Honeywell DHC, Service Manual

Page: 161 / 262

SDC / DHC Hydraulic Components
EN2H-0221GE51 R0812 161
7.2.17.1 Bypass pump (RBP)
The simplest way of controlling the return flow temperature is by
means of a bypass pump. When the return temperature in the
heat generator drops below the set boiler return minimum
temperature limit, flow mixing is initiated by switching on a bypass
pump parallel to the heat generator. As soon as the return
temperature rises above the return minimum temperature plus the
return switching differential, the bypass pump will be deactivated
after the set delay time (extended pump running time "bypass
pump"). As the mixing itself is not controlled, the bypass cross
sections must be taken into account for the system layout.
When the switch-off condition is reached, the bypass pump is
switched off with a time delay in accordance with the set value.
To avoid intermittent operation of the bypass pump, the return
sensor must always be positioned downstream of the mixing point
for this mode of return temperature control.
7.2.17.2 Return maintenance through controlled feed water addition
If the control unit is equipped with a mixed heating circuit output,
this output can be programmed for controlled flow mixing.
In this mode of return control the programmed mixed heating
circuit adjusts the return temperature to the return temperature
setpoint. The adjustment is independent of the status of any start-
up protection of the heat generator. The return sensor for this
function is connected at the sensor input of the respective mixed
heating circuit (e.g. flow sensor 1 for mixed heating circuit 1).
The mixed heating circuit pump operates like a boiler circuit pump
without boiler start-up protection for this purpose.
Function
NOTE
Function