Siemens RVL471 - 9 Function Block Cascade Slave; Operating Lines; Mode of Operation; Boiler Sequence Release Integral (KFI)

36/118
Siemens Building Technologies Basic Documentation RVL471 CE1P2524E
HVAC Products 9 Function block "Cascade slave" 23.10.2002
9 Function block "Cascade slave"
This function block facilitates integration of the controller as a cascade slave into a heat
source cascade. A heat source cascade is the combined operation of several oil- / gas-
fired boilers.
9.1 Operating lines
Line Function, parameter Unit Factory
setting
Range
59 Release integral for boiler sequence °C*min 200 0...500
60 Reset integral of boiler sequence °C*min 50 0...500
9.2 Mode of operation
The surplus heat or heat deficit of the boiler is ascertained with the help of the boiler
sequence integral and communicated to the cascade master via LPB.
9.2.1 Boiler sequence release integral (KFI)
The boiler sequence release integral is a variable generated from the progression of
the cascade flow temperature and time (t). If the variable falls below the setpoint, the
difference will be communicated to the cascade master as the heat deficit.
KFI =
∆Tdt
t
0
∫
where: ∆T = ( T
VKw
− 0,5
*
SD − T
VKx
) > 0
TVKw Flow temperature setpoint of the cascade
TVKx Actual value of cascade flow temperature
SD Switching differential of the boiler
tTime
9.2.2 Boiler sequence reset integral (KRI)
The boiler sequence reset integral is a variable generated from the progression of the
cascade flow temperature and time (t). If the variable exceeds the setpoint, the differ-
ence will be communicated to the cascade controller as surplus heat.
KRI =
∆Tdt
t
0
∫
where: ∆T = ( T
VKx
− T
VKw
+ 0.5
*
SD ) > 0
Automatic boiler sequence changeover according to the number of burner operating
hours is not possible with the RVL471 since this controller does not acquire the number
of burner operating hours. Boiler management functions must be provided in the cas-
cade master.
Note