Electric water heater

A water heater comprising:

• a body having an elongated hollow, and an inlet opening and an outlet opening in communication with said hollow for flowing fluid therethrough;
• an electrical resistance heater having a heating element of a material exhibiting a positive temperature coefficient of resistance, said heating element disposed in said hollow of said body and in heat transfer communication with fluid flowing through said hollow;
• an input terminal for receiving electrical power and supplying said electrical power to said heating element to produce a current in said heating element to generate heat;
• and
• a controller for sensing current flow through said heating element and determining a resistance related value of said heating element, said controller further determining a first derivative of said resistance related value as a function of time and a second derivative of said resistance related value as a function of time, and controlling said electrical power supplied to said heating element as a function of said first and second derivatives.

A heater comprising:

• a polymeric body having an elongated hollow, and an inlet opening and outlet opening in communication with said hollow for flowing fluid therethrough;
• an electrical heater having a heating element disposed in said hollow of said polymeric body and in heat transfer communication with fluid flowing through said hollow said heating element having an inner conductor and an outer conductive jacket separated by a dielectric material;
• an input terminal for receiving electrical power and supplying said electrical power to said heating element to produce a current in said heating element to generate heat;
• a conductive member disposed in said hollow and in contact with said outer conductive jacket of said heating element for collecting stray currents in said fluid;
• a ground fault detector in electrical contact with said outer conductive jacket for detecting a ground fault condition;
• and
• a controller for controlling the electrical power to said heating element, said controller controlling said electrical power supplied to said heating element based on said ground fault detection.

A heater comprising:

• a body having an elongated hollow, and an inlet opening and an outlet opening in communication with said hollow for flowing fluid therethrough;
• a heater disposed in said hollow of said body and in heat communication with fluid flowing through said hollow;
• an input for receiving power and supplying said power to said heater to generate heat;
• a sensor for sensing a temperature dependent value indicative of temperature of said fluid;
• and
• a controller for determining a first derivative of said temperature dependent value as a function of time and a second derivative of said temperature dependent value as a function of time, and controlling said power supplied to said heater as a function of said first and second derivatives.

A method of controlling a heating comprising:

• sensing current flow through a heater element that is disposed in a hollow of a body having an inlet and an outlet in communication with the hollow flowing fluid therethrough, said heating element having a material exhibiting a positive temperature coefficient of resistance and providing heat transfer with fluid flowing through said hollow;
• determining a resistance related value of said heating element as a function of said sensed current;
• determining a first derivative of said resistance related value as a function of time;
• determining a second derivative of said resistance related value as a function of time;
• and
• controlling electrical power supplied to said heating element as a function of said first and second derivatives.