Patent Application
20090158762
The subject invention generally pertains to refrigerant chillers and more specifically to a chiller that includes a main condenser and a heat-recovery condenser.
With conventional refrigerant systems, known as chillers, an evaporator provides a cooling effect that can be used wherever needed, and a main condenser releases waste heat to atmosphere. In cases where there is a use for the waste heat, such as, for example, to heat domestic water or to heat some other external process, a chiller may be provided with a second condenser or heat-recovery condenser. Instead of the main condenser releasing heat to the atmosphere, heat from the heat-recovery condenser can be used for driving the external process. Depending on the need for heat, the chiller might switch between which of its two condensers it activates, or perhaps the two condensers might operate simultaneously to share the condensing function.
When activating a heat-recovery condenser while deactivating the main one, it can be difficult avoiding adverse refrigerant flow between the two. Some gaseous refrigerant from an inactive main condenser, for instance, might flow counter to that of liquid refrigerant leaving the heat-recovery condenser. Such counter flow of fluids can reduce the system's overall effectiveness.
In some cases, the flow pattern of gaseous refrigerant flowing from an inactive main condenser to an active heat-recovery condenser can produce a pressure drop sufficient to create an excessively high pressure differential between the two condensers. An excessive pressure differential can force liquid refrigerant to back up into the shell of the heat-recovery condenser, which reduces the chiller's performance in the a heat-recovery mode.
Due to the drawbacks of current heat-recovery chiller systems, there is a need for a refrigerant system that can recover waste heat more effectively without adverse system effects.
It is an object of the present invention to provide a heat-recovery chiller system that includes a liquid seal or gas trap between the outlets of two condensers, wherein the gas trap has a liquid head that is kept above a minimum level yet is below the bottom of the heat-recovery condenser.
Another object of some embodiments is to provide a heat-recovery chiller with a condensate sump that includes an internal weir to create a reliable source of liquid refrigerant to cool the chiller's compressor motor.
Another object of some embodiments is to provide a chiller with a refrigerant flow path to and through the heat-recovery condenser in such a way as to minimize the pressure differential between the chiller's two condensers.
Another object of some embodiments is to bias the position of a heat exchanger tube bundle toward the bottom of a heat-recovery condenser so as to create above the tubes an open passageway for gaseous refrigerant to flow. This creates within the condenser generally unidirectional flow from above the tube bundle to a drain tube that is below the tubes.
Another object of some embodiments is avoid creating a counter flow pattern of liquid and gaseous refrigerant leaving and entering a heat-recovery condenser.
Another object of some embodiments is to provide a heat-recovery chiller with a condensate sump that includes an internal weir that produces a trap for collecting relatively heavy debris that might exit either of the chiller's two condensers.
One or more of these and/or other objects of the invention are provided by a chiller with a heat-recovery condenser, wherein the chiller includes a condensate sump with an internal weir.
In some cases, system 10 comprises a single or multistage refrigerant compressor 16 (e.g., centrifugal, screw, scroll, reciprocating, etc.) driven by a motor 18, a main condenser 20 (e.g., shell-and-tube heat exchanger) for condensing the refrigerant discharged from compressor 16, the alternate second condenser 12, a gas trap 22 between the outlets of condensers 12 and 20, a main expansion device 24 (e.g., orifice plate, capillary tube, flow-throttling valve, or some other type of flow restriction) for cooling the refrigerant by expansion, and an evaporator 26 for transferring the cooling effect to a building or some other application. Gas trap 22 is created by the combination of a condensate sump 28 at the bottom of main condenser 20, a weir 30 inside sump 28, and a drain tube 32 that runs from the bottom of second condenser 12 to condensate sump 28.
For the illustrated embodiment, system 10 also includes an intermediate expansion device 34 and an economizer 36 that through a line 40 provides flashed refrigerant gas at intermediate pressure to an intermediate stage 38 of compressor 16. Economizer 36 is schematically illustrated to represent any system for feeding a multistage compressor with refrigerant at intermediate pressure.
Condensers 12 and 20 can be separately operated in active or inactive modes. When external process 14 demands heat, second condenser 12 can be active while main condenser 20 is inactive, as shown in
Selectively activating and deactivating second condenser 12 can be accomplished by controlling the volume of cooling fluid (e.g., water) pumped between process 14 and a bundle of heat exchanger tubes 42 inside the shell of condenser 12. Lines 44 schematically represent pipes that convey cooling fluid between process 14 and tubes 42. Likewise, controlling the volume of cooling fluid through lines 46 is one way of activating and deactivating main condenser 20, wherein lines 46 convey fluid between heat exchanger tubes 48 of condenser 20 and a heat-releasing system 50 (e.g., a cooling tower or air-cooled heat exchanger). Lines 44 and 46 can be and preferably are two separate circuits.
In operation, compressor 16 discharges generally hot pressurized refrigerant gas through an outlet 52 of compressor 16 and into main condenser 20. During a heat-recovery mode, as shown in
As the refrigerant condenses, drain tube 32 drains the refrigerant condensate from the bottom of second condenser 12 to sump 28. The liquid refrigerant in drain tube 32 and sump 28 provides a liquid seal of variable liquid head 56 between the outlets of condensers 12 and 20. This liquid seal (gas trap 22) promotes unidirectional flow through feed pipes 54 and drain tube 32. The unidirectional flow means that gaseous refrigerant does not backflow up through drain tube 32, wherein such backflow of gas could obstruct the flow of condensate attempting to drain down through the same line.
The variable liquid head 56 of gas trap 22 is due to the pressure differential between condensers 12 and 20. Liquid head 56 is generally greatest when second condenser 12 is active during the heat-recovery mode, as shown in
In a currently preferred embodiment, minimal flow restriction is achieved in several ways. One, feed pipe 54 is relatively large (i.e., pipe 54 has an inner diameter that is larger than that of drain tube 32). Two, the bundle of heat exchanger tubes 42 is biased toward the bottom of second condenser 12 to create a more wide open flow path above tubes 42 for gaseous refrigerant to enter and flow through the shell of condenser 12. And three, instead of a single feed pipe 54, refrigerant from main condenser 20 can flow through two or more feed pipes connected in parallel flow relationship with each other, as shown in
Head 56 is appreciably less or even zero when second condenser 12 is inactive, as shown in
In addition to providing system 10 with gas trap 22, sump 28 and weir 30 also provide a reliable source of liquid refrigerant for a motor cooling line 62. Line 62 conveys liquid refrigerant from sump 28 into the housing of motor 18, thus cooling motor 18. After cooling motor 18, the refrigerant can be returned to the rest of the refrigerant circuit by any suitable means such as, for example, by flowing through a line or passageway leading to a compressor inlet 66 or some other low-pressure side of system 10. Sump 28 and weir 30 also provide a trap for collecting debris and foreign particles 68 that may have circulated through refrigerant system 10.
Although the invention is described with respect to a preferred embodiment, modifications thereto will be apparent to those of ordinary skill in the art. The scope of the invention, therefore, is to be determined by reference to the following claims:
