Slant fin corp – Slant/Fin CHS-399 User Manual
Page 49
CHS Series
Installation and Operation Instructions │
Slant Fin Corp.
49
Multiple Boiler Applications
The CHS controller has the internal capacity to stage or Lead-Lag up to 8 boilers configured in a cascade. This
Lead-Lag capability allows a designated “Master” boiler to communicate with and effectively control each
boiler in a multiple boiler system. This function is accomplished by “Daisy Chaining” a 3-wire cable between
each of the boilers and enabling the Master parameter in the boiler of your choice. The boiler with the Master
parameter enabled becomes the single point of contact for Central Heating and Outdoor Reset set-points as well
as system control wiring such as the Thermostat demand and Outdoor and System Water Temperature. See
section on Low Voltage Connections for wiring and control set-up details. Figures 10-7 and 10-8 are examples
of multiple boiler plumbing configurations illustrating small and large DHW applications.
Modbus Address – Each boiler in a cascade arrangment (lead-lag) must have a unique
modbus address between 1 and 8, inclusive. For detailed instructions on how to set the
modbus address for each CHS controller, refer to "System ID & Access" in Appendix A.
Figure 10-7: Multiple Boiler Applications with Small DHW Requirements – Used in applications where the
DHW load can be satisfied by a single boiler. In this example, Boiler 1 provides DHW priority over Central
Heating, while Boilers 2 and 3 provide Central Heating only; furthermore, the DHW demand to Boiler 1 comes
directly from the Aquastat of the Indirect Fired Water Heater.
Figure 10-8: Multiple Boiler Applications with Large DHW Requirements – Used in applications where the
DHW load is too large to be satisfied by a single boiler. In this example, Boilers 1 and 2 provide DHW priority
over Central Heating, while Boiler 3 provides Central Heating only. In contrast to small DHW requirements, the
Aquastat(s) of the Indirect Water Heater(s) is used to activate the main DHW pump and a relay is used to trigger
individual contacts for the DHW inputs of Boilers 1 and 2. Refer to Figure 11-3 for relay wiring details.
During a Lead-Lag Central Heat demand [CH2 (LL)], the Master communicates the call to the applicable
boiler(s); boilers attempting to satisfy the Central Heat demand will energize their local pump contacts B
(Boiler) and C (Central Heat). Boilers not responsible for heating DHW use pump contact B for controlling their
local Central Heat Pump (see Boilers 2 and 3 in Figure 10-7). Boilers responsible for heating DHW use pump
contact C for controlling the local Central Heat Pump (see Boilers 1 and 2 in Figure 10-8). A boiler receiving a
local DHW demand will turn off pump contact C for Central Heat and will activate pump contact A for DHW,
thus providing DHW priority.
With the exception of the Main System circulator in Figures 10-7 and 10-8 and the Main
DHW circulator in Figure 10-8, all circulators must be sized to support adequate water
flow through the boiler.
System Circulator - The installer can designate one of the boilers, preferably one not responsible for DHW
heating, to control the operation of the System Circulator. Via the user interface, under “Pump Configuration”
and “Central Heat Pump”, check the box labeled “Use for Lead Lag Master demand”. This forces the local
pump output C to activate when the Master gets a Lead-Lag Central Heat demand [(CH2 (LL)]. Pump output C
can then be used to power the System Circulator. Due to the large load of a typical system circulator, it is
recommended that a 120VAC isolation relay be used instead of powering the system circulator directly from
pump output C (i.e. pump output C is limited to 3 Amps or 1/6hp).
Table 10-5 Minimum Pipe Sizes for Multiple Boiler Applications
# of
Units
CHS-85
CHS-110
CHS-155
CHS-175
CHS-200
CHS-250
CHS-300
CHS-399
Pipe Size
Pipe Size
Pipe Size
Pipe Size
Pipe Size
Pipe Size
Pipe Size
Pipe Size
2
1-1/4”
1-1/2”
1-1/2”
2”
2”
2”
2-1/2”
2-1/2”
3
1-1/2”
2”
2”
2”
2-1/2”
2-1/2”
3”
3”
4
2”
2”
2-1/2”
2-1/2”
2-1/2”
3”
3”
3”
5
2”
2-1/2”
2-1/2”
3”
3”
4”
4”
4”
6
2”
2-1/2”
3”
3”
4”
4”
4”
5”
7
2-1/2”
2-1/2”
3”
4”
4”
4”
4”
5”
8
2-1/2”
3”
3”
4”
4”
4”
5”
5”
Note: Minimum pipe size based on assumed temperature rise of 25ºF at maximum firing rate.