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Low-water cutoff: It is a mechanical means (usually a float switch) or an electrode with a safety switch that is used to turn off the burner or shut off fuel to the boiler to prevent it from running once the water goes below a certain point. If a boiler is "dry-fired" (burned without water in it) it can cause rupture or catastrophic failure.
In variable-flow hydronic systems, reducing pump speed or staging of pumps with boilers and chillers to suit part-load conditions is an energy efficient method of control. [5] VAV (variable air flow) systems meet the needs of large modern commercial-use buildings, with internal spaces divided into open-plan areas.
The control system can compare the temperature of the outside air vs. return air, or it can compare the enthalpy of the air, as is frequently done in climates where humidity is more of an issue. In both cases, the outside air must be less energetic than the return air for the system to enter the economizer mode.
The energy cost of heating is one of the main costs of operating a building in a cold climate. Some central heating plants can switch fuels for reasons of economy and convenience; for example, a home owner may install a wood-fired furnace with electrical backup for occasional unattended operation.
An application example is a room temperature controller connected to a heat recovery unit, which is connected to a boiler. The heat recovery unit is then functioning as gateway. In another possible configuration, a thermostat or room controller is connected to a sequencer with further Opentherm interfaces connected to more than one boiler.
The lower the return temperature to the boiler the more likely it will be in condensing mode. If the return temperature is kept below approximately 55 °C (131 °F), the boiler should still be in condensing mode making low temperature applications such as radiant floors and even old cast iron radiators a good match for the technology.