65
YORK INTERNATIONAL
FORM 100.50-NOM1 (604)
5
5
The
Þ
xed minimum position is set by adjusting the
mechanical stops on the damper actuator.
Simply opening the OA damper to a
Þ
xed minimum
position can be quite effective for bringing in a
Þ
xed
volume of outside air with Constant Volume (CV)
equip ment. However, with Variable Air Volume (VAV)
equip ment, the amount of outside air brought into the
air han dler varies because the Supply Fan speed and
total sys tem air volume varies.
To compensate for VAV equipment, a minimum po si tion
reset scheme will be implemented as follows:
The two Unit Setup parameters
"OAD Damper Posi-
tion #1"
and
"OAD Damper Position #2"
will be used
to indicate two minimum positions of the OA damper.
Both OAD Min Position settings will be used to linearly
reset the min i mum position of the OA Damper based
on the out put to the VFD.
"OAD Damper Position #1"
will indicate the Min i mum Position of the OA Damper
when the output to the VFD is at 100% (10 VDC).
"OAD
Damper Position #2"
will indicate the Minimum Posi-
tion of the OA Damper when the output to the VFD is
at 50% (5VDC).
Figure 31 indicates how this algorithm will function:
Outdoor Air Measurement Operation
The outdoor air measurement operation uses air
mea sure ment stations with the outdoor and return air
damp ers to control the amount of outdoor air entering
the unit to a setpoint. Two outdoor air measurement
op er a tion con
Þ
g u ra tions are used. The control will read
the con
Þ
guration setting Air
ß
ow Measurement Ca pa -
bil i ty to determine which outside air
ß
ow mea sure ment
equipment is installed on the unit. If the setting is set to
0, then there is no air
ß
ow measurement equipment in-
stalled and the control will use
Þ
xed minimum position
approach to ventilation. Because of the characteristics
of the air
ß
ow measurement transducers, an auto-ze ro ing
process will be used to ensure that the air
ß
ow sen sor or
sensors are cal i brat ed at zero air
ß
ow . The
"Al ti tude "
setting
of the unit’s location will be used to provide ad-
di tion al mea sure ment accuracy. Calibration parameters
will be used for the air
ß
ow station type with the air
ß
ow
station area, with the altitude correction pa ram e ter to
cal cu late air
ß
ow .
Because the installation of the rooftop unit with its air
distribution system will affect the air
ß
ow char ac ter is tics,
a means to adjust the air
ß
ow station mea sure ments using
air balancer supplied data is pro vid ed.
Minimum Flow Measurement Operation
The
"Airfl ow Measurement Confi guration"
parameter
is set to minimum. Minimum Flow Measurement is
an approach where only the minimum required OA
ß
ow rate is measured. This is accomplished by using a
small Air Mea sure ment Station (AMS) capable of only
measuring 25% of the full
ß
ow capability of the unit.
This is a somewhat less expensive
ß
ow measurement
option and provides reasonable accuracy at low
ß
ows.
However, only air
ß
ow s up to 25% are measurable by
the system. This will be acceptable since maintaining
only the minimum ventilation requirements is what is
most important.
Full Flow Measurement Operation
The
"Airfl ow Measurement Confi guration"
parameter
is set to full. Full Flow Measurement is an approach
where the full OA
ß
ow is measured by one large AMS.
This ap proach is more expensive than the Minimum
Flow Mea sure ment approach; however, full OA
ß
ow
is mea sur able. The only disadvantage to this approach
is that
ß
ow measurement accuracy decreases as
ß
ow
rate de creas es and the inaccuracies can become quite
sub stan tial at relatively moderate
ß
ow rates.
100%
80%
60%
40%
20%
0%
0%
50%
100%
OUTPUT TO VFD
O
AD MINIMUM POSITION
2
4
3
1
Note:
For units confi gured for Constant Volume Operation, the OAD
Min Position #2 setting will be ignored and only OAD Min Po si tion
#1 will be used to set the Minimum Position of the outside air
damper.
FIG. 31 –
OAD MINIMUM POSITION RESET
LD06562
CURVE
OAD MIN.
POSITION #1
OAD MIN.
POSITION #2
1
25%
10%
2
25%
3
50%
4
80%
