In an embodiment of the present disclosure, a method for determining power consumption of a unit of a heating, ventilating, and air conditioning (HVAC) system includes providing conditioned air to the unit from an HVAC unit of the HVAC system. The method also includes receiving power data indicative of a total power consumed by the HVAC unit, receiving airflow data indicative of a rate of the conditioned air received by the unit from the HVAC unit, determining a power consumption of the unit based on the power data and the airflow data, and outputting the power consumption of the unit.

Embodiments of an electric power measuring system capable of computing accurate electric power information using a low voltage measuring instrument in a small-scale electric power system are provided. The electric power measuring system may include a first measuring instrument for measuring and detecting a current and a zero-cross point from a distribution line and for generating and outputting current information of the distribution line from the current and the zero-cross point, and a second measuring instrument for computing electric power information of the distribution line according to a voltage thereof and the current information output from the first measuring instrument.

Embodiments of an electric power measuring system capable of computing accurate electric power information using a low voltage measuring instrument in a small-scale electric power system are provided. The electric power measuring system may include a first measuring instrument for measuring and detecting a current and a zero-cross point from a distribution line and for generating and outputting current information of the distribution line from the current and the zero-cross point, and a second measuring instrument for computing electric power information of the distribution line according to a voltage thereof and the current information output from the first measuring instrument.

A power detection device includes a set of power detectors, a set of voltage-to-current converters, a temperature compensation circuit, a current-to-voltage converter, and a level shifter. The set of power detectors is used to generate a set of power detection voltages. The set of voltage-to-current converters are coupled to the set of power detectors to generate a set of power detection currents according to the set of power detection voltages. The temperature compensation circuit is used to generate a temperature compensation current. The current-to-voltage converter is coupled to the set of voltage-to-current converters and the temperature compensation circuit to accumulate the set of power detection currents and the temperature compensation current to generate a summed current, and convert the summed current into a summed voltage. The level shifter is coupled to the current-to-voltage converter, and is used to receive the summed voltage to generate an output power voltage.