Using temp sensor at hvac output detect equipment failure and degradation

by Daniel Born: Using a temperature sensor located at the output of the hvac equipment, detect that heatpump is not generating heat or cool (due to malfunction or other) and automatically switch to alternate heating source (such as aux heat) if appropriate.

Also detect if hvac filter may be clogged by comparing output temperature with known performance values at different interior and exterior (for heatpumps) values.