30
Operation
6.0 NORMAL SEQUENCE OF OPERATION
The following sections provide details on how
the (-)P20 heat pump 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
Outdoor 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
percentage. 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 ramping up or down as
required to meet the building load exactly rather
than simply cycling on and off as conventional
systems do. Should the building load exceed
the capacity of the system, 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 Overdrive Mode can be lowered
using the EcoNet
TM
Control 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 compressor
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 dehumidification 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. (-)P20 heat pumps are equipped with
a special low ambient 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 adequate condensing
temperature and subcooling level based on an
input from the coil temperature thermistor.
6.4 Heating Mode
The EcoNet
TM
Control Center will determine
when heating is necessary and the percentage
of capacity required and will then communicate
this information to the EcoNet
TM
Variable Speed
Outdoor 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
