2-11
BOILER SYSTEMS AND OPERATION
SL 20-115 MODULATING GAS BOILER
5.
Each of the boiler’s 3 Load positions can be configured for any type of
heating. sl boilers are factory shipped with default settings as follows: load
1 set as
Space Heating
or
Reset Heating,
with H
igh Mass Radiant Floor
set
as the terminal type; load 2 as set Point; and load 3 as dHW. the factory
defaults can be changed using the
Define Load 1-2-3
lines to reverse the
order, turn off a load or do whatever the installer desires.
6.
once the appropriate
Loads
are set, use the left-hand key to move back to the
Setup Heating Loads
screen, then move down to
Configure Load 1
(and hit enter).
7.
The screen will display the input fields appropriate to the nature of the load
selected, e.g.
Design Outdoor Temp.
for a
Space Heating
(or
Reset Heating
)
load. Note: these fields are pre-loaded with default values that are to be
altered to reflect the desired parameters.
8.
For reset loads, the initial selection to be made addresses the “emitter” type
– choices include H(high) Mass radiant, l(ow) Mass radiant, Baseboard, air
Handler etc. an appropriate reset curve is called up through this procedure.
reset loads carry a default value for
Design Outdoor Temp.
of -10°F (-23°C).
raise or lower this as appropriate – e.g. for Vancouver or seattle, use 19°
to 25°F, while for edmonton or Fargo -30°F would be more appropriate.
note: - for some users, this adjustment may seem counter-intuitive. Moving
the setting toward a colder design value will have the effect of
reducing
the
boiler’s target temperature for any given weather, because a given current
condition is relatively warmer than the designated “coldest” day.
Moving down the screen, set the
Design Supply Temperature
– the targeted
temp. for circulating water on the coldest day. For an in-slab radiant floor
this would typically be 125°F (50°C). For finned tube baseboards typically
driven at 180°F, try 160°F max. instead, to promote combustion efficiency.
For air handlers, try running 20°F lower than typically used. of course, the
appropriate setting will depend on the characteristics of the emitter and the
building but in general the sl modulating boiler’s large throttle turndown will
allow better
average
temp. control, permitting lower
maximums.
9.
For reset loads, move down the screen again to display more lines;
use the
Summer Shutdown
field to enter a threshold temperature for the
avoidance of heating during warmer times. this is typically set at 60° to 65°F
so as to eliminate excessive boiler cycling in marginal heating conditions.
use the
Minimum Temp.
field to optimize boiler run times on low mass loads.
Finned tube baseboards sink very little heat when operated below 100°F;
application of a “full reset curve” (e.g. 160°F right down to a 70°F room
target) would cause boiler cycling in light-to-moderate heating conditions.
set baseboard minimums at 100-120°F and aim for 4 or less cycles/hr. a
minimum setting can also be used to enhance home comfort with single or
excessive speed air handlers to avoid the cool blast effect. set the lowest
possible level for combustion efficiency.
10.
For all loads, select and enter a
Maximum
allowable temperature and on/
off
Supply Differential Temp.
note these values must be input; they are not
automatically assigned as done within some boiler controls. ensure the
Maximum takes account of the construction and safety requirements of each
application – e.g., 140°F max. for typical in-slab radiant floor, for avoidance of
thermal stress. the differential shall be set to offer a reasonable temperature
control range (suggested values: 22°F for high mass radiant // 30°F for low
mass baseboards // 16°F for dHW). ensure that the spread between the
Target
and
Maximum
temps is greater than one half of the
Differential
(e.g.
for a radiant floor
Design Supply Temperature
of 125°F and a
Maximum
of
140°F, a differential of 20°F (half of which is 10°F) fits nicely.
