Watts tekmar 294 - System Operation - Boiler Rotation and Flow; Boiler Group Rotation; Boiler Plant Flow Control; Pressure Monitoring

IOM-T-294 2205 © 2022 tekmar
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Boiler Group Rotation
The control has two boiler rotation groups:
• Condensing Boiler Rotation Group
• Non-condensing Boiler Rotation Group
The Rotate feature changes the firing order of the boilers
whenever one boiler accumulates 48 hours more run time than
any other boiler. Rotation will be forced if any boiler accumu-
lates 60 hours more run time. After each rotation, the boiler
with the least running hours is the first to fire and the boiler
with the most running hours is the last to fire. This function
ensures that all of the boilers receive equal amounts of use.
When Rotation is Off, the firing sequence always begins with
lowest boiler to the highest boiler.
720 hours
1 2
672 hours
720 hours
2 1
672 hours
Boiler Run Time Monitoring
The running time of each boiler is logged in the Boiler Status
screen. Select the boiler hours to view the Boiler Hours and
select CLEAR to zero the running hours. This action also zero’s
the boiler for the boiler Equal Run Time sequence.
Fixed Lead
When the boiler plant includes only one boiler group, either a
condensing or a non-condensing group, a selection must be
made regarding operation of the lead boiler.
In some applications, it may be desirable to have the first
boiler fire first at all times while the firing sequence of the
remaining boilers is changed using Equal Run Time Rotation.
This configuration is typical of installations where the boiler
plant includes similar boilers but the first boiler is required to
be the first to fire in order to establish sufficient draft for vent-
ing. With a fixed lead rotation, the lead boiler is always turned
on first and turned off first. The Fixed Lead is always applied
to the boiler 1 output.
Fixed Last
When the boiler plant includes only one boiler group, either a
condensing or a non-condensing group, a selection must be
made regarding operation of the last boiler.
In some applications, it may be desirable to have the last boiler
fire last at all times while the firing sequence of the remaining
boilers is changed using Equal Run Time Rotation. This config-
uration is typical of installations where the boiler plant includes
higher efficient boilers and a single lesser efficient boiler. The
lesser efficient boiler is only desired to be operated when all
other boilers in the plant are on and the load cannot be satis-
fied. With a fixed last rotation, the last boiler is the last to turn
on and the first to turn off. The Fixed Last is always applied to
the last available boiler on the 294 or 294EXP (boiler 4, 8,
12, or 16).
Boiler Plant Flow
The control supports the option of having all boilers in the plant
to use either a pump or an isolation valve.
Boiler Pump
Select Boiler Pump if each boiler has its own pump to provide
flow in the near boiler piping. Boiler pump can be selected if the
system is piped in reverse-return with a single system pump.
Boiler Isolation Valve
Select Isolation Valve when each boiler in the plant includes
an isolation valve and a single or parallel system pumps that
include a Variable Frequency Drive (VFD) to reduce speed to
reduce electrical energy.
The purpose of the isolation valve is to isolate the boiler from
plant operation when the boiler is turned off. As a boiler is
isolated, the VFD will adjust the flow rate accordingly. The
isolation valve must include a spring return motor that is of
the normally open / fail open type. As the control does not
include a proof input for proving that the isolation valve is fully
open prior to burner ignition, the motor end switch, if available,
should be wired into the burner’s safety circuit.
Boiler isolation valve operation is dependent on whether the
Heat Call is permanent or intermittent.
• Permanent Central Heat Call
As the heating load becomes satisfied and a boiler is required
to be turned off, the boiler will turn off while its isolation valve
remains open for the boiler purge period time. After the boiler
purge time expires, the isolation valve will close. When the last
boiler in the plant turns off, its isolation valve will remain open,
allowing for a flow path of the primary pump.
When there is a subsequent requirement for plant operation
and a boiler is required to be turned on, its isolation valve will
be opened (if not already open) prior to burner ignition. Also, if
applicable, the isolation valve of the last boiler turned off in the
previous cycle will be turned off.
• Intermittent Central Heating Call (e.g. interlocked with space
heating thermostat)
When the Central Heat Call is present, operation is consistent
with the operation defined for a Permanent Heat Call.
When the external Heat Call is removed, the isolation valve of
every boiler will be opened. When the external Central Heat
Call is re-applied, the control will keep open the valve of the
boiler that is due to be turned on first. The isolation valves of all
other boilers will be closed.
Pressure Monitoring
The control has the capability to monitor system pressure from
0 to 150 psi (1034 kPa) when the Pressure Sensor 088 is
installed.
Once installed set the Pressure Sensor to On. The control
include a Low Pressure Alert and a High Pressure Alert notifi-
cation to alert users of pressure related problems. The pres-
sure alerts to do not prevent boiler staging operation.