Maximum Limitation Of The Temperature Differential (Drt Function); Mode Of Operation; Purpose - Siemens RVD230 Basic Documentation

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Siemens Building Technologies
HVAC Products
27.4 Maximum limitation of the temperature dif-
ferential (DRT function)

27.4.1 Mode of operation

With all types of plant (with the exception of 0–x), the temperature differential (DRT,
differential of primary and secondary return temperature) can be limited to a maximum.
Precondition is that the required sensor B71 is fitted in the secondary return of the
heating circuit.
If the differential of the 2 return temperatures exceeds the adjusted maximum limit
value, 2-port valve Y1 in the primary circuit will be throttled.

27.4.2 Purpose

Maximum limitation of the temperature differential generally ensures that a smaller
amount of heat will be drawn from the network or that the volumetric flow will be throt-
tled when heat is demanded for the first time in the morning when the pipes have not
yet reached their normal operating temperature (prevention of idle heat and no unnec-
essary supply of heat back to the network).
In addition, maximum limitation of the temperature differential
• acts as a dynamic limitation of the return temperature
• shaves peak loads
Impact of maximum limitation of the return temperature differential:
DRT
V [%]
OFF
P
100
90
80
70
60
50
40
30
20
10
0
DRT With active maximum limitation of the temperature differential
ON
DRT Without maximum limitation of the temperature differential
OFF
t Time
Volumetric flow on the primary side
V Volume saved
S
The temperature differential of the return is usually 2...5 °C and depends on the type of
heat exchanger. Maximum limitation of the temperature differential can be deactivated
on operating line 179 (entry of --.-).
Maximum limitation of the return temperature differential has priority over minimum
limitation of the flow temperature in the heating circuit.
During d.h.w. heating cycles, maximum limitation of the temperature differential is deac-
tivated with all types of plant.
Basic Documentation RVD230
27 Function block DRT and maximum limitation of the return temperature
V
S
DRT
on
t
CE1P2383en
27.05.2004