PREVENTION OF REFRIGERANT SOLIDIFICATION
A refrigerant system may utilize CO2 as a refrigerant. Should the sensed operating conditions indicate that the refrigerant might be approaching a condition at which the refrigerant could solidify, corrective actions are taken to prevent refrigerant transformation to a solid thermodynamic state. In one embodiment, hot gas from a compressor discharge is bypassed to a location upstream of the evaporator. In another embodiment, the high-side pressure of a refrigerant system is adjusted. In yet another embodiment, an additional charge of refrigerant is delivered on demand into the refrigerant system. In still another embodiment, a defrost cycle is initiated on demand. These embodiments prevent the refrigerant from approaching the conditions at which it may solidify.
This application relates to refrigerant systems, which utilize CO2 as a refrigerant, and which take preventive steps to reduce the likelihood of the CO2 refrigerant transforming to a solid thermodynamic state.
Generally, refrigerant systems are utilized to circulate a refrigerant throughout a refrigerant circuit to condition a secondary fluid to be delivered to an indoor environment. As one example, air conditioning systems circulate a refrigerant to condition air being delivered into a climate-controlled space or zone.
Over recent years, a heightened concern about global warming, as well as, in some cases, ozone depletion, caused by some of the most commonly used refrigerants, such as R22, R123, R134a, R410A and R404A, forced HVAC&R industry to search for alternative fluids and refrigerant system solutions. Therefore, much attention has been drawn to so-called natural refrigerants, such as R744 (CO2), R718 (water) and R717 (ammonia). CO2 is one of these promising natural refrigerants that has zero ozone depletion potential and extremely low (one) global warming potential. Thus, CO2 is becoming more widely used as a replacement for the conventional HFC refrigerants. However, utilizing CO2 as a refrigerant does raise challenges for the refrigerant system designer. One challenge raised by CO2 is that it can transform to a solid thermodynamic state at pressures which can be experienced in typical refrigerant system applications. The CO2 refrigerant has a relatively high triple point. As an example, with a pressure of about 75.1 psia, which would correspond to a saturated temperature of −69.8 degrees Fahrenheit, the CO2 refrigerant can solidify.
If the CO2 refrigerant transforms to a solid thermodynamic state, the refrigerant system ceases to operate. The solid refrigerant could plug up the expansion device, the distributor and distributor tubes, the evaporator refrigerant heat exchange channels and associated refrigerant pipes. Among other undesired phenomena, it could also cause compressor damage. With the possibility that pressure in the refrigerant system could drop, on some occasions, below 75.1 psia, the potential for CO2 solidification raises challenges for the refrigerant system designer. Such situations can occur, for example, if the refrigerant system loses substantial amount of charge, the expansion device has malfunctioned, the evaporator fan has ceased to operate properly, the evaporator heat exchanger got plugged, a low pressure sensor has malfunctioned, a low pressure switch failed, etc. or a combination of thereof.
SUMMARY OF THE INVENTIONIn disclosed embodiments of this invention, various preventive steps are taken should the refrigerant system be approaching a situation wherein a CO2 refrigerant can transition to a solid thermodynamic state. In one embodiment, a bypass line selectively bypasses hot compressed refrigerant gas upstream of an evaporator. This design concept will increase pressure and temperature in the evaporator, preventing the CO2 refrigerant from transitioning to a solid thermodynamic state.
In another embodiment, in transcritical applications, the refrigerant system high-side pressure is reduced, should the conditions in the evaporator be approaching solidification conditions for the CO2. By reducing the pressure on the discharge (high-pressure) refrigerant side, the refrigerant distribution throughout the system is affected, causing the evaporator pressure to change, preventing the solidification of the CO2.
In another embodiment, a receiver may contain an additional CO2 refrigerant charge, which can be selectively delivered into the refrigerant system to increase the evaporator pressure, when the refrigerant system operation is approaching a situation where the CO2 refrigerant could solidify.
In yet another embodiment, should the conditions indicate that the refrigerant system is approaching a condition, which could cause solidification of the CO2 refrigerant, a defrost operation at the evaporator is initiated, preventing the transformation of the CO2 refrigerant to a solid thermodynamic state.
In using those techniques, the refrigerant system can still continue to operate without being shutdown, as would have been the case if the refrigerant system were stopped, for example, using a low-pressure switch, which would trip the refrigerant system if the suction pressure decreases below a certain specified pressure limit.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
In the present invention, should the control 32 sense that the refrigerant system could be approaching conditions at which the CO2 refrigerant could solidify, the hot gas bypass line 34 will deliver hot refrigerant gas from the compressor discharge to a location upstream of the evaporator 28, by opening a refrigerant flow control device such as a valve 36. Potential locations for solidification include the evaporator 28 and the vicinity of the exit from the refrigerant system expansion device 26. In this manner, the low pressure conditions within the evaporator 28 will be avoided, and the CO2 refrigerant will not solidify.
It should be pointed out that many different compressor types could be used in this invention. For example, scroll, screw, rotary, or reciprocating compressors can be employed.
The refrigerant systems that utilize this invention may have various options and enhancement features, such as, for instance, tandem components, economizer branches, reheat circuits, intercooler heat exchangers, etc., and can be used in many different applications, including, but not limited to, air conditioning systems, heat pump systems, marine container units, refrigeration truck-trailer units, and supermarket refrigeration systems.
While preferred embodiments of this invention have been disclosed, a worker of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. For that reason the following claims should be studied to determine the true scope and content of this invention.
Claims
1. A refrigerant system comprising:
- a compressor for compressing a refrigerant and delivering it downstream to a heat rejection heat exchanger, refrigerant from said heat rejection heat exchanger passing through an expansion device and then through an evaporator, refrigerant from the evaporator returning to said compressor; and
- a control for said system taking a corrective action, if said refrigerant system is approaching a condition at which said refrigerant may solidify.
2. The refrigerant system as set forth in claim 1, wherein said control takes the corrective action to prevent system shutdown.
3. The refrigerant system as set forth in claim 1, wherein said refrigerant system is charged with CO2 refrigerant.
4. The refrigerant system as set forth in claim 1, wherein said control takes the corrective action utilizing a sensor for sensing a condition at which said refrigerant could solidify.
5. The refrigerant system as set forth in claim 1, wherein said refrigerant can solidify in said evaporator.
6. The refrigerant system as set forth in claim 1, wherein said condition is a pressure of the refrigerant.
7. The refrigerant system as set forth in claim 6, wherein said pressure is taken at a location associated with said evaporator.
8. The refrigerant system as set forth in claim 1, wherein said condition is a temperature of the refrigerant.
9. The refrigerant system as set forth in claim 8, wherein said temperature is taken at a location associated with said evaporator.
10. The refrigerant system as set forth in claim 1, wherein a hot gas bypass line is positioned to take at least a portion of refrigerant compressed by said compressor and deliver this portion of refrigerant directly to said evaporator, and said control operating a valve on said hot gas bypass line to expand this portion of refrigerant to a lower pressure, if said refrigerant system is approaching a condition at which said refrigerant may solidify.
11. The refrigerant system as set forth in claim 10, wherein said portion of refrigerant is delivered to a location upstream of the evaporator.
12. The refrigerant system as set forth in claim 1, wherein said control changes a high-side pressure of the refrigerant system, if said refrigerant system is approaching a condition at which said refrigerant may solidify.
13. The refrigerant system as set forth in claim 12, wherein said high-side pressure is changed by controlling a valve opening.
14. The refrigerant system as set forth in claim 1, wherein said refrigerant system further includes a receiver for storing an additional charge of refrigerant, and a valve on a line communicating said receiver into the refrigerant system, said control opening said valve to deliver additional refrigerant into the refrigerant system, if said refrigerant system is approaching a condition at which said refrigerant may solidify.
15. The refrigerant system as set forth in claim 1, wherein a defrost cycle is associated with said evaporator, and said control actuating said defrost cycle, if said refrigerant system is approaching a condition at which said refrigerant may solidify.
16. The refrigerant system as set forth in claim 15, wherein a defrost coil is associated with said evaporator to provide said defrost cycle, and wherein said defrost coil being actuated by the control.
17. A method of operating a refrigerant system comprising the steps of:
- providing a compressor for compressing a refrigerant and delivering it downstream to a heat rejection heat exchanger, refrigerant from said heat rejection heat exchanger passing through an expansion device and then through an evaporator, refrigerant from the evaporator returning to said compressor; and
- a control for said system taking a corrective action, if said refrigerant system is approaching a condition at which said refrigerant may solidify.
18. The method as set forth in claim 17, wherein said control takes the corrective action to prevent system shutdown.
19. The method as set forth in claim 17, wherein said refrigerant system is charged with CO2 refrigerant.
20. The method as set forth in claim 17, wherein said control takes the corrective action utilizing a sensor for sensing a condition at which said refrigerant could solidify.
21.-32. (canceled)
Type: Application
Filed: Mar 9, 2007
Publication Date: Jan 21, 2010
Inventors: Alexander Lifson (Manlius, NY), Michael F. Taras (Fayetteville, NY)
Application Number: 12/527,719
International Classification: F25B 45/00 (20060101); F25B 1/00 (20060101); F25B 43/00 (20060101); F25B 41/04 (20060101); F25D 21/06 (20060101);