Condensing Boiler, Primary/Secondary Piping

F Reynolds

Ok, the meter reading was wrong. I looked at instructions on how to read the meter, and found that it was read incorrectly. I'll call them tomorrow about it. Sorry for the confusion.

F Reynolds

P/S Piping

Dan, maybe this could be a topic for an article in the Magazine.

(Condensing Boilers, Primary/Secondary Piping)

My heating professional is laughing at me. Calls me the internet guy because I’ve picked up all the lingo. I think he is enjoying our conversations, but then again, I may be annoying him.

He piped my Weil-McLain Ultra without a boiler loop (P/S) configuration. He said he though it would work better that way, and I can't diagree. )It appears to be running great, however I only have about an 8 degree Delta T. Maybe if I slowed it down I could transfer more of that energy to warm the rooms, and not return the water to the boiler hot.) Kal hooked me up with Weil-Mclain guy who said it should be piped P/S.

Now, I have searched this vast internet for a site, document, or little known transcript for any discussion, information or insight as to WHY it must or should be piped P/S. I post this not only for me, but for others who find themselves with a condensing boiler and the same question.

If I have only one zone, and am desirous of having the coolest return water possible returning to my condensing boiler, why do I have to pipe it P/S? P/S piping (when I say that I mean a boiler loop) is talked about often as a way to protect the non-condensing boiler from thermal shock and to prevent condensation, but that is not an issue with my boiler. I have read a lot of Dan’s information, articles and postings on piping (Yes Dan, you are the King!) However, I haven’t read anything about P/S piping and condensing boilers other than “that is the way to do it”. I don’t want my return water blended with supply to provide a warmer return that won’t shock my boiler, I want it as cold as possible. Ask Floyd, I don’t think you can shock it.

After all I’ve read, and the information posted by Dan on gravity conversions needing slower, high volume flow when installing a circulator, I can only see two reasons for P/S piping:

a. To assist in configuring multi-zone systems

b. To allow addition of an additional circulator, like the B& G Series 100 as Dan suggests to provide high volume, low head pressure flow to mimic gravity flow, as there is not much resistance in the piping. (I can’t imaging a 25 GPM, 3/12 head pressure circulator being able to push enough water through the Ultra to keep it from shutting down).

I'm leaning towards a Taco 0011 on the loop and a Taco 007 for the secondary (system flow), becuase it is a gravity conversion. Any comments?

Thanks again for the information and assistance. Reynz

Boilerpro_3

P/S piping

P/S piping is often used for boiler temperature protection, which it does not necessarily provide, but also to make sure that the boiler has adaquete flow in all types of systems. P/S piping of a boiler allows the boiler pump to be chosen for the boiler flow requirements, while a separate pump is chosen for the system requirements.

Also, boiler thermal load shock protection and protection from low temps are two separate issues, IMHO. I believe many condensing boilers can be damaged or the life greatly reduced by rapid flucuations is temperature. Shock protection for condensing boilers is a subject that has not come to the forefront yet, it seems, and I beleive the industry is going to suffer for not paying attention. The dynamics that cause damage to convectional cast iron or steel boilers are still in place with many condensing designs, so I cannot see how the problem has been solved just by making a boiler that can operate at low steady temps for improved efficiency.

It would be great to hear from the condensing boiler manufacturers on the subject of thermal load shock. I suspect that the cast block of the Ultra can be damaged by thermal load shock and this may be why, in part, P/S piping is recommended. Ask Weil- Mclain, and I'm sure they will tell you the whys of their installation recommendations. Most boiler manufacturers are getting pretty specific how they want thier boilers piped, and for good reason. Poor installs are a plague on the industry and it makes the manufactureer look bad when their product only fails after a few years of use.

Boilerpro

F Reynolds

P/S Piping

Thanks. I'll tell you there is absolutely no information about WHY out there.

Boilerpro_3

Well, you came to the right place

However, at this time of year most of the great minds here are pretty busy, so replys will be a little slow in coming.

Boilerpro

hr

The main reason

those condensors like PS is the pressure drop through the HX. Usually this is much higher than the requirement for the zones. As you noted the PS method "disconnects" the high head pump in the boiler loop from the zone pumps. In your case with a converted gravity system?? you would want the two, or more, different spec pumps.

If you can assure adequate flow is maintained under all loads, then the condensor would not need PS piping. But why risk it? Keep the boiler happy with the required pump and flow, and size the zone pumps to the loads.

Go to www.hydronicpros.com and print off this months tech topic. Siggy graciously allows one copy, thanks:) This is one of the best explanations of PS, the ins and outs, and common mistakes, I have seen.

hot rod

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Floyd_5

Wow, Got to weigh in on this one....

of course everyone knew that I would..:-)
Don't know where to start though....
I remeber talking to one of the tech's in the lab at WM in march and it seems to me that they were running an Ultra boiler and cold shocking it with water just above freezing, coming straight from the chiller that they use to cool the water that they test the boilers with....cycle after cycle, trying to "kill" it....also I remember them talking of cutting the flow off to the boiler while heating at high fire to see if it would shut down before damage occured.... and it did.
HR I believe hit the nail on the head as far as the P/S recommendation... for the boiler to operate most effectively there needs to be proper flow though the boiler, so that the delta T does not fluctuate too rapidly and the boiler can modulate effectively. That boiler will heat water so rapidly that if the flow is not adequate that it will shut down before it has the chance to modulate back.... the modulation of the boiler is a bit slower than the Munchkin, I wish that the rate could be varied but that would open up another whole can of worms that I'm quite sure that WM does not want to be in the hands of just anyone, so I'm sure that they went with a one-rate fits most program.
Yes, there are possible applications that I could see where this boiler could be hooked up without P/S piping....it can be done, I have done it... but you better have just exactly the right application for it and there are VERY few heating systems out there that will fit that bill.
You mentioned the 8 degree differential... that is not a problem and slowing the water down to achieve a higher diferential is not correct thinking with these boilers, because when you slow the flow the delta T goes higher and the boiler increases the firing rate to try to close the delta T....get my drift???
The deal with the condensing technology is that it works so much differently than the boilers of old... the way of thinking and the reactions of the boiler are totally different. Instaed of dealing with large volumes of water in theboiler you are dealing with quarts of water and almost "flash" heating....the delta T through the boilers are intended to be low... instaed of returns at 140 and supply at 180... or 40 degree delta T you are working with a maximum of 20 degree delta T.....IF you have proper flow through the boiler.

Reynz, yes you do want the coldest water possible through the boiler, that is why you want to have the boiler running at the coldest temp. possible and still provide the BTU's that are needed to jump off the train as they race around your house and keep you warm. Yes, some of the water will probably recycle back to the boiler, but in your case you need that to maintain the flow through the boiler and not be flying around so fast as to screw with your converted gravity system. Howver you still can rest assured that you are making that heat in one of the most eff. ways possible!!!

There is going to be an up hill battle with the "establishment" as far as these boilers and the "new thechnology" that is involved here....the old "show me the money" atttitude, but I am confident after working with these things that they are here to stay and that they are the "future" of the heatig business... for oh maybe ten years or so.... then???? who knows what will be coming....
Just hope that I can keep an open mind...kinda tough sometimes!

Floyd

joel_14

P/S

P/S piping is to protect cast boilers from shock and to make sure you have adequate flow through the boiler at all times, especially on copper or other small heatexchanger type boilers. You are correct in thinking that we want the water as cold as possable to a condensing boiler and P/S piping will absolutely hurt getting the cold back to the boiler continuously. I would have no problem skipping P/S on the Viessemann boilers i'm used to. If i'm sure I've got the right flow through it. With the low loss header arrangement they have I think the mixing and cooling of the return is much more effective than a small primary loop. I would like to try a large califie (sp?) header on one if I need lots of system pumps. These headers function like a low loss header but are bigger with greater volume and taps for pump flanges.Since they have a large open mixing chamber this should help keep colder water getting back into the return which is what your after. I see other brands piped with traditional P/S piping and I'm sorry to disagree with the others here but i just don't get it. If the boiler company says to do it well then CYA,but alot of those systems would seem to keep the water pretty hot in the primary loop. Remember guys if that primary loop is hotter than about 137f you are NOT condensing. You might blow a white plume when the flue gass hits atmosphere (esp when really cold out)but put an anlyzer on there and see what's hapening with hotter water in that primary loop probably 86-88% eff. Not that that's too shaby at all but not trully condensing either. My concern with those aluminum blocks is corosion. Aluminum was tried and failed in condensing hot air furnaces 15 years ago. What do the boiler guys know that lennox didn't about keeping alumnium together. personally IMHO i like stainless on condensing heat exchangers,

joel_14

Correction

I guess I'm not disagreeing totaly with the other posts as the other guys are mentioning the advantage of colder return water. i just feel it needs to be emphasised that in theory that is the goal we're really after and P/S can keep us from getting there.

F Reynolds

Thanks for Piping in, so to speak

Floyd, can't tell you how happy I was to read your post. I was hoping you would comment.

But, but, but, You recommended that a Taco 0011 was probably too fast for my converted gravity system in a different posting. Right now, I have no P/S piping, and a Taco 0011 pushing the water through the entire system. You said something about water "whirling or whizzing around" (and I still laugh out loud when I think about what you wrote), and you suggested I probably only needed a Taco 007. Water going too quickly through my gravity converted system is not what I want. I want to slow it down. I did take your advice on that and checked the curves of the 007. About 10 head and 25 GPM is what it looks like to me.

So, to recap,…..
- I should keep the Taco 0011 on the boiler loop.
- Have my HVAC professional repipe my system to give me P/S and put a Taco 007 on my gravity system zone. 11

If I did that, I could probably maintain a 10 degree delta T on the boiler loop and get a wider delta T on my system zone, BECAUSE, warmer water would be blending with the return water in the boiler loop to give me a warmer return temp, and a closer Delta T, right? (Glad I didn’t try to say that, I would have passed out without a breath)

It would also help slow the water down to act more like a gravity system, and then more BTUs could get off at each train station. Now I think I understand what the WM factory rep meant when he said 10 degree on the loop and 20 on the system. Am I making sense?

Floyd, don’t you agree that there is not a lot of information out there about this? I can imagine some in the HVAC world are having a difficult time also. Just as you said, a different way of thinking about it.

Now if we could only hear from Kal and Leadpipe. It would be just like “old home week”.

F Reynolds

Hummmmm

Joel,

A lot of good stuff to think about here. Could it be that there is no definitive answer, but it is a bit subjective?

We need proper flow through the boiler, so, it would be natural to pipe P/S. Maybe that is the only reason WM says to pipe it P/S, so there would be no errors in flow rate.

Dave_13

How about.....

A supply and return header with a differential pressure bypass valve?????? If all your zones are calling- you would probably get the coldest return temps. As they close the bypass opens keeping the coreect flow through the boiler at all times..... Whatta think?????

Boilerpro_3

Interesting Floyd

Now that you mention it, I think I remember that too about shocking. I wonder, though, what happens to the life expectancy under that condition? It may hold up well for 10 years, but how about 15 or 20? Maybe by that time the erosion of the aluminum from condensate would have already killed the boiler. The only way we are going to find out for sure is wait about 15 years, but it is great to see Weil Mclain actually trying to find out. I suspect that with the modulating outdoor reset control it is hard to shock the boiler. All the zones are running nearly continuously due to water temp reset.

Boilerpro

Mark J Strawcutter

005

you might want to check and see if the curve of a Taco 005 isn't a better fit than an 007 for the system loop.
Mark

Cliff Brady

What the manufacturer literature says

For example, the Munchkin/Pinnacle piping supplement states for the 140M a minimum flow rate of 6 GPM which equates to a 37.33 degree delta-t. The flow rate at 'classic' 20 degree deltat-t is 11.2 gpm. The circulator sizing graph show flow rates and pressure drops for 6 GPM to 18 GPM. The above
delta-t's from the literature are calculated at 80% efficiency which is what I assume is close to the actual efficiency at high temps well out of condensing range.

What I have learned here, but I think needs more dicussion, is that a higher delta is more efficient, ie condenses more.

The other advantage of the higher delta-t is smaller pipe and fitting sizes and a smaller, cheaper and more efficient pump. I would stay away form the extremes of the flow rates, but it does show there is quite a range of flexibility.

The lower flow rates lend themselves to direct connect to single pipe gravity conversion, while two pipe systems take a little more consideration and the need for a bypass valve. Constant circulation is big plus particularly if you don't want hotter water stagnating and oversupplying radiators near supply end of the loop while not getting the hotter water to the farther radiators. YMMV.

I think it was good of HTP to come out with a range of acceptable flow rates for the Munchkin line. It would be good to see the same from other condensing boiler lines, if not for all boilers.

I welcome comments on the statements I have made but the most contentious issue is the relative efficiencies of higher or lower delta-t's for condensing boilers.

F Reynolds

Gas Bill (Floyd, Help)

Floyd, what am I doing wrong here. First month I say about a 25% savings over last year. At the end of this past month, I turned down the target temp, as we had discussed in an earlier post. The result, my gas bill shows I used the same amount of gas as last year, no change. But this year it is to the tune of $500. Do you think they read the meter wrong, or did turning down the target temp hurt me?? Any ideas?

Cliff Brady

Not Floyd but

make sure you compare periods on a therms per degree-day basis to wash out the weather anomolies. My gas bills show degree-days for the period and the therms used, but I have to do the math to get therms per degree-day. Make sure the bills are for actual readings and not estimates. We like our 'cheaper' heat so much we use it more and probably wash out some of the savings that way. I have found, but not really verified that in colder outdoor temperatures with higher supply temperature the boiler condenses less or not at all so efficiency gets closer to the cast-iron behemoths the condenser replaced. The savings really come in the shoulder seasons.

Floyd_5

Very well said...

my thoughts exactly.

Floyd