Separate Dhw Circuit In Cascade Applications; Operation With The Rva65 - Siemens LMU54 Series Basic Documentation

Separate DHW circuit in
cascade applications
Operation with the
RVA65...
Siemens Building Technologies
HVAC Products
In a cascade application, a BMU can provide temporary DHW heating, in spite of an
overriding controller.
In that case, the respective LMU... «disengages» itself from the cascade for the period
of time DHW is heated and is then not available as a heat source.
This special case is extremely unfavorable for the RVA47... since its cascade control
will be disturbed by the sudden switching actions of a boiler. But there are certain types
of heating plant where this feature is required (e.g. plants with instantaneous DHW
heaters).
Also, this special case can only be covered by the cascade user having device address
2.
In addition to the address, the correct hydraulic diagram must be parameterized on the
LMU... that provides DHW heating. Depending on the type of DHW heating, diagrams
81 through 85 are available here.
The other cascade boilers remain set to 80. In addition, sensors, pumps and valves and
an optional flow switch that are used in conjunction with DHW heating are to be
connected to this special LMU... .
Although all relevant sensors and actuating devices are to be connected to a special
unit from which they are also operated, the DHW setpoint is predefined by the overriding
cascade controller.
In general, all settings in connection with DHW heating are to be made on the RVA47...
(DHW operating mode, nominal and reduced setpoint, etc.).
When using an LMU... together with an RVA65..., the same preconditions apply as with
the RVA47... .
Although the LMUs are not cascaded in this case, here too, the RVA65... controls several
heat sources (e.g. oil-, gas- or wood-fired boilers ).
For this reason, there is no difference to cascade applications as far as the BMU is
concerned. A separate DHW circuit is also supported with this type of application,
provided the LMU... has been configured to device address 2!
Basic Documentation LMU54... / LMU64...
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CC1P7494en
07.11.2002