Dan !

Jamie_6

Question?



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DanHolohan

The valves,

and there are two involved, would be on the bypass line, and between the bypass tee and the boiler on the return side. The water follows the path of least resistance.

Terry H.

Jamie

I don't know the whole story, just wondering. What are you trying to accomplish with the bypass?

Terry H.

DanHolohan

It's a high-volume system,

like an old gravity system. The bypass allows the boiler to come up to temperature.

Terry H.

Then

In this case the system side is taking advantage of the bypass, slowing flow through the boiler and the flow control valve is in charge of setting boiler's flow right? Would you set the flow control valve with one or both pumps running? This must be a high mass boiler.

Terry H.

DanHolohan

It's more about

limiting than setting in this case, Terry. And it can be for any boiler. What often happens with the old gravity systems, or with any old system that has large-volume radiators, is that there's so much water in the system that it exceeds the normal 15% piping/pick-up factor set by the boiler manufacturers. The bypass tricks the boiler into thinking that it's operating within a more modern system because there's less water flowing through the boiler. It gives the boiler a chance to come to temperature and shutoff. Without the bypass, the boiler runs for hours on end and uses a lot more fuel.

Yes, I'd set it with both zones calling.

Unknown

Dan , I had the same situation yesterday

There more pics under the topic - Old gravity conversion - . I piped the bypass into the return . Even with the bypass valve full open the return temp was pretty low , and the low limit would trip very fast . There are 2 returns in 1 inch copper , with ball valves on each . If I partially close both valves , the return temp will increase , giving me a longer run time on the circ ?

Unknown

Wait !

I think I might've thought like water for the first time . If I partially close the 1 1/4 inch purge valve on my return , the bypass will circulate water around the boiler - not through it , bringing it up to temp . But how do you know when it is closed enough ?

DanHolohan

When it

stops doing what it's doing. ;-)

Jamie_6

O.K.

So I put one valve (1 1/4" in this case) between the supply and the return tee in the bypass? Then I fire up the system and throttle this valve to maintain a x degree between the supply and return?

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Unknown

And you will need

a valve between the bypass tee and the boiler , on the return pipe . You throttle this valve to force water through the bypass instead of the boiler . New found knowlege is great .

DanHolohan

That's correct.

Boilerpro_3

Dan, I don't see

How the boiler would fire anymore with or without a bypass....assuming a cold start. Also, related to this,I have never figured out why one would want the boiler to run at the high temp limit.
It seems to be saying to me, "let"s get the boiler up to its highest temp and least efficient operation as quickly as possible and then cycle on the limit so we can keep it operating at that inefficient temp as long as possible". A cooler heat exchanger is more efficient, within limits for noncondensing boilers, so why do we want to get the boiler as hot as possible as much as possible? Seems to directly contradict the purpose of outdoor reset... keep the boiler cooler and more efficient as much as possible.

Attached is how I deal with low operating temp systems....P/S piping with Thermostatic mixing valve on the boiler return.

Boilerpro

DanHolohan

Your way

is better, for sure, Dave. What the bypass does is give the contractor a low-cost way of keeping the boiler from condensing for a very long time as it tries to make high-limit. It just runs on and on and on. I'd choose P/S every time, but it's often done this way here in the East because it's in the boiler manufacturer's I/O books, and it does work. Not as well, but it does work.