Note: Descriptions are shown in the official language in which they were submitted.
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Title
VariablEa capacity Condenser Coil and Cooling
System Incorporating The Same
Field of Invention
This invention relates to cooling systems of
medium to large size with condenser coils located
outdoors where the ambient temperature varies and
more particularly to a cooling system that
automatically compensates for pressure loss/gain
in response to temperature change by controllably
varying the condenser coil capacity.
Background of Invention
In cooling ;systems with an outdoor condenser
coil, as the ambient temperature drops, there is
pressure loss in the condenser coil and liquid
lines. However certain pressures must be
maintained in the condenser coil and liquid lines
to ensure the cooling system works properly. The
colder the ambient air the greater the pressure
a>0 loss .
One traditi~~nal method of controlling this
refrigerant ;pre.osure has been to turn on and off
the condenser fa.n motor, or modulate its speed,
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to reduce air flow though the coil and thereby
artificially raising the refrigerant pressure.
There has been limited success using this method
in some installations. Most condenser coils of
medium and large size are horizontal and have a
very large area of finned tubing. Because the
coil is warm it creates a chimney effect and
draws air across the coil even when the fans are
turned off in cold weather. This causes the coil
to drop refrigerant pressure and it begins
logging refrigerant in the coil creating a back
flooding condition. This uses a large amount of
refrigerant which is relatively costly. Also as
much as 90$ of the coil can fill with liquid
refrigerant and should a leak develop it becomes
not only exp~ensi.ve to refill but also the loss of
refrigerant is environmentally unfriendly.
Some other method of controlling pressure
must be used when two or more cooling systems are
~'.0 circuited in the: same condenser coil as is often
done in commercial systems. It is next to
impossible t~~ cycle fans in this instance because
of the plura:Lity of systems and thus it is
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impossible to control the pressures evenly.
Another instance where fan cycling is next to
impossible is where heat reclaim coils are used
to make use of t:he heat rejected by cooling
systems and use that reclaimed heat to heat a
building or heat. water etc. In most instances
these reclaim heat exchangers are connected in
series with the condenser coils and often cause
the condenser coils to partially fill with liquid
l0 refrigerant. Controlled back flooding is used in
the installations where controlled air flow is
not a satisfactory solution. A back flooding
valve controls the refrigerant pressure and flow
by controlling t:he back flooding of the condenser
coils sometimes to the extent of 97$ being liquid
refrigerant. A back flooding valve works well, it
is very durable and trouble free. It provides
good refrigerant: pressure control and there is no
need to cycle the condenser fans. A back flooding
;?0 valve however is required on each and every
cooling system individually circuited inside a
common condenser coil.
A problem with the two forgoing methods of
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pressure contro:L is the enormous amount of
refrigerant required. It is referred to as a
winter refrigerant charge and a summer
refrigerant charge, the former normally being
three or more times the latter. A fully charged
system will have 1000 pounds or more of
refrigerant and costs in the range of $20 to $60
per pound.
Refrigerants are expensive and since leaks in
a system are not: uncommon replacement of lost
refrigerant can,, in the medium to large cooling
systems, be a major expense. Proposals to reduce
the quantity of refrigerant in a system have
included reducing the tube size in the outdoor
l5 condenser coil and still use a back flooding
valve. While this partially reduces the charge it
is not particularly effective since it causes an
increase in the pressure drop across the coil.
The acceptable normal pressure drop is 10 PSI
;?0 while a reduced tube size can result in a
pressure drop of up to 30 PSI.
Another method of reducing the quantity of
refrigerant, commonly used in supermarket cooling
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systems, is to monitor the liquid line and in
response thereto control a set of solenoid
valves, that under certain conditions, will
isolate the recs~iver from the cooling system for
certain periods of time. During cooling cycles,
where the system charge becomes critical, the
controller has t:o continuously re-adjust the
refrigerant charge .
In the forgoing the cooling system closed
l0 loop refrigerani~ piping has a constant volume and
the refrigerant pressure in the condenser is
controllably varied by using liquid refrigerant
to vary the effective condensing area of the
coil.
l5 Summary of Invention
A principle object of the present invention
is to provide a cooling system in which the
winter refrigerant charge is equal in quantity to
the present summer charge.
;?0 A furthE~r principal object of the present
invention is to provide a condenser coil and
means to controllably vary the volume of the
tubing thereof i.n response to condenser pressure
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requirements
In substance the present invention involves
controlling the refrigerant flow through the
condenser coil by in affect adding tubing to or
removing tubing from the refrigerant flow path.
In accordan~~e with the present invention a
programmed central processing unit(CPU),
responsive to ambient temperature and refrigerant
pressures, variEas the tubing volume as required
l0 to maintain a predetermined condenser pressure
for the sensed ambient temperature and
refrigerant pre:>sures. The tubing volume is
adjusted by 'what: is referred to herein as 'coil
splitting'. The term 'coil splitting' refers to a
l5 coil subdivided into a plurality of parallel coil
sections and having valves to vary the number of
sections that are in parallel. Valve means,
responsive to the CPU, is used to control
refrigerant flov~r to the condenser coil sections
~!0 ie the number of sections as may be required in
the particular circumstances. This coil splitting
controls the condenser size to meet requirements
for the system. The CPU processes information
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received from an ambient air temperature sensor,
a first pressure sensor that detects the
refrigerant pressure on the exhaust side of the
compressor, ie upstream of the condenser and a
second pressure sensor, downstream of the
condenser, that detects the liquid refrigerant
pressure. Pressure transducers are preferably
used. The CPU determines what to do and how many
coil sections are required and self adjusts as
the system operates. The colder the weather the
lesser the number of coil sections required and
the warmer it gets the more coil sections
required. In some systems there are two further
sensors one relating to the mechanical room and
l5 that is to t~=11 the CPU how many compressors are
operating in the refrigerant loop and the other
is when there are heat recovery coils in which
case a sensor provides signals from the diverter
valve.
~',0 The present cooling system with its
components a:nd C:PU provides good control of
refrigerant :pressure and system operation in all
seasons and 'temperatures while using only a
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normal summer refrigerant charge. This means the
refrigerant charge is only 1/3 that of existing
cooling systems and thus a tremendous saving not
only in the initial charge but also replacement
of the refrigerant should a leak occur. There is
no cycling of the condenser fans and there are no
back flooding valves.
Li s t of Drawi nQ:~
The invention is illustrated by way of
example in the accompanying drawing wherein:
Figure ~l diagrammatically illustrates a
cooling system of the present invention in its
simplest form; and
Figure 2 is similar to figure 1 but
including additional components.
Description of Preferred Embodiment
Referring to figure 1 there is illustrated,
in its simplest form, a cooling system comprising
a compressor 10, a condenser coil 20, an
~?0 evaporator coil 30 and an expansion valve 40
connected by refrigerant piping in a closed loop.
The refrigerant piping includes a first pipe
A connected ;at one end to the exhaust side of the
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compressor 10 and at the other end to the intake
side of the condenser coil 20, a second pipe B
connected at onEa end to the output side of the
condenser coil 20 and at the other end to the
expansion valve 40, a third pipe C connected at
one end to the expansion valve 40 and at the
other end to the evaporator coil 30 and a fourth
pipe D connected at one end to the evaporator
coil 30 and .at the other end to the intake side
of the compressor 10. A sight glass CG is in the
pipe B as well a.s a line filter FR.
The condenser coil has a plurality of
coil sections ds~signated respectively 20A, 20B,
20C, 20D, 20E, fOF, 20G, 20H, and 20I which are
l5 connected in parallel. The coil sections 20B to
20I inclusive are selectively connected in and
out of the refrigerant circuit by respective
solenoid operated valves 21B, 21C, 21D, Z1E, 21F,
21G, 21H and 21I. These valves are actuated by
:>.0 signals from a suitably programmed central
processing unit (or a programmed logic
controller) CP in response to signals from a
liquid refrigerant first pressure sensor (or
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transducer) 50, a second gaseous refrigerant
pressure sen.sor(or transducer) 60 and an ambient
air temperature sensor 70. In systems having more
than one compressor a further sensor will tell
5 the CPU how many compressors are in operation and
in systems having heat recovery coils a further
sensor provides signals from the diverter valve
to the CPU.
Each coi:L section, at its outlet end, has a
10 one way flow control valve that prevents back
flow into the condenser. The coil sections 20A to
20I inclusive have respective flow control valves
22A to 22I inclusive .
The cool~.ng system of figure 2 is the same as
that in figure 1 but optionally includes a
receiver 80 and an evaporator pressure regulator
valve 90 Also there is one or more compressors
l0A connected ira parallel with the compressor 10
(there may b~e as many as required for the system
~~0 at hand) and the tubing of the condenser is in a
series-parallel relation.
Various types of sensors can be used for
example pressure switches, pressure transducers,
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thermostats, thermocouples, diodes and
thermistors. They central processing unit can be
variously programmed to accomplish the results
required for the system at hand and, by way of
example, it may be a micro programmed logic
controller (PLC) available from G.E. Fanuc
Automation sold under the TM ~~Series 90".
The sequence in which the valves are opened
and closed is such as to ensure that refrigerant
logged in the various circuits is pushed or
flushed out. It is preferred that the last valve
to close on 'the last cycle is the first to open
on the next ~:ycle. Generally the valves will be
opened in the reverse order in which they
previously clossad.
In large commercial and industrial cooling
systems there normally are two or more
compressors connected to one condenser coil and
at some time all will be required to be in
~?0 operation. However if only one compressor is
operating then only a portion of the coil is
required. The central processing unit can readily
be programmed for that situation.
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The condenser coil 20 can be variously
positioned, for example vertical or horizontal,
and the tubing c:an be variously constructed. Also
all of the coil sections may be in parallel or
alternatively in a series-parallel relation.
Figure 1 is illustrative of all coil sections
being in parallel relation while figure 2
represents the coil sections as being in a
parallel-series relation.
l0 Referring further to figure 2 there are four
coil sections designated respectively 101, 102,
103 and 104. and these sections are connected in
parallel. Each section has a zig-zag arrangement
of tubing in series. There are solenoid operated
valves, at t:he inlet end, permitting bringing the
coil sections into or out of the refrigerant
circuit by respectively opening and closing the
valve associated therewith. The solenoid operated
valves are designated 105, 106, 107 and 108 for
a!0 respective coil sections 101,102,103, and 104 and
further one way flow control valves 109,110,111
and 112, at i~he outlet side, prevent back flow
into the res~~ect.ive coil sections .
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One coil section of coils 20 and 100 can be
an open circuit without a solenoid valve because
anytime the sy~:tem is running, or has to run, it
will always need at least one flow path to
circulate the refrigerant regardless of the
outdoor ambient temperature(note coil section 20A
in figure 1 does not have an inflow control
valve). As the pressure increases more valves are
opened to use more coil. As pressure drops the
valves are closed(in the reverse sequence) and an
appropriate number closed to maintain the
requisite pressure. By way of example the
compressor exhaust pressure will be maintained at
about 100 psi when medium pressure refrigerants
~5 as are used ouch as FR12, 134or 414 and about 170
to 180 PSI wizen medium pressure refrigerants are
used such as R22, 408 or 502. There are of course
many other refrigerants and the foregoing are
only by way of example.
~'.0 Referring further to figure 2 there is a
receiver tank 80~ in the refrigerant pipe 8. In
some installations there will be such a tank but
as previouslyy mentioned the control of the
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present system is such that a receiving tank
normally is not necessary. There is about a 10$
saving in energy when the system does not have a
receiver and thus should not be used unless
really needed. In this figure the control unit CP
has respective leads L1 and L2 for receiving
signals from sensors associated respectively with
a diverter valve: and the number of compressors in
operation in sy.~tems where applicable.
l0 In each of f.-'igures 1 and 2 the sensors are
illustrated as being hard wired to the CPU but
obviously wireless operation is feasible.
During operation the sensors provide
information to t:he suitably programmed controller
l5 CP. The information includes how many compressors
are operating, urhat is the outdoor temperature
and the refrigerant pressures at the intake and
outlet sides of the condenser relative to the
target pressure:.. A selected number of the coil
~'.0 sections are in circuit and if the two pressures
meet the target pressure ie a 'yes' condition no
changes are made. On the other hand should the
sensed conditions not meet the preselected
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conditions ie a 'no' situation then more, or less
circuits, are switched in, or out, as the case
may be. If the gas pressure is too high then more
coil sections ie more circuits are switched in
5 until the preselected conditions are met. Should
the pressure be too low coil circuits are cut out
until the preselected conditions are met. If the
pressure conditions are still not met (ie
pressure too low) the controller switches into
IO search mode in which coil sections are
al ternately swi 1=ched in and out of ci rcui t to
flush out logged refrigerant or the number of
coil circuits are reduced and then starts
alternating circuits to flush out the refrigerant
15 putting it back into the system. After being
flushed out coil. sections will then be switched
in, or out a;s the case may be, until the desired
preselected conditions are reached.
If there is a heat reclaim coil in series
?0 with the out doer condenser, and if the 'yes'
situation is applicable, then one or two circuits
in the roof ~~ond.enser are turned on to act as a
pipe. On the other hand if it is a series-
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parallel system then there is no need to turn on
circuits in the roof condenser.
There is a power driven condenser cooling fan
130 suitably located to drive air across the coil
tubing of the parallel coil sections.
l0
l5
a? 0
