Method and system for controlling frequency of variable-frequency compressor in heat pump water heater

Abstract

Disclosed are a method and a system for controlling frequency of a variable-frequency compressor in a heat pump water heater. The method includes: detecting water temperature of water flowing out from a heat exchanger and water tank temperature of a water tank; determining preset water temperature of the water flowing out from the heat exchanger according to the water tank temperature; and controlling the frequency of the variable-frequency compressor according to the water temperature and the preset water temperature. The present method and system propose a control mode of frequency of the compressor based on the water temperature of the water flowing out from the heat exchanger.

1 . A method for controlling frequency of a variable-frequency compressor in a heat pump water heater, comprising:
 detecting a water temperature of water flowing out from a heat exchanger and a water tank temperature of a water tank;   determining a preset water temperature of the water flowing out from the heat exchanger according to the water tank temperature; and   controlling the frequency of the variable-frequency compressor according to the water temperature and the preset water temperature.   
     
     
         2 . The method according to  claim 1 , wherein the preset water temperature is determined according to:
     T 1 S=f ( T 5),   where T1S is the preset water temperature and T5 is the water tank temperature.   
     
     
         3 . The method according to  claim 2 , wherein T1S is computed according to:
     T 1 S=a 1 *a 2 *a 3 *T 5 +b,      where a1 is a first correction factor for a water-water heat exchanger in the water tank, a2 is a second correction factor for a capacity of a heat pump group, a3 is a third correction factor, and b is a temperature difference correction factor.   
     
     
         4 . The method according to  claim 1 , wherein controlling the frequency of the variable-frequency compressor according to the water temperature and the preset water temperature comprises:
 acquiring a temperature difference between the water temperature and the preset water temperature;   determining a temperature range comprising the temperature difference, and acquiring a correction value according to the temperature range; and determining a target frequency of the variable-frequency compressor according to the frequency of the variable-frequency compressor and the correction value.   
     
     
         5 . The method according to  claim 4 , further comprising:
 comparing the target frequency of the variable-frequency compressor with a working frequency of the heat pump group in a set of working frequencies; and   acquiring a working frequency closest to the target frequency, and determining the working frequency closest to the target frequency as the target frequency.   
     
     
         6 . The method according to  claim 5 , wherein determining the working frequency closest to the target frequency as the target frequency further comprises:
 acquiring a minimum working frequency and a maximum working frequency of the heat pump group under the water tank temperature;   comparing the working frequency with the minimum working frequency and the maximum working frequency respectively; and   determining the working frequency as the target frequency if the working frequency is between the minimum working frequency and the maximum working frequency.   
     
     
         7 . The method according to  claim 6 , wherein acquiring a minimum working frequency and a maximum working frequency of the heat pump group under the water tank temperature further comprises:
 determining the minimum working frequency and the maximum working frequency according to an outdoor temperature T4 and the water tank temperature T5;   determining the minimum working frequency and the maximum working frequency according to a first preset frequency range, if the outdoor temperature T4 is smaller than or equal to a first preset temperature threshold and the water tank temperature T5 is greater than or equal to a second preset temperature threshold or if the outdoor temperature T4 is greater than a third preset temperature threshold and the water tank temperature T5 is greater than or equal to the second preset temperature threshold such that the variable-frequency compressor is working at the frequency in the first preset frequency range, wherein the first preset temperature threshold is smaller than the third preset temperature threshold; and   determining the minimum working frequency and the maximum working frequency according to a second preset frequency range, if the outdoor temperature T4 is in a first preset temperature range and the water tank temperature T5 is in a second preset temperature range such that the variable-frequency compressor is working at the frequency in the second preset frequency range, wherein the first preset frequency range is narrower than the second preset frequency range.   
     
     
         8 . The method according to  claim 6 , further comprising:
 determining the maximum working frequency as the target frequency if the working frequency is greater than the maximum working frequency; and   determining the minimum working frequency as the target frequency if the working frequency is smaller than the minimum working frequency.   
     
     
         9 . A system for controlling frequency of a variable-frequency compressor in a heat pump water heater, comprising:
 the variable-frequency compressor;   a heat exchanger connected to the variable-frequency compressor;   a first temperature sensor disposed at a water outlet of the heat exchanger, configured to detect a water temperature of water flowing out from the heat exchanger;   a water tank connected to the heat exchanger;   a second temperature sensor disposed in the water tank, configured to detect a water tank temperature; and   a controller, configured to acquire the water temperature from the first temperature sensor and the water tank temperature from the second temperature sensor, and to determine a preset water temperature of the water flowing out from the heat exchanger according to the water tank temperature, and to control the frequency of the variable-frequency compressor according to the water temperature and the preset water temperature.   
     
     
         10 . The system according to  claim 9 , wherein the controller determines the preset water temperature according to:
     T 1 S=f ( T 5),   where T1S is the preset water temperature and T5 is the water tank temperature.   
     
     
         11 . The system according to  claim 10 , wherein T1S is computed according to:
   T1 S=a 1 *a 2 *a 3 *T 5 +b,      where a1 is a first correction factor for a water-water heat exchanger in the water tank, a2 is a second correction factor for a capacity of a heat pump group, a3 is a third correction factor, and b is a temperature difference correction factor.   
     
     
         12 . The system according to  claim 9 , wherein the controller is configured to:
 acquire a temperature difference between the water temperature and the preset water temperature;   determine a temperature range comprising the temperature difference, and acquire a correction value according to the temperature range; and   determine a target frequency of the variable-frequency compressor according to the frequency of the variable-frequency compressor and the correction value.   
     
     
         13 . The system according to  claim 12 , wherein the controller is further configured to:
 compare the target frequency of the variable-frequency compressor with a working frequency of the heat pump group in a set of working frequencies; and   acquire a working frequency closest to the target frequency, and determine the working frequency closest to the target frequency as the target frequency.   
     
     
         14 . The system according to  claim 13 , wherein the controller is further configured to:
 acquire a minimum working frequency and a maximum working frequency of the heat pump group under the water tank temperature;   compare the working frequency with the minimum working frequency and the maximum working frequency respectively; and   determine the working frequency as the target frequency if the working frequency is between the minimum working frequency and the maximum working frequency.   
     
     
         15 . The system according to  claim 14 , wherein the controller is further configured to:
 determine the minimum working frequency and the maximum working frequency according to an outdoor temperature T4 and the water tank temperature T5;   determine the minimum working frequency and the maximum working frequency according to a first preset frequency range, if the outdoor temperature T4 is smaller than or equal to a first preset temperature threshold and the water tank temperature T5 is greater than or equal to a second preset temperature threshold or if the outdoor temperature T4 is greater than a third preset temperature threshold and the water tank temperature T5 is greater than or equal to the second preset temperature threshold such that the variable-frequency compressor is working at the frequency in the first preset frequency range, wherein the first preset temperature threshold is smaller than the third preset temperature threshold; and   determine the minimum working frequency and the maximum working frequency according to a second preset frequency range, if the outdoor temperature T4 is in a first preset temperature range and the water tank temperature T5 is in a second preset temperature range such that the variable-frequency compressor is working at the frequency in the second preset frequency range, wherein the first preset frequency range is narrower than the second preset frequency range.   
     
     
         16 . The system according to  claim 14 , wherein the controller is further configured to:
 determine the maximum working frequency as the target frequency if the working frequency is greater than the maximum working frequency; and   determine the minimum working frequency as the target frequency if the working frequency is smaller than the minimum working frequency.   
     
     
         17 . The system according to  claim 9 , wherein the heat exchanger is one of a water-refrigerant heat exchanger and air-refrigerant heat exchanger. 
     
     
         18 . The system according to  claim 17 , wherein the water tank comprises a water-water heat exchanger connected to the water-refrigerant heat exchanger via a circulating water pump. 
     
     
         19 . A heat pump water heater, comprising a system for controlling frequency of a variable-frequency compressor in a heat pump water heater according to  claim 9 .