System and method for calculating the thermal mass of a building

A system for calculating a value for an operational efficiency of an heating, ventilation, and air conditioning (HVAC) system comprising:

• at least one HVAC control system that receives temperature measurements from at least a first location conditioned by at least one HVAC system, and receives status of said HVAC system;
• one or more databases that store at least said temperatures measured at said first location over time;
• and
• one or more processors that receive outside temperature measurements from at least one source other than said HVAC system and compare said temperature measurements from said first location with expected temperature measurements wherein the expected temperature measurements are based at least in part upon past temperature measurements and said outside temperature measurements, wherein said one or more processors are configured to calculate one or more first rates of change in temperature at said first location for periods during which the status of the HVAC system is “on” and wherein said one or more processors are further configured to calculate one or more second rates of change in temperature at said first location for periods during which the status of the HVAC system is “off”, and to relate said first and second calculated rates of change to said outside temperature measurements.