Honeywell SDC Service Manual page 206

Hydraulic Components
206
Heating circuit controls send their demand value to buffer control.
Hot-water and buffer controls demand energy from the heat
generator when required. The buffer loading pump output is ON
during buffer discharge and hot-water loading.
Any active hot-water priority is not effective here.
Control mode 6 – Discharge control to heat generator
System hydraulics
a Buffer tank
b Heat generator
This hydraulic layout is used when an alternative-energy buffer
tank is added to an existing system. In such systems it is often the
case that there are existing unit boilers with integrated hot-water
circuit loading tank and hot-water loading in the boiler.
All heat demand is forwarded to the heat generator.
When the buffer tank can cover the energy demand, the heat
generator nominal temperature is maintained by the buffer via
buffer loading pump instead of the burner.
In this way the heat generator always operates at its setpoint
temperature and cannot be exposed to excessive buffer
temperatures.
c Hot-water tank
EN2H-0221GE51 R0812
SDC / DHC