CONTROL METHODS
HeatNet Control V3 3.x
Page 28
(4) 2 million BTU HeatNet boilers = 8 million BTUs and
(1) 6 million BTU Base Load boiler.
When all (4) HeatNet boilers are running @ 95%, the Base
Load boiler is called on (demand is approx. 8 million
BTUs). As the Base load boiler comes on it introduces 6
million BTUs and the HeatNet boilers modulate down to
25% for a total output of 2 million BTUs and running at
high efficiency. The HeatNet boilers can now modulate to
the load from 1.6 million BTUs (20% mod) to another 8
million BTUs.
Not Preferred:
Example of having a larger Base Load boiler that is not of
the modulating type: If there is a 6 Million BTU Base Load
boiler running with (3) 2 million BTU HeatNet boilers, a
short cycling situation will arise when the (3) 2 million BTU
boilers are running @ 95% and the Base Load boiler is
called on. At this point there is a need for approximately 6
million BTUs. The (3) smaller boilers will then modulate
down to low fire. At this point, the (3) smaller boilers need
to shut off or the Base load boiler would need to shut off.
There is no overlap. A selection for stopping the boiler now
needs to be determined. Setting the Stop qualifier;
Modulation to 40% or a low fire rate will shut the Base
Load boiler off and allow the (3) smaller boilers to modulate
up again (short cycle of the Base Load boiler; Use the Delay
Timer and Min OFF timer). The Stop qualifier: Outside Air
is above xxF may also be used if the system design
temperature is known. Then let the Base Load boiler cycle
off its limits, whether a 2 stage, Hi/Lo, or modulating boiler.
The default setting is for the Base Load boiler to stop first
once the water temperature
exceeds the top of the heating
band.