SYSTEM OPERATION
27
NOTE
: If a heat pump is installed it will be treated
as a priority heat for a W call. To test gas heat only,
without waiting for the system to stage between the
heat pump and furnace, disconnect communications
between the indoor and outdoor unit before running
the heating test.
Control System – General Information
The furnace contains internal logic to control equipment stag
-
ing. An adjustable target runtime is available (range from 1 to
240 minutes) and set through the appropriate system menu.
The system will constantly be adjusting staging in an effort
to satisfy the thermostat call for cooling (Y only) or heating
(W Only) as close to the set target runtime as possible. See
information below for setting options.
Comfort Setting Menu (CFS): There are 6 options
available in the Comfort Setting Menu which impacts both
the System Target Runtime and Dual Fuel Operation. Dual
Fuel operation adjustments only apply if a communicating
heat pump is installed Comfort Setting Options 1 – 5 have
set values for the System Target Runtime and option
6 enables additional menus to customize all comfort
settings. See list below for the System Target Run times
associated with the first 5 Comfort Settings. These first
5 options are setup to help satisfy the thermostat slower
or faster based on the selection where option 1, with a
10 minute Target Runtime, is attempting to satisfy much
faster than option 5, with a 30 minute Target Runtime.
System Target Runtime:
Comfort Setting Option 1) 10 Minute System Target
Runtime
Comfort Setting Option 2) 15 Minute System Target
Runtime
Comfort Setting Option 3) 20 Minute System Target
Runtime
Comfort Setting Option 4) 25 Minute System Target
Runtime
Comfort Setting Option 5) 30 Minute System Target
Runtime
Dual Fuel Adjustment: This system will automatically
determine if the heat pump is capable of satisfying the
thermostat in the selected System Target Runtime. If the
heat pump is unable to satisfy in the selected time, dual
fuel settings will determine how many attempts should
be given to the heat pump before temporarily locking it
out and using the furnace. These dual fuel settings also
determine at what time the system should remove the
temporary heat pump lockout and run the heat pump again.
There are four adjustable items associated with Dual Fuel
control. In the same way as the System Target Time, each
of these items have defaulted values for Comfort Settings
1 – 5. Only when Comfort Setting 6 is selected will each
item be available for full adjustment.
1. Stage Up Percent (7 segment menu SUP): This is
a value that determines how far past the target
runtime the system should continue running the
heat pump before transitioning to the furnace. For
example, assume this menu was set to 20% with
a target runtime of 20 minutes. If the thermostat
did not remove the heating call after 20 minutes,
the system would allow for an additional 20%
heat pump run (20% of the 20 minute target is an
additional 4 minutes). In this case, the system
would transition to gas heat after 24 minutes if
the thermostat call was still present. Each time
this occurs, the system records this as a strike
against the heat pump (the strike is important
when looking at the Over Target Threshold)
2.
Over Target Threshold (7 segment menu Ott): If
the heat pump has consecutively transitioned to
gas heat for the selected Over Target Threshold
amount of times, meaning for this many
consecutive cycles it has been unable to satisfy
the target time by itself, then the heat pump will
be temporarily locked out and the furnace will
become the primary heat source.
3. Stage Down Percent (7 segment menu SdP): This
only applies when the heat pump is in a temporary
lockout condition. In this case, the system will
be trying to determine when the best time is to
remove the lockout and run the heat pump again.
To determine the best time to remove the heat
pump lockout the system looks at how easily the
furnace is able to satisfy the thermostat using
Low Stage Gas Heat Only. Assume this setting
is 15% and the target time is 20 minutes. If Low
Stage Gas Heat can satisfy the thermostat in less
than 17 minutes (20 minutes - 15% = 17 minutes)
then the algorithm records a strike against the
gas furnace. (this strike is important when looking
at the Under Target Threshold).
4. Under Target Threshold (7 segment menu Utt): If
the furnace is able to satisfy the thermostat using
Low Stage Gas Heat Only for the selected number
of consecutive cycles the heat pump lockout will be
temporarily removed. The heat pump will then be used
during the next cycle. If the heat pump can satisfy the
thermostat in less than the System Target Runtime
the temporary heat pump hold will be completely
removed and the heat pump will become the primary
heat source again. If it fails to do so, the strike count
against the furnace will be reset and the furnace will
remain the temporary primary heat source until the
Under Target Threshold is reached again.
