Gas Heat Control Mode; Variable Capacity Furnace Operation; Variable Capacity Control Of Gas Heat Mode - Lennox iComfort Wi-Fi Setup Manual

Gas Heat Control Mode

THERMOSTAT
DEMAND
SYSTEM
IDLE
Table 9. Variable Capacity Furnace Operation
Thermostat
Operation
Demands
None Furnace is off
1.Furnace BTU rate is calculated by the iComfort
tegrating algorithm.
First level heat
2.Furnace firing rate will continue at current heating
demand.
rate until first stage demand is satisfied or an addi­
tional thermostat demand is received.
1.Thermostat will immediately increase variable capa­
city furnace firing rate to the calculated BTU percent­
age representing the second stage thermostat de­
mand.
Second level
heat demand 2.Furnace firing rate will increase by 5% every 5
added
minutes (up to 100% if second stage thermostat is
not satisfied.) If thermostat second stage demand is
satisfied the current firing rate will continue until all
thermostat demands are satisfied.
1.Thermostat will immediately increase variable capa­
city furnace firing rate to the calculated BTU percent­
age representing the third stage thermostat demand.
Third level heat
2.Thermostat will increase the firing rate by 5% every
demand added.
5 minutes (up to 100% if third stage thermostat is not
satisfied.) If thermostat third stage demand is satis­
fied the current firing rate will continue until all ther­
mostat demands are satisfied.
®
Fourth level iComfort
heat demand capacity furnace firing rate to 100% until all thermo­
added. stat demands are satisfied.
®
iComfort Wi-Fi
Differential
less than 2nd stage
NO
differential
?
YES
Starting firing rate
as determined by
variable capacity
algorithm (35 to
100%)
Differential Differential
less than 2nd stage less than 2nd stage
NO
differential differential
? ?
YES
Continue at
starting firing rate
T'stat
demand
NO
satisfied
?
YES
Figure 43. Variable Capacity Operation Flow Chart
thermostat will immediately set variable
Differential
less than 3rd stage less than 4th stage
NO
differential
?
YES
Increase firing rate Increase firing rate
to calculated 2nd to calculated 3rd
stage firing rate stage firing rate
T'stat
demand sat-
isfied in less than
isfied in less than
YES YES
5 minutes
?
NO
Differential
less than 4th stage
less than 3rd stage
NO
differential
?
YES
Firing rate
increased by
5% every 5
minutes up to minutes up to
100% firing rate 100% firing rate
T'stat
demand
NO
satisfied
?
YES

Variable Capacity Control of Gas Heat Mode

The thermostat includes a feature that provides variable
capacity control of the gas heat mode. The purpose of variable
capacity control is to keep the room temperature at, or near,
the desired set point with minimum system cycling.
®
in­
The thermostat bases its "decisions" for furnace operation
control using the following inputs:
•
Room temperature,
•
History of cycle times (how long does it typically take to
bring the room temperature to the desired set point),
•
Target set point, and
•
Differential temperature settings between 1st - 4th stage.
The thermostat uses this information to vary the heating
capacity to efficiently satisfy the heating demand. The full
range of the furnace heating capacity (low end is a percent of
the 1st stage capacity; high range is 100% of full capacity) is
used. When in variable capacity gas heat mode, the furnace
operation includes longer run times at lower heat stages.
Table 9 details the variable capacity furnace operation.
SLP98 variable capacity furnaces BTUs firing rates can be
incremented by as little as 1% (35% to 100% range available)
as the thermostat may dictate. The thermostat monitors room
temperature, previous heat cycle times, and target set point to
Page 39
Increase firing
Differential
rate to 100%
until thermostat
NO
differential demand is
?
satisfied
YES
T'stat
demand sat-
5 minutes
?
NO
Differential
NO
differential
?
YES
Firing rate
increased by
5% every 5
T'stat
demand
NO
satisfied
?
YES
(G71MPP and SLP98V)
7-Day Programmable Communicating Thermostat