CONTROL METHODS HeatNet Control V3
Page 26
Figure 24 Base loading with Dominator boiler
Enable the base load feature by setting:
ADVANCED SETUP: SYSTEM: OPTION to BASE
LOAD. This setting the OPTION Relay to be used as
control for a Base Load Boiler.
1. ADVANCED SETUP: SYSTEM: OPTION to BASE
LOAD. This setting the OPTION Relay to be used as
control for a Base Load Boiler.
2. The ADVANCED SETUP: BASE LOAD BOILERS:
BASE LOAD BOILERS: to 1. Currently allows (1)
base load boiler.
3. The START & STOP qualifier condition to the method
discussed below.
4. The DELAY TIME to the amount of time required
after the start qualifier condition has been met to start
the boiler.
If a MINIMUM OFF time of the Base Load boiler is
needed, the Base Load boiler will share the MIN OFF TIME
of the boiler controlling it. If the base load boiler was
running and shuts off, the MIN OFF TIME will need to
expire before the boiler can start again. Once this time
expires, the DELAY TIME also needs to expire to start the
boiler. This will help in minimizing short cycle conditions
and can be set at: ADVANCED SETUP: FIRING MODE:
MODE: MIN OFF TIME.
Preferred:
A modulating base load boiler that can accept a 4-20mA
control is preferred or a non-modulating base load boiler
that is sized correctly to the H-Net boilers. Consider the
Futera II or the Dominator series for the Base Load role.
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
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.
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; OA T > 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
.
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