YORK INTERNATIONAL
68
Sequence of Operation
FORM 100.50-NOM1 (604)
The Primary Unit Controller will use the difference
be tween the Supply Air Temperature setpoint during
econ o miz er operation and the measured SAT and will
increase the air
ß
ow above the
"Min. Outside Airfl ow"
to maintain the Supply Air temperature setpoint. The
result is air
ß
ow through the damper will always be =>
the
"Min. Outside Airfl ow".
• Mode 1 - Damper #1 and Damper #3 will be op-
er at ed as described in
Airfl ow Control - Econ o miz er
Not Avail able
to satisfy the SAT tem per a ture re-
quire ment using the increased air
ß
ow.
The Mode 1 to Mode 2 transition occurs when:
• The maximum AMS #1 velocity con di tion for Mode
1 air
ß
ow is present for 5 minutes or
• Damper #3 (Return Air) is closed for 5 min utes
Mode 2 operation is as follows:
• Damper #2 is modulated open to main tain the SAT
Tem per a ture Setpoint (as in economizer control
with out an AMS)
• Damper #1 and Damper #3 will be controlled to
main tain the
Minimum Flow Setpoint
• During this Damper #1 and #3 op er a tion, the max-
i mum closure of the Damper #3 (Return Air) will
be de ter mined by that required to limit the air
ß
ow
rate through AMS #1 to =< 1500 fpm. Divide the
air
ß
ow by the area in Table 18 to determine the
velocity.
The Mode 2 to Mode 1 transition will occur when
Damp er #2 is continuously closed for 5 minutes.
The following
Þ
gure illustrates the control functions.
FIG. 34 –
MINIMUM FLOW MEASUREMENT
OPTION,
ECONOMIZER
SEQUENCE
Full Flow Measurement
If the Con
Þ
guration setting
"Airfl ow Measurement Con-
fi g"
is set to 2 (full), then the unit will be equipped with
full
ß
ow measurement equipment. This ar range ment
consists of one AMS sized for 100% total unit
ß
ow.
The following
Þ
gure details this arrangement. With
this arrangement, the outside and return air dampers
are mechanically tied together. Only one Analog Output
(AO) is required for this option.
FIG. 35 –
FULL FLOW MEASUREMENT
ARRANGEMENT
A differential pressure transmitter is used to mea sure a
differential pressure across the AMS, which will cor-
respond to an average velocity through the AMS. The
measured dif fer en tial pressure (AI 11) will be con vert ed
by the con trol ler to an approximate
ß
ow as given in
the section on
Air fl ow Mea sure ment Computation
. The
entered data is for AMS #1.
In the unoccupied mode of operation the OA Damper
is at 0% and the RA Damper is at 100%.
Flow Control - Economizer Not Available
When the unit is in the occupied mode of operation,
and:
•
Airfl ow Meas Confi g
= 2 (full)
•
Economizer Enable
= OFF or
Open (100%)
Damper
Position
Closed (0%)
Mode 1 CFM required for
transition to Mode 2
(1.10" Minimum Flow
Setpoint)
Mode 1
Mode 2
#1
#2
AMS #1 MEASURED
CFM
OUTDOOR AIR
FLOW CFM
LD06565
Return Air
Exhaust
Air
Outside
Air
OA
DAMPER
#1
OA
DAMPER
#2
Air
Measuring
Station
LD06566
