OPTIONAL FEATURES
HeatNet Control V3
Page 57
Preferred:
A modulating base load boiler that can accept a 4-20 mA
control signal such as the Futera series is preferred, or a non-
modulating base load boiler that is sized correctly to the If the
base load boiler is not of the modulating type, stopping the
Base Load boiler will require that the size of the Base Load
boiler in BTUs to be known relative to the H-Net boilers.
HeatNet boilers. Boiler selection is ideally; having more total
BTUs in the HeatNet boilers than total BTUs of the Base
Load boiler. This will prevent short cycling. Example: (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.
Example: Base loading relay
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 of 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.
