tekmar 284 Boiler Control - Manual (Page 9)

© 2014 284_D - 08/14 9 of 60 A Watts Water Technologies Company
The 284 supports operation of a condensing & a non-condensing
boiler group. A condensing boiler group is created when at least
one boiler is selected to be condensing & a non-condensing
boiler group is created when at least one boiler is selected to
be non-condensing. The condensing boiler group is always
sequenced on first, followed by the non-condensing boiler
group.
Boiler Plant Flow (PLANT FLW) ------------------- -------------------
The control supports the option of having all boilers in the plant
to use either a pump or an isolation valve.
Boiler Pump (PUMP)
PUMP is to be selected when each boiler in the plant includes
its own circulator. This is typical of a conventional boiler plant
configuration that includes boilers that are flow sensitive.
PUMP is also to be selected when each boiler in the plant
neither includes a pump nor an isolation valve. This boiler
plant configuration could be used with boilers that are not flow
sensitive. It is expected that the primary pump provides flow
through all boilers, regardless of whether they are on or off.
Boiler Isolation Valve (VALV)
VALVE is to be selected when each boiler in the plant includes
an isolation valve. This boiler plant configuration could be used
with boilers that are not flow sensitive & is typical of systems that
incorporate a variable frequency drive (VFD) with the primary
pump. Systems incorporating variable speed primary pumping
(via a VFD) allow for increased pump electrical energy savings
during milder heating loads.
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 Heat Call (e.g. external Heat Call shorted)
As the heating load becomes satisfied & 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.
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Intermittent Heat Call (e.g. external Heat Call interlocked
with space heating thermostat)
When the 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 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.
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