LAARS NeoTherm NTV (Sizes 150–850 MBTU/h) - Install and Operating Manual - Manual (Page 46)

Page 42 LAARS Heating Systems
Boiler Pump Interrupt Function -
The Boiler pump interrupt feature is used in some applications
when the boiler is being used for both hydronic and domestic
hot water heating. The interrupt jumper is used to turn off
the boiler pump during a domestic hot water demand. For
this to work properly the system must be plumbed and
pumped to allow the DHW pump to supply the flow and head
requirements for both the boiler and indirect water heater. It is
not necessary to use the interrupt jumper in all applications.
To turn off the Boiler pump in this situation, the “boiler pump
interrupt” jumper should be installed between R1 and R2 on
TB5.
If your system includes several boilers, is controlled using the
Lead/Lag system, and the indirect DHW tank is connected
to the boiler acting as the Lead/Lag master, install the boiler
interrupt jumper on the Lead/Lag master only.
WARNING
Failure to plumb, pump and install the appliance
correctly when using this feature may lead to reduced
or no water flow through the heat exchanger, causing
premature failure of the heat exchanger, personal
injury or death. Please consult the factory with any
questions regarding the use of this feature.
Setup for DHW Control Functions -
1. Set up the correct priority for the DHW function in relation
to Central Heat or Lead/ Lag demands. If a call for heat
and a DHW demand arrive at the same time, which will
have the higher priority?
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 Configuration.” Select “DHW Priority vs
Central Heat.”
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
Configuration.” Select DHW Priority vs Lead/Lag.”
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 Configuration.” 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
Configuration.” Select “DHW Setpoint.”
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 Configuration.” 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
Configuration.” Select “DHW Priority Time.”
8C.8 Cascading Lead/Lag Operation
About Lead/Lag Operation -
If an installation includes two or more boilers, they may be
set up for “Lead/Lag” operation. One boiler will be set up as
the “Master”, and the others will operate as “Slaves.” 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.
See Fig. 40.
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.)
NOTE: If your NeoTherms are Lead / Lag configured,
you will find it very useful to customize your Home
Display to show LL Operating Temp and LL Setpoint
Temp.
Please refer to Section 7.5 to learn how to customize
your Home Display. Various parameters can be displayed
on the Home Display to suit your needs.