York MILLENNIUM Y22, Руководство по установке

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102777-YIM-E-0206
Unitary Products Group 87
section [not to be found by that name...]. Once requested by
this Space Sensor algorithm, the occupied heating is con-
trolled by the RAT control algorithm described in paragraph
"Morning Warm Up / VAV Occupied Heating Control Algo-
rithm" earlier in this section.
CONTROLLING EXCESSIVE SAT (SUPPLY AIR
TEMPERATURE)
This is required in cooling operation in order to prevent a dan-
ger of "slugging" and damage to the DX compressors. Roof-
top units do not use accumulators on compressor intake, and
liquid refrigerant could enter the intake of a compressor in
case of a low heat transfer on the evaporator coil. In heating
operation, the Excessive SAT control is not used.
SAT CONTROL CONFIGURATION
SAT control for cooling is configurable to enable or disable
(on/off). The default setting for cooling is ON. The user is not
normally expected to turn this mode OFF, but the possibility of
turning it OFF is provided mainly for troubleshooting purposes.
SAT CONTROL FOR COOLING
This control has priority over any other zone temperature or
SAT control and is used at all times, during CV as well as
VAV operation. The Excessive SAT Control state is entered
any time the SAT drops below the trip point of a compressor
(as the trip points are programmed in an ascending
sequence, the compressor that trips will always be the high-
est- numbered one).
While in this state, the control will continue monitoring the
SAT and turning off compressors any time the SAT drops
below the respective trip point. There is a 2 minute time delay
between compressor trips in cases when the SAT drops
below trip points of multiple compressors. This assures that
multiple compressors will not be turned off simultaneously.
ECONOMIZER LOADING OPERATION DURING AN
EXCESSIVE SAT FOR COOLING:
CV ECONOMIZER OPERATION
Economizer dampers allow mixing of outdoor and return air.
The dampers are coupled and controlled with a single actua-
tor such that when the Outdoor Air damper is fully closed, the
Return Air damper is fully open (and vice versa). The position
of the Economizer dampers is controlled based on:
• Energy considerations (“free cooling”)
• Ventilation considerations (minimum Outdoor Air damper
position and Demand Ventilation)
• Space static pressure considerations (minimum Outdoor
Air damper position).
Economizer dampers are also controlled in certain situations
to perform ”economizer loading” - which minimizes SAT tem-
perature swings resulting from turning cooling, or heating
stages on / off. This function is separate from normal econo-
mizer operation, and is separately described at the end of this
section.
When is the Economizer operation used?
If the rooftop unit is equipped with an economizer (and that
option is selected), and free cooling is available (“economizer
suitable”), then the Economizer Operation as specified in this
section will be used in the following operation modes:
CV cooling with thermostat, or zone temperature sensor con-
trol (note that in the zone sensor mode, the compressor stag-
ing algorithm defined in this Economizer section will replace
the zone sensor based control described in Sensor Operation
in CV Operation section, earlier in this document).
Minimum Ventilation Position setting
The minimum position setting represents the minimum open-
ing of the outdoor air damper (% open). This setting will be
maintained any time the unit is in Occupied mode. The mini-
mum position setting will be determined by an “Economizer
Min Position” programmable parameter set by a Palm Pilot.
The minimum position setting will be ignored during the Unoc-
cupied mode. During the Unoccupied mode, the minimum
position is 0% (the Economizer may not remain closed during
the Unoccupied mode, in case the temperature control to an
unoccupied setpoint can use Outside Air for free cooling).
Minimum Position during Heating and Occupied Mode
During heating while in Occupied mode, the economizer will
be at its programmed minimum position.
Minimum Position during Cooling and Occupied Mode
During cooling while in Occupied Mode, the economizer may
be at its programmed minimum or may be modulated
between its minimum position and 100% open position by the
economizer control.
SAT SETPOINTS USED DURING COOLING WITH
ECONOMIZER OPERATION
As long as the Economizer Operation is enabled and “free
cooling” is available, the economizer will be controlled (with,
or without any compressors running) to maintain the following
SAT setpoints: In CV cooling mode:
• With a call for first stage cooling, a programmed Econo-
mizer First Stage Setpoint. This setpoint is programma-
ble in the range of 40
°
F to 65
°
F, default setting is 55
°
F.
• With a call for second stage cooling, a programmed Econ-
omizer Second Stage Setpoint. This setpoint is program-
mable in the range of 40
°
F to 65
°
F, default setting is 50
°
F.
Criteria for Economizer Suitable decision Sensor avail-
ability:
There are three different methods of deciding whether the
economizer is suitable:
• Differential enthalpy (highest preference from energy
viewpoint)
• Outside enthalpy (middle preference) and
• Outside temperature method (lowest preference)