Honeywell EXCEL 5000 User Manual page 156

ALPHABETIC REFERENCE
74-5577–33 (US)
EN2B-0184 GE51 R0518 (Europe)
CAUTION
It is absolutely essential that the switch point for cool-down is the latest
possible time point in the Time Program. This precaution prevents premature
cool-down and problems with rooms being outside required conditions.
Heating Optimization with Room Sensor
EOH can calculate the residual heat in a building and the exact preheat points only if
there is a room sensor (X1). With preheat optimization with a room sensor, EOH
chooses two alternatives, variable temperatures preheat or variable time preheats.
Variable temperature preheat fixes preheat time as a constant (Parameter P4,
minimum preheat time). The following figure illustrates this alternative:
EOH calculates demand flow temperature (output Y1) at the beginning of the
preheat phase as a function of outdoor air temperature using a heating curve. If
outdoor air temperature changes during the optimization phase, EOH adapts flow
setpoint accordingly.
Parameters P18 (curvature) and P19 (Slope) establish the heating curve. Parameter
P17 limits the supply temperature demand (Y1) to the maximum permissible supply
temperature.
Variable time preheat is a transition from variable temperature optimization to
variable time optimization as a function of the maximum allowable supply
temperature (P17) and minimum preheat time (P4). If room temperature setpoint is
not reached within the prescribed minimum preheat time (P4) even with a maximum
supply temperature for the preheat, EOH can displace the preheat time point
independently to an earlier time. With this type of optimization, preheat begins at the
calculated point in time with the maximum preheat temperature (P5). The next two
diagrams illustrate this operation for day and day/night operation.
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EXCEL CARE CONTROL ICONS