AERCO BMS 168 - Manual (Page 33)

4.3.5 SYS START TEMP
When in the Field Adjust Mode, the SYS
START TEMP key has two functions. First,
It lets you select the outdoor temperature at
which the system starts. Second, it lets you
select the system start option (TEMP ONLY
or TEMP AND LOAD).
For example, with the system start
temperature set at 70°F (SYS. START
RELAY 70°F), the system start relay will
close and enable the boilers when the
outside air temperature falls to 69°F (or
lower).
To always enable the boilers, regardless of
the system start temperature, or if an
outside air temperature sensor is not used,
see paragraph 4.4.2 in the System
Configuration Mode section.
• Pressing and releasing the SYS START
TEMP key once displays the System
Start Relay temperature. (AERCO
presets System Start to an outside air
temperature of 70°F). To change the
displayed start temperature, press the ▲
or ▼ arrow key.
• Pressing and releasing this key a second
time displays the System Start Option
which can be set to either outside air
temperature only (TEMP ONLY) or
outside air temperature and load (TEMP
AND LOAD). To change Start Option,
press ▲ or ▼ key to toggle the setting.
If TEMP ONLY is chosen, the BMS will
close the system start relay contacts when
the outdoor air temperature drops below the
system start temperature setting, without
regard to load.
The TEMP AND LOAD feature is used
when the System Start Relay will control
dampers. It keeps dampers closed until it is
necessary to open them for combustion.
This is designed to ensure that cold air is
not always entering the boiler room.
If TEMP AND LOAD is chosen, two
conditions are necessary for the system
start relay contacts to close and enable the
boilers. First, the firing rate (displayed as %
LOAD) must be above 11%. Second the
outdoor air temperature must be below the
system start temperature. The system start
relay contacts will open when the load
percentage falls below 7%.
4.3.6 REF TEMP
The REF TEMP key has two functions,
depending on the operating mode used by
the boilers connected to the BMS.
• In the Indoor/Outdoor Reset or Remote
Setpoint Mode, pressing and releasing
this key displays the Building Reference
Temperature (BLDG REF TEMP).
• In the Constant Setpoint Mode, pressing
this key displays the header supply water
temperature setpoint (HEADER REF.
TEMP).
To change the displayed Reference
Temperature, press the ▲ or ▼ arrow key.
4.3.7 HDR TEMP LIMIT
This key allows you to view or change the
low and high temperature limits for the
header supply water temperature.
In addition, when in the 4-to-20 mA Remote
Setpoint Mode, it automatically scales the 4-
to-20 mA signal. Accordingly, 4 mA will be
equal to the header low limit setting and 20
mA will be equal to the header high limit
setting.
• Pressing and releasing this key once
displays the header high limit
temperature (HDR HIGH LIMIT).
• Pressing and releasing this key a second
time displays the header low limit
temperature (HDR LOW LIMIT).
• Pressing and releasing this key a third
time displays the header offset
temperature (HEADER OFFSET).
To change the displayed header high, low
or offset temperature limits, press the ▲ or
▼ arrow key.
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