Slant/Fin Oil Hot Water - Manual (Page 15)

15
THE BOILER STAGING CONCEPT
The heart of the Caravan boiler plant is a temperature-actuated
control system that automatically stages only those boiler
modules needed to meet the heating demand in a given period,
thereby conserving fuel.
In a staging control system, each stage ordinarily activates one
boiler module. With appropriate wiring, multiple modules can be
grouped within a stage.
During a fluctuation in heating requirements, a large central boiler
cycles on and off to match heat output to building demand. A
staged modular boiler system, on the other hand, will energize
only as many modules as the system load requires. Only one
stage cycles at a time. The other stages remain off or operate
continuously, thereby performing at peak efficiency. For example,
in a 10 module boiler system, with the heating load at 61% of
capacity, six of the modules operate continuously at peak
efficiency. Fractional heating requirements are supplied by the
seventh "cycling" module, while the remaining three modules are
"off." This is in contrast to a single large central boiler that simply
cycles on and off, resulting in lower efficiency.
Over-sizing is a major factor in poor system efficiency. Most of the
time a single central boiler is oversized. Historical data shows
that many single central boilers are considerably oversized even
at the outdoor temperature for which they were designed.
Modular boiler systems are not oversized by more than a portion
of one module, regardless of the load.
The Caravan control system automatically compensates for
seasonal temperature changes. It energizes more or fewer
modules depending on changes of outside temperature, system
water temperature, or both. Modules save energy by operating in
long cycles at full-rated output and maximum efficiency.
CONTROL SYSTEM SELECTION
Slant/Fin offers two controls to step fire a hot water Caravan sys-
tem. The SC-3 and SC-9 controls fulfill a wide range of applica-
tions. They control the boiler system and are not intended to be
the sole building temperature control. They do not replace zoning
the system or the thermostats that control these zones.
SC-3 Control
The SC-3 control allows up to 3 stages in a Caravan system.
Generally each stage controls 1 module. However, it is possible to
have more than 1 module activated with each stage.
Standard programmable features include: system activation or
de-activation based on outdoor temperature; minimum target
supply water temperature; adjustable design target supply water
temperature; adjustable delay between stages; adjustable
outdoor temperature and indoor design temperatures.
The view menu on the control includes error messages, actual
outdoor air temperature, actual supply water temperature,
target supply water temperature and running time for each stage.
This control can be programmed as follows:
1. Outdoor reset: The supply water temperature is
automatically adjusted up or down based on outdoor
temperature. The control automatically controls the
number of modules required to maintain required supply
water temperature.
2. Setpoint temperature: The control can be programmed
to maintain a set supply water temperature. The control
automatically controls the number of modules activated to
maintain the setpoint temperature.
SC-9 Control
The SC-9 control allows up to 9 stages of operation for space
heating, domestic water or combination, in a Caravan system.
Generally each stage controls 1 module. However, it is possible
to have more than one module activated with each stage.
Standard programmable features include: system activation or
de-activation based on outdoor temperature; minimum target
supply water temperature; adjustable design target supply water
temperature; adjustable delay between stages; adjustable
outdoor and indoor design temperatures; delay to allow
combustion air damper to open; ability to provide equal run time
rotation of boiler modules; fixed lead of a module when Caravan
system activates; first on/last off or first on/first off for modules;
control of primary circulator and periodic exercising of primary
circulator when system is inactive.
The view menu on the control includes error messages, actual
outdoor air temperature, actual supply water temperature,
target water temperature, running time for each stage and the
difference between supply water and return water
temperatures.
The SC-9 can be programmed as follows:
1. Outdoor reset: The supply water temperature is
automatically increased as outdoor temperature
decreases and decreased as outdoor temperature
increases. The control activates only the number of stages
required to maintain the required supply water
temperature.
2. Setpoint temperature: The control maintains a set supply
water temperature. The control activates only the number
of stages required to maintain the setpoint temperature.
Setpoint temperature may be used for a Caravan system
that is dedicated for use as volume water heating.
3. Domestic hot water: The domestic hot water controls
override the SC-9 control for only those modules used to
heat the domestic hot water. The modules for domestic
hot water are isolated from space heating system until
demand for domestic hot water is satisfied. The modules
not used for domestic hot water heating remain under
control of SC-9 control.
Slant/Fin offers domestic hot water control packages and
external tankless heaters as options for use with the SC-9
control.
CONTROLS