Water heater with mix tank fluid time delay for causal feedforward control of hot water temperature

A method for controlling a hot water temperature of a water heater comprising:

• providing a heat exchanger having a hx cold water inlet fluidly coupled to a source of cold water and a mix tank, said mix tank having a cold water inlet and a constant flow hot water inlet;
• mixing said source of cold water with a constant flow of hot water from said heat exchanger in said mix tank to provide a mixed water;
• delaying said mixed water by a fluid delay time to provide a fluid time delayed mixed water;
• measuring a temperature of said fluid time delayed mixed water in said mixing tank to provide a temperature measurement of said fluid time delayed mixed water;
• and
• setting by a processor running a feedforward control process, a position of a proportional valve based on said temperature measurement of said fluid time delayed mixed water to control a flow of boiler water into said heat exchanger.

A water heater comprising:

• a heat exchanger (hx) having a hx hot water inlet, a hx water return outlet, a hx domestic cold water inlet, and a hx domestic hot water outlet;
• a controllable three-way linearized proportional valve having a boiler water hot water inlet adapted to accept a boiler water, and to provide a proportionally controllable flow to said hx hot water inlet and boiler return water outlet, and said boiler return water outlet adapted to return a boiler return water to a boiler;
• a flow rate sensor disposed in fluid communication with said hx domestic cold water inlet to provide a domestic cold water flow rate;
• a processor operatively coupled to said flowrate sensor and operatively coupled to said controllable three-way linearized proportional valve, said processor to run a feedforward control process based on said domestic cold water flow rate to control a flow of boiler water into said heat exchanger;
• and
• wherein said feedforward control process adjusts a proportional operating position of said controllable three-way linearized proportional valve to regulate a temperature of hot water at said hx domestic hot water outlet based on said domestic cold water flow rate.