Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND AND SUMMARY OF THE INVENTION
This invention relates to a novel heat pump and more particularly,
to a heat pump utilizing a multispeed compressor so as to provide for more
efficient overall operation and to an improved method for operating a heat ;;
pump utilizing a multispeed compressor.
Prior heat pumps have generally included a single speed compressor,
reversing means, an indoor coil, expansion means and an outdoor coil
interconnected in a refrigerant circuit. When the reversing means is posi-
tioned for a cooling mode of operation, refrigerant is forwarded from the
compressor to the outdoor coil. The vaporous refrigerant is condensed in
the outdoor coil which functions at this $ime as a condenser. Liquid re-
frigerant passes from the outdoor coil through the expansion means to the
indoor coil. The refrigerant expands within the indoor coil, cooling the
air passing thereover. The cooled air is transmitted to the area to be cooled.
With the reversing means positioned for a heating mode of operation,
refrigerant is forwarded from the compressor to the indoor coil which now
~unctions as a condenser. The hot vaporous refrigerant is condensed and
the heat given off from the refrigerant passes to the air moving over the
indoor coil to the environment to be heated. Refrigerant is metered through
the expansion means and flows to the outdoor coil where it expands. As
the coil temperature approaches freezing, frost will form on the outdoor
coil reducing the heating capacity of the system. Periodically, the outdoor
coil must be defrosted to remove the frost. The frequency of frost removal
or deicing depends upon the amount of moisture in the air at the time that
icing occurs and thle operating temperature of the outdoor coil. The rate of
icing is a function of numerous variables, but in general, it will increase
as the ambient temperature around the outside coil decreases from 45 F to
approximately 35F. The temperature of the outdoor coil will be about 30F.
As the ambient temperature decreases below 35F, the rate of icing also
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decreases since the amount of free moisture in the air decreases. Icing is
very slow at ambient temperatures below 15F to 20F to none existing.
One way of accomplishing defrost:ing of the outdoor coil during
heating operation is to reverse the revers;ng means from the heating mode to
the cooling mode. However, this is inefficientJ inasmuch as cool air may be
discharged from the indoor coil into the area to be heated during the deicing
process or defrost cycle. Strip heat or fossil fuel has been used to add
heat to the area to be heated during this period of time, however, this is
also inefficient and wasteful of energy.
At about 0F, outdoor ambient temperature, the COP of the conven-
tional heat pump refrigeration system drops below one and the heat pump is
cycled off. Auxiliary strip heat is turned on to heat the environment to be
warmed. It is desirous to extend the lower range of operation to use heat
from the more efficient heat pump system than from less efficient auxiliary
strip heat.
An object of the present invention is to provide a heat pump wherein
the disadvantages and deficiencies of prior heat pumps are obviated.
According to one aspect of this invention there is provided a heat
pump including a multispeed compressor, reversing means, an indoor coil, an
outdoor coil, and expansion means connected in a refrigerant circuit and
control means for operating the compressor, said control means preventing
frosting of the outdoor coil during the heating mode of operation without ~;
actuating the revers;ng means from the heating mode to the cooling mode by
sensing a predetermined condition and changing the compressor operation from
relatively high speed to relatively low speed.
According to another aspect of this invention there is provided a
method of operating a heat pump including a multispeed compressor, reversing
means, an indoor coil, an outdoor coil, and expansion means connected in a
refrigerant circuit~ the method of operation preventing frosting of the out-
door coil during the heating mode of operation without actuating the reversing
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means from the heating mode to the cooling mode, comprising the steps of
operating the compressor at a relatively high speed in a heating mode so as
to provide heat from the indoor coil to heat an environment, operating the
compressor at a relatively low speed in response to a predetermined condition
so as to reduce the indoor coil capacity and elevate the temperature of the
outdoor coil so as to defrost the outdoor coil without actuating the reversing
means.
According to yet another aspect of this invention there is provided
a method of extending the lower operating range of a heat pump during heating
operation comprising the steps of operating a two-speed compressor at rela-
tively high speed during normal operation and at relatively low speed during
ambient temperatures causing the outdoor coil to operate below 32F to there-
by elevate the outdoor coil temperature to above freezing and make more heat
available at the outdoor coil for system operation.
BRIEF DESCRIPTION OF THE DRAWING
There is illustra~ed in the attached drawing a presently preferred
embodiment of the present invention wherein:
Figure 1 is a schematic illustration of a heat pump system embody-
ing the present invention; and
Figure 2 is a graph illustrating the operation of the novel heat
pump of the present inventior
DETAILED DESCRIPTION OF THE PRESENT INVENTION
With reference to Figure 1 there is shown a heat pump embodying the
present invention. The heat pump 10 of this invention comprises basically a
two-speed compressor 12 which is adapted to forward refrigerant through the
line 14 to a reversing means 16 that is operated by control means 18 as will
be more fully described hereinafter. The refrigeration system also includes
an outdoor coil 22, expansion means 26, 28 and indoor coil 30. Associated
with the expansion means 26, 28 are one-way check valve means 34, 36.
Consider first the cooling mode of operation. The reversing means
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16 is properly actuated by control 18. The compressor 12 is actuated by
control 13 so as to pump refrigerant through the line 14 to the reversing
means 16 to line 17 to the outdoor coil 22 where the hot vaporous refrigerant
is condensed. As shown, the outdoor coil may be air-cooled by the fan means
24. The outdoor coil 22 can be water cooled if desired. The refrigerant
condensed in the outdoor coil 22 passes through the line 25, the one-way
check valve 34, line 27 and through the expansion means 28 which may
comprise a thermal expansion valve. From the expansion means 28, the
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refrigerant passes through the line 29 to the indoor coil 30 where the re-
frigerant vaporizes. Air to be cooled may be passed over the indoor coil
30 by the fan means 31. During the cooling mode of operation, the cooled air
may be ducted or otherwise communicated with the area to be cooled. The
refrigerant passes through the line 32 from the indoor coil 30 (which acts
as an evaporator) to the reversing valve 16 and then through line 33 to the
compressor 12.
During the heating mode of operation, the refrigerant forwarded from
the compressor 12 passes through the discharge line 14 to the reversing
valve 16 and line 32 to the indoor coil which now functions as a condenser.
The fan means 31 passes air over the indoor coil which air is heated. The
heated air is communicated to the area to be heated. The refrigerant passes
from the indoor coil 30 through the line 29, one-way check valve 36 and
line 27 to the expansion means 26. The refrigerant metered through the
expansion means 26 passes through line 25 to the outdoor coil 22 which now
functions as an evaporator. The refrigerant returns to the compressor via
line 17, reversing means 16, and line 33.
A feature of the present invention is the provision of a two-speed
compressor operable at a relatively high speed (nominal 3600 RPM at
two-pole high speed) for normal heating operation and operable at a rela-
tively low speed (nominal 1800 RPM at four-pole low speed) in response to
a predetermined condition to reduce the indoor coil capacity and elevate the
temperature of the outdoor coil so as to defrost the outdoor coil without
actuating the reversing means which may be of a conventional type.
The control means 13 for operating the compressor 12 may be
responsive to a predetermined outdoor temperature or may be responsive to
a predetermined temperature differential of the outdoor coil or air pressure
drop across the outdoor coil. In any event, the control 13 will operate the
compressor during the heating mode of operation to reduce the speed from
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high speed to low speed, so as to decrease the cooling capacity of outdoor
coil, and thereby increase the temperature of the outdoor coil. At low
speed operation, there is effectively twice the surface of outdoor coil as
compared to high speed operation. The outdoor coil temperature will in-
crease so as to defrost the outdoor coil without actuating the reversing `'
means. Also, at low speed operation, the capacity of the compressor is
about one half that at high speed. This too is a factor in elevating the
temperature of the outdoor coil. Since there is no reverse cycle operation
required for this defrost mode of operation, no cool air will be dumped into
the area to be treated and there will be no necessity for utilization of strip
heat or other auxiliary heat to offset a cooling effect during this mode of
operation. This results in energy conservation and stress on the compressor
is greatly reduced. The reduction in stress is not linear, but is reduced
more sharply. The exact magnitude of the reduction is not known.
In the past, it has been kno~,vn to initiate the defrost cycle responsive
to the ambient temperature, responsive to a temperature differential across
the outdoor coil, responsive to an air pressure drop across the outdoor coil
and by timing means. Similar sensors are required to terminate the defrost
operation and return the system to normal heating operation.
Another aspect of this invention is to increase the range of operation
of a heat pump system. At very low ambient temperature, on the order of
0F, the outdoor coil surface cannot pick up sufficient heat. The coefficient
of performance (COP) of the heat pump will drop to or below 1. Under these
circums tances, standard heat pump operation must be terminated. By use
of the present invention, the speed of the compressor is reduced from full
speed to half speed, so as to effectively double the cooling surface of the
outdoor coil and thereby, enable the heat pump system to continue operating
to a lower ambient temperature and maintain the COP above 1.
With reference to Figure 2, there is illustrated a graph of BTU per hour
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versus the outdoor coil temperature in degrees Fahrenheit. The lines
sloping upwardly to the right have been marked with appropriate legends
(compressor at high speed and compressor at low speed) and the lines A
and B are indicative of outdoor coil capacities at varying degrees of a~bient
temperature. The line A assumes an ambient temperature of 40F and the
line B assumes an ambient temperature of 0F. With reference to line A,
it will be noted that the intersection of line A and the compressor at high
speed operation line occurs at about 30F. At this condition, there would
be frosting of the outdoor coil. When the compressor is switched to low
speed, it will be noted that the intersection of line A with the compressor at -
low speed line, increases to about 36F. The effective surface of the outdoor
coil is doubled as compared to the effective surface at high speed operation, ~;
resulting in warming of the outdoor coil. This will be sufficient to defrost
the outdoor coil.
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A refinement would be to cycle the fan 31 for the indoor coil in con-
junction with the operation of the compressor 12. ~uring high speed opera-
tion, as the evaporating temperature approaches 32F, the indoor fan 31 is
cycled. If the indoor fan 31 speed is substantially reduced or stopped, the -
head pressure will be increased, thus the pumping capacity of the compressor
will be decreased significantly and the outdoor coil temperature will be in-
creased, thus helping to defrost the outdoor coil 2Z. At this time, the out-
door coil fan 24 is kept running so as to maximi~e heat pick up by the out-
door coil 22, thereby enhancing defrost of coil 22. If this does not defrost theoutdoor coil, then after a programmed time delay, the compressor 12 can be
switched to half speed operation. Another aid to defrost if a few more degrees
of heat were needed at the outdoor coil 22, would be to switch the operation
of the outdoor fan 24 from low to high speed. If defrost of the outdoor coil
is still not adequate, then the heat pump system reversing valve 16 could be ;;
operated in a conventional fashion.
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Considering next system operation at an outdoor ambient temperature
of about 0F, it will be noted that the intersection of line B and the compressor
at high speed line is at approximately -6F, evaporating temperature. At
these conditions, there is insufficient heat in the air and the heat pump
operates at a COP of less than 1. Normally, the operation of the compressor
is terminated if the outdoor temperature drops below 0 F to prevent damage
to the compressor and strip heat or auxiliary heat is used to provide heat in
the area to be heated. If the compressor operation is reduced to low speed
operationJ the intersection occurs of line B with the compressor at low speed
at approximately 1F. In this example, therefore, the compressor which
would otherwise have to be shut down may continue to be operated so as to
increase the lower range of system operation.
Yet another means of extending the lower range of operation is contem-
plated by the present invention. This is to provide a secondary coil in
parallel with the outdoor coil of an equal capacity to that of the outdoor coil.
By utilization of both coils during low ambient conditions through suitable
controls and in conjunction with the compressor at low speed operation, there
is more outdoor coil surface and more heat can be picked for a given heat
pump system. The lower range of operation can be extended several degrees
in this manner.
There has been provided by the present invention an improved heat pump
system provided with a two-speed compressor which is operable in a rela-
tively low speed mode in response to a predetermined condition during heating
so as to reduce the indoor coil capaci$y and elevate the temperature of the
outdoor coil so as to defrost the outdoor coil without actuating the revarsing
means. Another aspect of the invention is the utilization of a heat pump system
having a two-speed compressor operable in such fashion as to extend the lower
range of operation to very low ambient conditions, on the order of 0 to -6F.
While I have shown a presently preferred embodiment of the present
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invention, it will be understood that specific variations in construction and
arrangement of the heat pump disclosed can be made by those skilled in
the art without departing from the invention as defined in the appended
claims.
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