2-9
BOILER SYSTEMS AND OPERATION
SL 20-115 MODULATING GAS BOILER
if outdoor reset is selected and there is no signal received from the sensor,
the controller assigns a provisional 0°C value and will adopt the appropriate
temperature target from the relevant reset curve.
See Section 2.7 Set Up & Load Definition
for activation procedure.
2.6.4 variable Speed Pumping
This section reserved
.
2.6.5 Temperature Setback
For heating loads declared as space Heating (e.g. with
Outdoor Reset
) and/
or
DHW (where a thermistor probe is used),
there are provisions for entering
temperature setback intervals. during the setback period, the boiler supply
water temperature target is adjusted from the pre-set fixed or floating (with
Outdoor Reset
) levels. there is a simultaneous movement in the
Indoor Setpoint
Temperature
or
DHW Tank Setpoint,
to yield a consistent spread and avoid
undesirable cycling. normally users would apply this feature to achieve fuel
savings during night-or-away hours. it is also possible to use the feature to
set forward (up) the temperature; this may be of use for certain commercial
applications where short-term high temperature dHW service is desired.
up to 56 events / week can be programmed for each eligible load – for example,
dHW can be set back twice and returned (twice) each day. the routine can be
applied by specific day (Mon-Sun).
the automated setback feature cannot be applied to setpoint loads, including
dHW with simple aquastat control. this is due to the lack of linkage with the
thermostat; setback without linkage could lead to unacceptable cycling.
access is via the
User Setup
screen.
2.6.6 Unoccupied Mode
users can further reduce energy consumption by switching the boiler to the
unoccupied mode during holidays or other away periods.
While in the unoccupied mode, the dHW load is turned off, while space Heating
loads for which outdoor reset is activated will drop both the circulating water and
the indoor setpoint temperature parameters to 50°F. set Point controlled loads
are not adjusted through this process, to avoid the potential for boiler cycling as
there is no linkage with the relevant thermostat.
on the main
User Setup
Menu, select
“Occupancy Status”
, then toggle between
Occupied
(top button) and
Unoccupied
(lower button) as desired.
2.6.7 Summer Shutdown
during the installer set up process, a cut-off level for outdoor temperature can be
selected - to curtail any further space heating. this is typically used to turn off an
outdoor reset enabled load once the outdoor temperature reaches a threshold
level e.g. 60°F. the load will be automatically reactivated once the weather
returns to levels below the selected threshold. use of this feature with a value 5°
- 10°F below the
Indoor Setpoint Temperature
is strongly recommended to avoid
short cycling of the boiler during very marginal heating conditions.