Plate Heat Exchanger vs Storage

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maybewood

New Member
Dec 11, 2010
2
Southwest Michigan
Getting ready to buy a wood boiler as a secondary heat source for my multi zone radiant floor heating system. Is there anything wrong with simply utilizing a plate heat exchanger in the loop instead of storage?
 
Apples and oranges.

The role of storage is to allow a hot full-tilt burn of a wood unit so that the fire remains highly efficient throughout the entire burn (damping a fire back robs efficiency and leads to creosote build-up in the boiler and/ or flue) while the storage absorbs any extra heat that exceeds the current needs. Then the storage can be "drawn upon" at later times when there is not even a fire. Think of it as a "heat bank" or a thermal flywheel.

A plate exchanger is merely a way to move heat from one flow to another, while keeping the liquids separate. While some people use a plate HX as part of their storage configuration (such as in my case to couple unpressurized storage to the pressurized boiler sytem) the HX itself contributes none of the flywheel effect of storage.

Hope that helps.
 
The "Simplest Pressurize Storage System" sticky https://www.hearth.com/econtent/index.php/forums/viewthread/19086/ has diagrams for a combo system with and without storage (although you only need one expansion tank, sized correctly). If your current setup is a closed system, you can just tie in the wood boiler, no heat exchanger needed. You can also tie in pressurized storage with no heat exchanger. Remember, a boiler setup (oil, gas, wood) is only a 15 PSI system so you do not need a fancy tank (unless you live is Mass). Most people here use old propane tanks, 500 to 1000 gallons. I have two 500 gallon tanks stacked horizonatally (10' wide, 4' deep, 7' high). Storage lets you run your 150,000 BTU/Hr wood gassifier full out for the typical butn time 4 hours or so). My peak house load is less than 100,000 BTU/Hr and typically it is only drawing one or maybe two of the three zones at 30,000 BTU/hr each. Storage can feed a zone long after the fire is out.
 
IF your radiant floor heat is concrete slabs, and IF the house is relatively tight, and IF the boiler is not oversized, then it may work quite well to store the wood boiler heat in the slab. It won't have the precise control that seperate isolated storage would give you, but it may be worth considering.
 
I have a wood boiler with radiant heat and don't have any storage. It works perfectly! I am confused by the guys that talk about storage, they clearly sound very smart or in the business. I have a Wood Gun "gasification" E-100 and it just turns on when the aquastat calls for heat, then seals off all the air and kills the fire. That is, I don't have a stinky smoldering fire when the unit is not running, no "idling". I do understand about the full burn at best efficency but I thought that all "gassers" were about equal in efficiency. (in using the fuel - wood) My radiant design people spoke to the folks at AHS that make the wood gun and were convinced that they (AHS) knew what they were talking about because they (my radiant people) wanted to include some storage in my system. I have only been burning now for about 3 weeks but I am very happy with it all.
 
711mhw said:
I have a wood boiler with radiant heat and don't have any storage. It works perfectly! I am confused by the guys that talk about storage, they clearly sound very smart or in the business. I have a Wood Gun "gasification" E-100 and it just turns on when the aquastat calls for heat, then seals off all the air and kills the fire. That is, I don't have a stinky smoldering fire when the unit is not running, no "idling". I do understand about the full burn at best efficency but I thought that all "gassers" were about equal in efficiency. (in using the fuel - wood) My radiant design people spoke to the folks at AHS that make the wood gun and were convinced that they (AHS) knew what they were talking about because they (my radiant people) wanted to include some storage in my system. I have only been burning now for about 3 weeks but I am very happy with it all.

I have a brother-in-law that has burned an old Heatmore for the past 13 years and I have an aquaintance that uses a pot belly stove and they're both tickled pink with what they have although more than 12 cords a year go up in smoke in the Heatmore and the pot belly turns cherry red at times and you can observe the condition of the fire through the numerous cracks. If you don't think about or are not able to understand what's going on in these units you will be happy with what you have. I would suggest that anyone looking for advice on these units should not place much credibility on someone offering advice that has only run his unit for 3 weeks.

You're right, the Woodgun has the most positive shut down of any unit I am familiar with. My EKO and most other units will continue to burn a little more but that shut down in the Woodgun and other units is costly in terms of efficiency and creosote build-up. With storage you get a continuous burn at peak efficiency drawing the energy from the wood at a "usable" temperature. Upon shut-down (idle mode) the burn temperatures become waste heat and the refractory cools so that upon start-up it takes some time to get back to "usable" temperatures, all the while using fuel.
There is only one person on this forum, that I know of that is "in the business" (tanks)and he has offered nothing but honest and unbiased information on storage tanks. Most of the others that have posted results about storage are speaking from experience and their knowledge of the process.
 
Look at storage as a battery you charge. Once charged it releases BTU's as the house calls for heat, even if the fire is out. It allows you to not run your wood boiler all the time and it keeps the boiler from idliling.

711mhw-Your boiler is idiling when it shuts off. Keep researching the benefits of storage and you'll see the beauty of it... Some of the newer Tarms require storage, it will prolong the life of your boiler.

Maybewood-A plate heat exchanger is just a device to transfer heat from one pile of water to another. Like from the boiler to the storage tank, or from the storage to the house.
 
Varmebaronen boilers require storage as well. There induced draft boilers do not(read can not)idle, they just shut down the fan in an overtemp
situation and require a manual reset. They also have natural draft boilers which can function with no power, they charge the tank via thermosiphon.
Would be great for off grid home.

As far as storage it's all about convenience for me, I build the fire and load wood when it suits me. When I left for work a few days ago it was 15F at 5:00 am, no fire since the
night before and when I came home at 5:00 pm the house was toasty. Not coming home to a cold house and having to build a fire right away is PRICELESS.
 
I have a brother-in-law that has burned an old Heatmore for the past 13 years and I have an aquaintance that uses a pot belly stove and they're both tickled pink with what they have although more than 12 cords a year go up in smoke in the Heatmore and the pot belly turns cherry red at times and you can observe the condition of the fire through the numerous cracks. If you don't think about or are not able to understand what's going on in these units you will be happy with what you have. I would suggest that anyone looking for advice on these units should not place much credibility on someone offering advice that has only run his unit for 3 weeks.

Fred 61 whoa buddy, I am all ears! I wish that I had found this site before I had made all my decisions. My (mention) 3 weeks experience was intended to show my wetness behind the ears! Also no disrespect (or opinion) was aimed at anybody pro or not. I'm here to learn! I would like to know what type of efficiency I might gain from storage? In my limited experience burning I am supprised by how little wood I use. I have only used wood stoves up until this point for my reference/comparison on wood comsumption. One of my objections to storage in my situation is not willing to give up the extra space. Is the more storage the better and does a guy with storage use his boiler only as needed to "charge" his storage? I may be wrong but it seems like you would allways be building fires. THanks in advance for your thoughts.
 
And I don't know s**t about computers either!
 
When I was looking around, and before I found out the cost, I looked at continuous feed system using wood chip and/or pellets. Interestingly they need a small storage to operate at max efficiency.

If you look at the European systems and their recommendations, I have not seen one that did not specify storage. They usually show smaller storage than you tend to see here, but that may be more down to heat loads.

I am sure part of there reasoning has to do with complying with much stricter emission regulations, you can not turn wood on and off. That goes with anything, just with propane/oil etc you have a very small amount of fuel in the chamber at any given time.

Putting all those high tec controls etc and not having storage, just does not make sense.

In the US the emissions issue is generally less of an issue and maximum efficiency not so important. So storage does not have the same level of consequence.
 
711mhw said:
Fred 61 whoa buddy, I am all ears! I wish that I had found this site before I had made all my decisions. My (mention) 3 weeks experience was intended to show my wetness behind the ears! Also no disrespect (or opinion) was aimed at anybody pro or not. I'm here to learn! I would like to know what type of efficiency I might gain from storage? In my limited experience burning I am supprised by how little wood I use. I have only used wood stoves up until this point for my reference/comparison on wood comsumption. One of my objections to storage in my situation is not willing to give up the extra space. Is the more storage the better and does a guy with storage use his boiler only as needed to "charge" his storage? I may be wrong but it seems like you would allways be building fires. THanks in advance for your thoughts.

You just hit 2 of the 3 biggest (IMO) downsides to storage...

1. it takes a lot of space, some just do not have the space to spare.
2. You end up building a fire every day when it's cold...
and
3. heat loss from storage.

#1 I don't like but live with it.
#2 is a small price to pay IMO. when the wife is cold there is always heat in the tank, to her it's no different than the oil boiler. Can you say WAF
#3 is not an issue IF you can spare the space WITHIN the heated structure. If the storage is outside or in an un-heated building this can be a BIG loss.
 
There are almost as many different benefits of storage as there are people with storage. For me, the biggest benefit is boiler longevity. I ran my wood Gun for 10 years and ended up junking it because the walls of the firebox ate right through. Like you, I didn't run storage. Didn't know any better. I also wish there had been information such as what can be found on this forum. I wish I had a computer in 1980. Anyway, the boiler was sized to maintain the house on the coldest days (nights). The house was oriented to receive the maximum solar gain and during the warmer weather and shoulder season the boiler was in idle mode a good share of the time. The firebox walls were always coated with a black tar that at times would actually flow. That nasty stuff contained enough acids to eventually cause the walls to become paper thin. Toward the end it was too thin to weld on a patch.

My first year with the EKO, I set it up with a 100 gallon tank and experienced the same thing I did with the Wood Gun. Even had to place a drip pan under the flue pipe to collect the dripping smelly liquid. Last season was my first one with a 500 gallon storage tank. Now the walls are dry scaly soot. The benefit that nearly everyone appreciates every day is the ability to fire up the boiler at their convenience. I light one fire a day and burn for 5 hours and usually by 9:00 pm the boiler master switch if shut off. Everyone's situation is different. In my case, along with tweeking my wood burning system I have been insulating and tightening the house like a madman. I know that most people shy away when they hear that you have to light a fire every day but for me it isn't a problem. I just lay three or four smaller splits over the nozzle and aim a propane torch up through the nozzle from below and I have a fire which is hot enough to gas in 5 to 10 minutes. Two 16 oz. bottles of propane purchased at Wal Mart for $6.00 have more firepower than $25.00 worth of kindling. With the Wood Gun it's even easier. If there is the smallest amount of pyrolyzed wood in the chamber all it takes is a crumpled up piece of newspaper lit and thrown in, close the door and let the fan do the rest. Everyone's situation is different and everyone's heat load is different. I would have liked a couple hundred more gallons of storage but space was also a problem for me.

I can't tell you the efficiency gain with storage but I can say that there was a noticable difference in consumption and I'm keeping the smoke output to a minimum. If you've been heating for only three weeks and if it has been as cold there as it has been here, you've been burning under almost ideal conditions. When you get into weather that causes your unit to idle for longer periods or if you get into less ideal wood you will see different things happen and you'll learn from them.
 
The storage buys you time and good behavior. The time you can run without a fire burning can be calculated if you know the load of the building at design conditions.

Heat loads are ever changing so most calculate the buffer at design conditions. At design conditions there nay not be much, or any energy going to the buffer, if the boiler is sized to the load closely.

Also with multi zoned homes the buffer helps prevent short cycling (good behavior) on the boiler, seeing as the boiler does not have a way to modulate to small loads.

Here is a calculator I use and it shows my shop. With 500 gallons I can get through the night. I load the boiler, and EKO 40 at bed time, and it runs maybe 4- 5 hours. I generally have enough coals to get it going in the morning.

Storage is the holy grail of wood burning just as it is with solar thermal. Get it and store it when the going is good. It's hard to overdo storage, if you have the room and budget.

If you want large, here is a solar tank for an 8 unit apartment building in Switzerland. 205,000 l will provide 100% solar heating and DHW for the building.

hr
 

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That is the latest Garn WHS 1000000, firebox will take trees whole.

Found it on YouTube http://www.youtube.com/watch?v=D0wPnlQBVUM&feature=player_embedded#!
 
Ok all. Thanks for the advice on the use of storage. I am attempting to set this up so my propane boiler will automatically come on if the wood boiler runs out. Any one have suggested schematics for this? Excuse my ignorance I am kind of new to the wood boiler methods.
 
OK storage is king! Fred 61, you got my attention when you start talking about the life of the unit! This brings me to ask 2 things,
1 has anybody tried using a septic tank, burried as deep as you could and insulate the heck out of the exterior? I have the equipment to do this myself and a 1500 gal tank is only about $600 and I could locate it within a few feet of the building.
2 This would obviously be un-pressurised and is there a reasonable way around this or am I smokin crack?
My building is basically a nice big shop with an attached house (900sf) stuffed in the end, super insulated and air sealed to the point of insanity. With a Bock Hot water heater providing the heat up until the point that I start to heat the shop. Last winter I did not have the wood boiler and therefore did not heat the shop, and we used only about 150 gal. of oil . You guys are a great source of experiance and knowledge,thanks again
 
You really want pressurized storage if you can pull it off (that way you can skip one or more heat exchangers and a pump or two, and run higher storage temperatures).

If there is any way you could do something like this in or attached to your shop, it'd be a great way to go:

https://www.hearth.com/econtent/index.php/forums/viewthread/18299/
 
When we put in our new septic system I noticed that one of the manufacturers had a tank specifically for storage, so they would not have it on their site unless there was some sort of demand.

http://www.valleyprecast.com/water.php

They call them solar containment vessels.
 
Why do you want to go to this trouble to replace 150 gallons of oil?

I see you want to heat the shop, which could be considered a lower priority heat load than the house. If it was me, I'd put a small tank (maybe 500 gallon propane vertically) next to the house for heat and hot water, and just heat the shop when the wood gun is burning. Then run the wood gun until it's down to coals, charcoal won't produce water or tar. If you have a radiant concrete slab in the shop, then it will take hours to move the temperature and even longer for it to drop, especially if you have anything like the miracle shop that Cannuck described in a recent thread.
 
Needs to be a concrete or metal tank, not MOST fiberglass or plastics. The fiberglass and plastic tanks are not rated for the high boiler storage temps approaching 200F. The "They call them solar containment vessels" look like cisterns to me. The Potable water has more appropriately sized fttings. I can't imagine running a 2600 gallon tank with 3/4 pipe! My 1000 gallons and a 137K BTU boiler uses 1 1/4 pipe.
 
Welcome to the OP'r and the other new guy that commented. Please excuse the sometimes over eager reaction from some members here.

Storage is not the end all/be all of residential heating. Most of the guys here have only run one way. Either with or without storage. Only the guys that have run both ways can give you anything more than theory on the benefits of storage. And for that matter, the benefits they derived for their setup may not be the same you would derive.

Now b4 the disciples of storage get all wound up, I'm not telling anyone storage is bad. But here's what I'd like you think about:

1)How much Oil/gas does a guy save when he puts in a wood-fired smoke dragon?
2)Then how much wood does he save when he goes from a smoke dragon to a 'gasifier'?
3)The how much does he save when he adds storage to his 'gasifier' system?

Now take him from fossil directly to a gassifier. Does he not save way more than the last step which you insist is a must?

The point is, if you convince newbies that they must have storage, and the costs keep him from doing it - even one year - he wastes fuel. The reality is, nearly every 'gasifier' here can be and is run without storage. Conceptually storage is going to be more efficient use of fuel. The reality is though, the efficiency savings of storage is coming from eliminating idle, not from storage itself. So if you could eliminate idle without storage, you would run as efficiently as with storage. Of course, there is virtually no way to eliminate idle without storage. But there are clearly ways to minimize idle.

Would I like to have storage? Yes, id I had solar to go with it. Not just for my wood-fired hydronic though.

Right now I burn three loads a day when its a 'normal work day'. I try to keep the loads appropriate (quality/quantity of fuel) so that they will be down to a small coal bed at 8 hours. Then repeat.

Ok, so now lets say I incorporate storage. I burn flat out for, what, say 5 hours? Now I have to reload, which is not going to work during the day, and would require going to bed later or getting up in the middle of the night. Yup, the heated water is going to continue to heat my house from hours 5 to 8. But now I have to restart a fire and storage is down. I'm not imagining all that great amount of fuel savings. Plus, with a small load idling, the refractory CC stays hot, meaning that upon the introduction of air, 'gassification' resumes nearly immediately. That is not going to happen starting a 'cold' fire.

Anyway, welcome to the forums. If you are thinking storage is in your future, just remember you need a boiler to heat the storage. You could run the boiler without storage for a year or two, saving fossil money for investment in storage.
 
711mhw said:
OK storage is king! Fred 61, you got my attention when you start talking about the life of the unit! This brings me to ask 2 things,
1 has anybody tried using a septic tank, burried as deep as you could and insulate the heck out of the exterior? I have the equipment to do this myself and a 1500 gal tank is only about $600 and I could locate it within a few feet of the building.
2 This would obviously be un-pressurised and is there a reasonable way around this or am I smokin crack?
My building is basically a nice big shop with an attached house (900sf) stuffed in the end, super insulated and air sealed to the point of insanity. With a Bock Hot water heater providing the heat up until the point that I start to heat the shop. Last winter I did not have the wood boiler and therefore did not heat the shop, and we used only about 150 gal. of oil . You guys are a great source of experiance and knowledge,thanks again

I like to be as independant as possible and don't like to feel "trapped". This is why I decided to burn wood instead of pellets. One more guy in the chain to limit supply and manipulate prices. So when the oil shortage rolled around in the seventies, I read every book, publication and article on solar heat, storage and overall living with alternative heat. That's when I learned that any heat lost to the ground is lost forever. I don't know what the soil is like where you are but if is like everywhere else in New England where I've dug a hole, it's wet down there. Even digging up old drains with several feet of crushed stone. I just don't believe anyone can bury a tank and keep it totally dry, at least in this neck of the woods. I would find a way to have it above ground and in the space that is going to be heated if possible.

The size of your boiler and your description of your heat load leads me to believe that a 500 gallon tank would do the job for you. Although more is better, with a low heat load such as yours you should consider standby heat loss of a larger tank. My tank is a 500 gallon unpressurised upright tank about 4 feet in diameter and a little more than 6 feet tall and in the basement of my little house it is still overwhelming in size but I have learned to love it because of what it does for me. I typically start a fire at 4:00 pm and burn 'till around 9:00 pm and then shut the boiler down. I've not had a fire overnight since installing the 500 gallon tank. (wife loves that) The heat emitted from the boiler, flue pipe and associated plumbing goes into the basement and stratifies to the living space for several hours after the burn. Also by that time of the day the zone circulators have been calling for heat and the last usable btus in the tank are being circulated through my staple-up tubing. Being on old seventies ranch, there has been a substantial amount of re-work done to it and consequently the floors are over two inches thick. Although it cannot be touted as a "responsive" floor, it does have the benefit of emitting heat long after the thermostat has stopped calling for heat. Porcelain tile, cement board and Brazilian hardwood make for pretty good storage. Everyone's situation is different but if I were you I would try to incorporate at least 500 gallons of storage in the envelope of the house or other heated space.
 
OK a few answers to fill in the blanks. And thanks for the responce!
The 150 gal. used last year was only for the living area. The shop stayed cold last year not having the time to use it as I was still finishing the living area. The whole bldg. is 38' x 78', of whitch 14' of the 78' is living. The whole building at grade has radiant in the slab with a very simple 3 zone system. The shop is one zone and the living area it the other two, (1st fl. slab and 2nd. fl. ceiling) are for the house. Now, the shop with it's 16' ceiling ht. and 3 12'wX14'h over head doors are insulated but only about a r-12 or so but as you guys know, it all comes down to the chicken s**t weather strip that tries it best to keep out the wind. The 3 doors equal to over 150' of wind chill! Enter my wood gasser. I laid under my truck the other day on a 65 degree floor changing the oil -- it was about 15 outside and now I am officially spoiled!
Fred61 I am new to Maine but I have dug several deep holes aroung here to bury stumps and some very large boulders that were too big to move as well as the house septic tank, seems pretty dry, at least to about 10' or so I must have lucked out in my bldg site because I deffinetly hit water at only 4'-6' during the elec. pole installation! but that was summer, you got me wondering about the water table during the winter months (btw we had over 2" of rain and a 47.8 mph gust sun.) On the septic tank for storage idea, providing that I don't have water sucking away heat, I have talked to more than one guy who sets the tanks (delivery guys) that all have told me that the sticky roll gasket that they put between the two halves of the tank (tob & btm) will hold the whole thing togher, that is picking up the whole tank with the bottom half just stuck to the top, and that leads me to ask I wonder if it could withstand the 15psi or so to be under pressure? Rather than ordering some heavy specialised tank, and paying to ship it from who knows where, get the local guy to make one with no cleanouts or the normal openings but just set in the mold a few pair of threaded pipe for use and a spair. Am I nuts?
 
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