Honeywell SDC Service Manual page 183

SDC / DHC Hydraulic Components
Special mixing circuit functions (district heating control
devices only)
Return limit By setting an additional return sensor in the mixed heating circuit,
the return temperature can be limited using this function. This is a
maximum temperature limit.
With some applications, an excessively high return temperature
causes problems (e.g. district heating or condensing
applications). They can occur if heat is not being extracted in the
occupied room (e.g. thermostat valve closed).
If the return temperature exceeds the set maximum value, the
mixed heating circuit valve is adjusted to this maximum
temperature. The flow temperature then remains ignored.
7.3.4.10.1 Mixed heating circuit control
7.3.4.10.1.1 Proportional part Xp
The proportional band Xp defines how a step change of the
setpoint effects a change of the corresponding actuator according
to the selected setting.
Example:
Consider an actuator moving though an angle of 90°C in an action
time of two minutes. When a sudden flow temperature control
deviation of 10 K occurs (e.g. when the system switches from
reduced to daytime operation) and the P-part setting is 5%/K, the
actuator has to open by 50% (5%/K x 10 K). Consequently, the
duration of the actuation pulse is one minute (= 50% of the
actuator runtime).
EN2H-0221GE51 R0812 183