Thermostat system having an optimized temperature recovery ramp rate

Abstract

An adaptive recovery method for a setback thermostat using the intersection of the space temperature with a sloped recovery temperature line which approximates the change in temperature as a function of time during recovery of the temperature controlled space from a setback temperature, to determine the time at which recovery to the occupancy temperature should begin. The thermostat starts recovery when the current space temperature crosses the recovery temperature line. A useful feature of the apparatus and method which implement the invention, computes and constantly updates the slope of the temperature recovery line. The update of the temperature recovery line slope is based on miss time, i.e., the time between actually achieving the desired next set point temperature and the next set point time associated with the next set point temperature, the space temperature, the outdoor air temperature, the temperature recovery ramp rate during the previous recovery period, and the current and past thermal time constants. If the heating or cooling load on the space changes, the current space temperature will cross the recovery temperature line at a different time, causing recovery to start at a time more compatible with the current heating or cooling load in order to complete recovery at or near the desired time. Variables may be added to the system.