tekmar 654 Snow Melting Control Installation - Manual (Page 32)

© 2013 654_D - 06/13 32 of 44
Priority = None
All zones have the same priority and can operate at the same
time.
This setting is recommended when the boiler plant capacity is sized
larger than the heat loss of all zones at design conditions.
Priority = Conditional
The zone with the lower priority starts melting when the zone
with higher priority is warm enough to melt snow or ice.
This setting is recommended when the boiler plant capacity
is sized to be larger than the heat loss of each zone with
some extra capacity.
Priority = Full
The zone with the lower priority starts melting once the
zone with higher priority has finished melting all snow or
ice from the slab.
This setting is recommended when the boiler plant capacity
is sized to be the same as the heat loss of each zone at
design conditions.
Hydronic Priority Levels -------------------------------------------------------------------------------- --------------------------------------------------------------------------------
Electric Priority Levels --------------------------------------------------------------------------------- ---------------------------------------------------------------------------------
Electric snow melting offers three levels of priority: None,
Conditional and Full. The None and Full priority options function
the same as with the hydronic operation. The Conditional
priority is unique to electrical operation. The highest priority
zone operates first. Whenever the highest priority zone shuts off its relay, the lower priority zone is allowed to start melting
and close its relay. Only one electrical relay is allowed to be
on at any time. This eliminates large instantaneous demands
and avoids surcharges from the electrical utility.
Zone 1
MELT
OFF
Zone 2
MELT
OFF
Zone 1
MELT
OFF
Zone 2
MELT
OFF
Zone 1
MELT
OFF
Zone 2
MELT
OFF
Zone 1
MELT
OFF
Zone 2
MELT
OFF
Zone 1 Relay
ON
OFF
Zone 2 Relay
ON
OFF