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Bosch Buderus SSB255 | SSB399 | SSB512 Boilers Control Operations Guide
03.2018 | Bosch Thermotechnology Corp.
Data subject to change
Central Heating Mode 2
(Full Outdoor reset with no heat demand)
CH Mode“2” - Boiler demand is generated when the outdoor temperature falls
below the value of “Weather Setpoint” (par.#29). When this occurs the Boiler and
CH pump contacts are energized and the Boiler will target a system supply water
temperature corresponding to a point on the installer programmed heating curve.
(See “How to Program the Heating Curve” for details). If the System Temperature
sensor exceeds the calculated heating curve temperature by “CH Hysteresis”
(par.#7) the burner will shut off until the System Temperature sensor reads “CH
Hysteresis” below the target Setpoint Temperature. This CH Mode is for constant
circulation applications. The Boiler and CH pump contacts will remain energized
as long as the outdoor temperature is less than the value of “Weather Setpoint”
(par.#29). Using the low voltage contacts #11 and #12 it is possible to apply a
set-back to the heating curve. “Night Setback Dif” (par.# 28) controls the parallel
temperature shift that is applied to the curve when #11 and #12 contacts are
“closed” using a clock or switch.
Example:
“Weather Setpoint” is programmed for 60°F. The outdoor temperature falls below
this value. The boiler energizes Boiler and CH pump contacts. Based on the heating
curve programmed by the installer in this application, the calculated supply water
temperature on this particular temperature day corresponds to a target boiler
water temperature of 140°F. If CH Hysteresis is set for 10°F, and and the outdoor
temperature remains below the value of “Weather Setpoint”, then the burner will turn
on when the Boiler Supply Temperature sensor (System Supply Temperature sensor
for cascade) reads a temperature of 130°F or less and will remain operating until
the outdoor temperature exceeds the value of “Weather Setpoint” or if the sensor
reads a temperature of 150°F or greater. As long as the outdoor temperature remains
below the value of “Weather Setpoint” the Boiler and CH Pump contacts will remain
energized. The burner will remain off until the system supply temperature falls to
130°F.
Central Heating
(CH) Mode
Description
Set these Parameters
Parameter # Description Default Range
CH Mode = “2”
Full Outdoor reset
with no heat demand
19 Design Supply °F 176°F 68 - 194°F
20 Design Outdoor °F 24.8°F -13 - 77°F
21 Baseline Supply °F 104°F 68 - 194°F
22 Baseline Outdoor °F 69.8°F 35.6 - 86°F
23 Design Supply min 68°F 39.2 – 179.6°F
24 Design Supply max 194°F 80.6 - 194°F
25 WWSD 69.8°F 35.6 - 95°F
26 Boost Temp Incr. 0°F 0 - 54°F
27 Boost Temp Delay 20 min. 1 – 120 min.
28 Night Setback 18°F 0 - 90°F
29 Weather Setpoint 68°F 32 - 122°F
Table 4
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