Abstract:
A chiller for supplying chilled fluid for cooling a room includes two distinct power inputs. A critical power input is configured to supply power to a controller and to a pump in a chilled-fluid loop that circulates a cool working fluid through an air handler  34  to cool the air in the air handler. A non-critical power input is configured to supply power to a compressor and, possibly, other elements of a refrigeration loop that includes an evaporator, the compressor, and a condenser to provide refrigeration via an evaporation/condensation cycle. When power is lost to the non-critical power input, the critical power input can continue to independently power the circulation of the working fluid through the chilled-fluid loop to continue to provide a level of cooling in the air handler.

Description:
BACKGROUND 
   A chiller is a component of an air-conditioning system that can be used to cool the air in a room. One or more pumps, which may or may not be integral to the chiller, circulate a working fluid, such as water, in a chilled-fluid loop from an air handler to an evaporator. In the air handler, the working fluid can extract heat from air in the room to be cooled. In the evaporator, the heat that was picked up by the working fluid in the air handler is then transferred from the working fluid to the colder refrigerant fluid in the refrigeration loop. 
   In one variety of chillers, the refrigeration loop that cools the chilled-fluid loop is a compression direct-expansion refrigeration circuit. This refrigeration loop includes, in addition to the evaporator, a compressor, a condenser and an expansion mechanism. The refrigerant fluid absorbs heat from the working fluid in the evaporator, where the refrigerant fluid is vaporized, and then dumps that heat in the condenser as the vaporized refrigerant fluid is re-condensed. 
   The chiller typically includes four main types of power-consuming components, including compressors, chilled-water circulating pumps, a controller, and condenser fans. All of these components are typically fed from a common point of power application to the chiller. When power is lost to the chiller, the operation of each of these components thereby ceases, resulting in a prompt loss of heat-removal capacity from the building or equipment being cooled. 
   In one application, chillers are used to cool computer rooms, where computer components can generate substantial operational heat. By removing this heat, a desired room temperature can be maintained to thereby help ensure that the computer components therein do not overheat. Generators are sometimes employed to allow continued operation of the chiller during a power loss. 
   SUMMARY 
   Disclosed in greater detail, below, is a chiller that includes a chilled-fluid loop in which a working fluid is circulated and a refrigeration loop in which a refrigerant fluid is circulated, each loop powered by a distinct power input. While a non-critical power input is configured to supply power to a compressor in the refrigeration loop, a critical power input is configured to supply power to a controller and to a pump in the chilled-fluid loop. When power is lost to the non-critical power input, a critical power source, such as an uninterruptible power source can continue to power the circulation of the cool working fluid in the chilled-fluid loop, absent operation of the refrigeration loop. 
   These apparatus and methods can enable a chiller to maintain critical-component operation during a power loss by exploiting the low level of stored energy in the working fluid in the chilled-fluid loop to provide a period of continued heat removal from the air after a power loss. 
   In computer rooms, an uninterruptible power source possessing, e.g., chemically stored energy can be provided to continue to supply power to the computer components for a period of time following a power outage. Absent continued cooling, however, the investment of an uninterruptible power source may be rendered useless because excessive room temperature resulting from the interruption in power supply to the cooling system can occur in a period of time as short as 60 seconds or less. These high temperatures can result in the shut down or improper operation of critical computer equipment prior to the expiration of the power supply from the uninterruptible power source. By using the remaining heat-removal capacity in the working fluid in the chilled fluid loop [typically at a cool temperature of 42° F. to 50° F. (about 6° to 10° C.) upon exiting the evaporator] by operating a pump and controller absent operation of the compressor and other components in the refrigeration loop, sufficient cooling can nevertheless be provided to prolong the operation of the computer components without overheating in the event of a power loss. Further still, the run time of component operation via an uninterruptible power supply can be matched or nearly matched with the run time of the cooling provided by the uninterruptible cooling supply, described herein. 
   The apparatus and methods of this disclosure can be used as a substitute or in addition to the use of a generator to power chiller components in the event of a power loss. The generator requires a period of time to start, during which cooling is lost; and the generator can fail to start. The continued circulation of the working fluid in the chilled-fluid loop during power outage, however, can remedy both of these problems. Further, these methods and apparatus for continued cooling offer a period for safe and graceful shutdown of computer equipment from the moment of power loss. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, described below, like reference characters refer to the same or similar parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating particular principles of the methods and apparatus characterized in the Detailed Description. 
     The FIGURE is a schematic illustration of an embodiment of a chiller apparatus of this disclosure. 
   

   DETAILED DESCRIPTION 
   I. The Chiller Apparatus 
   As shown in the embodiment of the FIGURE, the chiller apparatus  10  includes a refrigeration loop  12  and a chilled-fluid loop  26 . 
   (A) The Refrigeration Loop: 
   Refrigerant fluid, typically R-22 (HCFC-22) is circulated through the refrigeration loop  12  via a conduit  14 . Alternatively, a variety of other refrigerant fluids, such as R-134A, R-407C, and R-410A, can be used. The conduit  14  passes through an evaporator  16 , wherein the refrigerant fluid is vaporized. The conduit  14  next passes through a compressor  18 , which compresses the vaporized fluid. The conduit  14  then passes through a condenser  20 , which can include one or more fans configured to pass fluid across the conduit  14  to extract the heat of vaporization and condense the refrigerant fluid therein. Next, an expansion mechanism  22  (e.g., a valve or a constricted orifice) is provided, across which a pressure differential in the conduit  14  is created. Finally, the conduit  14  returns to the evaporator  16 , where the refrigerant fluid can again be vaporized as it is heated. 
   A non-critical power input  24  in the form of a terminal input block is wired to the fan(s) of the condenser  20  and to the compressor  18  (i.e., to the components that consume the most power in the chiller). A non-critical power source  25  (most commonly from raw utility power and optionally backed up by an on-site generator but lacking an uninterruptible power source) is coupled with the input  24  for distributing power to the components wired thereto. For these components, the non-critical power source  25  can be the sole source of power. 
   (B) The Chilled-Fluid Loop: 
   A working fluid, such as water or a mixture of water and ethylene glycol (or other freeze- and/or corrosion-protection agents), is circulated through the chilled-fluid loop  26  via a return line  28  and a supply line  30  of a conduit  32 . The conduit  32  extends between the evaporator  16  and an air handler  34 . The air handler  34  is coupled with a hot-air input duct  42  and a cool-air output duct  44 , each duct  42 / 44  having an inlet/outlet in the room to be cooled. The air handler  34  also includes a fan for drawing air from the room through the air handler  34  to achieve continuous circulation of the air. Where it passes through the air handler  34 , the conduit  32  of the chilled-fluid loop  26  is exposed and can be in the form of a coil to increase the surface area for heat exchange from the air to the conduit  32  (and to the working fluid passing through the conduit  32 ). The conduit  32  can likewise be in the form of a coil in the evaporator  16  to increase the surface area for heat exchange between the chilled-fluid loop  26  and the refrigeration loop  12 . 
   A pump  36  is provided in the return line  28  of the conduit  32  for pumping the working fluid through the chilled-fluid loop  26 . A storage tank  38  for storing working fluid after it leaves the evaporator  16  is provided in the supply line  30  of the conduit  32 . Alternatively, the pump  36  can be placed in the supply line  30  and the storage tank  38  in the return line  28 , or both can be placed in the same line  28 / 30 . 
   A critical power input  40  in the form of a terminal input block is wired to a control computer  46  and to the pump  36 . A critical power source  41  is electrically coupled with the critical power input  40  to thereby enable the critical power source  41  to power the controller  46  and pump  36 . 
   The critical power source  41  can be, e.g., an uninterruptible power source, such as a “static” uninterruptible power source (e.g., from the Silicon Series or from the Symmetra Series, both from American Power Conversion Corp., W. Kingston, R.I., USA). Static uninterruptible power sources are characterized by the following: a rectifier that converts alternating-current power to direct-current power and that charges batteries, an inverter that converts the direct current back to alternating current for supply to the load, and a storage element, most commonly a lead-acid battery to supply the direct-current bus when the rectifier is unable to do so for lack of reliable input alternating-current power. 
   Alternatively, the critical power source  41  can be, e.g., an engine generator, a flywheel uninterruptible power source, a fuel cell/inverter combination, a solar/inverter combination, an independent utility, or an onsite turbine generation plant. 
   II. The Cooling Process 
   (A) Normal: 
   Absent any power disruptions, in the “normal” operation of the chiller  10 , the compressor  18  pumps the refrigerant fluid through the condenser  20  and thereby drives the refrigerant-fluid flow through the refrigeration loop  12 . As it pumps the refrigerant fluid, the compressor  18  also increases the pressure and temperature of the refrigerant fluid. 
   As the refrigerant fluid is pumped into the condenser  20  by the compressor  18 , heat from the refrigerant fluid is extracted (e.g., to the outdoor environment) by a cooling gas or liquid passed across the refrigeration conduit  14 , which can be in the form of a coil to increase its exposed surface area in the condenser  20 . As the temperature of the refrigerant fluid drops in the condenser  20 , its pressure remains relatively constant until the refrigerant fluid reaches a saturation (condensation) point. The heat released from the refrigerant fluid upon condensation can be approximately equal to the heat of vaporization picked up by the refrigerant fluid in the evaporator  16  (discussed, below). After condensing, the refrigerant fluid leaves the condenser  20  as a liquid. 
   The refrigerant fluid then flows through the expansion mechanism  22 , which serves to maintain the pressure differential between the evaporator  16  and the condenser  20  in the refrigeration loop  12 . As the refrigerant fluid passes through the expansion mechanism  22  and into the evaporator  16 , it undergoes a pressure drop and its temperature is lowered. The evaporator  16  serves as a heat exchanger, transferring heat from the comparatively warm working fluid (e.g., water or a mixture of water and ethylene glycol) in the chilled-fluid loop  26  to the refrigerant fluid in the refrigeration loop  12  as the refrigerant fluid is vaporized. 
   The pump  36  controls the rate of fluid flow through the chilled-fluid loop  26 . The pump  36 , in turn, is controlled by the controller  46 . The controller  46  can also be coupled with a temperature sensor in the computer room or in the conduit through which the hot air flows, and the rate of pumping can be increased or decreased (to respectively provide more or less cooling) as the temperature readings from the computer room respectively increase or decrease. The heat generated by computer components and dissipated to the air of the computer room rises and falls as the workload demand on the computer components in the computer room respectively rises and falls. The component-generated heat is extracted from the air of the computer room by the working fluid in the air handler  34 . 
   As the working fluid is pumped from the air handler  34  to the evaporator  16 , and as heat is transferred from the working fluid in the chilled-fluid loop  26  to the refrigerant fluid in the refrigeration loop  12 , the temperature of the working fluid in the chilled-fluid loop  26  drops to about 42° to about 50° F. (about 5° to about 10° C.) as it leaves the evaporator  16  under normal chiller  10  operation. 
   (B) With a Power Disruption: 
   In the event of a disruption in the power supply from the non-critical power source  25  (e.g., where a storm forces down a supplying power line), the compressor  18  stops pumping, and the refrigeration cycle shuts down. 
   Nevertheless, the critical power source  41  can continue to supply power to the controller  46  and pump  36  when the non-critical power source  25  fails. Consequently, the cool working fluid continues to circulate through the chilled-fluid loop  26 , notwithstanding the shutdown of the adjoining refrigeration loop  12 . The role of the refrigeration loop  12  as a heat sink for the chilled-fluid loop  26  will now be greatly reduced; and the temperature of the working fluid will gradually rise with each pass through the air handler  34 . Nevertheless, the working fluid will continue to extract heat from the air of the computer room as long as the temperature of the working fluid is below that of the air. 
   Eventually, the temperature of the working fluid may rise to that or nearly that of the air and may, consequently, no longer be able to effectively cool the computer room. Nevertheless, the period of time for which cooling is provided by the working fluid from the time of power failure enables the continued or prolonged safe operation of the computer components in the computer room and/or the safe and graceful shut down of the computer components. 
   The stored cooling capacity in the chilled-fluid loop  26  is increased by the inline storage tank  38 , which increases the volume of chilled working fluid in the loop  26 . The greater the volume of the storage tank  38 , the greater the potential stored cooling capacity of the working fluid in the chilled-fluid loop  26 . 
   The controller  46  can also be coupled with components in the refrigeration loop  12  or with the non-critical power input  24  and can therefore be made “aware” of a power outage at the non-critical power input  24 . The controller  46  can optionally adjust (e.g., accelerate) operation of other components, such as the pump  36 , in response thereto. However, responsive adjustments of this nature are unnecessary for basic operation of the chiller during a power outage to maintain the flow of fluid through the chilled-fluid loop  26 . 
   In describing embodiments of the invention, specific terminology is used for the sake of clarity. For purposes of description, each specific term is intended to at least include all technical and functional equivalents that operate in a similar manner to accomplish a similar purpose. Additionally, in some instances where a particular embodiment of the invention includes a plurality of system elements or method steps, those elements or steps may be replaced with a single element or step; likewise, a single element or step may be replaced with a plurality of elements or steps that serve the same purpose. Moreover, while this invention has been shown and described with references to particular embodiments thereof, those skilled in the art will understand that various other changes in form and details may be made therein without departing from the scope of the invention.