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Siemens Building Technologies
Basic Documentation RVP540 / RVP550
CE1P2488en
HVAC Products
General control processes
04.11.2009
6.7 Temperature differential of flow / return
temperature
6.7.1 Purpose of the function
The controller makes possible the control of a variable speed heating circuit pump.
Operation at a reduced speed offers the following advantages:
•
Less pumping power
•
Reduced
noise
level
•
The temperature differential across the radiator will be increased. This leads to a
lower return temperature. The efficiency is thereby improved, especially in connec-
tion with condensing boilers
6.7.2 Variants
If a speed-controlled pump is used, 2 function variants are available (setting on operat-
ing line 743):
1. Speed according to the operational level:
Changeover to reduced speed in operating modes ”Reduced” and ”Standby”.
2. Speed according to the heating curve:
Reduced speed with the higher heating curve until the maximum flow temperature
is reached (maximum temperature differential of flow and return).
Variant 1: Speed according to the operational level
With variant 1, the reduced speed is only used in ”reduced” operation. In that case, the
heating curve will not be raised. This means that the demand for heat in reduced oper-
ation will possibly not be covered if the heating curve is correctly adjusted for nominal
operation. However, since in normal situations the operational level will only be lowered
for a limited period of time, this shortage of heat supply will hardly ever pose a problem.
Variant 2: Speed according to the heating curve
With variant 2, the circulating pump is operated at reduced speed for a large part of the
heating season. The speed will be raised only if the heating circuit approaches its
maximum heating capacity. For this reason, the heating curve will be adjusted such that
the heating output at reduced speed will be correct. In that case, the heating curve
adjustment must be higher than that with a fixed maximum speed to ensure the mean
radiator temperature will be maintained.
