On/Off Operation Of The District Heating Valve; Continuous Heat Exchanger Valve Control - Honeywell SDC heating and district heating controller Service Manual

SDC / DHC
7.2.1
7.2.2
EN2H-0221GE51 R0808

On/Off operation of the district heating valve

To always ensure a minimum flow so that the heat meter can
work precisely, pure on/off switching is provided in low load mode.
Code 03 is suitable for this function as shown in the following
diagram.
x
100 %
a
0 %
a Minimum travel
x Valve travel
Para- Designation
meter
03 Minimum
travel
Should the secondary flow temperature controller output fall
below the settable minimum travel in % (code 03), two-step
operation begins and the valve is closed. The valve remains
closed until the internal controller output reaches 10% again. If a
10% controller output is reached, the valve opens again to the
minimum travel. If the controller output drops below 10% again,
the valve closes again and the cycle starts from the beginning.
This means that whenever there are demands of up to 10% on
the heat generator the valve is operated in On/Off mode and the
secondary flow temperature is controlled this way.

Continuous heat exchanger valve control

If the output of the secondary flow temperature controller rises
above 10%, the PI controller controls the secondary flow
y Controller output
Range Presetti
ng
0 ... 50 10
Hydraulic Components
y
100 %
Step Unit
1 %
145