leak. Furthermore, since the system is designed to remove only sensible heat (sensible heat), there is no need to remove condensate. As is known in the art, cooling the air to a low temperature increases the relative humidity, which means that condensation may occur. For example, if the evaporator is mounted on an electronic device package, condensation may occur within the package, which may pose a significant risk to the electronic equipment. Within the present system, the temperature of the environment surrounding the equipment is maintained above the dew point to ensure that condensation does not occur. Since the disclosed cooling system does not perform latent cooling, the full cooling capacity of the system may be used to cool the computing device.

The disclosed cooling system 10 can handle varying thermal loads without the need for the complex controls required by conventional direct evaporation systems. The system is self-regulating in that the pump 20 provides a constant flow of volatile fluid to the system. The flow regulator 32 operates to limit the maximum flow to each of the first heat exchangers 30. This operation balances the flow to each of the first heat exchangers 30 so that each heat exchanger receives substantially the same fluid flow. If a heat exchanger is at a "high" load, the volatile fluid will flash off (flash off) at a higher rate than a heat exchanger at a lower load. Without the flow regulator 32, more fluid would flow to the heat exchanger since the "lower" duty heat exchanger is a cooler location and has a lower fluid pressure drop. This action will "starve" the heat exchanger at high load and the heat exchanger will not be able to cool the load properly.

A key system control parameter for maintaining all sensible cooling is the dew point within the space to be controlled. The disclosed cooling system 10 controls a cold water or vapor compression system so that the fluid flowing to the first heat exchanger 30 described above will always be above the dew point within the space to be controlled. Maintaining above the dew point ensures that no latent cooling occurs.

The foregoing description of preferred and other embodiments is not intended to limit or restrict the scope or applicability of the applicants' inventive concept. The applicants desire to replace the inventive concept contained in the disclosure with all patent rights afforded by the appended claims. It is therefore intended that the following appended claims cover all such modifications and changes as fall within the scope of the appended claims or their equivalents.

Claims (16)

1. A cooling system for transferring heat from a thermal load to a heat exchange system, the cooling system comprising:

a volatile working fluid;

a pump;

an air-to-fluid heat exchanger in fluid communication with the pump and in thermal communication with the thermal load;

a fluid-to-fluid heat exchanger having a first fluid passageway in fluid communication with the air-to-fluid heat exchanger and pump and a second fluid passageway connected to the heat exchange system, the first and second fluid passageways being in thermal communication with each other,

wherein the cooling system is controlled to prevent condensation.

2. The cooling system of claim 1, further comprising a flow regulator between the pump and the air-to-fluid heat exchanger.

3. A cooling system for transferring heat from a thermal load to an environment, the cooling system comprising a first cooling cycle comprising a volatile working fluid and a second cooling cycle thermally coupled to the first cooling cycle,

wherein the first cooling cycle includes a pump, a first heat exchanger in fluid communication with the pump and in thermal communication with the thermal load, and a second heat exchanger having a first fluid passage for the working fluid connecting the first heat exchanger to the pump and a second fluid passage connected to the second cooling cycle, the first and second fluid passages being in thermal communication with each other;

the second cooling cycle includes a refrigeration system in thermal communication with the environment,

the cooling system is controlled to prevent condensation.

4. The cooling system of claim 3, wherein the refrigeration system comprises:

a compressor connected to one end of the second fluid passage;

a condenser in thermal communication with the environment, the condenser having an inlet connected to the compressor and an outlet connected to the other end of the second fluid passageway; and

an expansion device disposed between an outlet of the condenser and the other end of the second fluid passageway.

5. A cooling system for transferring heat from a thermal load to an environment, the cooling system comprising:

a first cooling cycle comprising a volatile working fluid; and

a second cooling cycle thermally coupled to the first cooling cycle;

wherein the first cooling cycle comprises:

a pump;

an air-to-fluid heat exchanger in fluid communication with the pump and in thermal communication with the thermal load; and

a second heat exchanger having a first fluid passage for a working fluid in communication with the air-to-fluid heat exchanger and the pump, and a second fluid passage comprising a portion of the second cooling cycle, the first and second fluid passages being in thermal communication with each other,

the second cooling cycle includes a chilled water system in thermal communication with the environment and adapted to maintain the first cooling cycle above the dew point.

6. A cooling system for transferring heat from a thermal load to an environment, the cooling system comprising:

a pump for pumping the volatile working fluid through the system;

an air-to-fluid heat exchanger connected to the pump and having a fluid pathway in thermal communication with the thermal load; and

a second heat exchanger having a first fluid passage and a second fluid passage in thermal communication with each other, wherein the first fluid passage provides fluid communication from the air-to-fluid heat exchanger to the pump, the second fluid passage is adapted to connect the air-to-fluid heat exchanger to another cooling system in thermal communication with the environment,

wherein the further cooling system is controlled such that the first cooling system takes away only sensible heat from the load.

7. The system of claim 6, wherein the heat load is a room heat load.

8. The system of claim 6, wherein the thermal load is a thermal load of the electronics compartment.

9. The system of claim 6, wherein the volatile working fluid is selected from the group consisting of: chlorofluorocarbons, hydrofluorocarbons and hydrochlorofluorocarbons.

10. The system of claim 6, wherein the volatile working fluid is a non-aqueous based fluid.

11. The system of claim 6, further comprising a flow regulator coupled to the air-to-fluid heat exchanger and adapted to control an amount of working fluid flowing through the air-to-fluid heat exchanger.

12. The system of claim 11, wherein the flow regulator is adapted to control the amount of volatile working fluid flowing through the air-to-fluid heat exchanger independent of fluid pressure.

13. The system of claim 11, wherein the flow regulator is adapted to substantially constant fluid flow through the air-to-fluid heat exchanger.

14. The system of claim 11, further comprising a receiver in fluid communication with said air-to-fluid heat exchanger for accumulating a portion of said volatile working fluid.

15. The system of claim 14, wherein the receiver is adapted to accumulate a portion of the volatile working fluid as a function of temperature and/or heat load.

16. The system of claim 6, wherein the second heat exchanger is selected from the group consisting of: double-tube heat exchangers, shell-and-tube heat exchangers, and plate-and-frame heat exchangers.