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6.0 NORMAL SEQUENCE OF OPERATION
Operation
The following sections provide details on how
the (-)A20 air-conditioning systems are designed
to operate under normal conditions. Under
abnormal conditions, Active Compressor and
Inverter Protection features built into the controls
may alter how the system operates to protect
the compressor and inverter from damage. The
sequence of operation is based on the system
being set up for EcoNet
TM
communications using an
EcoNet
TM
enabled air-handler or gas furnace
and an EcoNet
TM
Control Center. A section is
provided at the end that describes how the system
will operate if a conventional 24VAC 2-stage
thermostat is used in emergency situations when
communication issues are encountered to allow
the system to operate until the communication
issues are resolved.
NOTE: The use of a conventional 24VAC
thermostat eliminates many of the advanced
operating and diagnostic features the customer
has paid for and is strongly discouraged
except in temporary emergency situations until
communication issues are resolved.
6.1 Cooling Mode
The EcoNet
TM
Control Center will determine
when cooling is necessary and the percentage
of capacity required and will then communicate
this information to the EcoNet
TM
Variable Speed Out
-
door Control (VSODC) which will direct the
Power Inverter to ramp the compressor up to the
appropriate speed to meet the required capacity
percentage being requested. The percentage
of capacity required is based on the difference
between the temperature set-point and the room
temperature measured at the Control Center. One
second after the compressor starts, the VSODC
will direct the variable speed ECM outdoor motor
to operate at the appropriate speed to deliver
the necessary outdoor air-flow for that capacity per
-
centage. Upon a call for cooling, the EcoNet
TM
Control Center accesses the indoor air-flow
parameters found in the model data residing in the
VSODC memory card and directs the EcoNet
TM
enabled air-handler or gas furnace control board
to deliver an appropriate indoor air-flow level
based on the capacity percentage required at
that point in time. The EcoNet
TM
air-handler or
gas furnace control board will then direct the
variable speed ECM indoor blower motor to start
and operate at the requested cooling air-flow level.
As the building load changes throughout the call for
cooling operation, the compressor speed, outdoor fan
speed, and indoor air-flow level will respond by ramp
-
ing up or down as required to meet the building load
exactly rather than simply cycling on and off as con
-
ventional systems do.
Should the building load exceed the capacity of the
system and if the outdoor ambient temperature is be
-
tween 100
o
F [37.8
o
C] and 110
o
F [43.3
o
C], the inverter
will direct the compressor to speed up and operate at
greater than 100% capacity (Overdrive Mode) in an
attempt to meet the building load until the maximum
compressor speed is reached. Since the noise level
of the compressor increases as speed increases, the
maximum allowable compressor speed in the Over
-
drive Mode can be lowered using the EcoNet
TM
Con-
trol Center Installer Menu (RPM Blocking) should the
homeowner find the compressor noise objectionable
in the Overdrive Mode. When the call for cooling
has ended, the EcoNet
TM
Control Center will direct the
outdoor and indoor units to shut down. The compres
-
sor and outdoor fan motor will ramp down to zero RPM
and the indoor blower motor will ramp down to the
minimum air-flow level for 30-45 seconds to extract
the residual cooling from the cold indoor coil before it
stops.
6.2 On-Demand Cooling
Dehumidification
The EcoNet
TM
Control Center can be configured for
On-Demand Dehumidification. This feature allows the
system to automatically increase the level of dehumid
-
ification in the cooling mode by decreasing the indoor
air-flow by 15% when the indoor relative humidity
measured at the Control Center rises above the set-
point. Once the relative humidity drops to or below the
set-point, the indoor air-flow level returns to normal.
6.3 Low Ambient
Cooling Mode
Some applications require for space cooling when the
outdoor ambient temperature is below normal (<55°F
[13ºC]) such as a computer room or an interior space
with a heat source that must be cooled. (-)A20
condensing units are equipped with a special low am
-
bient cooling mode that allows the system to provide
cooling when the outdoor temperature is below 55°F
[13ºC] by cycling the outdoor fan to maintain an ade
-
quate condensing temperature and subcooling level
based on an input from the coil temperature thermistor.
