Bharat B Sahay, James J Jones: Electrically controlled programmable digital thermostat and method for regulating the operation of multistage heating and cooling systems. Texas Instruments Incorporated, John A Haug, James P McAndrews, Melvin Sharp, April 17, 1984: US04442972 (223 worldwide citation)

An electronically controlled programmable wall thermostat provides better control of comfort temperature and permits improved energy-saving temperature setback at selected intervals of the day or night in multistage heating and cooling systems and is particularly useful in achieving improved energy ...

Jed Margolin: System to provide a backchannel to an HVAC thermostat. April 18, 2017: US09625179

In an HVAC system Polarity Splitting is used to provide for one or more backchannels from the furnace to the thermostat. Polarity Splitting is also used to allow a four-wire house cable to provide for three thermostat functions as well as furnace power to the thermostat while also providing for one ...

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