Laars MASCOT LX, Service Manual

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54
Mascot LX Service Manual
Fig. B18-1 - Setpoint Corrections Using Outdoor Reset
About Outdoor Reset
The “outdoor reset” function allows the system to
automatically use a lower setpoint for Central Heat
when the outdoor temperature rises. This allows the
unit to run more efficiently in warmer weather. Fig.
B18-1 shows some different setpoints at different
outdoor temperatures.
First, let’s see how the system behaves when out -
door reset is not turned on. Point “A” represents a
cold day. The outdoor temperature is 20°F, and the
control system is using a CH setpoint of 170°. Even
on a much warmer day, with an outdoor temperature
of 80°F, the CH setpoint is still the same - 170°. The
unit will run correctly when it is set up this way, but
the setup could be more efficient. At 80°F, the unit
will fire occasionally at 100%, and do this for short
periods of time. This is not the most efficient way for
this unit to operate.
Now let’s say that the unit is using Outdoor Reset.
At point “A”, the conditions are still the same - out -
door temperature 20°F, CH setpoint 170°. But using
Outdoor Reset, you can set the controller to lower the
CH setpoint as the outdoor temperature rises. (To
put this another way, the SIT controller allows you
to set the “slope” of the Outdoor Reset correction.)
At point B, the outdoor temperature is 80°F. In this
example we have set the controller to automatically
lower the CH setpoint to 50°.
The SIT controller in the Mascot LX allows you to
set the starting and stopping points for the Outdoor
Reset correction. You can do this by changing some
settings using the “Installer” mode.
Changing the Outdoor Reset Setpoints -
Go to the “Installer” mode:
1. Press and hold the OK/Select and Down buttons
for 5 seconds to go to Installer mode.
2. Use the Up and Down buttons to go to the setting
you want to change - P61 through P64 for Out -
door Reset.
3. To make a change, press the OK/Select button.
Use the Up and Down buttons to change the
value.
4. Press and hold the OK/Select button to save the
new setting and leave Installer mode.
180
160
140
120
100
80
60
40
0 20 40 60 80
With outdoor reset
A
B
With no Outdoor Reset correction
Starting Point for Outdoor Reset Correction -
We have shown this as point “A” on the chart.
P61 - Low Outdoor Temperature Setpoint (LOD)
This is the outdoor temperature where you want the Out -
door Reset correction to begin. In the example shown here,
this would be 20°F. You could also start the Outdoor Reset
correction at another temperature.
P62 - High Boiler Temperature Setpoint (HBT)
This is the boiler setpoint temperature at that outdoor tem -
perature (point “A”). In this example, this would be 170°, but
you could enter a different temperature.
End Point for Outdoor Reset Correction -
This is shown as point “B” on the chart.
P63 - High Outdoor Reset Temperature Setpoint (HOD)
This is the outdoor temperature where you want the Out -
door Reset correction to end. In this example, this is set to
80°F, but you could use another value.
P64 - Low Boiler Temperature Setpoint (LBT)
This is the boiler setpoint temperature at that outdoor tem -
perature (point “B”.) We used 50° in this example.
• The warm weather shutdown feature is always active
when the outdoor sensor is installed. See Installer Pa -
rameter P65 - Warm Weather Shutdown.”
• If the outdoor temperature sensor is disconnected or not
working, you may see the message “N06 - Outdoor tem -
perature sensor not working.” If this condition contin -
ues, the controller will operate at a setpoint of 140°F or
the value of Installer Parameter P62, whichever is lower.
B18
cont.
Outdoor Reset (continued)