Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
BACKGROUND OF THE INVENTION
The invention relates generally to multiple
compressor refrigeration systems, and more particularly to
improvements in time delay controls for the refrigeration
system.
In recent years many advances have been made in
the refrigeration art and especially in the commercial
refrigeration field, which includes supermarket refrigeration
and like installations having heavy refrigeration requirements
over a wide range of temperatures from about -40 E'. to
about 50 F. (-40 C. to about 10 C.). So-called central
refrigeration systems of the heavy multiplexing type utilize
several compressors (typically either two or four) connected
for parallel operation to effect refrigerant flow to and
from the evaporators of a large number of refrigerated
fixtures. Multiple compressor systems are generally con-
trolled by pressure sensitive switches responsive to the
suction pressure at the compressors intake so that as the
suction pressure fluctuates in response to increases or
decreases in system loads, the compressors will cycle on and
off to maintain the common suction pressure on the system
within prescribed limits to maintain proper temperature
control of the refrigerated fixtures.
Fluctuation of the suction pressure is influenced
by various internal (system) factors including temperature
controls, defrosting apparatus and the like, and by several
external factors including product loading of refrigerated
fixtures, ambient temperatures and the like, and at times
sudden transient increases in suction pressure may cause one
or more idle compressors to start thereby rapidly reducing
~'
i f,~
the suction pressure to the point where such compressors
will cycle off again. Since these suction pressure changes
are frequently transient in nature, the capacity of the
operating compressors in the sysl:em would often be adequate
to restore a normal suction pressure before there is any
significant influence on the temperatures of the refri-
gerating fixtures. However, if t:he thermal load change
causing the suction pressure (temperatuxe) rise is of long
duration, then the operation of one or more additional
compressors may be necessary to maintain normal refrigerating
fixture temperatures.
Wide fluctuations of the compressor head pressure
may also be influenced by the same types of internal and
external factors, and transient decreases in head pressure
may be caused, for instance, by initial reduction of refrigerant
loads as when a defrost cycle is started on selected fixture
evaporators. Regulation of the effective condensing capacity
can be controlled by the sequential and cyclical operation
of a series of "zone" condenser fans controlled by pressure
sensitive on-off switches so that, as the head pressure
fluctuates, the fans will cycle on and off to change the
condenser capacity toward maintenance of the head pressure
on the system within prescribed limits. If such head
pressure changes are transitory in nature, it may be desir-
able to maintain the operation of the condenser fans unless
the decrease in head pressure persists.
It is apparent that electric power consumption
will be reduced in the overall operation of the refrigeration
system if additional compressors are not started in response
to transient load increases, or if other system components
--2--
are left idle during transient pressure fluctuations. It
will also be apparent that the eEficiency of such compressors
will be increased when operated at lower head pressures,
thereby effecting additional power savings. In the past,
electric time delay relays have been used for delaying the
start of additional compressors sensing an increase in
suction pressure or for effecting sequential operation of
other system components, but such electric relays are
insensitive to the actual magnitude of the refrigerant
pressure at the critical or predetermined location within
the system, whereby -the compressor, fan or other component
controlled thereby will start no matter how small the
difference is between actual pressure and the pressure
switch setting. In short, heretofore there has been no
simple, positive acting, pressure sensitive, time delay
system for effectively obviating on/off component cycling
due to sudden temporary or transient pressure changes.
SUM~ARY OF T~E INVENTION
The invention is embodied in a fluidic time delay
system for operating a plurality of control switches having
preselected pressure settings to effect sequential component
operations in response to variations in refrigerant pressure
at a predetermined location within the refrigeration system,
the time delay system including restrictor means for delaying
refrigerant flow and concomitant pressuxe communication in
one direction of flow between the predetermined location and
the control switches, and one-way flow means for providing
unrestricted refrigerant flow and concomitant pressure
communication in the other direction of flow between the
control switches and the predetermined location.
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2~L
The principal object of the present invention is
to provide a fluidic time delay system capable of immediate
pressure equalization in one direction and delayed pressure
equalization in the other direction between a given location
in a refrigeration system and a plurality of pressure
sensitive switching means for controlling refrigeration
system components.
Another object is to provide high side or low side
pressure responsive control apparatus for operating refri-
geration system components at optimum pressures and obviatingpremature component cycling in response to sudden and
transitory pressure changes.
Another object of the present invention is to
provide improved suction pressure controls for a multiple
compressor refrigeration system to substantially reduce
short term on/off compressor cycling due to sudden transient
changes in suction pressure.
Another object is to provide a fluidic time delay
interposed between the suction header and the pressure
sensitive switching means of multiple parallel compressors
for delaying the transmission of sudden pressure increases
in the suction header to the pressure switches and affording
immediate pressure equalization from the pressure switches
to the suction header upon decreases in suction pressure.
Still another object of the present invention is
to provide a fluidic time delay interposed between the
compressor discharge and pressure sensitive switching means
of multiple condenser fans for providing immediate pressure
equalization to the switching means upon increases in the
head pressure and delaying pressure release in the switching
means upon sudden decreases in the head pressure.
Another object is to provide a simple, positive
acting, pressure delay control for operating the pressure
sensitive switches of multiple parallel refrigeration
system components and -Eor stabilizing fluctuating transitory
loads to minimize on/off component cycling.
These and still other objects and advantages will
become more apparent hereinafter.
B~IEF DESCRIPTION OF THE DRAWINGS
.
In the drawings which illustrate embodiments of
the invention,
FIGURE 1 is a diagrammatic illustration of a
multiple compressor refrigeration system showing one embodi-
ment of ~he invention, and
FIGURE 2 is a diagrammatic illustration of a
refrigeration system showing another embodiment of the
invention.
DESCRIPTION OF THE PREFERRED E~BODIMENT
Referring to FIGURE 1, a central or multiplexed
refrigeration system of the type having plural (at least
two) compressors will be described as being installed in a
supermarket for operating a multiplicity of separate refri-
gerated fixtures, such as refrigerated storage and display
cases, but it will be understood and readily apparent to
those skilled in the art that such a system can be adapted
to other commercial or industrial installations. For
disclosure purposes, the terms "high side" and "low side"
are used herein in a conventional refrigeration sense to
mean the portions of -the system from the compressor dis-
charge to the evaporator expansion valves and from the
expansion valves to the suction intake of the compressors,respectively.
The central refrigeration system illustrated in
FIGURE 1 includes four parallel compressors C-l, C-2, C-3
and C-4, each of which has a suction or low pressure intake 11
operating within a range of preselected suction pressures
(as will be described more fully~ and a discharge or high
pressure side 12 with a common discharge header or conduit 13
through which hot compressed gaseous refrigerant is discharged
to a condenser 14. The refrigerant is reduced to its con-
densation temperature in the condenser 14, which is connected
by conduit 15 to a receiver 16 forming a liquid refrigerant
source Eor operating the system. A conventional equalization
line 17 with a one-way valve 18 connects the top of the
receiver 16 to the top of the condenser 14. The bottom of
the receiver 16 is connected to a liquid header 19 for
conducting liquid refrigeran-t to branch liquid lines or
conduits 20,21 leading to evaporator coils 22a, 22b, 22c,
22d and 22e, which are representative of a multiplicity of
different refrigerated fixtures (not shown). The branch
liquid line 20 for each evaporator 22a/ 22b, 22c, 22d and
22e is connected to a solenoid valve 23, and branch liquid
line 21 leading therefrom is broken to illustrate an indeter-
minate length from the machine room to the refrigerated
fixture. Expansion valves 24 are provided in the liquid
lines 21 for metering refrigerant into the evaporator coils
22a-22e in a conventional manner during their refrigeration
cycle. The outlets of the evaporators are connected by
branch suction lines 25 (also broken to illustrate an
indeterminate length) to three-way valves 26 and, under
normal refrigerating operation, are connected through these
valves and branch suction lines or conduits 27 to a common
suction line or header 28 connected by compressor suction
lines 28a to the suction inlets :Ll of the compressors C-l,
C-2, C-3 and C-4 and through which vaporous refrigerant from
the evaporators is returned to the compressors to complete
the basic refrigeration cycle. ]3vaporator pressure regu-
lator (EPR) valves 29 are shown interposed in the branch
suction lines 27 for illustrating that the suction pressure
on the respective evaporator coils 22a-22e can be adjusted
so that the respective refrigerated fixtures can be operated
at different temperatures within the range of suction
pressures maintained by the compressors C-l, C-2, C-3 and
C-4.
The refrigeration system operates in a conventional
manner in that each fixture evaporator absorbs heat from the
fixture or its product load thereby heating and vaporizing
the refrigerant and resulting in the formation of frost or
ice on the evaporator coils 22a-22e, and periodic defrosts
are therefor required. A main gas defrost header 30 is
provided for conducting gaseous refrigerant selectively to
the evaporator coils for defrost purposes and is connected
through branch defrost lines or conduits 31 to the three-way
values 26, the three-way. valve for the euaporators 22e being
shown in defrost position.
In a conventional "hot gas" defrost arrangement
the:defrost header 30 would be connected to the compressor
discharge conduit 13 so that this source of highly super-
heated hot compressed gaseous refrigerant would be used for
selectively defrosting the evaporators 22a-22e. However,
for disclosure purposes, the defrost header 30 is connected
to the top of the receiver 16, as at 32, so that "saturated
gas" from the receiver is used for defrosting purposes; that
is, the sensible and latent heat of gaseous refrigerant at
its normal or desuperheated saturation temperature is utilized
for defrosting the evaporators. Accordingly, the
gas defrost header 30 is connected to the top (32) of the
receiver 16, which provides a continuous supply of saturated
gas at substantially the head pressure of the compressors,
so that such gaseous refrigerant will flow through the
header 30, the branch line 31 and the three-way valve 26
into the evaporator coil 22e as shown (or other selected
evaporators by actuating their respective -three-way valves
26 and solenoid valves 23) for heating the coil and thereby
condensing the refrigerant to its liquid phase as in a
conventional condenser. A unidirectional by-pass or check
valve 33 is provided in a by-pass line 34 connecting the
inlet of each of the evaporators 22a-22e to the liquid
header l9 in by-pass relation with the expansion valves 24.
In accordance with the teachings of U. ~. Patent No. 3,150,498,
the defrost system disclosed provides for the return of the
liquid refrigerant resulting from the defrost of each
evaporator coil directly into the liquid header l9 through
the by-pass line 34 and check valve 33 for immediate use by
the normally refrigerating evaporators. A pressure reducing
or regulating valve 35 is positioned in the liquid header l9
upstream of the branch liquid supply lines 20; the pressure
drop effected by the valve 34 from the receiver side of
liquid header 19 to the evaporator side being in the range
of about 15 to 40 p.s.i.g. (l to 2.8 kilo/sq.cm). Accord-
ingly, a pressure differential between the defrost gas
header 30 and the liquid header 19 is maintained to provide
an incentive for the rapid flow of refrigerant through the
defrosting evaporator 22e (or other selected evaporator)
back into the high side of the refrigeration system.
The compressors in conventional refrigeration
systems are typically controlled by one or more multi-switch
pressure controllers or a series of separate pressure
switches having preselected high and low pressure settings
which sense and are directly responsive to the low side
suction pressure at the compressor intake 11 for starting
and stopping the compressors. In such a system, the high or
cut-in pressure settings for the multiple compressors are
arranged in a preselected increasing progression to sequentially
start the compressors only as required ~o meet increasing
load demands and the cut-out or low pressure settings also
vary in a preselected progression to stop the compressors
sequentially as the system load evidenced by the suction
pressure is reduced. In other words, the normal refri-
geration load of the system may normally produce a suctionpressure in the range of 10 p.s.i.g. to 12 p.s.i.g. (0.7
to 0.85 kilo/sq.cm3 whereby the operation of two or three
compressors in a four compressor system will be sufficient
to satisfy the refrigerant requirements or load demands.
However, in the event of sudden transient increases in
suction pressure as when one or more selected evaporators
(22e) ends a defrost cycle, the suction header pressure may
rise very rapidly, such as to 35 p.s.i.g. (2.45 kilo/sq.cm)
or the like, whereby the cut-in or high pressure settings of
the control switches for all of the sys-tem compressors may
be e~ceeded and normally all of these compressors would be
started thereby rapidly reducing the suction pressure back
below the cut-out or low pressure control settings of some
compressors so that they would then cycle off. Manifestly,
such rapid on-off cycling of compressors consumes unnecessary
energy by reason of the fact that the operative compressors
at the time of the surge in suction pressure may have been
adequate to restore substantially normal suction pressure
levels.
According to the EIGURE 1 embodiment of the present
invention, conventional types or arrangements of pressure
responsive control switches 40a, 40b, 40c and 40d may be
provided for controlling the operation of the compressors
C-l, C-2, C-3 and C-4, respectively; i.e. such control
switches 40a-40d may be of the conven-tional multi-switch
controller type having a multiplicity of ganged switch
contacts simultaneously actuated by a single pressure
element or may be a series of separate or paired sets of
conventional switches actuated by different pressure elements,
the construction and operation of these conventional switch
means being well known in the refrigeration art. It will
also be understood that in conventional systems the location
of suction pressure control switches is generally at the
suction intake 11 of the compressors or in communication
with the compressor suction lines 28a leading thereto from
the suction manifold 28; whereas in the present system, the
physical location of the control switches 40a-40d may be
remoteIy located away from the compressors electrically
controlled thereby. For disclosure purposes, however, these
switches 40a, 40b, 40c and 40d are diagrammatically illus-
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~ ~a~
trated as being positioned adjacent to the suction intake 11
of each of the compressors C-l, C~2, C-3 and C-4, respectively,
but they are isolated from the compressor suction inlets 11
and suction lines 28,28a and are arranged for compressor
control operation through a fluidic time delay system 41, as
will now be described.
The time delay system 41 is interposed between the
suction header 28 and each of the pressure responsive
control switches 40a-40d for regulating the vapor pressure
imposed on these switch means to thereby electrically
control the operation of the compressors C-l through C-4.
The time delay relay 41 is physically positioned above the
suction header 28 to prevent the entrapment of oil therein,
and comprises fluid restrictor means in the nature of a
capillary tube 42 and an accumulator tank 43 to restrict
refrigerant flow from the suction header 28 and thereby
delay the concomitant vapor pressure increase effective on
the pressure switches during increasing suction header
pressures. A conduit 44 connects the suction header 28 to
one end of a fine mesh strainer 45 for trapping any solid
particles entrained in the refrigerant vapor flow and
preventing the passage of such matter into the capillary
tube restrictor 42 connected to the outlet of the strainer
45. It will be noted that the strainer is vertically
disposed and in gravity flow relationship with the suction
header 28. The capillary tube 42 comprises a substantial
length of small bore tubing which is helically wound around
the upper portion of the accumulator tank 43 in a gravity
flow, downward spiralling series of turns 42a (shown broken
to illustrate additional turns) and having its inlet con-
nection 46 in the side wall of the accumulator intermediate
its top and bottom ends. A conduit 47 is connected to the
top 48 of the accumulator, and is connected by branch
conduits 49 to each of the pressure control switches 40a,
40b, 40c and 40d to provide open fluid communication be-tween
the internal pressure actuator elements (not shown~ of the
switches and the upper portion of the accumulator 43.
Nomally open service hand valves 50 and 51 are provided in
the conduits 44 and 47, re~pectively. It will be understood
that the restrictor means utilizes capillary (flow restricting)
tubing 42 of predetermined length and bore size and an
accumulator 43 of predetermined volume which together are
calculated to obtain optimum time delay in the flow of
refrigerant vapor from the suction header 28 to the pressure
switches 40a-40d. Manifestly, a capillary of smaller bore
and/or an accumulator of larger size will result in longer
time delays.
The time delay system 41 also includes fluid
return or pressure equalizing meàns comprising a conduit 53
connecting the bottom 52 of the accumulator tank 43 to the
conduit 44 between the strainer 45 and the hand valve 50,
and a one-way check valve 54 is provided in the conduit 53
to provide relatively unrestricted, but unidirectional,
refrigerant flow from the bottom of the accumulator tank
back to the suction header 28 upon any relative decrease in
the suction pressure therein.
The components of the time delay system 41 may be
conveniently arranged in a suitable housing (not shown)
mounted in gravity flow position above the suction manifold
28 and the compressors C-l, etc.; and the pressure control
switches 40a-40d may be incorporated into such housing
thereby requiring only relatively short conduit connections
47,49 between the accumulator 43 and the internal pressure
actuator (not shown~ of the compressor sequencing switches
40a-40d.
In the operation of the FIGURE 1 embodiment, it
will be understood that the pressure settings of the compressor
control switches 40a-40d will be determined primarily by the
requirements of the refrigeration system, type of refri-
gerant, load variables and the like. In a four compressorsystem (as illustrated) for low temperature (frozen food)
operation at 25 F. (-32 C.) using Refrigerant 502, a
typical suction header pressure range of about 4 p.s.i.g. to
15 p.s.i.g. (0.28 to 1 kilo/sq.cm) would be maintained
and a normal suction pressure level of about 10 p.s.i.g. to
12 p.s.i.g. (0~7 to 0.85 kilo/sq.cm) would typically be
established during normal, stable refrigerating conditions.
Accordingly, in describing the operation of the fluidic time
delay system 41 under these conditions, the sequencing
switches 40a-40d may have the following high or cut-in and
low or cut-out pressure control settings for starting and
stopping the compressors:
Compressor Switch ~ Cut-:In Cut-Out
psig kilo/sq.cm psig kilo/sq~cm
C-4 40d 15 1 10 0.7
C-3 40c 13 0.9 8 0.56
C-2 40b 11 0.77 6 0.42
C-l 40a 9 0.63 4 0.28
It will also be assumed that compressors C-l, C-2 and C-3
are running and that the suction header pressure is stable
-13-
and balanced with the accumula-tor tank 43 at 10 p.s.i.g.
(0.7 kilo/sq.cm), that compressor C-4 is stopped, and that
all evaporators 22a-22e are connected for normal refri-
geration.
Under such circumstances, a defros-t cycle is
initiated for evaporator 22e by l~losing its solenoid valve
23 and switching the three-way valve 26 to the position
shown, thereby resulting in a drop in the system load and
reducing the suction header pressure to 6 p~s.i.g.
(0.42 kilo/sq.cm). A pressure differential is thus created
between the suction header 28 and the accumulator tank 43
causing the check valve 54 to open and the accumulator
pressure to rapidly equalize at 6 p.s.i.g., which is below
the 8 p.s.i.g. cut-out pressure of compressor C-3 causing
that compressor to stop. The suction header pressure will
slowly rise to 8 p.s.i.g. (0.56 kilo/sq.cm) due to the
reduced compressor capacity, and the accumulator pressure
will also slowly rise but lag behind the increase in the
suction header due to the restrictive flow throuyh the
capillary tube 42. However, compressor C-3 remains idle and
will not start until the accumulator pressure again rises to
13 p.s.i.g. (0.9 kilo/sq.cm).
When the defrost cycle of evaporator 22e is
terminated and refrigeration is resumed, the coil is hot
from defrosting and the suction pressure affected thereby
rapidly rises to 35 p.s.i.g. (2.45 kilo/sq.cm) and this
pressure increase is imposed on the fluidic time delay 41.
Since the check valve 54 prevents direct pressure equalization
to the accumulator 43, vapor flow in the accumulator is
restricted through the capillary tube 42 and the concomitant
-14-
vapor pressure increase in the accumulator 43, which is
effective on the pressure switches 40a-40d, is relatively
slow. The suction pressure in the header 28 drops rapidly
as the warm coil 22e becomes cold and may read 11 or 12 p.s.i.g.
~ 0.77 or 0.85 kilo/sq.cm) before the effective pressure in
the accumulator 43 can reach 13 p.s.i.g. (0.9 kilo/sq.cm),
which is the cut-in pressure of compressor C-3. Even if the
suction pressure leveled out and came down to about 15 p.s.i.g.
(I kilo/sq.cm) as is typical, the rate of fluid flow and/or
pressure increase to the accumulator 43 wou]d be slowed down
thereby allowing more time for compressors C-l and C-2 to
bring the suction pressure to below 13 p.s.i.g. (0.9 kilo/sq.cm)
before the accumulator pressure effective on the pressure
switch 40c reaches this cut-in pressure of compressor C-3.
In the event the suction pressure on header 28 still exceeds
15 p.s.i.g. (1 kilo/sq.cm) when the accumulator pressure
reaches 13 p.s.i.g. (0.9 kilo/sq.cm), the compressor C-3
will start thereby rapidly reducing the suction header and
accumulator tank pressure back to the 10 p.s.i.g. (0.7
kilo/sq.cm) level.
From the foregoing it will be apparent that the
time deIay system 41 provides a variable time delay based
upon pressure differen-tial. If the suction header pressure
rises slowly as when the load changes are due to increasing
ambient temperatures or the like, the accumulator pressure
will closely follow the suction pressure so that an additional
compressor will start when needed without any significant
time delay. If the rise in suction header pressure is rapid
and substantial, such as 20 to 25 p.s.i.g. (1.4 to 1.76
kilo/sq.cm), due to surges occasioned by defrost operations
-15-
(as described) or momentary load fluctuations as when cooler
doors are opened, the accumulator pressure will follow
relatively rapidly if the high pressure differential is
sustained. However, if the pressure surge peaks and then
drops rapidly, the differential will, of course, be decreased
and the length of time for the accumulator pressure to reach
the cut-in point of the next compressor will be increased.
It will also be apparent that there is no significant delay
in stopping a compressor when the suction header pressure
drops below the accumulator pressure, as the one-way check
val~e 54 provides substantially unrestricted pressure
equalization to stop compressors due to lighter load con-
ditions. Effective time delays ranging from about 3 or 4
minutes up to about 15 or 20 minutes due to increasing
suction pressures, together with substantially no delay due
to pressure drop substantially eliminates short cycling of
the compressors.
Referring now to FIGURE 2 of the drawings, the
components of another refrigeration system are identiEied by
numerals similar to those in the FIGURE 1 embodiment, but in
the "100" series. The basic refrigeration cycle is similar
to that previously described, but for illustration purposes,
only two compressors C101 and C102 are shown (such a system
is frequently referred to in the commercial refrigeration
trade as a "twin" system), and it will be understood that
the invention may be useful even in a single compressor
system. Also, only three evaporators 122a, 122b and 122c
for refrigerated fixtures are shown with the evaporator 122c
being in the defrost mode.
In the FIGURE 2 embodiment of the invention it
-16-
will be seen that a fluidic time delay system 141 may be
piped in a reverse manner to tha-t shown in FIGURE 1 to
facilitate different sequential pressure control functions.
In the FIGURF 2 embodiment the condenser 114 is air-cooled
by a plurality of area or zone fans 161, 162, 163 and 164,
each of which is selectively operated to control one quadrant
of the condenser 114, as is typical, and the condensing
capacity is thereby effectively regulated toward maintaining
the compressor head pressure within a prescribed optimum
temperature range of approximately 175 p.s.i.y. (12.25
kilo/sq.cm) to 185 p.s.i.g. (12.95 kilo/sq.cm). The com-
pressor head pressure will, of course, vary widely depending
on climatic conditions and system loads and it is desirable
that a minimum head pressure of about 175 p.s.i.g. (12.95
kilo/sq.cm) be maintained to provide effective refrigerant
pressure in the system, and that the condenser fans 161-164
be operated as needed to prevent the head pressure from
exceeding a maximum of about 225 p.s.i.g. (15.75 kilo/sq.cm)
as during summer operations.
According to the FIGURE 2 embodiment of the present
invention, a conventional pressure sensitive, multi-stage
sequencer 165 having plural control switch contacts 166 may
be provided for operating the motors of the condenser fans
161-16~ in a sequential manner as needed in response to the
compressor head pressure. It will be understood that a
series of separate or paired sets of conventional pressure
switches may be used as previously described in the FIGURE 1
embodiment, but a multi-switch controller 165 is presently
preferred for cycling electrical loads at remote locations
from the refrigeration control point; in this case the
~ 3
compressor discharge line 113.
The fluidic time delay system 141 is interposed
between the discharge line 113 and the control switch
sequencer 165 for regulating the high side pressure imposed
on these switch means to electrically control the operation
of the condenser fans 161-164, a:nd the time delay system 141
and sequencer 165 may be conveniently encased in a control
box or housing 167. The -time delay relay 141 is physically
positioned in gravity flow relation above the discharge line
113 to prevent entrapment of oil therein, and includes a
unidirectional valve 154 having its inlet side connected by
an unrestricted take-off conduit 144 to the discharge line
113, and is being connected on its outlet side by another
unrestricted conduit 147 to the multi-switch controller 165
so that substantially unrestricted refrigerant flow is
provided from the high pressure discharge line 113 through
the one-way valve 154 to the sequencer 165 for immediate
pressure equalization upon relative increases in the head
pressure of compressors C101 and C102. The sequencer 165 is
pre-programmed to sequentially close the contacts 166 to the
different fan motors at selected incremental pressure increases,
as follows:
Fan Cut-In Pressure
p.s.i.g. kilo/sq.cm
161 175 12.25
162 177 12.39
163 179 12.53
164 181 12.67
Thus, at each two pound increase in the head pressure an
additional condenser fan will be started to immediately
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increase the condensing capacity toward maintaining head
pressures in the 175 to 185 p.s.i.g. (12.25 to 12.67 kilo/sq.cm)
range.
It will be apparent that the head pressure is
subject to relatively rapid fluctuations due to changes in
system and environmental conditions and due to changing
condenser capacity by reason of the starting and stopping of
the fans 161-164. Accordingly, the condenser fans 161-164
are subject to short cycling on and off, and it is desirable
to stabilize fan operation and prevent hammering as well as
maintain condenser capacity during transitory surges and
drops in compressor head pressure as may occur at the start
of an evaporator defrost cycle.
Accordingly, the time delay system utilizes fluid
restrictor means in the form of a capillary tube 142 and an
accumulator 143 to restrict the flow of vapor pressure from
the pressure switches 165 back to the discharge line 113 for
delaying pressure equalization during short term decreases
in the head pressure. The accumulator 143 has an upper
connector 170 in open pressure flow communication with the
conduit 147 so that the pressure in the accumulator will
become equalized to the compressor head pressure acting
through the unidirectional valve 154 and conduit 147 directly
to the control switches 165,166, although such pressure
equalization in the accumulator will be delayed depending
upon the size of the accumulator 143 and the precise physical
hook-up, e.g. the outlet of valve 154 and the sequencer 165
may both be directly connected into the upper portion of the
accumulator 143. The bottom of the accumulator has a bottom
outlet conduit 153 connected to a strainer 145 in~ediately
--19--
adjacent to the capillary tube 142, which has a single short
upward turn and is then helically wound around the upper
portion of the accumulator tank 143 in a gravity ~low,
downward spiralling series of turns 142a. The lower end of
the capillary 142 is connected into the conduit 144 connected
to the discharge line 113. Thus, the sequencer 165 is
directly responsive to pressure increases in the compressor
head pressure acting through the one-way valve 154 and
conduit 147 to sequentially operate the condenser fans 161-
164, and the restrictor means utilizes capillary tubing 142
of predetermined length and bore size and an accumulator 143
of predetermined volume which together are calculated to
obtain an optimum time delay in releasing pressure from the
sequencer 165 back to the discharge line 113.
The fluidic time delay 141 and sequencer 165 maybe housed together as a unit 167 arranged in gravity flow
relation to the discharge line (except for the short verti-
cal section of capillary 142) to prevent oil entrapment
therein so that entrained oil in the high side of the
system downstream of the conventional oil separator 171 will
be returned to the system. Normally open service valves 150
and 151 are provided in the conduits 144 and 147, respectively.
It will be understood that the fluidic time delay
141 will often be operating in an ambient temperature below
that of the condensing pressure and, therefore, is subject
to liquid condensation in the accumulator 148. Accordingly,
if needed, heating means in the form of an electric heater
172 or the like may be provided within the housing 167
or adjacent to the accumulator 148~ and suitable thermo-
static or other controls (not shown) may be utilized to
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3~
minimize operation and power consumption.
The operation of the FIGURE 2 embodiment will be
readily understood from the foregoing description. The
fluidic time delay 141 provides :Lmmediate condenser Ean
operation in response to increaslng head pressures, and
maintains such operation for sufficiently long intervals to
eliminate short cycling and hammering in the fans as well as
during short term decreases in compressor head pressure in
order to maintain efficiency in condenser cooling. However,
if the head pressure slowly decreases as when load changes
are due to climatic conditions or the like, the pressure in
the accumulator 143 will closely follow so that only the
appropriate condensing capacity will be provided.
It will be readily apparent that the fluidic time
delay 41,141 may be utilized in a refrigeration system to
operate pressure responsive switches for high side or low
side component control. Thus, the foregoing description is
given only by way of illustration and example, and the
invention is only to be limited by the scope of the claims
which follow.
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