Power management in energy buffered building control unit

A method of controlling an HVAC (heating, ventilation, and air conditioning) system, the method comprising:

• connecting one or more HVAC control wires to corresponding HVAC wire connectors in a thermostat, which includes a rechargeable battery and is configured to at least partially control the operation of the HVAC system;
• extracting electrical power from the one or more received HVAC control wires up to a first level of electrical power;
• during a first time period in which the electrical load power required by the thermostat is less than said first level of electrical power, supplying the required electrical load power to the thermostat and charging the rechargeable battery, if needed, using the extracted power;
• and
• during a second time period in which the electrical load power required by the thermostat is greater than said first level of electrical power, discharging the rechargeable battery and supplying the required electrical load power to the thermostat using a combination of the extracted power and power from the discharging rechargeable battery.

A thermostat, comprising:

• a plurality of HVAC (heating, ventilation, and air conditioning) wire connectors configured to receive a plurality of HVAC control wires corresponding to an HVAC system;
• a thermostat processing and control circuit configured to at least partially control the operation of the HVAC system;
• and
• a powering circuit coupled to the HVAC wire connectors and configured to provide an electrical load power to the thermostat using electrical power extracted from one or more of the plurality of received HVAC control wires and electrical power from a rechargeable battery;
• wherein the thermostat includes a main processor and a display, each having a low-power usage state and a high-power usage state, wherein the processor and display are selectively operated such that:
• in the low-power usage state, only the extracted power is used to provide the electrical load power to the thermostat and to charge the rechargeable battery, if needed;
• and
• in the high-power usage state, the required electrical load power is supplied to the thermostat using a combination of the extracted power and power from the discharging rechargeable battery.