Installation / Operation Instruction Manual

Page 69
8.D.4 Cascade (Lead / Lag)
An installation with two or more units may be congured for cascade operation (Lead / Lag). Up to eight units can be
cascaded and controlled together.
To navigate to the Cascade Screen, touch the Cascade Icon on the Conguration Screen.
The Cascade Screen provides four navigation icons to congure the system for cascade operations. These navigation icons are:
• Cascade CH – This icon navigates to the setup screen for hydronic boiler cascade operations. This icon is available on hydronic
boilers (MGH) only.
• Cascade DHW – This icon navigates to the setup screen for water heater cascade operations. This icon is available on water
heaters (MGV) only.
• Rotation – This icon navigates to the cascade rotation screen.
• Redundancy – This icon navigates to the setup screen for cascade Leader redundancy options.
About Cascading (Lead / Lag)
The Lead boiler/heater uses the Base Load Value to determine when to re the
Lag units and at what ring 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/heater will dictate which
unit will re rst based on the cascade rotation logic. As the ring rate of this unit
reaches the Base Load Value, once the Min On Time timer expires, the next unit in
the sequence will re and both units will modulate up or down together at the same
ring rate in reaction to changes in heat demand. This pattern will continue until
the ring rates of all cascaded units reach the base load value. Once all units are
ring at the base load value, the ring rate can exceed the base load value, with
all units maintaining the same ring rate. Refer to the Lead / Lag gures below for
additional clarication.
With boilers/heaters ring at the same ring rate, minimum ring rates need to be
taken into consideration. Units with varying turndown ratios can be cascaded
together, therefore, the unit with the highest minimum ring rate dictates the
minimum ring 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 re at the same ring rate as the 5:1, which
CONFIGURATION
Table 20. Recommended
Base Load Values
Boiler Qty Recommended
Base Load
1 N/A
2 65%
3 50%
4 40%
5 40%
6 40%
7 40%
8 40%
NOTE: A system supply sensor
(supplied with each unit) must be
installed and connected to the
Lead boiler/heater. The Lead
boiler/heater will use this system
supply sensor as the temperature
control sensor for cascade
operations.