Thermostatic condensing gas water heater and control method therefor

Abstract

A thermostatic condensing gas water heater, comprising a burner; a first heat exchanger ( 7 ), a second heat exchanger ( 4 ), a water inlet pipe ( 10 ), and a water outlet pipe ( 9 ) provided in succession along the flow direction of the burnt flue gas; a controller; and a water flow channel connecting the first heat exchanger ( 7 ) and the second heat exchanger ( 4 ) in parallel between the water inlet pipe ( 10 ) and the water outlet pipe ( 9 ), wherein flow control valves ( 3, 5 ) capable of adjusting the water flow distribution of the first heat exchanger ( 7 ) and the second heat exchanger ( 4 ) are provided on the water flow channel and controlled by the controller.

What is claimed is: 
     
         1 . A method of controlling a thermostatic condensing gas water heater, the method comprising:
 providing a burner;   providing a first heat exchanger, a second heat exchanger, a water inlet pipe, and   a water outlet pipe in succession along a flow direction of the burnt flue gas;   providing a controller;   providing a water flow channel connecting the first heat exchanger and the second heat exchanger in parallel between the water inlet pipe and the water outlet pipe;   providing flow control valves in the water flow channel;   controlling with the controller the flow control valves to adjust the water flow distribution of the first heat exchanger and the second heat exchanger;   providing an electrical heating device in the second heat exchanger;   controlling with the controller the electrical heating device in the second heat exchanger to heat the water in the second heat exchanger;   acquiring with the controller an outlet water temperature (Te) of the first heat exchanger and an outlet water temperature (Tc) of the second heat exchanger;   reading with the controller a set temperature (Ts) and a controller preset temperature (Ta);   controlling with the controller the electrical heating device so that the outlet water   temperature (Tc) of the second heat exchanger approaches the controller preset temperature (Ta) when the outlet water temperature (Te) of the first heat exchanger is less than a sum of the set temperature (Ts) and a predetermined temperature tolerance (ΔT).   
     
     
         2 . The control method according to  claim 1 , wherein the second heat exchanger is a housing-and-tube heat exchanger which enables its housing to be communicated with the water inlet pipe and the water outlet pipe, and enables the burnt flue gas to pass through a pipeline in the housing. 
     
     
         3 . The control method according to  claim 1 , further comprising the step of adjusting with the controller the flow control valves according to a target flow proportion (β 1 =(Ts-Te)/(Tc-Te)) of the second heat exchanger, so that an outlet water temperature (To) of the water outlet pipe approaches the set temperature (Ts). 
     
     
         4 . The control method according to  claim 3 , further comprising the steps of acquiring with the controller the outlet water temperature (To) of the water outlet pipe, and adjusting with the controller the flow control valves in a predetermined step length according to an actual flow proportion (βs=(To-Te)/(Tc-Te)) of the second heat exchanger, so that the actual flow proportion (βs) approaches the target flow proportion (β 1 ). 
     
     
         5 . The control method according to  claim 1 , further comprising the step of acquiring with the controller the outlet water temperature (Te) of the first heat exchanger, the outlet water temperature (Tc) of the second heat exchanger, and an outlet water temperature (To) of the water outlet pipe by detecting temperature sensors provided on the first heat exchanger, the second heat exchanger and the water outlet pipe, respectively.