Modulating Outdoor Units With Duel-Fuel; Transition From Heat Pump To Gas; Furnace Starting Point After Switching; Duel-Fuel Defrost - Lennox iComfort Wi-Fi Setup Manual

Modulating Outdoor Units with Duel-Fuel

TRANSITION FROM HEAT PUMP TO GAS

•
Steady-State: If heating demand rises above 95% Btu
capacity for 10 minutes or greater, and the temperature is
greater than 1.5ºF less then the set point then the system
will switches the heat source to gas heating.
•
Step Change State: If heating demand rises above 95%
Btu capacity for at least ten minutes and the minute slope
of the temperature sensor is less than 1°F/Hr, then the
system switches the heat source to gas heating.

FURNACE STARTING POINT AFTER SWITCHING

•
Modulating Furnace: The firing rate starts with the
minimum capacity of the furnace, and begins gas heating
using step change gains, It will switch to steady state
gains when the room temperature reaches the set point.
•
Staged Furnace: The staged algorithm is used to
determine the starting heating stage of the furnace.

DUEL-FUEL DEFROST

When the system is heating using the heat pump and defrost
cycle is initiated, the following will occur:
•
After the defrost cycle is completed, the system will return
to heat pump heating for ten minutes. During the ten
minutes period no heating mode changes will be made.
•
After the ten minute ignore period is completed, the
system conditions are checked to determine if the current
heating mode meets the system requirements.
NOTE: The defrost cycle and the 10 minute ignore time
following heat pump heating mode termination do not count
towards any timer based requirement to switch heat sources.
TRANSITIONING FROM GAS TO HEAT PUMP
1. Step Change Mode: While in step change mode, the
thermostat will not switch back to the heat pump heating.
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2. Steady-State Mode:
• With Modulating Furnace: In steady state when the
temperature is less than 0.5ºF from set point, furnace
has been running for more than 15 minutes and the
heat rate is less than 85% BTU capacity, then the heat
pump will become the primary source of heat.
• With Staged Furnace (assumes a staged control
routine): In steady-state when the staged furnace
demand satisfies the heat set point, the system will
switch back to heat pump heating as the primary heat
source again.
HEAT PUMP STARTING POINTS AFTER SWITCHING
1. From Modulating Furnace to Modulating Heat Pump:
The thermostat uses step change gains for the first 20
minutes, and a starting heat rate at least 10% higher than
the minimum rate.
2. From Staged Furnace to Modulating Heat Pump:
Starts with 70% demand.
3. Modulating Gas Furnace:
• The installer sets the maximums heating CFM
required in each zone. The sum of all the active zones
CFMs allows the thermostat to interpolate the furnace
heating rate. This correlates to the set zone CFM by
using the high heating airflow and low heating airflow
parameter values from the furnace. This is used as
the starting
temperature that has been set, and will be used each
time the blower CFM changes its value.
• If the DAS temperature is lower than the target, the
thermostat increases the demand by 5% every two
minutes until the DAS is within the target window. If
the DAS is higher than the target, the thermostat
lowers the demand by 5% every two minutes until the
DAS temperature is within the target window.
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point for maintaining the DAS