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Sequence of Operation
Central Heating Operation
The control operates either one or two steam boilers to heat a
building using an Outdoor Reset algorithm to progressively run
the steam boiler longer when the outdoor air temperature is
colder . In this way the building heat loss is replaced by heat from
the boilers .
The central heating operates on a cycle that consists of four
phases:
1 . Establishing Steam
2 . Heat On
3 . Heat Off
4 . Cool Down
The cycle repeats until the central heating system is shut off
when the outdoor air temperature exceeds the Warm Weather
Shut Down (WWSD) setting . The Cool Down phase requires
the installation of a condensate return sensor and this phase
will be skipped when not installed .
Establishing Steam
In steam heating systems, there is a time delay between
when the steam boiler or steam valve is turned on and when
the steam reaches the furthest radiator in the system . It is
important for the control to determine this time delay to ensure
proper heating in all rooms . The control uses either a con-
densate return sensor or a minimum run time to complete the
Establishing Steam phase .
Condensate Return Sensor
The best method to determine establishing steam is to measure
the condensate return temperature when steam enters the
furthest radiator in the building . If possible, install condensate
return sensor on the return pipe of the furthest radiator .
Alternatively, the condensate return sensor may be installed in
the boiler room . It is important that the Universal Sensor 071
be strapped to the bottom of the return pipe in order to
measure the condensate return temperature .
To set the Establishing Steam setting, use the Max Heat
Override at 100% output to operate the system . Record the
Condensate sensor reading when steam reaches the furthest
radiator . Then exit the Max Heat Override, and enter the
recorded condensate return temperature into the Establishing
Steam setting in the System menu .
Minimum on Time
In cases where a condensate return sensor cannot be
installed, a Minimum On Time can be set to account for the
establishing steam time period . Setting a Minimum On Time for
a steam system can be problematic because a system takes
more time to reach operating temperature from a cold start
than when it is hot from a previous cycle .
To set the Minimum On Time setting, use the Max Heat
Override at 100% output to operate the system . At the same
time, start a stopwatch timer . Measure the amount of time
required for steam to reach the furthest radiator . Then exit
the Max Heat Override and enter the recorded time as the
Minimum On Time setting .
Last Radiator
One Pipe System:
Radiator
Vent
Best
Main
Air Vent
OK
Supply Main
Condensate Return
Sensor Location
Two Pipe System:
Most Distant Radiator
Thermostatic
Trap
Best
Supply
Air Vent
Return
Air Vent
Condensate Return
Sensor Location
Float and
Thermostatic
Trap
