U.S. patent application number 13/008057 was filed with the patent office on 2011-05-12 for parallel condensing unit control system and method.
This patent application is currently assigned to EMERSON CLIMATE TECHNOLOGIES, INC.. Invention is credited to Brian J. Akehurst, Hans-Juergen Bersch, Raymond Steils.
Application Number | 20110107775 13/008057 |
Document ID | / |
Family ID | 37873167 |
Filed Date | 2011-05-12 |
United States Patent
Application |
20110107775 |
Kind Code |
A1 |
Akehurst; Brian J. ; et
al. |
May 12, 2011 |
Parallel Condensing Unit Control System And Method
Abstract
A system comprises a condenser for a refrigeration system and a
control module. The condenser has a plurality of variable speed
condenser fans. The control module controls the plurality of
variable speed condenser fans. The control module increases
condenser fan operation by activating a deactivated variable speed
condenser fan at a first fan speed when at least one variable speed
condenser fan of the plurality is deactivated and by increasing a
fan speed of an activated variable speed condenser fan to a second
fan speed when each variable speed condenser fan of the plurality
is activated and operating at the first fan speed. The second fan
speed is faster than the first fan speed.
Inventors: |
Akehurst; Brian J.; (East
Sussex, GB) ; Bersch; Hans-Juergen; (Simmerath,
DE) ; Steils; Raymond; (Embourg, BE) |
Assignee: |
EMERSON CLIMATE TECHNOLOGIES,
INC.
Sidney
OH
|
Family ID: |
37873167 |
Appl. No.: |
13/008057 |
Filed: |
January 18, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11299285 |
Dec 9, 2005 |
7878014 |
|
|
13008057 |
|
|
|
|
Current U.S.
Class: |
62/89 ;
62/177 |
Current CPC
Class: |
F25B 49/022 20130101;
F25B 2700/21152 20130101; F25B 49/027 20130101; Y02B 30/743
20130101; F25B 2400/075 20130101; F25B 2600/111 20130101; F25B
2600/0251 20130101; Y02B 30/70 20130101; F25B 2700/21151
20130101 |
Class at
Publication: |
62/89 ;
62/177 |
International
Class: |
F25D 17/06 20060101
F25D017/06; F25D 17/00 20060101 F25D017/00 |
Claims
1. A system comprising: a condenser for a refrigeration system,
said condenser having a plurality of variable speed condenser fans;
a control module controlling said plurality of variable speed
condenser fans, said control module increasing condenser fan
operation by activating a deactivated variable speed condenser fan
at a first fan speed when at least one variable speed condenser fan
of said plurality is deactivated and by increasing a fan speed of
an activated variable speed condenser fan to a second fan speed
when each variable speed condenser fan of said plurality is
activated and operating at said first fan speed, said second fan
speed being faster than said first fan speed.
2. The system of claim 1 wherein said control module increases
condenser fan operation by increasing a fan speed of an activated
variable speed condenser fan from said first fan speed to said
second fan speed when each variable speed condenser fan of said
plurality is activated and when at least one variable speed
condenser fan of said plurality is operating at said first fan
speed and each remaining variable speed condenser fan of said
plurality is operating at one of said first fan speed and said
second fan speed.
3. The system of claim 1, wherein said control module decreases
condenser fan operation by decreasing a fan speed of an activated
variable speed condenser fan from said second fan speed to said
first fan speed when each variable speed condenser fan of said
plurality is operating at said second fan speed.
4. The system of claim 1, wherein said control module decreases
condenser fan operation by decreasing a fan speed of an activated
variable speed condenser fan from said second fan speed to said
first fan speed when at least one variable speed condenser fan of
said plurality is operating at said second fan speed and each
remaining variable speed condenser fan of said plurality is
operating at one of said first fan speed and said second fan
speed.
5. The system of claim 1, wherein said control module decreases
condenser fan operation by deactivating an activated variable speed
condenser fan when each variable speed condenser fan of said
plurality is operating at said first fan speed.
6. The system of claim 1, further comprising a discharge pressure
sensor that generates a discharge pressure signal based on a
discharge pressure of said condenser, wherein said control module
compares said discharge pressure to a set point and controls
condenser fan operation based on said comparison.
7. A method comprising: controlling, with a control module, a fan
speed for each variable speed condenser fan of a condenser for a
refrigeration system, said condenser having a plurality of variable
speed condenser fans; increasing condenser fan operation of said
condenser, with said control module, by activating a deactivated
variable speed condenser fan at a first fan speed when at least one
variable speed condenser fan of said plurality is deactivated and
by increasing a fan speed of an activated variable speed condenser
fan to a second fan speed when each variable speed condenser fan of
said plurality is activated and operating at said first fan speed,
said second fan speed being faster than said first fan speed.
8. The method of claim 7 further comprising increasing condenser
fan operation, with said control module, by increasing a fan speed
of an activated variable speed condenser fan from said first fan
speed to said second fan speed when each variable speed condenser
fan of said plurality is activated and when at least one variable
speed condenser fan of said plurality is operating at said first
fan speed and each remaining variable speed condenser fan of said
plurality is operating at one of said first fan speed and said
second fan speed.
9. The method of claim 7, further comprising decreasing condenser
fan operation, with said control module, by decreasing a fan speed
of an activated variable speed condenser fan from said second fan
speed to said first fan speed when each variable speed condenser
fan of said plurality is operating at said second fan speed.
10. The method of claim 7, further comprising decreasing condenser
fan operation, with said control module, by decreasing a fan speed
of an activated variable speed condenser fan from said second fan
speed to said first fan speed when at least one variable speed
condenser fan of said plurality is operating at said second fan
speed and each remaining variable speed condenser fan of said
plurality is operating at one of said first fan speed and said
second fan speed.
11. The method of claim 7, further comprising decreasing condenser
fan operation, with said control module, by deactivating an
activated variable speed condenser fan when each variable speed
condenser fan of said plurality is operating at said first fan
speed.
12. The method of claim 7, further comprising comparing a received
discharge pressure to a set point and controlling condenser fan
operation, with said control module, based on said comparing.
13. A system comprising: a condenser for a refrigeration system,
said condenser having a plurality of condenser fans including a
first variable speed condenser fan and a fixed speed condenser fan;
a control module controlling said plurality of condenser fans, said
control module increasing condenser fan operation, when said
plurality of condenser fans are deactivated, by activating said
first variable speed condenser fan, and said control module
increasing condenser fan operation by increasing a fan speed of
said first variable speed condenser fan to a maximum fan speed
prior to activating said fixed speed condenser fan.
14. The system of claim 13, said plurality of condenser fans
including a second variable speed condenser fan, said control
module increasing condenser fan operation by increasing a fan speed
of said second variable speed condenser fan to a maximum fan speed
prior to activating said fixed speed condenser fan.
15. The system of claim 13, further comprising a discharge pressure
sensor that generates a discharge pressure signal based on a
discharge pressure of said condenser, wherein said control module
compares said discharge pressure to a set point and controls said
plurality of condenser fans based on said comparison.
16. A method comprising: controlling, with a control module, a
plurality of condenser fans of a condenser for a refrigeration
system, said plurality of condenser fans including a first variable
speed condenser fan and a fixed speed condenser fan; increasing
condenser fan operation, when said plurality of condenser fans are
deactivated, by activating, with said control module, said first
variable speed condenser fan; increasing condenser fan operation by
increasing, with said control module, a fan speed of said first
variable speed condenser fan to a maximum fan speed prior to
activating, with said control module, said fixed speed condenser
fan.
17. The method of claim 16, said plurality of condenser fans
including a second variable speed condenser fan, said method
further comprising: increasing, with said control module, a fan
speed of said second variable speed condenser fan to a maximum fan
speed prior to activating said fixed speed condenser fan.
18. The method of claim 16, further comprising comparing a received
discharge pressure to a set point and controlling condenser fan
operation, with said control module, based on said comparing.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/299,285 filed on Dec. 9, 2005. The entire
disclosure of the above application is incorporated herein by
reference.
FIELD
[0002] The present teachings relate to refrigeration systems and,
more particularly, to parallel condensing unit control.
BACKGROUND
[0003] Refrigeration systems typically include a compressor, an
evaporator, an evaporator fan, an expansion device, a condenser,
and a condenser fan which operate together to cool a refrigerated
space. The compressor, expansion device, condenser, and evaporator
are fluidly coupled such that a loop or a closed system exists for
circulation of a refrigerant therein. The compressor receives the
refrigerant in a gaseous form from the evaporator and pressurizes
the gas such that the gas changes from the gaseous state into a
liquid state as it unloads heat to an air stream moving through the
condenser. Once the refrigerant reaches the liquid state in the
condenser, the refrigerant is sent through an expansion device
before reaching the evaporator, which is held at a low pressure by
the operation of the expansion device and compressor. The low
pressure of the evaporator causes the refrigerant to change state
back to a gas and, as it does so, to absorb heat from an air stream
moving through the evaporator. In this manner, the air stream
flowing through the evaporator is cooled and the temperature of the
refrigerated space is lowered.
[0004] The evaporator fan is typically disposed proximate the
evaporator and is operable to generate a flow of air through the
evaporator and into a refrigerated space. An air flow through the
evaporator is cooled as a liquid refrigerant passes therethrough.
In this regard, the air flow may be regulated to control the
temperature of the exiting air stream and the overall temperature
of the refrigerated space.
[0005] A bank of parallel condensing units may be used in
conjunction with a bank of evaporators to cool a plurality of
refrigerated spaces. Each condensing unit includes one or more
compressors fluidly coupled to the bank of evaporator units,
whereby the evaporator units are disposed within a building
generally proximate a refrigerated space and the condensing units
are disposed outside of the building and are operable to expel heat
absorbed by the evaporators. Having the condensing units in fluid
communication with the evaporator units provides the refrigeration
system with flexibility as each condensing unit may be
independently activated to provide a desired amount of liquid
refrigerant to each of the evaporator units, thereby evenly
controlling the cooling of each refrigerated space.
[0006] Conventionally, the condensing units operate independently
according to local set points. The conventional system, however,
results in certain inefficiencies. For example, compressors on each
of the condensing units may be activated and deactivated
independent of condenser capacity across the bank of condensing
units. In such case, one condensing unit may be operating at or
near maximum compressor capacity while a parallel condensing unit
may be operating at or near minimum compressor capacity.
SUMMARY
[0007] A system comprises a condenser for a refrigeration system,
the condenser having a plurality of variable speed condenser fans,
and a control module. The control module controls the plurality of
variable speed condenser fans. The control module increases
condenser fan operation by activating a deactivated variable speed
condenser fan at a first fan speed when at least one variable speed
condenser fan of the plurality is deactivated and by increasing a
fan speed of an activated variable speed condenser fan to a second
fan speed when each variable speed condenser fan of the plurality
is activated and operating at the first fan speed. The second fan
speed is faster than the first fan speed.
[0008] A method comprises controlling, with a control module, a fan
speed for each variable speed condenser fan of a condenser for a
refrigeration system, the condenser having a plurality of variable
speed condenser fans. The method may also comprise increasing
condenser fan operation of the condenser, with the control module,
by activating a deactivated variable speed condenser fan at a first
fan speed when at least one variable speed condenser fan of the
plurality is deactivated and by increasing a fan speed of an
activated variable speed condenser fan to a second fan speed when
each variable speed condenser fan of the plurality is activated and
operating at the first fan speed, the second fan speed being faster
than the first fan speed.
[0009] A system may also comprise a condenser for a refrigeration
system, the condenser having a plurality of condenser fans
including a first variable speed condenser fan and a fixed speed
condenser fan. The system may also comprise a control module that
controls the plurality of condenser fans. The control module may
increase condenser fan operation, when the plurality of condenser
fans are deactivated, by activating the first variable speed
condenser fan. The control module may increase condenser fan
operation by increasing a fan speed of the first variable speed
condenser fan to a maximum fan speed prior to activating the fixed
speed condenser fan.
[0010] A method may also comprise controlling, with a control
module, a plurality of condenser fans of a condenser for a
refrigeration system, the plurality of condenser fans including a
first variable speed condenser fan and a fixed speed condenser fan.
The method may also comprise increasing condenser fan operation,
when the plurality of condenser fans are deactivated, by
activating, with the control module, the first variable speed
condenser fan. The method may also comprise increasing condenser
fan operation by increasing, with the control module, a fan speed
of the first variable speed condenser fan to a maximum fan speed
prior to activating, with the control module, the fixed speed
condenser fan.
[0011] Further areas of applicability of the present teachings will
become apparent from the detailed description provided hereinafter.
It should be understood that the detailed description and specific
examples are intended for purposes of illustration only and are not
intended to limit the scope of the teachings.
DRAWINGS
[0012] The present teachings will become more fully understood from
the detailed description and the accompanying drawings,
wherein:
[0013] FIG. 1 is a schematic of a refrigeration system according to
the teachings;
[0014] FIG. 2 is a flow chart illustrating steps performed to
activate and deactivate compressors according to the teachings;
[0015] FIG. 3 is a flow chart illustrating steps performed to
activate and deactivate condenser fans according to the teachings;
and
[0016] FIG. 4 is a flow chart illustrating steps performed to
control condenser fan speed according to the teachings.
DETAILED DESCRIPTION
[0017] The following description is merely exemplary in nature and
is in no way intended to limit the teachings, application, or
uses.
[0018] With reference to FIG. 1, a refrigeration system 10 includes
condensing units 100 connected in parallel, an expansion device
102, an evaporator 104, and an evaporator fan 106. Each condensing
unit 100 includes at least one compressor 110, a coil 112, and at
least one condenser fan 114. As can be appreciated, while three
condensing units 100 are shown, the refrigeration system 10 may
include any number of condensing units 100. Additionally, while
condensing units 100 are shown with two, three, and four
compressors 110, condensing units may have any number of
compressors 110. Further, while the condensing units 100 are shown
with two condenser fans 114, condensing units 100 may include any
number of condenser fans 114.
[0019] The compressors 110 receive refrigerant in a gaseous state
from the evaporator 104 and return the gaseous refrigerant to the
liquid state through cooperation with the coil 112 and condenser
fans 114. Specifically, each compressor 110 is fluidly coupled to
the evaporator 104 by a fluid conduit and a suction manifold 116
such that gaseous refrigerant exiting the evaporator 104 is
received by the compressors 110 via the suction manifold 116.
Refrigerant exiting the compressors 110 is received by a discharge
manifold 118. In FIG. 1, the flow of refrigerant is shown by solid
arrowed lines. The compressors 110 may be scroll compressors as
disclosed by U.S. Pat. No. 6,350,111 assigned to Copeland
Corporation of Sidney, Ohio, U.S.A., which is expressly
incorporated herein by reference.
[0020] Upon receiving the gaseous refrigerant, the compressors 110
increase the pressure of the gaseous refrigerant, thereby causing
the refrigerant to circulate through the coil 112 under high
pressure. As the refrigerant is circulated through the coil 112,
the refrigerant is cooled by the condenser fans 114 circulating an
air flow over the coil 112. As the high pressure, gaseous
refrigerant is circulated through the coil 112, heat is rejected
from the refrigerant and carried away from the coil 112 by the air
flow generated by the condenser fans 114. Such a concurrent
reduction in temperature and increase in pressure causes the
gaseous refrigerant to change state and revert back to the liquid
state.
[0021] The expansion device 102 reduces the pressure of the liquid
refrigerant to thereby ease the transition of the refrigerant from
the liquid state to the gaseous state. Such conversion causes the
refrigerant to absorb heat from an area surrounding the evaporator,
thereby cooling the surrounding area. While one evaporator 104 and
expansion device 102 are shown, the refrigeration system 10 may
include any number of evaporators 104 with expansion devices
102.
[0022] As the liquid refrigerant expands via the expansion device
102, the refrigerant starts to transition from the liquid state to
the gaseous state. An evaporator fan 106 circulates an air flow
through the evaporator 104 such that heat from the air flow is
absorbed by the refrigerant, thereby cooling a refrigerated space
disposed proximate the evaporator 104. The heat absorption,
combined with the decrease in pressure caused by the expansion
device 102, causes the refrigerant to change state back into the
gaseous state. Once the refrigerant reaches the gaseous state, the
gaseous refrigerant is drawn toward the condensing units 100 once
again due to a suction imparted thereon by the compressors 110. As
the compressors 110 are fluidly coupled to the evaporators 104 via
conduit, the compressors create suction in the conduit as gaseous
refrigerant is compressed in the condensing units 100. In this
manner, the gaseous refrigerant disposed in the evaporator 104 is
drawn into the compressors 110 and the cycle begins anew.
[0023] Distributed condensing units are disclosed in assignee's
commonly-owned International Application Number PCT/US2004/033001,
filed Oct. 8, 2004, with priority claim to U.S. provisional Patent
Application No. 60/509,469, filed Oct. 8, 2003, both of which are
incorporated herein by reference.
[0024] Each condensing unit 100 includes a control module 120 that
controls operation of the condensing unit. Specifically, the
control module selectively operates the compressors 110 and
condenser fans 114. The control module 120 receives operating
signals based on operating parameters of the refrigeration system
10. Received operating signals include a suction pressure signal, a
suction temperature signal, and a discharge pressure signal. As can
be appreciated, other refrigeration system operating signals may
also be received.
[0025] A suction pressure sensor 122 generates the suction pressure
signal based on suction pressure on the suction side of the
condensing unit 100. A suction temperature sensor 124 generates the
suction temperature signal based on suction temperature on the
suction side of the condensing unit 100. A discharge pressure
sensor 126 generates the discharge pressure signal based on
discharge pressure on the discharge side of the condensing
unit.
[0026] The control module 120 receives feedback signals from the
compressors 110 and condenser fans 114. The feedback signals
indicate the operating state of the specific compressor 110 or
condenser fan 114. In this way, when the control module 120
activates or deactivates a compressor 110 or a condenser fan 114,
the control module 120 is able to verify that the compressor 110 or
condenser fan 114 has responded accordingly.
[0027] Each of the control modules 120 is connected to a
communication link 130 that enables the control modules 120 to
communicate with each other to coordinate operation of the
condensing units 100. The communication link may include an
Ethernet connection, an internet connection, a LAN, an intranet, or
other suitable network connection enabling the control modules 120
to send and receive messages. Additional network hardware (not
shown) such as a router, switch, or hub may be included. The
communication link 130 may be a wired or wireless connection.
[0028] The control modules 120 selectively activate compressors 110
and condenser fans 114 based on the received operating signals. The
control modules 120 compare the suction pressure signal, or the
suction temperature signal, to a predetermined, or user inputted,
set point. The control modules 120 activate a compressor 110, if
any are deactivated, when the suction pressure or suction
temperature is greater than the set point. The control modules 120
deactivate a compressor 110, if any are activated, when the suction
pressure or suction temperature signal is less than the set point.
As described in more detail below, the control modules 120
communicate via the communication link to coordinate compressor
operation.
[0029] Generally, the control modules 120 increase compressor
capacity along with condenser capacity. To this end, compressor
capacity is increased and decreased in a concurrent manner across
the bank of condensing units 100. When selecting a compressor 110
for activation, the control modules 120 communicate to find a
deactivated compressor 110 on a condensing unit 100 with the least
number of activated compressors 110. Likewise, when selecting a
compressor 110 to deactivate, the control modules 120 communicate
to find an activated compressor on a condensing unit 100 with the
most activated compressors 110.
[0030] The control modules 120 also coordinate condensing unit and
compressor operation time. When multiple condensing units 100 are
available to satisfy a compressor activation or deactivation
request, a rotating condensing unit schedule is used to select the
condensing unit. When multiple compressors 110 on a condensing unit
are available to satisfy a compressor activation or deactivation
request, a rotating compressor schedule is used to select the
compressor 110.
[0031] To coordinate operation of the condensing units, one of the
condensing unit control modules 120 functions as the master control
module 120', or MCM 120', while the remaining control modules 120
function as the slave control modules 120'', or SCM's 120''. The
MCM 120' communicates with the SCM's 120'' and selectively
activates compressors across all of the condensing units. The MCM
120' controls all of the compressors across the bank of condensing
units 100.
[0032] The MCM 120' may individually poll each of the SCM's 120''
to coordinate compressor operation. In such case, the MCM 120' may
determine the number of activated and deactivated compressors 110
on each condensing unit 100. Alternatively, the MCM 120' may
communicate a request message that is passed along to each SCM
120'' until the request can be satisfied, or until the request is
returned unsatisfied. When an SCM 120'' is able to satisfy the
request, it communicates an answer to the MCM 120' indicating
so.
[0033] The MCM 120' directly controls the compressors 110 located
on its condensing unit 100 by the direct connections from the MCM
120' to its associated compressors 110. The MCM 120' indirectly
controls the compressors 110 located on other condensing units 100
by communicating with the SCM's 120'' located on the other
condensing units 100.
[0034] Operation of the MCM 120' is now described with continued
reference to FIG. 1 and with reference to FIG. 2, which illustrates
steps performed by the MCM 120' to coordinate compressor operation
across condensing units 100. In step 202, the MCM 120' checks the
refrigeration system operating parameter. The operating parameter
may be suction pressure (P.sub.s) or suction temperature (T.sub.s),
or other suitable refrigeration system operating parameter. For
example, the MCM 120' may simply monitor the local suction pressure
or suction temperature signal from the suction pressure sensor 122
or suction temperature sensor 124 on its own condensing unit.
Alternatively, the MCM 120' may monitor an average suction pressure
or suction temperature across all the condensing units 100.
Alternatively, the MCM 120' may monitor an operating parameter from
a refrigeration system operating sensor not attached to a
refrigeration unit. For example, the MCM may receive an evaporator
discharge temperature signal from an evaporator discharge
temperature sensor 132 via the communication link 130.
Additionally, the MCM 120' may receive an ambient temperature
signal from an ambient temperature sensor (not shown), and may
monitor a difference between discharge temperature and ambient
temperature.
[0035] In step 204, the MCM 120' compares the operating parameter
with the set point. The set point may be predetermined or received
as a user input. The set point may be adjusted during operation of
the refrigeration system. When in step 204 the operating parameter
is greater than the set point, the MCM 120' takes steps to activate
a compressor starting with step 206.
[0036] In step 206, the MCM 120' determines whether any available
condensing unit 100 has zero compressors 110 activated. An
available condensing unit 100 is a condensing unit 100 with less
than all of its compressors 110 activated. When in step 206 an
available condensing unit 100 has zero compressors 110 activated,
the MCM 120' activates a compressor 110 on a condensing unit 100
with zero compressors 110 activated in step 208. When in step 206
the MCM 120' determines there are no condensing units 100 with zero
compressors 110 activated, the MCM 120' proceeds to step 210.
[0037] In step 210, the MCM 120' determines whether any available
condensing unit 100 has one compressor 110 activated. When in step
210 an available condensing unit 100 has one compressor 110
activated, the MCM 120' activates a compressor 110 on a condensing
unit 100 with one compressor 110 activated in step 212. When in
step 210 the MCM 120' determines there are no available condensing
units 100 with one compressor 110 activated the MCM 120'
proceeds.
[0038] The MCM 120' continues in this fashion, incrementing the
compressor number by one, up to X, the maximum number of
compressors 110 on any condensing unit 100. In step 214, the MCM
120' determines whether any available condensing unit 100 has X-1
compressors 110 activated. When in step 214 an available condensing
unit 100 has X-1 compressors 110 activated, the MCM 120' activates
a compressor 110 on a condensing unit 100 with X-1 compressors 110
activated in step 216. When in step 214 the MCM 120' determines
there are no available condensing units 100 with X-1 compressors
110 activated, all of the compressors 110 in the refrigeration
system 10 are activated, and the MCM 120' loops back to step 202.
As can be appreciated, the MCM 120' may wait a predetermined cycle
time before continuing with another iteration starting with step
202.
[0039] When in steps 208, 212, and 216 there is more than one
available condensing unit 100 with the given number of activated
compressors 110, the MCM 120' chooses the condensing unit 100 based
on a rotating schedule. In this way overall operating time is
roughly equal across the condensing units.
[0040] In steps 208, 212, and 216, activation of a compressor 110
is accomplished by a local condensing unit control module 120. For
example, when the compressor 110 to be activated is located on the
same condensing unit 100 as the MCM 120', the MCM 120' activates
the compressor 110 directly. When the compressor 110 to be
activated is located on a condensing unit 100 controlled by an SCM
120'', the MCM 120' communicates a compressor activation request to
the SCM 120''. The SCM 120'' receives the request, and activates a
compressor 110. Like selection of the condensing units 100, the
compressors 110 on a given condensing unit 100 are also activated
according to a rotating schedule. In this way compressor operating
time is roughly equal for compressors 110 on a given condensing
unit 100.
[0041] Condensing units 100 may have one or more variable capacity
compressors 110'. In such case, the variable capacity compressors
110' may be activated prior to activation of the fixed capacity
compressors 110. The variable capacity compressors 110' may be
operated at varying capacity until reaching a threshold capacity,
such as the maximum compressor capacity. When the threshold
capacity is reached, the fixed capacity compressors 110 may be
activated as set forth above.
[0042] The control modules 120 receive feedback signals from the
compressors 110 indicating an operating state of the compressor
110. When a control module 120 attempts to activate a compressor
110 and the feedback signal indicates that the compressor 110 is
not responding, the control module 120 may attempt to activate
another compressor 110 on the condensing unit. When an SCM 120'' is
not able to activate any compressor 110 on the condensing unit, the
SCM 120'' communicates to the MCM 120' that it is not able to
satisfy the request. When the MCM 120' is not able to activate any
compressor on its condensing unit 100, it may attempt to activate a
compressor 110 on another condensing unit 100.
[0043] In steps 208, 212, and 216, the MCM 120' waits until it
receives a feedback signal from a compressor 110 or a response from
an SCM 120'' indicating that a compressor 110 was successfully
activated and loops back to step 202. As can be appreciated, the
MCM 120' may wait a predetermined cycle time before continuing with
another iteration starting with step 202.
[0044] When in step 204 the operating parameter is not greater than
the set point, the MCM 120' takes steps to deactivate a compressor
110 starting with step 220. In step 220, the MCM 120' determines
whether any condensing unit 100 has X compressors 110 activated,
where X is the maximum number of compressors 110 on any condensing
unit 100. When in step 220 a condensing unit 100 has X compressors
110 activated, the MCM 120' deactivates a compressor 110 on a
condensing unit 100 with X compressors 110 activated.
[0045] When in step 220 the MCM 120' determines there are no
condensing units 100 with X compressors 110 activated, the MCM 120'
proceeds to step 224 and determines whether any condensing unit 100
has X-1 compressors 110 activated. When in step 224 a condensing
unit 100 has X-1 compressors 110 activated, the MCM 120'
deactivates a compressor 110 on a condensing unit 100 with X-1
compressors 110 activated in step 226.
[0046] The MCM 120' continues in this fashion, decrementing the
compressor number by one, down to 1 in step 228. In step 228, the
MCM 120' determines whether any condensing unit 100 has 1
compressor 110 activated. When in step 228 a condensing unit 100
has 1 compressor 110 activated, the MCM 120' deactivates a
compressor 110 on a condensing unit 100 with 1 compressor 110
activated in step 230. When in step 228 the MCM 120' determines
there are no condensing units 100 with 1 compressor 110 activated,
all of the compressors 110 in the refrigeration system 10 are
deactivated, and MCM 120' loops back to step 202. As can be
appreciated, the MCM 120' may wait a predetermined cycle time
before continuing with another iteration starting with step
202.
[0047] When in steps 222, 226, and 230 more than one condensing
unit 100 has the given number of activated compressors 110, the MCM
120' again chooses the condensing unit 100 based on the rotating
schedule. When the compressor 110 to be deactivated is located on a
condensing unit 100 controlled by an SCM 120'', the MCM 120'
communicates a compressor deactivation request to the SCM 120''.
The SCM 120'' receives the request, and deactivates a compressor
110. Like the condensing units 100, the compressors 110 are also
deactivated according to a rotating schedule.
[0048] In steps 222, 226, and 230, the MCM 120' waits until it
receives a feedback signal from a compressor 110 or a response from
an SCM 120'' indicating that a compressor 110 was successfully
deactivated and loops back to step 202. As can be appreciated, the
MCM 120' may wait a predetermined cycle time before continuing with
another iteration starting with step 202.
[0049] In the event the communication link 130 fails or is
disconnected, the control modules 120 selectively activate
compressors 110 based on local operating parameters. In such case,
each of the control modules 120 monitor the local suction pressure
or temperature, and selectively activate compressors 110 based on a
local default set point. In the event the local sensors fail as
well, the control modules 120 may simply operate a default number
of compressors 110.
[0050] The control modules 120 also control condenser fan
operation. Condenser fan operation is controlled by the local
control modules 120 based on discharge pressure. The control
modules 120 receive the discharge pressure signal and control
condenser fan operation based on a local discharge pressure set
point. Generally, the control modules 120 increase condenser fan
operation, if possible, when discharge pressure is greater than a
predetermined or user inputted set point.
[0051] The condenser fans 114 may be fixed speed condenser fans 114
or variable speed condenser fans 114'. Operation of a control
module 120 is now described with continued reference to FIG. 1 and
with reference to FIG. 3, which illustrates steps performed by a
control module 120 to control condenser fan operation for fixed
speed condenser fans 114.
[0052] In step 300, the control module 120 checks the discharge
pressure (P.sub.D) and proceeds to step 302. When P.sub.D is
greater than the set point, the control module 120 proceeds to step
304 and determines whether any condenser fan 114 is deactivated.
When a condenser fan 114 is deactivated, the control module 120
activates a condenser fan 114 in step 306 and loops back to step
300. When in step 304 all condenser fans 114 are on, the control
module 300 loops back to step 300. The control module 120 may wait
a predetermined cycle time before continuing with another iteration
starting with step 300.
[0053] In step 302 when P.sub.D is not greater than the set point,
the control module 120 proceeds to step 310 and determines whether
any condenser fan 114 is activated. When a condenser fan 114 is
activated, the control module 120 deactivates a condenser fan 114
in step 312 and loops back to step 300. When in step 310 all
condenser fans 114 are deactivated, the control module loops back
to step 300. The control module 120 may wait a predetermined cycle
time before continuing with another iteration starting with step
300.
[0054] The condenser fans 114 may also be variable speed condenser
fans 114' with a lowest fan speed and a highest fan speed. There
are two modes of variable speed fan control. First, the variable
speed condenser fans 114' may be controlled in silent mode, wherein
fan speed is minimized to reduce environmental noise, while
maintaining P.sub.D at or below the set point. Second, the variable
speed condenser fans 114' may be controlled in efficiency mode,
wherein fan speed is maximized to hold P.sub.D as low as
possible.
[0055] Silent mode operation is now described with continued
reference to FIG. 1 and with reference to FIG. 4, which illustrates
steps performed by a control module 120 in silent mode. In step
400, the control module 120 checks P.sub.D. In step 402, the
control module 120 determines whether P.sub.D is greater than the
set point. When P.sub.D is greater than the set point, the control
module 120 proceeds to step 404 and checks the variable condenser
fan speeds for the condensing unit 100.
[0056] In step 406 the control module 120 determines whether all
condenser fans 114' on the condensing unit 100 are at the highest
speed. When all condenser fans 114' are at the highest speed, the
control module 120 loops back to step 400. When all condenser fans
114' are not at the highest speed, the control module 120
determines whether any condenser fan 114' is deactivated in step
410. When a condenser fan 114' is deactivated in step 410, the
control module 120 activates a condenser fan 114' at the lowest
speed in step 412 and loops back to step 400.
[0057] When all condenser fans 114' are activated in step 410, the
control module 120 determines whether all condenser fans 114' are
at the same speed in step 414. When all condenser fans 114' are not
at the same speed, the control module 120 increases the speed of a
slower condenser fan 114' in step 416 and loops back to step 400.
When all condenser fans 114' are at the same speed in step 414, the
control module 120 increases the speed of any condenser fan 114' in
step 418 and loops back to step 400.
[0058] When in step 402 P.sub.D is not greater than the set point
the control module 120 checks the condenser fan speeds in step 420.
When in step 422 all the condenser fans 114' are deactivated, the
control module 120 loops back to step 400. When all of the
condenser fans 114' are not deactivated, the control module 120
determines whether any condenser fan speed is greater than the
lowest fan speed in step 424. When no fan speed is greater than the
lowest fan speed, the control module 120 deactivates a condenser
fan 114' in step 426 and loops back to step 400.
[0059] When in step 424 a condenser fan speed is greater than the
lowest fan speed, the control module 120 determines whether all the
condenser fans 114' are at the same speed in step 428. When all of
the condenser fans 114' are not at the same speed, the control
module 120 decreases the speed of a faster condenser fan 114' in
step 430, and loops back to step 400. When all of the condenser
fans 114' are at the same fan speed, the control module 120
decreases the speed of any condenser fan 114' in step 432 and loops
back to step 400. The control module may wait a predetermined cycle
time before proceeding with another iteration starting in step
400.
[0060] In this way overall condenser fan speed is minimized while
maintaining P.sub.D below the set point. As can be appreciated, a
condensing unit 100 may have a combination of fixed speed condenser
fans 114 and variable speed condenser fans 114'. Such a condensing
unit 100 operating in silent mode may adjust the variable speed
condenser fans 114' before activating the fixed speed condenser
fans 114. When the variable speed condenser fans 114' are at
maximum speed, the control module 120 may then activate fixed speed
fans.
[0061] The description of the teachings is merely exemplary in
nature and, thus, variations that do not depart from the gist of
the teachings are intended to be within the scope of the teachings.
Such variations are not to be regarded as a departure from the
spirit and scope of the teachings.
* * * * *