Methods and Systems for Controlling a Hybrid Heating System
In at least some embodiments, a hybrid heating system includes a heat pump and an auxiliary furnace. The 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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BACKGROUNDIn 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).
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 DISCLOSUREIn 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.
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.
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.
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.
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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.
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.
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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.
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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
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Although windows 400C-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.
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.
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.
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, Rl, 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=Rl+k*(Ru−Rl), 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 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.
Claims
1. A hybrid heating system, comprising:
- a heat pump;
- an auxiliary furnace; and
- a controller coupled to the heat pump and the auxiliary furnace,
- wherein 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.
2. The hybrid heating system of claim 1 wherein the economic balance point algorithm comprises an auxiliary furnace fuel cost parameter, a heat pump electricity cost parameter, a heat pump efficiency parameter, and an auxiliary furnace efficiency parameter.
3. The hybrid heating system of claim 2 wherein the economic balance point algorithm implements default values for at least one of the auxiliary furnace fuel cost parameter, the heat pump electricity cost parameter, the heat pump efficiency parameter, and the auxiliary furnace efficiency parameter.
4. The hybrid heating system of claim 2 wherein the controller comprises a user interface and wherein values for at least one of the auxiliary furnace fuel cost parameter, the heat pump electricity cost parameter, the heat pump efficiency parameter, and the auxiliary furnace efficiency parameter are based on user input via the user interface.
5. The hybrid heating system of claim 1 wherein the economic balance point algorithm determines an outdoor temperature balance point at which operating the auxiliary furnace is less expensive than operating the heat pump.
6. The hybrid heating system of claim 5 wherein the controller, in response to receiving a heat request, compares a current outdoor temperature with a previously determined outdoor temperature balance point and selects either the heat pump or the auxiliary furnace based on the comparison.
7. The hybrid heating system of claim 1 wherein the controller comprises a user interface that enables a user to selectively disable and enable the economic balance point algorithm.
8. The hybrid heating system of claim 1 wherein the controller couples to a user interface that enables a user to manually set an outdoor temperature at which the auxiliary furnace operates in response to a heat request instead of the heat pump.
9. The hybrid heating system of claim 1 wherein the controller selectively implements a thermostat control algorithm instead of the economic balance point algorithm based on user input.
10. The hybrid heating system of claim 9 wherein the thermostat control algorithm, for each heating cycle, initializes a first heating stage in which the heat pump is active without the auxiliary furnace and, if needed, initializes a second heating stage in which the auxiliary furnace is active without the heat pump.
11. A control system for a hybrid heating system, the control system comprising:
- 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;
- 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.
12. The control system of claim 11 wherein the economic balance point logic determines the output temperature threshold based on an auxiliary furnace fuel cost parameter, a heat pump electricity cost parameter, a heat pump efficiency parameter, and an auxiliary furnace efficiency parameter.
13. The control system of claim 12 wherein the economic balance point logic implements default values for at least one of the auxiliary furnace fuel cost parameter, the heat pump electricity cost parameter, the heat pump efficiency parameter, and the auxiliary furnace efficiency parameter.
14. The control system of claim 11 further comprising a user interface in communication with the economic balance point logic, wherein values for at least one of the auxiliary furnace fuel cost parameter, the heat pump electricity cost parameter, the heat pump efficiency parameter, and the auxiliary furnace efficiency parameter are based on user input via the user interface.
15. The control system of claim 12 further comprising a user interface in communication with the selection logic, wherein the selection logic is configured to select either the auxiliary furnace or the heat pump for a heat cycle based on an outdoor temperature value or a thermostat control scheme selected manually by a user via the user interface.
16. A method for controlling a hybrid heating system, comprising:
- determining, by a controller, an outdoor temperature threshold at which operating an auxiliary furnace is less expensive than operating a heat pump;
- receiving, by the controller, a heat request; and selecting, by the controller, either the auxiliary furnace or the heat pump based on the determined outdoor temperature threshold.
17. The method of claim 16 wherein said determining the outdoor temperature threshold is based on an auxiliary furnace fuel cost parameter, a heat pump electricity cost parameter, a heat pump efficiency parameter, and an auxiliary furnace efficiency parameter.
18. The method of claim 16 further comprising overriding the determined outdoor temperature threshold with an outdoor temperature provided by a user.
19. The method of claim 16 further comprising disabling use of the determined outdoor temperature threshold for said selection and enabling use of a thermostat control scheme to select either the auxiliary furnace or the heat pump based on the determined outdoor temperature threshold.
20. The method of claim 19 wherein the thermostat control scheme comprises initializing a first heating stage in which the heat pump is active without the auxiliary furnace and, if needed, initializing a second heating stage in which the auxiliary furnace is active without the heat pump.
Type: Application
Filed: Mar 30, 2011
Publication Date: Oct 4, 2012
Applicant: TRANE INTERNATIONAL INC. (Piscataway, NJ)
Inventors: Timothy Wayne Storm (Tyler, TX), Gerson L. Gavin (Frisco, TX), Jonathan David Douglas (Lewisville, TX), John R. Edens (Kilgore, TX), Willem M. Lange, IV (Tyler, TX)
Application Number: 13/076,240
International Classification: F24D 19/10 (20060101); F24D 15/04 (20060101); F24D 12/02 (20060101);