Strebel S-CB Px 120, Installation Operating & Maintenance Manual

Page: 81 / 118

S-CB Px 120 Manual 81
When cascade connection is programmed correctly the boiler display will show the following.
Explanation "Cascade communication indicator"
NO CASCADE COMMUNICATION
> > > no.1
Always showing the fixed ">>>"
CORRECT CASCADE COMMUNICATION
> > no.1
no.2
>
Showing alternating no.1 & no.2 with 1 second interval.
11.4.2. M
ONITOR SCREENS
To obtain cascade information, see § 10.4. on page 40.
11.4.3. O
UTPUT CONTROL AND BOILER SEQUENCE
The total cascade set-up will act as one single big boiler, switching on- and off boilers, depending on the total load
necessary to adjust and keep the flow temperature at the calculated value.
When the heat demand rises, more boilers are switched on, and when heat demand falls, one or more boilers will
be switched off. The boiler that was switched on last, will be switched off first, see table below.
To distribute operating hours equally over all boilers, the working sequence of the boilers will change every two
hours.
Hour Switching ON sequence Switching OFF sequence
X
Master – Slave 1 – Slave 2 – Slave 3 –
Slave 4 – Slave 5 – Slave 6 – Slave 7 Slave 7 – Slave 6 – Slave 5 – Slave 4 –
Slave 3 – Slave 2 – Slave 1 – Master
X+2
Slave 7 – Master – Slave 1 – Slave 2 –
Slave 3 – Slave 4 – Slave 5 – Slave 6 Slave 6 – Slave 5 – Slave 4 – Slave 3 –
Slave 2 – Slave 1 – Master – Slave 7
X+4
Slave 6 – Slave 7 – Master – Slave 1 –
Slave 2 – Slave 3 – Slave 4 – Slave 5 Slave 5 – Slave 4 – Slave 3 – Slave 2 –
Slave 1 – Master – Slave 7 – Slave 6
X+6
Slave 5 – Slave 6 – Slave 7 – Master –
Slave 1 – Slave 2 – Slave 3 – Slave 4 Slave 4 – Slave 3 – Slave 2 – Slave 1 –
Master – Slave 7 – Slave 6 – Slave 5
……… .. ………………………………………………… …………………………………………………
Table : boiler sequence example of an eight boiler cascade.
In this table a total of eight boilers (one master, seven slaves) is mentioned as an example, in practice the maxi-
mum number in a cascade, without extra (external) control, is twelve boilers.