U.S. patent application number 12/527719 was filed with the patent office on 2010-01-21 for prevention of refrigerant solidification.
Invention is credited to Alexander Lifson, Michael F. Taras.
Application Number | 20100011787 12/527719 |
Document ID | / |
Family ID | 39759780 |
Filed Date | 2010-01-21 |
United States Patent
Application |
20100011787 |
Kind Code |
A1 |
Lifson; Alexander ; et
al. |
January 21, 2010 |
PREVENTION OF REFRIGERANT SOLIDIFICATION
Abstract
A refrigerant system may utilize CO.sub.2 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.
Inventors: |
Lifson; Alexander; (Manlius,
NY) ; Taras; Michael F.; (Fayetteville, NY) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD, SUITE 350
BIRMINGHAM
MI
48009
US
|
Family ID: |
39759780 |
Appl. No.: |
12/527719 |
Filed: |
March 9, 2007 |
PCT Filed: |
March 9, 2007 |
PCT NO: |
PCT/US07/63662 |
371 Date: |
August 19, 2009 |
Current U.S.
Class: |
62/77 ; 62/222;
62/234; 62/474; 62/498 |
Current CPC
Class: |
F25B 2309/06 20130101;
F25B 9/008 20130101; F25B 2700/2117 20130101; F25B 2700/197
20130101; F25B 2600/2501 20130101; F25B 49/005 20130101; F25D 21/06
20130101 |
Class at
Publication: |
62/77 ; 62/498;
62/474; 62/222; 62/234 |
International
Class: |
F25B 45/00 20060101
F25B045/00; F25B 1/00 20060101 F25B001/00; F25B 43/00 20060101
F25B043/00; F25B 41/04 20060101 F25B041/04; F25D 21/06 20060101
F25D021/06 |
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)
Description
BACKGROUND OF THE INVENTION
[0001] This application relates to refrigerant systems, which
utilize CO.sub.2 as a refrigerant, and which take preventive steps
to reduce the likelihood of the CO.sub.2 refrigerant transforming
to a solid thermodynamic state.
[0002] 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.
[0003] 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 (CO.sub.2), R718 (water) and R717 (ammonia). CO.sub.2
is one of these promising natural refrigerants that has zero ozone
depletion potential and extremely low (one) global warming
potential. Thus, CO.sub.2 is becoming more widely used as a
replacement for the conventional HFC refrigerants. However,
utilizing CO.sub.2 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
CO.sub.2 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
CO.sub.2 refrigerant can solidify.
[0004] If the CO.sub.2 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 CO.sub.2
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 INVENTION
[0005] In disclosed embodiments of this invention, various
preventive steps are taken should the refrigerant system be
approaching a situation wherein a CO.sub.2 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 CO.sub.2
refrigerant from transitioning to a solid thermodynamic state.
[0006] 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 CO.sub.2. 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
CO.sub.2.
[0007] In another embodiment, a receiver may contain an additional
CO.sub.2 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 CO.sub.2 refrigerant could solidify.
[0008] In yet another embodiment, should the conditions indicate
that the refrigerant system is approaching a condition, which could
cause solidification of the CO.sub.2 refrigerant, a defrost
operation at the evaporator is initiated, preventing the
transformation of the CO.sub.2 refrigerant to a solid thermodynamic
state.
[0009] 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.
[0010] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 shows a first schematic of the present invention.
[0012] FIG. 2 shows a second schematic of the present
invention.
[0013] FIG. 3 shows a third schematic of the present invention.
[0014] FIG. 4 shows a fourth schematic of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] FIG. 1 shows a refrigerant system 20 having a compressor 22
delivering a compressed refrigerant through a heat exchanger 24.
For operation above the critical point (supercritical operation),
the heat exchanger 24 is normally called a gas cooler and, for
operation below the critical point (subcritical operation), the
heat exchanger 24 is normally called a condenser. From the heat
exchanger 24, the refrigerant is delivered to an expansion device
26, and then to an evaporator 28. As shown, a pressure sensor 30
senses the evaporator pressure and transmits the sensed reading to
a control 32. While the pressure sensor is shown at the evaporator,
other appropriate locations, such as a suction line or a suction
port of the compressor 22, can be utilized, and parameters other
than pressure, such as refrigerant saturation suction temperature,
may be sensed and deduced to the low-side refrigerant pressure.
[0016] In the present invention, should the control 32 sense that
the refrigerant system could be approaching conditions at which the
CO.sub.2 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 CO.sub.2 refrigerant will not solidify.
[0017] FIG. 2 shows another embodiment 40, wherein when operating
conditions approaching the transformation conditions of the
CO.sub.2 refrigerant into a solid thermodynamic sate are sensed by
the sensor 30, the control 32 reduces the high-side pressure for
the refrigerant system 40, by controlling the opening of a variable
(adjustable) orifice valve 232. When the opening of the valve 232
is strategically changed, the refrigerant is re-distributed
throughout the refrigerant system such that the evaporator pressure
is changed accordingly. Thus, the likelihood of the CO.sub.2
refrigerant solidification is reduced.
[0018] FIG. 3 shows another embodiment 50, wherein a receiver 52
contains additional refrigerant charge to be selectively delivered
into the refrigerant system 50. Should the conditions sensed by the
sensor 30 indicate that the refrigerant system is approaching a
potentially problematic situation causing CO.sub.2 refrigerant
solidification, a flow control device such as a valve 54 is opened
and additional refrigerant is delivered into the refrigerant system
50. In this manner, the pressure in the evaporator 28 is raised,
and the solidification of the CO2 refrigerant is avoided.
[0019] FIG. 4 shows yet another embodiment 60, wherein a defrost
cycle is initiated by the control 32, should the conditions
indicate the CO.sub.2 refrigerant is approaching a solidification
line. In the illustrated embodiment, a defrost coil 62 associated
with the evaporator 28 may be actuated to raise the temperature and
pressure within the evaporator 28.
[0020] 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.
[0021] 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.
[0022] 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.
* * * * *