SERVICING
37
STATIC PRESSURE DROP
If the total external static pressure and/or static pressure
drop exceeds the maximum or minimum allowable statics,
laid out duct work.
AIRFLOW CONSIDERATION
-
nicating system than in a non-communicating wired system.
The system operating mode (as determined by the thermo-
-
mand. If the indoor unit is responsible for determining 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
motor. The table below lists the various communication sys-
System
System Opera�ng
Mode
Airflow Demand
Source
Cooling Outdoor Unit
Heat Pump Hea�ng
Only
Outdoor Unit
Con�nuous Fan Thermostat
HP + Electric Heat
Strips
Either Outdoof Unit
or Indoor Unit,
which has higher
Airflow demand
Electric Heat Strips
Only
Indoor Unit
Gas Furnace Combus�on Heat Indoor Unit
Any
Air Handler or
Modular Blower
For example, assume the system is an outdoor unit matched
with an indoor unit. With a call for cooling, the outdoor unit
-
door unit will then send a fan request along with the cooling
-
tinuous fan mode, the communicating thermostat provides
-
uous fan speeds (25%, 50%, 75% and 100% of maximum
sends a fan request along with the continuous fan demand
to the indoor unit. The indoor unit, in turn, sends the demand
to the ECM motor. The ECM motor delivers the requested
To Next Page
