Note: Descriptions are shown in the official language in which they were submitted.
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Self-contained air conditioning units of the reversible
type which are adapted to be mounted in the outer wall of an -`
enclosure and utilized for heating the air from the en-
closure during the winter and cooling the air from the
enclosure during the summer comprises a housing divided
into an indoor section and an outdoor section. An indoor
hea~ exchanger is disposed in the indoor section while an -
outdoor heat exchanger and usually the compressor are
located in the outdoor section. The compressor is re- `
10 versibly connected to the heat exchangers so that the in- `
door heat exchanger functions as an evaporator when the
unit is operating on the cooling cycle and the outdoor heat
exchanger functions as the evaporator on the heating cycle.
Suitable independent fan means are provided for circulating
indoor air oVer the indoor heat exchanger and outdoor air
over the outdoor heat exchanger during operation of the
system on either the heating or cooling cycle.
Under certain operating conditions, the outdoor heat
exchanger functioning as the evaporator may operate at
such a low temperature as to cause the accumulation of a
coating or layer of frost thereon. Since such a frost
layer operated as a barrier to heat transfer between the
evaporator and the air being circulated over the evaporator,
the efficiency of the unit is markedly reduced. Also,
unless means are provided for interrupting this accumula-
tion of frost, the evaporator can become completely filled
with a layer of frost which may eventually cause motor
or other damage to the unit.
Accordingly, by the present invention, there is provided
a self-contained heat pump including control circuitry
including a pair of thermostats comprising sensing elements
subjected to both ambient and selected component surface
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temperature whereby the operation of the heat pump is
maintained as long as the temperature sensed by the ther-
mostate is above a preselected frosting level and is in-
terrupted by the coldest preselected temperature sensed by
the elements.
U.S. Patent 3,159,981 dated December 8, 1964 - Huskey,
assigned to the General Electric Company, assignee of the
present invention, discloses a self-contained air condition-
ing unit including a reversible refrigeration system and
a control circuitry designed to interrupt the operation
of the refrigeration system whenever either the outdoor
- or indoor heat exchanger attains a frosting temperature
and to supply auxiliary heat to an enclosure whenever the
operation of the refrigeration system is thus interrupted
during a heating cycle. The frost control switch includes
a vapor-filled bellows and capillary tube sensing element
connected to the bellows. The tube is arranged with a
first portion in contact with one of the heat exchangers ~ t
and a second portion in contact with the other heat ex-
changer whereby the bellows operated switch will stop the
compressor when either heat exchanger attains a frosting
temperature.
Another prior art attempt at solving the frosting of
the outdoor heat exchanger when in the heating cycle it is ~
operating as an evaporator, is disclosed in U.S. patent ~ ~;
3,466,888 dated September 16, 1969 - Kyle. The control
circuitry includes a first thermistor in heat exchange
contact with the outdoor coil and a second thermistor is ~;
exposed to the temperature of the outdoor air. The two ~ ;
thermistors are connected in series. When frost forms
on the surface of the outdoor heat exchanger, the tempera-
ture of the refrigerant therein decreases, and the voltage
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at the junction of the thermistor changes, and operates
a control circuit which stops the fan of the outdoor ;` ~;
coil, and reverses the flow of refrigerant so that the
outdoor coil operates as a condenser coil to melt the
frost.
U.S. patent 3,348,607 dated June 10, 1969 - Cootey ~ `
discloses a split-bulb or dual-bulb thermostat wherein a
sensing element is located in the path of return air and
the other in the outdoor or ambient air. The sensing
10 elements are proportioned in size relative to each other -
and both elements transmit motion to a single power element
in response to changes in the temperature of the air
affecting the elements.
The present invention is an improvement of the ~ ~-
control system disclosed in Canadian Patent Application
:
Serial No. 276,629 - William J. McCarty, dated May 2],1977 ~-
and assigned to the General Electric Company, the assignee -~
of the present invention, and relates to a self-contained
air conditioning unit for heating and cooling an enclosure. `-
- 20 The refrigeration system includes an outdoor heating ex-
changer, an indoor heat exchanger, a compressor, a valve `
for selectively connecting the compressor to the heat ~
exchangers whereby the outdoor heat exchanger functions - ~i
as an evaporator during operation of the unit on the heating
cycle and the indoor heat exchanger functions as an evaporator
during operation of the unit on the cooling cycle, and air
circulating fans including a fan for moving enclosure air
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through the indoor heat exchanger and a fan for moving
outdoor ambient air through the outdoor heat exchanger. ~
More particularly, the invention relates to an air con- ~ ;
dition heating cycle control for preventing excessive -
frosting of the outdoor heat exchanger by selectively con-
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trolling the operation of the refrigeration system, and for
energizing auxiliary heating means when the refrigeration
heat pump system cannot maintain a selected comfort level.
The control system includes a first thermostat having
a vapor filled bellows and a capillary tube sensing element
connected to the bellows. One portion of the element is
exposed to the surface temperature of the outdoor heat ex-
changer and another portion of the element is exposed to
the outdoor condensate drain area. A switch operable by
the bellows is effective in de-energizing the compressor
when either of the portion's elements sense a preselected
frosting temperature.
A second thermostat similar to the first thermostat
has a portion of its element exposed to refrigerant line
temperature adjacent the reversing valve tube which is
on the suction side during heating and another portion
of the element exposed to the ambient outdoor temperature.
A switch operable if ether of the elements senses a pre-
" selected frosting temperature is effective to control
operation of the outdoor fan through the first thermostatwhen the switch of the first thermostat is positioned
to de-energize the compressor and to control operating
of the fan independent of the first thermostat when the ;
ambient and sensed refrigerant line temperature are above
a preselected frosting temperature.
The first and second thermostats are operable through
a two-stage room termostat that is effective in placing
the unit in the heat mode and energizing the compressor at
a predetermined temperature in one stage and for de-
energizing the compressor and energizing a heating meansat a second predetermined temperature in the second stage.
Figure 1 is a diagrammatic view of a self-contained
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heat pump air conditioner unit embodying this invention; and
Figure 2 is a simplified schematic diagram of electrical
control circuitry adapted to control the unit in accordance
with the present invention.
Referring to Figure 1 of the drawing, there is shown
schematically an air conditioning refrigeration system
of the reversible or heat pump type divided by means of
a partition 10 into an outdoor section 11 and an indoor
section 12. A reverse cycle refrigeration system com- '
prises a compressor 14 and an outdoor heat exchanger 16
mounted within the outdoor section 11 and an indoor heat
exchanger 18 mounted within the indoor section 12. The
outdoor heat exchanger 16 and indoor heat exchanger 18 ;-
are connected by means of a suitable flow restriction
means such as a capillary tube 19 while the compressor is
connected to the heat exchangers through a reversing valve
20 operated by a solenoid 21 so that the indoor heat ex-
changer 18 can be connected to the compressor either as
an evaporator or as the condenser component of a refrigera-
tion system.
During operation of the system as a heat pump or in
heating cycle, the reversing valve 20 directs the flow ~ -
of high temperature refrigerant gas from the discharge
line 22 of compressor 14 through a line 23 into the in-
door heat exchanger 18 which then functions as a condenser
to warm the air to be conditioned, and to condense the re- -
frigerant gas into liquid form. The refrigerant is
partially or completely condensed by the air circulated
through the indoor heat exchanger 18 by fan 26. The
refrigerant then flows through line 25 including expansion
device 19 to the outdoor heat exchanger which is now
functioning as an evaporator and then back through valve
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20, suction line 27, and into the compressor 14.
During operation of the system in the cooling cycle,
high pressure refrigerant gas is directed by the reversing
valve 20 into the outdoor heat exchanger 16 through a line
28 where the high pr~ssure refrigerant gas is condensed by
the air circulated through heat exchanger 16 by fan 29.
The refrigerant then flows through line 25 including ex-
pansion device 19 to the indoor heat exchanger 18 which is
now functioning as an evaporator and then back through line
23, valve 2Q, suction line 27 and into the compressor 14.
An auxiliary heater in the form of an electrical re-
sistance heat 30 is preferably provided in the indoor
section in the path of air flowing through the indoor
heat exchanger 18 for the purpose of supplying heat to the
airstream under certain operating conditions when heat
supplied by the indoor heat exchanger 18 operating as a
condenser cannot satisfactorily maintain the enclosure
being heated at a preselected temperature.
Positioned within the unit at some point in the
airstream upstream from the heat exchanger 18 is a staged
thermostat 32 which controls the operation of the unit
on either the heating or the cooling cycle. This thermo-
stat 32 is of the type well known in the art and, as
employed in the present embodiment of the inven-tion, in-
cludes sensing means 33 responsive to the temperature of
the indoor air for actuating switching means 57 and 58
in the control circuit in a manner to be fully explained
hereinafter. In the illustrated embodiment of the invention,
this temperature responsive means 33 is arranged in the air-
stream flowing from the enclosure and into the indoor section.
The unit is also provided with a main or selector switch 34
(Figure 2) through which electrical supply from supply lines
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36-37 is connected to the unit and by means of which the
operator of the unit may select operation thereof of the i~
unit on either the heating or the cooling cycle.
In accordance with the present invention, the unit
also includes a pair of frost control thermostats or switches
38 and 30 which may be conveniently mounted on the outdoor
section 11 and which are activated by a vapor-filled bellows
41, 42 respectively, and include capillary tube sensing
elements 43, 44 connected to the bellows 41, 42 respectively.
The sensing element 43 of switch 38 is arranged to
maintain operation of the refrigeration system compressor
14 energized in the heat pump mode when the drain area and
surface temperature of heat exchanger 16 are both above
a preselected frost accumulation level, and to interrupt
the operation of the compressor 14 whenever either heat
exchanger 16 or the drain area temperature indicates an
excessive frosting condition or temperature during operating
of the unit on the heating cycle. To this end, the
capilla~y sensing element 46 is arranged so that it includes
a first portion 46 which continuously senses the temperature
of the outdoor heat exchanger 16 and a second portion 47
which continuously senses the drain area temperature, and
more particularly the presence of ice.
The sensing element 44 of switch 40 is arranged to
maintain operation of the outdoor fan motor 28 when the -
temperature of the relatively cold line 28 in the heating
mode and the ambient outdoor temperature are both above
the freezing range, and to interrupt operation oE the fan
29 when either line 28 or the ambient temperature is below
freezing temperature, when the unit is on in the heating cycle
and control 38 has interrupted operation of the compressor
14. To this end, the capillary sensing element 44 is arranged `
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so that it includes a first portion 48 which continuously
senses the outdoor or ambient temperature and a second
portion 49 which continuously senses the temperature of
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the line 28 adjacent the reversing valve 20.
As is well known, a vapor-filled capillary-bellows
type of thermostat has the characteristic of controlling
from the coldest point of the bellows-capillary system
due to the fact that a vapor-liquid boundary is formed
at the coldest point and this boundary establishes the
vapor pressure of the capillary-bellows system. Hence,
the operation of the frost control switch 38 will be
controlled by either of its sensing portions 46, 47 de-
pending on which is colder, while the operation of the
frost control 40 will be controlled by either of its
sensing portions 48, 49 depending on which is colder. ;~
While in the preferred embodiment of the invention dis-
closed, vapor-filled capillary-bellows type thermostat
controls have been used successfully, it should be under- `
stood that other controls and components may be employed
that provide control from the coldest point sensed.
Generally, during repeated defrosting cycles, ice
will re-form in the drain area quickly since it is the
last place to melt or leave the drain area. Accordingly,
positioning portion 41 adjacent the drain will, since ;
switch member 61 does not trip until 35F. is sensed,
assure that all of the ice has melted from the drain area
and in fact water is running through the drain. However,
it may be possible that other points or areas of the unit
could provide adequate temperature readings relative to
ice or frost accumulation; for example, any area where ice
or frost would normally accumulate in a unit.
For a more complete understanding of the control circuitry,
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and the manner in which frost buildup is controlled,
reference is made to the wiring diagram shown in Figure
2 of the drawing. As mentioned hereinbefore, the main or
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selector switch 34 allows energization of the air condition-
ing unit, and selects the operation thereof on either the
heating or cooling cycle. Switch 34 includes a plurality
of switching means 51 movable between a cooling contact 52
and a heatlng contact 53 by which the operation of the unit
on either the cooling cycle or the heating cycle can be
selected. Switch 34 also provides a circuit through its
contacts 54 to selectively operate the indoor fan motor
26 on high or low fan speed. -
In operation with the selector switch 34 in the heat
position, a circuit is completed from line 36 through
contact 53, solenoid 21 to activate the reversing valve
20 thereby placing the refrigeration system in the heat
pump mode. Cooling contact 52 and heating contact 43 of ;
selector switch are connected to cooling and heating con-
tacts 55, 56 respectively, of thermostat 32. Accordingly,
the switching means 57 of thermostat 32 is arranged to
supply power to the remaining control circuit through
contact 55 in the cooling mode with contact 56 in the
heating mode. Thermostat 32 is also provided with switching
means 58 electrically connected to switching means 57 which
are movable between a contact 59 which controls operation
of the compressor 14 and outdoor fan motor 29 through ~-
controls 38 and/or 40, and a contact 60 which controls
operation of heater 30.
Power from supply line 36 passes through switch means
58 and contact 59 of thermostat 32 to the switching means ~ `~
61 of the frost control 38 whose contacts are arranged to
be closed above a preselected temperature and open below a
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preselected temperature. It should be noted that the indoor
fan 26 will run continuously at its preselected speed during
operation of the unit on either the heating or the cooling
cycle. The switching means 62 of frost control ~0 which
controls the operation of the outdoor fan motor 29 is ar-
ranged to move between an upper temperature contact 63 and
a lower temperature contact 64. Accordingly, power is
supplied to contact 63 through switching means 58 from
contact 59 of thermostat 32 through line 65, while contact
64 receives power from contact 66 of control 38 through line
67.
In operation, when the drain area sensed by portion -
47, and the surface temperature of heat exchanger 16 sensed
by portion 46 of capillary 43 are both above a preselected
upper or frost accumulation temperature, a circuit is
completed through control 38, switch means 61, contact 66,
line 68, and compressor 14, to energize the refrigeration
system in the heat pump mode. In the event that the
ambient or outdoor temperature sensed by portion 48 and ;~
the temperature of the line 28 adjacent the valve 29 sensed
by portion 49 of capillary 44 are both above a preselected
upper or frost producing temperature, a circuit is com-
pleted from line 65, contact 63, switch means 62, fan speed
selector 69, to energize the outdoor fan motor 29. While
the present embodimen`t of the control circuit includes a
fan speed selector 69 capable of modulating between a high
and low fan speed, determined by compressor outlet line
temperature, it whould be noted that the frost control
system of the present invention is not dependent on modulat-
ing the outdoor fan speed and, accordingly, the use of a
fan speed selector switch is optional. ~-
In the event either portion 46 or 47 of capillary 43
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senses a predetermined frost accumulation temperature in .. ::~
the heating mode, the bellows 41 will cause the switching :
means 61 to move from contact 66 to the open position.
The circuit to the compressor 14 will be broken, thereby
de-energizing the refrigeration circuit to prevent addi-
tional frost from forming on heat exchanger 16. If, during
the time the control 38 is positioned by a frosting tem- :
perature to de-energize the compressor 14, either of the
portions 48, 49 of capillary 44 sense a low frost producing
temperature, the bellows 42 will cause switching means 62
of switch 4Q to move from contact 63 to contact 64, so
that the outdoor fan will be de-energized.
It should be noted that the surface temperature of .~
the heat exchanger 16 and line 28 adjacent the valve 20 ~-
will normally be colder than ambient when the unit is
operating in the heat pump mode. Accordingly, portions
46 and 49 will sense the frost producing temperature and :~
in effect be the controlling point. With regard to the
operation of outdoor fan motor 29, the portion 49 sensing .~ ~;
the colder temperature of line 28 has caused switching
means 62 to de-energized the fan motor 29. In this ~ .
situation, the relatively ~arm operating temperatures of .
the discharge line 22 of the compressor 14 will migrate ;~
or be transferred through the reversing valve 20 to the
portion of the line 28 that is provided with element 49,
so that the temperature sensed by portion 49 will very
~ quickly be above the frost producing level, causing switch
: means 62 to switch to contact 63, provided portion 48 is
above preselected temperature, and one again energize ~ .
fan motor 29 to raise the temperature of heat exchanger 16
. relative to ambient to eliminate any frost that may have
collected on the surface of heat exchanger 16. The operation
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of the outdoor fan 29 at this time is beneficial in that
by raising the surface temperature of the heat exchanger
so that the surface temperature of heat exchanger 16 is once
again above the preselected frost producing temperature,
causing switch means 61 to move to contact 66 so that the
compressor 14 will be energized and the refrigeration system
will operate in the heat pump mode to maintain the com-
fort level selected by the thermostat 32. Operation of,
or energization of, heater 30 is controlled by switching
10 means 58 through its contact 60 as will be explained fully -~
after the compressor is de-energized. -
While operation of the control circuit of the present
invention is controlled by the upper and lower temperatures -~
sensed by the capillaries 43 and 44, it should be noted
however that the exact temperatures selected may vary
depending on several factors, including geographic location
of the unit and the exact location of the portions 46 and
49 relative to the refrigeration components. The frost
control system of the present invention has been success-
fully carried out when the temperature range of control
38 was between a high 35F. and a low of 10F. with a
temperature s~ing of 25F., and the temperature range of
control 40 was between a high of 35F~, and a low of 20F.,
with a temperature swing of 5 F.
In summary, the switching means 61 will complete a
circuit through contact 66 when both the surface temperature
of heat exchanger 16 and the ambient air are above 3SF.
and will switch to open the contacts to de-energize the ~ r
compressor if either gets down to 10F., keeping in mind,
; 30 however, that the surface temperature of heat exchanger
16 will be lower than ambient. With regard to switching
means 62, a circuit to the fan motor 29 will be completed
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through contact 63 when both the surface temperature of
line 28 and the ambient are above 350F. and will switch
to contact 64 if either gets down to 25F. to deenergize
the fan motor 29 only if control 38 has sensed a frost
producing 10F. temperature. If control 38 has not sensed
a frost producing temperature then the fan motor will
continue to operate through line 67. ~~`
In operation, regarding the function of the two-stage
thermostat 32 when the temperature of the enclosure being
heated in the heat mode reaches a predetermined comfort
level switching means 57 moves away from contact 56 while
switching means 61 remains in contact with 59 as shown in
Figure 2. In this situation, the circuit to the compressor
14 is open and the heating operation is interrupted. In
the event the temperature drops below the predetermined
comfort level, the switching means 57 will engage contact
56 energizing compressor 14 to supply heat in the heat
pump mode.
If the temperature of the area being heated drops
while the compressor is energized, then switching means
58 will move from control 59 to de-energize the compressor
; 14 and close a circuit through contact 60 thereby energizing
heater 30. The above operation or heating cycle is re-
peated in reverse as the temperature in the are to be
heated rises, switching member 58 will move from contact
60 to de-energized heater 30 and close on contact 59 to
energize the compressor 14. A further rise in temperature
to the predetermined comfort level will move switching
means 57 from contact 56 to contact 55 to de-energize the
compressor 14.
The above operation, with the use of a two-stage
thermostat provides fully automatic switch over from heat
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pump refrigerant mode to electric resistance heat during .
those times that the system in the heat pump mode cannot
provide sufficient heat to satisfy the room thermostat
set at a predetermined comfort level.
It should be apparent to those skilled in the art `:
that the embodiment described heretofore is considered
to be the presently preferred form of this invention. In
accordance with the patent statutes, changes may be made
in the disclosed apparatus and the manner in which it is
used without actually departing from the true spirit and ..
scope of this invention.
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