Patent Publication Number: US-9416980-B2

Title: Economically-operated, dual-energy hot water supply system and method of operating the same

Description:
BACKGROUND 
     This invention relates to a dual-energy hot water supply system. In a more specific embodiment, the invention relates to an economically-operated, dual-energy hot water supply system and its operating method. 
     In the past few years, hot water supply systems combine gas water heaters and heat pump water heaters. For example, Chinese patent application no. 200820202823.2 discloses a heat pump water heater with a gas auxiliary heating unit. The system includes a confined water tank, a control device, and outlet piping. The mentioned gas auxiliary heating unit is installed in series with the outlet piping of the confined water tank. The downdraft temperature probe, water flow sensor, and gas control valve are connected to the control unit respectively. The system is characterized by compensating the heat pump effectively in the insufficient heat supply conditions and expanding the applicable areas of the heat pump water heater. For another example, Chinese patent application no. 200920300786.3 discloses a solar water heater with two auxiliary heating methods, i.e. a heat pump water heater and a gas water heater. The system integrates the advantages of the gas water heater and heat pump water heater, and avoids their disadvantages. 
     SUMMARY 
     However, as for the heating method changeover, the prior technology only takes into consideration the additional heating, but fails to make the hot water supply system more economical from the view of saving operating cost. 
     In at least one embodiment, the invention addresses the shortcomings in the above-mentioned prior technology by presenting an economically-operated, dual-energy hot water supply system. The supply of hot water to users is based on a minimal operating cost. 
     To achieve the above, the economically-operated, dual-energy hot water supply system comprises, in one embodiment, at least a heat pump heating unit and a gas heating unit. The system includes an insulated water tank equipped with a water temperature sensor, the hot water system is equipped with an ambient temperature sensor, the signal output terminals of the water and ambient temperature sensors are connected to the monitoring input terminal of a centralized controller, whose control output terminal is connected to startup control terminals of the heat pump heating unit and the gas heating unit. The centralized controller can include the following units. 
     A storage unit used to store the derivation rules of energy efficiency coefficient corresponding to different water and ambient temperatures. 
     A computation unit used to call the corresponding energy efficiency coefficient from the storage unit according to the water and ambient temperature signals from the detection input terminals. The computation unit calculates the energy consumption of the heat pump heating unit to generate a unit heat at an energy efficiency coefficient and calculates the gas consumption of the gas heating unit to generate a unit heat based on the combustion efficiency of the gas heating unit and the local gas heat value. 
     An input unit used to input the present electricity price, gas price, and the combustion efficiency of the mentioned gas heating unit and the local gas heat value. 
     A comparing unit used to compare the power cost of the heat pump heating unit with the gas cost of the gas heating unit, in order to generate the unit heat. 
     A control unit used to select and start the heat pump heating unit or the gas heating unit based on the most economic rule. 
     One exemplary operating method for the above-mentioned dual-energy hot water supply system includes the following. 
     A storage procedure to store the derivation rules of energy efficiency coefficient corresponding to different water and ambient temperatures. 
     A computation procedure to call the corresponding energy efficiency coefficient from the storage unit according to the water and ambient temperature signals from the detection input terminals, to calculate the energy consumption of the heat pump heating unit to generate a unit heat at the current energy efficiency coefficient, and to calculate the gas consumption of the gas heating unit to generate a unit heat based on the combustion efficiency of the gas heating unit and the local gas heat value. 
     An input procedure to input the present electricity price, gas price, and the combustion efficiency of the mentioned gas heating unit and the local gas heat value. 
     A comparing procedure to compare the power cost of the heat pump heating unit with the gas cost of the gas heating unit, in order to generate a unit heat. 
     A control procedure to select and start the heat pump heating unit or the gas heating unit based on the most economic rule. 
     With embodiments of this invention, when the ambient and water temperatures are measured and the local electricity and gas prices are input, the invention will put the air source heat pump heating unit or the gas heating unit into operation based on an optimal operating cost rule, which minimizes the operating cost of the hot water system. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a structure diagram of Example I of the invention. 
         FIG. 2  is a structure diagram of Example II of the invention. 
         FIGS. 3A and 3B  show a schematic circuit diagram for Example I in  FIG. 1 . 
         FIG. 4  is a control process block diagram for Example I in  FIG. 1 . 
         FIG. 5  is a structure diagram of Example III of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
     EXAMPLE I 
     An economically-operated dual-energy hot water supply system is shown in  FIG. 1 . The system includes a heat pump water heater  1  and a gas water heater  2 . The water outlets of the heat pump water heater  1  and the gas water heater  2  are connected by a flow switch respectively to an insulated water tank  3  that supplies hot water to users. The water heaters form a circulation loop with the insulated water tank  3  through circulating water pump  1 -M and  2 -M, respectively. A water temperature sensor  4 - 1  is installed at the insulated water tank  3 , an ambient temperature sensor  4 - 2  is installed around the hot water system, and C is a makeup water inlet. The signal output terminals of both sensors and  4 - 1  and  4 - 2  are connected to the monitoring input terminal  11  of a programmable logic controller (PLC)  4  that works as a centralized controller through a temperature measurement model. The control output terminal  12  of the controller  4  is connected to relay coils K 1  and K 2  ( FIG. 3B ) that work as the startup control terminals of the heat pump water heater  1  and the gas water heater  2 , respectively. The control output terminal  12  of the controller  4  is also connected to the control relay coils K 3  and K 4  of the circulating water pumps  1 -M and  2 -M, as shown in  FIG. 3B , so that it can break and make the corresponding relay contacts L 1  L 2 , L 3 , and L 4 , which further control the heat pump water heater  1  and the gas water heater  2  as well as the corresponding circulating water pumps  1 -M and  2 -M. 
     An exemplary control procedure of the above-mentioned PLC is as follows (refer to  FIG. 4 ). 
     The storage procedure, performed by a storage unit  10  of the controller  4 , stores the derivation rules of an energy efficiency coefficient, which corresponds to different water and ambient temperatures, and includes power consumption of the heat pump water heater to generate a unit heat and gas consumption of the gas water heater to generate a unit heat. In this example, a group of energy efficiency coefficients corresponding to different water and ambient temperatures can be obtained through testing (among them: the energy efficiency coefficient is 4.2 when the ambient temperature is forty degrees Celsius and the water temperature is forty degrees Celsius). 
     The computation procedure, performed by a computation unit  13  of the controller  4 , calls the corresponding energy efficiency coefficient from the storage unit  10  according to the water and ambient temperature signals from the detection input terminals. The procedure calculates the energy consumption of the heat pump water heater and the gas consumption of the gas water heater in order to generate a unit heat at the current energy efficiency coefficient. In one example, the water and ambient temperature inputs are forty degrees Celsius and forty degrees Celsius, respectively, based on which, the energy efficiency coefficient 4.2 is called. The energy consumption of the heat pump water heater to generate 1 MJ heat is further calculated: 1000/(4.2*3600)=0.06614 kWh. In addition, the gas consumption of the gas water heater to generate 1 MJ heat according to the combustion efficiency of the gas heating unit and the local gas heat value (e.g., a combustion heating value for a gas) is calculated:
 
1/(36.5*0.85)=0.3223 m 3 .
 
     The input procedure inputs the present electricity and gas prices, which are 0.75 RMB/kWh (0.1166 $/kWh) for electricity price and 2.2 RMB/m 3  (0.3419 $/kWh) for gas price, in one example. The combustion efficiency of the mentioned gas heating unit, which is 0.85 in one example, and the local gas heat value. 
     The comparing procedure, performed by a comparison unit  14  of the controller  4 , compares the power cost of the heat pump water heater with the gas cost of the gas water heater to generate a unit heat. In the above example, the power cost of the heat pump water heater to generate 1 MJ heat is 0.06614*0.75=0.0496 RMB/MJ (0.0077 $/MJ), which is lower than the gas cost of the gas water heater to generate 1 MJ heat: 2.2*0.3223=0.0709 RMB/MJ (0.0110 $/MJ). 
     The control procedure selects and starts the heat pump heating unit or the gas heating unit based on the most economic rule. In the above example, the control procedure opens the flow switch of the heat pump water heater and starts the corresponding circulating water pump. 
     Therefore, when the ambient and water temperatures are measured and the local electricity and gas prices are input, the invention puts the air source heat pump water heater (or the gas water heater) into operation based on an optimal operating cost rule, so that the procedure minimizes the operating cost of the whole hot water system. 
     EXAMPLE II 
     An economically-operated, dual-energy hot water supply system in this example is shown in  FIG. 2 . The system includes a group of heat pump water heaters  1 - 1 ,  1 - 2  . . .  1 - n  in parallel and a group of gas water heaters  2 - 1 ,  2 - 2  . . .  2 - n  in parallel. The water outlets of the heat pump water heater group and the gas water heater group are connected through flow switches, respectively, to an insulated water tank  3  that supplies hot water to users. The water heater groups form a circulation loop with the insulated water tank  3  through circulating water pumps, respectively. A water temperature sensor  4 - 1  is installed at the insulated water tank  3 , and an ambient temperature sensor  4 - 2  is installed around the hot water system. The signal output terminals of both sensors are connected to the monitoring input terminal of a centralized controller  4 , whose control output terminals  12  are connected to the startup control terminals K 1  and K 2  of the heat pump water heater group  1  and the gas water heater group  2 , respectively (refer to  FIGS. 1, 3A, and 3B ). The control procedures of this example are the same with that of Example I. 
     EXAMPLE III 
     The economically-operated dual-energy hot water supply system in this example is shown in  FIG. 5 . Some differences from the above examples are that the heat exchange coil of a heat pump heating unit is wound around the insulated water tank  3  and the burner  6  of a gas heating unit is installed directly on the bottom of the insulated water tank  3 , thus to supply heat to the insulated water tank  3 . However, in the above examples, heat is supplied to the insulated water tank  3  indirectly through the heat pump water heater and gas water heater. In Example III the hot water supply system includes a gas valve  5 —the startup control terminal of the gas heating unit. The operating principle and control procedures of this example are similar to that of Example I. 
     Thus, the invention provides, among other things, a new and useful economically-operated, dual-energy hot ware supply system and method of operating the same. Various features and advantages of the invention are set forth in the following claims.