York MILLENNIUM Y22, Installation Manual

Page: 91 / 140

102777-YIM-E-0206
Unitary Products Group 91
When the IAQ sensor is detected as available, the control will
use the Demand Ventilation Setpoint to control the IAQ levels
in the building by modulating the Economizer more open.
The Demand Ventilation will operate in units equipped with an
Economizer (Economizer option is turned ON) any time the
control is in Occupied mode. The Demand Ventilation Opera-
tion is applicable in heating, or cooling mode, and will modu-
late the Economizer damper more open, if necessary, from its
programmed minimum position (in heating, or in cooling
when economizer is not "suitable"), or from its modulated
position determined as defined in the Economizer Operation
section (in cooling, when economizer is "suitable").
An appropriate control algorithm is used to accomplish this
control. Preferably, this algorithm is a "step-and-wait" type,
with the step size calculated as a function of offset between
the Demand Ventilation Setpoint and the current IAQ level,
and with a fixed "wait", or sampling time. This algorithm is
activated whenever the IAQ level exceeds the setpoint and
will override the economizer position more open, as needed,
up to a pre 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 pro-
vide 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 heat-
ing 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 pro-
vided by Supply Air Alarm Setpoint for Cooling and
Supply Air Alarm Setpoint for Heating, and the con-
trol function associated with these setpoints (see
the respective 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 depen-
dent 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 Econo-
mizer 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 Econo-
mizer 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 run-
ning and the Economizer (Outdoor Air Damper) is com-
manded 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, Econo-
mizer 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 pro-
grammed 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