Lennox iComfort G71MPP-03 Setup Manual page 23

HIGH BALANCE POINT
If the outside temperature is above the programmed high balance point (set by default at
50°F), auxiliary electric heat operation or furnace operation (in dual fuel system) is not
allowed. This ensures that the lower cost heat pump operation will satisfy the heating
demand, rather that the more expensive auxiliary electric heat. The high and low balance
points will not lock out both compressor heat and auxiliary heat/furnace at the same time.
DUAL-FUEL APPLICATIONS
The following information is applicable to communicating systems only.
1. Staged Operations
Dual fuel applications, which include both a Heat Pump (XP17 or XP21 only) and a
gas furnace, will provide multiple stages of heating. For example, a two-stage heat
pump would deliver two stages of heat. The gas furnace can add two to four more
stages of heat. Figure 37 flow chart illustrates Dual Fuel operation with Balance
Points.
2. Variable Capacity (Modulating) Operations
YES
if
T'stat
outdoor
heat
temperature
YES
demand
is...
?
YES
Shut down FURN
®
iComfort Wi-Fi
Shut down HP
Stg 1...Stg 2
NO
T'stat
heat
demand
?
FURN
heat
Operate HP
lockout
Stg 1...Stg 2
at
HP stage(s) operate first;
or above
then FURN stage(s) (if
HBP
needed; see NOTE 1)
between
Operate HP
HBP and LBP
Stg 1...Stg 2
(See NOTE 2)
at or
below
LBP
Operate FURN
Stg 1...Stg 2
Operate FURN
Stg 1...Stg 2
T'stat
heat
Heat pump
demand
? lockout
NO
Stg1...Stg 2
Figure 37. Dual Fuel Operation with Balance Points
Dual-fuel applications, which include both a variable capacity heat pump (XP25)
and a variable capacity gas furnace (SLP98), will provide variable capacity heating.
3. Tempering — Staged Furnace
Dual-fuel tempering staged furnace employs no sensor implementation. Furnace
cycles on and off at first stage rate.
S
First cycle on-time is longer than subsequent times to bring temperature up.
S
Subsequent times are shorter to maintain temperature.
4. Tempering — Variable Capacity (Modulating) Furnace (SLP98)
Dual-fuel tempering staged furnace employs no sensor implementation. Furnace
starts heating at minimum heat rate while defrost is active.
S
Testing has shown the entering air is within acceptable limits.
S
During defrost the airflow will run at second-stage CFM.
Abbreviations:
FURN = auxiliary heat provided by gas furnace
HP = compressor heat
LBP = Low Balance Point
HBP = High Balance Point
T'stat = thermostat
NOTE 1 - Each Heat Pump and Furnace Heat stage will operate
until it meets the demand or until its stage timer lapses (20
minutes by default). If the timer lapses before the demand is
met, the system brings on the next stage in order of:
NOTE 2 - The chart below illustrates how the balance points
control whether HP or FURN will operate to provide heat.
50ºF
T'stat
heat
NO
demand
25ºF
?
YES
YES
NOTE 3 - If emergency heat is selected, Furnace is used.
T'stat
YES
heat
demand
?
NO
Page 23
HP-stg-1, HP-stg-2, FURN-stg-1, FURN-stg-2.
COMPRESSOR ONLY
HBP - FURNACE LOCKOUT
TEMPERATURE
EITHER COMPRESSOR OR
FURN HEAT
LBP - COMPRESSOR LOCK
OUT TEMPERATURE
FURN ONLY
7-Day Programmable Communicating Thermostat