Note: Descriptions are shown in the official language in which they were submitted.
CA 02618397 2008-01-17
HEAT PUMP APPARATUS AND METHOD
BACKGROUND OF THE INVENTION:
This invention relates to the field of heat pumps. More particularly, this
invention
relates to the field of air source heat pumps having a primary compressor and
a booster
compressor connected in series, the heat pumps being suitable for heating
operation at
temperatures down to zero degrees Fahrenheit and lower.
RELATIONSHIP TO OTHER APPLICATIONS:
This application relates to heat pumps of the type disclosed and claimed in my
previously issued Unites States patents 6,931,871, 6,276,148, 5,927,088, and
5,839,886
and my pending United States patent applications Ser. Nos. PCT/US05/34651 and
10/959,254 . The entire contents of my said United States patents and patent
applications
are incorporated herein by reference.
SUMMARY OF THE INVENTION:
In accordance with the present invention, a primary compressor and a booster
compressor are connected to operate in series in a heat pump system. The
primary
compressor is a variable capacity or partially unloadable compressor, and the
booster is
preferably a single speed compressor. The system also incorporates a
temperature sensor
for sensing the temperature of outdoor ambient air, a two stage indoor
thermostat and a
microprocessor. For heating operation, the system is capable of operation in
any one of
three modes, M 1, M2, M3, depending on outdoor air temperature and the heating
load on
the system. Ml is partial capacity operation of the primary compressor; M2 is
full
capacity operation of the primary compressor; and M3 is full capacity
operation of each
of the primary compressor, the booster compressor, and an.economizer. For
outdoor
temperatures in a first range between about 60 F and up (i.e., up to where
heating
operation is no longer allowed), only operation in M1 is allowed. For outdoor
air
1
CA 02618397 2008-01-17
temperatures in a second range of from about 38 F to about 59 F, operation in
M1 is
allowed, and, if Ml operation does not provide enough heat, operation in M2 is
also
allowed. For outdoor air temperatures in a third range of from about 31 F to
about 37 F,
operation in only M2 is allowed. For outdoor air temperatures in a fourth
range of from
about 19 F to about 37 F, operation in M2 is allowed, and, if M2 operation
does not
provide enough heat, operation in M3 is allowed. For outdoor air temperatures
in a fifth
range of from about 18 F and below, operation in M3 is allowed, and, if M3
operation
does not provide enough heat, the system may also include an M4 mode in which
electrical resistance heat is added to the system.
The temperature sensor delivers signals to the microprocessor, and the
microprocessor enables or allows operation in M1, M2 and M3 (and M4), i.e.,
conditions
are created wherein operation in those modes will occur if the thermostat
calls for heat.
When the thermostat calls for heat, the microprocessor will generate signals
to cause
operation in M1, M2, M3 or M4 depending on the outdoor air temperature.
For cooling operation, only the primary compressor operates in either Mode 1
or 2
depending only on which indoor thermostat stage is calling for cooling
operation.
The heat pump system also incorporates a demand defrost cycle in modes M2, M3
and M4 (if M4 is present). Outdoor air temperature is sensed by a temperature
sensor
external to the outdoor (evaporator) coil, and a signal representing that
temperature is
delivered to a system microprocessor. Based on the sensed outdoor air
temperature, the
microprocessor calculates a defrost trigger temperature Tl for each of modes
M2 and M3
(M4 is identical to M3 for demand defrost purposes). A temperature T2 is also
sensed
that is commensurate with the temperature of the refrigerant boiling in the
outdoor coil.
T2 is sensed by a sensor mounted on one of the tubes feeding an evaporator
circuit directly downstream of the normal pressure reduction/flashing process.
Whenever
T2 then drops to a value equal to or less than the calculated T1 continuously
for 10
2
CA 02618397 2008-01-17
minutes, a defrost cycle is triggered to defrost the outdoor coil. The defrost
cycle
continues until T2 rises to a predetermined defrost terminating value.
BRIEF DESCRIPTION OF THE DRAWINGS:
Referring to the drawings, where like elements are numbered alike in some of
the
figures:
Figure 1 is a schematic drawing of the heat pump system of the present
invention
for heating modes M 1 and M2;
Figure 2 is a schematic drawing of the heat pump system of the present
invention
for heating mode M3, and M4 if present.
Figure 3 is a schematic drawing of the heat pump system of the present
invention
for cooling modes M1 and M2.
Fig. 3A is a schematic drawing of the heat pump system of the present
invention
for cooling modes M3 or M3-C.
Figure 4 is a table showing the temperature ranges of operation for heating
modes
M1, M2, M3, and M4, if present.
Figure 4A is a modified version of the table of Fig. 4.
Figure 5 is a chart illustrating the determination of trigger temperatures for
defrost
operation.
Fig. 6 is a schematic showing incorporation of a refrigerant compensator for
modes M3 and M4.
3
CA 02618397 2008-01-17
DESCRIPTION OF THE PREFERRED EMBODIMENT:
Referring to Figs. 1 and 2, a closed loop heat pump system for heating
operation
is shown. The system includes a first or booster compressor 22, a second or
high stage
primary compressor 24, an indoor coil or condenser 26 that delivers heated air
to a space
to be heated, an outdoor coil or evaporator 28 which receives outdoor air from
which heat
energy is to be extracted, an economizer 30 which has a solenoid operated
control valve
31, a four way flow control valve 32, and a conduit system 34 for connecting
the
foregoing components in a closed loop system for the flow of refrigerant. Flow
control
valve 32 operates to reverse the flow of refrigerant to effect cooling
operation and for
defrost operation. The system also has a microprocessor 36 and a two stage
thermostat
38, such as is available from White Rogers. The system also has thermal
expansion
valves 40 and 42 in conduit 34 associated, respectively, with indoor coi126
and outdoor
coi128, and check valves 44 and 46 for bypassing refrigerant flow around
expansion
valves 40 and 42, respectively, depending on the direction of refrigerant flow
in the
system. The check valves 44 and 46 may actually be internal parts of their
respective
expansion valves, but they are shown separately to facilitate the description
of operation.
The system also includes a first temperature sensor 48 positioned near outdoor
coi128 for
sensing the temperature of outdoor air flowing over outdoor coil 28, and a
second
temperature sensor 50 on or just adjacent to conduit 34 where it enters
outdoor coil 28 to
sense temperature commensurate with the boiling refrigerant in outdoor coil
28. Air
handlers and/or fans for coils 26 and 28 are not shown, but the flow or air
over these coils
is indicated by arrows.
Primary compressor 22 is preferably a Bristol twin single (TS) compressor
having
two reciprocating pistons and cylinders. However, it can also be any multi-
capacity or
unloadable positive displacement or multi-speed compressor. Booster compressor
22 is
any type of a positive displacement single speed compressor. The flow capacity
of the
primary compressor is preferably split 50%/100%, i.e., where 100% is the flow
capacity
when both cylinders are operating, and 50% is the percentage of total flow
capacity when
4
CA 02618397 2008-01-17
only one piston is reciprocating. In addition, the flow capacity of booster
compressor is
larger than the flow capacity of primary compressor, preferably by a ratio of
from about
1.3/1 to about 1.7/1, depending on the climate where the system is to be used.
In initial operation of the system in the heating mode, a signal representing
the
ambient air temperature sensed by temperature sensor 48 is delivered to
microprocessor
36, and the microprocessor will enable or allow partial capacity operation of
primary
compressor 24 upon receipt of a signal from thermostat 38 calling for heat if
the outdoor
ambient temperature is in a first range between about 60 F and above. A signal
calling
for heat is delivered to microprocessor 36 from stage I of thermostat 38 when
the
temperature of the space to be heated falls below the set point of the
thermostat by, e.g.,
0.6 F-1.2 F. If the temperature sensed at sensor 48 is in the first range of
at or between
about 60 F and above, the microprocessor causes operation of one cylinder of
primary
compressor 24. That is, partial capacity operation of primary compressor 24 is
effected.
When that happens, compressed hot refrigerant vapor is circulated in conduit
system 34
by delivery from primary compressor 24 through 4 way valve 32 and then to
indoor
condenser coi126 where heat is extracted by air from an air handler passing
over indoor
coi126 to be delivered to the space to be heated. On leaving the indoor
condenser coi126,
the refrigerant is in the form of a warm liquid, and it flows through check
valve 44, which
.is open, bypassing expansion valve 40. The warm refrigerant liquid then flows
directly
through the liquid side of economizer 30 and is delivered toward thermal
expansion valve
42. Since direction of flow and pressure of the refrigerant close check valve
46, the warm
liquid refrigerant is delivered to and flows through thermal expansion valve
42 where
part of the refrigerant is flashed or boiled to vapor. The two phase
refrigerant mixture
then flows to outdoor coil 28 where the remaining liquid refrigerant is
vaporized due to
extraction of heat from the outside air. The resulting cool vapor is then
delivered through
4 way valve 32 'and through check valve 52 and conduit section 54 to the inlet
to primary
compressor 24. The refrigerant then goes through repeat cycles of compression;
subsequent vapor cooling and condensation into liquid; then liquid flashing or
expansion;
subsequent boiling or evaporation while it is concurrently transferring heat
energy into
5
CA 02618397 2008-01-17
indoor air while cooling and condensing and extracting heat energy from the
outside air
while boiling or evaporating. The operating cycle described above with partial
capacity
operation of the primary compressor is termed Mode 1, or M 1. When the set
point of
thermostat 38 is reached, a signal is sent from the thermostat to the
microprocessor to
terminate operation of primary compressor 24 in Ml. If the temperature of the
space to be
heated again falls below the set point of the thermostat by 0.6 F-1.2 F, the
thermostat
again delivers a heat calling signal to microprocessor 36, and if the
temperature sensed by
sensor 48 is still in the first range of between about 60 F and up, the system
is again
cycled through operation in M1. As long as the outdoor ambient temperature
sensed at
sensor 48 is in the first range between about 60 F and up, the microprocessor
will only
allow operation in Ml, i.e., with partial capacity operation of primary
compressor 24.
Also, if the outside air temperature, as sensed by sensor 48 is not at or
below a selected
upper first range temperature of, e.g., about 75 F, the microprocessor will
not allow
operation of primary compressor 24, and heating operation will not occur. This
prevents
inefficient use of the heating system.
The system continues to operate in Ml until sufficient heat has been delivered
to
the space being heated to satisfy the setting called for by thermostat 38.
When the setting
of the thermostat is satisfied, a signal is delivered from the thermostat to
the
microprocessor, and operation of the compressor system is terminated. However,
if
sufficient heat has not been delivered to the internal space to be heated
within a pre-
programmed period of time (typically from 5 to 10 minutes) or if the rate of
increase in
temperature is not fast enough, the thermostat calls for stage 2 operation by
sending a
second signal to microprocessor 36 to call for more heating capacity from the
system. If
the outdoor ambient temperature sensed at sensor 48 is in a second and lower
range of
temperature between about 38 F and 59 F, the microprocessor then delivers an
enabling
signal to primary compressor 24 to operate both pistons of the primary
compressor 24 to
effect operation of the primary compressor at full capacity. This full
capacity operation of
the primary compressor is termed Mode 2 or M2. In M2, the flow of refrigerant
through
the system is as in Ml, but at a higher flow rate, whereby a greater volume of
hot vapor is
6
CA 02618397 2008-01-17
delivered to indoor condenser coil 26 to heat the indoor space to be heated.
Note, again,
that if the outdoor temperature sensed at sensor 48 is not at or below the
upper limit of
about 59 F of the second operating range of outdoor temperatures, the
microprocessor
will not. enable M2 operation of the system. Again, this prevents inefficient
operation of
the heating system. The system continues to operate in M2 until sufficient
heat has been
delivered to the space being heated to satisfy the setting called for by
thermostat 38.
When the setting of the thermostat has been satisfied, a signal is delivered
from the
thermostat to the microprocessor to terminate operation of the compressor
system. If the
temperature of the space to be heated again falls below the set point of the
thermostat by
0.6 F-1.2 F, the thermostat again delivers a heat calling signal to
microprocessor 36, and
if the temperature sensed by sensor 48 is still in the second range of between
about 38 F
and 59 F, the system is again cycled through operation first in M1 and then in
M2. As
long as the outdoor ambient temperature sensed at sensor 48 is in the second
range
between about 38 F and 59 F, the microprocessor will only allow operation in
M1 and
M2, i.e., first with partial capacity operation and then full capacity of
primary compressor
24.
At a third and lower range of outdoor ambient air temperatures, from about 31
F
to 37 F the temperature signal delivered by sensor 48 to microprocessor causes
the
microprocessor to skip M1, and go directly to enabling or allowing M2
operation.
Accordingly, upon receipt of a heat calling signal from stage I of thermostat
38 being
delivered to microprocessor 36 (as the result of the temperature in the space
to be heated
falling below the set point of the thermostat), the microprocessor delivers a
signal to
primary compressor 24 to operate the primary compressor at full capacity. The
system
continues to operate in M2 until sufficient heat has been delivered to the
space being
heated to satisfy the setting called for by thermostat 38. If the setting of
the thermostat is
satisfied, a signal is delivered from the thermostat to the microprocessor,
aiid operation of
the compressor system is terminated. However, if sufficient heat has not been
delivered
to the internal space to be heated within a period of time (typically from 5
to 10 minutes),
or if the rate of temperature increase is not fast enough, the thermostat
calls for stage 2
7
CA 02618397 2008-01-17
operation by sending a second signal (calling for more heating capacity from
the system)
to microprocessor 36. However, in this third range of outdoor ambient air
temperatures,
from about 31 F to 37 F, the microprocessor is programmed to still only allow
M2
operation upon receiving the stage 2 signal from the thermostat. This prevents
inefficient
use of the heating system as higher capacity operation is not to be permitted
by the
microprocessor until it is really needed.
At a fourth and lower range of outdoor ambient air temperatures, from about 19
F
to about 30 F the temperature signal delivered by sensor 48 to the
microprocessor causes
the microprocessor to again skip M1, and go directly to allowing M2 operation.
Accordingly, upon receipt of a heat calling signal from stage 1 of thermostat
38 being
delivered to microprocessor 36 (as the result of the temperature in the space
to be heated
falling below the set point of the thermostat by from about 0.6 F-1.2 F), the
microprocessor delivers a signal to primary compressor 24 to operate the
primary
compressor at full capacity. The system continues to operate in M2 until
sufficient heat
has been delivered to the space being heated to satisfy the setting called for
by thermostat
38. If the setting of the thermostat is satisfied, a signal is delivered from
the thermostat to
the microprocessor, and operation of the compressor system is terminated.
However, if
sufficient heat has not been delivered to the internal space to be heated
within a period of
time (typically from 5 to 10 minutes), or if the rate of temperature increase
is not fast
enough, the thermostat calls for stage 2 operation by sending a second signal
(calling for
more heating capacity from the system) to microprocessor 36. If the outdoor
ambient
temperature sensed at sensor 48 is still in the range of between about 19 F
and 30 F, the
microprocessor then generates enabling signals to operate all of the booster
compressor
22, the primary compressor 24 at full capacity, and the economizer at full
capacity. This
operation of the booster compressor, the primary compressor at full capacity
and full
capacity operation of the economizer is termed Mode 3 or M3.
Referring to Fig. 2, when the system is operated in M3, the high pressure
discharge from booster compressor 22 closes check valve 52, whereby the
refrigerant
8
CA 02618397 2008-01-17
vapor from outdoor coi128 is delivered through 4 way valve 32 and conduit
segment 55
to the inlet to booster compressor 22. After compression in booster compressor
22, the
higher pressure refrigerant vapor discharge from compressor 22 is delivered
via conduif
segment 56 to primary compressor 24 after first mixing with the additional
refrigerant
saturated vapor emanating from the boiling side of economizer 30 (see
description below
re economizer 30). The now combined and somewhat desuperheated vapor (after
mixing) is further compressed by primary compressor 24 and is then delivered
to
condenser indoor coil 26. The increased mass flow of the refrigerant resulting
from both
the high flow rate low compression booster and the heat recovering economizer
enters, the
primary compressor resulting in significantly increased heating capacity for
the system,
which can be transferred to the air flowing over indoor coi126 to be delivered
to the
space to be heated.
The warm liquid refrigerant discharged from indoor coil 26 is delivered to
economizer 30. However, the economizer enabling signal from the microprocessor
opens
solenoid valve 31, whereby some of the liquid refrigerant is bled through
bleed line 58
and expanded through an orifice in solenoid valve 31 thereby entering the
boiling side of
the economizer where it boiled (or evaporated) into saturated vapor. This
boiling liquid in
the boiling side of the economizer significantly subcools the warm refrigerant
flowing
through the liquid side of the economizer as it extracts the thermal energy
originally
present in the warm liquid. This results in significantly subcooled liquid
refrigerant being
delivered to expansion valve 42 of evaporator outdoor coi128. This results in
an
increased refrigerant capacity (per unit of mass flow) which absorbs more heat
energy
from the ambient air passing over outdoor coi128 thereby further increasing
the heating
capacity of the system.
The saturated refrigerant vapor from the boiling side of economizer 30 is
delivered via conduit segment 60 to a location in conduit segment 56 between
the
discharge from primary compressor 22 and the inlet to primary compressor 24
where it
9
CA 02618397 2008-01-17
joins and mixes with the vapor stream going form the discharge of the booster
compressor to the inlet to the primary compressor.
In M3, the flow of refrigerant through the system is at a higher flow rate and
pressure than in M 1 or M2, whereby a greater volume of hot vapor is delivered
to indoor
condenser coil 26 to heat the indoor space to be heated. Note, again, that if
the outdoor
temperature sensed at sensor 48 is not at or below the upper limit of about 30
F of the
fourth operating range of outdoor temperatures, the microprocessor will not
enable M3
operation of the system: Again; this prevents inefficient operation of the
heating system.
The system continues to operate in M3 until sufficient heat has been delivered
to
the space being heated to satisfy the setting called for by thermostat 38.
When the setting
of the thermostat has been satisfied, a signal is delivered from the
thermostat to the
microprocessor to terminate operation of the compressor system. If the
temperature of the
space to be heated again falls below the set point of the thermostat by about
0.6 F-1.2 F,
the thermostat again delivers a heat calling signal to microprocessor 36, and
if the
temperature sensed by sensor 48 is in the fourth range of between about 19 F
and 30 F,
the system is again cycled through operation first in M2 and then in M3. As
long as the
outdoor ambient temperature sensed at sensor 48 is in the fourth range between
about
19 F and 30 F, the microprocessor will only enable operation in M2 and M3,
i.e., first
with full capacity operation of primary compressor 24, and then adding in the
operation
of the booster compressor and the economizer.
For the sake of clarity, it should be noted that although the M3 enabling
signal
from the microprocessor calls for operation of both the booster compressor and
the
economizer, there is a slight delay in the operation of the economizer
relative to operation
of the booster compressor. The booster compressor operates at full capacity
almost
immediately upon receipt of the enabling signal from the microprocessor.
However, there
is a time delay in operation of the economizer because of the time needed to
bleed the
fluid through the orifice of solenoid valve 31 and deliver the saturated vapor
from the
boiling side of the economizer through conduit segment 60 to conduit segment
56.
CA 02618397 2008-01-17
When ambient air temperatures in a fifth range of 18 F and below are sensed at
sensor 48, and when therrnostat 32 is calling for heat in stage 1,
microprocessor 36 allows
and effects operation of the heat pump system in M3, i.e., with full capacity
operation of
the primary compressor, and with operation of the booster compressor and with
operation
of the economizer. However, if sufficient heat has not been delivered to the
internal space
to be heated within a period of time (typically from 5 to 10 minutes) or if
the rate of
temperature rise is not fast enough, the thermostat calls for stage 2
operation by sending a
second signal (calling for more heating capacity from the system) to
microprocessor 36.
The microprocessor then allows and effects operation of backup electrical
resistance
heater 62, which is positioned downstream of the air flow over indoor coil 26.
This is
designated as Mode 4 or M4 operation. Note, again, that if the outdoor
temperature
sensed at sensor 48 is not at or below about 18 F of the fifth operating range
of outdoor
temperatures, the microprocessor will not allow M4 operation of the system.
Again, this
prevents inefficient operation of the heating system. The system continues to
operate in
M4 until sufficient heat has been delivered to the space being heated to
satisfy the setting
called for by thermostat 38. When the setting of the thermostat has been
satisfied, a signal
is delivered from the thermostat to the microprocessor to terminate operation
of the
compressor system. If the temperature of the space to be heated again falls
below the set
point of the thermostat by 0.6 F-1.2 F, the thermostat again delivers a heat
calling signal
to microprocessor 36, and if the temperature sensed by sensor 48 is in the
fifth range of
between below 18 F, the system is again cycled through operation first in M3
and then in
M4. As long as the outdoor ambient temperature sensed at sensor 48 is in the
fifth range
below about 18 F, the microprocessor will only enable operation in M3 and M4,
i.e., first
with full capacity operation of primary compressor 24 and booster compressor
22 and the
economizer 30, and then adding in operation of electrical resistance heater 62
if the
thermostat is not satisfied.
It will be understood that when the booster compressor and economizer are
. operating, the primary compressor is also operating at full capacity. That
is, operation in
M3 includes operation in M2. Also, when supplemental electrical resistance
heat is
11
CA 02618397 2008-01-17
operation, the primary compressor is operating at full capacity and both the
booster
compressor and the economizer are. operating. That is, operation in M4
includes operation
in M3.
Referring to Fig. 4, a table is presented showing the various modes of
operation
allowed and effected by the system depending on outdoor ambient temperature as
sensed
at sensor 48. When the outdoor ambient temperature is in the first range
between about
60F and up, operation only in M1 is allowed and effected regardless of whether
stage 1 or
stage 2 of the thermostat is calling for heat. When the outdoor ambient
temperature as
sensed at sensor 48 is in the second temperature range between about 38 F and
about
59 F, operation first in M1 is allowed and effected when stage 1 of the
thermostat is
calling for heat, and operation in M2 is allowed and effected when stage 2 of
the
thermostat is calling for heat. When outdoor ambient temperature as sensed at
sensor 48
is in the third temperature range between about 31 F and about 37 F, operation
only in
M2 is allowed and effected, regardless of which stage of the thermostat is
calling for
heat. When outdoor ambient temperature as sensed at sensor 48 is in the fourth
temperature range between about 19 F and about 30 F, operation first in M2 is
allowed
and effected when stage 1 of the thermostat is calling for heat, and then
operation in M3
is allowed and effected when stage 2 of the thermostat is calling for heat.
When outdoor
ambient temperature as sensed at sensor 48 is in the fifth temperature range
below about
18 F, operation first in M3 when stage 1 of the thermostat is calling for
heat, and then
operation in M4 is allowed and effected when stage 2 of the thermostat is
calling for heat.
In an alternative embodiment of the heat pump system, an on-off booster
operation may be utilized to reduce the net capacity being delivered to the
system
condenser when more heat capacity than M2 is needed, but when full M3 system
capacity
is not absolutely necessary. As an example, instead of allowing full Mode 3
operation as
the outdoor temperature falls into the fourth range of temperatures (from
about 19 F-
F) and the thermostat is calling for heat, microprocessor 36 is programmed to
first
allow and effect booster compressor 22 to start and stop for pre-determined
relatively
12
CA 02618397 2008-01-17
short periods of time until the outdoor temperature eventually falls to a
point where it is
desirable to allow continuous M3 operation. This cycling mode of operation of
booster
22 is designated as Mode 3-C (M3-C) and will be incorporated approximately
half way
down in outdoor temperature between where M2 operation and the full M3
operation are
allowed as indicated previously (e.g., for a temperature range of from about
24 F to about
30 F). Full M3 operation would be enabled for the lower half of the M3
operating
temperature range. The booster "on" and "off' intervals can be of equal time
or unequal.
Alternatively, the relative "on" and "off' times for the booster compressor
can be made
to vary in steps as outdoor air temperature falls through the entire outdoor
door
temperature range for M3 operation, with booster "on" time being lowest when
outdoor
air temperature is higher in the M3 enabling temperature range and booster
"on" tirne
being highest when outdoor ambient temperature is lower in the M3 enabling
temperature
range. This variable on-off time ratio inversely proportional to the outdoor
temperature
may further enhance operating efficiency.
Referring to Fig. 4A, another modification is illustrated if the M3-C mode of
operation is utilized. In this modification, M3-C operation is allowed and
effected when
the sensed outdoor ambient air temperature is in the third range of from about
31 F to
about 37 F and stage 2 of the thermostat is calling for heat; and M3-C
operation is also
allowed and effected when the sensed outdoor ambient air temperature is in the
fourth
range of from about 19 F to about 30 F and the first stage of the thermostat
is calling for
heat.
In another embodiment intended for use warmer winter climates such as in the
southeastern or southwestern U.S., the heating demand on the system may be
reduced.
For use in such climates, economizer 30 can be eliminated from the system, and
M3 or
M3-C operation would then involve only full capacity operation of primary
compressor
24 and operation of booster compressor 22
It is typical to incorporate a defrost cycle or operation in heat pump systems
to
prevent accumulation of ice on the outdoor evaporator coil. In the system of
the present
13
CA 02618397 2008-01-17
invention, temperatures are not low enough for icing of the evaporator coil to
be a
problem where only M1 operation is enabled. Accordingly, no provision is made
for
defrost operation whenever the system is enabled foi= operation only in M1.
However, whenever the system is enabled for operation in M2, (M3-C if that
embodiment is incorporated), M3, or M4, provisions must be made for defrost
cycling or
operation. In the present invention, defrost cycling is accomplished on a
demand basis,
i.e., when defrosting is needed, as opposed'to systems where defrosting
operation is
always initiated on a timed basis, whether needed or not.
In the present invention, microprocessor 36 uses an algorithm to calculate a
defrost trigger temperatureTl based on the outdoor ambient temperature sensed
by sensor
48. A second temperature sensor, sensor 50, is positioned on conduit 34 just
upstream of
the entrance to outdoor evaporator coi128, whereby sensor 50 senses the
temperature T2
of the boiling refrigerant entering the evaporator coil, and a signal
commensurate with
T2, i.e., the temperature of the boiling refrigerant entering the evaporator
coil, is sent to
microprocessor 36. When T2 is less than or equal to T1, i.e., T2 :91, for a
predetermined
period of time, e.g., ten minutes, thus indicating a possible icing condition
at outdoor coil
28, then defrost operation is triggered. In the present invention, separate
algorithms are
used to calculate the defrost trigger temperature (DTT) depending on whether
the system
is operating in M2 or M3. -
When the system in operating in M2, a typical algorithm is as follows:
Mode 2 DTT (Tl) = 0.850 x A F - 10.50
When the system is operating in M3, a typical algorithm is:
Mode 3 DTT (T1) = 0.7075 x A F - 19.625
where, in both cases, A F is the outdoor ambient air temperature sensed by
sensor 48 and
delivered to microprocessor 36. These algorithms, which are linear functions
of outdoor
14
CA 02618397 2008-01-17
air temperature, are illustrated in Fig. 5. Referring to Fig. 5, line 100
represents the
outside air temperature; line 102 represents a temperature commensurate with
the
temperature of boiling refrigerant in outdoor coi128 when the coil is free of
frost or ice in
M2 operation of the system; line 104 represents a temperature commensurate
with the
temperature of boiling refrigerant in outdoor coi128 in M2 operation with a
sufficient
accumulation on the coil of frost or ice to trigger defrost operation if the
temperature
sensed by sensor 50 stays at or below line 104 for a predetermined time; line
106
represents a temperature commensurate with the temperature of boiling
refrigerant iri
outdoor coi128 when the coil is free of frost or ice in M3 operation; and line
108
represents a temperature commensurate with the temperature of boiling
refrigerant in
outdoor coil 28 in M3 operation with a sufficient accumulation on the coil of
frost or ice
to trigger defrost operation if the temperature sensed by sensor 50 stays at
or below line
108 for a predetermined time.
When microprocessor 38 determines that T2 _<Tl for ten minutes, the
microprocessor generates a signal to commence defrost operation. That defrost
operation
signal effectively puts the heat pump system in the cooling mode of operation
(See Fig.
3). To that end, a signal is delivered from the microprocessor to 4 way valve
32 to move
the valve to reverse the flow of refrigerant in conduit system 34. A signal is
also
delivered from the microprocessor to primary compressor 24 to operate the
primary
compressor at full capacity, i.e., in cooling M2. The booster compressor and
the
economizer are not operative in the defrost mode. During the defrost
operation, airflow
over outdoor coil 28 is terminated, but airflow over indoor coil 26 is
maintained in order
to absorb sufficient thermal energy to effect ice/frost removal on the outdoor
coil.
As shown in Fig. 3, with 4 way valve 32 moved to the cooling position to
effect
defrost operation, refrigerant vapor discharged from primary compressor 24 is
delivered
to outdoor coil 28, which is now functioning as a condenser. The vapor gives
up its heat
of condensation as it cools while circulating through outdoor coi128 thus
melting any ice
or heavy frost that has accumulated on coil 28 to effect the defrost
operation. The
CA 02618397 2008-01-17
refrigerant then flows through check valve 46 and around expansion valve 50
and is
delivered as cool liquid to the liquid side of economizer 30. The liquid
refrigerant flows
through the liquid side of the economizer and is expanded through expansion
valve 40
and is delivered as cool liquid (along with some flashed vapor) to indoor coil
26 which is
now functioning as an evaporator. The resulting cool refrigerant vapor is then
delivered
through 4 way valve 32 and check valve 52 in conduit 54 to the inlet to
primary
compressor 24 to continue the defrost cycle.
The defrost cycle continues to operate until the condensed liquid refrigerant
exiting the outdoor coil becomes sufficiently warm thus indicating complete
removal of
ice or heavy frost from the outdoor coil. At this point, responding to a now
warm T2
(about 70 F) the microprocessor sends a signal effecting 4 way valve movement
to the
position shown in Figs. 1 and 2, and the system resumes operation in the
heating modes.
To operate the system in a cooling or air conditioning mode, thermostat 38 is
moved to its air conditioning position, whereby a first stage signal is
delivered from the
thermostat to microprocessor 36 whereby a signal is delivered from the
microprocessor to
4 way valve 32 to position the valve as shown in Figure 3, and to enable
operation of
only primary compressor 24. Without regard to the outside air temperature
signal from
thermostat 48, whcn cooling is called for by the room temperature exceeding
the
thermostat setting, the signal from the microprocessor to primary compressor
24 operates
the primary compressor first in partial capacity mode M1 to circulate
refrigerant flow as
described above for defrost operation. Air flowing over indoor coi126 is then
cooled to
cool the space to be cooled. If partial capacity operation M1 proves
insufficient to satisfy
the thermostat after a predetermined time, or if the rate of the temperature
of the
temperature of the air being cooled is not fast enough, the thermostat
delivers a stage 2
signal to the microprocessor, and the microprocessor operates the primary
compressor in
full capacity M2.
In the preferred embodiment of this invention, neither M3 nor M3-C operation
is
enabled for cooling operation. However, for very hot climates, such as the
southern or
16
CA 02618397 2008-01-17
southwestern U.S. in summertime, an alternative embodiment would enable M3-C
and/or
full M3 operation of the system in cooling operation. In this embodiment, M1
and M2
operation are effected by the microprocessor when the signal from air
temperature sensor
48 indicates an outdoor air temperature in a first range of temperatures, and
the first and
second stages of the thermostat call for M 1 and M2 operation, respectively.
For an
outdoor air temperature sensed by temperature sensor 48 above the first range
of
temperatures, microprocessor 36 would effect full capacity operation of
primary
compressor 22, booster compressor 24 and economizer 30 for cooling operation
(M3), or
cyclical on-off (M3-C) operation of those components, if operation in M2 is
not sufficient
to satisfy the thermostat setting. The M3 or M3-C operation in cooling is
shown in Fig
3A.
The heat pump system may also include a refrigerant charge compensator that
acts to reduce the refrigerant charge active in the system condenser during
any operating
mode causing booster compressor operation. Whenever the booster compressor is
idle
for any significant period of time, a significant amount of refrigerant vapor
will condense
into the booster oil in the booster sump. This occurs because the refrigerant
is essentially
100% miscible in the oil. The refrigerant vapor condenses into the booster oil
when
agitation ceases upon shutdown of the booster compressor, and continues to
condense as
the booster oil temperature falls with the end result being that about 10%
more refrigerant
charge must be added to the system charge to ensure all operating modes
without the
booster will always have sufficient operating refrigerant charge. However, the
refrigerant
thus absorbed into the booster oil comes out of the booster oil-refrigerant
solution very.
quickly upon booster startup and can overcharge the refrigerant system. This
excess
charge can cause a backup of liquid refrigerant in the condenser, thus
reducing the
effectiveness of condenser operation. This, in turn, can result in the primary
compressor
drawing more power and result in a reduction in the overall efficiency of the
heat pump
system. This problem can be avoided by incorporation of a refrigerant charge
compensator 64 in the system (see Fig. 6). The compensator vesse164 can be
located
almost anywhere in the cold air stream leaving the system evaporator 28.
Charge
17
CA 02618397 2008-01-17
compensator 64 is connected via conduit 65 to conduit 60, and thus it is
connected both
to line 56 and the discharge from booster compressor 22. Compensator 64 serves
to
condense and accumulate the excess refrigerant charge coming out of the
booster oil
whenever the booster is operational. This happens because the compensator is
connected
to the booster discharge line, and the pressure in the booster discharge line
always
exceeds the saturation temperature/pressure existing in the cold compensator
vessel
whenever the booster is operating: When the booster is not operating the
refrigerant
liquid charge accumulated in compensator 64 is released from the compensator
and is
subsequently reabsorbed by the oil in the booster sump.
While preferred embodiments have been shown and described, various
modifications and substitutions may be made thereto without departing from the
spirit
and scope of this invention. Accordingly, it is to be understood that the
present invention
has been described by way of illustration and not limitation.
18
