Ventilation Option Operation - York eco2 050 Installation Operation & Maintenance

Sequence of Operation
Sequence of Operation
Control of Compressors with Economizer
In Economizer Operation, compressors are started only
when the speciÞ ed SAT setpoint cannotbe achieved
through outside air and return air mixing. Compres-
sors will be turned ON / OFF individually.
Turning ON of Compressor #1:
If no compressors are ON, and the economizer con-
trol ler is saturated high (i.e. the economizer is 100%
open and can no longer maintain the SAT setpoint by
just free cooling),
• Calculate a temporary SAT setpoint as (SAT set-
point) T = (SAT setpoint + 5°F);
• When the SAT is 0.5°F < (SAT Setpoint) T, turn ON
compressor #1;
• Resume SAT control at SAT setpoint.
This is done in order to read and store the SAT
tem per a ture differential (drop) due to turning on
com pres sor #1, while assuring that turning it on will
not drop the SAT below compressor #1 trip point
(where the Ex ces sive SAT control would turn it off
again). The same staging sequence is used for the
re main ing compressors.
Turning on compressors #2 through #6:
If the economizer controller is saturated High (i.e. the
economizer is 100% open while one or more com pres -
sors are running and the control can no longer maintain
the SAT setpoint requested by the space control),
• Calculate a temporary SAT setpoint as (SAT set-
point) T = (SAT setpoint + 5°F);
• When the SAT is 0.5°F < (SAT Setpoint) T, turn ON
compressor #N;
• Resume SAT control at SAT setpoint.
Turning Compressors Off
Compressors are turned OFF as described in the re-
spec tive sections for CV and VAV cooling operation
with economizer suitable.
Compressor Control When Exiting Cooling Lock-
out on OAT
A situation may arise when in Economizer Mode and
one or more compressors are required in addition to
full available free cooling in order to maintain the SAT
set point, but "Cool Lockout OAT" prevents the com pres -
sors' use. This situation may arise when the SAT setpoint
is set very close to, or even below, the tem per a ture set
for Cooling Lockout on OAT – a relatively unusual case.
If the OAT then increases above the Cooling Lockout
64
on OAT parameter value while the call for several com-
pressors exists, the compressors in this case (and only
in this case) will turn ON si mul ta neous ly.
Economizer Loading Operation
Economizer Loading Operation will be used when:
• Economizer - ON
• Economizer Enable - ON
• Economizer Loading to Control SAT is ON
(SAT ECONO LOADING = ON)
• Conditions for Economizer Operation are not
suitable
• Required sensors are reliable
This is a programmable option. The user has the ability
to turn this function off. It is automatically dis abled if the
unit does not use an economizer. The on/off program-
ming choice is common to both cooling and heating.
The default setting is ON. This "Economizer Loading"
function is used only outside the normal Econ o miz er
operation.
See also corresponding description in the section on
Controlling Excessive SAT for cooling.
Economizer Loading Option In Cooling/Heating
This feature should not be used and the parameter "SAT
Econo Loading" should always be set to OFF

VENTILATION OPTION OPERATION

The 50-105 ton eco 2 rooftop units support sev er al
dif fer ent ventilation options including true Outside
Air ß ow measurement and control. Each option will be
con trolled differently, depending upon what equipment
is installed and how the unit is conÞ gured. For any Ven-
ti la tion option operation, the unit must be conÞ gured
for Economizer Operation. The ventilation options are
de scribed as follows:
Fixed Minimum OA Damper Position
This is the most common approach to ventilation con-
trol used with air handling equipment today. With this
approach, the OA and RA dampers are mechanically
linked together such that when the OA damper is open,
the RA damper is closed, and vice versa. The se quence
of operation for a Þ xed minimum position system sim ply
controls the OA damper open to a Þ xed minimum posi-
tion during the occupied mode of operation.
FORM 100.50-NOM1 (604)
YORK INTERNATIONAL