simplified pensotti thread, water path/pressure drop of boiler?

archibald tuttle

my questions are much reduced after talking to the American importer/manufacturer so thought I'd try this without the 20 paragraph preamble.

the only perplexity I face relative to this particular boiler is, apparently and according to Granby, if you want to move either feed or return manifold to the front, you have to move both. As best I can understand this is somewhat analogous in water jacket geomtry to keeping the passes of water within the boiler in similar order to the multiple flue passes. But I cannot for the life of me understand if there are limited vertical water passages between water layers how changing one end would affect that but not both. IF the water is normally forced to the front of the boiler and then the back as it rises through the boiler from the return to the feed I don't know how you would get 'triple' pass if the feed and return are on the same end, it would have to be double or quadruple but maybe i'm being pedantic in assuming that the number of passes is the same as the flue. further if some kind of S bent internal circulation is cast in, I can't see how moving both the feed and return to the front would equally capitalize on this if that were cast to service back entries. I kind of wish I could go to AHR and they had one of these sawed open in their booth so i could wrap my mind around it. But i might have to settle for a theoretical dissection.

It does also make me wonder if the path and direction changes give this more pressure drop than typical cast iron boiler where i really don't think about it compared to a low mass water tube style for instance. I was going to put my PONPC just where the return enters and pump away from the boiler feed thinking that the drop in the boiler itself was neglible but wondering if i should rethink.

thanks,

brian

Jamie Hall

Your suggestion of putting the PONPC in the return before the boiler and the pump after is, in my humble opinion, not a good idea. For two reasons, which are related. First, the pressure drop in the boiler may be a significant fraction of the total system head. Second, by putting the pump at the outlet, not only are you asking it to run at a lower intake pressure -- but at the highest possible intake temperature. Both of these conditions will combine to make cavitation in the pump a significant threat.

hot_rod

I would think you want that circulator discharge pumping into the boiler. Add the delta P but also assure good turbulent conditions for best heat transfer.
The only concern is with a high head circ in some cases you could end up close to relief valve setting with the circ pumping into the boiler.

archibald tuttle

damn, won't let me tag Jamie Hall so

Jamie Hall said:

Your suggestion of putting the PONPC in the return before the boiler and the pump after is, in my humble opinion, not a good idea. . . .

i'm going to call granby to check the pressure drop. i never used to consider that much on cast iron boiler. the old boiler was piped typically opposite, i.e. pump on the return and PONPC on the feed.

I think as much discussed here and given that the system basically worked fine that way even though it is the exact opposite of pumping away (with a few up and down loops needing careful bleeding attention but not any kind of day to day or week to week problem) is there a a real over under on putting the PONPC and pump on the return vs. on the feed?

My early fixation with pumping away focused on the boiler and even though the PONPC has come to be the proper focus it was perhaps that predilection and a couple physical space constraints that had me favoring the feed. although now that i find i have to put the feed and return on the same end of the boiler I could put the PONPC and pump on either pretty easily.

And now seeing @Hotrod response I'm tending to the return as he suggests. I don't need to push the system operating pressure. This is a short two story. When I get taller, I really like to push up the pressure and use the system and boiler pressure drop to protect against the 30 lbs blow off. So i'm showing more than 30 lbs going upstairs but I never hit the blowoffs because its down to mid 20s by the time it comes around and through the boiler. Nice balance.

So far the circulators (in taller buildings running higher pressure) are happy on the feeds and this is a reset system so temps aren't as high as experienced with nonresetting oil although the pensotti uses some kind of demand logic in the hydrolevel 3250 and perhaps with the sophisticated water path it can handle lower water return temps without condensing. another question for granby.

Erin Holohan Haskell

archibald tuttle said:

damn, won't let me tag Jamie Hall so

If a username is more than one word, put quotes around the username (like this "Jamie Hall") after the @ and it will tag them.

archibald tuttle

Erin Holohan Haskell said:

If a username is more than one word, put quotes around the username (like this "Jamie Hall") after the @ and it will tag them.

got it. thank you. sometimes it seems to work so i thought that wasn't it, but maybe that is when there is some punctuation mark between the two words even though i didn't notice.

archibald tuttle

@Hotrod and @Jamie Hall (see @Erin Holohan Haskell , even the slow amongst us can learn)

moving the PUMP to just upstream the boiler on the return jsut downstream of the PONPC, the convenient piping for the spiro-vent (meant in the kleenex sense, forget what brand kind I left over there) is on the horizontal return before it drops to the PONPC and Pump, and i always like them to be just upstream of the pump to help prevent cavitation by grabbing gas just before the fluid gets drawn through the pump, although IIRC there is also a case that the fluid is the hottest and turbulent through the boiler so maybe locate the vent on the horizontal of the feed just off the boiler?