Serial Optimised Cascade; Serial Cascade With Peak Load Coverage; Parallel Cascade; Output Control - Bosch MC 400 Manual De Instalación Para El Técnico

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2.3.2

Serial optimised cascade

The aim of this control strategy is to operate the heat source with
equivalent burner runtimes.
The connected heat sources are switched on and off according to the
burner runtime. The burner runtimes are compared every 24 hours, and
the sequence is reestablished.
The heat source with the shortest burner runtime is switched on first,
and the one with the longest runtime is switched on last.
If the heat source is switched off, the sequence is reversed. The heat
source which was switched on last is switched off first.
The controls take into account that performance increases or decreases
suddenly when a heat source is switched on or off.
2.3.3

Serial cascade with peak load coverage

This control strategy is recommendable when the heat energy demand is
even over a long time (base-load output) with brief peaks (peak load).
The heat sources connected to terminals BUS1 and BUS2 cover the
base-load output. The heat sources connected to the terminals BUS3
and BUS4 are switched on to cover the energy demand in peak loads.
The heat sources at terminals BUS3 and BUS4 are switched on if the
required flow temperature rises above an adjustable limit, or the outside
temperature falls below an adjustable limit.
If the heat source is switched off, the sequence is reversed. The heat
source which was switched on last is switched off first.
The controls take into account that performance increases or decreases
suddenly when a heat source is switched on or off.
2.3.4

Parallel cascade

This control strategy should be used if the heat sources have a similar
degree of modulation.
If the performance is achieved 68 % on a switched on device, the next
will be switched on.
The heat sources are operated with approximately similar burner
runtimes, since all heat sources are simultaneously in operation. If all
heat sources are switched on, they are operated modulating to the same
degree.
2.3.5

Output control

This control strategy is used when the heating system is controlled using
a building management system with a 0–10 V controller output.
The negative hysteresis is 0.5-1.0 V:
P / %
100
10
0,5 1
Fig. 8 Linear relationship between the 0-10 V signal (U in volts) and
the required performance P (in percent with reference to the
maximum system performance)
The connected heat sources are switched on and off according to the
required performance as per the module code as is the case with a serial
standard cascade or a serial optimised cascade.
16
2.3.6
This control strategy is used when the heating system is controlled using
a building management system with a 0–10 V controller output.
The negative hysteresis is 1.0-1.5 V:
/ °C
90
20
Fig. 9
The connected heat sources are switched on and off according to the
demanded flow temperature as per the module code as is the case with
a serial standard cascade or a serial optimised cascade.
2.3.7
For all control strategies a pump flow of 2 minutes takes place before
starting the burner in the heat sources. This reduces the temperature
gradient in the flow and prevents the activation of gradient monitoring.
2.3.8
Instead of a low loss header, a heat exchanger with hydraulic separation
of cascade circuit (primary circuit) and heating circuit can also be used.
Positioning of the low loss header temperature sensor T0: The
temperature sensor (T0) must be mounted on the flow downstream of
the heat exchanger on the secondary side (wet sensor) ( Fig. 87 at the
end of the document). The device circuit pump of the guiding device
remains permanently in operation as long as there is a system heat
demand.
For this purpose, the parameterisation must be adapted: In Service
menu> System data> call up Low loss hdr. sensor instll. and select
Setting No: No low-loss header.
Optimised sensor installation downstream of the heat exchanger
There are two ways to ensure optimised sensor installation downstream
of the heat exchanger ( Item [1] with angled screw connection and
Item [2], Fig. 10):
1
U / V
10
0010013227-002
Fig. 10 Optimised sensor installation

Flow temperature control

1 1,5
Linear relationship between the 0-10 V signal (U in volts) and
the demanded flow temperature  (in °C with reference to the
minimum flow temperature range to the maximum flow
temperature range [default setting 20 °C to 90 °C])

Pump flow

Cascade with heat exchanger operation

24
A B
T0
U / V
10
0 010 013 228-001
24
A B
2
T0
0010024454-001
MC 400 – 6720890243 (2018/12)