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16 COMFORTNET™ SYSTEM
16.1 Overview
The ComfortNet system is a system that includes a ComfortNet
compatible air handler and air conditioner or heat pump with
a CTK04 thermostat.
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
commands to the indoor and outdoor units via analog 24 VAC
signals. It is a one-way communication path. The indoor and
outdoor units typically do not return information to the ther-
mostat.
On the other hand, the indoor unit, outdoor unit, and ther-
mostat comprising a ComfortNet system “communicate” digi-
tally with one another. It is now a two-way communications
path. The thermostat still sends commands to the indoor and
outdoor units and may also request and receive information
from both the indoor and outdoor units. This information 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) 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 air handler controls are pow-
ered with 24 VAC. A maximum of 4 wires between the air
handler and thermostat is required to operate the system.
An inverter equipped outdoor unit does not require 24 VAC.
Only the 2 digital communication wires are required between
the air handler and inverter unit (pins 1 and 2 on the thermo-
stat connector.)
16.2 Airflow Consideration
Airflow demands are managed differently in a fully commu-
nicating system than in a non-communicating wired system.
The system operating mode (as determined by the thermo-
stat) 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
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 mo-
tor. The table below lists the various ComfortNet systems,
the operating mode, and airflow demand source.
For example, assume the system is a heat pump matched with
an air handler. With a call for low stage cooling, the heat
pump will calculate the system’s low stage cooling airflow
demand. The heat pump will then send a fan request along
with the low stage cooling airflow demand to the air handler.
Once received, the air handler 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.
I
n continuous fan mode, the CTK04 thermostat provides the
airflow demand. The CTKO4 provides 4 continuous fan speeds
(25%, 50%, 75% and 100% of maximum airflow). During
continuous fan operation, the thermostat sends a fan request
along with the continuous fan demand to the air handler. The
air handler, in turn, sends the demand to the ECM motor. The
ECM motor delivers the requested continuous fan airflow.
