Siemens AVS75.390 - Compressor Control in Plants with Buffer or Combi Storage Tank

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Siemens Switzerland Ltd
User manual RVS61.843 CE1U2355en_02
HVAC Products 6 The settings in detail 23. November 2007
Required sensors:
To enable the controller to put the heat pump into operation without control of a buffer
or combi storage tank, at least the return temperature sensor (B71) and the relevant
source temperature sensor must be installed. In the case of air-to-water heat pumps,
the evaporator sensor (B84) is required also.
Line no. Operating line
2840 Switching diff return temp
If the return temperature exceeds the setpoint by half the switching differential, the heat
pump will be switched off; if it falls below the setpoint by half the switching differential,
the controller will put the heat pump into operation.
If the return temperature setpoint drops below 30 °C, the switching differential is
reduced in a way that the switch-on point approaches the setpoint. With a return
temperature setpoint of 20 °C, the switch-on point is identical with the return
temperature setpoint.
2840
T
OFF
ON
Ta
20°C
30°C
TRLw
OFF Switch-off point
ON Switch-on point
2840 Switching diff return temp
Ta Outside temperature
T Temperature of heat pump return
TRLw Return temperature setpoint
The calculation of the return temperature setpoint is explained on operating line 5810
(“Differential HC at OT –10 °C”).
The function is not active when heat compensation is switched on.
Compressor control in plants with buffer or combi storage tank
The settings apply to compressor 1 and – if present – to compressor 2 also.
If a buffer or storage tank is connected to the same controller as the heat pump, the
controller uses sensors B4 and B41 for control of the compressor. The switching
differential (2840) has no impact.
If there is no sensor B41, heat pump return temperature sensor B71 is used.
The setting on operating line 2841 defines whether the minimum compressor running
time (2842) is observed.
As soon as the temperature at both sensors (B4 + B41) drops 1 Kelvin below the flow
temperature setpoint, a heat request is forwarded to the heat pump. This heat request
is maintained until the temperature at both sensors reaches the flow temperature
setpoint.
Switching diff return temp
Control