Install Instructions

Page 39
NEOTHERM Residential Boilers
HIGH EFFICIENCY RESIDENTIAL BOILERS
®
8.J Outdoor Air Temperature Sensor
The outdoor air temperature sensor is used with the
Outdoor Reset and Warm Weather Shutdown functions.
Connect the outdoor air temperature sensor to terminal
block 7 (TB7), using the connections labeled Outdoor
Temp Sensor.
8.K Outdoor Reset
About Outdoor Reset -
The Outdoor Reset feature calculates a correction for the
hydronic (Central Heat) setpoint depending on the outdoor
temperature. This allows the system to compensate
for changes in the outdoor temperature and run more
e󰀩ciently. (If the unit will operate as part of a Lead Lag
system, the Outdoor Reset function will adjust the Lead
Lag setpoint. For details, see “Cascading Lead Lag
Operation” - Section 8.14.)
The graph below shows how the system will behave at
di󰀨erent outdoor temperatures:
22 27 32 37 42 47 52 57 62 67 72
77
90
100
110
120
130
140
Setpoint
Outdoor Temperature °F
The sloping line in Figure 31 shows the setpoint which
is actually used by the system. Without Outdoor Reset,
this would be a constant 130°F (or whatever other value
you choose), regardless of the outdoor temperature. The
line in the graph would run straight across the display.
However, with the Outdoor Reset feature turned on, the
system will adjust for changes in the outdoor temperature.
Let’s take a detailed look at the way the setpoint is
adjusted.
• For cold outdoor temperatures (below 32°F), the
setpoint remains unchanged (130°F).
• As the temperature begins to rise above 32°F, the
Outdoor Reset function causes the setpoint to be
lowered. At these warmer temperatures, the heating
load on the system is not as great, so the system does
not have to reach as high a temperature to handle the
load.
• As you can see from the display, at an outdoor
temperature of about 70°F, the system stops adjusting
the setpoint. Above 70°F, the setpoint is constant at
100°F (or another value that you choose).
When Outdoor Reset is enabled, and the outdoor
temperature falls between the maximum and minimum
outdoor temperatures (70° and 32° in the example
above), the setpoint will be adjusted down by about .8° for
every 1° increase in the outdoor temperature.
For example, if the outdoor temperature rises by 10°, the
Outdoor Reset function will adjust the setpoint down by
about 5°. This ratio between outdoor temperature and
water temperature is adjustable.
Figure 30. - Control Panel Layout
Figure 31. – Outdoor Reset Operation