Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEMS AND METHODS FOR
CONTROLLING A HYBRID HEATING SYSTEM
BACKGROUND
[0001] In a heat pump and refrigeration cycle, refrigerant alternately
absorbs and
rejects thermal energy as it circulates through the system and is compressed,
condensed, expanded, and evaporated. In particular, a liquid refrigerant flows
from a
condenser, through an expansion device (e.g., expansion valve) and into an
evaporator.
As the refrigerant flows through the expansion device and evaporator, the
pressure of
the refrigerant decreases, the refrigerant phase changes into a gas, and the
refrigerant
absorbs thermal energy. From the evaporator, the gaseous refrigerant proceeds
to a
compressor, and then back to the condenser. As the refrigerant flows through
the
compressor and condenser, the pressure of the refrigerant is increased, the
refrigerant
phase changes back into a liquid, and the refrigerant gives up thermal energy.
The
process is implemented to emit thermal energy into a space (e.g., to heat a
house) or to
remove thermal energy from a space (e.g., to air condition a house).
[0002] In a heating cycle, the efficiency of a heat pump system is reduced
as the
outdoor temperature drops. In other words, for every heat pump system, there
is an
outdoor temperature threshold (referred to herein as "the thermal balance
point") below
which the heat pump system is no longer effective. Accordingly, some heating,
ventilation, and air conditioning (HVAC) systems implement a hybrid (or dual)
fuel
system for heating, which comprises a heat pump system and an auxiliary
furnace. The
auxiliary furnace may burn gas, oil, propane or other combustibles. With the
auxiliary
furnace, the hybrid fuel system is capable of heating an indoor environment
even if the
outdoor temperature drops below the thermal balance point of the heat pump
system.
SUMMARY OF THE DISCLOSURE
[0003] In at least some embodiments, a hybrid heating system includes a
heat pump
and an auxiliary furnace. The hybrid heating system also includes a controller
coupled
to the heat pump and the auxiliary furnace. The controller, in response to
receiving a
heat request, selects either the heat pump or the auxiliary furnace based on
an
economic balance point algorithm.
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[0004] In at least some embodiments, a control system for a hybrid heating
system
includes economic balance point logic configured to determine an outdoor
temperature
threshold at which operating an auxiliary furnace is less expensive than
operating a
heat pump. The control system also includes selection logic configured to
select, in
response to a heat request, either the auxiliary furnace or the heat pump
based on the
outdoor temperature threshold.
[0005] In at least some embodiments, a method for controlling a hybrid
heating
system includes determining, by a controller, an outdoor temperature threshold
at which
operating an auxiliary furnace is less expensive than operating a heat pump.
The
method also includes receiving, by the controller, a heat request. The method
also
includes selecting, by the controller, either the auxiliary furnace or the
heat pump based
on the determined outdoor temperature threshold.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIGURE 1 illustrates an HVAC system with hybrid heating in
accordance with
an embodiment of the disclosure;
[0007] FIGURE 2 illustrates a control system configuration for the HVAC
system of
FIGURE 1 in accordance with an embodiment of the disclosure;
[0008] FIGURE 3 illustrates a block diagram of a system in accordance with
an
embodiment of the disclosure;
[0009] FIGURES 4A-4J show windows of a user interface program for
controlling
hybrid heating in accordance with an embodiment of the disclosure; and
[0010] FIGURE 5 shows a method in accordance with an embodiment of the
disclosure.
DETAILED DESCRIPTION
[0011] FIGURE 1 illustrates an HVAC system 100 with hybrid heating in
accordance
with an embodiment of the disclosure. In the HVAC system 100, refrigerant
cycles
through a heat pump comprising outdoor coil 102, compressor 106, indoor coil
122, and
expansion valve 112. The arrows 104, 108, 110 and 114 show the direction of
flow for
refrigerant in a heating cycle. For a cooling cycle, the direction of flow for
refrigerant in
HVAC system 100 would be reversed.
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[0012] In a heating cycle, the outdoor coil 102 causes refrigerant to
evaporate. As
the liquid refrigerant evaporates it pulls heat from the outside air. The
gaseous
refrigerant flows (arrow 104) from the outdoor coil 102 to compressor 106,
where the
gaseous refrigerant is compressed to produce a high-pressure, superheated
refrigerant
vapor. The vapor leaves compressor 106 and flows (arrow 108) to the indoor
coil 122.
At the indoor coil 122, air from fan (blower) 124 removes heat from the vapor
(warming
the indoor air) and, when enough heat is removed, the vapor condenses into a
high-
pressure liquid. This high-pressure liquid flows (arrow 110) from the indoor
coil 122 to
the expansion valve 112, which meters the flow (arrow 114) of the high-
pressure liquid
to the outdoor coil 102. The heating cycle process described herein can be
repeated as
needed. For example, the heating cycle of HVAC system 100 may be activated
and/or
maintained in response to a thermostat control signal.
[0013] As shown in FIGURE 1, the indoor coil 122 and the fan 124 may be
components of an air handler 120. The air handler 120 may also comprise an
auxiliary
furnace 126, which is selectively activated as part of a hybrid heating scheme
as
disclosed herein. Alternatively, the auxiliary furnace 126 may be separate
from the air
handler 120. In either case, the auxiliary furnace 126 may be selectively
activated (e.g.,
instead of the heat pump components) based on an economic balance point
algorithm.
In operation, the economic balance point algorithm determines when operating
the heat
pump of HVAC system 100 is more expensive to run than the auxiliary furnace
126. In
such case, the economic balance point algorithm causes the auxiliary furnace
126 to
run instead of the heat pump. The economic balance point algorithm also may
account
for user inputs to adjust or override the determined economic balance point as
described herein.
[0014] FIGURE 2 illustrates a control system configuration 200 for the HVAC
system
100 of FIGURE 1 in accordance with an embodiment of the disclosure. The
control
system configuration 200 illustrates a hierarchical control for HVAC systems,
including
those with hybrid heating as disclosed herein. As shown, the thermostat 202
operates
as the overall system controller of configuration 200 and is configured to
communicate
with an indoor subsystem controller 222 of indoor subsystem 220 and an outdoor
subsystem controller 212 of outdoor subsystem 210. The indoor subsystem 220
may
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comprise, for example, indoor heat pump components 224 (e.g., indoor coil 122
and fan
124) and auxiliary furnace components 226 (e.g., auxiliary furnace 126) such
as those
described for FIGURE 1. Meanwhile, the outdoor subsystem 210 comprises outdoor
heat pump components 214 such as the compressor 106 and the outdoor coil 102
described for FIGURE 1. In at least some embodiments, the indoor subsystem
controller 222 implements some or all of the economic balance point algorithm
features
described herein.
[0015]
FIGURE 3 illustrates a block diagram of a system 300 in accordance with an
embodiment of the disclosure. As shown, the system 300 comprises a controller
310
coupled to a hybrid heating system 320 having a heat pump 322 and an auxiliary
furnace 324. In at least some embodiments, the controller 310 and the user
interface
302 corresponds to the indoor subsystem controller 222 of FIGURE 2. In various
embodiments, the user interface 302 corresponds to an interface on a
thermostat or
other control unit that enables user interaction to control operations of the
hybrid heating
system 320. Alternatively, the user interface 302 may correspond to a computer
program or web portal accessible via a handheld computing device (e.g., a
smart
phone), a laptop and/or a desktop computer.
[0016]
As shown, the controller 310 comprises economic balance point logic 312
configured to select whether to operate the heat pump 322 or the auxiliary
furnace 324
in response to a heat request. In accordance with at least some embodiments,
the
economic balance point logic 312 employs control parameters 314 to determine
when
operating heat pump 322 is more expensive than operating auxiliary furnace
324.
Values for the control parameters 314 may be based on previously stored
default values
and/or dynamic values received via a user interface 302 coupled to the
controller 310.
As an example, the control parameters 314 may correspond to an auxiliary
furnace fuel
cost parameter, a heat pump electricity cost parameter, a heat pump efficiency
parameter, and an auxiliary furnace efficiency parameter.
Using such control
parameters 314, the economic balance point logic 312 determines an outdoor
temperature balance point at which operating the heat pump 322 is more
expensive
than operating the auxiliary furnace 324.
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[0017] The outdoor temperature balance point may be determined before or
after a
heat request is received. In either case, the economic balance point logic 312
may
respond to a heat request by comparing a current outdoor temperature with the
determined outdoor temperature balance point, and then selecting either the
heat pump
or the auxiliary furnace based on the comparison.
[0018] More specifically, in FIGURE 3, the selection logic 316 coupled to
the
economic balance point logic 312 may receive a recommendation or control
signal from
the economic balance point logic 312. In response to a control signal from the
economic balance point logic 312, the selection logic 316 asserts a control
signal to
activate either the heat pump 322 or the auxiliary furnace 324. In accordance
with at
least some embodiments, the heat pump 322 and the auxiliary furnace 324 are
independently activated, but are not typically operated together.
[0019] The selection logic 316 is also configured to receive a manually
selected
control scheme for the hybrid heating system 320 from the user interface 302.
The
manually selected control scheme may correspond to adjusting or overriding the
determined outdoor temperature balance point discussed previously. In other
words,
the user interface 302 enables a user to selectively disable and enable the
economic
balance point algorithm performed by the economic balance point logic 312.
Additionally or alternatively, the user interface 302 enables a user to
manually set an
outdoor temperature at which the auxiliary furnace 324 operates in response to
a heat
request instead of the heat pump 322. Additionally or alternatively, the user
interface
302 enables a user to manually select a thermostat control algorithm instead
of the
economic balance point algorithm for control of the hybrid heating system 320.
The
thermostat control algorithm (e.g., implemented by thermostat 302) may, for
each
heating cycle, initialize a first heating stage in which the heat pump 322 is
active without
the auxiliary furnace 324 and, if needed, initialize a second heating stage in
which the
auxiliary furnace 324 is active without the heat pump 322.
[0020] FIGURES 4A-4J show windows of a user interface program for
controlling
hybrid heating in accordance with an embodiment of the disclosure. The user
interface
program may be part of the user interface 302 described for FIGURE 3. In
FIGURE 4A,
window 400A shows a "settings" menu including a dual fuel icon 402 that can be
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selected by clicking on it. Selection of the dual fuel icon 402 enables a user
to adjust
control features for a hybrid heating system (e.g., the hybrid heating system
320 of
FIGURE 3). The other icons of FIGURE 4A correspond to other control features
or
utilities accessible via the user interface program.
[0021] In FIGURE 4B, window 400B shows a dual fuel menu that appears in
response to clicking the dual fuel icon 402 of FIGURE 4A. The dual fuel menu
of
window 400B enables a user to manually adjust control features and/or control
parameter values for a hybrid heating system. For example, clicking on the
comfort box
408 and then clicking the "next" button 410A enables a user to pass control of
the hybrid
heating system to a thermostat (e.g., thermostat 202 of FIGURE 2). When the
thermostat controls the hybrid heating system, use of the economic balance
point
algorithm is temporarily disabled or is otherwise ignored. The thermostat may
implement a thermostat control algorithm that, for each heating cycle,
initializes a first
heating stage in which the heat pump 322 is active without the auxiliary
furnace 324. If
needed (e.g., when the heat pump 322 is insufficient), the thermostat control
algorithm
initializes a second heating stage in which the auxiliary furnace is active
without the
heat pump.
[0022] Clicking on the operating cost box 404 and then clicking on the
"next" button
410A enables a user to input values for control parameters (e.g., control
parameters
314 of FIGURE 3) of an economic balance point algorithm. In other words,
selection of
the operating cost box 404 causes implementation of the economic cost balance
algorithm for the hybrid heating system 320. The control parameter values for
the
economic balance point algorithm are input by a user via the user interface
program as
shown in the windows of FIGURES 4C-4F. Additionally or alternatively, one or
more
default values may be provided in the user interface program for the economic
balance
point algorithm as shown in the windows of FIGURES 4G-4H.
[0023] FIGURES 4C-4H show various windows that enable selection of control
parameter values for an economic balance point algorithm. The windows of
FIGURES
4C-4H may be displayed in series, for example, after clicking on the operating
cost box
404 and the "next" box 410A. In FIGURE 4C, the window 400C enables a user to
select
a gas furnace box 412 or an oil furnace box 414. In other words, the economic
balance
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point algorithm accounts for the type of fuel used with the auxiliary furnace
324. Upon
clicking the gas furnace box 412 and the "next" button 410B, the window 400E
of
FIGURE 4E is displayed by the user interface program. Alternatively, upon
clicking the
oil furnace box 414 and the "next" button 410B, the window 400F is displayed
by the
user interface program. In window 4000, selection of the "back" button 416A
causes
the dual fuel menu window 400B to be displayed again.
[0024] In FIGURE 4D, a window 400D with an electricity cost utility 418 is
shown.
The electricity cost utility 418 enables a user to enter an electricity cost
(dollars/kwh).
After entering the electricity cost, a user selects the "next" button 4100 to
use the
entered electricity cost with the economic balance point algorithm. More
specifically,
the electricity cost is used to determine a cost of operating the heat pump
322. In
screenshot 400D, selection of the "back" button 416B causes window 4000 to be
displayed again.
[0025] In FIGURE 4E, a window 400E with a gas cost utility 422 is shown.
The
window 400E is displayed if the gas furnace box 412 is selected in window
4000. The
gas cost utility 422 enables a user to enter a natural gas cost in
dollars/therm by clicking
the "natural gas $/therm" button 420. Alternatively, the gas cost utility 422
enables a
user to enter a natural gas cost in dollars/MCF by clicking the "natural gas
$/MFC"
button 424. Alternatively, the gas cost utility 422 enables a user to enter a
propane gas
cost in dollars/gallon by clicking the "propane gas $/gal" button 426. After
entering a
gas cost, a user selects the "next" button 410D to use the entered gas cost
with the
economic balance point algorithm. More specifically, the gas cost is used to
determine
a cost of operating the auxiliary furnace 324. In window 400E, selection of
the "back"
button 4160 causes window 400D to be displayed again.
[0026] In FIGURE 4F, a window 400F with an oil cost utility 430 is shown.
The
window 400F is displayed if the oil furnace box 414 is selected in window
4000. The oil
cost utility 430 enables a user to enter a fuel oil cost in dollars/gallon by
clicking the "fuel
oil $/gal" button 428. Alternatively, the "fuel oil $/gal" button 428 need not
be clicked
since only one fuel oil cost option is provided. After entering a fuel oil
cost, a user
selects the "next" button 410E to use the entered fuel oil cost with the
economic balance
point algorithm. More specifically, the fuel oil cost is used to determine a
cost of
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operating the auxiliary furnace 324. In window 400F, selection of the "back"
button
416D causes screenshot 400D to be displayed again.
[0027] In FIGURE 4G, a window 400G with an Annual Fuel Utilization
Efficiency
(AFUE) rating utility 432 is shown. The AFUE rating utility 432 enables a user
to adjust
an AFUE rating corresponding to the auxiliary furnace 324. The AFUE rating for
the
AFUE rating utility 432 may be initially set to a default value (e.g., 78) and
may be
adjusted within a predetermined range (e.g., 78-98). After entering an AFUE
rating, a
user selects the "next" button 410F to use the entered AFUE rating with the
economic
balance point algorithm. More specifically, the AFUE rating is used to
determine a cost
of operating the auxiliary furnace 324. In window 400G, selection of the
"back" button
416E causes either window 400E or window 400F to be displayed again.
[0028] In FIGURE 4H, a window 400H with a Heating Season Performance Factor
(HSPF) rating utility 434 is shown. The HSPF rating utility 434 enables a user
to adjust
an HSPF rating corresponding to the heat pump 322. The HSPF rating for the
HSPF
rating utility 434 may be initially set to a default value (e.g., 7.7) and may
be adjusted
within a predetermined range (e.g., 7.7-12). After entering an HSPF rating, a
user
selects the "next" button 410G to use the entered HSPF rating with the
economic
balance point algorithm. More specifically, the HSPF rating is used to
determine a cost
of operating the heat pump 322. In window 400H, selection of the "back" button
416F
causes the window 400G to be displayed again.
[0029] In FIGURE 41, a window 4001 with a determined outdoor temperature
balance
point utility 436 is shown. The determined outdoor temperature balance point
utility 436
shows results of an outdoor temperature balance point determined by the
economic
balance point algorithm (referred to as the "furnace heating outdoor
temperature" in
utility 436) based on control parameter values entered via the user interface
program
(e.g., via the utilities of window 400D-400H). The determined outdoor balance
point
utility 436 also enables a user to adjust the determined outdoor temperature
balance
point up or down. To accept the determined outdoor temperature balance point
or an
adjusted outdoor temperature balance point, the user selects the "accept"
button 438A.
The user may alternatively click the "cancel" button 440A to cancel use of the
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determined outdoor temperature balance point or adjusted outdoor temperature
balance
point to control a hybrid heating system 320.
[0030] Returning to FIGURE 4B, clicking on the outdoor temperature box 406
and
then clicking on the "next" button 410A enables a user to manually set an
outdoor
temperature balance point. When the outdoor temperature is at or above the
outdoor
temperature balance point, the heat pump 322 is selected in response to a heat
request.
When the outdoor temperature is below the outdoor temperature balance point,
the
auxiliary furnace 324 is selected in response to a heat request. FIGURE 4J
shows a
window 400J with a custom outdoor temperature balance point utility 437. The
custom
outdoor temperature balance point utility 437 enables a user to select a
custom outdoor
temperature balance point (referred to as the "furnace heating outdoor
temperature" in
utility 437) between 0 ¨ 70 degrees Fahrenheit. Other temperature ranges could
or
selection means could alternatively be used. Once a custom outdoor temperature
balance point is selected in utility 437, a user clicks the "accept" button
438B to
implement use of the custom outdoor temperature balance point. The user may
alternatively click the "cancel" button 440B to cancel use of a custom
temperature
balance point.
[0031] Although windows 4000-400J describe various features and utilities
in a
particular order, the windows presented herein are not intended to limit other
user
interface embodiments that may implement an economic balance point algorithm
as
described herein. In other words, user interface embodiments may vary with
regard to
how information is presented to a user and how a user enters information.
[0032] FIGURE 5 shows a method 500 in accordance with an embodiment of the
disclosure. The method 500 may be performed by a controller (e.g., controller
310) or
control system for hybrid fuel heating of an HVAC system as described herein.
As
shown, the method 500 comprises determining an outdoor temperature balance
point at
which operating an auxiliary furnace is less expensive that operating a heat
pump (block
502). The determined outdoor temperature balance point may be based on control
parameters such as an auxiliary furnace fuel cost parameter, a heat pump
electricity
cost parameter, a heat pump efficiency parameter and an auxiliary furnace
efficiency
parameter. At block 504, a heat request is received. Finally, an auxiliary
furnace or
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heat pump is selected (responsive to the heat request) based on the determined
outdoor temperature balance point (block 506).
[0033] In at least some embodiments, the method 500 may enable
determination of
the outdoor temperature balance point to be disabled or overridden by a user.
For
example, a user may enter a custom outdoor temperature balance point. Further,
a
user may select to implement a thermostat control scheme instead of an
economic
balance point algorithm. The thermostat control scheme comprises, for example,
initializing a first heating stage in which the heat pump is active without
the auxiliary
furnace. If needed, thermostat control scheme initializes a second heating
stage in
which the auxiliary furnace is active without the heat pump.
[0034] Preferred embodiments have been described herein in sufficient
detail, it is
believed, to enable one skilled in the art to practice the disclosed
embodiments.
Although preferred embodiments have been described in detail, those skilled in
the art
will also recognize that various substitutions and modifications may be made
without
departing from the scope and spirit of the appended claims.
[0035] At least one embodiment is disclosed and variations, combinations,
and/or
modifications of the embodiment(s) and/or features of the embodiment(s) made
by a
person having ordinary skill in the art are within the scope of the
disclosure. Alternative
embodiments that result from combining, integrating, and/or omitting features
of the
embodiment(s) are also within the scope of the disclosure. Where numerical
ranges or
limitations are expressly stated, such express ranges or limitations should be
understood to include iterative ranges or limitations of like magnitude
falling within the
expressly stated ranges or limitations (e.g., from about 1 to about 10
includes, 2, 3, 4,
etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example,
whenever a
numerical range with a lower limit, RI, and an upper limit, Ru, is disclosed,
any number
falling within the range is specifically disclosed. In particular, the
following numbers
within the range are specifically disclosed: R=RI +k * (Ru-RI), wherein k is a
variable
ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1
percent, 2
percent, 3 percent, 4 percent, 5 percent,...50 percent, 51 percent, 52
percent,..., 95
percent, 96 percent, 97 percent, 98 percent, 99 percent, or 100 percent.
Moreover, any
numerical range defined by two R numbers as defined in the above is also
specifically
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disclosed. Use of the term "optionally" with respect to any element of a claim
means
that the element is required, or alternatively, the element is not required,
both
alternatives being within the scope of the claim. Use of broader terms such as
comprises, includes, and having should be understood to provide support for
narrower
terms such as consisting of, consisting essentially of, and comprised
substantially of.
Accordingly, the scope of protection is not limited by the description set out
above but is
defined by the claims that follow, that scope including all equivalents of the
subject
matter of the claims. Each and every claim is incorporated as further
disclosure into the
specification and the claims are embodiment(s) of the present invention.
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