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Siemens Building Technologies Basic Documentation RVL471 CE1P2524E
HVAC Products 18 Function block "D.h.w. priority and flow temperature setpoint" 23.10.2002
18.3.2 Shifting priority
During d.h.w. charging, the heating circuits will be throttled if the heat generating
equipment (the boiler) is not able to maintain the required setpoint. In that case, the
display of the boiler controller shows
.
• Controller with no bus connection:
If, during d.h.w. heating with shifting priority, the boiler is not able to maintain the set-
point, the differential between setpoint and actual value will be integrated and an inte-
gral-dependent uncritical locking signal in the range 0…100 % delivered to the own
heating circuit.
Since shifting priority is determined by the boiler, this kind of priority is only possible
with plant type 2–x. With plant types 1–x and 3–x, the setting "Shifting priority" has the
same impact as the setting "No priority".
• Controller with bus connection:
During d.h.w. heating, the controller signals the heat source in the same segment
(controller and heat source could be identical) that it presently provides d.h.w. heating
with shifting priority. If, now, the boiler is not able to maintain its setpoint, the differential
between setpoint and actual value will be integrated and an integral-dependent uncriti-
cal locking signal in the range 0…100 % generated. If the heat source is located in
segment “0”, it delivers the locking signal to all controllers in all segments. If the heat
source is in segment 1…14, it only sends the locking signal to the controllers in the
same segment.
18.3.3 No priority
No priority means parallel operation. D.h.w. charging has no impact on the heating
circuits.
18.4 Flow temperature setpoint
With "Shifting priority" and "No priority", the temperature setpoint of the common flow,
which is used for both d.h.w. charging and space heating, can be generated in 2 differ-
ent ways:
• Flow temperature setpoint according to the maximum selection
• Flow temperature setpoint according to the d.h.w. demand
With plant types 1–x, 3–2, and 3–4, the temperature setpoint of the common flow is
transmitted to the primary controller via the data bus.
With plant types 2–x, 3–1, 3–-3, 4–x, 5–x, and 6–x, the temperature setpoint of the
common flow is valid for sensor B1.
With the plant types that have no own heating circuit (4–x, 5–x, and 6–x), the heating
circuit demand is transmitted to the controller via the data bus.
18.4.1 Maximum selection
In the case of d.h.w. heating, the temperature setpoint of the common flow for the
d.h.w. and the heating circuit is generated from the two demands by maximum selec-
tion.
It is assumed that the mixing heating circuit calls for 40 °C, the d.h.w. circuit for 65 °C.
With d.h.w. charging, the setpoint of the common flow temperature will then be the
higher of the 2, namely 65 °C.
Example
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