New Boilers, Old Building

ChicagoEngineer

I have a client asking to run his large multi-family residential building at "condensing temperatures", but is not replacing the fin tube radiation.

Original plans call for the heating system to operate 210F - 190F. He wants us to design for a return water temp of 150 F. I think we can do a reset schedule based on OA temp... but won't I have flow and heat output issues trying to get existing equipment to run at these lower temps?

Does anyone have experience with something like this? Horror stories? I can't see a way to magically make the fin tube run at a higher delta T... and an average temp that much lower derates the output by 50% at least.

THANKS FOR YOUR HELP AND EXPERTISE!

Rich_49

You will need to perform or have someone else perform a detailed heat loss calc , room by room . Then a survey of the installed radiation to determine what AWT will be sufficient at various OAT .

Quite possible that this can be done if the envelope allows such .

There are now Delta T circs that are reasonably priced which allow one to flow at differing heads and gpm throughout . They vary flow based on the real time Delta of the system which we all know is determined by the amount of heat delivered to the space .

This strategy works out quite well in fact

Gordy

Hopefully you are over radiated to make it work.

EBEBRATT-Ed

@ChicagoEngineer , I believe you have to get the return water temperature down in the 130 range to get any condensing. 150 doesn't cut it. Designing for 150 return at design temp you will probably get some condensing in the spring & fall.

To really know you have to do a heat loss as the building now exists (or will exist after the renovation). Then look at the fin tube and the average water temperatures and see where you stand. Adding fin tube will help.

Depending on the radiation you have condensing may not be worthwhile

Gordy

Curious if boilers are condensing modulating variety.

Zman

Aside from the excellent comments above, be sure to scan the building for other emitters/loads. I am working on one now where they did not consider the sizing of the DHW and Pool heat exchangers when they decided to lower the temps. They were forced to turn the temp back up to satisfy the loads.

DZoro

Keep in mind your design temps. Here north of you our systems are designed for -25. But our "average" winter temperature is 17f. My point is that is a 42* difference, that's huge. So most of the time, but not all, we are able to run on condensing temperatures. Especially the shoulder months Sept-Nov and March-May. But yes even dead of winter sometimes....Not so much lately.... Let and trust your odr do the work, and your load calcs. If you have a home owner who understands what these new boilers can do. Turn the temps down, really low part of your comfort zone. Hopefully he maybe able to adjust the temps during the extremes, without you babysitting it. Non program stats only. Like others said hopefully they over killed the rads. Proceed with caution

NY_Rob

Wanting to go modern and efficient is great- but Keep in mind that local supply houses don't keep parts for mod-con boilers in stock like they do for cast iron boilers where the same aquastat works on 100's of different boilers that were produced over a 50 year span.

A 2am Sunday morning outage because of a fried $5 flame sensor my keep the heat off till Tuesday 10am till the part arrives from the manufacturer. Not good when it's 6F outside and the "multi-families" are screaming.
Check for local parts availability if any before deciding on new tech mod-cons or be willing to invest a few hundred $$ for ready, on-hand spares that you can grab when needed.

Rich_49

NY_Rob said:

Wanting to go modern and efficient is great- but Keep in mind that local supply houses don't keep parts for mod-con boilers in stock like they do for cast iron boilers where the same aquastat works on 100's of different boilers that were produced over a 50 year span.

A 2am Sunday morning outage because of a fried $5 flame sensor my keep the heat off till Tuesday 10am till the part arrives from the manufacturer. Not good when it's 6F outside and the "multi-families" are screaming.
Check for local parts availability if any before deciding on new tech mod-cons or be willing to invest a few hundred $$ for ready, on-hand spares that you can grab when needed.

That there is why good contractors and / or building managers keep those low dollar parts on hand . just sayin

NY_Rob

^ some homeowners do that too

Some of the mod-con's (HTP UFT's for example) are so reasonably priced vs. buying $$ spare parts it's worth considering keeping a full replacement boiler on hand as a parts donor.

JohnNY

This has trouble written all over it. Fin-tube sucks at low temperatures and, as @Gordy suggested, if your living spaces are not over-radiated you are going to have cold rooms. If I were you I'd prepare my client for the fact that he can have his 150° return water *sometimes* but it's going to take more energy to heat the rooms on a lot of days. I don't have a horror story for this particular application, and believe me I've backed myself into plenty of corners over the years, but I have had great experiences with oversized cast iron radiators and running replacement boilers at condensing temperatures. I only bring that up because these good experiences are the opposite of what you're looking to do.

Rich_49

Nonsense John . Fin tube runs just fine at lower temps , I have had nothing but positive experiences when the system and installed radiation allows running at condensing temps . I have baseboard radiation out here running and keeping people comfortable at temps as low as 110 AWT . Some systems will not allow for that but will allow a retrofit to run at condensing temps for 60 - 80 % of the heating season . The building , radiation , heat loads all must be looked at well . Problem is that the contractor capable of doing this properly rarely exists . One must find him , this gent has found several all in one place to help him make good decisions .

Gordy

I’m still unclear from original post as to condensing temperatures. Since 150 is hardly condensing as a return water temp. At a 20 delta that puts supply at 170 with an average of 160.

Condensing is 130, and below. Also yet to be told is the type of boiler in this scenario. Unless it is a condensing boiler return water protection is needed iF condensing temps are realized.

Gordy

I must presume that the owner wishes to reduce supply water temps as much as possible through an outdoor reset strategy.

This strategy will indeed work. How well, and how much awt can be reduced depends on as mentioned a detailed heatloss, and existing radiation survey. Room by room. Only then can you accurately propose an ODR schedule as aggressive as possible to meet the loads at a given OAT. If the emitter sizing at design is just enough the plan should work as OAT is reduced. If under radiated which could be possible if the design supply was indeed 190-210 you could be screwed until OAT is in the upper 30’s before the 160 AWT will work.

Gotta do the math.

JohnNY

Rich said:

Nonsense John .
...Problem is that the contractor capable of doing this properly rarely exists .

The published ratings suggest it's true and I happen to be a big fan not relying solely on convection to provide comfort in a room. To that end I prefer high mass radiation run at appropriate OA reset temperatures.

Tinman

I've done my share of multi-family buildings in Chicago and you better make sure you look under the hood and verify that the fin tube is not smashed, installed wrong, or covered in dirt and pet hair.

EBEBRATT-Ed

It's going to take more fin tube than they have or want to install to accomplish what they want. And as @Stephen Minnich said dirty or crushed fins or empty baseboard enclosure doesn't count

Tinman

Finned tube oriented the wrong way so that convective currents are nil.