351579-YTS-B-0608
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Johnson Controls Unitary Products
programmed Maximum Economizer Position for Demand
Ventilation. The algorithm is deactivated, and the previous,
normal mode of economizer position control resumed when the
IAQ level becomes 50 ppm lower than the setpoint.
The programmed "Maximum Economizer Position for Demand
Ventilation" is used to minimize the possibility that the Demand
Ventilation may open the Economizer damper too much, such
that at fairly high OA temperatures, even combined cooling
output of all compressors would not provide sufficient cooling
(as a rule of thumb, all compressors combined achieve approx.
20 °F SAT decrease). Similarly, at fairly low OA temperatures,
the combined output of all heating stages may not be able to
provide sufficient heating. This Economizer max. position limit
is simpler to implement than a closed loop SAT low-limit control
that would operate with a programmed high-limit for cooling and
a programmed low limit for heating.
NOTE:
An added measure of protection against excessive
SAT during Demand Ventilation Operation is provided
by Supply Air Alarm Setpoint for Cooling and Supply
Air Alarm Setpoint for Heating, and the control func-
tion associated with these setpoints (see the respec-
tive paragraphs in the Option Operation section earlier
in this document).
EXHAUST OPERATION
Building static pressure is controlled through one of three
methods. One method incorporates a fixed speed fan that is
controlled from the position of the Economizer dampers. A
second method uses proportional control that modulates the
exhaust damper and operates the fan based on the position of
the dampers. A third method uses a variable speed fan control
that looks at building static pressure. All are dependent on the
supply fan being ON.
TWO-POSITION CONTROL (NON MODULATING POWER
EXHAUST)
This mode is a fixed speed, ON/OFF Power exhaust fan, with a
barometric relief damper, controlled from position of the
Economizer damper. The Power Exhaust and the Economizer
options must be ON.
This mode is a fixed speed, ON/OFF Power exhaust fan, with a
barometric relief damper, controlled from position of the
Economizer damper. The Power Exhaust and the Economizer
options must be ON.
The Exhaust Fan (EF) is controlled with a relay output of the
controller and "slaved" to the Economizer damper position
value.
The EF relay is energized whenever the Supply Fan is running
and the Economizer (Outdoor Air Damper) is commanded open
more than the programmed Economizer Damper Position for
Exhaust Fan to turn ON.
The EF will be de-energized when supply fan is off or when the
OAD opening is less than the EF Turn OFF set point or 10%
open, whichever is greater. Default Setpoint settings for the EF
to turn ON at Economizer 60% open, turn OFF at Economizer
20% open. The EF has a minimum run time of 10 seconds and
a minimum off time of 60 seconds.
PROPORTIONAL CONTROL (FAN WITH MODULATING
EXHAUST AIR DAMPER (EAD) CONTROLLED FROM
BUILDING STATIC PRESSURE)
In this mode the Power Exhaust, Modulating Exhaust,
Economizer and Building Pressure Sensor Enable options must
be ON and the Supply Fan must be running. The EAD actuator
is modulated to maintain building static pressure to a
programmed Building Pressure Setpoint. An appropriate closed
loop control algorithm is used to accomplish this control.
The control will modulate from full closed to full open over a 2-
minute period. The proportional band is from 0.015 in w.g. (3.7
Pa) below the Building Pressure Setpoint to 0.015-in. w.g. (3.7
Pa) above the set point.
The control algorithm is disabled and exhaust air damper
commanded closed whenever the supply fan is off. Building
pressure is sensed with a -0.250 to +0.250 in. w.g. (-31 to + 31
Pa) 0 - 5V output pressure differential transducer. The
transducer senses the building pressure as referenced to an
appropriate reference point outside the building. Transducer
output signal is filtered (e.g. time averaged over 15 second
period) to compensate for wind gusts.
The Exhaust Fan (EF) is controlled with a relay output of the
controller and "slaved" to the Exhaust Air Damper position. The
EF relay is energized whenever the Supply fan is running
and
the EAD is open more than the programmed Exhaust Damper
Position for Exhaust Fan to turn ON. The EF relay is de-
energized when Supply fan is off or when the EAD opening is
less than the programmed Exhaust Damper Position for
Exhaust Fan to turn OFF, or 10% open, whichever is greater.
The minimum run time is 10 seconds and minimum off time is
60 seconds. (Non-adjustable). Default Setpoint settings are for
the EF to turn ON at Exhaust Air Damper 80% open and turn
OFF at Exhaust Air Damper 20% open. The Building Pressure
Setpoint default is 0.100" w.g.
PROPORTIONAL CONTROL WITH VFD FAN
This is similar to the proportional EAD option, except that the
damper signal is used to control motor speed using a variable
frequency drive.
TWO-POSITION CONTROL (POWER EXHAUST WITH
BAROMETRIC RELIEF, CONTROLLED FROM BUILDING
STATIC PRESSURE)
In this mode the Power Exhaust, Economizer and Building
Pressure Sensor Enable options must be ON. The Exhaust Fan
(EF) is controlled with a relay output of the controller. The EF
relay is energized whenever Supply fan is running and building
static pressure is above a programmed Building Pressure
Se 0.015 “ w.g. (3.7 Pa). The EF relay is de-energized
when supply fan is off, or when building static pressure is less
than a programmed Building Pressure Setpoint - 0.015” w.g.
(3.7 Pa). The minimum run time is 10 seconds and minimum off
