Honeywell EXCEL 5000 User Manual page 172

ALPHABETIC REFERENCE
74-5577–33 (US)
EN2B-0184 GE51 R0518 (Europe)
The reheat time cannot be greater than 48h (P2, 2880 minutes) or shorter than the
minimum preheat time (P1).
If the minimum preheat time is reached, the temperature variable preheating begins
immediately.
The next two diagrams illustrate this operation for day and day/night operation.
optimum start – time variable pre-heating
room temperature
°C
room temperature
day setpoint
night setpoint
t
1
You can influence the type of optimization procedure that EOH3 uses by adjusting
parameter P1, minimum preheat time. For very small values of P1, for example,
zero minutes, EOH3 only uses the variable time preheat (rapid preheating) because
it is never possible to reach the setpoint in zero minutes regardless of the boost
temperature. Large values of P1, such as several hours, have the opposite effect.
Large values lead to variable temperature preheat with moderate supply
temperatures. During the preheat phase, EOH3 sends a logical 1 to output Start
(YD2).
If the room temperature TRm (X2) reaches the setpoint of the Time Schedule TSet
(X1) before the target time point, EOH3 switches over to room control automatically.
The room control uses an internal PI controller whose integral action time (P14) and
room control P-band (P13) can be set. After reaching the target point, EOH3 still
works half an hour longer as a room controller. EOH3 then writes a logical 0 to the
output Start (YD2) to allow the application program to take control. This extended
control by EOH3 compensates the cool-down effect from the walls and furniture
after a rapid preheating so that an almost constant room temperature is guaranteed
with the transfer to temperature-dependent control after ending the preheat
optimization.
Variable Temperature Preheat
If the time variable preheat has not started when the minimum preheat time is
reached, then temperature variable preheating begins immediately.
Since for temperature-variable preheating, the preheat time is fixed, the required
flow temperature can be calculated by first finding the required room temperature
limit (asymptotic) T1lim using the building model defined by the parametersP8 to
P11.
Then the required flow temperature setpoint can be calculated from the heating
curve equation.
TSup = HC (T1lim, TOat, P16, P17)
174
EXCEL CARE CONTROL ICONS
T1lim increase
P1
120min
4:00 6:00
8:00
calculated time start point
variable start point time schedule
time