LAARS NeoTherm NTV (Sizes 150–850 MBTU/h) - Install and Operating Manual - Manual (Page 42)

Page 38 LAARS Heating Systems
8C.1 24 VAC Transformer
with Integral Circuit Breaker
24Vac is supplied by a transformer mounted underneath the
control panel. All 24Vac power is supplied through a circuit
breaker that is part of the transformer. The transformer is then
connected to terminal blocks 3 and 4 (TB3 and TB4).
8C.2 Hydronic Heating Demand
When using the NeoTherm for hydronic heating, a call for
heat must be supplied to the “T-T or Interlock” terminal. Once
the call is supplied, the control starts the Boiler and System
pumps, and begins the ignition process. The ignition process
consists of a prepurge, trial for ignition, and run period. The
prepurge period starts on a call for heat once the fan RPM
reaches a preset level. The trial for ignition period follows
once the start-up RPM of the fan has been reached. The trial
for ignition period lasts four seconds, During this period the
direct spark ignition system and gas valve are energized.
At the end of the trial for ignition period, the flame signal is
compared with the preset flame threshold value. If the flame
signal is higher than the flame threshold, the NeoTherm enters
Run. If the flame signal is below the threshold, the NeoTherm
returns to prepurge and starts the ignition process over. When
operating in Run, the NeoTherm monitors the flame signal,
call for heat input, safety switches, and water temperatures
and modulates as needed between 100% and 20% of rate to
satisfy the call for heat.
Connect the call for heat to terminal block 7 (TB7),
connections labeled “T-T or interlock” in the control panel.
The CH Setpoint can be set from the Quick Start menu.
How to get there: From the “Home” screen, press “I” to
go to “Info/ Install.” Choose “Quick Start,” then go to
“CH Setpoint.”
8C.3 Anti-Short-Cycle (ASC)
The anti short cycle function helps to prevent short-cycling
when the call for heat switches on and off quickly.
To reach the anti-short-cycle function, select Info/ Advanced
Setup/ System Config./ System Config.
How to get there: From the “Home” screen, press “I”
to go to “Info/ Install.” Choose “Advanced Setup,” then
“System Configuration,” then “System Configuration”
again.
8C.4 Outdoor Air Temperature Sensor
The outdoor air temperature sensor is used with the Outdoor
Reset and Warm Weather Shutdown functions.
Connect the outdoor air temperature sensor to terminal block
7 (TB7), using the connections labeled Outdoor Temp Sensor.
8C.5 Outdoor Reset
About Outdoor Reset -
The Outdoor Reset feature calculates a correction for the
hydronic (Central Heat) setpoint depending on the outdoor
temperature. This allows the system to compensate for
changes in the outdoor temperature and run more efficiently.
(If the unit will operate as part of a Lead/Lag system, the
Outdoor Reset function will adjust the Lead/Lag setpoint. For
details, see “About Lead/Lag Operation” - Section 8C.8.)
The graph below shows how the system will behave at
different outdoor temperatures:
22 27 32 37 42 47 52 57 62 67 72 77
90
100
110
120
130
140
Setpoint
Outdoor Temperature °F
Fig. 37 – Outdoor Reset Operation
In the graph shown above, the sloping line shows the setpoint
which is actually used by the system. Without Outdoor Reset,
this would be a constant 130°F (or whatever other value you
choose), regardless of the outdoor temperature. The line in
the graph would run straight across the display. However,
with the Outdoor Reset feature turned on, the system will
adjust for changes in the outdoor temperature. Let’s take a
detailed look at the way the setpoint is adjusted.
• For cold outdoor temperatures (below 32°F), the setpoint
remains unchanged (130°F).
Section 8C -
DETAILED SETUP INSTRUCTIONS and DIAGRAMS
Section 8 is divided into three parts. Section 8A includes instructions for using the Quick Start
menu. Section 8B covers basic installation and wiring. Section 8c includes more detailed setup
instructions and wiring diagrams.