In this case mod/con worth it?

D107

I think Mike T (Swampeast) was basically saying that given my existing series loop, I wasn't going to get the efficiency of a better piped system. And since I'd like to do a really complete job someday--and the fact that I'm in the midst of other projects-- I felt maybe this lesser efficiency would justify putting off the job.

fyi basement baseboard circuit length totals 80ft, out of which 30ft is heating element. (Slantfin 15) Main and 2nd floor CI rad circuits are about 150 ft each. Envelope is much improved with 4" blown cellulose added last March soon to have vinyl added with 3/4" polystyrene. Before the insulation, fireplace flue sealing, and other sealing measures I got .9ACH blower door test (not good I know) and I'm hoping now with the cellulose etc we could be down to .5 ach.

David

D107

due to poorly designed conversion loop system?

In my 1924 40Kbtu loss/77K btu gain 3 zone; main & 2nd floors cast iron. baseboard in cellar. Before gravity system converted probably 1.25-1.5" direct or reverse return. 1st three rads all supplied with 3/4" to push heat to farther rads. However they made it into a loop system with 3/4" copper except for old 1" risers to all the rads after the first 3.

In a prior thread, Mike T had said that there would be "somewhat reduced efficiency in a loop system driven by a condensing and modulating boiler...”. But I shouldn't take that to mean that a mod-con isn't a worthwhile upgrade here as opposed to just a good atmospheric with outdoor reset, should I? (I have read some wallie posts that say that a mod-con will not necessarily be a great benefit for every situation.)

My current boiler is 1981 7 section weil mclain 210Kbtu firing rate/165Kbtu net--way oversized. I'm hoping that the undersized 3/4 piping could be handled by a buderus gb142 smallest size. Or does the restricted piping NEED the overfiring boiler to push through the water fast enough? (Probably my poor understanding of the physics involved.)

Thanks,

David

Empire_2

Hi Dave......

Depending on if you have baseboard or other, 3/4" pipe @ 4 gpm @ 65' of effective base will give you aprox....40M give or take. Now if you want to go Mod/Con with Od reset, I can Make it sing. Since I must know your envelope,.. I am only guessing,.


Mike T.

Floyd

From what I can see...

you would be crazy NOT to go with a Mod-con here. You will be able to run some very nice temps. for condesing most of the year, no matter how you pipe it.

Floyd

Mike T., Swampeast MO

Different Mike T. and no offense taken in the least regarding the initial thread title.

Mike T had said that there would be "somewhat reduced efficiency in a loop system driven by a condensing and modulating boiler...”. But I shouldn't take that to mean that a mod-con isn't a worthwhile upgrade here as opposed to just a good atmospheric with outdoor reset, should I?

No, don't take it to mean not worthwhile. Just consider the effect of the emitter system on the operation of the boiler.

Your piping does sound rather goofy. A 3/4" one-pipe loop supplying iron rads via their original 1" branch piping sure raise a warning flag. If any of the iron radiators are hooked up in series, such is another big warning flag.

165 mbh net boiler output with a loss of 40 mbh? Yikes! Talk about oversized!!! With only 40 mbh loss, the the smallest mod-con from any line that I've heard of would be sufficient for the load. The key is transferring that energy to the emitters effectively. Really sounds to me like the entire system needs a thorough evaluation before any new boiler is installed. Significant changes in the piping may well be recommended.

Was the system significantly re-piped to divide into zones and increase headroom in the cellar? If it was in fact a two-pipe gravity system, TRVs would likely have been a more effective and less expensive way of "zoning".

D107

yes, significant repiping done back in '82

Thanks...yes they removed--probably the original boiler--which had been converted from coal to oil and put the gas-fired weil mclain in. Yes, main and 2nd floor zones are all in series going from one rad to another with the 3/4" copper in the cellar going to the 1" risers (except for those 3/4" risers in first three rads.) And yeah, i'm sure it was the basement headroom they were concerned about. Though I think with soffits one could work around the aesthetics.

To make matters worse on main floor they interrupted the loop just before the final rad (dining room) with an additional run to the sun room on slab which had never been heated. That should have been on its own zone. All that being said, I can't say, even before the cellulose, that we really had serious heat problems. Dining room rad does take a bit longer to heat. We use large setbacks so sometimes it might take a few hours to go from 60 to 65 on design days, and I think all gas usage --including direct HW, dryer and stove has been around 1400 therms. Of course we'll go indirect now. But since our direct is 17 yrs old and our boiler 25, I'd like to get an install in now before it becomes an emergency.

Main Floor: Loss: 20Kbtu; gain: 43K US radiator triton (except for 3 small ci gouvernales in porch and bathroom.)
2nd Floor: Loss: 12K btu; gain: 20K US radiator triton
basement: Loss: 7.5Kbtu; Gain: 17Kbtu Slantfin 15.

Yes I'd agree probably could have kept main and 2nd floor zones together and used TRVs....And if basement slantfin had been done with cast iron, I might not need a 3-way mixing valve to deal with the different supply temp requirements for outdoor reset.

(A pro came out and did a very quick heat loss calc and, using lower outdoor design temp and other changes, came up with 55K heat loss. Still way oversized.)

Bottom line, even w/o repiping right now would there be any ill effects on a GB 142? Probably a reduced delta T as you said...would I need stronger circs than indicated by rule of thumb calcs to increase flow? {main and 2nd zones 9ft head each; basement 5ft.)

Thanks again,

David

Perry_2

Great Question

You seem to grasp the reality that not every system can be retrofit effectively to optimal mod-con operation at a reasonable cost.

I have only been haning arround for about a month; and what amazes me is the number of people who seem to say that it is always better to convert to a mod-con.

I am well on board that in "most cases" that a mod-con is worthwhile; but "Always..." "always" sounds like religon to me... (i.e.; the facts don't count).

In your case you site a need for a 40,000 Btu/Hr heating load. So idealy - to take advantage of all the efficiencies possible - and support reasonable Domestic Hot water a 12,000 - 48,000 mod con would be ideal.

This is close to the Munchkin T-50 (16,000 - 46,000); but this size does not exist in other US available mod-cons.

You list 150 Ft of Cast Iron baseboard - it probably needs a max of 140F for the coldest weather. Then you list 80 Ft of copper tube baseboard - which normally needs 180 F water - unless it was specifically sized to work on less (was it).

How to connect it to the existing loops (can you direct feed it, or will you need an secondary circulator), what kind of controls will be needed, will you need separate controls or mixing valves? Finally, how much will it all cost?

But, a counterpoint. How much will a normal boiler (sized arround 50,000 Btu/Hr) cost to install as well. What is the price differece between the systems.

Great question. I don't have an answer. If you needed three times the heat load I think the answer is obvious in favor of the mod-con. Two times the heat load - I think it is usually the mod-con. At your heat load with your existing system - I'm not so sure.

I am wrestling with the same issue myself; although with a simpler system (I only have about 100 Ft of CI baseboard).

Perry

D107

yes, many angles here

thanks perry. by the way, the 150 ft is the length of each of the main and 2fl zones; and those zones have old cast iron radiators not baseboard but your point still holds.

When I'm in this situation I try to work first with what is more easily known and a sure thing. So the blown-in cellulose, fireplace flue top cap, electic outlet/switch gaskets, caulking etc. were no brainers. I have gathered that the 95% efficiencies of a mod/con are only achieved when it condenses; in my case with the reduced delta T from an underpiped series loop, I'm not sure it would do that. But I'd still have the outdoor reset and modulating feature until such a time as I can re-pipe.

I also consider that a good stainless steel, insulated chimney liner is going to cost me quite a bit of change as well with an atmospheric. It might mean the cost of the mod con might not be more overall.

So many pros and cons...When I was a kid my engineer Dad liked to toss out conundrums that I didn't appreciate then as much as now. "The more you know, the more you realize you don't know." And "if you keep moving towards a fixed point at half the distance each step, you'll never get there." At 7 or so I did spend part of an afternoon trying to disprove the latter....I'm still not there...

David

Mike T., Swampeast MO

We use large setbacks so sometimes it might take a few hours to go from 60 to 65 on design days

Sounds like another warning flag to me. With such an oversized boiler you should be able to raise space temperature quite rapidly. What is the current aquastat setting? Have you observed the boiler during recovery? Is it cycling frequently?

Bottom line, even w/o repiping right now would there be any ill effects on a GB 142?

If installed properly, there shouldn't be any ill effects on the boiler itself, but you might not get the performance you expect. Increasing flow through the emitters to "compensate" for piping insufficiencies is contrary to efficient performance of a mod-con as it increases return temperature. Also, never forget that the zone with the highest temperature requirement defines your general efficiency with a mod-con.

D107

Aquastat is at 180 though I haven't verified actual supply temp

though I'm thinking I could safely lower that to 160 maybe lower since delta T is probably less than 20deg with this series piping. This is a cold start boiler. (And it's also pumped on return --with no bypass--BEFORE expansion tank. Last year I lowered it to 170 in Oct, then raised it when it got colder and the relief valve popped perhaps due to the PONPC problem causing a false call to feed boiler new water.

I'd expect quicker recovery time from now on since there was NO insulation before in walls. Cellulose being installed in March didn't give much of a test but I think I noticed the main floor overshooting the thermostat a bit on warmer days.

Don't know how short a cycle has to be before it's called short cycling, but morning recovery on a 20 degree day seems to take from 6-8pm at least. I'm not sure our Honeywell t-stats--always in last room of zone-- allow the boiler to go off before making temp. I would think that the 3/4" piping has alot to do with the recovery time. ALSO the fact that the return manifold at boiler was piped with ONLY 3/4" AS WELL! with the three 3/4" lines coming back. (probably an unintentional roundabout way of achieving a boiler bypass since only a small amount of cooler return water could get in to the boiler. And this loop series has a lower delta T anyway.)

At the very least, this is damn interesting. I just feel in my gut somehow that with proper piping/circing and a mod con
alone I'd save 40%. Of course at what cost and TIME for my research to ensure it all went down the wallie way....

Thanks,

David

D107

some further comments from Mike T (Swampeast)

FYI Got some interesting comments from Mike which shed some further light on the subject: (though I'm not sure why putting reset on a mod/con with this piping system would cause balancing problems,I'll certainly take his word for it.)

"...Hooking up standing iron rads in series is a BIG no-no.

Your extremely oversized boiler, three zones and deep daily setback are likely combining to achieve at least reasonable space temperature balance. I suspect (but certainly do not know) that installing a mod-con with the current piping using any form of reset would cause BIG TIME balance problems.

I'm sure you're imagining a serious bill--in that regard you're likely VERY correct. While I can't see the house and system from what you describe it sounds like you need to either address the piping first and then install the mod-con later or do both at once. It's possible that TRVs could still make the re-piping issues easier and less expensive. Adding additional fin baseboard element area to the baseboard may also help considerably if they currently require significantly higher supply temperature than the radiators."

Floyd

Don't get tooo carried away here....

David,
It is possible to way over think things.... it is amazing what will and won't work!!! I have seen systems that I NEVER would have installed that way, and would have never bet on them working, that made people very happy. There is often a ton of forgiveness in a hydronic system, sometimes not.... you never know till you try, and I really don't see it as that big of a gamble in your case. I would go the mod/con reset route, and if you have a bit of a balancing issue, so what, you can than address that then.

JMHO

Floyd

D107

Thanks for your input Floyd

Tony_23

My thoughts

Seems like "paralysis by analysis", an affliction I fight all too often

If your load is 40K, and the head is 9 ft, what's the problem ? How many common circs are out there that will move 4 GPM at 9 ft ? 3 ? 4 ?.

You're going to pipe a GB or most any mod/con in a P/S arrangement anyway. Put a 007 or an NRF22 on the system loop, or whatever Grundfos matches the curve, and go with it. ODR and scrap the setback. You'll be amazed at how things balance out when the circ runs pretty much continuous.

One last thing, it won't get any cheaper to do it later. It'll only cost more fuel money to the supplier while you wait.

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