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Need help understanding Boiler valve
QUESTION:I got a call for this commercial building with a boiler problem. The
problem was a bad sensor for a bypass or mixing controller with a valve. I
opened the valve and seem to have fixed the problem for now.
Here is the question: What is the intent of this valve? If the valve is
fully open then the water is pumped through the boiler and to the building.
If the valve is modulated then the water bypasses the boiler and is pumped
only to the building, isolating the boiler. I have looked on the boiler
company websites to try to understand this but found nothing.
Anybody come across this before?
ANSWER: Several applications come to mind - it could be an
'anti-shock' set up, IE, do not flood the boiler with cold building
loop water. In this case, the valve will modulate open as the loop
comes up to temperature. The purpose is to protect the boiler from
thermal shock, and, in extreme cases, condensation on the outside of
the shell.
Another common application is to control supply temperature
based on an OA reverse-reset sensor, IE, the loop temp gets higher as
the outside temps get lower. The boiler then cycles on it's own
setpoint, IE 180, etc, while the loop may be very happy at 120, etc.
It could also be both in one, depending on the controls.
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