1. A method of determining energy savings from an HVAC system in a building operating in an energy saving mode, the method comprising: running the HVAC system to maintain a comfort mode temperature during a learning period; determining the energy consumed by the HVAC system at multiple outside ambient conditions during the learning period; determining a correlation between a specific ambient condition and energy consumed by the HVAC system; running the HVAC system to maintain an energy saving setpoint temperature; determining the energy consumed by the HVAC system at an ambient condition while maintaining the energy saving setpoint temperature; and calculating the energy savings as a function of the difference between the energy that would have been consumed by the HVAC system at the ambient condition based on the determined correlation and the energy consumed by the HVAC system while maintaining the energy saving setpoint temperature at the ambient condition.