Modulating Vs. Condensing

Brad White_22

Proof once again that condensing boiler technology is unorthodox :)

(Sorry, had an episode. I am better now.)

Another benefit to condensing boilers, high in anti-oxidants. Seriously with all of these LEED points we scramble to go after, use of gray water for irrigation has me thinking now...

Good call, Wayne.

Xc8p2dC_2

The benifits

Still researching a more efficient replacments to replace my NEW oversized NG cast boiler {WM Ultra 80 at top of list]

Am I correct to assume the biggest benifit from a Mod/Con is on the Modulating side? especially with an outdoor reset

How much more do you get [other than the lower exh-vent temp]in BTU from the Condensing side, provided by extrapulating[sp] heat from the burn

I currently to not have any floor drainage in the basement other than PVC plumbing [ I think I read you can't connect, to that is that correct?]

I noticed in a post the Laars said Mod but not Con>> any other manufactures build them that way?

<< Background > Heatloss 30K btuh @ 9 deg > 2 Zone > Fin Tube BB > non- DHW > Direct vent >> current boiler DE-05 140,000 btu in >>

TIA> RC

Rodney Summers

In your case, yes

since you're probably not going to run copper fin tube BB below condensing temps. You'll see saving from OD and running your temps between 140-180°

Some of the wall hung boilers like BAXI and Tagaki modulate
but don't condense.

Steve Goldstein

Baxi and condensing

Don't the Baxi Luna HT boilers modulate AND condense?

Brad White_9

They are not mutually exclusive

I would go for both. Condensing for obvious reasons and modulating to forestall cycling. Plus at low fire, efficiency is increased. Lower mass flow versus all of that exchanger surface.

Recent posts on the subject of a Brookhaven National Labs study should be sought. The study found that OA reset and fin-tube is more efficient across a season than most people believed.

Unknown

Yes, but they have their older boilers which modulate but do not condense as well.

Xc8p2dC_2

over emmited

Yeah, I agree, it's probably foolish not to go both, just trying to weigh all my options

The only thing I have going for me is, Fin tube is probably 1/3+ oversized as well, so I may have the benifit of running at the lower temps

I do have a small opening [12"] in the cement under the stairs in the bulkhead, outside of the main foundation about 15' from the boiler

Would that meet the requirement if I could create a crushed stone well?

Brad White_21

Do you mean to

dispose of condensate? I would think it would be alright if the drywell you describe is well drained and not subject to freezing. You should also neutralize it by running it through marble chips before pumping out.

Xc8p2dC_2

Yep

Brad, yes to dispose of Condensate

I think I read that some Mod/Con's, condensate out put can be up to a gallon an Hr at really low temps, but not sure what I could expect from a Fine tube BB running at maybe 140-160 deg?

Brad White_9

Condensate quantity is roughly

one pound per 970 btu's saved. That is the value of the water vapor change of state to liquid. Every gallon represents 8080 BTU's in other words. That would seem right for a 100 MBH input boiler when condensing.

BUT- unless you run your BB at below the dewpoint, forget condensation like we are talking about.

At 140-160 (HWS temperatures I assume) you are marginal to reach dewpoint for condensing. I would start at 140 and return at 120 on a design day if I could and drop the temperatures from there.

The point about using ModCon with baseboard should not be lost. On cold design days you will not likely condense. That is reserved for milder weather, where it is most of the time in winter. Key is, you have to be able to re-set your water downward accordingly and automatically.

Xc8p2dC_2

dewpoint

Thanks again Brad/others >This one has always confused me

"""""BUT- unless you run your BB at below the dewpoint, forget condensation like we are talking about. """""

Room ambient dewpoint? >> outside dewpoint>> cellar??

Brad White_9

I should have been more clear,

I mean the dewpoint of the exhaust gasses, products of combustion. Depending on excess air and CO2 levels, this will range between 125 and 138 degrees more or less. Elevation is also a factor.

Point is the return water should be about ten degrees F below these levels before really productive condensation takes place. This is why I recommend a re-set schedule that takes the water temperatures (supply and hence return) as low as possible and which will still heat the house. But this is all germaine to condensing boilers or conventional boilers with a de-coupling or injection arrangement to protect the boiler. Condensing boilers LOVE cold return water.

It has little to do with the ambient dewpoint around the equipment.

Rodney Summers

Condensate outdoors?

Might there be an issue with dumping the condensate drain outdoors and freezing?

Brad White_9

I think that

so long as it is not over a walkway where icing would be an issue or plantings that you value, there should be no harm.
As with any discharge it should not form a nuisance or impact masonry (freeze-thaw cycles and all).

Mine has been watering my garden (over a pile of marble chips) for years without any problems.

The condensate is just water with a low pH, not unlike vinegar. I would not put it in the balamic category though.

Xc8p2dC_2

Hmmmm

""""I mean the dewpoint of the exhaust gasses, products of combustion. Depending on excess air and CO2 levels, this will range between 125 and 138 degrees more or less. Elevation is also a factor. """""

Yep,,that explained it perfectly, thanks

Will have to do some tests on freezing, It is 6-7' below grade, but under an uninsulated bulkead, gotta wait for a cold snap and throw a thermo down there

Question>>>> Is there pressure in the condensate line that will "pump up and over" say a 8' foot rise? or is it gravity drain only?

Brad White_9

Drainage of Condensate

Hello again- I had to start a new topic line because we were getting a little too vertical there. Hurts my neck!

The discharge from a condensing boiler is by gravity. You cannot pitch upward. The drain is usually trapped within the boiler to seal in the products of combustion.

If elevation is an issue then yes, you would pump it. Little Giant, Teel and others make pumps for "condensing furnace" (boiler same thing) applications. Remember though, these are made to lift an allow gravity to take over from another level. They have low head so not made to force flow through equipment or long runs of small diameter piping. Think of them as lift stations.

Generally your ground temperature below frost line is your annual average temperature so should not freeze. The passage through your bulkhead? Another matter. I would sleeve it in PVC (carrier tube within say 1.5" PVC and insulate the PVC with Armaflex both well into the building and well into the ground. Pitch it continuously so it drains dry each cycle.

Xc8p2dC_2

Sounds doable

Thanks, Brad for your input

Looks like the Ultra 80, will be the unit, lots of nice features but most importantly is FITMENT as this is an existing prepiped system and the U80 is ver close [supply on R, return on L, gas in on R, in/exh in center>>> The GB142 and Munchkin were in the running but would have ended up criscrossing the piping

I also like the Ultra80 for it's easy conversion to propane, it's supplied o/d reset, the extended HO warranty, and the potential to monitor by home computer
PLUS it's an American made [well hopefully most of it]

Now just need to get it done by March end, to get the extra MA. energy tax credit

Thanks all

Wayco Wayne_2

Condensate slightly acidic

Over 25 years ago I installed a condensing furnace at my parents house. Condensing furnaces were relatively new at the time. I used a condensate pump that lifted the water to the top of a slanted pvc pipe that ran outside so the water would run out fast before it could freeze. Has worked fine for years. An unfornseen benefit was that the pipe came out right behind his blueberry bush patch. The very next year his blueberry bushes, which love acidic soil, went crazy. They grew fast and produced berrys way bigger than before. I could only smile whenever I'd stop by for a visit and he would lead me out to show off his enourmous blueberrys.

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Ted_9

heatloss

I find it odd that you have a 30,000 btu heatloss. Unless the house is super insulated and about 750 sq. feet.

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Xc8p2dC_2

Give or take

Ted> Ran the program a couple of times>> New construction 3 bed, 1250 sqft ranch>> Worst was @ 0 deg design, was around 36K btuh, Area designed @ +9deg [on the Cape] best was at +20, 26K btuh

Many have said a well built home should be 25-35 btuh per sqft so sounds like I'm inline

ALH_4

Modulation

Here is how I see it:

Unless you design a boiler for condensation, you are seriously limiting the modulation range. Condensing boilers are primarily designed to modulate as low as possible and not fall apart because of the condensation. There is the added benefit of recovering the latent heat, but the primary reason for the development of condensing boilers is to let them modulate to match the load.

-Andrew