Heat pump system and control method thereof

Abstract

A heat pump system, the operation of which is controlled using a temperature difference between a water inlet and a water outlet of a heat exchanger, exchanging heat between a refrigerant and water, and a control method thereof. The heat pump system includes temperature sensors installed on a water circulation pipe unit at water inlet and outlet sides of a heat exchanger, and heats a load to a set temperature by controlling a compressor or an expander according to a difference between temperatures sensed by the temperature sensors. Here, a temperature of water transmitted to the load is set to be greater than a target load temperature by a reference value, and if the temperature difference is smaller than a designated value, the operation of the heat pump system is stopped.

1 . A heat pump system comprising:
 a compressor to compress a refrigerant into a high-temperature and high-pressure state;   a refrigerant circulation pipe unit to circulate the refrigerant;   a first heat exchanger to exchange heat between the refrigerant and water;   a water circulation pipe unit to circulate the water heated or cooled by the first heat exchanger toward a load;   an expander to expand the refrigerant into a low-temperature and low-pressure state;   a second heat exchanger to exchange heat between the refrigerant and air;   a first temperature sensor installed at the water circulation pipe unit to sense a temperature of the water transmitted to the load;   a second temperature sensor installed at the water circulation pipe unit to sense a temperature of the water transmitted to the first heat exchanger; and   a control unit to control the compressor or the expander according to a difference between the temperature sensed by the first temperature sensor and the temperature sensed by the second temperature sensor so as to set a temperature of the load to a first set temperature, which is a target temperature.   
     
     
         2 . The heat pump system according to  claim 1 , wherein, in the control of the compressor or the expander according to the difference between the temperature sensed by the first temperature sensor and the temperature sensed by the second temperature sensor so as to set the temperature of the load to the first set temperature:
 the control unit increases an rpm of the compressor and an opening degree of the expander, if the difference between the temperature sensed by the first temperature sensor and the temperature sensed by the second temperature sensor is increased; and   the control unit decreases the rpm of the compressor and the opening degree of the expander, if the difference between the temperature sensed by the first temperature sensor and the temperature sensed by the second temperature sensor is decreased.   
     
     
         3 . The heat pump system according to  claim 2 , wherein the first temperature sensor or the second temperature sensor is installed at a part of the water circulation pipe unit adjacent to the first heat exchanger. 
     
     
         4 . The heat pump system according to  claim 3 , wherein the load is a hot water tank to supply hot water. 
     
     
         5 . The heat pump system according to  claim 4 , wherein:
 the control unit determines a second set temperature, which is a temperature of a water outlet side of the first heat exchanger, according to the first set temperature; and   the control unit controls the compressor or the expander so as to adjust the temperature of the water outlet side of the first heat exchanger to the second set temperature.   
     
     
         6 . The heat pump system according to  claim 5 , wherein, upon judging that the second set temperature does not exceed the maximum temperature suppliable by the heat pump system, the control unit sets the second set temperature to be greater than the first set temperature by a first reference value. 
     
     
         7 . The heat pump system according to  claim 6 , wherein, if the difference between the temperature sensed by the first temperature sensor and the temperature sensed by the second temperature sensor is lower than a second reference value, the control unit stops the operation of the heat pump system. 
     
     
         8 . The heat pump system according to  claim 5 , wherein, upon judging that the second set temperature exceeds the maximum temperature suppliable by the heat pump system, the control unit sets the second set temperature as the maximum temperature suppliable by the heat pump system. 
     
     
         9 . The heat pump system according to  claim 8 , further comprising a first sub heater to heat the water circulation pipe unit, or a second sub heater to heat the hot water tank,
 wherein, upon judging that the second set temperature exceeds the maximum temperature suppliable by the heat pump system, the control unit operates the first sub heater or the second sub heater.   
     
     
         10 . The heat pump system according to  claim 9 , wherein, if the difference between the temperature sensed by the first temperature sensor and the temperature sensed by the second temperature sensor is lower than a second reference value, the control unit stops the operation of the heat pump system. 
     
     
         11 . A control method of a heat pump system, which has a compressor, an expander, a refrigerant circulation pipe unit, a water circulation pipe unit, a first heat exchanger to exchange heat between the refrigerant and water, a second heat exchanger to exchange heat between the refrigerant and air, a first temperature sensor installed at a part of the water circulation pipe unit at a water outlet side of the first heat exchanger, and a second temperature sensor installed at another part of the water circulation pipe unit at a water inlet side of the first heat exchanger, and circulates the water through the water circulation pipe unit to heat or cool a load, comprising:
 determining a second set temperature, which is a temperature of the water outlet side of the first heat exchanger, according to a first set temperature, which is a target temperature of the load;   adjusting a temperature of the water at the water outlet side of the first heat exchanger to the second set temperature, and then circulating the water through the water circulation pipe unit;   sensing the temperature of the water at the water outlet side of the first heat exchanger through the first temperature sensor;   sensing a temperature of the water at the water inlet side of the first heat exchanger through the second temperature sensor; and   controlling the compressor or the expander according to a difference between the temperature sensed by the first temperature sensor and the temperature sensed by the second temperature sensor so as to maintain the temperature of the water at the water outlet side of the first heat exchanger at the second set temperature.   
     
     
         12 . The control method according to  claim 11 , wherein the control of the compressor or the expander according to the difference between the temperature sensed by the first temperature sensor and the temperature sensed by the second temperature sensor so as to maintain the temperature of the water at the water outlet side of the first heat exchanger at the second set temperature includes:
 increasing an rpm of the compressor and an opening degree of the expander, if the difference between the temperature sensed by the first temperature sensor and the temperature sensed by the second temperature sensor is increased; and   decreasing the rpm of the compressor and the opening degree of the expander, if the difference between the temperature sensed by the first temperature sensor and the temperature sensed by the second temperature sensor is decreased.   
     
     
         13 . The control method according to  claim 12 , wherein, upon judging that the second set temperature does not exceed the maximum temperature suppliable by the heat pump system, the second set temperature is set to be greater than the first set temperature by a first reference value. 
     
     
         14 . The control method according to  claim 13 , wherein, if the difference between the temperature sensed by the first temperature sensor and the temperature sensed by the second temperature sensor is lower than a second reference value, the operation of the heat pump system is stopped. 
     
     
         15 . The control method according to  claim 12 , wherein, upon judging that the second set temperature exceeds the maximum temperature suppliable by the heat pump system, the second set temperature is set as the maximum temperature suppliable by the heat pump system. 
     
     
         16 . The control method according to  claim 15 , wherein, if the difference between the temperature sensed by the first temperature sensor and the temperature sensed by the second temperature sensor is lower than a second reference value, the operation of the heat pump system is stopped. 
     
     
         17 . The heat pump system according to  claim 1 , wherein the load is not provided with a temperature sensor. 
     
     
         18 . The heat pump system according to  claim 4 , wherein the hot water tank is not provided with a temperature sensor.