U.S. patent application number 10/991039 was filed with the patent office on 2005-04-28 for method and apparatus for variable frequency controlled compressor and fan.
Invention is credited to Neve, Donald A., Thomas, William B., Wilson, James J..
Application Number | 20050086959 10/991039 |
Document ID | / |
Family ID | 24376994 |
Filed Date | 2005-04-28 |
United States Patent
Application |
20050086959 |
Kind Code |
A1 |
Wilson, James J. ; et
al. |
April 28, 2005 |
Method and apparatus for variable frequency controlled compressor
and fan
Abstract
The present invention provides a variable frequency controlled
refrigerant compressor in a dehydrator for compressed air or other
cases. In particular, the present invention detects changes in a
demand on the pneumatic air supply by monitoring a pressure of a
refrigerant system associated with the air supply. Based on the
changes in the refrigerant system pressure, a motor speed
controller generates and sends a control signal to the variable
speed compressor to adjust the speed of the variable speed
compressor based on the demand in the air supply.
Inventors: |
Wilson, James J.;
(Westminster, CO) ; Neve, Donald A.; (Westminster,
CO) ; Thomas, William B.; (Aurora, CO) |
Correspondence
Address: |
DORSEY & WHITNEY, LLP
INTELLECTUAL PROPERTY DEPARTMENT
370 SEVENTEENTH STREET
SUITE 4700
DENVER
CO
80202-5647
US
|
Family ID: |
24376994 |
Appl. No.: |
10/991039 |
Filed: |
November 16, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10991039 |
Nov 16, 2004 |
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10271345 |
Oct 14, 2002 |
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6817198 |
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10271345 |
Oct 14, 2002 |
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09593977 |
Jun 13, 2000 |
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6516622 |
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Current U.S.
Class: |
62/228.3 |
Current CPC
Class: |
F04B 2205/10 20130101;
F25B 2600/025 20130101; F04B 2205/01 20130101; F25B 41/20 20210101;
F25B 2400/075 20130101; F25B 2700/1933 20130101; F25B 2700/21151
20130101; F25B 2600/2501 20130101; F25B 2600/021 20130101; B01D
53/265 20130101; F25B 2700/21175 20130101; F04C 28/08 20130101;
F25B 49/025 20130101; F04B 23/06 20130101; F04B 2203/0204 20130101;
F25B 2600/111 20130101; F04B 39/16 20130101; F25B 2700/1351
20130101 |
Class at
Publication: |
062/228.3 |
International
Class: |
F25B 007/00; F25B
001/00; F25B 049/00 |
Claims
We claim:
1. An apparatus for controlling the operating speed of at least one
condenser fan motor in a refrigerated gas drying system having
changing demand or a gas supply, the apparatus comprising: a demand
sensor capable of sensing changes in the demand on the gas supply
and generating a change in demand signal; and a fan speed
controller that receives the change in demand signal to generate a
condenser fan speed signal, wherein the fan speed controller is
adapted to send the condenser fan speed signal to the at least one
condenser fan to change the speed of the at least one condenser fan
such that the speed of the at least one condenser fan is based on
the sensed demand.
2. The apparatus of claim 1 wherein the demand sensor senses
condensing pressure.
3. A refrigerated gas drying system, comprising: a refrigerant
circuit having an evaporator, at least one variable speed
compressor, and a condenser; a gas supply demand sensor adapted to
sense changes in a demand on a gas supply circuit; and a motor
speed controller for receiving the sensed changes in the demand of
the gas supply and supplying a motor speed control signal to the at
least one variable speed compressor to control the speed of the
compressor based on the demand on the air supply.
4. The refrigerated gas drying system of claim 3 wherein the gas is
air.
5. The refrigerated gas drying system of claim 3 wherein the motor
speed control signal is supplied to a condenser fan motor to
control the speed of the condenser fan motor based on the demand on
the air supply.
6. The refrigerated air drying system of claim 3 wherein the demand
sensor generates a demand signal and sends the demand signal to the
motor speed controller.
7. The refrigerated air drying system of claim 3, further
comprising at least one non-variable speed compressor such that the
motor speed controller turns on the at least one non-variable speed
compressor when demand on the air supply is greater than a capacity
of the variable speed compressor.
8. The refrigerated air drying system of claim 7 wherein a capacity
of the at least one non-variable speed compressor is approximately
one-half the capacity of the variable speed compressor.
9. The refrigerated gas drying system of claim 3, further
comprising at least one unload device such that the motor speed
controller de-energizes the at least one unload device when demand
on the gas supply is greater than a capacity of the variable speed
compressor with the at least one unload device energized.
10. The refrigerated gas drying system of claim 9 wherein a
capacity with the at least one unload device energized is
approximately one-third the total capacity of the variable speed
compressor.
11. The refrigerated air drying system of claim 3, further
including at least a second variable speed compressor.
12. The refrigerated air drying system of claim 11 wherein a
capacity of the at least one variable speed compressor is
approximately equal to a capacity of the at least a second variable
speed compressor.
13. A motor speed control system for a heat exchanger system having
a pump with a pump motor, a fan with a fan motor, and a demand
sensor, the motor speed control system comprising: a pump motor
speed controller adapted to receive the sensed demand, the pump
motor speed controller determines a pump motor speed based on the
sensed demand and generates a pump motor speed signal, wherein the
pump motor speed controller is adapted to send the pump motor speed
signal to the pump motor so that the pump motor speed corresponds
to the sensed demand; and a fan motor speed controller adapted to
receive the sensed demand, the fan motor speed controller
determines a fan motor speed based on the sensed demand pressure
and generates a fan motor speed signal, wherein the fan motor speed
controller is adapted to send the fan motor speed signal to the fan
motor so that the fan motor speed corresponds to the sensed
demand.
14. The system according to claim 13 wherein the pump motor speed
controller is adapted to receive the sensed demand from the fan
motor speed controller.
15. The system according to claim 13 wherein the fan motor speed
controller is adapted to receive the sensed demand from the pump
motor speed controller.
16. The system according to claim 13 wherein the pump motor speed
is controllable between a pump motor minimum speed and a pump motor
maximum speed.
17. The system according to claim 16 wherein the fan motor speed is
controlled independent the pump motor speed.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims is a divisional application of U.S.
patent application Ser. No. 09/593,977 filed by James J. Wilson,
Donald Neve and William B. Thomas on Jun. 3, 2000 and entitled
METHOD AND APPARATUS FOR VARIABLE FREQUENCY CONTROLLED COMPRESSOR
AND FAN,
FIELD OF THE INVENTION
[0002] This invention relates to compressor controls and more
particularly to compressor controls in compressed gas systems
having refrigerated dryers.
BACKGROUND OF THE INVENTION
[0003] Refrigerant compressors are used in a variety of systems.
One type of system that uses refrigerant compressors is a
compressed gas system. Compressed gas systems typically provide
high volumes of dry, pressurized air or other gases to operate
various items or tools (while a multitude of gases can be used,
this application typically refers to air as a matter of
convenience). Conventional systems dry the air using heat
exchangers first to cool the air and lower the dew point of the
air, which causes water vapor to condense out of the air, and
second to reheat the air and raise the outlet temperature of the
air. This system provides a relatively dry air source. FIG. 1 shows
a conventional refrigerated dryer 100 for a compressed gas system.
Refrigerated dryer 100 includes both an air heat exchanger circuit
110 and a refrigerant heat exchanger circuit 120. Air heat
exchanger circuit 110 includes an inlet 112, an air-to-air heat
exchanger 114, a air-to-refrigerant heat exchanger or evaporator
116, a water separator 120a and an air outlet 118. Refrigerant heat
exchanger circuit 120 includes evaporator 116, a compressor 122, a
condenser 124, a throttling device 126, and a hot gas by-pass valve
128.
[0004] Notice that temperatures used below to describe the
operation of dryer 100 are exemplary only. Many different air
temperatures and saturation levels are possible. The temperatures
and saturation levels of the final operating system depend on a
large variety of factors including for example system design
specifications and local environmental factors. The factors that
determine actual temperatures are beyond the scope of this patent
application and, in any event, are well known in the art.
[0005] In operation, dryer 100 receives a high temperature,
saturated, pressurized air or gas stream at inlet 112. For example,
the air or gas may be at 100 degrees (all degrees represented are
degrees Fahrenheit) with a dew point of 100 degrees (i.e., 100%
humidity), although any inlet temperature and dew point is
possible. The air or gas stream passes through an inlet side of
air-to-air heat exchanger 114. The air or gas stream cools down to,
in this example, 70 degrees with a dew point of 70 degrees (i.e.,
still 100% humidity). However, because 100 degree air or gas can
carry a larger volume of water vapor than 70 degree air or gas,
some water vapor condenses. The condensed moisture precipitates out
and collects in the separator 120a. The 70 degree air or gas then
travels through the air side of evaporator 116 where the air or gas
is further cooled to approximately 35 degrees with a dew point of
35 degrees (i.e., still at 100% humidity). Again, moisture
condenses out of the air or gas stream and collects in the
separator 120a. The 35 degree air or gas then travels through the
outlet side of air-to-air heat exchanger 114. This reheats the air
or gas stream to approximately 85 degrees with a pressure dew point
of 35 degrees. The air or gas stream then exits the dryer 100 at
air outlet 118. Because 85 degree air can hold significantly more
moisture vapor than 35 degree air, dryer 100 provides a source of
dry, unsaturated, pressurized air or gas at air outlet 118.
[0006] In refrigerant heat exchanger circuit 120, refrigerant
enters the refrigerant side of evaporator 116 as a cool liquid.
While passing through evaporator 116, the refrigerant heats up and
is converted to a gas by the exchange of heat from the relatively
hot air side to the relatively cool refrigerant side of evaporator
116. The low pressure gas travels to compressor 122 where the
refrigerant is compressed into a high pressure gas. The refrigerant
than passes through air or water cooled condenser 124 where the
refrigerant is condensed to a cool, high pressure liquid. The cool,
high pressure refrigerant passes through throttling device 126
(typically capillary tubes or the like) to reduce the pressure and
boiling point of the refrigerant. The cool, low pressure, liquid
refrigerant than enters the evaporator and evaporates as described
above.
[0007] When air heat exchanger circuit 110 and refrigerant heat
exchanger circuit 120 operate at or near full capacity, hot gas
by-pass valve 128 has no particular function. However, as the
demand on air heat exchanger circuit 110 decreases, refrigerant
heat exchanger circuit 120 has excessive capacity that could cause
the liquid condensate in dryer 100 to freeze. Thus, when used in
this situation, hot gas by-pass valve 128 functions to prevent the
liquid condensate in dryer 100 from freezing. In particular, the
hot gas by-pass valve opens feeding hot, high pressure gas around
the evaporator (i.e., by-passes) maintaining a constant pressure
and temperature in the evaporator preventing any condensate from
freezing. The particulars regarding the operation of hot gas
by-pass valve 128 are well known in the art. Typically, a
temperature sensor associated with the hot gas by-pass valve (not
specifically shown in FIG. 1) monitors the refrigerant temperature
at the outlet of evaporator 116. When the temperature at the outlet
decreases below a predetermined threshold, the hot gas by-pass
valve 128 opens feeding hot, high pressure gas around the
evaporator maintaining a constant pressure and temperature in the
evaporator preventing any condensate from freezing.
[0008] The capacity of compressor 122 depends, in large part, on
the maximum required capacity or expected air flow (measured in
standard cubic feet per minute) of air heat exchanger circuit 110.
At full capacity (or air flow), compressor 122 operates at 100%
capacity and the air temperature and dew point of the air stream
is, for example, approximately as described above. The demand on
the air system, however, is not always 100% of the designed
capacity. Frequently, the demand on air heat exchanger circuit 110
is somewhat below full capacity. With less than 100% demand on air
heat exchanger circuit 110, the refrigerant heat exchanger circuit
120 described above still operates at 100% capacity, thus wasting
energy or electric power because compressor 122 does not need to
operate at full capacity. Some systems, as described above,
compensate using hot gas by-pass valve 128. Hot gas by-pass solves
the problem of providing to much cooling through refrigerant heat
exchanger circuit 120, but does not solve the problem that the
compressor is operating at a higher than necessary capacity and
consuming a larger amount of electrical power than necessary. Other
systems cycle the compressor on and off when the system operates at
less than 100% capacity. These systems reduce power consumption
somewhat, but cause excessive on and off cycling of compressor 122,
wide fluctuations in the dew point at air outlet 118, and introduce
inefficiencies associated with the heat exchange of mass media.
Thus, it would be beneficial to control operation of compressor 122
based on the demand of air heat exchanger circuit 110 to reduce the
power consumed by compressor 122 and increase the overall power
efficiency of dryer 100.
SUMMARY OF THE INVENTION
[0009] To attain the advantages of and in accordance with the
purpose of the present invention, as embodied and broadly described
herein, apparatus for controlling the operating speed of a variable
speed compressor in a refrigerated air drying system having
changing demands on an air supply, include a demand sensor capable
of sensing changes in the demand on the air supply and generating a
change in demand signal. A motor speed controller receives the
generated change in demand signal and generates a motor speed
signal. The motor speed controller sends the motor speed signal to
a motor of the variable speed compressor to change the speed of the
variable speed compressor.
[0010] Other embodiments of the present invention provide methods
for controlling the operating speed of a variable speed compressor
in a refrigerated air drying system having changing demands on an
air supply. These methods include sensing a demand on the air
supply. Determining an operating speed for a variable speed
compressor based on the sensed air supply demand. Controlling a
speed of the variable speed compressor based on the determined
operating speed.
[0011] Still other embodiments of the present invention provide
computer program products having computer readable code for
processing data to control a speed of the variable speed
compressor. The computer program product has a demand sensing
module configured to sense changes in the demand of the air supply.
A generating module is configured to generate a signal indicative
of the sensed change in demand. A motor speed controlling module is
configured to receive the signal indicative of the sensed change in
demand and generate at least one motor speed signal. The motor
speed controlling module is adapted to send the motor speed signal
to the variable speed compressor.
[0012] The foregoing and other features, utilities and advantages
of the invention will be apparent from the following more
particular description of a preferred embodiment of the invention
as illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
[0013] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate embodiments of
the present invention, and together with the description, serve to
explain the principles thereof. Like items in the drawings are
referred to using the same numerical reference.
[0014] FIG. 1 is a system block diagram of a prior art refrigerated
air drying system;
[0015] FIG. 2 is a system block diagram of a refrigerated air
drying system in accordance with the present invention;
[0016] FIG. 3 is a flow chart describing the motor speed control
drive of FIG. 2 in accordance with the present invention;
[0017] FIG. 4 is a block diagram showing compressors arranged in
parallel in accordance with an embodiment of the present
invention;
[0018] FIG. 5 is a flow chart describing the operation of the motor
speed controller with compressors as arrayed in FIG. 4;
[0019] FIG. 6 is a block diagram showing two variable speed
compressors arranged in parallel in accordance with another
embodiment of the present invention;
[0020] FIGS. 7A and 7B are a flow chart describing the operation of
the motor speed controller with compressors arrayed as in FIG.
6;
[0021] FIG. 8 is a block diagram showing a compressor with two
unload devices in accordance with an embodiment of the present
invention; and
[0022] FIG. 9 is a flow chart describing the operation of the motor
speed controller with a compressor as shown in FIG. 8.
[0023] FIG. 10 is a block diagram showing an alternate embodiment
of a refrigerated air drying system in accordance with the present
invention.
DETAILED DESCRIPTION
[0024] Some embodiments of the present invention are shown in FIGS.
2 through 9. FIG. 2 shows a refrigerated air dryer 200 in
accordance with one possible embodiment of the present invention.
Air dryer 200 includes both an air heat exchanger circuit 210 and a
refrigerant heat exchanger circuit 220. Air heat exchanger circuit
210 includes an inlet 212, an air-to-air heat exchanger 214, a
air-to-refrigerant heat exchanger or evaporator 216, and an air
outlet 218. Air heat exchanger circuit 210 also has a conventional
separator and automatic drain system (not shown) that is known in
the art.
[0025] Air heat exchanger circuit 210 operates by receiving an air
or gas stream at inlet 212. The air or gas stream travels through
air-to-air heat exchanger 214. The air or gas stream circulates in
piping 214i along the inlet side of air-to-air heat exchanges 214
to cool. After cooling, the air or gas stream exists into piping
240. The air or gas stream travels along piping 240 and enters air
side piping 216a of evaporator 216. The air or gas stream is
further cooled by evaporator 216. After this additional cooling,
the air or gas stream exists into piping 242. The air or gas stream
travels along piping 242 and enters the reheat side of air-to-air
heat exchanger 214. The air or gas stream circulates in piping
214o, along the outlet side of air-to-air heat exchanger 214 to
reheat. After reheating the air or gas steam exits air heat
exchanger circuit 210 as hot, dry air or gas at outlet 218.
[0026] Refrigerant heat exchanger circuit 220 includes evaporator
216, a compressor 222, a condenser 224, a throttling device 226,
and a hot gas by-pass valve 228. Refrigerant heat exchanger circuit
220 also has a hot gas by-pass controller 230, a temperature sensor
232, a motor speed control 234, and a pressure sensor 236. Also,
one of ordinary skill in the art would now recognize that the
pressure sensors could be replaced with other sensors capable of
monitoring system pressure, such as, for example, temperature
sensors. Similarly, one of ordinary skill in the art would now
recognize that the temperature sensors could be replaced with other
sensors, such as, for example, pressure sensors.
[0027] Refrigerant heat exchanger circuit 220 operates by
circulating a refrigerant through evaporator 216 along piping 216r
to cool down the air stream. While circulating through piping 216r,
the refrigerant changes from a liquid to a low temperature vapor
and exists evaporator 216 into piping 250. The pressure sensor 236
is connected to piping 250 to measure the pressure at the inlet to
compressor 222. Compressor 222 receives the low pressure, gas
refrigerant traveling in piping 250 and outputs the refrigerant as
a high pressure, high temperature gas refrigerant into piping 252.
The refrigerant circulates from piping 252 into condenser piping
224c where the refrigerant is condensed to a liquid and cooled. The
refrigerant exits condenser 224 as a high pressure liquid into
piping 254. Piping 254 includes throttling device 226. Piping
segments 256 and 258 connect the hot and cool sides of refrigerant
heat exchanger circuit 220 through hot gas by-pass valve 228.
[0028] When dryer 200 is operated at full capacity, compressor 222
operates at its normal operating capacity or frequency similar to
the description of dryer 100 above. When air flow through air heat
exchanger circuit 210 decreases, however, pressure sensor 236
detects the decrease in demand as a decrease in the system pressure
of refrigerant heat exchanger circuit 220 from an expected
operating pressure at the inlet of compressor 222. On sensing the
decrease in pressure, sensor 236 generates and sends a decreased
pressure signal to motor speed controller 234 through a signal
conduit 260. Motor speed controller 234 registers the decreased
pressure signal as a decrease in demand on air heat exchanger
circuit 210 and, thereby, sends a signal over signal conduit 262 to
compressor 222 that decreases the speed of the compressor motor,
i.e. decreases the motor's operating frequency, which will be
described in more detail below. This causes the system pressure of
refrigerant heat exchanger circuit 220 at the inlet of compressor
222 to increase back to the expected operating pressure. The
decrease in the motor operating frequency of compressor 222 causes
a corresponding decrease in energy consumption.
[0029] When demand on air heat exchanger circuit 210 increases,
pressure sensor 236 detects the increase in demand as an increase
in the system pressure of refrigerant heat exchanger circuit 220
from an expected operating pressure at the inlet to compressor 222.
On sensing the increase in pressure, sensor 236 generates and sends
an increased pressure signal to motor speed controller 234 over
signal conduit 260. Motor speed controller 234 registers the
increased pressure signal as an increase in demand on air heat
exchanger circuit 210 and, thereby, sends a signal over signal
conduit 262 to compressor 222 that increases the speed of the
compressor motor, i.e., increases the motor's operating frequency,
which will also be described in more detail below. This causes the
system pressure of refrigerant heat exchanger circuit 220 at the
inlet of compressor 222 to decrease back to the expected operating
pressure.
[0030] When demand on air heat exchanger circuit 210 remains
constant, pressure sensor 236 can, depending on design choice, send
an expected operating pressure signal to motor speed controller 234
or simply not send a signal to motor speed controller 234. In
either case, motor speed controller 234 maintains the operating
frequency of compressor 222 to maintain the expected operating
pressure of refrigerant heat exchanger circuit 220 at the inlet of
compressor 222.
[0031] In the present example, compressor 222 is sized so that one
compressor can satisfy the cooling requirements of dryer 200.
Compressor 222 has a minimum operating frequency. If the motor
speed is reduced below that minimum the internal lubrication of the
compressor will be insufficient and/or the refrigerant flow rate
will not provide adequate oil return. Thus, motor controller 234
can only reduce the operating frequency of compressor 222 to
compressor 222 to a predetermined minimum speed. (Note that motor
controller 234 could control the speed of compressor 222 over its
full range of speeds, i.e., 0 Hz to full frequency, if the minimum
speed was not dictated by the compressor.) When compressor 222
operates at its minimum frequency, motor speed controller 234 sends
a signal over signal conduit 264 to hot gas by-pass controller 230
to begin hot gas by-pass control of refrigerant heat exchanger
circuit 220 to prevent the suction pressure/temperature from
falling that, in turn, prevents condensed water vapor from
freezing, which will be explained further below.
[0032] FIG. 3 shows a flow chart 300 indicating operation of
refrigerant heat exchanger circuit 220. First, dryer 200 is
initialized, step 310. This can include starting compressor 222
using a "soft-start" mode. A soft start mode is a procedure that
brings the motor of compressor 222 up to speed following the motor
control curves for the motor of compressor 222. The motor curves,
not shown but generally known in the art, provide ideal voltage
supplies to the motor of compressor 222 when the motor is operating
at a given frequency. Additionally, these curves supply an optimal
rate of change in frequency for a given unit of time. While it is
preferred that motor speed controller 234 functions according to
the motor control curves it is not necessary.
[0033] Once the system is initialized and compressor 222
soft-started, motor speed controller 234 is placed in an automatic
mode, step 320. In automatic mode, motor speed controller 234
begins monitoring the pressure at the inlet to compressor 222, step
330. Next, motor speed controller 234 determines whether the motor
speed of compressor 222 is greater than the minimum speed allowed,
step 340. As noted above, the minimum speed of the motor of
compressor 222 is based largely on the lubrication ability of the
motor and is not a function of motor speed controller 234.
[0034] If the motor of compressor 222 is operating at greater than
the minimum operating speed, motor speed controller 234 next
determines whether the pressure at the inlet to compressor 222, as
measured by pressure sensor 236, is greater than a first
pre-established pressure threshold, step 350. If pressure is
greater than the first pre-established pressure threshold, motor
speed controller 234 increases the operating speed of the motor,
step 360. Otherwise, motor speed controller 234 determines whether
the pressure at the inlet to compressor 222 is less than the first
pre-established pressure threshold, step 370. If pressure is less
than the first pre-established pressure threshold, motor speed
controller 234 decreases the operating speed of the motor, step
380. Of course, if the monitored pressure is approximately the same
as the first pre-established pressure threshold, motor speed
controller 234 simply maintains the operating speed of the
compressor. After any required operating speed adjustments, the
control loop is returned to step 330.
[0035] In the preferred embodiment, the above control is referred
to as a "pressure mode" 300p because motor speed controller 234
uses a pressure signal from pressure sensor 236 to control motor
speed. Alternative means of controlling the motor speed are
possible. For example, a flow meter in air heat exchanger circuit
210 could be used to measure system demand and control the motor
speed of compressor 222.
[0036] Alternatively, a temperature sensor could be used in place
of pressure sensor 236 to measure the system demand. Essentially
any conventional demand sensor could be used to control the motor
speed.
[0037] If at step 340 motor speed controller 234 had determined
that the motor of compressor 222 was already operating at its
minimum operating speed, motor speed controller would begin a "hot
gas mode" 300t of refrigerant heat exchanger circuit 220. In hot
gas mode, motor speed controller 234 maintains the speed of the
motor of compressor 222 at the minimum operating speed, step 390.
Pressure sensor 236 continues to monitor the pressure at the inlet
to compressor 222, step 400. Motor speed controller determines
whether the pressure at the inlet of compressor 222 is less than a
second pre-established pressure threshold, step 410. If pressure is
less than the second pre-established pressure threshold, hot gas
by-pass controller 230 senses the temperature at the outlet of
evaporator 216 using sensor 232, step 420. Next, hot gas by-pass
controller 230 determines whether the temperature at the outlet of
evaporator 216 is below a hot gas by-pass pre-established
temperature threshold, step 430. If the temperature is below a hot
gas by-pass pre-established temperature threshold, hot gas by-pass
controller 230 causes hot gas by-pass valve 228 to cycle and inject
hot gas from piping 252 on the outlet side of compressor 222 into
piping 250 on the outlet side of evaporator 216, step 440. After
the hot gas is injected or if pressure was above the hot gas
by-pass pre-established pressure threshold, control reverts back to
step 400.
[0038] If at step 410 motor speed controller 234 had determined
pressure was not less than the second pre-established pressure
threshold, then motor speed control 234 reverts back to pressure
control at step 350, above. In the preferred embodiment, the second
pre-established pressure threshold is sufficiently higher than the
first pre-established pressure threshold to prevent excessive
cycling between hot gas mode 300t and pressure mode 300p. The
settings for the first and second pre-established pressure
thresholds is, however, largely a matter of design choice. The hot
gas by-pass threshold settings are well known in the art.
[0039] The embodiment of the present invention described above
shows dryer 200 with one compressor 222 that is sized to
accommodate 100% or full demand on air heat exchanger circuit 210.
Under this configuration, the motor speed of compressor 222 could
be varied from minimum to full capacity to vary the power
consumption of the overall system. Also, as is known in the art,
condenser 224 has a fan 224f and a fan motor 224m associated with
it to assist in cooling and condensing the refrigerant. The fan
motor 224m could be a variable speed motor controlled by motor
speed controller 234. In this case, the fan motor would receive a
motor speed control signal over conduit 262 so that the fan motor
speed and the speed of the compressor motor would coincide. Thus,
if air supply demand on air heat exchanger circuit 210 was 80%,
under the above described control scheme, the motor of compressor
222 would be operating at 80% and the fan motor associated with the
condenser would be operating at 80%.
[0040] Notice that the fan motor could be controlled by a separate
motor speed controller. It is currently preferred to use a separate
motor speed controller for fan motor 224m to prevent excessive
cycling of fan motor 224m that could occur if fan motor 224m was
controlled at the same speed as the motor of the compressor. In one
present preferred embodiment, the fan motor is controlled using the
same control scheme as outlined in flow chart 300, but using a
separate controller. Using a separate control has the additional
advantage that the fan motor can be controlled from 0 Hz to its
maximum frequency because the fan motor does not have the same
lubrication requirements as the compressor motor. When using a
separate motor speed controller to control the operating speed of
fan motor 224m, it is preferable to control the speed based on a
demand sensor that measures condensing pressure (a demand sensor
that measures condensing pressure is not specifically shown in the
drawing, but is generally known in the art) instead of the demand
sensor that measures the pressure at the inlet to the
compressor.
[0041] More precise control over the power consumption could be
obtained by using more compressors or compressors with unloading
devices and/or variable speed controlled condenser fan motors. This
would be helpful in systems where power consumption is of greater
concern, or more precise control over the coolant system is needed.
For example, FIG. 4 shows three compressors 460, 470, and 480
arranged in parallel. In this embodiment, motor speed controller
234 would control compressor 460 in a variable speed mode and
control compressors 470 and 480 by simple on/off instructions.
Additionally, compressor 460, being the variably controlled
compressor, is preferably capable of twice the capacity of
compressors 470 and 480. In this manner, demand on the air source
could be controlled down to about 25% capacity of the air flow. As
one of ordinary skill in the art would now recognize, adding more
or less compressors allows more or less precise control of the
power consumption. While the variably controlled compressor is
preferred to be about twice the size of the other compressors,
almost any arrangement is possible.
[0042] FIG. 5 is a flow chart 500 representing operation of the
present invention with multiple compressors 460, 470 and 480.
First, the motor speed controller would be placed in automatic
control, step 510, and the pressure sensor would monitor pressure
at the inlet of compressors 520. Next, the motor controller would
determine whether the variable speed compressor motor is operating
at a minimum frequency, step 530. If compressor 460 is operating at
a minimum speed, motor speed controller 234 next determines whether
two or more compressors are currently operating, i.e., compressor
460 and compressors 470 and/or 480, step 540. If only compressor
460 is operating, refrigerant heat exchanger circuit 220 enters hot
gas mode control, step 550. Step 550 is substantially as described
in steps 390 to 440 of FIG. 3. If motor speed controller 234
determines that one or both of compressors 470 and 480 are
operating in addition to variable speed compressor 460, then motor
speed controller turns one of the compressors 470 or 480 off, step
560, and returns the control to the control loop at step 570,
below.
[0043] If motor speed controller 234 had determined that variable
speed compressor 460 was not operating at its minimum, step 530,
motor speed controller 234 would then determine whether pressure at
the inlet to compressors 460, 470, and 480 was greater than the
first pre-established pressure threshold, step 570. If pressure is
greater than the first pre-established pressure threshold, which
indicates an increase in demand on air heat exchanger circuit 210,
then motor speed controller 234 checks whether variable speed
compressor 460 is operating at its maximum, step 580. If variable
speed compressor 460 is not operating at its maximum, motor speed
controller 234 increases the speed of variable speed compressor
460, step 590, and the control loop returns to step 520. If,
however, motor speed controller 234 determines that variable speed
controller 460 is operating at its maximum, step 580, then motor
speed controller turns on another compressor, either compressor 470
or 480, and brings that compressor up to its normal operating
speed, step 600. After turning on the additional compressor, motor
speed controller 234 would decrease the speed of variable speed
compressor 460, step 610, and the control loop would return to step
520.
[0044] If, at step 570, motor speed controller 234 had determined
that pressure was not greater than the first pre-established
pressure threshold, it would determine whether pressure was less
than the first pre-established pressure threshold, step 620. If
motor speed controller 234 determines pressure is less than the
first pre-established pressure threshold, then it decreases the
speed of variable speed compressor 460, step 630, and control
returns to the control loop at step 520.
[0045] In this embodiment, if the demand on air heat exchanger
circuit 210 is 25% of full capacity, compressor 460 is operating at
50% and both compressors 470 and 480 are off. As demand of air heat
exchanger circuit 210 increases, the speed of compressor 460 is
increased until demand on air heat exchanger circuit 210 is 50% and
compressor 460 is operating at 100% capacity. As demand on air heat
exchanger circuit 210 increases past 50%, a second compressor 470
would be turned on to supply 25% of the necessary flow and the
speed of compressor 460 would drop down to 50% to supply the other
25%. In other words compressor 460 would be operating at 50%
capacity and compressor 470 would be operating at 100% capacity. As
demand on air heat exchanger circuit 210 increased from 50% to 75%,
the speed of compressor 460 is increased until it is operating at
100% capacity. When demand increases over 75%, compressor 480 is
turned on and the speed of compressor 460 is reduced to 50% such
that compressor 460 is at 50%, and compressors 470 and 480 are at
100%. Similarly, other combinations of parallel compressors could
be used. One example includes a variable speed compressor capable
of 40% capacity and three on/off compressors capable of 20%
capacity each. Another example includes one variable compressor
capable of 70% capacity and two on/off compressors capable of 15%
capacity, which is useful when precise control is only necessary at
higher capacities. In general, however, any percentage combination
is possible. It is beneficial that the variable compressor capacity
be larger than the nonvariable speed compressors to avoid gaps in
the control.
[0046] In still another embodiment of the present invention, it is
possible to control two or more variable speed compressors. For
example, FIG. 6 shows first and second variable speed compressors
660 and 670 arranged in parallel. In this case, motor speed
controller 234 could control the speed of both compressors or, in
the alternative, a second motor speed controller could be added,
not shown. In the preferred embodiment, each compressor is sized to
accommodate equal portions of full capacity on refrigerant heat
exchanger circuit 220. Additionally, if only one motor speed
controller is used, it is preferable that the compressors be of
equal capacity. In this case, compressors 660 and 670 are each
capable of approximately one-half of full capacity.
[0047] FIGS. 7A and 7B show a flow chart 700 indicating operation
of the present invention with first and second variable speed
compressors 660 and 670, respectively. As with the previous
embodiments, dryer 200 is placed in operation and motor controller
234 is operating in automatic mode, step 710. In automatic mode,
pressure sensor 236 monitors pressure of refrigerant heat exchanger
circuit 220 at the inlet of first and second compressors 660 and
670, step 720. The motor speed controller next determines whether
first and second variable speed compressors are operating, step
730.
[0048] If first and second variable speed compressors 660 and 670
are not operating, it is further determined whether first variable
speed compressor 660 is operating at its minimum speed, step 740.
If first variable speed compressor 660 is operating at the minimum
speed, dryer 200 enters hot gas mode as described in Steps 390 to
440 of flow chart 300 of FIG. 3, step 750. Otherwise, it is further
determined whether first variable speed compressor 660 is operating
at its maximum speed, step 760. If first variable speed compressor
660 is operating at its maximum speed, second variable speed
compressor 670 is turned on, step 770. If second variable speed
compressor 670 is turned on, control moves to step 820, as will be
described below, otherwise the speed of first variable speed
compressor 660 is controlled in steps 780, 790, 800, and 810, in a
manner substantially identical to steps 350, 360, 370, and 380
described in flow chart 300 of FIG. 3, above.
[0049] If first and second variable speed compressors are
operating, motor speed controller 234 determines whether pressure
is greater than a first pre-established pressure threshold, step
820. If pressure is determined to be greater than the first
pre-established pressure threshold, it is further determined
whether first variable speed compressor 660 is operating at its
maximum operating speed, step 830. If first variable speed
compressor 660 is not operating at its maximum operating speed, the
speed of compressor 660 is increased, step 840, otherwise the speed
of compressor 670 is increased, step 850. The control loop then
returns to step 720.
[0050] If it is determined that pressure is not greater than the
first pre-established pressure threshold, it is next determined
whether pressure is less than the first pre-established pressure
threshold, step 860. If pressure is less than the first-established
pressure threshold, it is next determined whether second variable
speed compressor 670 is operating at it minimum speed, step 870. If
compressor 670 is not operating at its minimum speed, then its
speed is decreased, step 880, and the control loop returns to step
720. If compressor 670 is operating at its minimum speed, then it
is determined whether first variable speed compressor 660 is
operating at its minimum speed, step 890. If compressor 660 is not
at its minimum speed, then its speed is decreased, step 900, and
the control loop returns to step 720. If it is determined that
first variable speed compressor is also operating at its minimum
speed, then second variable speed compressor 670 is turned off,
step 910, and the speed of first variable speed compressor 660 is
increased, step 920, and the control loop returns to step 720. As
before, if pressure is neither greater than nor less than the first
pre-established threshold, control simply returns to step 720
without altering the speed or configuration of the compressors.
[0051] FIG. 8 shows a variable speed compressor 1800 with two
unload devices 1810 and 1820 arranged in parallel. As one of
ordinary skill in the art would now recognize, any number of unload
devices could be arranged in parallel. In this embodiment, motor
speed controller 234 would control the motor speed of compressor
1800 in variable speed mode and control unload devices 1810 and
1820 by simple on/off instructions. In general terms, compressor
1800 has multiple cylinders. The compressor is controlled using a
variable speed motor and, in this example, two unloading devices
are controlled by on/off instructions that de-energize and energize
the unload devices. When demand on the air supply is low, the
variable speed motor controlled compressor is operated and unload
devices 1810 and 1820 are energized, which causes the output of the
cylinders to be reduced. As the demand ncreases, the unload devices
are de-energized as necessary. When all unload devices re
de-energized, the compressor supplies its rated output.
[0052] Compressor 1800, being the variably controlled compressor,
supplies 100% of its total capacity when both unload devices are
de-energized, 66% of its total capacity with one unload device
energized and one unload device de-energized, and 33% of its total
capacity with both unload devices energized. In this manner, demand
on the air source could be controlled down to approximately 16%
capacity of the air flow. As one of ordinary skill in the art would
now recognize, altering the number of unload devices allows more or
less precise control of the power consumption. While the variably
controlled compressor is preferred to have two unloading devices,
almost any arrangement is possible.
[0053] FIG. 9 is a flow chart 930 representing operation of the
present invention with variable speed compressor 1800 having two
unload devices 1810 and 1820. First, the motor speed controller
would be placed in automatic control, step 940, and the pressure
sensor would monitor pressure at the inlet of compressor 1800, step
950. Next, the motor controller would determine whether the
variable speed compressor motor is operating at greater than a
minimum speed, step 960. If compressor 1800 is operating at a
minimum speed, motor speed controller 234 next determines whether
two or more unload devices are currently de-energized, i.e.,
variable speed compressor 1800 and associated unload devices 1810
and 1820 are operating, step 970. If compressor 1800 is operating
with both upload devices energized, hot gas control mode is
initiated, step 980. Step 980 is substantially as described in
steps 390 to 450 of FIG. 3. If motor speed controller 234
determines that one or both of unload devices 1810 and 1820 are
energized in addition to variable speed compressor 1800, then motor
speed controller de-energizes one of the unload devices 1810 or
1820, step 990, and returns the control to the control loop at step
1000, below.
[0054] If motor speed controller 234 had determined the variable
speed compressor 1800 was not operating at its minimum, step 960,
motor speed controller 234 would then determine whether pressure at
the inlet to compressor 1800 was greater than the first
pre-established pressure threshold, step 1000. If pressure is
greater than the first pre-established pressure threshold, which
indicates an increase in demand on air heat exchanger circuit 210,
then motor speed controller 234 checks whether variable speed
compressor 1800 is operating at its maximum, step 1010. If variable
speed compressor 1800 is not operating at its maximum, motor speed
controller 234 increases the speed of variable speed compressor
1800, step 1020, and the control loop returns to step 950. If,
however, motor speed controller 234 determines that variable speed
compressor 1800 is operating at its maximum, step 1010, then motor
speed controller de-energizes an unload device, either 1810 or
1820, step 1030. After de-energizing the additional unload device,
motor speed controller 234 would decrease the speed of variable
speed compressor 1800, step 1040, and the control loop would return
to step 950.
[0055] If, at step 1000, motor speed controller 234 had determined
that pressure was not greater than the first pre-established
pressure threshold, it would determine whether pressure was less
than the first pre-established pressure, step 1050. If motor speed
controller 234 determines pressure is less than the first
pre-established pressure threshold, then it decreases the speed of
variable speed compressor 1800, step 1060, and control returns to
the control loop at step 950.
[0056] In this embodiment, if the demand on air heat exchange
circuit 210 is 16% of full capacity, compressor 1800 is operating
at 50% and both unload devices 1810 and 1820 are energized. As
demand of air heat exchanger circuit 210 increases, the speed of
compressor 1800 is increased until demand on air heat exchanger
circuit 210 is about 33% and compressor 1800 is operating at
maximum speed. As demand on air heat exchanger circuit 210
increases past 33%, an unload device 1810 would be de-energized to
supply 33% of the necessary flow and the speed of compressor 1800
would drop down to 50% to supply the other 16%. In other words,
compressor 1800 would be operating at 50% capacity and unload
device 1810 would be off. As demand on air heat exchanger circuit
210 increased to 66%, the speed of compressor 1800 is increased
until it is operating at maximum speed. When demand increases over
66%, unload device 1820 is de-energized and the speed of compressor
1800 is reduced to 50% such that compressor 1800 is at 50%, and the
unload devices are de-energized. Many combinations of unload
devices and compressors could be used. The above embodiments are
only exemplary of the possible combinations. For example, a
variable speed compressor could have three unload devices capable
of 25% capacity each. Another example includes one variable
compressor with five unload devices capable of 15% capacity. In
general, however, any percentage combination is possible.
[0057] While the invention has been particularly shown and
described with reference to a preferred embodiment thereof, it will
be understood by those skilled in the art that various other
changes in the form and details may be made without departing from
the spirit and scope of the invention. Additionally, other
embodiments of the invention will be apparent to those skilled in
the art from consideration of the specification and practice of the
invention disclosed herein. It is intended that the specification
and examples be considered as exemplary only, with the true scope
and spirit of the invention being indicated by the following
claims.
* * * * *