Install Instructions

Page 41
NEOTHERM Residential Boilers
2. Set the setpoint for the DHW function.
If your system has just one boiler –
How to get there: From the “Home” screen, press “I” to
go to “Info/ Install.” Choose “Advanced Setup,” then go
to “DHW Conguration.” Select “DHW Setpoint.”
If your system has more than one boiler, and is controlled
using the Lead/ Lag function –
How to get there: On the unit used as the Lead Lag
Master, from the “Home” screen, press “I” to go to “Info/
Install.” Choose “Advanced Setup,” then go to “DHW
Conguration.” Select “DHW Setpoint.”
Figure 32. -Lead/LagOperation,2boilers.
Low demand -
The first boiler in
sequence fires at
less than 65%
First
boiler
Second
boiler
Demand increases -
Once the first boiler
reaches 65%,
the second boiler
switches on, and
both modulate
together between 20%
and 65% (adjustable up to 20% and 85%).
Nearing max. demand -
Once both reach 65%,
then they are both
allowed to go over
65%
8.14 AboutLeadLagOperation
If an installation includes two or more boilers (up to 8
residential Neotherms), they may be set up for “Lead Lag”
operation. One boiler will be set up as the “Master”, and
the others will operate as “Followers.” Figure 38 shows
an installation with four boilers. (A Lead Lag system can
include up to eight boilers.) The boiler controllers are
connected in a “daisy chain” using a Modbus connection.
For the full wiring diagram for lead lag, See Figure
17 on page 26.
A single System sensor is used to monitor the demand
for heat. The input from this sensor is used by the Master
controller to control the modulation rates of all of the
operating boilers.
Lead Lag Modulation Cycle -
Note - We will explain the modulation cycle here, in case
you need to understand how the Lead Lag system actually
operates. If you are installing the unit(s) and want to skip this
section, just remember that, as the heating demand increases,
the Lead Lag system puts more boilers on-line. As the
heating demand is reduced, the Lead Lag system shuts off
some of the boilers.
The signal from the System sensor is sent to the unit
operating as the Lead Lag Master. A Run sequence is
initiated when the system temperature falls to the Lead Lag
Central Heat setpoint. (Actually this is the LL CH setpoint
less the On Hysteresis value. The default setting for On
Hysteresis is 5°F, but this is adjustable.)
Notice that, when a boiler is operating as part of a Lead Lag
system, it does not use the normal CH setpoint – it uses the
special LL CH setpoint on the Lead Lag Master.
The unit acting as the Lead Lag Master decides which
boiler is assigned to start rst. This assignment is rotated
across all of the available boilers so that any one boiler
does not run signicantly longer than the others. The
3. Set the DHW priority time. If the DHW function has the
priority, the priority will continue during the priority time.
If your system has just one boiler –
How to get there: From the “Home” screen, press “I” to
go to “Info/ Install.” Choose “Advanced Setup,” then go
to “DHW Conguration.” Select “DHW Priority Time.”
If your system has more than one boiler, and is controlled
using the Lead/ Lag function –
How to get there: On the unit used as the Lead Lag
Master, from the “Home” screen, press “I” to go to “Info/
Install.” Choose “Advanced Setup,” then go to “DHW
Conguration.” Select “DHW Priority Time.”
Lead Lag controller tracks the run times for all of the
boilers, and uses this to calculate the starting order
for the boilers. This means that each time the system
starts up, a different boiler may start rst.
• When the Run sequence is initiated, the boiler with
the least amount of runtime will re.
• If the heating demand increases so that the ring rate
of that rst boiler rises to your boiler congurations
Base Load Value (see Table 19), the next boiler in the
sequence will start up and begin ring at 20 to 35%
fan speed (depending on your conguration). After