12
LAT & OAT Sensors
The HeatPumPro uses both Leaving Air Temperature (LAT) and Outside Air Temperature (OAT) sensors to protect
the HVAC equipment and proactively choose the most appropriate mode of operation.
BOTH SENSORS MUST BE INSTALLED
FOR PROPER SYSTEM OPERATION
High and Low limit protection:
There are individual high end set-points for Heat Pump heating, auxiliary heat (or FF furnace) and low temperature
operating limits for cooling.
The LAT ensures that the HVAC equipment will always be operated inside the OEM specifications.
The L
AT
functions in a staged-manner:
As soon as the LAT exceeds the operative limit the equipment is staged down.
If the LAT stays outside acceptable limits for three (3) minutes then it will cycle off the equipment, leaving only
the fan running.
Proactive Staging:
The HeatPumPro can handle up to four stages of heating (two-stage heat pump with two stages of electric heat
strips or two stages of gas furnace operation). It handles two stages of cooling. The HeatPumPro manages all
staging with single stage inputs from all thermostats.
Staging is managed by continually comparing the Leaving Air Temperature to field
adjustable heating and cooling
thresholds. If the system is not maintaining the appropriate temperature then it will automatically stage up. If it
starts to move to the extremes then it will stage down. The table below outlines how the system stage
s.
The Decision Points (HST, CST, and AHS
T
) are all adjustable through the Setup Wizard. The contractor is
responsible for choosing appropriate staging settings. Multistage thermostats are not required. The HeatPumPro
will stage up as required to maintain the amount of cooling or heating that is required by the space based on the
Leaving Air Temperature and the Outdoor Air Temperature. It will stage the blower (Multi/Variable Speed Motors)
according to the Zone Weight of the ductwork being se
rved.
HVAC
Equipment
Decision Point
Function
HeatPump
Heating
Heat Stage
Threshold (HST) at
or above 30
o
F OAT
Minimum acceptable temperature in the plenum. If the system cannot
maintain HST then it will automatically stage up.
Note: If the OAT drops below 30ºF, the HST rises 1/2 ºF for every 1ºF
below 30ºF. So the system will stage more aggressively on colder
days.
Fossil Fuel
Furnace
Auxiliary Heat
Strips
Multi/Variable
Speed Blowers
Air Handler
Staging
Threshold (AHS
T
)
For Aux heat or Furnace Operations,
the system
Stages up and down
based upon the AHST
. If the system is serving more zone weight
than the
AHST
it will stage up. If it is serving less than AH
ST
then it will
stage down.
Airflow with multi/variable speed systems is controlled in
the same
manner
.
HeatPump A/C
Cooling
Cool Stage
Threshold (CST)
Maximum acceptable temperature in the plenum. If the system
cannot maintain CST then it will stage up to high stage automatically
.
