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Siemens Building Technologies Basic Documentation LMU54... / LMU64... CC1P7494en
HVAC Products 5 Clip-in module OCI420... for communication via LPB 07.11.2002
In general, the type of priority of DHW heating is selected on the relevant unit and has
an impact on all heating circuits in the system.
However, the LMU… only supports the types of priority «Absolute» and «None», which
results in restrictions.
The types of priority «Shifting» and «Mixed», which can be selected on the RVA…, are
treated by the LMU… like absolute priority and are passed to all heating circuits in the
system.
Also, local DHW heating with absolute priority always prevails over external DHW
heating that is active at the same time!
5.1.3 Multiboiler plants with LMU (cascade applications)
If the capacity of a single boiler is not sufficient to cover the demand of a heating plant,
several boilers can be cascaded.
This type of application can be straightforwardly implemented with the ALBATROS
cascade controller RVA47... and several LMU... .
The RVA47... is a cascade controller that enables a central RVA47... to control up to 15
LPB-compatible LMUs.
In that case, the BMUs are operated as pure boiler controllers without having their own
consumers. This means that the only pieces of equipment to be connected are the flow
and return sensors (B2 and B7) and the boiler pump (Q1).
The cascade controller evaluates the heat demand from the consumers and controls the
boilers assigned to it according to a selectable strategy.
For this application, all connected LMUs must be used with hydraulic diagram no. 80.
In general, all boiler-specific configurations are to be made on the respective BMU while
cascade-related values are to be set on the RVA… .
In addition to LPB-compatible BMUs, the RVA47... is capable of controlling BMUs
connected via the PPS interface.
The cascade controller can easily cope with this kind of mixed operation, but there are a
number of differences between the 2 types of devices in terms of operating and display
values on the RVA.... .
With the LMU…, the following operating lines are not available or are deactivated:
Ø Enduser parameter:
− BMU error code display (line 49)
Ø Heating engineer parameters:
− Actual value of the boiler temperature BMU (line 55)
− Boiler temperature setpoint BMU (line 65)
− Burner hours run (lines 80 through 83)
− Rated output BMU 1...4 (lines 91 through 94). This value is to be set directly on the
respective unit (parameter 145, «PmaxHuKw»)
Ø OEM parameters:
− Calibration of actual output of BMU 1...4 (lines 25 through 28). This value is to be
set directly on the respective unit (parameter 440, calibration factor)
Type of priority of
DHW heating
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