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Thermostat system having an optimized temperature recovery ramp rate
| Details |
Inventors: Shah, Dipak J.;
Assignee: Honeywell Inc. (Minneapolis, MN)
Primary Examiner: Wayner; William E.
Assistant Examiner:
Attorney, Agent or Firm: Shudy, Jr.; John G.
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. |
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DETAILED DESCRIPTION In a first embodiment of the present invention, an outdoor air temperature sensor is used in a thermostat to more accurately determine the straight line temperature recovery ramp rate at which a space returns to its occupancy temperature (recovery rate or ramp rate hereafter) from its current temperature (CT) and thus provides for an accurate selection of the time at which recovery should start.
In this scheme, the CT is periodically measured and when the CT crosses the time-temperature line defined by the ramp rate, then recovery is started.
This invention employs regular calculations of the time required to recover to the next occupancy temperature (OTE) from the current space temperature as prescribed by the equations presented herein.
When the difference between the present time and the next occupancy time becomes less than the time which the ramp recovery approximation predicts will be needed to return to the occupancy temperature at the desired occupancy time, then recovery starts.
In a second embodiment of the present invention, the recovery rate is approximated by a straight line which is then used to predict the time required to recover to the next occupancy temperature.
The use of a ramp-based determination of the proper recovery start time takes into account the current temperature of the space, the current outdoor air temperature, the recovery rate during the previous recovery period, and the thermal time constants.
For example, in some circumstances, the space may cool only a few degrees during a setback interval.
In this case, the ramp will be crossed by the CT relatively late in the setback period, because the space need only be warmed a few degrees.
If the slope of the ramp has been chosen with reasonable accuracy, only an increased thermal load can make the predicted recovery time too short.
But fortunately, a too short recovery time is only briefly inconvenient or uncomfortable rather than injurious.
Decreases in the assumed thermal load may result in a predicted recovery time which is too long
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Control Computers 
