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XII. Operation
(continued)
Setpoint or is automatically adjusted as Outdoor
.
Air Reset
5. Outdoor Air Reset
If an outdoor temperature sensor is connected
to the boiler and Outdoor Reset is enabled, the
Central Heat setpoint will automatically adjust
downwards as the outdoor temperature increases.
When the water temperature is properly matched
to heating needs there is minimal chance of room
air temperature overshoot. Excessive heat is not
sent to the room heating elements by "overheated"
(supply water temperature maintained too high
a setting) water. Reset control saves energy
by reducing room over heating, reducing boiler
temperature & increasing combustion efficiency
and, reducing standby losses as a boiler and
system piping cool down to ambient following
room over heating.
6. Boost Time
When the Central Heat Setpoint is decreased by
Outdoor Air Reset settings the Boost function can
be enabled to increase the setpoint in the event
that central heat demand is not satisfied for longer
than the Boost Time minutes. The Boost feature
increases the operating temperature setpoint by
10°F (5.6°C) every 20 minutes (field adjustable)
the central heat demand is not satisfied. This
process will continue until heat demand is
satisfied (indoor air is at desired temperature),
or the central heat setpoint is reached. Once the
heat demand is satisfied, the operating setpoint
reverts to the value determined by the Outdoor
Air Reset settings. If Boost Time is zero, then the
boost function is not used.
7. Domestic Hot Water (DHW) Setpoint
Upon a DHW call for heat the setpoint is the user
entered DHW setpoint . The optimal value of this
setpoint is established based on the requirements
of the indirect water heater.
8. Domestic Hot Water Priority (DHWP)
When domestic hot water priority is selected
and there is a DHW call for heat, the system
pump will be turned off (when "System Pump
Run Pump for" parameter is set for "Central
Heat Optional Priority") and the DHW pump
will be turned on. Additionally, if outdoor reset
is active, the active setpoint is adjusted to the
DHW Setpoint. Priority protection is provided
to ensure central heat supply in the case of
excessively long DHW call for heat.
C. Boiler Protection Features
1. Supply Water Temperature High Limit
The control is equipped with internal operating
106
control and high limit features. The control monitors
a dual element temperature sensor that is mounted
in the supply water manifold and provides UL353
and UL1998 internal safety algorithms. If supply
water temperature increases above the active
setpoint plus diff above, default 190°F (87.7°C)
the boiler is cycled off. If the temperature exceeds
210°F (98.9°C), a manual reset hard lockout
results. If the boiler is responding to the internal
Multiple Boiler Control Sequencer, Header Sensor
or an External EMS demand and the supply water
temperature increases above 190°F (87.7°C) the
control begins to reduce the blower maximum
speed setting and if the temperature increases to
200°F (93°C) a forced recycle results. Additionally,
if the supply temperature rises faster than the
degrees Fahrenheit per second limit a soft lockout
is activated.
2. High Differential Temperature Limit
The Control monitors the temperature difference
between the return and supply sensors. If this
difference exceeds 52°F (29°C) the control
begins to reduce the maximum blower speed.
If temperature difference exceeds 62°F (34°C) a
forced boiler recycle results. The unit will restart
automatically once the temperature difference
has decreased and the minimum off time has
expired. If the temperature difference remains
above 72°F (40°C) for longer than 3 minutes a
manual reset hard lockout results.
3. Return Temperature Higher Than Supply
Temperature (Inversion Limit)
The Control monitors the supply and return
temperature sensors.
temperature exceeds the supply water temperature
for longer than a limit time delay the Control shuts
down the boiler and delays restart. If the inverted
temperature is detected more than five times the
boiler manual reset Hard Lockout is set. This
condition is the result of incorrectly attaching the
supply and return piping.
4. External Limit
An external limit control can be installed on the
low voltage terminal strip. Be sure to remove the
jumper when adding an external limit control to
the system. If the external limit opens, the boiler
will shut down and an open limit indication and
error code are provided. If the limit installed is a
manual reset type, it will need to be reset before
the boiler will operate.
5. Boiler Mounted Limit Devices
The control monitors individual limit devices:
External Limit, Optional Low Water Cut-Off (LWCO)
and Blocked Flue/Inlet Switch. If any of these limits
open the boiler will shut down and an open limit
If the return water
107672-03 - 5/18
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