Meridian
Systems
21
Zoning Design Guide
036-21478-001 Rev. A (0802)
Auxiliary Heat Control Options
The Meridian
Zoning system offers the user a variety
of methods to deal with zone heating requirements. In
order to control zone heat, an optional Relay Expan-
sion Board is required. When deciding how to handle
zone heating requirements the user should consider the
following:
•
Does the rooftop unit have heat?
•
Are you using fan-powered boxes with reheat?
•
Is auxiliary heat such as baseboard or radiant
ceiling panels used?
If the zone has some type of heat, the user must con-
sider how the heat is to be used. Typical questions that
should be asked:
Q: Should the zone heat be used as a first stage where
it will become active before a heating demand is
created at the rooftop unit?
A: This mode is useful if you expect to have both
heating and cooling demands at the same time. The
zone will use it’s own heat and allow the rooftop
unit to continue to provide cooling for other zones.
This mode is also useful if the roof top unit does
not have any heating capabilities.
Q: Is the zone heat only to be used as a second stage,
where it will be activated only if the roof top unit
cannot maintain the space temperature, such as
during very cold weather?
A: In this mode of operation the rooftop will examine
the heating and cooling demands and try to satisfy
all of the zones by switching between heating and
cooling as required. The zone heat will only be
activated if the zone temperature falls below a
selected limit.
Q: Should the zone heat be locked out if the rooftop
unit is supplying warm air?
A: Many times it is desirable to use the rooftop
heating whenever possible and only use zone heat
when the rooftop unit is in cooling. This mode of
operation will lockout zone heat if the rooftop is
delivering heated air.
Relay Expansion Board Outputs
The following describes the operation of each of the
relays on the optional relay expansion board. The user
can choose the appropriate relays for any given appli-
cation.
Relay #1 - Parallel Fan
If the Zone is in cooling or vent mode, the parallel fan
can activate anytime the zone temperature drops 0.5° F
below the heating setpoint. It deactivates when the tem-
perature rises above the heating setpoint.
Relay #2 - Box Heat
If the zone is in cooling or vent mode then the box heat
can activate anytime the zone temperature drops 1.5° F
below the heating setpoint. It deactivates when the tem-
perature rises to within 1.0° F of the heating setpoint.
Box heat is not allowed to activate in the heating mode
when there is hot air being supplied by the air handling
unit. This output was intended to allow zone reheat while
the Zone Manager is satisfying cooling demands in other
zones.
Relay #3 - Aux. Heat
In the occupied mode, the aux heat can activate any-
time the zone temperature is 0.5° F below the aux heat
setpoint. It deactivates when the temperature rises 0.5°
F above the aux heat setpoint. In the unoccupied mode,
the aux heat uses the unoccupied heating setpoint with
the same deadband values mentioned above. This pre-
vents the zone from maintaining the same aux heat
setpoint at night that it does during the daytime. The
Parallel Fan and Box Heat are prevented from coming
on until the aux heat is energized.
This output was intended to allow zone heating to aug-
ment the normal heating mode and also to allow a zone
an attempt to satisfy its own heating needs before cre-
ating a heating demand at the Zone Manager.
Relay #4 - Series Fan
The series fan runs anytime the main fan is running.
This includes occupied and unoccupied modes. The fan
can only start running when the zone damper is closed,
so it determines that the damper is closed before start-
ing the fan.
Summary of Contents for Meridian
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