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8.D.4 Cascade
An installation with two or more units may be configured for cascade operation. Up to eight units can be
cascaded and controlled together.
To navigate to the Cascade Screen, touch the Cascade Icon on the Configuration Screen.
The Cascade Screen provides four navigation icons to configure the system for cascade operations. These
navigation icons are:
• Cascade – This icon navigates to the Cascade Parameters screen for hydronic boiler cascade operations. This
icon is available on hydronic boilers (MGH) only.
• Rotation – This icon navigates to the cascade rotation screen.
• Redundancy – This icon navigates to the setup screen for cascade leader redundancy options.
NOTE: A system supply sensor
(supplied with each unit) must be
installed and connected to the
Lead boiler. The Lead boiler will
use this system supply sensor as
the temperature control sensor for
cascade operations.
About Cascading (Lead / Lag)
The Lead boiler uses the Base Load Value to determine when to fire the Lag units
and at what firing rate. The Base Load Value should be adjusted based on the
number of units installed, with a default value of 65%. Recommended base load
values based on the number of units installed is shown in the table below. The
Base Load Value is adjustable via the DU with installer login credentials.
Upon an active cascade heat demand, the Lead boiler will dictate which unit will
fire first based on the cascade rotation logic. As the firing rate of this unit reaches
the Base Load Value, once the Min On Time timer expires, the next unit in the
sequence will fire and both units will modulate up or down together at the same
firing rate in reaction to changes in heat demand. This pattern will continue until
the firing rates of all cascaded units reach the base load value. Once all units are
firing at the base load value, the firing rate can exceed the base load value, with
all units maintaining the same firing rate. Refer to the Lead / Lag figures below for
additional clarification.
With boilers firing at the same firing rate, minimum firing rates need to be taken
into consideration. Units with varying turndown ratios can be cascaded together,
therefore, the unit with the highest minimum firing rate dictates the minimum firing
rate of the total cascaded system. For example, if a 5:1 unit is cascaded with a
20:1 unit, and the 5:1 unit has reached the base load value, the 20:1 will be called
to run. The 20:1 will fire at the same firing rate as the 5:1, which is limited to 20%
(All about Lead / Lag)
LAARS Heating Systems
Boiler Qty
Recommended
Base Load
N/A
1
2
65%
3
50%
4
40%
5
40%
6
40%
7
40%
8
40%
Table 18. Recommended
Base Load Values
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