Control Strategies; Serial Standard Cascade; Serial Optimised Cascade; Serial Cascade With Peak Load Coverage - Bosch MC 400 Installationsanleitung, Bedienungsanleitung

2.3

Control strategies

2.3.1

Serial standard cascade

The connected heat sources/modules are turned on and off according to
the wiring.
For example, the heat source connected to the BUS1 terminal is
designated as heat source 1, BUS 2 is heat source 2 etc.
If the heat source is turned off, the sequence is reversed. The heat
source which was last fired is turned off first.
The module takes into account that the performance increases or
decreases suddenly when a heat source is fired or turned off
(see chapter 2.2.1).
2.3.2

Serial optimised cascade

The aim of this control strategy is to operate the heat sources according
to the burner runtime.
The connected heat sources are turned on and off according to the
burner runtime. The burner runtimes are compared every 24 hours, and
the sequence is re-established.
The heat source with the shortest burner runtime is fired first, and the
one with the longest runtime is fired last.
If the heat source is turned off, the sequence is reversed. The heat
source which was last fired is turned off first.
The controls take into account that performance increases or decreases
suddenly when a heat source is fired or turned off ( chapter 2.2.1).
2.3.3

Serial cascade with peak load coverage

This control strategy is recommended 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 in the
base-load output. The heat sources at terminals BUS3 and BUS4 are
connected to cover and the energy demand in peak loads.
The heat sources connected to terminals BUS3 and BUS4 are fired when
the required flow temperature rises above an adjustable limit, or the
outdoor temperature falls below an adjustable limit.
If the heat source is turned off, the sequence is reversed. The heat
source which was last fired is turned off first.
The controls take into account that performance increases or decreases
suddenly when a heat source is fired or turned off ( chapter 2.2.1).
2.3.4

Parallel cascade

This control strategy can be selected for cascades containing heat
sources with similar modulation ratios, for example, where all outputs
are the same.
The first heat source will modulate up to 68 %. At this point, if the heat
demand has not been met, the second heat source will modulate up to
68%, and so on with additional heat sources. Once the set temperature
has been reached then the heat sources will modulate down with the
same control logic.
The parallel cascade setting ensures that burner runtimes within the
cascade are closely matched, thus evenly distributing heat source wear
and tear.
MC 400
2.3.5

Output control

This control strategy can be used when the heating system is controlled
using a building management system with a 0-10 V controller output.
P / %
100
10
1 1,5
Fig. 1 Linear relationship between the 0-10 V signal (U in volts) and
required performance P (in percent with reference to the
maximum cascade output)
The connected heat sources are turned on and off according to the
required performance as per the module code. This setting can be
combined with serial standard or optimised cascade strategies.
2.3.6

Flow temperature control

This control strategy can be used when the heating system is controlled
using a building management system with a 0-10 V controller output.
/ °C
90
20
1 1,5
Fig. 2 Linear relationship between the 0-10 V signal (U in volts) and
required 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])
The connected heat sources are turned on and off according to the
required flow temperature as per the module code. This setting can be
combined with serial standard or optimised cascade strategies.
2.3.7

Pump pre-run

For all control strategies ( chapter 2.3.1 to 2.3.6) a pump flow period
of 2 minutes takes place before firing the burner in the heat sources.
This enables optimised burner start-up performance via careful flow and
temperature control, in addition to the avoidance of burner lock-outs.
Product details | 13
U / V
10
6 720 809 449-21.1O
U / V
10
6 720 809 449-22.2O
6 720 819 669 (2016/05)