Heat pump water flow control

Abstract

An electronic controller for controlling a heat pump water heater is configured to receive a first signal from a first sensor and receive a second signal from a second sensor. The first signal is indicative of a first variable the second signal is indicative of a second variable. The electronic controller is configured to determine a target flow rate based on the first variable and the second variable and control a water flow rate of the heat pump water heater based on the target flow rate.

What is claimed is: 
     
         1 . An electronic controller for controlling a heat pump water heater, the electronic controller configured to:
 receive a first signal from a first sensor, the first signal indicative of a first variable;   receive a second signal from a second sensor, the second signal indicative of a second variable;   determine a target flow rate based on the first variable and the second variable; and   control a water flow rate of the heat pump water heater based on the target flow rate.   
     
     
         2 . The electronic controller of  claim 1 , wherein the first variable is a water inlet temperature and the second variable is an ambient temperature. 
     
     
         3 . The electronic controller of  claim 2 , wherein determining the target flow rate based on the first variable and the second variable comprises:
 determining a first estimated refrigerant pressure based on the first variable;   determining a second estimated refrigerant pressure based on the second variable;   determining an available heating rate based on the first estimated refrigerant pressure and the second estimated refrigerant pressure; and   determining the target flow rate based on the available heating rate and an adjustment factor.   
     
     
         4 . The electronic controller of  claim 1 , wherein the first variable is a first refrigerant pressure and the second variable is a second refrigerant pressure. 
     
     
         5 . The electronic controller of  claim 4 , wherein determining the target flow rate based on the first variable and the second variable comprises:
 determining an available heating rate based on the first refrigerant pressure and the second refrigerant pressure; and   determining the target flow rate based on the available heating rate, a water inlet temperature, and an adjustment factor.   
     
     
         6 . The electronic controller of  claim 5 , wherein the water inlet temperature is determined from the first signal. 
     
     
         7 . The electronic controller of  claim 5 , wherein the water inlet temperature is determined from the second signal. 
     
     
         8 . The electronic controller of  claim 5 , wherein the electronic controller is further configured to:
 receive a third signal from a third sensor, the third signal indicative of a third variable;   update the adjustment factor based on the third variable;   determine an updated target flow rate based on the available heating rate and the updated adjustment factor; and   control the water flow rate of the heat pump water heater based on the updated target flow rate.   
     
     
         9 . The electronic controller of  claim 8 , wherein the water inlet temperature is determined from the third signal. 
     
     
         10 . The electronic controller of  claim 8 , wherein:
 the third variable is a water outlet temperature; and   updating the adjustment factor based on the third variable comprises:
 increasing the adjustment factor in response to the water outlet temperature being above a set-point temperature, and 
 decreasing the adjustment factor in response to the water outlet temperature being below the set-point temperature. 
   
     
     
         11 . The electronic controller of  claim 4 , wherein the first sensor is a pressure sensor positioned to measure a pressure of a refrigerant as the refrigerant flows from a compressor to an expansion device. 
     
     
         12 . The electronic controller of  claim 4 , wherein the second sensor is a pressure sensor positioned to measure a pressure of a refrigerant as the refrigerant flows from an expansion device to a compressor. 
     
     
         13 . The electronic controller of  claim 1 , wherein controlling the water flow rate of the heat pump water heater based on the target flow rate comprises:
 controlling a flow control valve to operate at a fixed valve position; and   adjusting an operating speed of a water pump.   
     
     
         14 . A method for controlling a heat pump water heater, comprising:
 receiving a first signal from a first sensor, the first signal indicative of a first variable;   receiving a second signal from a second sensor, the second signal indicative of a second variable;   determining a target flow rate based on the first variable and the second variable; and   controlling a water flow rate of the heat pump water heater based on the target flow rate.   
     
     
         15 . The method of  claim 14 , wherein the first variable is a water inlet temperature and the second variable is an ambient temperature. 
     
     
         16 . The method of  claim 15 , wherein determining the target flow rate based on the first variable and the second variable comprises:
 determining a first estimated refrigerant pressure based on the first variable;   determining a second estimated refrigerant pressure based on the second variable;   determining an available heating rate based on the first estimated refrigerant pressure and the second estimated refrigerant pressure; and   determining the target flow rate based on the available heating rate and an adjustment factor.   
     
     
         17 . The method of  claim 14 , wherein the first variable is a first refrigerant pressure and the second variable is a second refrigerant pressure. 
     
     
         18 . The method of  claim 17 , wherein determining the target flow rate based on the first variable and the second variable comprises:
 determining an available heating rate based on the first refrigerant pressure and the second refrigerant pressure; and   determining the target flow rate based on the available heating rate, a water inlet temperature, and an adjustment factor.   
     
     
         19 . The method of  claim 18 , wherein the water inlet temperature is determined from the first signal. 
     
     
         20 . The method of  claim 18 , wherein the water inlet temperature is determined from the second signal. 
     
     
         21 . The method of  claim 18 , further comprising:
 receiving a third signal from a third sensor, the third signal indicative of a third variable;   updating the adjustment factor based on the third variable;   determining an updated target flow rate based on the available heating rate and the updated adjustment factor; and   controlling the water flow rate of the heat pump water heater based on the updated target flow rate.   
     
     
         22 . The method of  claim 21 , wherein the water inlet temperature is determined from the third signal. 
     
     
         23 . The method of  claim 21 , wherein:
 the third variable is a water outlet temperature; and   updating the adjustment factor based on the third variable comprises:
 increasing the adjustment factor in response to the water outlet temperature being above a set-point temperature, and 
 decreasing the adjustment factor in response to the water outlet temperature being below the set-point temperature. 
   
     
     
         24 . The method of  claim 17 , wherein the first sensor is a pressure sensor positioned to measure a pressure of a refrigerant as the refrigerant flows from a compressor to an expansion device. 
     
     
         25 . The method of  claim 17 , wherein the second sensor is a pressure sensor positioned to measure a pressure of a refrigerant as the refrigerant flows from an expansion device to a compressor. 
     
     
         26 . The method of  claim 14 , wherein controlling the water flow rate of the heat pump water heater based on the target flow rate comprises:
 controlling a flow control valve to operate at a fixed valve position; and   adjusting an operating speed of a water pump.