BACKGROUND
Embodiments relate generally to refrigerant vapor compression systems
used in air conditioning systems, and more particularly to a system for recovering
energy from a hot gas bypass line in a refrigerant vapor compression system.
Existing refrigerant vapor compression systems may employ a centrifuga5 l
compressor. Capacity control of a centrifugal compressor may be achieved using
inlet guide vanes. In some installations, however, the sizing of the compressor
inlet prohibits the ability to use inlet guide vanes to control capacity. Hot gas
bypass is another technique used to control capacity, but hot gas bypass is not
10 energy efficient.
SUMMARY
In one embodiment, a refrigerant vapor compression system includes a
compressor having a compressor suction port and a compressor discharge port; a
heat rejection heat exchanger fluidly coupled to the compressor discharge port; an
15 expansion device fluidly coupled to an outlet of the heat rejection heat exchanger;
a heat absorption heat exchanger fluidly coupled to the expansion device; a hot gas
bypass line fluidly coupled to the compressor discharge port; an ejector comprising
a motive port fluidly coupled to the hot gas bypass line, a suction port fluidly
coupled to an outlet of the heat absorption heat exchanger and a discharge port
20 fluidly coupled to the compressor suction port; a hot gas bypass valve positioned
between the compressor discharge port and the motive port of the ejector; a flow
control valve fluidly coupled to the outlet of the heat absorption heat exchanger,
and fluidly coupled to the suction port of the ejector and the compressor suction
port.
25 Additionally or alternatively, in this or other embodiments, a controller is
configured to control the hot gas bypass valve and the flow control valve.
3
Additionally or alternatively, in this or other embodiments, the controller
is configured to open the hot gas bypass valve and set the flow control valve to
fluidly couple the outlet of the heat absorption heat exchanger with the suction port
of the ejector.
Additionally or alternatively, in this or other embodiments, the controlle5 r
is configured to open the hot gas bypass valve when a temperature of a fluid exiting
the heat absorption heat exchanger is less than a setpoint.
Additionally or alternatively, in this or other embodiments, the controller
is configured to open the hot gas bypass valve when a temperature of a fluid exiting
10 the heat absorption heat exchanger is less than a setpoint and one of (i) a ratio of
pressure at the heat rejection heat exchanger to pressure at the heat absorption heat
exchanger is greater than a limit or (ii) pressure pulsations are present at the
compressor discharge port.
Additionally or alternatively, in this or other embodiments, the controller
15 is configured to open the hot gas bypass valve when a ratio of pressure at the heat
rejection heat exchanger to pressure at the heat absorption heat exchanger is greater
than a limit.
Additionally or alternatively, in this or other embodiments, the controller
is configured to close the hot gas bypass valve and set the flow control valve to
20 fluidly couple the outlet of the heat absorption heat exchanger with the compressor
suction port.
Additionally or alternatively, in this or other embodiments, wherein the
controller is configured to close the hot gas bypass valve when a temperature of a
fluid exiting the heat absorption heat exchanger is greater than a setpoint.
25 Additionally or alternatively, in this or other embodiments, the controller
is configured to close the hot gas bypass valve when a temperature of a fluid exiting
the heat absorption heat exchanger is greater than a setpoint and one of (i) a ratio
4
of pressure at the heat rejection heat exchanger to pressure at the heat absorption
heat exchanger is less than a limit or (ii) pressure pulsations are not present at the
compressor discharge port.
Additionally or alternatively, in this or other embodiments, the compressor
is a centrifugal compressor5 .
In another embodiment, a method of controlling a refrigerant vapor
compression system including a compressor having a compressor suction port and
a compressor discharge port, a heat rejection heat exchanger, a hot gas bypass line
fluidly coupled to the compressor discharge port, an ejector comprising a motive
10 port fluidly coupled to the hot gas bypass line, a suction port fluidly coupled to an
outlet of the heat absorption heat exchanger and a discharge port fluidly coupled
to the compressor suction port, a hot gas bypass valve positioned between the
compressor discharge port and the compressor suction port and a flow control valve
fluidly coupled to an outlet of a heat absorption heat exchanger, and fluidly coupled
15 to the suction port of the ejector and the compressor suction port, the method
including: opening the hot gas bypass valve and setting the flow control valve to
fluidly couple the outlet of the heat absorption heat exchanger with the suction port
of the ejector.
Additionally or alternatively, in this or other embodiments, the method
20 includes opening the hot gas bypass valve when a temperature of a fluid exiting the
heat absorption heat exchanger is less than a setpoint.
Additionally or alternatively, in this or other embodiments, the method
includes opening the hot gas bypass valve when a temperature of a fluid exiting the
heat absorption heat exchanger is less than a setpoint and one of (i) a ratio of
25 pressure at the heat rejection heat exchanger to pressure at the heat absorption heat
exchanger is greater than a limit or (ii) pressure pulsations are present at the
discharge port of the compressor.
5
Additionally or alternatively, in this or other embodiments, the method
includes opening the hot gas bypass valve when a ratio of pressure at the heat
rejection heat exchanger to pressure at the heat absorption heat exchanger is greater
than a limit.
Additionally or alternatively, in this or other embodiments, the met5 hod
includes closing the hot gas bypass valve and setting the flow control valve to
fluidly couple the outlet of the heat absorption heat exchanger with the suction port
of the compressor.
Additionally or alternatively, in this or other embodiments, the method
10 includes closing the hot gas bypass valve when a temperature of a fluid exiting the
heat absorption heat exchanger is greater than a setpoint.
Additionally or alternatively, in this or other embodiments, the method
includes closing the hot gas bypass valve when a temperature of a fluid exiting the
heat absorption heat exchanger is greater than a setpoint and one of (i) a ratio of
15 pressure at the heat rejection heat exchanger to pressure at the heat absorption heat
exchanger is less than a limit or (ii) pressure pulsations are not present at the
discharge port of the compressor.
Technical effects include the ability recover energy from a hot gas bypass
operation through the use of an ejector in the hot gas bypass line.
20 These and other advantages and features will become more apparent from
the following description taken in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGs
The subject matter is particularly pointed out and distinctly claimed at the
conclusion of the specification. The foregoing and other features, and advantages
25 of the present disclosure are apparent from the following detailed description taken
in conjunction with the accompanying drawings in which:
6
Figure 1 depicts a refrigerant vapor compression system in an example
embodiment; and
Figure 2 depicts operating points for the refrigerant vapor compression
system.
The detailed description explains embodiments, together with advantage5 s
and features, by way of example with reference to the drawings.
DETAILED DESCRIPTION
Figure 1 illustrates a refrigerant vapor compression system 10 in an
example embodiment. The refrigerant vapor compression system 10 may be a
10 chiller, a rooftop unit, or other type of system. In the refrigerant vapor compression
system 10, refrigerant flows in a closed loop from a compressor 12, to a heat
rejection heat exchanger 14, to an expansion device 16, to a heat absorption heat
exchanger 18 and then back to the compressor 12 in a fluidly coupled loop. The
compressor 12 may be a variable speed compressor, having a speed controlled by
15 a controller 50. The compressor 12 may be a centrifugal compressor in an example
embodiment. In the heat rejection heat exchanger 14, the refrigerant is cooled by
transferring heat to a fluid 17 flowing in heat exchange relationship with the
refrigerant (e.g., air). In the heat absorption heat exchanger 18, the refrigerant is
heated by transferring heating from a fluid flowing in heat exchange relationship
20 with the refrigerant (e.g., air or liquid). In the example in Figure 1, liquid (e.g.,
water) from a loop, generally designated at 22, flows in heat exchange relationship
to the refrigerant and is cooled by transferring heat to the refrigerant.
A hot gas bypass line 24 is fluidly coupled to the discharge port of the
compressor 12. The hot gas bypass line 24 is fluidly coupled to a motive port 32
25 of an ejector 30 through a hot gas bypass valve 26. A suction port 34 of the ejector
30 is fluidly coupled to the outlet of the heat absorption heat exchanger 18 through
a flow control valve 36. A discharge port 38 of the ejector 30 is fluidly coupled to
the suction port of the compressor 12. The outlet of the heat absorption heat
7
exchanger 18 is also connected to the suction port of the compressor 12 through
the flow control valve 36. Flow control valve 36 can direct the refrigerant leaving
the heat absorption heat exchanger 18 to one of the suction port 34 of the ejector
30 and the suction port of the compressor 12. In other embodiments, the flow
control vale 36 may divert a first portion of the refrigerant leaving the hea5 t
absorption heat exchanger 18 to the suction port 34 of the ejector 30 and a second
portion of the refrigerant leaving the heat absorption heat exchanger 18 to the
suction port of the compressor 12. Check valves 37 prevent flow of refrigerant
back into the heat absorption heat exchanger 18.
10 A number of sensors monitor operating parameters of the refrigerant vapor
compression system 10. Sensor 42 monitors discharge pressure of the compressor
12 and may be used to detect discharge pressure pulsations, as described in further
detail herein. Sensor 44 monitors pressure of the heat rejection heat exchanger 14.
Sensor 46 monitors pressure of the heat absorption heat exchanger 18. Sensors 48
15 and 49 monitor temperature of fluid entering the heat absorption heat exchanger
18 (e.g., entering water temperature EWT) and temperature of fluid exiting the heat
absorption heat exchanger 18 (e.g., leaving water temperature LWT). It is
understood that other sensors may be used in the control of the refrigerant vapor
compression system 10, which are not depicted in Figure 1.
20 A controller 50 receives sensed operating parameters from the various
sensors and controls operation of one or more of the speed of the compressor 12,
the opening of the hot gas bypass valve 26 and the flow of refrigerant through the
flow control valve 36 by providing control signals to the compressor 12, the hot
gas bypass valve 26 and the flow control valve 36. The controller 50 can be any
25 type or combination of processors, such as a microprocessor, microcontroller,
digital signal processor, application specific integrated circuit, programmable logic
device, and/or field programmable gate array. The hot gas bypass valve 26 and the
flow control valve 36 may operate in unison. For example, when the hot gas bypass
valve 26 is closed, the flow control valve 36 is configured to fluidly couple the
30 outlet of the heat absorption heat exchanger 18 with the suction port of the
8
compressor 12, avoiding the ejector 30. If the hot gas bypass valve 26 is opened,
the flow control valve 36 is configured to fluidly couple the outlet of the heat
absorption heat exchanger 18 with the suction port 34 of the ejector 30.
The ejector 30 is used to lower energy usage of the compressor 12 when
the hot gas bypass valve 26 is open. The flow of refrigerant from the discharg5 e
port of the compressor 12 through the ejector 30 causes refrigerant to be drawn
from the heat absorption heat exchanger 18, increasing the compressor suction
pressure thereby reducing work needed by the compressor 12.
Figure 2 depicts three operating modes for the refrigerant vapor
10 compression system 10. As shown at 102, the controller 50 receives various inputs
including the temperature of fluid exiting the heat absorption heat exchanger 18
(e.g., leaving water temperature), pressure at the heat rejection heat exchanger 14
(e.g., condenser pressure), pressure at the heat absorption heat exchanger 18 (e.g.,
evaporator pressure) and the presence of discharge pressure pulsations at the
15 discharge port of the compressor 12.
At the operating point shown at 104, the leaving water temperature is less
than a setpoint. This means that the capacity of compressor 12 may be reduced
since the setpoint is met. At 104, if the leaving water temperature is less than a set
point, and a pressure ratio is less than a limit or no pressure pulsations are detected
20 at the discharge port of the compressor 12, then the controller 50 reduces the speed
of the compressor 12. The pressure ratio is the ratio of pressure in the heat rejection
heat exchanger 14 to pressure in the heat absorption heat exchanger 18. If,
however, either the pressure ratio is greater than a limit or pressure pulsations are
detected at the discharge port of the compressor 12, then the controller opens the
25 hot gas bypass valve 26 as shown at 106. Opening the hot gas bypass valve 26
initiates a corresponding change in flow control valve 36. For example, if the hot
gas bypass valve 26 is opened, then the flow control valve 36 is adjusted to direct
refrigerant leaving the heat absorption heat exchanger 18 to the suction port 34 of
the ejector 30.
9
At the operating point shown at 108, the leaving water temperature is
greater than a setpoint. This means that the capacity of compressor 12 may be
increased since the setpoint is not met. At 108, if the leaving water temperature is
greater than a set point, and a pressure ratio is less than a limit or no pressure
pulsations are detected at the discharge port of the compressor 12, then 5 n the
controller closes the hot gas bypass vale 26 (if opened) and increases speed of the
compressor 12. The pressure ratio is the ratio of pressure in the heat rejection heat
exchanger 14 to pressure in the heat absorption heat exchanger 18. Closing the hot
gas bypass valve 26 initiates a corresponding change in the flow control valve 36
10 so that no refrigerant leaving the heat absorption heat exchanger 18 is directed to
the suction port 34 of the ejector 30.
At the operating point shown at 110, the pressure ratio is compared to a
pressure ratio limit. The pressure ratio is the ratio of pressure in the heat rejection
heat exchanger 14 to pressure in the heat absorption heat exchanger 18. If at 110,
15 the pressure ratio is greater than a pressure ratio limit, then the speed of compressor
12 is increased. If the speed of the compressor is already at a maximum or if the
leaving water temperature is less than a set point, then the controller 50 opens the
hot gas bypass valve 26 and adjusts the flow control valve 36 to direct refrigerant
exiting the heat absorption heat exchanger 18 to the suction port 34 of the ejector
20 30.
While the invention has been described in detail in connection with only a
limited number of embodiments, it should be readily understood that the invention
is not limited to such disclosed embodiments. Rather, the invention can be
modified to incorporate any number of variations, alterations, substitutions or
25 equivalent arrangements not heretofore described, but which are commensurate
with the spirit and scope of the invention. Additionally, while various
embodiments of the invention have been described, it is to be understood that
aspects of the invention may include only some of the described embodiments.
Accordingly, the invention is not to be seen as limited by the foregoing description,
30 but is only limited by the scope of the appended claims.

We Claim:
1. A refrigerant vapor compression system comprising:
a compressor having a compressor suction port and a compressor discharge
port;
a heat rejection heat exchanger fluidly coupled to the compressor discharg5 e
port;
an expansion device fluidly coupled to an outlet of the heat rejection heat
exchanger;
a heat absorption heat exchanger fluidly coupled to the expansion device;
10 a hot gas bypass line fluidly coupled to the compressor discharge port;
an ejector comprising a motive port fluidly coupled to the hot gas bypass
line, a suction port fluidly coupled to an outlet of the heat absorption heat
exchanger and a discharge port fluidly coupled to the compressor suction port;
a hot gas bypass valve positioned between the compressor discharge port
15 and the motive port of the ejector;
a flow control valve fluidly coupled to the outlet of the heat absorption heat
exchanger, and fluidly coupled to the suction port of the ejector and the compressor
suction port.
2. The refrigerant vapor compression system of claim 1 further comprising:
20 a controller configured to control the hot gas bypass valve and the
flow control valve.
11
3. The refrigerant vapor compression system of claim 2 wherein:
the controller is configured to open the hot gas bypass valve and set
the flow control valve to fluidly couple the outlet of the heat absorption heat
exchanger with the suction port of the ejector.
4. The refrigerant vapor compression system of claim 3 wherei5 n:
the controller is configured to open the hot gas bypass valve when
a temperature of a fluid exiting the heat absorption heat exchanger is less than a
setpoint.
5. The refrigerant vapor compression system of claim 3 wherein:
10 the controller is configured to open the hot gas bypass valve when a
temperature of a fluid exiting the heat absorption heat exchanger is less than a
setpoint and one of (i) a ratio of pressure at the heat rejection heat exchanger to
pressure at the heat absorption heat exchanger is greater than a limit or (ii) pressure
pulsations are present at the compressor discharge port.
15 6. The refrigerant vapor compression system of claim 3 wherein:
the controller is configured to open the hot gas bypass valve when
a ratio of pressure at the heat rejection heat exchanger to pressure at the heat
absorption heat exchanger is greater than a limit.
7. The refrigerant vapor compression system of claim 2 wherein:
20 the controller is configured to close the hot gas bypass valve and set
the flow control valve to fluidly couple the outlet of the heat absorption heat
exchanger with the compressor suction port.
12
8. The refrigerant vapor compression system of claim 7 wherein:
the controller is configured to close the hot gas bypass valve when
a temperature of a fluid exiting the heat absorption heat exchanger is greater than
a setpoint.
9. The refrigerant vapor compression system of claim 8 wherei5 n:
the controller is configured to close the hot gas bypass valve when
a temperature of a fluid exiting the heat absorption heat exchanger is greater than
a setpoint and one of (i) a ratio of pressure at the heat rejection heat exchanger to
pressure at the heat absorption heat exchanger is less than a limit or (ii) pressure
10 pulsations are not present at the compressor discharge port.
10. The refrigerant vapor compression system of claim 1 wherein:
the compressor is a centrifugal compressor.
11. A method of controlling a refrigerant vapor compression system
including a compressor having a compressor suction port and a compressor
15 discharge port, a heat rejection heat exchanger, a hot gas bypass line fluidly
coupled to the compressor discharge port, an ejector comprising a motive port
fluidly coupled to the hot gas bypass line, a suction port fluidly coupled to an outlet
of the heat absorption heat exchanger and a discharge port fluidly coupled to the
compressor suction port, a hot gas bypass valve positioned between the compressor
20 discharge port and the compressor suction port and a flow control valve fluidly
coupled to an outlet of a heat absorption heat exchanger, and fluidly coupled to the
suction port of the ejector and the compressor suction port, the method comprising:
opening the hot gas bypass valve and setting the flow control valve to
fluidly couple the outlet of the heat absorption heat exchanger with the suction port
25 of the ejector.
13
12. The method of claim 11 further comprising:
opening the hot gas bypass valve when a temperature of a fluid
exiting the heat absorption heat exchanger is less than a setpoint.
13. The method of claim 11 further comprising:
opening the hot gas bypass valve when a temperature of a fluid exiting 5 the
heat absorption heat exchanger is less than a setpoint and one of (i) a ratio of
pressure at the heat rejection heat exchanger to pressure at the heat absorption heat
exchanger is greater than a limit or (ii) pressure pulsations are present at the
discharge port of the compressor.
10 14. The method of claim 11 further comprising:
opening the hot gas bypass valve when a ratio of pressure at the heat
rejection heat exchanger to pressure at the heat absorption heat exchanger is greater
than a limit.
15. The method of claim 11 further comprising:
15 closing the hot gas bypass valve and setting the flow control valve
to fluidly couple the outlet of the heat absorption heat exchanger with the suction
port of the compressor.
16. The method of claim 15 further comprising:
closing the hot gas bypass valve when a temperature of a fluid
20 exiting the heat absorption heat exchanger is greater than a setpoint.
17. The method of claim 16 further comprising:
closing the hot gas bypass valve when a temperature of a fluid exiting the
heat absorption heat exchanger is greater than a setpoint and one of (i) a ratio of
pressure at the heat rejection heat exchanger to pressure at the heat absorption heat
14
exchanger is less than a limit or (ii) pressure pulsations are not present at the
discharge port of the compressor.