Note: Descriptions are shown in the official language in which they were submitted.
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OUTDOOR FAN AND INDOOR BLOWER CONTROLLER FOR HEATING,
VENTILATION AND AIR CONDITIONING SYSTEM AND METHOD OF
OPERATION THEREOF
TECHNICAL FIELD
This application is directed, in general, to heating,
ventilation and air conditioning (HVAC) systems and, more
specifically, to an outdoor fan and indoor blower controller
for an HVAC system and method of operating the same.
BACKGROUND
HVAC systems should be capable of operating efficiently
under a wide range of outdoor temperatures.
Current HVAC
systems control outdoor (condenser) fan and indoor blower
speed based on the cooling required to be provided by the
system.
In many such systems, outdoor fan speed is
controlled such that refrigerant pressure remains within a
desired range.
Excessive pressure risks refrigerant
leakage, and inadequate pressure risks compressor damage or
failure.
Subject to maintaining pressure within a desired
range, the system as a whole is then controlled to operate
as efficiently as possible.
Some HVAC systems employ
multistage compressors and multiple outdoor fans to increase
operating efficiency.
SUMMARY
Certain exemplary embodiments can provide an HVAC
controller, comprising: a processor couplable to at least
two refrigerant pressure sensors via separate data paths to
receive input signals therefrom and further couplable to a
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compressor stage and a condenser fan to provide output
signals thereto; and memory coupled to said processor and
storing a software program having program instructions
capable of causing said processor to command said compressor
stage and said condenser fan to turn on irrespective of a
state of an input signal generated by either of said at
least two refrigerant pressure sensors and generate
alternative error messages at least partially depending upon
whether or not a high pressure shutdown occurs after said
processor commands said compressor stage and said fan to
turn on.
Certain exemplary embodiments can provide an HVAC
system, comprising: an outdoor unit, including: at least two
compressor stages, at least two corresponding condenser
fans, at least two corresponding refrigerant pressure
sensors, at least one condenser coil, and an outside air
temperature sensor; an indoor unit, including: at least one
evaporator coil, at least one indoor blower, and at least
one expansion valve; and an HVAC controller, including: a
processor couplable to said at least two refrigerant
pressure sensors via separate data paths to receive input
signals therefrom and further couplable to said at least two
compressor stages and said at least two condenser fans to
provide output signals thereto, and memory coupled to said
processor and storing a software program having instructions
capable of causing said processor to command one of said at
least two compressor stages and a corresponding one of said
at least two condenser fans to turn on irrespective of a
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state of an input signal generated by either of said at
least two refrigerant pressure sensors and generating
alternative error messages at least partially depending upon
whether or not a high pressure shutdown occurs after said
processor commands said one of said at least two compressor
stages and said corresponding one of said at least two
condenser fans to turn on.
One aspect provides an HVAC controller. In one
embodiment, the HVAC controller includes: (1) a processor
couplable to at least two refrigerant pressure sensors via
separate data paths to receive input signals therefrom and
further couplable to a compressor stage and a condenser fan
to provide output signals thereto and (2) memory coupled to
the processor and configured to store a software program
capable of causing the processor to command the compressor
stage and the condenser fan to turn on irrespective of a
state of an input signal generated by either of the at least
two refrigerant pressure sensors and generate alternative
error messages at least partially depending upon whether or
not a high pressure shutdown occurs after the processor
commands the compressor stage and the fan to turn on.
Another aspect provides a method of operating an HVAC
system.
In one embodiment, the method includes: (1)
commanding a compressor stage and an associated condenser
fan to turn on irrespective of a state of an input signal
generated by a refrigerant pressure sensor associated with
the condenser fan and (2) generating alternative error
messages at least partially depending upon whether or not a
high pressure shutdown occurs after the commanding.
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Another aspect provides an HVAC system. In
one
embodiment, the HVAC system includes: (1) an outdoor unit,
including: (la) at least two compressor stages, (lb) at
least two corresponding condenser fans, (lc) at least two
corresponding refrigerant pressure sensors, (1d) at least
one condenser coil and (le) an outside air temperature
sensor, (2) an indoor unit, including: (2a) at least one
evaporator coil, (2h) at least one
indoor
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blower and (2c) at least one expansion valve and (3) an
HVAC controller, including: (3a) a processor couplable to
the at least two refrigerant pressure sensors via
separate data paths to receive input signals therefrom
and further couplable to the at least two compressor
stages and the at least two condenser fans to provide
output signals thereto and (3b) memory coupled to the
processor and configured to store a software program
capable of causing the processor to command one of the at
least two compressor stages and a corresponding one of
the at least two condenser fans to turn on irrespective
of a state of an input signal generated by either of the
at least two refrigerant pressure sensors and generating
alternative error messages at least partially depending
upon whether or not a high pressure shutdown occurs after
the processor commands the one of the at least two
compressor stages and the corresponding one of the at
least two condenser fans to turn on.
BRIEF DESCRIPTION
Reference is now made to the following descriptions
taken in conjunction with the accompanying drawings, in
which:
FIG. 1 is a block diagram of one embodiment of an
HVAC system including one embodiment of an outdoor fan
and indoor blower controller constructed according to the
principles of the invention;
FIG. 2 is a block diagram of one embodiment of the
controller of FIG. 1;
FIG. 3A and 3B are flow diagrams of one embodiment
of a method of operating an outdoor fan of an HVAC system
carried out according to the principles of the invention;
and
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FIG. 4 is a flow diagram of one embodiment of a
method of operating an outdoor fan of an HVAC system
carried out according to the principles of the invention
DETAILED DESCRIPTION
FIG. 1 is a block diagram of one embodiment of an
HVAC system 100 including one embodiment of an outdoor
fan and indoor blower controller constructed according to
the principles of the invention. The HVAC
system 100
includes an outdoor unit 110, which may be a rooftop
unit, and an indoor unit 120. The outdoor unit 110 and
the indoor unit 120 are represented as being separate,
but in fact may be housed in a common enclosure.
The illustrated embodiment of the outdoor unit 110
includes one or more compressors each having one or more
stages 111. One or more
condenser fans 112 are
associated with one or more condenser coils 113 to move
air across the one or more condenser coils 113. An
outside air temperature sensor 114 is situated in or on
the outdoor unit 110 to detect an ambient outdoor air
temperature, and one or more refrigerant pressure sensors
115 are situated in or on the outdoor unit to detect
refrigerant pressure in the one or more condenser coils
113. In the
illustrated embodiment, at least one
refrigerant pressure sensor, a low ambient pressure
switch, is associated with each condenser coil and is
configured to change switch state (open or close) as a
function of the pressure of refrigerant in its associated
coil relative to a pre-established pressure at a lower
end of an acceptable pressure range. In
another
embodiment, a high ambient pressure switch is also
associated with each condenser coil and is configured to
change switch state as a function of the pressure of
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refrigerant in its associated coil relative to a pre-
established pressure at a higher end of an acceptable
pressure range.
The illustrated embodiment of the indoor unit 120
includes one or more evaporator coils 121. One or more
blowers 122, sometimes known as indoor blowers, are
associated with the one or more evaporator coils 121 to
move air across the one or more evaporator coils 121.
One or more expansion valves 123 are coupled to one or
more corresponding refrigerant conduits 124. The one or
more refrigerant conduits 124 couple the one or more
stages 111 of the one or more compressors, the one or
more condenser coils 113, the one or more expansion
valves 123 and the one or more evaporator coils 121 to
form a loop within which a refrigerant (e.g., a
hydrofluorocarbon fluid) is repeatedly compressed,
cooled, decompressed and warmed to effect air
conditioning. In one embodiment, the indoor unit 120
includes one or more heater coils (not shown) associated
with the one or more blowers 122 to effect heating. In
another embodiment, the one or more blowers 122 may be
activated separately to effect ventilation.
As stated above, the illustrated embodiment of the
system 100 further includes an outdoor fan and indoor
blower controller 130. The illustrated embodiment of the
controller 130 is configured to receive input signals
from, perhaps among other things, the outside air
temperature sensor 114 and the one or more refrigerant
pressure sensors 115 and generate output signals to
control, perhaps among other things, the one or more
condenser fans 112 and the one or more blowers 122. A
user interface (not shown), perhaps including an indoor
temperature sensor, is coupled to the controller 130 and
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configured to allow a user to select a setpoint indoor
temperature and perhaps a system operational mode (i.e.,
air conditioning, heating or ventilation). Those skilled
in the pertinent art are familiar with the manner in
which HVAC systems, such as the HVAC system 100 of FIG.
1, may be controlled by a user.
FIG. 2 is a block diagram of one embodiment of the
outdoor fan and indoor blower controller 130 of FIG. 1.
In the embodiment of FIG. 2, the controller 130 takes the
form of a general purpose microcontroller and contains a
processor 210 configured to execute software (e.g.,
firmware) instructions, a volatile memory 220 coupled to
the processor 210 and configured to store software
instructions, data or both software instructions and data
and nonvolatile memory 230 coupled to the processor 210
and configured to store software instructions, data or
both software instructions and data. In the embodiment
of FIG. 2, the nonvolatile memory 230 stores the software
instructions and persistent data (e.g., factory settings
and messages) that enable the operation of the controller
130, and the volatile memory 220 stores data that the
controller 130 collects during its operation and stores
temporarily for internal use or external recall (e.g.,
scratchpad data and operational logs).
As FIG. 2 shows, an outside air temperature sensor
114 and first and second refrigerant pressure sensors
115-1, 115-2 are coupled to the processor 210 to provide
input signals thereto.
Likewise, the processor 210 is
coupled to first and second compressor stages 111-1, 111-
2 and corresponding first and second condenser fans 112-
1, 112-2. Thus the specific embodiment of the controller
130 illustrated in FIG. 2 is configured for use in an
HVAC system that has two compressor stages, two condenser
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coils and two corresponding condenser fans. Of
course,
as stated above, other embodiments of the controller 130
accommodate other numbers of compressor stages, condenser
coils and condenser fans.
It should be noted that each of the sensors 114,
115-1, 115-2 has a separate data path to the processor
210, and that the processor 210 has a separate data path
to each of the stages and fans 111-1, 111-2, 112-1, 112-
2. The
provision of the separate data path may be
colloquially referred to as "home running." The separate
data paths may be separate wireline buses or wireless
channels or time-divided or code-divided allocations of a
shared wireline bus or wireless channel. The
object of
the separate data paths is that each of the sensors 114,
115-1, 115-2 can transmit its input signal separately to
the processor 210, and the processor can transmit its
output signals separately to each of the stages and fans
111-1, 111-2, 112-1, 112-2. Thus the
output of each of
the sensors 114, 115-1, 115-2 can be separately sensed,
and each of the stages and fans 111-1, 111-2, 112-1, 112-
2 can be separately controlled.
As stated above, many HVAC systems control outdoor
fan speed such that refrigerant pressure remains within a
desired range. In
systems having only a single
compressor stage, a pressure sensor on the condenser coil
directly controls the one or more fans; no effort is made
to control the condenser fans based on outside air
temperature. In
systems having multiple compressor
stages, some applications benefit from controlling the
condenser fans based on both condenser coil pressure and
outside air temperature. Unfortunately, the controller's
hardware interlock prevents this from being achieved
directly. Instead,
it is achieved by bypassing the
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interlock and connecting multiple pressure sensors in
parallel. Besides being cumbersome, the parallel-coupled
sensors cannot be separately detected or diagnosed. As a
result, a single faulty sensor can needlessly impair the
operation of the HVAC system as a whole, either by
wasting energy by causing one or more fans to operate
when they need not or by risking harm to one or more
compressors by preventing the one or more fans from
operating when they should. The controller 130 of FIG. 2
does not have a hardware interlock and thus accommodates
home running of the multiple pressure sensors. As a
result, the controller 130 avoids the need to couple
pressure sensors in parallel and allows sensor-specific
diagnostics.
In various embodiments, the controller 130 allows
multiple fans to be controlled based on pressure,
temperature, or both pressure and temperature at
different setpoints, even for a single compressor system,
without additional control apparatus other than that
needed to power the fan. In various
other embodiments,
the controller 130 can control more than one fan based on
different temperature setpoints or based on the input
signals produced by any of the pressure sensors. As a
result, the controller 130 can detect the status of the
different pressure sensors, act according to a pre-
programmed sequence of operation, and determine based on
the different conditions whether a given pressure sensor
is good or faulty. Once a faulty sensor is identified,
various embodiments of the controller 130 can provide
error messages (e.g., codes or phrases) for service,
including component repair or replacement, while
continuing to run the one or more fans without the faulty
sensor. The ability to continue to run the HVAC system
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even when a pressure sensor is faulty prevents potential
damage that may result from a faulty pressure sensor and
increases the overall reliability of the HVAC system.
FIG. 3A and 3B are flow diagrams of one embodiment
of a method of operating an outdoor fan of an HVAC system
carried out according to the principles of the invention.
The method of FIG. 3A begins in a start step 305, when
conditions are such that air conditioning is desirable.
In a step 310, the one or more refrigerant pressure
sensors (e.g., one or more low and/or high ambient
pressure switches) are read. In a
step 315, the outside
air temperature sensor is also read. Based on the states
of the one or more refrigerant pressure sensors and the
outside air temperature sensor, one or more stages of the
compressor are controlled (e.g., turned on or off) in a
step 320. Also, based on the states of the one or more
refrigerant pressure sensors and the outside air
temperature sensor, one or more condenser fans are
controlled (e.g., turned on or off) in a step 325. For
example, if an outdoor air temperature is 85 F and a
desired indoor setpoint temperature is 72 F, the size of
the HVAC system may have been chosen such that only a
single stage of a two-stage compressor is needed to
maintain the desired setpoint temperature at that given
outdoor air temperature.
Accordingly, the controller
produces an output signal that commands the single stage
to begin operation. As a
result, refrigerant pressure
downstream of the compressor stage increases, causing the
associated low ambient pressure switch to change state
and generate a corresponding input signal to the
controller. This
input signal, perhaps in conjunction
with other input signals or parameters such as time, in
turn causes the controller to turn on an associated fan
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to reduce the rate of increase of the refrigerant
pressure. The method ends in an end step 330.
However, turning now to FIG. 35, it will now be
assumed that either a low ambient pressure switch or a
condenser fan has failed. The method of FIG. 3B presents
one embodiment of a method by which diagnostics may be
performed with respect to the HVAC system and begins in a
start step 340, when it is desired to activate air
conditioning.
Accordingly, the controller turns on at
least one compressor stage in a step 345. Assuming a
high ambient pressure switch located downstream of the
compressor stage is coupled to the controller, the output
signal from that switch determines the outcome of a
decisional step 350. The
purpose of the high ambient
pressure switch is to protect the HVAC system against the
harm that may result from excessive refrigerant pressure.
A failure of a fan to operate to cool its associated
condenser coil is often the cause of excessive
refrigerant pressure. If the
output signal indicates
that refrigerant pressure remains in the acceptable
range, normal operation ensues in a step 355, and the
method ends in a step 360.
On the other hand, if excessive refrigerant pressure
causes the high ambient pressure switch to change state,
it cannot directly be determined whether a faulty low
pressure ambient switch failed to change state to
activate the condenser fan, or whether the low ambient
pressure switch did close, but the fan was unable to
respond, perhaps due to a fault in wiring leading to the
fan, an actuator providing power to the fan, or the fan
itself.
Irrespectively, if the output signal of a high
ambient pressure switch causes the controller to respond
with a high pressure shutdown of the HVAC system, a
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preprogrammed delay ensues, after which the controller
generates an output signal to command the at least one
compressor stage to turn on again in a step 365. The
controller then generates an output signal to command the
associated at least one condenser fan turn on again in a
step 370. If a
high pressure shutdown does not again
ensue in a decisional step 375, the controller can then
assume that the associated at least one fan did turn on
and that a faulty low ambient pressure switch likely
prevented the at least one fan from turning on
previously. The controller then generates an appropriate
error message indicating that a low ambient pressure
switch is faulty in a step 380. The
controller then
causes the HVAC system to operate under a fault condition
(namely the faulty low ambient pressure switch) in a step
385, whereupon the method ends in the end step 355. In
various embodiments, the controller may also alert the
customer that the system is operating under a fault
condition if the controller is part of a network, e.g., a
Building Automation System (BAS).
If, on the other hand, a high pressure shutdown does
again ensue in the decisional step 375, the controller
can then assume that the at least one fan did not turn on
as commanded and that the at least one fan or wiring
leading to it is faulty. The
controller then generates
an appropriate error message indicating that one or more
condenser fans are not operating in the step 380. The
controller can then attempt continued operation of the
HVAC system under fault condition. As above,
the
controller may also alert the customer that the system is
operating under a fault condition if the controller is
part of a network. In one
embodiment, the controller
determines whether alternative compressors or stages
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associated with operable condenser fans may be turned on.
In another embodiment, the controller operates the fewer
remaining operable fans at a higher speed if the system
has a variable speed fan or Electronic Conmutated Motor
(ECM). In yet
another embodiment, the controller turns
on one or more fans that had been turned off. In still
another embodiment, the controller determines that other
fans are not available and commands the HVAC system to
shut down pending repair. In a more specific embodiment,
the controller broadcasts an alarm signal through a
network to inform the customer of a shutdown condition so
the system can be repaired.
Various embodiments of the controller can perform
other operations that allow the HVAC system to operate
under conditions in which outside air temperatures are
exceptionally cold, for example, less than 55 F.
Conventional HVAC systems have trouble operating under
such exceptionally cold conditions, because while their
condenser fans should operate to avoid excessive
refrigerant pressure in the condenser coils, operation of
the fans in such low outside air temperatures can over-
cool the condenser coils, causing inadequate refrigerant
pressure. As
stated above, operation either above or
below an acceptable refrigerant pressure range can harm
the HVAC system. Introduced
herein are various
embodiments of an HVAC controller and method for
accommodating HVAC system operation under relatively low
outside air temperatures. FIG. 4
is a flow diagram of
one embodiment of a method of operating an outdoor fan of
an HVAC system carried out according to the principles of
the invention. The method begins in a step 410. In a
step 420, refrigerant pressure is detected.
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In one embodiment, refrigerant pressure is detected
by determining if it is within or without an acceptable
range. This can be performed with low and high ambient
pressure switches. Depending upon the states of the two
pressure switches, it can be determined whether the
refrigerant is: (1) below a lower pressure threshold, (2)
above the lower threshold but below an upper pressure
threshold, or (3) above the upper threshold.
In a decisional step 430, if the refrigerant
temperature is above the upper threshold (indicating a
refrigerant pressure above the acceptable range), the
outcome of the decisional step 430 is YES, and the
controller commands a condenser fan to increase its speed
to the next higher speed in a step 440. For example, if
the condenser fan is running at a low-low speed, the
controller commands the condenser fan to increase its
speed to a low speed. If the condenser fan is running at
a low speed, the controller commands the condenser fan to
increase its speed to a high speed. The
refrigerant
pressure is detected again at a later time in the step
420. For purposes of this invention, a low-low speed is
a speed that is lower than the speed at which a fan or
blower normally runs when the HVAC system is first-stage
cooling. In the embodiment of FIG. 4, an example low-low
speed may be about 300 RPM, a low speed may be about 600
RPM, and a high speed may be about 900 RPM.
If the outcome of the decisional step 430 is NO, in
a decisional step 450 it is determined if the refrigerant
temperature is above the lower threshold (indicating a
refrigerant pressure within the acceptable range), the
outcome of the decisional step is YES, and the controller
does not command the condenser fan speed to change. The
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refrigerant pressure is detected again at a later time in
the step 420.
If the outcome of the decisional step 450 is NO
(indicating a refrigerant pressure below the acceptable
range), it is determined in a decisional step 460 if the
condenser fan is running at a low-low speed. If the
outcome of the decisional step 460 is YES, the method
proceeds to the step 470 in which the controller calls
for the condenser fan to continue to operate at the low-
low speed until the lower threshold is reached, at which
time the controller calls for the condenser fan to turn
off. The condenser fan then remains off until the upper
threshold is reached, at which time the controller calls
for the fan to turn back on at the low-low speed. The
refrigerant pressure is detected again at a later time in
the step 420.
If the outcome of the decisional step 460 is NO, and
the controller commands a condenser fan to decrease its
speed to the next lower speed in a step 480. For
example, if the condenser fan is running at a high speed,
the controller commands the condenser fan to decrease its
speed to a low speed. If the condenser fan is running at
a low speed, the controller commands the condenser fan to
decrease its speed to a low-low speed.
In certain embodiments, the controller can control
an indoor blower to operate at a low-low speed to improve
ventilation or for other purposes when the compressor is
turned off. In still
other embodiments, the controller
may command a damper to open to allow outdoor air to flow
to the blower, perhaps across a filter to reduce
particulate matter beforehand. This
ostensibly lowers
the temperature of the indoor air the blower is
circulating.
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Those skilled in the art to which this application
relates will appreciate that other and further additions,
deletions, substitutions and modifications may be made to
the described embodiments.
