Gasifier installation questions

[Piker]

Hello everyone. I am new to the site, and have a few questions... I will lay out my ideas and calculations for all of you to offer critiques, opinions and insight. Constructive criticism is appreciated.

I recently purchased a gasfication wood boiler rated at 200,000 Btu's/hour. I plan on installing it in my home which has a heat loss of about 125,000 Btu's/hr on the coldest day. (about 80 degree temp differential) The entire house is plumbed with radiant in-floor heat... not the staple up kind. The pex in my floors runs perpindicular to the floor joist through 1" bores about 2" below the sublfloor with a run every 2 feet and a finned aluminum radiator plate betwen each floor joist on every run. Right now floor coverings are non-existent... still working on the remodel... but plan on mostly laminate hardwood and tile, with some carpet upstairs in the bedrooms.

I oversized the wood boiler because I feel that thermal storage is the absolute best way to run a gasifier... the overhead should allow me to heat the house on the coldest day, plus charge the tanks in just a few hours. I plan on modifying two 500 gallon propane tanks to use as thermal storage. The tanks will be installed in the unused "crawlspace" portion of my basement where each tank will be wrapped in reflective bubble wrap insulation as well as surrounded by a wooden frame which can be filled with expanding foam to achieve approximately R-40 thermal resistance rating around the tanks. Is R-40 enough?

According to my calculations, if I run the boiler to 180 degrees, and have usable hot water to heat with down to about 120 degrees in a radiant floor system, I should be able to store about 580,000 Btu's in the tanks. According to what I have come up with, that means that on the coldest day (-10) with the house pulling 125,000 Btu's, it should take about 7.75 hours on a full bore burn to heat the house and charge the tanks, providing about 4.65 hours of usable heat stored in tanks. This basically gives me 12 or 12.5 hour cycle times on the coldest days.

Using the same boiler temperatures but on an average winter day of 20 degrees, and the house pulling approximately 80,000 Btu's, I should be able to pull a full bore run for about 4.85 hours to heat the house and charge the tanks, providing about 7.25 hours of usable heat energy stored in the tanks. Again, providing about 12 hour cycle times on average winter days.

Do you think the math is accurate? I have not taken into consideration the thermal mass in the floors... not sure if that matters or not.

Thermal storage is the most efficient... but it's kind of a pain to have to light the boiler from scratch every 12 hours. And if the boiler needs to run more than it's full bore cycle time of 4.5 or 5 hours to charge the tanks, you will likely not have enough heat to last the entire day if you can only fill it once before you leave for work in the morning. I am guessing there is sort of an art-form to figuring out how to get the greatest efficiency out of your burns... calibrating firebox load size with outdoor temps and the length of time your going to be gone.

According to some other figuring i have done, it doesn't look like it would pay to have more than 1000 gallons of thermal storage. Originally I thought it would be nice to utilise enough thermal storage to get 24 hour cycle times... but since the boiler only runs about 4.5 or 5 hours on a load of wood at full bore, I would be getting up in the middle of the night to achieve the 15 hour run on the boiler to charge the tanks. The 1000 gallon scenario would have me lighting the boiler at 4 pm and filling it with another full or partial load again before I go to bed... and by morning the useable energy in the tanks would not be totally depleted, so when I fire up again in the morning, nothing more than one full load of wood will be needed to carry the system until evening... granted, the boiler will probably idle a little bit during the end of it's load of wood. Make any sense?


My goals are not just the efficiency of the system, but also the longevity of the boiler. It's a pretty pricey unit that I have been told should last 20 or 25 years under normal use wihout thermal storage... but that with thermal storage could last much longer. The gasifiers are great at reducing creosote and acid from the combustion chamber on out... but the fireboxes, I am told, tend to cake up pretty drastically without thermal storage because there is so much smoldering going on in there. With the thermal storage, you can keep a hot fire not only in the combustion chamber, but also the firebox itself, thereby reducing the amount of stuff that will eat through your boiler over time and increasing it's lifespan. Does all this sound true?

Well, I have written a book here. I will wait to hear your opinions and insight on all of this before I start asking technical questions about the installation. I am going to do the install myself, as I understand hydronic heat basics, and I am pretty proficient at sweating pipes... but I have never worked with thermal storage. I am sure there is more than one way to approach the issue. The hotwater heat system will not have an additional gas or oil fired boiler as backup, and there will be 4 zones. Backup will be a small forced air system for emergency's only.

Thanks in advance.

 

[Nofossil]

Welcome to the boiler room.

You've clearly given this a lot of thought. Couple of questions, though:

First, how confident are you in the 125,000 BTU/hr figure? That seems really high to me, especially for a full 24 hours.

Second, are you sure that your radiant needs 120 degree water to deliver usable heat? If it would deliver enough to maintain your house temperature using water at 90 or 100 degrees, your effective storage would be much higher.

I'd suggest that your average output from your boiler will not be 200,000 BTU/hr - it's better to consider that as a peak output.

You've done a great job illustrating why I suggest getting a smaller boiler. If you did the same calcualtions assuming 140,000 BTU/hr, you'll find that you need a longer burn and you don't need the storage to carry you as far.

Here's my scenario: I have an 80,000 BTU/hr boiler that actually averages more like 60,000 BTU/hr. My 'coldest day' avearge hourly heat loss is about 30,000 BTU/hr. On the coldest day of the year, I need a 12 hour burn. I'll start around mid-afternoon (say 3:00), and pack the firebox for the last time at 10:00. That will carry the fire until about 3:00 in the morning. At that point, I'll have about 360,000 BTU of usable heat in storage. That will carry me through until mid-afternoon the next day. Towards the end, the water temp is cool enough so I won't be getting much out of it, but the sun is generally shining by that time so I'm OK.

If I had a bigger boiler, I'd need more storage. Not what you'd expect......

 

[Piker]

Welcome to the boiler room.

You've clearly given this a lot of thought. Couple of questions, though:

First, how confident are you in the 125,000 BTU/hr figure? That seems really high to me, especially for a full 24 hours.

Second, are you sure that your radiant needs 120 degree water to deliver usable heat? If it would deliver enough to maintain your house temperature using water at 90 or 100 degrees, your effective storage would be much higher.

I'd suggest that your average output from your boiler will not be 200,000 BTU/hr - it's better to consider that as a peak output.

You've done a great job illustrating why I suggest getting a smaller boiler. If you did the same calcualtions assuming 140,000 BTU/hr, you'll find that you need a longer burn and you don't need the storage to carry you as far.

Here's my scenario: I have an 80,000 BTU/hr boiler that actually averages more like 60,000 BTU/hr. My 'coldest day' avearge hourly heat loss is about 30,000 BTU/hr. On the coldest day of the year, I need a 12 hour burn. I'll start around mid-afternoon (say 3:00), and pack the firebox for the last time at 10:00. That will carry the fire until about 3:00 in the morning. At that point, I'll have about 360,000 BTU of usable heat in storage. That will carry me through until mid-afternoon the next day. Towards the end, the water temp is cool enough so I won't be getting much out of it, but the sun is generally shining by that time so I'm OK.

If I had a bigger boiler, I'd need more storage. Not what you'd expect......

Ok, it took me a second to wrap my head around the bigger boiler/more storage remark... but that makes sense... I think what it boils down to though, (pun intended) is that I don't have 12 or 15 hours in row to be at home to keep the boiler fired while it runs 3 consecutive 4.5 or 5 hour cycles. I get home at 4 pm bed by 9 or 9:30 most nights, and up again at 4 am. The reason for choosing the bigger boiler was simply to get the thermal storage charged up in relatively short order so I don't have to babysit. Going with a smaller boiler and less storage is like what I talked about in the previous post when I considered trying to get 24 hour burn times... the length of the burn times just aren't practical for me. Your suggestion is well placed however, and deserves contemplation.

As far as my confidence in the 125,000 Btu/hr figure... well... I am not that confident to be sure. I have used several heat loss calculators that came up with anywhere between 110,000 and 135,000. I went with the calculator that gave me somehwere about halfway between the highest and lowest. The house is a remodeled farm house over 200 years old. It's pretty tight as far as remodeled farm houses go... but it's definitely not like a new energy efficient home. Around 3000 square feet plus another 1300 sq feet of basement, which I will not be heating with anything more than the residual heat from the boiler and the piping. I know that our previous forced air propane was a 120,000 Btu unit, and it ran pretty frequently when it got cold out. I don't have exact specs other than to say it ran "frequently...." I mean, it didn't get overwhelmed, but it would work pretty hard.

I believe the boiler has an output of 200,000 Btu's/hr. I have seen the actual test reports for the 150,000 Btu model, and it's output was 163,000. I was told that the 200,000 Btu/hr model was also underated. By how much I do not know.

I do believe that the particular radiant floor system I am using does require 120 degree water since there is no physical contact between the aluminum finned plates and the sublfoor itself. The idea is to heat the entire air space between the joist so that the heat is distributed perfectly evenly across the floor instead of having hot and cold spots. The benefit of having more even heat comes with the price of greater water temps.

I am interested in your thoughts on some of the other ideas i put out there...

Do you think the tank insulation idea will work well?

Do you think longer than 25 year lifespan on a boiler that is used only with thermal storage is possible?

Will the long hot burns keep the creosote levels down in the fire box?

thanks so much for your insight. I appreciate it very much. I will be looking for some ideas with regard to piping this system up. If you have any ideas about any rescources that I could use, that would be great. I know there is some debate over the usefulness of stratification in the storage tanks... I think stratification is desireable... and if I am correct, I will have to modify the tanks with some extra fittings and piping to achieve this stratification. How to plumb 2 seperate tanks is a little confusing to me. One wouldn't be a big deal... but I am not sure how 2 of them in parallel have to be plumbed to utilize the stratification effect to it fullest potential.

Thanks again. I look forward to learning more about all of this.

 

[Piker]

There certainly are quite a few different ways to encorporate thermal storage into a gasifier system. I don't even know where to begin. I think the idea of running zones with circulators right out of the tops of the tanks would be the most efficient use of stratification... but that's alot of extra work to the tanks.

I am thinking I will run primary and secondary loops with the buffer tanks on their own secondary loop. I was wondering if the tanks should be run in parallel or series? It seems like the circ loop should be able to be reversed depending whether you are charging the tanks or discharging them. That or plumb the tanks with two loops. The reason for that would be because when you charge the tanks, you want supply water from the boiler coming in at the top and return water heading back to the boiler from the bottm... but if you are discharging the tanks... you would want the hot water at the top of the tank exiting from whence it originally came in. Make sense? Is there such a thing as a bi-directional pump?

I am not familiar with how the controls are set up on something like this either. I would imagine its alot like computer programming with alot of "if-then" statements. I think I know how I would want the controls to operate the pumps given boiler temp... tank temp... zone activity..., etc... but I am totally unaware of what type of products are on the market to do such things... any suggestions?

That is all for now...
thanks all.

 

[Nofossil]

There certainly are quite a few different ways to encorporate thermal storage into a gasifier system. I don't even know where to begin. I think the idea of running zones with circulators right out of the tops of the tanks would be the most efficient use of stratification... but that's alot of extra work to the tanks.

I am thinking I will run primary and secondary loops with the buffer tanks on their own secondary loop. I was wondering if the tanks should be run in parallel or series? It seems like the circ loop should be able to be reversed depending whether you are charging the tanks or discharging them. That or plumb the tanks with two loops. The reason for that would be because when you charge the tanks, you want supply water from the boiler coming in at the top and return water heading back to the boiler from the bottm... but if you are discharging the tanks... you would want the hot water at the top of the tank exiting from whence it originally came in. Make sense? Is there such a thing as a bi-directional pump?

I am not familiar with how the controls are set up on something like this either. I would imagine its alot like computer programming with alot of "if-then" statements. I think I know how I would want the controls to operate the pumps given boiler temp... tank temp... zone activity..., etc... but I am totally unaware of what type of products are on the market to do such things... any suggestions?

That is all for now...
thanks all.

If you haven't looked at the 'simplest pressurized storage' sticky, it might be worth spending a few minutes on it. So far, it really is the simplest way I've seen to incorporate storage.

It's certainly possible to use a lot of software - I think I've proved that - but there are silicon-free solutions as well. I suppose that relays are in effect if-then logic, but perhaps a bit less daunting.

Primary-secondry systems offer more precise flow control, but can involve more pumps and more complexity.

You're dead on about charging storage top to bottom and withdrawing bottom to top. There are no bidirectional circulators, but circulator pairs can be set up in opposite directions - circulators don't mind reverse flow if they're inactive. Integral check valves would mess this up of course.

To some of your other questions:

Expanding foam in sufficient quantities would be very expensive. Framed in and insulated with fiberglass should be fine. Seal against air infiltration. At R40, the floor above will be warm.

Not much experience here with long-term life expectancy for these boilers.

Creosote in firebox is not a problem - protects the steel, maybe.

 

[Piker]

You're dead on about charging storage top to bottom and withdrawing bottom to top. There are no bidirectional circulators, but circulator pairs can be set up in opposite directions - circulators don't mind reverse flow if they're inactive. Integral check valves would mess this up of course.

Wait a second... shouldn't you be discharging the tank from the top as well? Pulling the hottest water out first to feed your zones?

How many R's would you recommend? Reflective wrap on tanks?

will the tanks be best plumbed in parallel or series? LIke batteries.

 

[Nofossil]

You're dead on about charging storage top to bottom and withdrawing bottom to top. There are no bidirectional circulators, but circulator pairs can be set up in opposite directions - circulators don't mind reverse flow if they're inactive. Integral check valves would mess this up of course.

Wait a second... shouldn't you be discharging the tank from the top as well? Pulling the hottest water out first to feed your zones?

That's what I mean by bottom-to-top - I'm talking about flow direction.

How many R's would you recommend? Reflective wrap on tanks?

will the tanks be best plumbed in parallel or series? LIke batteries.

I'd always go with as much as I could reasonably get. 12" wouldn't be too much, especially on the top.

 

[Piker]

So basically then, in order to always be charging the tanks at the top, and also discharging from the top, you would have to run two loops into the tanks... unless you could get some internal plumbing into the tanks somehow with some check valves... but heaven forbid a check valve ever go bad. I suppose you could plumb the check valves outside of the tank too huh?

so how to plum tanks... in parallel? I will guess parallel... charging both tanks at the same time via a t from the supply.. discharge the same way.

I am going to draw thsi up and post if for you all to inspect for me.

 

[Piker]

I think I am making this more complex than it needs to be... just reversing the flow would be enough right? not really any need for check valves. I think.

I am definitely no plumber.

pardon me while I think outloud

 

[Piker]

I think I might be in trouble. The radiant floor system that I am using requires water temps to be around 150 to 180. Hmmm. That really doesn't make much use of the thermal storage then does it? If the water shouldn't drop below 150, I will have about half the usable storage capacity that I thought I did. Do people use thermal storage for baseboard systems that use gasifiers?

Here's a link to the website where they have a brochure on the radiant heating system I am using..

http://www.jupiterheating.com/ultra-fin-radiant-plates.html

 

[Willman]

Piker, I have been using the Ultra-Fin for two seasons so far. I run 145* water and think I could go a little lower. I have 2" foam insulation around rim joist and below as well as 3/4" subfloor with laminate on top. Optimum floor temps with any radiant system is around 87*.
Will

 

[Piker]

a little lower... meaning 5 degrees or so? That is still going to cut my cycle times short. Even if I run between 190 and 140, I will be probably an hour or so short of where I want to be. I may have to rethink this. I haven't put any of the tubing in any of the downstairs yet... i might be switching radiant methods for the rest of the house so I can lower the water temps.

Any suggestions anyone? Could use some help here.

 

[Piker]

Can someone tell me if thermal storage is even useful for systems that need 150 or 160 degree temps? Bottom line is, if I don't run the water hot enough in the pex in this system, there won't be enough heat penetrating the subfloor to keep the room warm. I can add more ultra fins which would help, but then I am adding a ton of expense to the system. Not sure which direction to take here.

 

[sdrobertson]

Can someone tell me if thermal storage is even useful for systems that need 150 or 160 degree temps? .

Thermal storage is going to help you increase the efficiency of the boiler alittle bit, but mostly it will help you keep the water temps up where you want them for longer times in between loading of the boiler. The more storage equates to more btu's stored which will equal more hours of 150 to 160 degree water.

 

[Piker]

It basically works out that then that because of the need for higher water temps, I am going to have to leave the boiler lit all the time to maintain the temps in the tanks... which means it's going to be in standby quite a bit... which means I am going to have creosote problems with a boiler that's too big. I guess the other option is to install enough baseboard to offset the minimal heat that I would be getting off of the ultra fins at 120* water.

All of this is of course, worst case scenario given the design temp of -10... which it does get to for a week or two out of the year. I could always install an air handler and a few ducts I suppose to make up the difference too... but I really wanted to get away from the forced air thing.

I need to go back to the drawing board and crunch some more numbers I think.

Any input that any of you have would be appreciated at this time.

 

[Nofossil]

If you have good stratification and a pressurized storage system, your typical scenario might look something like this (approximate numbers):

- Heat load: 50,000 BTU/hr
- Storage starting temp: 180 degrees
- Return temp: 160 degrees

This works out to a flow rate of 5gpm. At that rate, you'll be able to supply 180 degree water for a bit over 3 hours. At that point, the whole tank will be at 160 degrees. You're still OK. After another 3+ hours pumping out the 160 degree water, your storage is at 140. I still use 140 degree water in my baseboards, and generally radiant can use even lower temps. If you can get enough heat at 140, then you're good for another 3+ hours. At this point, you've gotten ten hours of heating and used 500,000 BTU.

In my case, my peak demand on the coldest day is more like 30,000 BTU/hr, and my average load is more like 15,000 BTU/hr. Anything you can do to get more heat at lower temps will increase the effective storage capacity.

 

[Piker]

Nofossil...

Am I doing something wrong in my heat loss calculations. I have used reputable heat load software, AND I have done the calculations by hand... and I always get over 100,000 Btu's when I do the house all at once. When I do rooms individually, I get significantly less though, around 65,000 Btu's.

Also, it seems like most people with boiler systems use quite a bit smaller boilers in terms of Btu's than folks with forced air furnaces... why is that? I mean... a Btu is a Btu isn't it? I understand the "comfort factor" with the radiant heat, but it doesn't seem like it should make THAT big a difference.

Is there a difference in how you calculate heat loss for home with hot water heat and a home with forced air?

Do you guys all put significant R-value insulation underneath your pex? Most contractors around here just use the foil faced double bubble stuff.

 

[Nofossil]

A BTU is a BTU, and heat loss is heat loss regardless of your heat source. If you have some history of oil or gas usage in past heating seasons you can do a quick sanity check at least. With fossil fuel boilers or furnaces, there's no significant penalty for oversizing them.

 

[Willman]

i might be switching radiant methods for the rest of the house so I can lower the water temps.

Check out the thick plate staple up, like thermo fin. Not certain of water temps. There is also another method of wrapping the tubing with a composite matting. Not certain on that method. I would call ultra fin and ask them about the lower temps, I read that they will be coming out with a low temp fin.

Will

 

[Piker]

I have been trying to figure out the most effecient way to utilize the thermal storage. I had originally thought that it would be best to use primary/secondary loops, with the storage tanks on a 2-way secondary loop... one way for charging the tanks... one way for discharging. That should yield the best use of the stratification.

So here's my question: what factors do you use to determine when the storage tank is charging, when it is discharging, and when it is idle? And how do I use the water in the system down to 120* if the boiler shuts the main loop circulator off and turns on it's circulating pump at 150*? I would need to keep that main loop pump running yes? And how do you get the blower on the boiler to shut down once it's out of wood and the system is just running on the tanks? I don't think this can be done unless you modify the electrical stuff on the boiler... which would void warranty I believe.

Ideally, when the fire goes out in the boiler, you would want the circulating pump on the storage tanks to start pumping water back into the primary loop. But what sort of device will tell you whether the fire is out or not? If you use boiler water temp as an indicator, you could turn the tank discharge pump on when the boiler's circulator pump turns on... (which would be at the wrong temp anyways... 150 instead of 120) but then once the circulator pump on the boiler turns on, the primary loop pump shuts off... and... if the primary loop pump and the boiler circulator were both on , you would be pulling hot water back into the boiler which would shut the circulator pump and the storage discharge pump off.... I am so conufused. Now I know why people go to school and get degrees in this stuff.

Maybe I am making this more difficult than it needs to be... maybe I should just plumb the storage as part of the primary loop? Again... I only know the very basics of how hot water heat work... and i know much less about control systems. At this point simple is better I suppose.

Help is definitely needed.

 

[Nofossil]

You may be overthinking this a bit. I'm not a primary / secondary guru, but I'll take a stab at it.

You want the primary loop circ to run whenever there is a heat demand - that is, at least one heat load is calling for heat. Probably should also run if the wood boiler is producing heat.

Each heat source has its own circ, which runs whenever that heat source is producing heat. For a wood boiler, that would typically be controlled by the wood boiler's own controller. Some folks use a mechanical timer to shut off the wood boiler after a certain time has passed.

Each heat load has its own circ which runs whenever that load wants heat.

Storage is both a heat source and a heat load. Storage should be an active heat source when the following conditions are met:

1) The storage is hot enough to be useful
2) The wood boiler is NOT hot enough to be useful
3) There is a zone that's calling for heat

Storage should act as a heat load when the following condition is met: The wood boiler is producing more heat than the active loads (if any) can absorb.

I've dealt with the control logic for this in my 'simplest pressurized storage' sticky, but that's a supply / return configuration rather than primary / secondary. Still be worth wrapping your heat around the control logic there.

 

[Piker]

That all makes good sense... I just can't figure out how to do all that with just relays and aquastats.

Almost need a pc to control the system. I am sure there is stuff out there that will do all this... but I would imagine the cost if reflective.

 

[DenaliChuck]

Probably been thought of already, but to shut down the boiler circ pump, how about a control that compares boiler output temp and storage "bottom of tank temp"?

 

[Piker]

Well, it took 2 guys, a compact tractor with a loader, a skidsteer, and 8 hours to get the new EBW-200 into the basement today... but the whole move went off without a hitch. It was actually kind of fun.

I am going to post a quick sketch I drew up of how i plan to work the thermal storage in my stystem... using the least amount of control equipment and thus reducing cost and complexity. Please let me know what you all think of this, as I am not a plumber, and I would like to avoid a disaster.

"A" is the boiler circulating pump
"B" is a zone valve
"C" is the primary loop circulator
"D1" is the storage discharge pump/primary loop circulator
"D2" is the storage charge pump

Here are the following 2 scenarios which basically just use the boiler's control

Hot Boiler (minimum operating temperature achieved)
"A" -OFF
"B" -OPEN
"C" -ON
"D1" -OFF
"D2" -ON (providing no zones are calling for heat)

Cold Boiler (boiler below minimum operating temperature)
"A" -ON
"B" -ClOSED
"C" -OFF
"D1" -ON (providing at least one zone is calling for heat)
"D2" -OFF

"D1" basically becomes the primary loop circulator when the boiler is cold, and the storage tanks are heating the house. The reason that I am reversing the flow to and from the storage tanks via "D1" and "D2" is to allow for proper stratification during charging and discharging.

I did not bother detailing the zones, but obviously they will each have a circulator.

 

[deerefanatic]

Looks like you've got a hybrid primary secondary system there. I like it.. It takes care of a major issue with primary secondary that has no good resolution (being able to reverse flow to the storage tank... Take me on my word, it doesn't work right on normal primary secondary setups.)