Note: Descriptions are shown in the official language in which they were submitted.
HEAT PUMP APPARATUS AND METHOD
OF OPERATING THE SAME
GOVERNMENT CONTRACT
The Government has rights in this invention
pursuant to Prime Contract No. W-7405-ENG-26 and Sub-
contract No. 86X-24712-C awarded by the United States
Department of ~nergy.
~ACKGROUND OF THE INVENTION
A refrigeration circuit in which the refrigerant
exiting the evaporator is saturated vapor or contains
small amo~mts of liauid has two important advantages over
a system where the refrigerant exiting the evaporator is
superheated. First, since the compressor is essentially a
constant volume device, the refrigerant flow is maximized
by ~xi~izing the density of the fluid entering the com-
pressor. Since superheating the vapor reduces its density,
it reduces the 10w of refrigerant. Second, since heat
transfer coefficients in two-phase flow are higher than
for single-phase flow, the utilization of the evaporator
heat transfer surface is maximized by eliminating super
heat. These advantages have been known for some years and
have been availed of in the com~r~ial application of heat
pump systems embodying the teachin~s of U.S. Patent
3,264,837. That system was designed to operate without
superheat of the refrigerant exiting the evaporator in
both the heating and cooling modes. In that system, as
commercially a~ailable, refrigerant flow was basically
s
controlled by the use of a subcooling control valve,
controlling in accordance with the temperature of the
refrigerant exiting whichever coil was functioning as the
condenser. The particular control valve commercially used
required that the 10w through the valve be in the same
direction in both heating and cooling modes and this
accordingly required the use of an arrangement of our
check valves, typically provided in the form of a manifold
check valve assembly of the character described and claimed
in U.S. Patent 3,299,661. Such assemblies are relatively
expensive, impose additional refrigerant pressure drop,
allow heat to be transferred from the hot liquid stream to
the cold two-phase stream, and can leak or stick causing a
loss in performance or failure of the system.
It is the aim of this invention to provide a
heat pump system in which part or all of the check valves
are eliminated, which utilizes a commercially available
refrigerant expansion device adapted to control refrigerant
flow in either direction through the device and which is
controlled in different ways in the heating and cooling
modes of operation of the system to provide advantages in
both modes and in particular in a heat pump system designed
especially for use in northern climates.
SUM~RY OF THE INVENTION
In accordance with the invention a heat pump
system of the type which includes a suction line accumu~
lator and heat exchanger means is provided with a single
refrigerant expansion device in the system, the expansion
device being an electrically operated device located in a
refrigerant line connected on one side of the expansion
device to the outdoor coil, and connected on the other
side of the expansion device at ~éast to the heat exchanger
means. Means are provided to control the expansion device
in the heating mode of operation of the heat pump to
obtain a degree of subcooling of refrigerant passing
through the indoor coil, which degree of subcooling coupled
with further subcooling of the refrigerant in its passage
-
through the heat exchanger means, provides for flooded
evaporator operation of the outdoor coil, and controlling
the expansion device in a cooling mode of operation to
pass refrigerant to the indoor coil at a rate to obtain a
degree of superheat of refri~erant eY~iting the indoor
coil.
Stated in another manner, the heat pump system
of the invention functions to provide subcool control of
the refrigerant iIl the hea-ting mode to give flooded evapor-
ator operation, and functions to provide superheated
control in the cooling mode Various advantages are
available from a system of this character, which advantages
will be noted later herein.
BRIEF DESCRIPTION OE THE DRAWING
Figure 1 is a schematic diagram of one form of
heat pump system according to the invention; and
Figure 2 is a schematic diagram of another form
of the heat pump system of the invention.
DESCRIPTION OE THE PREFERRED EMBODIMENTS
Most of the basic elements shown in both Figures
l and 2 are the same, and to the extent they are, the same
reference numerals are applied to both figures. In both
figures, the solid line directional arrows indicate the
direction of refrigerant flow in the heating mode of
operation, while the dash line arrows indicate the direc-
tion of flow in the cooling mode of operation.
In the Figures, the re~rigerant compressor lO
pumps hot gaseous refrigerant through discharge line 12 to
a conventional reversing valve 14 which, according to its
positioning, directs the hot gas either through line 16 to
the indoor coil 18 or, alternatively, through the line 20
to the outdoor coil 22.
Referring now to Figure l alone, and assuming
the heat pump is operating in a heating mode, the refrig-
erant leaving the indoor coil 18 passes through line 24,line 25, through a heat exchanger element 26 physically
located in a suction line accumulator 28, through line 30
containing a check valve 32, through line 34 to the elec-
trically controlled refrigerant expansion device 36 and
line 38 to the outdoor coil 22. From the outdoor coil the
refrigerant passes back through line 20 to the reversing
5 valve 14 which, in the heating mode position, directs the
returning suction gas through line 40 to the suction line
accumulator 28. Suction gas returns to the compressor 10
from the accumulator 28 through line 42.
In the cooling mode of operation the refrigerant
10 flow is from the compressor 10 through the discharge line
12, reversing valve 14 positioned to pass refrigerant to
line 20 leading to the outdoor coil 22, then line 38 to
the expansion valve 36, line 34 through the check valve
44, llne 24, indoor coil 18, line 16 to the reversing
15 valve 14 and then through line 40 to the suction accumula-
tor 28, and back to the compressor 10 through line 42. It
will be noted that in the heating mode of operation the
check valve 44 compells the refrigerant to pass through
the heat exchanger 26, while in the cooling mode of opera-
20 tion the check valve 32 compels the refrigerant to bypassthe heat exchanger 26.
The refrigerant flow paths for the Figure 2
system in both the heating and cooling modes of operation
are very similar except that while in the Figure 1 arrange-
25 ment the heat exchanger 26 is bypassed in the coolingmode, in the Figure 2 arrangement the heat exchanger 26
has refrigerant flow therethrough in both the heating and
cooling modes.
In contrasting the systems of Figures 1 and 2,
30 Figure 1 is advantageous in the cooling mode in that there
is no heat transfer between the suction gas and the accumu-
lator 28 and the refrigerant flowing to the indoor coil 18
from the expansion device 36, but is disadvantageous in
that it includes the t~o check valves 32 and 44 which
35 impose some additional pressure drop, add to the cost of
the system and sometimes are susceptible to leaking or
sticking. The disadvantage of the Figure 2 system is that
the heat exchanger 26 functions in the cooling mode as
well as the heating mode, and in the cooling mode there
will typically be some small degree of heat transfer which
will penalize cooling performance slightly.
It will be seen that in both systems a single
refrigerant expansion device 36 is used, which is electri-
cally operated and may be a commercially available valve
such as the No. 625 available from the Singer Company. It
will also be seen that it is located in a refrigerant line
which includes the part 38 connected to the outdoor coil,
and the part 34 on the other side of the valve 36 which is
connected at least to the heat exchanger 26 through line
30 in Figure 2, and through line 30 in check valve 32 in
Figure 1, and as well as connected to the second check
valve 44 in Figure 1.
The difference in control of the refrigerant
flow by the expansion device 36 in accordance with the
cooling or heating mode of operation is a very important
aspect of the invention. The temperature of the indoor
coil at a central or representative location is sensed by
the sensor 46. Another sensor 48 located at or adjacent
the exit end of the coil ~when the coil is operating in a
cooling mode) senses superheat temperature of the refriger-
ant leaving the coil. Another sensor 50 at or adjacent
the other ~nd of the coil which end of the coil is the end
through which refrigerant exits when the indoor coil is
functioning as a condenser, is used to sense the degree of
subcooling occurring in the coil. These three sensors are
connected through lines 52, 54 and 56, respectively, to
the controller 58 which in turn is connected by electric
line means 60 to provide the electrical signal to the
electric expansion valve 36.
In the cooling mode the indoor coil 18 functions
as an evaporator and the temperature difference between
the refrigerant exiting the coil as measured by sensor 48,
and the saturation temperature as measured by sensor 46 is
measured and the two temperatures compared to the set
poin~ in the controller 58. This signal is then fed back
to the expansion device 36 to control the flow of
refrigerant to the indoor coil to obtain the proper flow
for conditions.
In the heating mode the temperatures at 46 and
50 are measured and the difference compared to the set
point to obtain the proper refrigerant flow for the partic-
ular conditions. The degree of superheat, and subcooling
giving best performance in accordance with outdoor ambient
temperature can also be controlled in the systems by the
provision of an outdoor ambient temperature sensor as
indicated at 62 and fed into the controller 58 through
line 64. Thus in the heating mode of operation the valve
36 functions as a subcooling control valve which operates
to obtain the degree of subcooling of refrigerant exiting
the indoor coil 18. This degree of subcooling coupled
with the further subcooling of the refrigerant in its
passage through the heat exchanger 26 where it is in heat
a~c~ ~ r. relation with the cold suction gas, provides for
flooded evaporator operation of the outdoor coil 22. In
the cooling mode of operation, the indoor coil 18 functions
as the evaporator and the control of the refrigerant flow
through the valve 36 is that giving a rate to ohtain the
proper degree of superheat of the refrigerant exiting the
indoor coil.
It is noted that the basic operation of the
system in the heating mode, as distinguished from differ-
ences in parts of the systems, is essentially the same as
that of commercial devices based upon the concepts of U.S.
30 Patent 3,264,837. The operation of the systems in a
cooling mode is ~uite different from the concepts of that
patent with respect to its operation in the cooling mode.
Among the advantages of the system and method of
operation, in which the subcool control and flooded evap-
orator i5 used in the heating mode and the superheat
control is used in the cooling mode, is that all of the
control sensors may be located at the indoor coil 18. The
system may be provided with no check valves or, alter-
native.ly, with a reduced number of check valves as con-
trasted to the commercial devices based upon U.S. Patent
3,264,837. The system is adapted to using the conven-
tionally available suction accumulator with the built-in
heat exchanger. Another important advantage of the system
is it is adapted to be charged when it i5 set up for
operation in the cooling mode so that it is much easier to
obtain a proper charge of refrigerant. This is in contrast
to those commercial devices based upon U.S. Patent
3,264,837, for which were ound to present substantial
difficulty to typical service people in determining when
they were properly charged. Those prior art devices are
rather insensitive to excess charge, but undercharging
results in a precipitous loss in performance. The primary
difficulty is that the charging method is more dificult,
and is unfamiliar to many service people.
