PONPC with primary secondary piping

dobro23

Hey guys just asking for your opinions on where the expansion tank and feeder should be located on a wall hung condensing boiler such as a Navien Combi or NHB etc. Most piping diagrams show the air separator, tank, and feed on the primary loop supply header just prior to the zoning. Just wondering if it would be equally effective on the boiler loop? (secondary loop) For example, between the boiler supply tapping and the branch of the primary/secondary tees. As long as i have valves properly set up for purging etc I can't see that it would make too much of a difference. Maybe the piping diagrams are drawn that way for ease of explanation or installation? what do you guys think? Am I missing something?

neilc

take this light heartedly, I'm not trying to offend.

So you read the manuals, participate here, have seen the disasters, and you still want to go RE ENGINEERING this?
why ? (all the rest of the emojies)

The PONPC on the primary loop makes the primary the PONPC for all the secondaries / zones / boiler injector(s),
or, cause, Dan says so(?), (all of the emojies)
pretty sure I know this from Pumping Away, and all the hydronic manufacturers.

dobro23

not offended at all Neil and i appreciate the insight. just trying to understand. Again, not sure if the manuals are saying this for ease of illustration etc. In my situation of question, the HOUSE is the primary and the BOILER is the secondary.

Tinman

I like to look at it as system loop and boiler loop. @neilc is correct. Siggy says it. Dan says it. Manufactuers say it and it makes perfect sense.

rick in Alaska

May be so, but I don't see any particular reason you couldn't. As long as everythi ng is going away from the ponpc, why not.
Sorry, I am a "I don't care what so and so said" kind of guy, and am more of a "why" kind of guy. I like to know why, and in this case, just because it is different, what is the issue?
Rick

Tinman

Most manufacturer's drawings show the boiler loop as the secondary loop and from the runs of those two closely spaced tees is the primary loop or system loop. When the tank is installed in that system loop, all the zones would then be pumping away from the PONPC.

hot_rod

There are a number of ways to pipe primary secondary, here are some examples. I included my suggestion for the expansion tank connection.
With hydro-sept there are a number of connection points for the exp tank that are acceptable.

Often piping arrangements that are claimed to be primary secondary are not

If it doesn't involve closely spaced tees, a hydro separator or properly piped buffer, it is not a true P/S, in my mind.

Tinman

@dobro23 - I've gone to using hydraulic separators on almost every job. It's a no brainer for me especially when I'm using multiple boilers. They work great, serve multiple purposes, and clean up the near boiler piping. Forget about the cost difference. When customers see the work you do, your attention to detail, how well the systems work, and how professional your piping is; you'll make that up with all the referrals you're going to get.

Our industry's history has been pretty interesting. These concepts - P/S piping, low loss headers (hyd. seps.), pumping away, and others; have been around forever. It's taken some really smart people (manufacturers, writers) to bring them back.