Super condensing boiler... (ME)

Mark Eatherton1

I did it. I moved the drain waste heat exchanger over to the flue gas stack of my Munchkin T50 condensing boiler.

The battery on my camera is dead, so you'll have to wait for a picture.

I've got the data logger hooked up to this puppy and will share the information as it becomes available.

Stay tuned...

ME

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Larry (from OSHA)

as I breathlessly wait

I'm wondering, are you not running out of heating season yet? Here in Minnesota my boiler fired 3 times today. Twice for the DHW heater. So I want to know, as much as we appreciate spring and summer, do you get frustrated when you are nowhere near design days? (to borrow) Inquiring minds want to know. Really, I just want to say thanks for the great science you provide. The Wall continues to be really a wonderful place.

Larry

Mark Eatherton1

Waning Winter...

We got 6" of wet spring snow here last night and today.

That's tuff on blooming tree and shrubbery.

My boiler was off all day long today:-) At least until I turned it back on again.

Here's some Palm Pilot photos of the heat exchanger.

ME

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Brad_9

pre-heat combustion air

Mark,

I assume from this, that even though the T50 is a condensing boiler (right?) that it doesn't condense completely. So you're trying to get that last bit of latent heat out?

Do you think that running the flue pipes concentrically would increase efficiency also? With the incoming combustion air preheated by the exhaust, and the exhaust cooled so that it would condense, wouldn't that increase efficiency as much as this set up? The incoming combustion air would generally be much cooler than any system water, unless you've just run hot water in the house.

You could also use a heat exchanger either in or next to the preheat tank and hook it up to a solar collector, kill two birds with one stone. Get preheat from the boiler in winter and from the solar collector during the warmer months (or from the cooler months too if it's sunny).

Brad

Mark Eatherton1

A btu is a btu is a btu...

and if I can harvest as many btu's from a given source, the source efficiency climbs. Whether I'm preheating the incoming combustion air, or super cooling the exhaust gas stream I'm striping as many useable btu's as I can, and its all worth while IMHO.

My roof line is unfortunately facing the exact wrong direction for solar applications. My intent is to set a medium sized fan coil unit in the attic and take advantage of the "free heat" up there to preheat my DHW during the summer months. It should also serve to cool the attic, thereby helping to keep my home cooler during the blazing summer months.

BTW Brad, the combustion air IS being preheated by a concentric vent. The 2" PVC vent for the Munchie runs through the old 7" B vent, and the combustion air is connected to the base of that stack, so it is being preheated.

ME

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Mark Eatherton1

First run graphic results

Attached please find the first 12 hour thermal graphic results, and a 2 hour AM recovery frame from the same period.

Although it appears that the unit is doing an excellent job of cooling the flue gas temperatures down, the water temperatures are not as high as I'd have thought they'd be.

The points that were recorded pertain strictly to the inlets and outlets of the heat exchanger, and not the system as a whole. So I'm monitoring the water side inlet and outlet, and the flue gas inlet and outlet.

The system started out of night set back at about 5:30 AM and I started my shower just before 7:00 AM. The other drops in water temps are related to dishwashing etc..

Pretty interesting eh...

Questions, comments, observations?

ME

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hr

Got camera?

is you digital charged yet. I'd love to see the mechanical connections, etc.

hot rod

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Dave Yates (PAH)

Got the DT's?

Mark,

I'm curious about your Delta T's & flow rates. Seems like your potable flow rate might me too high for the length & contact surface of the HX to reveal a significant rise. Isn't that a copper HX?

Nice split on the flue temps. Did you insert any type of turbulator to stimulate surface contact between the flue gases and inner wall of the HX?

York's Triathlon gas fired heat pump employeed a HX that resembled a muffler. The expanded tube had a series of smaller tubes to hydronically strip away the heat from the exhaust. If I remember the numbers correctly, the exhaust dropped from something like 950F to 120F. Wishing I'd saved them when we scrapped several of those failed units.


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Mark Eatherton1

Not much to see...

The heat exchanger is 60" of 3" type M copper, with tightly wrapped slightly deformed 1/2" soft copper wrapped around it and tagged with a spot weld on each end.

The venting for the Munchy is 2" PVC non foam core pipe. Transition fittings between the copper and the PVC are your good ol' Mission no hub adapter clamps, 3" PVC to 3" copper.

I set it up so that the condensate the HXer produces rolls forward to another drip trap to keep the copper contaminants from rolling through the Munchies combustion chamber. Kinda like a one pipe parallel flow system.

The copper water side connections are standard sweat fittings.

I'm thinking that if the whole assembly were hot dipped into a vat of molten solder that the water side heat transfer characteristics would double... Anyone got a LARGE vat of molten solder I can borrow for a few minutes???

I've got the flux if you've got the time:-)

ME

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Mark Eatherton1

Unfortunately...

the flow meter I had on the water side during the intial testing I did with the munchie is back up at the cawlidge of hydronic nawlidge (Red Rocks), so I really don't know how many guppies per minute I'm pushing through the water side fo the HX.

I'm trying to locate another flow meter that I can purchase outright and install permenantly on the whole rig.

I do have a rheostat that I could lower the flow through the water side of the HXer, but my thought is that I can't push the water through there too fast.

It falls back to the old addage of which moves more energy, 1 GPM at a 100 degree rise, or 100 GPM at a 1 degree rise. I really don't think it much matters.

As for turbulators, no. I wanted to test this thing in stages. Adding turbulators comes later in the test.

The one positive thing is that the delta Tee is always positive, meaning I am definately gaining thermal energy, and the overall tank temperature increases steadily.

The amount of condensate produced is significantly higher than before based on my observation, so I know that it is effective.

ME

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Larry Weingarten

hot solder

Mark: Call around to see if a local automotive radiator shop still uses a "dipping tank" or whatever they call the vat of hot solder you dip radiator ends into. I'll bet however that GFX will know exactly the difference between soldered and non-soldered, performance-wise. From a corrosion point of view, dipping might be good!

jerry scharf

Mark,

First, these are very promising results.

Can you reproduce the chart and overlay the munchkin operating info onto that. Knowing the stack flow rate as well as the temps would help me to understand what's going on. In particular, I was puzzled by the drop in HX in water temp combined with increased stack temp.

As for corrsion resistance, I might recommend adding a gold film (leaf or deposit) onto the inside of the HX. Almost totally acid resistant and excellent heat transfer.

As for the limited water temp differential, I wouldn't be concerned with that until you have done some turbulent air testing. If my guess that the exit stack temp is a function of the blower speed is right, this would indicate that slowing it down will help.

Some day I would really like to see the HX characteristics at lower water temps. Maybe you could fill the storage tank with your coldest water and see how the HX performs as the temp increases.

When you get it characterized, then you get to run the economics.

A thought/question on flow meters. Can a mass flow meter which is typically used for air be used for water instead? There are some really cheap durable ones of these made for the automotive industry, and it could be a really cheap way to go. It would work a little differently that we're used to, because the mass flow rate will drop compared to the volume flow rate as temperature increases. It's what you really want for heating capacity, but not what you want for pipe flow... One way or the other you end up compensating.

good fun,
jerry

Mark Eatherton1

Jerry...

I wish I could, but the chart rate for the Munchkin is one per second. I can tell you this however, when the T-5- goes to hot water production, it goes to MAX burner rate. When its doing space heating, it modulates around a floating set point based on outdoor reset. That is when you see an increase in stack temp going into the HX, and a corelated drop in water temperature going inot the HXer. That is a DHW demand. Remember, it's a modulating boiler that prioritizes DHW calls.

What do you think it would cost to plate the inside of one of these HXers with gold flash?

With the cost of copper going the way it is, it might be cheaper to make the HXer out of gold, and plate it with copper on the outside:-)

My though was to line the inside with HydraLime like is used in Ford and Sepco stone lined tanks.

I may just take you up on your offer for sizing the trip vanes necessary to break up the laminar air flow.

I think a person would have to use something like a velometer to clock the velocity of the flue gases and then calculate the mass of flow for the gas side of the HX.

I don't think a person could use a typical flow meter for water to check air flow or visa versa, but maybe I misunderstood your comment:-)

Thanks for your comments and observations.

ME

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Mike T., Swampeast MO

Observations & Comments

Observation 1: Your incoming water is fairly warm to begin with--even during your shower it's about 65°.

Observation 2: When water is actually being used you DO get a decent temperature rise--about 6°. If your water is being raised from 70° (avg) to 130° this means you're getting about 12% of the temperature rise from your heat recovery system.

Observation 3: The rise in "flue gas out" temperature during periods of DHW use is a nearly perfect inverse of the incoming water temperature.

Observation 4: The delta-t of the flue gas is higher during periods of non-use.

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

Comment 1: The flue gas enters saturated AND leaves saturated. Any heat you can recover has to come from the vapor--not the air.

Comment 2: What I [think] is happening during periods of non-use is that the OUTER wall of the "super-condenser" is the COOLEST thing--thus this is where the condensation (bulk of heat transfer) occurs. The wall of the tube containing the domestic water heats and doesn't condense much.

Comment 3: As water flows, the wall of the tube (or whatever) containing the domestic water RAPIDLY becomes the coolest part of the system--and the amount of condensation actually DECREASES because there is less area on which to condense. The "flue gas out" actually increases in temperature!

Comment 4: My guess is that Viessmann engineers are working furiously to produce exhaust gas that isn't 100% vapor saturated.

Mark Eatherton1

Duly..

noted. Thanks Mike!

ME

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Nron_9

How much moisture does the flue gas of the viessman vitdens expell now , have seen some real icing problems with the trinity boiler which uses the same heat exchanger as the munchkin boiler ( about 1 gal moisture vapor for every 1oo mbh

bob_25

comment 4

mike, i don't think that's possible , once you hit the saturation line on the psycheatric chart any further removal of heat will just follow the line. I think? bob

jerry scharf

dont think comment 3 is right

Mike,

I asked ME, and indeed the exhaust fluid it moving much faster through the HX during hot water cycle as compared to the heating cycle. Unless we can get some correlation with the burner, it's hard to say the exact differences. As the flue gas has less contact time, there is less tranfer available even with the lower temperature. It's exacly how I would expect the HX to perform.

I'm thinking there may also be some other issues involved with the faster flow rates. Time to break out my aerodynamics for morons book.

jerry

jerry scharf

a couple things

Mark,

You are really going to have to start playing with the Dallas Semiconductor (now Maxim) 1-wire sensor system. They are just the cheapest best way to collect information I've found.

Also, not counting the 5' of HX, how much 2" effective intake/exhaust are you running right now?

Also, calling HTP folks. Can you give me the exhaust cfm flow rate across the range of firing for the T50? I'm trying to figure out how to produce a turbulent flow pattern without excessive drag, and need some numbers to work things against.

I've got a basic design I'm thinking of, but I still don't have a handle on it. My brain is too full now, so I'll push it to the background until I get the numbers.

jerry

Mike T., Swampeast MO

It's supposed to be "impossible" but that's never stopped people from trying to break the rules...