System and method for determining heat demand of a hydronic heating system

A water heating system comprising:

• a boiler including a boiler water inlet fluidly connected to a boiler water outlet via a boiler heat exchanger internal to the boiler;
• a heat source providing heat to the boiler heat exchanger;
• a storage tank separate from the boiler for storing water for the water heating system, the storage tank including a storage tank water inlet fluidly connected to a storage tank water outlet via a storage tank heat exchanger internal to the storage tank, wherein the boiler water outlet is fluidly connected to the storage tank water inlet, and the storage tank water outlet is fluidly connected to the boiler water inlet, such that water flows between the boiler heat exchanger and the storage tank exchanger;
• a hydronic heating system including a hydronic heating water inlet fluidly connected to the boiler water outlet, and a hydronic heating water outlet fluidly connected to the boiler water inlet, such that water flows between the boiler heat exchanger and the hydronic heating system;
• and
• a boiler controller, upon receiving a demand for domestic hot water heat from the storage tank, configured to:
• activate a pump such that the water flows between the boiler heat exchanger and the storage tank heat exchanger,
• perform PID control by firing the heat source at a PID firing rate based on measured temperatures of water at the boiler water inlet and at the boiler water outlet,
• upon receiving a demand for hydronic heat from the hydronic heating system, activate a valve supplying water from the boiler heat exchanger to the hydronic heating system and maintain the PID firing rate for a time period, and during the time period, measuring temperatures of water at the boiler water inlet and at the boiler water outlet,
• calculate temperature differences in the measured temperatures at different times during the time period, and
• control the heat source to provide heat to the boiler heat exchanger at a firing rate determined based on a comparison between the temperature differences in the measured temperatures.

A method for controlling a water heating system including a boiler including a boiler water inlet fluidly connected to a boiler water outlet via a boiler heat exchanger internal to the boiler, a heat source providing heat to the boiler heat exchanger, a hydronic heating system including a hydronic heating water inlet fluidly connected to the boiler water outlet, and a hydronic heating water outlet fluidly connected to the boiler water inlet, such that water flows between the boiler heat exchanger and the hydronic heating system, and a boiler controller, upon receiving a demand for hydronic heat from the hydronic heating system, the method comprising:

• activating, by the boiler controller, a pump such that the water flows between the boiler heat exchanger and the hydronic heating system,
• when the heat source is firing at a preexisting firing rate, maintaining, by the boiler controller, firing the heat source at the preexisting firing rate for a time period, and during the time period measuring temperatures of water at the boiler water inlet and at the boiler water outlet,
• when the heat source is not firing, preventing, by the boiler controller, firing the heat source for a time period, and during the time period measuring temperatures of water at the boiler water inlet and at the boiler water outlet,
• calculating, by the boiler controller, temperature differences at different times during the time period between the measured temperatures, and
• controlling, by the boiler controller, the heat source to provide heat to the boiler heat exchanger at a firing rate determined based on a comparison between the temperature differences.

A method for controlling a water heating system including a boiler including a boiler water inlet fluidly connected to a boiler water outlet via a boiler heat exchanger internal to the boiler, a heat source providing heat to the boiler heat exchanger, a storage tank separate from the boiler for storing water for the water heating system, the storage tank including a storage tank water inlet fluidly connected to a storage tank water outlet via a storage tank heat exchanger internal to the storage tank, wherein the boiler water outlet is fluidly connected to the storage tank water inlet, and the storage tank water outlet is fluidly connected to the boiler water inlet, such that water flows between the boiler heat exchanger and the storage tank exchanger, a hydronic heating system including a hydronic heating water inlet fluidly connected to the boiler water outlet, and a hydronic heating water outlet fluidly connected to the boiler water inlet, such that water flows between the boiler heat exchanger and the hydronic heating system, and a boiler controller, upon receiving a demand for domestic hot water heat from the storage tank, the method comprising:

• activating, by the controller, a pump such that the water flows between the boiler heat exchanger and the storage tank heat exchanger,
• performing, by the controller, PID control by firing the heat source at a PID firing rate based on measured temperatures of water at the boiler water inlet and at the boiler water outlet,
• upon receiving a demand for hydronic heat from the hydronic heating system, activating, by the controller, a valve supplying water from the boiler heat exchanger to the hydronic heating system and maintain the PID firing rate for a time period, and during the time period, measuring temperatures of water at the boiler water inlet and at the boiler water outlet,
• calculating, by the controller, temperature differences in the measured temperatures at different times during the time period, and
• controlling, by the controller, the heat source to provide heat to the boiler heat exchanger at a firing rate determined based on a comparison between the temperature differences in the measured temperatures.