Install Instructions

71
11 Operating information (continued)
Installation & Service Manual
Outdoor air reset
The Noble Fire Tube uses an advanced non-linear outdoor
reset curve to improve system efficiency by reducing the
boiler water set point as the outdoor temperature warms up.
The installer can set the reset curve by setting both the SH
SETPT (COLD DAY) parameter to the water temperature
required for the coldest design day outdoor temperature and
the COLDEST OUTDOOR TEMP parameter to the coldest
design day outdoor temperature. The installer should limit
the maximum set point for the system using the MAX SH
SETPT parameter. The user can adjust the SH SETPT (COLD
DAY) parameter up to the MAX SH SETPT as needed to
modify the reset curve. For advanced configuration, the
installer can also adjust the warm day point on the curve
using the installer menu, however because of the non-linear
curve, these settings typically do not need to be adjusted.
With the outdoor air sensor connected, the control module
will calculate the space heating demand water set point based
on the programmed reset curve to automatically match the
required heat load. For advanced configuration, the installer
can also adjust the warm day point from the Installer Menu.
Figure 11-4 Outdoor Reset Curve
WATER
TEMPERATURE
SET POINT
MAX SH SETPT
(DEFAULT = 185°F)
CURVE MAY BE LIMITED TO A
LOWER SET POINT
SH SETPT (COLD DAY)
(DEFAULT = 125°F)
USER ADJUSTABLE
SH SETPT (WARM DAY)
(DEFAULT = 75°F)
NOT TYPICALLY ADJUSTED
OUTDOOR
TEMP (COLDEST)
(DEFAULT = 10°F)
WARM WEATHER
SHUTDOWN
(DEFAULT = 70°F)
OUTDOOR RESET CURVE
WILL BE AUTOMATICALLY LIMITED
AT 15°F BELOW COLD DAY
OUTDOOR TEMPERATURE
OUTDOOR TEMP -
WARM
(DEFAULT = 75°F)
NOT TYPICALLY ADJUSTED
Outdoor Air Shutdown
Outdoor air shutdown speci es the outdoor air temperature at
which the Space Heating demand is blocked. DHW demands
will still be active. Space heating operation will resume once the
outdoor temperature falls below 10°F less than the Outdoor Air
Shutdown setting.
Space Heat Rate Limiting
Space Heat Rate Limiting can be used when the maximum
required space heating load is lower than the maximum input
rate of the unit.  is feature limits the maximum input rate
during a space heating demand to help keep the unit running
at lower input rates. Space Heat Rate Limiting does not a ect
DHW operation.
Combi Pre-Heat (Combi Only)
 e Noble Fire Tube includes an optional Pre-Heat feature
which is intended to maintain the boiler water temperature
within a pre-de ned range to improve the time it takes for the
unit to supply heated DHW water.  e Pre-Heat feature can
also be used to satisfy low  ow DHW demands or for heating
water during DHW recirculation where  ows through the
unit may be less than the setting of the  ow switch.  e Pre-
Heat feature will  rst try to satisfy these demands using the
integral boiler pump before  ring. Pre-heat operation will be
indicated on the display by a  ashing DHW icon. When the
unit  res for a Pre-Heat demand, it will immediately ramp to
low  re. Pre-Heat demands will only occur when no other
heating demand is present.
DHW Respond (Combi Only)
 e Noble Fire Tube includes a DHW respond feature to help
eliminate cold water sandwich issues associated with repeated
DHW demands. A er any DHW demand, the unit will go
into pre-purge for a pre-determined time a er post-purge has
ended. If a new demand occurs during this DHW respond time,
the unit will be able to immediately enter ignition, reducing the
time it takes for the unit to respond to the subsequent demand.
DHW respond time can be set by the installer for a duration of 0
minutes (disabled) up to 15 minutes.
Flame current support
To prevent nuisance shutdowns when the boiler is firing at low
rates, the control will increase the firing rate when the flame
signal drops too low.
FIRE TUBE
™