SYSTEM OPERATION
8
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.
The system will automatically make adjustments in an
attempt to satisfy the thermostat as close to this target
runtime as possible. After a power cycle or mode change
(cooling to heating or heating to cooling) the system will
run full capacity for the selected mode during the first
thermostat call. Based on the selected target runtime and
how long the initial cycle takes to satisfy the thermostat,
the control algorithm will adjust the system stage times for
a 2 stage unit or the capacity demand percentage for an
inverter / modulating unit for the next cycle. Note: actual
run times may change depending on variations of load
throughout the day.
The following table shows the default values for all Comfort
Setting Options (1 – 5)
Comfort
Setting
Option
Target
Time
(Minutes)
Stage Up
Percentage
(%)
Stage Down
Percentage
(%)
Over Target
Threshhold
(Strike Count)
Under Target
Threshhold
(Strike Count)
1
10
20
20
2
10
2
15
20
20
4
8
3
20
20
20
6
6
4
25
20
20
8
4
5
30
20
20
10
2
The following table shows the ranges for each of item
when the adjustable Comfort Setting Option 6 is selected.
The table shows the minimum value, the maximum value
and the defaulted value. All items can be adjusted up or
down by increments of 1 which provides full flexibility
for all items. Note: it is critical that these numbers be
set properly. If Comfort Setting option 3 is desired but
a target time of 60 is preferred, select Comfort Setting
Option 6 to enable all the adjustable menus, set the
Target Time to 60 and make sure the other menus are
set to match that of Comfort Setting Option 3.
Menu
Minimum
Value
Maximum
Value
Default
Value
Target Time (t9t)
1 minute
240 minutes
60 minutes
Stage Up Percent (SUP)
0%
100%
20%
Stage down Percent (SdP)
0%
100%
20%
Over Target Threshold (Ott)
1 strike
254 strikes
20 strikes
Under Target Threshold (Utt)
1 strike
254 strikes
20 strikes
