Tankless water heater with integrated variable speed pump

A hot water storage system comprising:

• a storage tank including a tank inlet and a tank outlet;
• a tank temperature sensor positioned adjacent to the tank outlet and configured to provide tank temperature information;
• and
• a tankless water heater system comprising:
• a heat exchanger including a heat exchanger inlet fluidically coupled to the tank outlet and a heat exchanger outlet fluidically coupled to the tank inlet;
• a variable speed pump configured to provide an adjustable output flow rate of water through the heat exchanger;
• an output temperature sensor disposed downstream of the heat exchanger outlet and configured to provide heat exchanger output temperature information;
• and
• a controller configured to:
• control an amount of heat added via the heat exchanger within a turndown ratio less than 13:1,
• control the output flow rate of the variable speed pump based on the heat exchanger output temperature information,
• turn off the variable speed pump when the tank temperature information is equal to or greater than a maximum temperature, and
• control the amount of heat added and the variable speed pump to maintain the heat exchanger output temperature information within a threshold of a set point temperature, wherein the threshold is greater than or equal to five degrees Fahrenheit and the set point temperature is greater than or equal to 120 degrees Fahrenheit and less than or equal to 183 degrees Fahrenheit.

A method of heating water comprising:

• receiving a signal to initiate circulation;
• generating a signal to a variable speed pump to circulate a flow of water at a first flow rate from an outlet of a heat exchanger to an inlet of a storage tank and from an outlet of the storage tank to an inlet of the heat exchanger, wherein the variable speed pump is configured to be adjustable to pump fluid at a plurality of flow rates;
• controlling an amount of heat added by the heat exchanger to the flow of water to be within a turndown ratio less than 13:1;
• receiving a first temperature reading from an output temperature sensor downstream of the heat exchanger and configured to measure a temperature of water output from the outlet of the heat exchanger;
• and
• generating a signal to the variable speed pump to circulate the flow of water at least at one additional flow rate of the plurality of flow rates in response to the first temperature reading, wherein the temperature of water output from the outlet of the heat exchanger is maintained within a threshold of a set point temperature, and wherein the threshold is greater than five degrees Fahrenheit.