Installation Guide

37
C OMFORT N ET ™ S YSTEM
OVERVIEW
The ComfortNet system is a system that includes a ComfortNet
compatible furnace and air conditioner or heat pump with a CTK0*
thermostat. A valid ComfortNet system could also be a compat-
ible furnace, CTK0* thermostat and non-compatible, single stage
air conditioner. Any other system configurations are considered
invalid ComfortNet systems and must be connected as a tradi-
tional (or non-communicating) system (see Electrical Connec-
tions for wiring connections).
A ComfortNet heating/air conditioning system differs from a
non-communicating/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 com-
mands to the indoor and outdoor units via analog 24 VAC signals.
It is a one-way communication path in that the indoor and out-
door units typically do not return information to the thermostat.
In a ComfortNet system, the indoor unit, outdoor unit, and
thermostat comprising a ComfortNet system “communicate” digi-
tally with one another, creating a two-way communications path.
The thermostat still sends commands to the indoor and outdoor
units. However, the thermostat may also request and receive
information from both the indoor and outdoor units. This infor-
mation may be displayed on the ComfortNet thermostat. The
indoor 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 between
the thermostat and subsystems (indoor/outdoor unit) and be-
tween subsystems is the key to unlocking the benefits and fea-
tures 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 equipment
and thermostat is all that is required to operate the system.
AIRFLOW CONSIDERATIONS
Airflow demands are managed differently in a fully commu-
nicating system than they are in a non-communicating wired
system. The system operating mode (as determined by the
thermostat) determines which unit calculates the system
airflow demand. If the indoor unit is responsible for deter-
mining the airflow demand, it calculates the demand and
sends it to the ECM motor. If the outdoor unit or thermo-
stat is responsible for determining the demand, it calcu-
lates 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 systems, the operating mode, and air-
flow 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 cool-
ing 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 instal-
lation manual for the airflow delivered during cooling or heat
pump heating.
In continuous fan mode, the CTK0* thermostat provides the
airflow demand. The thermostat may be configured for a
low, medium, or high continuous fan speed. The low, me-
dium, and high fan speeds correspond to 25%, 50%, and 75%,
respectively, of the furnaces’ maximum airflow capability.
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 continu-
ous fan airflow.
FOSSIL FUEL APPLICATIONS
This furnace can be used in conjunction with a ComfortNet com-
patible heat pump in a fossil fuel application. A fossil fuel appli-
cation refers to a combined gas furnace and heat pump installa-
tion which uses an outdoor temperature sensor to determine the
most cost efficient means of heating (heat pump or gas fur-
nace). When used with the CTK0* thermostat, the furnace/
heat pump system is automatically configured as a fossil
fuel system. The balance point temperature may be ad-
justed via the CTK0* thermostat advanced user menus (see
CTK0* instructions for additional information).