Hot water reset: Difference between revisions

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Hot water reset is a digital control specification for hot water boilers that are typically fired with fuel oil or natural gas. A hot water reset digital control system measures the outside air temperature using a thermistor. This information is used to estimate demand or heating load as the outdoor temperature varies and modulate the supply hot water temperature up and down range in a linear ratio. Typical range for conventional boilers is to vary the supply water temperature from 140 to 180 °F as the outside temperature varies from 65 to 0 °F, linearly.

Implementation

The digital control system can be made modulate the supply water temperature in two different ways.

By acting as an operating control on the boiler burners, either modulated on/off, high/low fire, or fully modulating fire, depending on the burner construction. When modulating the actual boiler temperature lower, water temperature needs to have a low limit and be maintained above the flue gas condensation temperature for non-condensing type boilers, typically above 140 °F. Condensing type boilers can be made to operate at temperatures below the flue gas condensation limit and raise stated efficiencies from the 85% to 95% range.
By acting as an operating control on a three-way powered mixing valve or proportional injection pump system that modulates the supply distribution hot water temperature. The mixing valve or mixing pump system recirculates the return water temperature and adds proportionally supply hot water from the boiler for tempering to achieve the desired supply water temperature.

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-'''Hot water reset''' is a [[digital]] control specification for hot [[water]] [[boiler]]s that are typically fired with [[fuel]] oil or [[natural gas]]. A hot water reset digital control system measures the outside air [[temperature]] using a [[thermistor]]. This information is used to estimate demand or heating load as the outdoor temperature varies and modulate the supply hot water temperature up and down range in a [[linear]] ratio. Typical range for conventional boilers is to vary the supply water temperature from 140 to 180 degrees F as the outside temperature varies from 65 to 0 degrees F, linearly.
+'''Hot water reset''' is a [[digital]] control specification for hot [[water]] [[boiler]]s that are typically fired with [[fuel]] oil or [[natural gas]]. A hot water reset digital control system measures the outside air [[temperature]] using a [[thermistor]]. This information is used to estimate demand or heating load as the outdoor temperature varies and modulate the supply hot water temperature up and down range in a [[linear]] ratio. Typical range for conventional boilers is to vary the supply water temperature from 140 to 180 °F as the outside temperature varies from 65 to 0 °F, linearly.
 == Implementation ==
 The digital control system can be made modulate the supply water temperature in two different ways.
-#By acting as an operating control on the boiler burners, either modulated on/off, high/low fire, or fully modulating fire, depending on the burner construction. When modulating the actual boiler temperature lower, water temperature needs to have a low limit and be maintained above the [[flue gas]] [[condensation]] temperature for non-condensing type boilers, typically above 140 degrees F. Condensing type boilers can be made to operate at temperatures below the flue gas condensation limit and raise stated [[Thermodynamic efficiency|efficiencies]] from the 85% to 95% range.
+#By acting as an operating control on the boiler burners, either modulated on/off, high/low fire, or fully modulating fire, depending on the burner construction. When modulating the actual boiler temperature lower, water temperature needs to have a low limit and be maintained above the [[flue gas]] [[condensation]] temperature for non-condensing type boilers, typically above 140 °F. Condensing type boilers can be made to operate at temperatures below the flue gas condensation limit and raise stated [[Thermodynamic efficiency|efficiencies]] from the 85% to 95% range.
 #By acting as an operating control on a three-way powered mixing valve or proportional injection pump system that modulates the supply distribution hot water temperature. The mixing valve or mixing pump system recirculates the return water temperature and adds proportionally supply hot water from the boiler for tempering to achieve the desired supply water temperature.