IBC Technologies Inc.
26
VFC 15-150 and VFC 45-225
interval, after which the ignition cycle is
refreshed (e.g. for 3 further attempts).
Alternately, the boiler can be powered
down and restarted to accelerate the re-
try sequence. The homeowner should
follow up persistent recurrence of the 1
hour reset routine by contacting a
qualified service technician, to evaluate
the cause of such ignition irregularity.
With a successful ignition, the output of
the boiler decreases immediately to a
low level, and the heating cycle begins.
2.5.4 Heating
The heating cycle lasts until the
Heating
Enabled
state ends (for all loads), or
until water temperature exceeds the
target temperature by ½ of the supply
differential for the last served load and
the throttle has fallen to the minimum
output. At the end of the heating cycle,
the boiler enters a
postpurge
.
During the heating cycle, the boiler
addresses the multiple defined loads in
accordance with its
Prioritization
algorithm (see
Section 2.6.1
). Boiler
output changes to meet heating demands
as indicated by the temperature
characteristics of the boiler supply and
return water. Boiler supply water
temperature targets vary according to
the set up parameters entered, and are
subject to further variation for loads
where Outdoor Reset has been selected.
Where thermal loads are within the
boiler's 15 to 150 MBH throttle range,
the control algorithm seeks to regulate
the boiler supply temperature within
±3°F of the target temperature. On/Off
differentials apply to loads below the 15
MBH minimum input rating. The
following default differentials are
automatically applied upon initial load
characterization: DHW and other
SetPoint loads (±20°F); space heating
with Outdoor Reset invoked (±11°F).
These default differentials can be
adjusted in the password protected
Installer
access area.
2.5.5 Circulating
This cycle operates when water
temperature exceeds target by ½ of the
supply differential for that load at
minimum output, and call for heat is
still present. After entering a
postpurge
,
the system pump remains on until water
temperature is ½ of the supply
differential below setpoint temperature.
The boiler can also enter the Circulating
mode during transition from a high
temperature load (e.g. DHW at 180°F)
to a cool target (e.g. radiant floor on
Outdoor Reset, at perhaps 90°F). In the
case in which the temperature is outside
the applicable differentials, the burner
will shut off while the pump remains on
until water temperature is 11°F below
the new load (radiant floor) target
temperature. Thermal shock avoidance
routine is employed to avoid
undesirable effects of large temperature
swings: the hot load pump remains on
until the boiler's return water sensor
detects temperature stability - to sink
excess heat. For example, upon
satisfaction of a DHW call the DHW
zone pump will remain running until the
boiler return water temperature falls to
the DHW tank target temperature. This
deposits legacy heat from the primary
loop into the water tank before
activation of a radiant floor load pump.
Always ensure that loads sensitive to
high temperatures are protected using
appropriate means - e.g. an aquastat (set
to130°F, for example) should be wired
to the boiler's auxiliary interlocks to
protect a radiant floor.
