CO Help

Mark Hunt_6

Bob

MUA= Make Up Air

CAZ= Combustion Appliance Zone

Have a great day!

Mark H

Bob Sweet

Thanks Mark



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Unknown

Bob Sweet

ODS Oxygen Depletion System is a type of pilot it is used on unvented heaters typically with a quick drop out thermocouple (30 seconds versus normal t'couple 180 seconds or less)it is designed to shut down the system if oygen levels reach 18% or less.

Mark answered the other two for you. Hope that helps!

jp_2

this is what you are seeing

this "might" be what you are seeing.

the theory that gases cool super quick and drop do not make a lot of sense. but gases that are forced into a recirculation pattern seems more reasonable, basically the same thing appears to be happening, but not gravity influenced.

what you find in chemistry books are looking at closed systems at a constant temperature. whats going on near the water heater s as far away from these theory as possible. such as close by air temperatures that are 100's of degrees different. so saying science is bunk is miss-understanding, you are not comparing apples to apples.

this reminds me of watching a lit cigarettes smoke curl, it doesn't just go straight up as convection suggests. watching a campfire is even more impressive, you can see fast moving down drafts, again it all doesn't go straight up.

jp_2

this is what you are seeing

this "might" be what you are seeing.

forced recirculation air currents caused by pressure differences, not due to gravity. a slight difference but rules out the idea that CO2 drops like a rock, an idea that does not explain why after time CO2 mixes evenly.

chemistry book theory is based on a closed system with constant temperature. what goes on near a water heater is completely different, one being air temps varying by 100's of degrees in close proximity of each other. not comparing apples to apples.

this reminds me more of the smoke off a cigarette, it curls, dips and doesn't go straight up as convection suggests. a campfire is even more impressive, you can see fast moving down drafts, again it doesn't go straight up as convection implies.

added: this could also explain what tim was seeing with ovens.

Unknown

Specific Gravity

of related gases

Air 1.0

CO2 1.5189 (Product of complete combustion)

CO .9667

Water Vapor .6218 (Product of complete combustion)

Nitrous Oxide 1.530 (Part of combustion analysis with Natural gas)

These related specific gravities would explain NOX AND CO2 being heavier than air tending to hover around the equipment and even accumulate low in the area. The subsequent draft pulling air into the combustion chamber plus these other elements into the combustion mix of air and gas will tend to quench(cool) the flame and result in CO. CO's specific gravity will change as air becomes cooler and actually become heavier than air. This is not a typical issue unless we have very cold air coming into the combustion zone from outdoors in the winter time.

jp_2

interesting Tim,

I'll have to think about that for awhile?

but off hand, how does this agree with a vent-free devices?
seems after hours of running the floor would have extremely high CO2 concentrations?

Dale

vent free

One thing about vent free is that they are very low input, some 8000 btu or so. So,the CO2 as a percent of room air is low also. And, the ods will trip if anything but the correct amount of oxygen enters it. When I say trip I mean the pilot flame lifts off the special thermocouple. Take a good look at an ods, most I see are made in Italy, they are primary areated and if you look close have a glass orifice for accuracy. You don't drill them for an LP to nat gas conversion. The smaller heaters aren't convertible.

Unknown

Vent free are

required to be used as a supplemental heat only and should be operated with windows open. The truth is in my servicing these units people complain they have to keep relighting them when used for long periods of time in unventialated spaces. The ODs I think must be working due to contaminated air supply.

I tested about six different versions of unvented heaters many years ago when I was with the utility. I found most of them produced about 25 to 30 PPM air free CO when used properly. In restricted environments CO2 levels at the floor increased and conversly I would see CO levels go up to over 100 PPM air free. At the point of ODS shut down the level of CO2 at the floor was almost double what it was with proper ventilation. O2 was down to about 18.5% and CO was approaching 200 PPM which is the ANSI allowable level. At that point within 10 to 15 minutes the pilot flame was pulled away from the quick drop out thermocouple and the system shut down safely.

The oriices by the way on those ODS pilots is actually a ruby.

Bob Harper

kudos Timmie

As usual, you are correct sir!
Those are typical readings with a VF. The orifice is an industrial ruby shot full of holes with a laser, which makes it very fragile and does not have just one hole. The primary air hole clogs often with dust bunnies causing the flame to curl up and away. In ODS shutdown, the flame speed slows (around 18.5% O2) to the point it appears to be advanced in front of the thermocouple. FYI, you cannot replace just the TC or adjust it--you must replace the entire pilot assy., which is a precision engineered component. Coprecci in Italy makes the most common ODS pilots in use today. The floor level CO2/ low O2 levels do cause a lot of nuisance shutoffs that get misdiagnosed. ANSI Z21.11.2b allows a max. input of 40,000 BTU/hr except bathroom units 6K and bedrooms at 10K. These flames look like Zippo lighters and are a joke.
Bob

jp_2

vent free's and specific grvity

a quick search seems to point out the average sized permanent room vent free heater is about 20,000 btu's.

if my calculations are correct this is what I came up with:
2.4 lbs of CO2/hr or 426 cubic ft /hr CO2. in a closed 15x15 room thats about 20% CO2 after an hour burn. that seems like a lot of CO2?

this comes from a value I found of 12 lbs CO2 from 100,000 btu's of nat gas.

as far as specific gravity, there is some complications to consider:

1.) the CO2 is hot, that changes its specific gravity, at 150F s.g is 1.2, at 350F its s.g. is .92. so this makes things more complex, by the time it reaches room temp it has diffused quite a bit.

but at real high concentrations I could see where it might sink, once it reached room temp?

the real question is, after that CO2 stops being dumped into the room, does the floor concentration stay the same, 1/2 hr, 1 hr, 1.5 hr later? or are you just seeing CO2 currents moving around the room. as in the campfire example, not easy questions to answer I agree.

remember, these seem more like transient conditions and not stable conditions as most chemistry books talk about.

Unknown

Igor and I will

be locked in the lab for the next ywo weeks then we will get back to you with an answer.

The truth is in the real world which I work in and have done so for 50 years things never behave the way you think they will. This is why patience and testing are important. It pays to wait when problems are expected so you are able to see something do what it is going to do.

That is wy I get $400 to $500 an hour when consulting on problems.

I have meaured CO levels on the floor and also at the ceiling as the same with CO2. Just the way things are as there are two many variables.

I do not like unvented appliances or fireplace inserts as they are not very efficient or good for your health.

Greg_40

How about doing a blower door test to see if the home is under negative pressure normally? A draft hood only flows at -3.0 Pascals, which is virtually nothing, pressure-wise. Opening a door, window or natural air leakage into an attic can create negative effects on a home's base pressure. Stack effect, wind, exposures, construction, etc. can all add to negative pressures in a home.

jp_2

truth lies in the lab.

in the real world you can be fooled by variables you are not aware of, leading you to false conclusions.

i look forward to your results.

Jim Davis_3

Absolutely correct. The truth does lie and lie and lie in a lab. What we measure in the field in peoples homes and buildings doesn't count.

jp_2

you are right jim

science is absolutely worth less.............

Jim Davis_3

Science is imperfect people, simulating perfect conditions in an imperfect world that come up with a lot of maybe's and could be's. Necessary evil when there is no other method for evaluation, but when there is, lab testing becomes useless.

I love a scientific study I just read on radon. Tested 60,000+ miners, most of which work in uranium mines and said they represent the normal persons living environment and exposure to radon. But then they said all their studies are inconclusive and not necessarily accurate and required more study but they are pretty sure that there is a possibility that radon does cause more lung cancer than smoking but there not sure because the smokers might not have been exposed to radon so their estimate could be high or low etc. etc. etc.

No, not all scientific studies are bad or useless, just a whole bunch of them.

jp_2

whats funny

is the same science that you insist is bogus, is the same science that developed the gas analyzer and proved the analyzers accuracy, is the same as you call bogus, now to me thats funny.

Jim Davis_3

Who said analyzers were accurate??? They are dependably inaccurate!!! Couldn't have picked a item that I have more experience with that proves my point exactly. I can take any amount of analyzers that have been lab calibrated and stick them in the same flue and every one of them reads different in the real world. And when it comes to the scientific calculations that are progammed into them you really find out how bogus some lab science can be!!

Steamhead (in transit)

This is why

we don't install any "vent-free" appliance, except for hooking up a kitchen stove. We only tear the things out.

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Jim Davis_3

Fortunately you don't work down south where you find unvented heaters everywhere. I've read more stories and been involved in more CO poisonings from unvented gas ovens than unvented space heaters. Don't like either one but that not our choice. Our choice is to test and make sure they operate safe as we can make them. An oven will run clean with the door closed and yet goes bonkers with the door open. Can't fix stupid.

Steamhead (in transit)

Well, we DO test everything we install

including stoves and ovens. Many ovens produce high CO from the factory, but not after we adjust them with the analyzer.

"Steamhead"

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Jim Davis_3

Which is fantastic and appreciated!!! But you are among the few.

It doesn't matter which appliance or device in the house kills the customer, you still lose a customer.

Steamhead (in transit)

Sometimes you can smell

not the CO itself, but its frequent companion, aldehydes.

Can't make this up:

Some years ago I stopped by my neighbor's house around the corner. I've forgotten why I went there, but do remember it was a winter day. The house has steam heat, which is how I first started working there.

She opened the front door and I smelled it right away. Aldehydes. LOTS of aldehydes. I asked her what the smell was and she said it was the stove, which is located in the back of the house. She had just started the oven to cook dinner, said it always smelled like that when it was on.

Uhhhh, we have a PROBLEM here.........

We shut off the oven and opened the windows. I went back to my house and got my Testo, which was fairly new at that time. The oven quickly passed 2500 PPM and I shut the Testo down. She was bug-eyed as she looked at the Testo screen. About an hour later I had it down to about 20 PPM, air-free. No more aldehydes, no more smells and I think her gas consumption went down a bit too ;-)

Now the kicker: A few years later, this was the same house, with the same owner, where I first met The Lovely Naoko.

So if I hadn't fixed that stove, I might not have met my wife!

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