U.S. patent number 3,777,505 [Application Number 05/164,540] was granted by the patent office on 1973-12-11 for defrosting method and apparatus.
This patent grant is currently assigned to Mitsubishi Jukogyo Kabushiki Kaisha. Invention is credited to Takashi Otaki.
United States Patent |
3,777,505 |
Otaki |
December 11, 1973 |
DEFROSTING METHOD AND APPARATUS
Abstract
In a method of defrosting a first heat exchanger, on the heat
source side of refrigerating apparatus having a second heat
exchanger on the utilization side and a fluid flow circuit
interconnecting the two heat exchangers, the maximum temperature
difference between the inlet fluid temperature and the outlet fluid
temperature of the second heat exchanger is determined. During
operation of the refrigeration apparatus, the difference between
the inlet and outlet fluid temperatures of the second heat
exchanger is detected and, when the ratio of the detected
temperature difference to the maximum temperature difference
decreases below a preset value, due to icing or frosting of the
first heat exchanger, defrosting of the first heat exchanger is
initiated. The apparatus includes temperature sensing means
detecting the inlet fluid temperature and the outlet fluid
temperature of the second heat exchanger and conjointly controlling
swinging of a first lever about a pivot. In moving toward the
maximum temperature difference, the first lever carries with it a
second lever which is pivoted coaxially with the first lever. When
the temperature difference decreases, the first lever moves in the
reverse direction with the second lever being retained in its
position and, after a preselected movement of the first lever
relative to the second lever, a switch means is operated to
initiate the defrosting operation, with the defrosting operation
being terminated upon return of the first lever to the position of
the second lever.
Inventors: |
Otaki; Takashi (Okazaki,
JA) |
Assignee: |
Mitsubishi Jukogyo Kabushiki
Kaisha (Tokyo, JA)
|
Family
ID: |
22594972 |
Appl.
No.: |
05/164,540 |
Filed: |
July 21, 1971 |
Current U.S.
Class: |
62/81; 62/156;
62/160 |
Current CPC
Class: |
F25D
21/002 (20130101) |
Current International
Class: |
F25D
21/00 (20060101); F25d 021/06 () |
Field of
Search: |
;62/140,156,80,81,22,160 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Perlin; Meyer
Claims
What is claimed is:
1. A method of defrosting a first heat exchanger on the heat source
side of refrigerating apparatus, having a second heat exchanger on
the utilization side, and a fluid flow circuit interconnecting the
two heat exchangers, comprising the steps of determining the
maximum temperature difference between the inlet fluid temperature
and the outlet fluid temperature of the second heat exchanger;
during operation of the refrigerating apparatus, detecting the
difference between such inlet and outlet fluid temperatures of the
second heat exchanger; and, when the ratio of the detected
temperature difference to the maximum temperature difference
decreases below a preset value, due to icing of the first heat
exchanger, initiating defrosting of the first heat exchanger.
2. A method of defrosting, as claimed in claim 1, including
continuing the defrosting until the ratio of the detected
temperature difference to the maximum temperature difference
re-attains the preset value; and then terminating the
defrosting.
3. A method of defrosting, as claimed in claim 2, including the
step of, when the ratio of the detected temperature difference to
the maximum temperature difference decreases below such preset
value to another and lower preset value, initiating forced heating
of the first heat exchanger.
4. Apparatus for controlling defrosting of a first heat exchanger,
on the heat source side of refrigerating apparatus, having a second
heat exchanger, on the utilization side, and a fluid flow circuit
interconnecting said two heat exchangers, comprising, in
combination, respective temperature sensing means detecting the
temperature of the fluid entering said second heat exchanger and
detecting the temperature of the fluid leaving said second heat
exchanger; first means operable by said temperature sensing means
to determine and store the maximum temperature difference between
the inlet fluid temperature and the outlet fluid temperature of
said second heat exchanger; second means operable by said
temperature sensing means, during operation of the refrigerating
apparatus, in accordance with the difference between the inlet and
outlet fluid temperatures of said second heat exchanger; and third
means operable conjointly by said first and second means, when the
ratio of the detected temperature difference to the maximum
temperature difference decreases below a preset value, due to icing
of said first heat exchanger, to iniitiate a defrosting cycle of
said first heat exchanger.
5. Apparatus, as claimed in claim 4, in which said first and second
means conjointly operate said third means to terminate defrosting
responsive to the ratio of the detected temperature difference to
the maximum temperature difference re-attaining said preset
value.
6. Apparatus, as claimed in claim 4, including fourth means
operable by said second means when the ratio of the detected
temperature difference to the maximum temperature difference
attains a predetermined value which is below said preset value, to
initiate forced heating of said first heat exchanger.
7. Apparatus for controlling defrosting of a first heat exchanger,
on the heat source side of refrigerating apparatus, having a second
heat exchanger, on the utilization side, and a fluid flow circuit
interconnecting said two heat exchangers, comprising, in
combination, respective temperature sensing means detecting the
temperature of the fluid entering said second heat exchanger and
detecting the temperature of the fluid leaving said second heat
exchanger; first means operable by said temperature sensing means
to determine and store the maximum temperature difference between
the inlet fluid temperature and the outlet fluid temperature of
said second heat exchanger; second means operable by said
temperature sensing means, during operation of the refrigerating
apparatus, in accordance with the difference between the inlet and
outlet fluid temperatures of said second heat exchanger; and third
means operable conjointly by said first and second means, when the
ratio of the detected temperature difference to the maximum
temperature difference decreases below a preset value, due to icing
of said first heat exchanger, to initiate a defrosting cycle of
said first heat exchanger; said second means comprising a first
lever pivoted intermediate its ends and subjected to both said
temperature sensing means operating on an end of said lever in
opposition to each other; said first means comprising a second
lever in opposition to each other; said first means comprising a
second lever pivoted coaxially with said first lever and movable by
said first lever in a direction corresponding to the maximum
temperature difference between the inlet fluid temperature and the
outlet fluid temperature of said second heat exchanger; said second
lever having a pointed free end; and a spring biased finely
serrated member engageable with the pointed end of said second
lever and operable to retain said second lever at a position
corresponding to the maximum temperature difference between the
inlet fluid temperature and the outlet fluid temperature of said
second heat exchanger; said first lever being movable away from
said second lever by said temperature sensing means responsive to a
decreaese in the temperature difference between the inlet fluid
temperature and the outlet fluid temperature of said second heat
exchanger.
8. Apparatus, as claimed in claim 7, including a first adjustable
resistor operable by said first lever; a second adjustable resistor
operable by said second lever; and a source of potential; said
third means comprising a bridge circuit connected to said source of
potential and including said first and second adjustable resistors
and a pair of fixed resistors, said bridge further including a
relay connected between a pair of junctions thereof.
9. Apparatus, as claimed in claim 7, in which said third means
comprises a switch carried by one of said levers and having an
operator, and an adjustable abutment carried by the other of said
levers and engageable with said operator to operate said switch
responsive to a predetermined displacement of said first lever in a
direction away from said second lever; said switch, when operated,
initiating a defrosting cycle of said first heat exchanger.
10. Apparatus, as claimed in claim 9, including a second switch
having a second operator; and a second abutment on said first
lever; said second abutment engaging said operator to operate said
second switch responsive to the ratio of the detected temperature
difference to the maximum temperature difference decreasing to a
second predetermined value below said preset value; said second
switch, when operating, initiating forced heating of said first
heat exchanger.
Description
FIELD OF THE INVENTION
This invention relates to defrosting methods and apparatus and,
more particularly, to a novel and improved method and apparatus for
defrosting a heat exchanger, on the heat source side of
refrigeration apparatus, responsive to measurement of the
temperature difference between the inlet fluid and the outlet fluid
of a second heat exchanger on the utilization side of the
refrigeration apparatus.
BACKGROUND OF THE INVENTION
In refrigeration apparatus of the conventional heat pump type
including a heat exchanger on the heat source side on which frost
is deposited, the defrosting time has been determined on the basis
of changes in state, such as windage loss, etc., due to the
frosting thereof or, alternatively, defrosting has been carried out
periodically by means of timers. Thus, defrosting can be carried
out by means of a timer or based on detection of air pressure loss
in an outdoor coil, on utilization of the temperature difference
between the outdoors and that of the refrigerant, or on detection
of a decrease in the rate of air flow through the outdoor unit. As
a consequence, changes in state of an indoor heat exchanger, on the
utilization side of the refrigeration apparatus, and which
accurately indicate a decrease in the efficiency of heat exchange,
have not been detected. The detection time has been determined
indirectly with reference to a decreased degree in the heat
exchange efficiency, from the operating conditions. Known methods
have the defects of being influenced by outdoor weather conditions
and by interior temperatures.
Thus, a heat exchanger on the heat source side of a refrigeration
apparatus, and placed outdoors, is coated with frost or ice in
dependence upon the operating conditions. As seen from the graph of
FIG. 1, when the frost accumulation exceeds a certain limit, the
heat exchangeability begins to decrease and the heat extraction due
to the outdoor heat exchanger begins to decrease and gradually
approach, in ability, the input of a compressor. In such a case,
the accomplishment coefficient, which is the ratio of heat
exchangeability to unit input, approaches 1, so that the heat pump
is of little effect. Thus, it is necessary to melt away the frost
prior to serious reduction of the efficiency due to the frost
accumulation.
This condition is shown in FIG. 2. In the condition shown in FIG.
2, an extremely frequent defrosting results in an increase of the
area of the hatched regions shown in FIG. 2, or an increase in the
heat exchange by defrosting, which is unfavorable. As a result, it
is necessary to detect the time for defrosting initiation as a
function of the least loss over the time period of operation. Based
on experience, this is the time when the ratio of the temperature
difference between A and B, shown in FIG. 2, attains a value of 0.8
to 0.9. ARI Standard 240, in the United States of America, requires
the ratio to be above 0.9 at the time of defrosting, and the ratio
of the defrosting period to the overall period of operation to be
less than 20 percent.
SUMMARY OF THE INVENTION
The present invention is directed to providing a defrosting method
and apparatus by which there is detected a defrosting initiation
time at which the loss of heat transfer capability, due to
deposition of frost and defrosting during an operating period of
refrigeration apparatus, is minimized. Briefly, in accordance with
the invention, the maximum temperature difference across a heat
exchanger on the utilization side of the refrigeration apparatus is
determined, and the time at which the ratio of the temperature
difference across this heat exchanger to the maximum temperature
difference thereacross is decreased to a certain value is detected.
The method of the invention may be practiced with mechanical,
electrical and electronic apparatus. Furthermore, the method and
apparatus of the invention are applicable equally to mechanical
refrigeration apparatus, electrical refrigeration apparatus, and
other types of refrigeration apparatus.
An object of the invention is to provide an improved method of
defrosting the heat exchanger on the heat source side of
refrigeration apparatus.
Another object of the invention is to provide improved defrosting
apparatus for defrosting the heat exchanger on the heat source side
of refrigeration apparatus.
A further object of the invention is to provide such a method and
apparatus in which defrosting of the heat exchanger, on the heat
source side of a refrigeration apparatus, is initiated responsive
to the temperature difference across a second heat exchanger, on
the utilization side of the refrigeration apparatus, decreasing to
a predetermined value.
For an understanding of the principles of the invention, reference
is made to the following description of typical embodiments thereof
as illustrated in the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
In the drawing:
FIGS. 1 and 2 are graphical illustrations of the changes in heat
exchangeability, as influenced by frost accumulation, in a heat
exchanger on the heat source side of refrigeration apparatus, with
FIG. 1 illustrating the case in which the frost is not melted and
FIG. 2 illustrating the case where defrosting is effected
periodically;
FIG. 3 is a somewhat schematic perspective view of apparatus
embodying the invention;
FIG. 3A is an enlarged sectional view of a portion of FIG. 3;
FIG. 4 is a diagrammatic illustration of the main elements of the
machine shown in FIG. 3;
FIG. 5 is a graphic illustration of the operation of the element
shown in FIG. 4;
FIGS. 6, 7 and 8 are schematic wiring diagrams of three different
embodiments of electric control means in accordance with the
invention;
FIG. 9 is a schematic diagram of apparatus embodying the invention
and utilizing adjustable resistors, in correspondence with FIG. 8;
and
FIG. 10 is a schematic diagram of refrigeration apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 3, a temperature-sensitive cylinder 1, arranged
at the outlet of a heat exchanger on the utilization side of a
refrigeration apparatus, is connected by capillary tubing 2 to a
bellows 4 one end of which is fixed against movement by a fixture
3. The movable end of bellows 4 carries a pin 5 on which is secured
to a disk 6 which transmits displacement of pin 5 to a pin 7 on one
end of a lever 8. A similar temperature-sensitive cylinder 1' is
arranged at the inlet of the heat exchanger on the utilization side
of the apparatus, and connected by capillary tubing 2' to a bellows
4' having one end fixed by a fixture 3' and whose movable end
carries a pin 5' secured to a disk 6' engaging pin 7 in opposition
to disk 6. Thus, the pin 7 is subjected to the difference between
the temperatures measured by cylinders 1 and 1', or the temperature
differs between the outlet and inlet sides of the heat exchanger on
the utilization side of the refrigeration apparatus.
Lever 8 is pivotal about a pin 10 mounted on a fixture 9, and has
arms 8', 8" and 20". Arm 8' adjustably receives a screw 16,
provided with a lock nut 17, for operating a switch 13 through the
medium of a switch operator 15. Arm 8" adjustably receives a screw
18, provided with a lock nut 17', for engagement with a second
lever 12 which is also pivoted on pin 10. Arm 20' adjustably
receives a screw 19, provided with a lock nut 17", for operating a
switch 22 through a switch operator 23. Lever 8 also has arms or
projections 20 and 20' to which respective springs 11 and 11' are
connected, at one end, the opposite ends of these springs being
connected to fixed points.
As stated, lever 12 turns about pin 10, or coaxially with lever 8.
Lever 12 mounts switch 13, and has a pointed tip 12' cooperable
with a finely serrated member 25 positioned in the housing 26 and
biased toward point 12' by a spring 27. Switch 13 has conductors 14
and 14' connected thereto, and switch 22 has conductors 24 and 24'
connected thereto.
When there is no difference in the air temperature between the
inlet and the outlet of the heat exchanger on the utilization side,
the pressures in temperature-sensitive cylinders 1 and 1' are
identical and lever 8 occupies a preselected position, such as the
position D--D, for example, shown in FIG. 4. When a heat exchange
operation is initiated, the pressure in temperature-sensitive
cylinder 1 increases and a force, corresponding to the pressure
difference between the temperature-sensitive cylinders 1, 1', is
applied to pin 7. As a result, lever 8 swings counterclockwise
about pin 10 to an extent determined by the springs 11, 11'. Screw
18 causes lever 12 to turn through the same angle against the
resistance of the serrations of member 25 engaging lever tipped end
12'.
At the maximum temperature difference, which is shown at B in FIG.
2, lever 12 is fixed against movement relative to member 25 by
engagement of tip 12' with the serrations, since there is no longer
any force exerted on lever 12 by screw 18 due to there being no
further motion of lever 8. Thus, the maximum temperature difference
is determined and stored by lever 12. The bias wich which member 25
is engaged with lever tip 12' is so determined as to resist the
force, in the working direction, required to operate the operator
15 of switch 13. As best seen in FIG. 3A, one pitch E of the finely
divided serrations of member 25 is considered to be the maximum
error, and is so determined so as not to interfere with the
operation, in dependence on the length of lever 12 and the pitch
magnitude.
Upon a decrease in the temperature difference from the maximum
value, lever 8 turns clockwise in the direction of a decreased
temperature difference, moving away from lever 12. After a
predetermined clockwise movement of lever 8, screw 16 on arm 8'
engages and depresses operator 15 of switch 13 mounted on lever 12,
which latter remains stationary. Thereupon, switch 13 is operated
so as to either establish a connection between conductors 14 and
14', or to break such a connection, to provide a defrosting
initiation signal. When defrosting has set in, operator 15 is
continuously pushed, switch 13 remaining operated, and lever 12
being pushed downwardly over a serration of member 25, due to the
rapid drop of the air temperature at the outlet of the heat
exchanger on the utilization side, since a switching valve for
cooling and heating of the refrigeration apparatus, and which has
not been shown, has a cooling position. On the other hand, when the
frost on the heat exchanger on the heat source side of the
refrigeration apparatus is melted away, the latter is generally
returned to its initial heat exchange operation by suitable means,
such as the temperaure of the heat exchanger on the heat source
side, or outdoors, pressure, reflection of light, or a change in
electrical resistance, in a known manner. Under these conditions,
lever 8 again turns in a counterclockwise direction responsive to
an increase in the temperature difference between the inlet and
outlet sides of the heat exchanger on the utilization side,
operation of switch 13 is discontinued, and screw 18 moves lever 12
against the resistance of member 25. Thus, the described cycle is
repeated.
If the heating operation does not start in spite of melting away of
the frost, for any reason, the outlet temperature of the heat
exchanger on the utilization side drops extremely. To prevent this,
screw 19 is so positioned as to operate the operator 23 of switch
22 and, responsive to operation of switch 22, a signal for a forced
heat exchange operation can be developed between the conductors 24
and 24'.
An outline of the operation during a normal defrosting cycle is
illustrated in FIG. 4. In this case, when the temperature
difference is zero, lever 8 is on the line D--D. At a maximum
temperature difference, the line connecting the axis of pin 10 with
the operating point of operator 15, and the line connecting the tip
of screw 16 with the axis of pin 10, make an angle .alpha. with
each other. The angle between the line connecting the center of
screw 16 with the axis of pin 10 and the line D--D is .theta.. The
angle .theta. is proportional to the temperature difference
determined in dependence on various operating conditions. The point
F is the intersection of a line drawn parallel to the line D--D,
through the center of screw 16, with the line connecting the center
of operator 15 and the axis of pin 10. The ratio of the temperature
difference at this time, where a signal for initiating defrosting
is provided, to the maximum temperature difference, which is the
ratio A/B of FIG. 2, is A/B in FIG. 4, and is indicated graphically
in FIG. 5. At this time, .theta., .alpha., and A/B have the
relation shown in FIG. 5. Of course, an adjustment may be effected
so that there is no change in the ratio A/B, by changing the angle
.theta..
FIG. 6 is a schematic diagram of the electric circuit of the
apparatus without the switch 22. An operating potential is applied
across the terminals 61, 62 and the reference character 63
indicates a switch forming part of the indoor thermostat and which
is closed when the refrigerating apparatus has stopped operating.
The switch 64 is the connection between the conductors 14, 14' of
FIG. 3, and the switch 65 provides the signal for termination of
defrosting. The operating winding for a switching valve in the
refrigerant circuit is indicated at 66, and the winding controlling
the outdoor fan motor is indicated at 67.
When the refrigerating apparatus stops operating under the control
of the indoor thermostat, the temperature difference at the
utilization side becomes near zero. At this time, switch 63 of the
thermostat operates in a manner so as not to provide a defrosting
start signal. Assuming that the switch 65 is a thermostat operated
switch, defrosting is not effected until the temperature of the
outdoor coil drops to a certain extent, depending upon the
preselection of its working point. For terminating defrosting, the
thermostat is so selected that the temperature of the outdoor coil
may indicate a condition under which the ice or frost has been
completely melted. When all the switches 63, 64 and 65 operate, the
control windings 66 and 67 are deenergized, and defrosting is
initiated. The switch 65 of the defrosting termination thermostat
provides a defrosting termination signal when it is closed, and the
heating operation is restarted.
The circuit diagram of FIG. 7 is used with the switch 22. Referring
to FIG. 7, an operating potential is applied at the terminals 71,
72, and the switch 73 constitutes a switch of the indoor thermostat
with the siwtch 74 being the connection between the conductors 14,
14' of FIG. 3. A switch 75 is provided to generate a defrosting
termination signal. A relay 78 has a normally closed contact 78'
and a normally open contact 78", with contact 78" controlling the
energizing circuit of relay or operating windings 76 and 77. Switch
79 represents the connection between conductors 24, 24' of switch
22, and 80' represents holding contacts of relay 80 which also has
normally open contacts 80".
If switch 79 is closed with switch 74 remaining open while lever 8
pushes lever 12, that is, defrosting has been terminated as switch
75 remains closed, the temperature of the refrigerant drops, switch
79 is closed, and thus switch 80" is closed to start the forced
heating operation.
As mentioned above, in accordance with the invention, defrosting is
initiated when the temperature difference between the fluid at the
inlet and the fluid at the outlet of a utilization side heat
exchanger is reduced a slight amount to a previously set ratio to
the maximum temperature difference. As a result, it is easily
possible to detect a decrease in heat exchange ability required for
substantive utilization, and to minimize the loss of heat
absorption due to accumulation of frost, over the entire period of
heating, and to defrosting, by selecting the time at which
defrosting actually is required by virtue of the system
conditions.
An electrical arrangement utilizing adjustable slide type
resistances is shown schematically in FIG. 8. In this arrangement,
the adjustable contacts of the resistances are secured to the
levers 8 and 12. The operating potential is applied across the
terminals 81, 82, with switch 83 being part of the indoor
thermostat, switch 84' controlling initiation of deicing and being
operated by relay winding 84, and switch 85 providing the signal
for termination of defrosting. The switching valve operating
winding and the operating or control winding for the outdoor fan
motor are illustrated at 86 and 87, respectively, and operate in
the same manner as previously described. Adjustable resistance 88
is adjusted by lever 8, and adjustable resistance 89 is adjusted by
lever 12. Together with resistances 88 and 89, fixed resistances 91
and 92 form a bridge circuit.
With respect to adjustable resistances 88 and 89, the positions of
lever 8 and lever 12 are so determined that the resistance value of
resistor 89 may correspond to the desired value of the previously
set ratio to the resistance value of resistor 88, at a maximum
temperature difference. The position of the maximum temperature
difference is mechanically memorized by lever 12, and then the
resistance value is determined. With the decrease in the
temperature difference, the resistance of resistor 88 begins to
decrease from the value corresponding to the maximum temperature
difference. When the value becomes equal to the resistance value
previously set on resistor 89, the voltage applied to relay winding
84 becomes zero, and relay contact 84' is closed. It will be
understood that relay winding 84 may have an amplifier associated
therewith. As in the case of FIG. 7, a forced heating circuit may
also be included in the control circuit shown in FIG. 8.
FIG. 9 illustrates the mechanical components corresponding to FIG.
8. It will be noted that taps on levers 8 and 12 are cooperable
with the resistances 88 and 89, respectively, to adjust the
effective values of these resistances.
FIG. 10, as stated, is a schematic diagram of refrigeration
apparatus embodying the invention and illustrating the first heat
exchanger with forced heating as well as illustrating the second
heat exchanger. It is believed that the other elements are
sufficiently apparent from FIG. 10 that further description would
seem unnecessary.
Although not illustrated in the drawing, it is possible to combine
a circuit, memorizing a maximum temperature difference, with a
circuit setting the ratio, comparing this with the temperature
difference in a practical situation, and amplifying and actuating a
relay in an electronic manner. The present invention can be applied
to heat pump air-conditioners with an air heat source, an to
refrigeration apparatus. It is also applicable to arrangements in
which the utilization side of the refrigerant is a liquid, such as
water.
While specific embodiments of the invention have been shown and
described in detail to illustrate the application of the principles
of the invention, it will be understood that the invention may be
embodied otherwise without departing from such principles.
* * * * *