Radiant heating system reset control

A hydronic heating system including a main boiler and a circulating pump for circulating a supply of heated water, the hydronic heating system heating a plurality of heating zones, the system comprising:

• a primary loop positioned between an output of the boiler and a return line for returning water to the boiler;
• a secondary, radiant loop coupled to the output of the boiler for circulating the supply of heated water to a plurality of heat exchangers for heating the plurality of heating zones;
• a modulating valve positioned between the primary loop and the secondary, radiant loop, the modulating valve being operable to mix varying amounts of heated water from the primary loop and return water from the secondary, radiant loop;
• a control unit in communication with the modulating valve to control the amount of heated water from the boiler to the secondary, radiant loop;
• a maximum radiant loop water temperature dial contained on the control unit for setting a maximum radiant loop water temperature in the control unit;
• a minimum radiant loop water temperature dial contained on the control unit for setting a minimum radiant loop water temperature in the control unit;
• a maximum outdoor air temperature dial contained on the control unit for setting a maximum outdoor air temperature in the control unit;
• a minimum outdoor air temperature dial contained on the control unit for setting a minimum outdoor air temperature in the control unit;
• an outdoor air temperature sensor coupled to the control unit for measuring the outdoor air temperature;
• a secondary loop water temperature sensor positioned in the secondary, radiant loop and coupled to the control unit for measuring the water temperature in the radiant loop;
• and
• a return water temperature sensor positioned in the return line and coupled to the control unit for measuring the water temperature in the return line;
• wherein the control unit calculates a linear reset curve based on the maximum radiant loop water temperature, the minimum radiant loop water temperature, the maximum outdoor air temperature, and the minimum outdoor air temperature and determines a desired temperature for the water in the secondary, radiant loop based on the linear reset curve and the measured outdoor air temperature.

A method of controlling the water temperature in a hydronic heating system that circulates a supply of heated water from a boiler to a radiant loop including a plurality of heating zones, the method comprising the steps of:

• providing a control unit;
• setting a maximum radiant loop water temperature and a minimum radiant loop water temperature in the control unit;
• setting a minimum outdoor air temperature and an maximum outdoor air temperature in the control unit;
• and
• coupling a sensor that measures the outdoor air temperature to the control unit;
• generating a reset curve in the control unit based on the maximum radiant loop water temperature, the minimum radiant loop water temperature, the maximum outdoor air temperature, and the minimum outdoor air temperature;
• determining a desired temperature for the water in the radiant loop based on the reset curve and the current measured outdoor air temperature;
• and
• operating the hydronic heating system to supply heated water at the desired temperature to the radiant loop.

A method of controlling the water temperature in a secondary, radiant loop of a hydronic heating system having a boiler and a primary loop, the method comprising the steps of:

• providing a control unit;
• controlling the operation of a modulating valve positioned between the radiant loop and the primary loop, the modulating valve controlling the flow of heated water from the boiler to the radiant loop;
• receiving a measured radiant loop water temperature in the control unit from a radiant loop water temperature sensor positioned in the radiant loop;
• receiving a measured outdoor air temperature in the control unit from an outdoor air temperature sensor positioned to measure the outdoor air temperature;
• setting a maximum radiant loop water temperature and a minimum radiant loop water temperature in the control unit;
• setting a minimum outdoor air temperature and a maximum outdoor air temperature in the control unit;
• generating a reset curve in the control unit based on the maximum and minimum radiant loop water temperatures and the maximum and minimum outdoor air temperature;
• determining a desired radiant loop water temperature for the water in the radiant loop based on the reset curve and the measured outdoor air temperature;
• and
• operating the modulating valve to control the flow of water from the boiler to the radiant loop such that the measured radiant loop water temperature is equal to the desired radiant loop water temperature.

A method of controlling the water temperature in a secondary, radiant loop of a hydronic heating system having a boiler and a primary loop, the method comprising the steps of:

• providing a control unit;
• controlling the operation of a modulating valve positioned between the radiant loop and the primary loop, the modulating valve controlling the flow of heated water from the boiler to the radiant loop;
• receiving a signal from a return water temperature sensor that measures a current return water temperature of the water returning to the boiler from the primary loop and the radiant loop;
• setting a minimum return water temperature in the control unit;
• determining the rate of change in the return water temperature;
• calculating a predicted return water temperature based on the rate of change in the return water temperature and the current return water temperature;
• and
• partially closing the modulating valve to decrease the flow of heated water form the boiler to the radiant loop when the predicted return water temperature is below the minimum return water temperature.