U.S. patent number 3,894,404 [Application Number 05/492,382] was granted by the patent office on 1975-07-15 for hot gas defrost refrigeration system.
This patent grant is currently assigned to Honeywell Inc.. Invention is credited to David J. Stanton.
United States Patent |
3,894,404 |
Stanton |
July 15, 1975 |
Hot gas defrost refrigeration system
Abstract
A control system for controlling the individual defrosting of a
plurality of evaporators connected to a common refrigeration system
wherein the defrosting is accomplished by the use of hot gas from
the refrigeration system. The need for defrosting of a particular
evaporator is called for either on demand by a frost sensor
associated with the evaporator or by time by a time control. A
sequential control apparatus is used to schedule the defrosting
operation of the evaporators when they are defrosted on demand to
limit the number of evaporators that are being defrosted at any
particular moment as a limited amount of hot gas is available from
the refrigeration system.
Inventors: |
Stanton; David J. (New
Brighton, MN) |
Assignee: |
Honeywell Inc. (Minneapolis,
MN)
|
Family
ID: |
23956045 |
Appl.
No.: |
05/492,382 |
Filed: |
July 29, 1974 |
Current U.S.
Class: |
62/155; 62/157;
62/196.1; 62/278 |
Current CPC
Class: |
F25B
47/022 (20130101); F25B 5/00 (20130101) |
Current International
Class: |
F25B
47/02 (20060101); F25B 5/00 (20060101); F25b
047/00 () |
Field of
Search: |
;62/140,157,158,196,278,155 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Perlin; Meyer
Attorney, Agent or Firm: Hanson; Henry L. Blinn; Clyde
C.
Claims
The embodiments of the invention in which an exclusive property or
right is claimed are defined as follows:
1. In a control system for controlling the individual defrosting of
at least one of a plurality of evaporators connected to a
compressor system wherein the defrosting is accomplished by the use
of hot gas from the compressor system,
frost sensor means adapted to be connected to each of at least two
of a plurality of evaporators of the refrigeration system for
providing an output signal upon the need of defrosting of one of
the evaporators,
sequential control means having a plurality of output circuits for
scanning and for individually initiating a defrost cycle of any one
of the two evaporators which needs defrosting,
a plurality of relay means each having two input circuits and an
output circuit, said relay means is energized when each of said
input circuits receive input signals, and
circuit means connecting said output signal of each of said frost
sensor means to one input of a respective relay means and one of
said output circuits of said sequential control means to a second
input of said relay means whereby upon a frost sensor means of one
evaporator having an output to demand defrost, said relay means is
energized when said sequential control means provides a signal to
said relay means,
said output of each of said relay means being adapted to control
valve means in the compressor system to provide a hot gas
defrosting operation for one of the evaporators at a time depending
upon a demand for defrosting operation by said frost sensor means
and said signal of said sequential control means while normal
operation of the other evaporator is maintained.
2. The invention of claim 1 wherein
each of said relay means has a second output circuit connected to
said sequential control means to inhibit other outputs on said
output circuits of said sequential control means until a defrosting
operation for the one evaporator is completed.
3. The invention of claim 1 comprising
input circuit means connected to said sequential control means
adapted to receive an input from a timer means controlling the
defrosting operation of other evaporators to inhibit said
sequential control means when a time defrost operation is
initiated.
4. The invention of claim 1 wherein said output circuit of said
relay means is adapted to close a refrigeration solenoid valve and
open a hot gas solenoid valve when a defrosting operation is needed
and comprising
time delay means connected in said output circuit so that upon a
termination of the defrosting operation said relay means is adapted
to close the hot gas solenoid, and after a predetermined time to
allow for the evaporator to drip free of water, said relay means is
adapted to open the refrigeration solenoid valve.
5. The invention of claim 1 wherein
said sequential control means is a BCD to decimal converter circuit
for sequentially providing outputs on said output circuits.
6. The invention of claim 3 wherein
each of said relay means has a second output connected to said
sequential control means to maintain a demand defrost operation
already initiated even though said input circuit of said sequential
control means has an input from the timer means.
7. In a control system for controlling a selective demand defrost
operation of individual sets of evaporators connected to a
refrigeration system by furnishing hot gas to a particular set of
evaporators
a plurality of frost responsive means adapted to be connected to
respond to the need of a defrosting operation of individual sets of
evaporators,
sequential control means having a plurality of output circuits upon
which an individual output is provided in a sequential operation
manner,
a plurality of relay means each of which is adapted to control the
delivery of hot gas to one set of evaporators,
circuit means connecting each of frost responsive means for one set
of evaporators to one of said relay means and one of said output
circuits of said sequential control means to said one relay means,
whereby upon said first responsive means of a set of evaporators
providing an output said relay means is energized when said
sequential control means output is available, and
circuit means connected between each of said relay means and said
sequential control means to inhibit said sequential operation once
a defrosting operation of a particular set of evaporators is
started until said relay means is de-energized at which time said
sequential control operates in a sequential manner to the next
relay means.
8. The invention of claim 7 wherein
said sequential control means has an input circuit adapted to be
connected to a timer control for controlling the time controlled
defrosting operation of other evaporators connected to the
compressor system,
said input circuit upon receiving an input signal, indicative of a
time controlled defrost operation taking place, inhibits the
sequential operation of said sequential control means to stop any
further demand defrost operation of other sets of evaporators.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
In refrigeration systems having a plurality of evaporators
connected to a compressor system, a defrosting operation making use
of hot gas from the compressor system is commonly done by the use
of valves to reverse the refrigeration flow so that hot gas
normally passing to the condenser flows through the evaporator to
heat the evaporator and remove any frost. To accomplish such in one
prior art system which has a number of evaporators having frost
sensors to provide an output should an evaporator or set of
evaporators need defrosting, an interlocking relay circuit is used.
When one frost sensor for a particular set of evaporators initiates
a defrosting operation to deliver hot gas to that set of
evaporators, the circuit is modified to prevent any other frost
sensor for other sets of evaporators from being capable of
initiating a defrost cycle. The interlocking relay circuit limits
the amount of hot gas which is drawn from the compressor system for
defrosting to only one set of evaporators at a time; however, such
an interlocking relay circuit is complex and expensive.
The present invention is concerned with an improved control system
for controlling the individual defrosting operation of each of a
plurality of evaporators or sets of evaporators connected to a
common compressor system. The evaporators are defrosted either in
accordance with a time schedule by a time control or upon demand by
a frost sensor responsive to the frost on the evaporator. To
provide for only one defrosting operation to take place at a time,
a sequential control apparatus has a plurality of output circuits
for scanning and individually initiating the defrost cycle of any
one of the sets of evaporators which needs defrosting from a frost
sensor. The sequential control apparatus upon initiating the
defrosting operation of one set of evaporators is then stopped
until that particular set of evaporators is defrosted, at which
time, the sequential control apparatus steps to the next evaporator
for its defrost operation. If a defrost operation is initiated by
the time control, the sequential control apparatus is inhibited to
prevent further demand defrost operations while the time controlled
defrost operation takes place.
FIG. 1 is a schematic showing of the refrigerstion system with
controls for hot gas defrosting.
FIG. 2 is a wiring diagram of the sequential control apparatus.
DESCRIPTION OF THE INVENTION
Referring to FIG. 1, a refrigeration system 10 of a conventional
type which has a plurality of evaporators 11 and 12 and a motor
compressor and a condenser or compressor system 13 provides cooling
to a number of cold storage boxes or spaces each of which having
evaporators through which air is blown by an associated fan.
Evaporator 11 is associated with a first set of evaporators.
Evaporator 12 is associated with a third set of evaporators. From
time to time as frost builds up on the evaporators, a defrosting
operation must be initiated. In this particular system which has a
large number of evaporators, the defrosting of an evaporator or set
of evaporators is accomplished in a conventional manner by
energizing solenoid valves to reverse the refrigeration flow to
deliver hot gas to the evaporator for raising its temperature and
thus melting off the frost. Evaporator 11 may have other
evaporators connected in parallel with/or without frost sensors as
only one evaporator in a set need have a sensor, the others being
slave units. Similarly, evaporator 12 may be a single evaporator or
connected in a third set. The number of evaporators and/or sets of
evaporators connected in the compressor system 10 can vary for
every installation. Since a plurality of evaporators are connected
in the system, the number to be defrosted by hot gas is limited to
the amount of hot gas available. Thus only a selected number of
evaporators can be defrosted at one time. Whether a defrosting
operation need be initiated for a particular evaporator is
determined by either the use of a frost sensor or by time selection
using a timer.
Evaporator 11, as well as others in the first set, has a frost
responsive or sensor apparatus 14 of the type shown in the Clifford
L. Sandstrom et al. U.S. Pat. No. 3,453,837 issued July 8, 1969
having a pair of air temperature sensors 15 and 16 responding to
air temperature difference between the upsteam and the downstream
air through the evaporator 11. A demand defrost operation output
signal is provided on conductor 17 to the input of a conventional
relay 20 through a diode 21. By means of diode 21 and several other
diodes 21', 21" and 21'", a plurality of temperature sensors (not
shown) for other evaporators of the first set, can be connected to
the input of relay 20 and only one sensor controls the relay as the
other diodes are back biased. Upon the presence of an input signal
to relay 20, relay contact 22 is closed to provide an input on a
circuit 23.
A sequential control apparatus 30 contains a stepping switching
device or sequencer 31 which is schematically shown to have a
member move along a plurality of output circuits or contacts 32,
33, 34, etc. to provide output signals in a sequential manner.
Output circuit 32 is connected to a second input 35 of a NAND gate
36 of a relay or switching device 40. A second input of gate 36 is
connected to circuit 23. Upon gate 36 receiving inputs over both
circuits 23 and 35, relay 40 is energized and switching circuits 41
and 42 are adapted to control valves 43 and 44 respectively. Upon
the operation of relay 40, valves 43 and 44 provide for the
termination of refrigerant flow to evaporator 11 as well as others
in the first set and for the flow of hot gas for the defrost
cycle.
While only one such set of valves 43 and 44 are shown, relays 40',
40" and 40'" are similarly connected to receive inputs from both
frost sensor and control 30 to terminate the flow of refrigeration
and initiate the flow of hot gas to other sets of evaporators. For
explanation purposes, the operation of the sequential control
apparatus 30 with one particular relay 40 is shown.
Relay 40 has a feedback circuit 47 connected to input 48 of
sequential control apparatus 30; so that, when relay 40 is
energized to provide for the defrosting operation, the feedback
circuit stops the operation of apparatus 30. Sequencer 31 then
maintains an output on circuit 32 until the defrost operation
associated with the evaporator of relay 40 is terminated. Upon the
termination of the defrost cycle to de-energize relay 40, the
feedback signal on circuit 47 is removed and sequential control 30
steps to the next circuit 33 for relay 40' and another set of
evaporators. NAND gate 36 has a feedback circuit 46 connected to
sequential control 30 for maintaining a defrost cycle in
progress.
Evaporator 12 while connected to the same compressor system 10 has
its defrost operation controlled by a conventional time control or
timer 49 having as a part a switching device or relay 50 which upon
being energized controls the operation of valves 51 and 52 to
terminate refrigerant flow and to provide for the flow of hot gas
to evaporator 12 for a predetermined period of time to defrost the
evaporator. Timer 49 has a plurality of switches which operate in
accordance with some preset time setting to operate a series of
relays similar to relay 50 for controlling valves of other
evaporators. If a time controlled defrosting operation of some
evaporators is provided which may not always be the case, relay 50
has a circuit 53 connected to the input of sequential control 30 to
provide for inhibiting the operation of sequencer 31 as long as the
defrost operation of a evaporator such as 12 by timer 50 is in
operation. Such a connection 53 between relay 50 and sequential
control 30 provides for no demand defrost operation, such as by
relay 40, in the system while a time defrost operation is being
accomplished by timer 50. Circuits 32, 33 etc. of the sequential
control 30 are inhibited to prevent a defrost operation on demand
by a sensor if timer 49 has provided for the defrost operation of a
set of evaporators through relay 50.
Referring to FIG. 2, the sequential control apparatus 30 and relay
40 are shown in more detail. Relay 40 has NAND gate 36 to which
input circuit 23 and 35 are connected, both of which must be
energized in order to energize relay 40. Relay 40 has a pair of
switching circuits or relays 41 and 42 to control valves 43 and 44.
Connected intermediate NAND gate 36 and relay 41 is a conventional
timing circuit 52 to provide a time delay in the de-energization of
relay 41 once the input signal is removed from the NAND gate 36.
Timing circuit 52 is adjustable by various values of resistor 56 to
provide for selected time delay periods. The time delay provides
for a delay in the operation of refrigeration valve 43 until the
evaporator coil has had sufficient time to drip dry of the moisture
after the defrosting operation.
Sequential control apparatus 30 comprises a conventional binary
counter 54 such as TTL Logic 7493 connected to a conventional BCD
to decimal converter 55 such as TTL Logic 74154 for providing for
the energization of the output circuits 32, 33, 34, etc. in a
sequential manner. Input circuit 47 provides for the
de-energization of counter 54 when relay 40 is energized. While
only one relay is shown in FIG. 2, inputs from the other relays
40', 40", 40'", are obtained over circuit 62.
Relay 50 which is operated by timer 49 to control a time controlled
defrost operation of certain evaporators, has an input 53 to
sequential control 30 for terminating the operation of control 30
whenever a time defrost operation is taking place. Specifically
feedback circuit 46 and circuit 53 are connected to the strobe
control circuit 60 of converter 55. If a demand defrost operation
is taking place as evidenced by a feedback on circuit 46, the
output on 46 overrides the effect of the timer output on 53. The
time defrost can not terminate the present output of converter 55
to circuit 32 until the demand defrost operation is completed. If
the system has no time controlled defrost control of evaporators,
input 53 is not used.
OPERATION OF THE INVENTION
As previously mentioned, the sequential control aparatus 30
provides for the energization of only one defrosting operation at a
time when the particular evaporator connected to a refrigeration
system calls for demand defrost as determined by a frost
sensor.
As the sequential control apparatus scans the various relays 40,
40', etc., any one of the relays which has an input signal from at
least one frost sensor is energized to bring about a defrosting
operation. To prevent a drain on the compressor system by having
more than a limited number of evaporators in a defrosting operation
at one time, as only a limited amount of hot gas is available, only
one set of evaporators is defrosted depending on which output
circuit of control 30 has an output.
For the call for defrosting operation of evaporator 11, sensor 14
has an output on circuit 17 to provide for the energization of
relay 20 to place a signal on circuit 23 to the input of NAND gate
36; however, even though the frost sensor 14 calls for a defrosting
of evaporator 11, nothing will take place in the refrigeration
system until the sequential control 30 selects that particular
relay 40 by the energization of circuit 35. At that time,
sequential control 30 is stopped by the signal over circuit 47 and
the defrosting of evaporator 11 is accomplished by the hot gas
delivered through valve 44. Upon the termination of the defrost
cycle as determined by the sensor 14, relay 40 is de-energized to
terminate the flow of hot gas to the evaporator and after a
selectable predetermined time delay determined by circuit 52,
refrigeration valve 43 opens to restore normal refrigeration
operation. Circuit 47 is then de-energized and sequential control
30 advances to the next relay which is shown as 40' in FIG. 1.
At anytime there is a time controlled defrost of the evaporators of
the third set such as evaporator 12, timer relay 50 provides a
signal over circuit 53 which may be connected to inhibit the output
of sequencer 30 and prevent a start of a demand defrosting
operation. Any demand defrost operation in progress will continue
as a result of the signal on circuit 46 which overrides the effect
of the signal on circuit 53.
* * * * *