Honeywell SDC heating and district heating controller Service Manual page 148

Hydraulic Components
148
By means of district heating return temperature limitation the
required temperature difference is assured. The maximum limit
can either be a fixed value limitation or a flexible limitation
according to the outside temperature. A fixed value limit of e.g.
50°C means that the district heating return temperature will not
exceed this value over the entire outside temperature range.
In case of higher outside temperatures it is desirable that the
maximum limit can be reduced, i.e. flexible district heating return
temperature limitation is to be adopted. Through the assignment
to the respective outside temperature, the lowest possible district
heating return temperature and thus good heat exploitation are
obtained.
The values for the maximum limitation of the district heating return
temperature (code 08) and the starting point of the flexible district
heating return temperature limitation (code 09) can be set for the
operation with heating circuits. The flexible return temperature
limitation can be switched off by selecting 10°C as the starting
point.
+40°C is set as the bottom return setpoint for the flexible return
temperature limit.
If the maximum limit is exceeded, a second Pl controller
intervenes with the same parameters as in the secondary control
(heating temperature control).
Return temperature limit
Example 1: 90°C
Example 2: 50°C
Example 3: 80°C
Example 4: 50°C
Starting point of the flexible
return temperature limitation
10°C Factory setting
10°C Fixed value limit
5°C
–10°C
EN2H-0221GE51 R0808
SDC / DHC