Goodman Mfg VC8 - Manual (Page 29)

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COMFORTNET™ SYSTEM
ECM motor. If the outdoor unit or thermostat is responsible
for determining the demand, it calculates the demand and
transmits the demand along with a fan request to the indoor
unit. The indoor unit then sends the demand to the ECM
motor. The table below lists the various ComfortNet sys-
tems, the operating mode, and airflow demand source.
System
System
Operating Mode
Airflow Demand
Source
Cooling Air Conditioner
Heating Furnace
Continuous Fan Thermostat
Cooling Heat Pump
Heat Pump Heating
Only
Heat Pump
Auxiliary Heating Furnace
Continuous Fan Thermostat
Cooling Furnace
Heating Furnace
Continuous Fan Thermostat
Furnace + Non-
Comm 1stg Air
Conditioner
Air Conditioner +
Furnace
Heat Pump +
Furnace
For example, assume the system is an air conditioner
matched with a furnace. With a call for low stage cooling,
the air conditioner will calculate the system’s low stage
cooling airflow demand. The air conditioner will then send a
fan request along with the low stage cooling airflow demand
to the furnace. Once received, the furnace will send the low
stage cooling airflow demand to the ECM motor. The ECM
motor then delivers the low stage cooling airflow. See the
applicable ComfortNet™ air conditioner or heat pump
installation manual for the airflow delivered during cooling or
heat pump heating.
In continuous fan mode, the CTK01AA thermostat provides
the airflow demand. The thermostat may be configured for a
low, medium, or high continuous fan speed. The low,
medium, and high fan speeds correspond to 25%, 50%, and
75%, respectively, of the furnaces’ maximum airflow capabil-
ity. During continuous fan operation, the thermostat sends a
fan request along with the continuous fan demand to the
furnace. The furnace, in turn, sends the demand to the ECM
motor. The ECM motor delivers the requested continuous
fan airflow.
C
OMFORT
N
ET
™ S
YSTEM
O
VERVIEW
The ComfortNet system (or CT system) is a system that in-
cludes a ComfortNet compatible furnace and air conditioner or
heat pump with a CTK01AA thermostat. A valid ComfortNet
system could also be a compatible furnace, CTK01AA thermo-
stat and non-compatible, single stage air conditioner. Any other
system configurations are considered invalid ComfortNet sys-
tems and must be connected as a traditional (or legacy) sys-
tem (see Electrical Connections for wiring connections). The
table below compares the valid CT systems.
CT compatible
Furnace
CT compatible
Air Conditioner
Full CT system
benefits and features
CT compatible
Furnace
CT compatible
Heat Pump
Full CT system
benefits and features
CT compatible
Furnace
Non-CT compatible
Single Stage
Air Conditioner
CT system
benefits and features
for furnace only
A ComfortNet heating/air conditioning system differs from a
legacy/traditional system in the manner in which the indoor
unit, outdoor unit and thermostat interact with one another. In
a traditional system, the thermostat sends commands to the
indoor and outdoor units via analog 24 VAC signals. It is a one-
way communication path in that the indoor and outdoor units
typically do not return information to the thermostat.
On the other hand, the indoor unit, outdoor unit, and thermo-
stat comprising a ComfortNet system “communicate” digitally
with one another. It is now a two-way communications path.
The thermostat still sends commands to the indoor and out-
door units. However, the thermostat may also request and
receive information from both the indoor and outdoor units. This
information may be displayed on the CT thermostat. The in-
door and outdoor units also interact with one another. The
outdoor unit may send commands to or request information
from the indoor unit. This two-way digital communications be-
tween the thermostat and subsystems (indoor/outdoor unit) and
between subsystems is the key to unlocking the benefits and
features of the ComfortNet system.
Two-way digital communications is accomplished using only
two wires. The thermostat and subsystem controls are power
with 24 VAC. Thus, a maximum of 4 wires between the equip-
ment and thermostat is all that is required to operate the sys-
tem.
A
IRFLOW
C
ONSIDERATIONS
Airflow demands are managed differently in a fully communi-
cating system than they are in a legacy wired system. The
system operating mode (as determined by the thermostat)
determines which unit calculates the system airflow de-
mand. If the indoor unit is responsible for determining the
airflow demand, it calculates the demand and sends it to the