Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to vapor compression cycle
devices and more particularly to a means and a method for
controlling the modulation of both thermal capacity and
evaporator superheat in such a device.
In a conventional vapor compression cycle device
such as a heat pump a working fluid liquid is circulated
through an expansion device into an evaporating heat
exchanger where the working fluid absorbs heat. The heai
vaporizes the working fluid liquid, and the resulting vapor
is then circulated by a suitable compressor through a
condensing heat exchanger where the vapor condenses inio a
liquid as heat is given off. The cycle is then repeated as
the workin~ fluid is recirculated through the system.
The quantity of heat required to vaporize the
working fluid liquid is known as the heat of vaporization.
Additional heat absorpiton by the resulting working fluid
vapor causes an increase in the vapor temperature above the
temperature of vaporization. This increase in vapor
temperature is defined as superheat.
In conventional vapor compression cycle devices it
is desirable to control the amount of superheat in the
device cycle to achieve optimum system performance. Typically
this control of superheat is effected by regulating the flow
rate of workingfluid liquid passing through the expansion de-
vice to the evaporator.
A vapor compression cycle device should also include
means to modulate the capacity of the device to absorb and
deliver heat, herein referred to as device thermal capacity,
in response to variable heating and cooling demands in
order to maximize efficiency. A device of this type is
disclosed in Canadian Application Serial Number
330,906, filed June 29, 1979, and assigned to the same
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assignee as the present application. The thermal capacity
of this device i5 modulated by regulating the amount of a ~ ;
multi-component working fluid allowed to flow from a first
accumulator through an evaporator to a second accumulator
located at a compressor inlet. As described in the cited
application, this results in a change in the molar flow
rate through ~he compressor and thus a change in device
ihermal capacity.
A device which includes means both for modulating
device thermal capaciiy and for controlling the amount of
evaporator superheai generated therein is disclosed in a -~
later filed Canadian application Serial No. 3C~ /~ Z
filed ~o~c~6~ c~ which is also assigned to the same
assignee as the present invention. As in the earlier
disclosed device described above, this latter device
includes two accumulators. However, the second accumulator
in the latter device is relocated intermediate two stages of
an evaporating heat exchanger, and is adapted to decrease ~ :
the time required to switch the device from a high to a
low capacity mode of operation. Additionally, the evaporator
superheat of the latter device is controllable through reg-
ulation of the amount of working fluid liquid allowed to
flow from the second accumulator into the final evaporator
stage.
The device disclosed in Canadian Application
S.N.3~/~ thus includes means whereby both evaporator super-
heat and device thermal capacity can be variably conlrolled.
However, optimal performance of this device can require the
coordinated adjustment of a plurality of flow restricting
devices in response to sensed conditions.
Accordingly, it is an object of this invention to
provide a new and improved means for controlling the modulation
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of the thermal capacity of a vapor compression cycle
device.
Another object of the present invention is to
provide a new and improved means for controlling the
evaporator superheat of such a device.
Still another object of the present invention is
to provide a new and improved means and met~od for the
control or a vapor compression cycle device thermal capacity
and evaporator superheat.
The above and other objecis and advantages of the
present invention are achieved through a means and a
method for controlling the thermal capacity and evaporator
superheat of a vapor compression cycle device employing a
multi-component working fluid in which the amount of working
fluid liquid allowed to flow from each of a pair of accum-
ulators is controlled either in response to sensed thermal
demand or to sensed working fluid vapor superheat.
For better understanding of the invention, reference
may be made to the accompanying drawing wherein:
FIGURE 1 is a schematic illustration of a vapor
compression cycle device constructed in accordance with an
embodiment of the present invention; and
FIGURE 2 is a view similar to that of Figure 1
illustrating a second embodiment of the present invention.
In the exemplary embodiments of the invention
depicted in Figures 1 and 2 of the drawing a heat pump 10
is shown in a heating mode of operation. However, it is to be
understood that the present invention is not limited to
heat pump applications. Furthermorel it is also understood
that the present invention can be operated in a cooling
mode of operation.
The device 10 is a closed cycle device in which a
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working fluid is circulated by a compressor 11 through a
tube 12 to a condensing heat exchanger 13. ~fter trans-
ferring its heat in the: condenser 13.'tQ the. household, the
working fluid flows through a tube 14.to a high pressure
accumulator 15. The accumulator .15 may be of a conventional ' ~
design or may be of a design such.'as disclosed in ': .
Çanadian Application Serial Number .331,333, filed. ~ '
~uly 6, 1979, and assigned to the same assi~nee:as the
present invention. The accumulator 15 is connected to an .
expansion valve 16 ~hich'controls the amount of the working
fluid allowed to flow through a tube 17. to an evaporator
assembly 18 where heat i.s absorbed by.the' fluid. ~he evap-
orator assembly includes a low pres.sure:accumulator 19
connected iniermediate a first evaporaior stage 20 and a second
evaporator stage 21. Thus, the working fluid entering the
evaporator assembly 18 from the:tube 17.f.1Ows through:the first
evaporator stage 20. to the low-pressure'accumulator 19 from
which. it then flows through lines.-22 and.23.'.to the second
evaporator stage 21. Tube 26 connects:thè.o.utlet side of
the evaporator assembly 18 to the inl.et of the compressor : '
11 to effect a closed system.
The working fluid circulated.in this closed system
is a multi-component mixture of fluids.which'have different
vapor pressures and which are mi.scibIe:over the operative
range of the device 10. In the preferred embodiment of
. the present inventi.on, the working:fluid is a multi-component
fluorocarbon mixture. Such multi-component fluorocarbon
mixtures can be selected for example from those disclosed
in U.S. Patent No, 4,003,215 issued January 18, 1977, to
John Roach.
The modulation of the. capacity of the device 10 is
accomplished by altering the density of the working fluid
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vapor at the inlet of the compressor 11. This effectively
varies the` molar flow rate through the compressor, thereby
affecting the capacity of the device 10 to absorb and
deliver heat to an associated household, or its thermal
capacity. The compressor inlet density is dependent upon
the vapor pressure thereat which is in part a function of the
composition of the working fluid liquid collected in the low
pressure accumulator 19. Thus, if the composition of this
liquid is enriched with a low boiling point component of the
working fluid mixture, the thermal capacity of the device 10
is correspondingly increased. Conversely, a decrease in the
concentration of the ~w boiling point component in theJ
liquid contained in the low pressure accumulator 19 will
effect a decrease in the thermal capacity of the device.
The changing of the concentrations of the components
of the liquid in the accumulator 19 is accomplished in part
by adjusting the rate of flow from the accumulator 15. The
high pressure accumulator 15 normally includes a higher
concentration of the working fluid low boiling point
component than.~does the liquid in the lo~ pressure accumulaior
19 due to equilibrium relationships between ihe working
fluid vapor and liquid contained therein. Thus, to increase
the capacity of the device 10 to transfer heat the valve
16 is adjusted to augment the flow from the accumulator 15
such that the liquid level in the low pressure accumulator
19 is raised and the composition thereof is enriched with
the low boiling point component of the working fluid. This
then causes an increase in the compressor inlet density, and
thus increases the thermal capacity o the device.
In order to decrease device thermal capacity upon
increased outdoor temperature and associated decreased
household thermal demand, Ihe steps described above are
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reversed. To thi:s end, ihe flow of ihe working fluid liquid
from the accumulator 15 to the low pressure: accumu~ator
19 is restricted by adjusting the valve 16. The low boiling
point component in the liquid contained in the low pressure
accumulator 19 is slowly depleted through evaporation by
means of heat transfer from the vapor interfacing therewith.
To accomplish a more rapid transition from a high
to a low capacity mode of operation, the device 10 as illus-
trated in Figures 1 and 2 includes tubes 23 and 24 and valve
25 which connect the liquid region of the accumulator 19
with the second evaporator stage 21. Thus, upon decreased
thermal demand, the valve 25 is opened a predetermined
amount to allow a portion of the liquid in the accumulator
19 to flow into ihe second evaporator .stage 21 along with the
working fluid vapor flowi.ng through:the.tube.22. The mixture
is therein vapor:i.zed prior. to entering the.compressor inlet
through a tube 26.
In th.is manner, the time required to deplete the
liquid level in the low pressure:.:accumulator 19, and thus
to decrease th.e thermal capacity of the device 10, is sig-
nificantly reduced.
Additionally,. th evaporator superheat of the device
10 is controlled by adjusting the valve 25.to augment or
decrease the flow of working ~luid li:quid from the accumulator
17 to the second staye evaporator 21. More speci.fically,
since the amount of heat transfer capabili~y available for
transfer to the working fluid flowing through the second
stage evaporator 21 is fixed for a given set of conditions,
then the amount of fluid flowing therethrough accordingly
governs the possible temperature rise therei.n. Thus the
tempera~ure of the working fluid exiting the second stage
evaporator 21, and hence evaporator superheat, i5 controllable
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by regulating the rate of working flu.id flow through the
valve 25.
Means for controlling. the:thermal capacity and the
evaporator superhea~ of the vapor compression cycle device
10 include superheat responsive actuation means 27 and thermal
demand responsive actuation means 28. More specifically,
as illustrated in Figures 1 and 2, actuation means 27
preferably includes a wetness sensing the`rmistor 29 and a valve
actuator 30 connected in series to a voltage supply 31 by
leads 32. The wetness sensing thermistor 29 controls voltage
output to the valve actuator 30 causing.it to position the
valve 16 such that a predetermined superheat condition in the
suction line 26 of the compressor 11 is maintained. Actuation
means of this type are commercially available from the
Control Division of the Singer Company, Milwaukee, Wisconsin.
Although the thermistor 29 is depicted in Figures 1
and 2 positioned in the working fluid flow path after the
second evaporator stage 21, ii is to be understood that the
thermistor could be positioned earlier in the flow path to
allow a higher degree of fluid superheat. In particular, the
~hermistor can be positioned to sense the vapor quality of
. the working fluid at a predetermined point within the second
evaporator stage, whereupon the fluid is heated a known amount
in the portion of the evaporator following the thermi.stor
to achieve a desired degree of fluid superheat at the inlet
of the compressor 11.
Actuation means 28 includes a valve actuator 33
responsive to si.gnals transmitted from a thermal demand
sensin~ controller 34. In the preferred embodiment of the
invention the thermal demand sensing controller 34 is a ther-
mostat, however, it is understood that other thermal demand
sensing devices canb e substituted therefor~ Thermal demand
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responsive actuation means of thiS type are also commercially
available from the above-noted Singer Co.
The embodiment of this invention illustrated in
Figure 1, the method of modulating the thermal capacity of
the device 10 ls initi:ated by a signal from the controller 34
corresponding to a sensed change in thermal demand. Upon a
demand for increased device thermal capacity controller 34
signals valve actuator 33 to close valve 25 a predetermined
amount, thereby decreasing the flow of working fluid liquid
from the accumulator 19 through the heat exchanger 21. The
decreased liquid flow results in an increased vapor superheat
in the suction line 26 as sensed by the thermistor 29. Upon
sensed increased vapor superheat the valve actuator 30 functions
~o open the cooperating valve 16 a predetermined amount,
thereby augmeniing the working fluid flow from the accumulator
15 to the evaporator assembly 18. The re:sulting increase in
the concentration of the low boiling point component of the
working fluid mixture in the accumulator 19 causes an increase
in the molar flow rate through the compressor 11, thereby
increasing the thermal capacity of the device 10.
Conversely, upon a decrease in thermal demand, as
sensed by the controller 34, the valve actuator 33 opens the
valve 25 a predetermined amount to permit more li~uid working
fluid to flow from the accumulator 19. This increased flow of
liquid causes a decrease of superheat in the working fluid
vapor exiting the second evaporator stage 21, thereby causing
the closing of the valve 16 the the actuator 30. This leads
to a gradual depletion of working fluid liquid in the
accumulator 19 and a ~radual increase in liquid level in the
accumulator 15. The thermal capacity of the device 10 thusly
makes a gradual transition to a ~ower level of operation.
A variation on this first embodiment of the invention
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is illustrated in Figure 2 of the dra~ing. In this embodiment
the valve 16 is controlled by the thermal demand responsive
actuation means 28, and valve 25 is controlled by the
superheat responsive actuation means 27. Upon a sensed in-
crease in thermal demand the controller 34 transmits a
signal causing the valve actuator 33 to open the valve 16.
This results in an increased flow of working fluid liquid from
the accumulator 15 to the evaporator assembly 18, thereby
increasing the concentration of the low boiling point component
of the working fluid in the liquid contained in the accumulator
22 and causing an increase in the thermal capacity of the
device 10. During this process the valve 25 is independently
controlled by the actuation means 27 to meter out the amount
of liquid required to maintain a predetermined degree of
superheat at the exii of ihe evaporator assembly 18.
Upon a sensed need to decrease device thermal
capacity the process is reversed wherein valve 16 is closed a
predetermined amount resulting in less working fluid li~uid
entering the accumulator 19. This leads to a gradual
depletion of the liquid in the accumulator 19 and a decrease
in device thermal capacity. As in the preceding case the
valve 25 is again independently controlled to maintain a
predetermined degree of superheat at the exit of the
evaporator assembly 18.
The above-described embodiments of this invention
are inlended to be examplative only and not limiting and it
will be appreciaied from the foregoing by those skilled in
the art that many substitutions, alternations and changes
may be made to the described structure and method without
department from the spirit or scope of the invention.
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