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Storage tank control
via thermostat
Stratification storage tank
96/171
Siemens Building Technologies
HVAC Products
Storage tank systems can also be operated with an external thermostat.
Storage tank control by a thermostat is released when a storage tank system has been
parameterized (systems 2, 3, 8, 34, 35, 40, 44, 50, 51, 56, 60, 66, 67, 72, 76, and 81).
The thermostat is to be connected to the DHW flow switch or, in place of the DHW
sensor 1 to the LMU... The input to be used must be selected via parameterization:
KonfigRg42 = 0:
DHW thermostat to be connected to the input of the DHW flow switch
KonfigRg42 = 1:
DHW thermostat to be connected to input «DHW sensor 1»
Connecting to the DHW sensor input
When connecting the thermostat to the DHW sensor input, high-quality contact material
is mandatory (e.g. gold-plated contacts) since the signal voltage at that input is DC 5 V.
The second DHW sensor must not be present.
If a short-circuit is detected at the input, no status code will be delivered. The signal is
interpreted directly as a DHW demand signal.
Read-in value ≤ open-circuit threshold
Read-in value ≥ short-circuit threshold
Connecting to the DHW flow switch input:
When using this connection, no DHW sensor may be connected to the LMU... (neither
«Bw1» nor «Bw2» sensor). Otherwise, the demand for DHW will be suppressed.
The demand for DHW follows from the state of the «Bw-Flow-Switch» input:
0: Stopping the demand for DHW
1: Triggering the demand for DHW
With both types of connection, the maximum DHW setpoint is used for calculating the
boiler temperature setpoint (during storage tank charging) when there is an active
demand for DHW:
DHW setpoint = TbwSmax
In that case, the DHW settings made on the HMI, RU or RVA... are of no importance.
The setting value on the QAA73... will be locked.
Control of the pump is the same as with «Storage tank control by sensor».
Stratification storage tank systems require a modulating pump in the DHW charging
circuit. That pump is controlled in accordance with the criteria described below.
The following table shows when modulating control of heating circuit 1 without the clip-in
module is possible with the LMU... basic unit.
Plant diagram
9, 41, 43, 57, 59, 73, 75
10, 42, 58, 74, 83
Basic Documentation LMU54... / LMU64...
7 DHW control (BWR)
Stopping the demand for DHW
Triggering the demand for DHW
Heating circuit 1
Multispeed
Multispeed or modulating
CC1P7494en
07.11.2002
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