User Manual

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Siemens HVAC central apartment unit with consumption data acquisition QAX903 CE1N2741en
Building Technologies 2016-01-30
Specific functions for heating and cooling plants
The central apartment unit forms a heating or cooling demand signal from the col-
lected heating or cooling requests and forwards it to the heating or refrigeration
generation controller.
The heating/refrigeration demand signal can be delivered via the universal relay
output (switching) or at the DC 0…10 V output (modulating) of an RRV912 heating
circuit controller or RRV934 multi-controller.
The flow temperature can be controlled via the RRV934 multi-controller. It is regu-
lated with the help of the heating/refrigeration demand signal. Based on an adjust-
able value, minimum as well as maximum limitation of the flow temperature is pos-
sible. If the temperature request is invalid, flow temperature control becomes inac-
tive and the actuating elements are closed during winter operation (no output). The
central apartment unit supports two room groups (e.g. floor heating/cooling and
radiators) that may be controlled independently.
The return temperature can be maintained at an adjustable high or low level. This
prevents, for example, water that is too hot from returning to generation. Return
temperature limitation takes priority over flow temperature limitation. Return tem-
perature limitation acts on the mixing valve for the room group.
Setpoint limitation limits the heating setpoint to a maximum value and the cooling
setpoint to a minimum value for the entire apartment.
The central apartment unit calculates the mean value and uses it for room tem-
perature control if a room unit and one or two room sensors are assigned to a
room.
Several heating circuits connected to an RRV912 / RRV918 heating circuit con-
troller can be combined to form one room and operated in parallel. In that case, the
first channel ensures actual room control while, at the same time, controlling the
other assigned channels.
Up to 6 SSA955 radiator control actuators can be combined to form one room and
operated in parallel.
In that case, the radiator control actuator connected first (lead controller) assumes
actual room control plus wireless control of the other assigned radiator control ac-
tuators (lag controllers).
Multiple heating circuits connected to common heat distributor can be controlled
jointly as a zone. The zone valve (3-point) is controlled based on the temperature
measured value from the room unit and/or room temperature sensor installed in the
reference room.
The central apartment unit enables the room group pumps. They can be either
connected to the internal relay output or a relay output of one of the RRV912 /
RRV918 heating circuit controllers or RRV934 multi-controller.
The QAX903 can trigger an antilime function at regular intervals to prevent valve
plugs and pump impellers from seizing during longer off periods. The function en-
sures the valve actuators extend to the fully open and fully closed position and the
pumps are activated for short periods of time (valve kick). Frequency and time of
day the function is performed can be adjusted.
The antilime function acts either locally or on components connected to the RRV912 /
RRV918 heating circuit controller as well as on wireless SSA955 radiator control
actuators.
Heating/cooling
request
Flow temperature
control/limitation
Return temperature
limitation
Setpoint limitation
Room unit/
Room temperature
sensor
Parallel operation of
heating circuit
controllers
Parallel operation of
radiator control
actuators
Zone control
Room group pumps
Antilime function