Welcome! Here are the website rules, as well as some tips for using this forum.

Vitodens Condensate- for Mike T.

Options
Member Posts: 1,935
you should be able to gain 10%(chemistry).

i wonder, if condensate doesn't collect in large 'grouped' quantities it could just be blown out the vent, like a fine mist, in other words, collecting drips might not be telling you the whole story. thats what you see when its cold, if it was just hot dry air you wouldn't see the 'smoke'

• Member Posts: 3,659
Options
One drop of condensate...

is 1/20 milliliter, or 1/20 gram (approx.-- A "drop" is so variable it barely qualifies as a unit).
The latent (vaporization) heat of water is 540 calories/gram.
So each drop is worth 27 calories of energy.
There are 252 calories in a Btu. So dividing 27 by 252 we find:
0.107 Btu/drop of condensed water vapor
Natural Gas is billed in Therms, which is 100,000 btu. So in Therms we
find:
.00000107 therms/drop
In Seattle gas costs about \$1.25 per therm. So the value of the energy in a drop of condensate:
.00000134 dollars/drop (at this point it's clear that watching water drip out the boiler drain isn't quite like watching coins clink into the bank).
There are 86,400 seconds in a day. If the condensate drips about once per second then per day is:
\$0.116, or a little over ten cents.
In a month this amounts to about \$3.48, a year yields \$41.76.

A little underwhelming! Not much in terms of an impressive statistic to sell condensing boilers (I thought it would be a lot higher). I guess the moral is that it's not the condensing that brings about efficiency, but the efficiency that causes condensing.

This is from a customer whom we installed a 6/24 two months ago.

• Member Posts: 1,790
Options
I'm not Mike, but...

I guess the moral is that it's not the condensing that brings about efficiency, but the efficiency that causes condensing.

That must be a very intelligent homeowner to have deduced that truth in two months in the face of all the marketing hype that promotes condensation as the primary benefit.

To be fair, the amount of condensation could be much more than that under the right conditions or with a larger boiler.
• Member Posts: 6,928
Options

Isn't that neglecting the fact that all the products of combustion are at a much lower temperature?

What about the reduction in sensible heat down to 212F as well that below 212F. Isn't 300F-400F (or more) stack temperature pretty common for a conventional boiler? Aren't both the flue gasses and condensate typically well below 212F?

If I have time today, I'll try with the math, but won't make any promises. That how much pressure when you heat confined air problem reminded me just how hairy things get with gasses. Have read numerous explanations on numerous occasions, but it still doesn't click in my brain how water vapor exists in air--let alone flue gasses at 100s of degrees F.
• Member Posts: 1,935
Options

read up an all the gas laws then laws of partial pressure
• Member Posts: 6,928
Options

Have on numerous occasions. While I can follow along it just doesn't click--perhaps because it's nearly impossible for me to visualize. I was sort of the same way with proportional control when all I was doing was reading about it--once I installed and observed however it "clicked" and I could actually see it in my mind.

I can see water turn to vapor when the sun comes out right after a rain. I can see that vapor turn back into water on a cold glass. I can feel the vapor in the air in the summer or if I stick my hand in the flue. I can even feel the lack of vapor in the air in the dead of winter when an indoor temp that's normally comfortable becomes "chilled"--similarly I can feel the excess of vapor in the air when sweating no longer works to cool me. With all that however I just can't "see" why any of this happens...
• Member Posts: 1,935
Options

best to start at the front of a chemistry book and read the whole thing. its impossible to just read somewhere in the middle and understand it, its all connected. can't do trig before you learn algebra and so forth.....

i'm not sure when a gas is a liquid and a liquid is a gas, wheres the boardline?

• Member Posts: 1,790
Options
and...

I wonder how much of the condensate is condensing directly on the heat exchanger. How much condenses on other surfaces?
• Member Posts: 6,928
Options

Paul:

I've been thinking about this whenever doing a job that didn't require me to actually think plus spend some time on the web.

I think your customer is improperly interpreting the difference between the gross calorific (high heat) and net calorific (low heat) values of fuel.

The gross value is simple to understand and likely easy to measure. Start with fuel and air at the same temperature, add spark and measure the energy gain with the products of combustion returning to the exact same temperature at which they began.

The net value on the other hand is MUCH more complex even though it's VERY typically defined as gross value minus the vaporization energy of the water produced by combustion and assumming that ALL water produced remains in vapor form.

Just how much energy does it take to keep ALL of the water produced via combustion in the form of vapor? Good question and from what I've seen there's no definitive answer as it all depends on the assumed conditions--not only the initial temperature of the air and fuel, but the vapor already present in the air as well. In general however it [seems] that the difference is somewhere between 10% and 12% (viewing the difference based on gross value).

We don't connect our boilers to an O2 tank--we use air--only a small percentage of which is O2. In addition gasses (nitrogen, carbon dioxide, etc.) that remain gasses as anywhere near "normal" pressures and temperatures, air also contains water in the form of vapor. While the "perfect" gas content of air stays constant, the imperfect gas content (water vapor) varies WILDLY. Normal combustion doesn't break the H-O bond so that water vapor STAYS water vapor.

The more water vapor in the combustion air to begin with the less water vapor of combustion can be accommodated before you hit the saturation point where you have liquid water.

I'm sure there's a standard for the relative humidity of combustion air as related to the net (lower) heating value but I have not found the complete standards and calculations used. I can assure you however that it gets HAIRY with molecular weights, mixed gasses (both "perfect" and imperfect), absolute temperatures, absolute pressures (of both perfect and imperfect gasses) etc.!!!

------------------------------------------------------

The point of this:

Within reason about 10% of the gross calorific value of natural gas can be recovered via condensation. An exceptionally performing boiler under ideal circumstances (including current relative humidity) can recover about 90% of the 10%.
• Member Posts: 6,928
Options

Believe I understood that LONG ago. After all, I can "see" atoms as well as "seeing" why they both stick together and form bonds with others.

It's water that CONTINUES to fascinate and perplex me.

NO OTHER SUBSTANCE exists as a solid, liquid and gas in the "real world". What makes it so special???

And why is it so hard to believe that a RADIANT burner transfers energy through a WATER system in a manner that corresponds PERFECTLY with the MEASURED TEMPERATURE of the emitter?
• Member Posts: 1,935
Options
i'm puzzled?

so, you do not understand evaporation then?

if you understand partial pressures so well, I do not understand what you don't understand then?

"""NO OTHER SUBSTANCE exists as a solid, liquid and gas in the "real world". What makes it so special???""""

I'm not sure than statement is correct? we played with a 'water like' substance that was solid around room temp and liquid at body temp, I wouldn't be surprised if its gasous temp was not that much higher. chem lab!

your last statement is just ridiculus! sorry. please provide some sort of theory here? what is 'this' energy that only exists in mod/cons and no where else?

if your theory is true why use a pump?
• Member Posts: 1,405
Options

I understand the explanation of evaporation but I have no idea why water is so transmutable. It [seems] to be able to act as though it's at a different temperature and/or pressure/and or state than can be measured or observed by normal means.

Chocolate commonly exists as a solid at "room" temperature and as a liquid (if quite viscous) at "body" temperature but I don't think you'll find chocolate gas in nature.

Perhaps I'm misquoting my teachers but I sure seem to remember that many said that water is the only common--does that mean "in nature"?--substance that occurs in all three states of matter at the same temperature and pressure. At 32F you can find ice, water and vapor in co-existence in the same environment.

Believe me please. I understand that my wild statements regarding heat transfer VIA RADIATION can seem ridiculous but my observations keep telling me that something is missing--most notably measurable temperature of the emitters. Try to ignore me when I say such things. I can "see" but I can't yet explain.
• Member Posts: 1,291
Options
Mike, anecdotal evidence

I was at a customers house connecting a rad to a previously installed Vitodens. This boiler is connected to a "high temp" baseboard/rad system. The OD temp at the time was 4*F and the boiler was running 156* supply temp with no observable condensation occurring. Just for kicks I stuck the combustion analyzer in the flue to see what was happening with the raw efficiency numbers. It was running 89.4% (LP gas)

The thing that really caught my eye was the fact that exhaust gas temperature was 143*. The HO, an engineer by trade, was astonished and couldn't see how that was possible but there it was, right in front of his eyes. I just winked at him and said "magic", with a grin.

The assumption that any increase in efficiency comes solely from the condensing nature of these boilers simply does not tell the whole story.
• Member Posts: 1,405
Options

Perhaps enough such anomolies will make people with far greater resources than me re-think the difference between "observed" and "behaved".

Oh wait! They do already as long as involves more efficient ways to kill people or destroy what people create. I can understand but perhaps it's time to let such thinking be used constructively instead of destructively.
• Member Posts: 1,405
Options

j paul:

I re-read that last statement and don't understand it myself but I do understand my intent. Both numbers and words fail me at times. Please forgive me. After all every neural connection in my brain tells me that Tesla was correct in that limitless (by our standards) energy and information can be collected and transmitted wirelessl. He saw the whole picture before it was polluted by the mere glimpses of those who followed.
• Member Posts: 1,935
Options
telsa???

if limitless energy could be transmitted and recieved wireless, why is no one doing it? why because it is incorrect!

you go near a radio tower, say an AM 50KW transmitter, walk around with a 15 ft pipe, tell me what you observe

i've heard this tail a couple times, never in a phyisc lecture though.

yes, i wish i had a vito so i could make experiments.
• Member Posts: 1,935
Options
where measured steve?

steve where exactly does the flue temp get measured?

are you sure it was in a stead state operation? did you see this measurement lasting 15-20 minutes or was it more of a snap shot?

i would also ask, where exactly is the supply temp measured?
• Member Posts: 3,659
Options
Mike

The customer is reading(and enjoying) these posts, and "re-interpreting" his data...I'm sure for the fun of it.

Enjoying the brain doodles.

• Member Posts: 306
Options
Mike

Moisture (water) is contained in air (or flue gases) in the form of superheated steam at low pressure. When you condense one drop of water out of some volume of mixed gases you lower the dew point temperature of the mixture. If you want to condense more you have to lower the temperature of the mixture more.
• Options
Return temp?

What is the delta-T of the system? If the outlet temp is 156F, with a delta of say 20F, the return would be at 136F. This is significantly lower than the flue gas exhaust at 143F, so heat transfer to the water is still possible. Usually the output end of the heat exchanger is exposed to the hottest combustion gasses, while the return end scavenges the residual heat of the exhaust.

So what is so surprising? Seems like the boiler is working as it should, operating just above the condensing temp range, with almost 90% efficiency.
• Member Posts: 1,291
Options
j paul

Viessmann provides threaded fittings in their concentric vent for testing not only the exhaust but also the intake air. They are located directly off the top of the HX in the flue pipe adapter.

The burner was not cycling, we were within about 10-12* of design temp. If it was cycling under those conditions, I would feel I really screwed up my sizing. I had the analyzer "plugged in" for probably 1/2 an hour while I did some detail work on the wiring. Definitely not a snapshot.

The temp is measured by a sensor installed directly on the supply header on the boiler. EDIT: Unless as in this case, a low loss header is used. Then the supply temp is measured at the header.
• Member Posts: 1,291
Options
You're right Mike

This is exactly how you would want a system to function. It's one of the beauties of the variable speed circ on the two smaller Vitodens in that it helps to maintain that high delta T through the HX. A system with constant flow through the boiler will rarely attain numbers like that. Boiler Supply/Return delta T across the low loss header was running just a tad over 21* measured on the surface of the steel pipe.
• Options

Yes, its really how you would want an optimized system to operate. Your example also shows that condensing is only part of the efficiency equation. Intelligent control and a superior heat exchanger design can combine to maximize efficiency under almost any operating condition.

I have attached the Viessman white paper which really explains well the sources of efficiency in a modern condensing boiler.
• Member Posts: 1,520
Options
the hydronic montra...

"a heating system should be run at a constant flow, but at a setback temp equal to the heat loss of the space", that's where condensing boilers shine - their ability to produce only as much btu's as are needed without having to worry about return temps, eg need to be able to do 6 steady showers, 300kbtu of snowmelt and radiant, at once, but not always so, so a Lochinvar knight 500, 399, and a 150 - on a Tekmar 265, will let be go from almost a million net down to 25k net - for just holding the radiant - the only disadvantage with the different sizes is less redundancy, which happens to be important with these type, because as the moving parts and electronics count goes up the reliability comes down  it was not uncommon for a natural draft cast iron boiler to go 30 years with no one even knowing it existed, and it will probably take 30years before the new ones are anywhere near as reliable  and by then we will all have switched to electric as the prime heat source  SlantFin Monitron anyone???
• Member Posts: 1,935
Options
steve & mike

It hit me late last night, it makes sense!

the vito has a radiant burner, I think we fall back and think convection burner without thinking?

so I have no math to back up what think, but i can see where/how the flue temp can be lower than the supply.

• Member Posts: 1,935
Options
cable TV

shine a flash light 100 yards, not too bright at that point, same principle.
• Member Posts: 6,928
Options

I've observed flue temps lower than supply temp in my system (Vitodens 6-24) a few times. Generally seems to occur after clear, sunny, cold days when the outside temp drops very rapidly after sunset and the boiler ramps up significantly and delta-t increases. Usually doesn't happen for very long (say 10-20 minutes) but the closer the heat curve is to 1.0 heat authority, the longer it seems to last.

Have also heard of this at least one other time--again with a Vitodens. Has anyone observed such with another mod-con?

According to their literature the "most favorable conditions" will find the flue gas only 3.5 degrees Kelvin above the boiler return temperature. 3.5 degrees Kelvin = 6.3 degrees Fahrenheit. Obviously they're aware that flue temp below supply temp is possible. These "most favorable conditions" may or may not coincide with conditions most favorable for extracting energy from condensate however.

Unfortunately I don't have accurate condensate production numbers as the rain gauge I tried to use was overwhelmed.

I can't find the spec right now but know the Vitodens burner transmitts a "high proportion" of its energy via radiation. (Believe it's about 35%.) So, compared to almost? every? other burner the combustion gasses will be MUCH cooler when they reach the heat exchanger. I suppose this only increases the efficiency of heat exchange from the flue gasses through those 0.8 mm wide by 36 mm long gaps between the HX coils.

At times it really seems that some of the energy that began as radiation from the burner moves faster than the water in the system--almost as if it's trying to "jump" to the coldest thing--the outside walls and windows and without appearing measurably in the emitters. (Before you ask John Paul, I have NO WAY to prove this--it's a suspicion based on observation.)
• Member Posts: 6,928
Options

That's an exceptional paper and I've posted a link to it here numerous times before.

While written by Viessmann and certainly heavy on their specific methods to achieve efficiency, much of it is general and will apply to any condensing boiler.
• Member Posts: 6,928
Options

Supposedly, conventional physicists agree that Tesla's Wardenclyffe Tower was certainly capable of worldwide communications on a vast scale. It's the wireless transmission of usable power--at least through the earth and supposedly through the atmosphere as well--that intrigues some people and causes others to consider him almost kooky.

It's an indisputable fact of history that entrenched interests resist and fear change and will do anything in their power to thwart.
• Member Posts: 1,935
Options
not sure

not sure what your last statement means?

what I do know, grad students everywhere scramble to study something new or make a discovery. so as far as fearing the unknown, theres no such thing in the research world, else we'd still be living in caves and grass hut.

of course radio waves and 'power' waves are the same thing, just different signal strenghts.
• Member Posts: 1,935
Options
its a good thing

I think everyone should have crazy ideas about this and that, thats where new technology comes from.......
This discussion has been closed.