Methods and Systems for Controlling a Hybrid Heating System

Abstract

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.

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.