Honeywell DHC 23 Operating Instructions Manual page 15

DHC 23
Maximum district heating return
temperature in heating mode (B),
onset point of floating district
heating return temperature
limitation. (C)
Reset time (D)
Controller gain(E)
Summer/winter time change
(D) + ( )
SERVICE BY THE HEATING SPECIALIST
Some district heating utilities require minimum volume flows in their networks, this
can be achieved by a high temperature difference between flow and return. The
required temperature spread is assured by the maximum limitation of the district
heating return temperature. With the maximum limitation, both a fixed value limitation
can be performed and a floating limitation can be realized according to the outside
temperature by setting the parameters. Fixed value limitation to 50°C, for instance,
means that the district heating return temperature will not exceed this value over the
entire outside temperature range.
However, it is desirable at higher outside temperatures to shift this maximum limitation
downwards, i.e. to perform a floating district heating return temperature limitation. In this
way the lowest possible district heating return temperature is achieved, assigned to the
relevant outside temperature and thus good heat utilization.
The values for the maximum limitation of the remote heating return temperature and
the onset point of the floating remote heating return temperature limitation in heating
mode can be set, the floating return temperature limitation can be switched off by
selecting 10°C as onset point.
Return temperature
limitation
Example 1: 90 °C
Example 2: 50 °C
Example 3: 80 °C
Example 4: 50 °C
The reset time of the flow temperature controller can be adapted in critical systems.
The stability of the control is influenced by the controller gain. If the district heating
valve oscillates constantly open and closed, the controller gain must be set to a smaller
value. If the system takes too long until the room setpoint is reached, then the controller
gain should be increased.
The DHC 23 switches over automatically from summer to winter time. The change from
winter to summer time is made in the last weekend in March. The change back is
made in the last weekend in October. If the change-over dates should change, these
can be adapted.
onset point of the floating
return temperature limitation
10 °C factory setting
10 °C Fixed value limitation
5 °C
–10 °C
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