Micro CoGen.

Hey guys and gals (do we have any gals here yet?),

I came across an advertisment for this system in homepower magazine last night, so I did more research:

http://www.sunequinox.com/Technical_Information.html

It uses a on-demand propane or natural gas water heater to keep a very highly
insulated plastic 79 gal or 132 gal tank hot. Heat exchanger coils go
through this tank to peripherals such as a masonry stove, forced air blower,
solar panels, or domestic hot water. The water to the peripherals, i.e.
heater, solar panels, masonry stove, etc. is circulated by 2 built-in
Grundfos pumps. The "water" in the tank just recirculates to the on-demand
heater. Domestic hot water just passes through the hot tank via exchanger
coils. It's highly efficient (>91%). It loses only 3 degrees of heat from
the tank per day if not in use, because of the 3 inches of foam around the
tank. Can supply up to 18 gal/min of hot water. Also, it only uses 82 watts when
heating.

It does exactly what I want, it's expandable to many uses (i.e. solar which we
don't have yet), and can connect to the masonry stove, can heat the whole
house. I'm going to look into it more. This company has only been in the
USA for 1 year, but the Rotex tanks have been in Europe for about 30 years
and they seem to use good quality Grundfos pumps.

There's a video on their website.  Pretty cool idea, I think.   8)  Seems like it would be pretty easy to hook up a Listeroid or other prime-mover cooling system to the unpressurized tank!   An off the shelf CHP system!!!!   Unfortunately my Listeroid is in its own powerhouse 100 ft from the new house under construction (because of noise abatement) and this system would be in the basement of the new house.   :(

Here's another link with a quick blurb about it:
http://www.greenjobs.com/Public/IndustryNews/inews06067.htm

The price is probably outrageous....

Marcus

QuoteAbout the only thing that seems new about this is the fact that it is non pressurized

High efficiency, non-pressurized, plastic tank, circ pumps and controller built in, and 3 inches of insulation also.   I was reading an earlier thread here on indirect fired tanks (found it after starting this new thread), where the tanks mentioned great efficiency of 1 degree heat loss/hour.  24 degrees/day seems pretty high if this sunequinox system claims 3 degrees/day.

Just looking for your opinions.  I guess I hadn't seen a complete system that matches what I was looking for.   Not an expert, though, by any means!

I was planning on doing something similar, but using an epoxy coated steel storage tank (600 gallons). I can get these fabricated locally for a good price.

Putting coils of copper in the tank would not be hard, since you could climb in.  The tank size was for in floor heat.  I planned on 6" of blueboard under the tank, which will be in my insulated shop.

My plumbing scheme was different, I have low efficiency, no electricty hot water heaters for backup dommestic and in foor heat.  They would be manually bypassed and shut down in all but the worst winter weather. 

The tank is on hold now, as my heating operating costs are so low that I'm not sure how much solar I need.  I may do a smaller system for domestic hot water.

Glad you mentioned EPDM, Jens, it slipped my mind. I have read about EPDM lined tanks in several active solar books.  They seem to be widely used.  I have a bargain local fabricator of steel water tanks, and don't tolerate rubber well, otherwise I'd probably go that route too.

One issue that is sometimes forgotten is the tremendous force that even a modest depth of water can create.  

For example, assuming a 4x8 foot plywood box with 3.5 foot depth of water (837 gallons):

The average outward force on the bottom foot is:  3/2.2 (pressure in psi 1/2 foot from bottom) x 12" x 96"= 1570 lbs.

The total outward force on one of the 4x8 panels is:  1.75/2.2 x 42 x 96= 3207 lbs.

So you must be thinking seriously about the forces involved, especially towards the bottom of the enclosure.  

Yes, I've often debated building my own storage tank.   The main concern was the forces involved in deeper tanks.    A 4' x 4' x 4' tank is 64 ft3 = 479 gal.   If you use 4 inches of foam insulation lining the inside, the volume is decreased to 367 gal.   Deeper is better because of heat stratification, but then you get those darn high pressures.   Do you think building with 2x4 studs 1 ft OC and 3/4" plywood is strong enough?   Use 2x6's, or closer stud spacing, or thicker plywood?  

One would think you could achieve tremendous efficiency by using more insulation.  The standard metal tanks that are cheaper seem to use 2" or less of insulation.   They also lose up to 1* per hour.   Why not achieve only 1* /day of heat loss?  My goal is to get it heated up with the masonry stove or on-demand water heater and not lose the heat.  (The solar panels come in to play later.)

The commercial tanks that are large volume I've found are STSS and Haase.   Both are very expensive, i.e. >$6-7k for 500 gallons.   The system I started this thread with is much smaller but it is a complete system with 3 heat exchangers, pumps, etc.

Marcus

P.S.  And what about building copper heat exchangers?  Have any of you ever made them?   I've read about using smaller diameter copper tubing, filling first with sand or salt to prevent buckling, then winding around a pipe.   Does this work well?   Multiple coils sets of a smallish diameter copper connected to form a larger heat exchanger.   Anyone with experience here, maybe when making when making Listeroid exhaust gas heat exchangers?

depending on the size of copper, soft or hard drawn there are various tools that work well to make nicely formed bends

for 1/2" od and under, rigid makes an excellent tool for forming up to 180 degree bends, without sand or other fillers

for larger rigid copper you might try a emt conduit bender, it would work well at making 90's and up to 180 in two passes.

another option is the use of an automotive AC condensor core, such as used on a hd truck, they are sometimes fairly large
and are often made of 1/2 od material.  if you can pick up one at a truck bone yard cheap it would make a nice exchanger mounted
down in a water tank.

i am considering two home built tanks, one for hot storage, one for cold storage, and i may end up using a single unit for both
because my need for both hot and cold is very limited anyway.

for side wall ribs i am thinking of probably 2x6's and 3/4" plywood as well, with the outside insulated, so maybe the wood should be all pressure treated stuff with marine grade plywood?

bob g

The outward expansion forces could be handled quite easily by using 1/2" through rods side to side and or end to end that engage the outside whalers. A tightly spaced piece of galvanized 3/4 pipe with flanges inside against the membrane could shield and allow the tension rods to be dry. Any exchanger coils placement would have to accommodate the tension rods placement. Sure save a lot of exterior work to get the same strength.

I have installed lots of embedded pipe in dam construction and often had to pipe around those tension rods. That is the method used to strengthen form work for the concrete which pushes lots harder than water. Even so I have seen the results of a few shit outs!

Thanks.   Here's a good link, if anyone is interested.   This guy documented his own tank build:

http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/Tank/Tank.htm

Good idea about using a propane tank for a core, Jens.  Thank you.

Marcus:

thanks for the link, it has some useful info that will save me from making a couple mistakes.

bob g

It concerns me in that link that the guy didn't use 2x4 ribs on the side, except in the middle.   He only has the bottom 4" of the walls bound by a ring of 2x4's around the outside.    The guy in the example/link made his tank 3 ft high.  i.e. Side wall force at 3 ft deep is 187.2 lbf/ft2 or 1.3 psi, and at 4 ft deep is 250 lbf/ft2 or 1.7 psi.  That doesn't seem like very much, but over a lateral span (like 8 ft) I suspect the wall would buckle if the tank was taller than 3 ft.

Hey, I was just talking to my dad on the phone about house efficiency, thermal storage, etc. etc.   He had an interesting idea:  What about lining the inside of a small septic tank w/ say, 8 inches of polyisocyanurate foam and EPDM liner?  No worry about leaks or rot, and they're not that expensive.   Wonder if anyone has tried it?

Brett, Smart guy, your Dad.  I've never read about that use of a concrete septic tank, but I think it's a gem of an idea for a buried, insulated tank.  Using foam board on the inside and EPDM liner is what makes it doable- a spray foam job on the outside would be expensive.   I don't know about EPDM prices.

Jens- do you have a link for the proven design you mentioned?  I googled and didn't find one as you described, which is beefier than most I've seen.  

I agree that the ply box Brett posted a link to looks a bit puny for a 4 foot deep enclosure.  Adding more vertical braces would help and is cheap.  The top rail then carries a lot of force, I'd want at least doubled 2x6s, bigger if the length got to 8 foot.  Or increase the number of steel braces across the top. 

The guy in the link buried his 36" tall tank 24" into the ground. Maybe that's why he didn't make it as strong as what's being discussed here.

Placement
"The tank should be placed on a flat and level surface that will take the 4200 lb water weight.  A concrete pad, gravel pad, or well compacted soil.  I think that it is best to keep the tank on the surface, and to provide drainage to make sure that the wood stays dry.  I violated this rule with my tank, in that it is sunk in the ground about 2 ft.  In my case, the soil is dry, the tank is inside a shed that protects it from weather, and the tank bottom sits on 3 inches of open gravel plus 4 inches of insulation -- I'm still not sure this is a good idea, and I would avoid it if you can."

I've been thinking about thermal storage as well. Especially in the summer when I dump most of the hot water my Listeroid makes. In general though I just don't use that much domestic hot water. I do understand you guys with families are in a much different situation.

Thanks, Geno

Thanks for pointing out the earth burial, Geno.  That's very important, and  means that this is not structurally proven as a freestanding tank.  

I've used Tigerfoam and Handifoam on a number of projects. (I can't spray the stuff myself but it cures fast and is not deadly to me the next day.) They are the same isocyanurate foam that is in the blond foam boards (usually foil faced) which is what's recommended for the layer of foam next to hot tank.  I have seen articles showing Isocyanurate foam used for spraying the outside of a (to be) buried tank.  It is not approved by the vendors for constantly saturated (wet) soils.  (Occasionally or seasonally wet is OK.)

The Tigerfoam or Handifoam system is really good for DIY stuff.  It's easy to use, just a bit expensive.

Hi group,

I've been lurking for a while and plan to get more involved. I come from the boating world where efficiency/co-gen is an important way to design and function...especially if your the type that reels at the thought of burning north of 10 gals per hour.

Now onto topic, My design proposes as follows: Dig a 6 foot deep hole laydown a bed of crushed rock, then cover with sand,  (don't forget the drain) then cover with 6" blue foam...top that with a 5in reinforced slab. Then form concrete walls to height, add a grid of DOW poly 55 drums interconnected with cpvc tank fittings. Then a perimeter lining with blue foam. After all connections are made, tested for leaks. The voids between the walls, and the tank grid is filled to depth with peat moss. The peat is an outstanding insulator, as well as generating some of it own heat.

Build a covering deck, that you can lift panels to top off the peat, and service. All circ pumps http://lainginc.itt.com/LG-pump-DC-Solar-Pumps.asp (http://lainginc.itt.com/LG-pump-DC-Solar-Pumps.asp) are operated from a dedicated mmpt controlled PV

It's that simple bet very effective.

Lloyd

Quote from: Lloyd on January 25, 2010, 01:17:40 PM
The voids between the walls, and the tank grid is filled to depth with peat moss. The peat is an outstanding insulator, as well as generating some of it own heat. 

if your peat moss is generating heat, it's gotten wet, and will continue to compost itself to something other than peat moss.  Filling the voids with styrofoam packing peanuts is a good way to dispose of the peanuts for 50 years, and add more insulation.

You may also need some "legs" in the slab, to transfer weight past the blue foam.  At some point, the foam is going to crush, and your tanks will tip/leak/break connections.

Regarding the ply box design:
Jens-
Hardly rocket science, but lots of guys don't have an intuitive feel for statics, strength of materials and structural design, and a failure of an above ground 500 gallon tank could be a serious matter as well as expensive.  

A proven design defining all the structural elements and attachment methods would save a lot of time and get rid of a lot of risk, especially for a TLAR design (that looks about right) with zero structural analysis.

Regarding the use of poly drums:
Some of the standard 55 gallon drums are HDPE, and can't be used for hot water storage. Polypropylene can, and I did find some sources that sell them.  Some used, cheap PP marked drums might make this approach appealing. At $63 bucks each plus shipping for new ones, perhaps not. The multi drum situation makes heat exchangers more difficult, too.  Polypropylene (PP) tanks are also available and might be a good in ground solution, if insulated (spray foam) on the outside.

Blue board shouldn't be used for the foam touching a hot water tank/barrel , at least that one layer needs to be isocyanurate foam board, at least that's what I've read.

It's unlikely that the foam below the slab would cause any settling issues, a five inch reinforced slab will be one big diaphragm, with the drums evenly distributed the weight will flow to the insulation evenly.

Here is one source for drums http://www.usplastic.com/catalog/default.aspx?catid=459&parentcatid=458 (http://www.usplastic.com/catalog/default.aspx?catid=459&parentcatid=458), I'm sure with a little local investigation used drums could be had for much cheaper.

At no point does the insulation come in direct contact with the heated barrels. The reason for the drains is for the moisture from the peat, replenishing the peat would be in relation to the anaerobic process controlled by moisture and oxygen allowed to the compost function of the peat. Less conductive lose will result.

Lloyd

Welcome Lloyd.   Your idea is interesting, but I agree about the rotting peat moss.   Lining some sort of cube shaped tank (whether plastic, steel, wood, or concrete) with polyisocyanurate foam would be far easier and cheaper by far, IMHO.   Making concrete forms for decent sized tank >300 gal is not as easy as building the whole thing out of wood, and not cheaper.   That was how my Dad and I got to talking about septic tanks, because we were talking about forming up concrete walls.

If I went with the buried septic tank idea, I don't think a drain on the bottom would be necessary.   If the tank needed to be emptied for any reason, it could be pumped or siphoned out, eliminating one more potential leak.  Anyone see any problems with this reasoning?   Think the building dept will let me put it under the slab of my basement?  That way it's a straight shot upstairs to the kitchen and baths, and the propane on-demand heater can heat it easier. 

I'm going down to the concrete place to get some info on tank interior dimensions, price, etc.   I've been on-call in the hospital for 3 days, so it's good to get outside.

Marcus

hi Marcus,

Thanks for the welcome.

My plan was also to use either a septic tank or utility vault.  But after considering the conductive losses to the ground. I had the peat moss epiphany.

It would take many inches of foam to get to the r value of peat that is active.

Lloyd

Marcus, (sorry Brett, I got your name here by mistake)-
I've seen plenty of solar home designs where the storage tank was under the floor.  With HDPE liner inside a concrete septic tank, that's pretty secure!  

I hope you can find a good deal on a single compartment concrete tank!

Llyod- I don't think you really want composting peat- once it breaks down, how will you replace it?

Quote from: mbryner on January 24, 2010, 03:04:23 PM
P.S.  And what about building copper heat exchangers?  Have any of you ever made them?   I've read about using smaller diameter copper tubing, filling first with sand or salt to prevent buckling, then winding around a pipe.   Does this work well?   Multiple coils sets of a smallish diameter copper connected to form a larger heat exchanger.   Anyone with experience here, maybe when making when making Listeroid exhaust gas heat exchangers?

A homebrewed heat exchanger?  Too easy:
http://www.olderascal.com/brewing/wortchiller/index.html

You get some piping hot water out of those things.  Ought to work just as well in the opposite direction.  This is the tube bender he's talking about:
http://www.homedepot.com/h_d1/N-5yc1vZ1xn8/R-100647978/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053
I'd rather do that than fill with sand and keep my fingers crossed.

Bruce,
Although I've been following this thread, I'm not involved......

-Brett

Sorry Brett, I put your name in my post where I meant Marcus.  My bad.

With the price of copper and the ammount of time you spend fabricating it, you can get a brazed flat plat heatex that will out perform it by a large margine on Ebay, for what you would spend in copper alone.  I had originallly planned on making my own heat exchanger for collecting the heat from my 6/1's cooling system.  After calculating the temperature differences I wanted/needed, I determined the ammount of surface area in copper pipe I would require.  At the going price in my area, it was well over $100 in copper pipe, plus fittings and my time to fab it.  I bought my 600 SQ/In flat plate heatex from a wood fired boiler vendor on Ebay for around $95 delivered...  Coiled copper pipe heat exchangers really are not all that efficient, especially considering the ammount of material used in their construction. Copper is a good thermal conductor, but low surface area and laminar flow or lack of turbulence are their largest drawbacks. 

My .02 after having done the math...

QuoteWhen I build my large heat storage tank I will depend on the heat stratification of the stationary hot water for additional efficiency.

Ditto.

ronmar, how would a flatplate heat exchanger work in a large tank?   Don't they have to have a counter-current set-up of transfer fluid and fluid to be transferred to?

So, just in case anyone is interested in what I came up with today (and documenting for my own purposes):

At the local concrete plant, at 1000 gallon septic tank is $970 + ~$30 delivery.   The tank is a rectangle, made on-site to order.  They can put in whatever I want for a manhole, but standard is a 24" plastic cylinder with cap.  They can insert any number/size of pipes desired in the lid during casting.   The tank is poured first and then the lid is poured on top after the bottom and sides are solid.   
The inner dimensions are 61" D x 86" W x 55" H.   
With 8" of interior insulation: the volume is reduced to 122,850 in3 or 531 gallons.   
With 6"       "           "                   "             "         155,918 in3 or 675 gallons.

My favorite local lumber yard (i.e. where I have an account) carries insulation in 1", 1.5", 2", and 3" thick 4'x8' sheets.   3" thick is $60/sheet.  Every 1.5" is about R value = 10.
8" of Rmax polyisocyanuate insulation: R = 53.
6" of Rmax           "                "         R = 40.
Think R40 is enough?
For 6" thick I'll need 12 sheets of R max = $720

Estimated cost of EPDM pond liner:  $150

Excavation costs are minimal because they are excavating the house foundation anyway next week.   I'll just have Derrick dig the hole at the same time.

Cost for 1000 gallon septic tank lined with 6" polyiso foam (R=40) and sealed with liner:   $1870

The local pipe and electrical store has flexible copper coils:  1/2" diameter = $3/foot,  3/8" diameter = $2/foot
Guessing I'll need to shell out about $500 for copper in the end.
Any of you engineers remember off hand the equations for heat exchange to help me figure out length of coils necessary?

For the domestic water exchanger I was figuring on using 1/2" coils at least.   Maybe one, or should I use 2 in parallel?    For the on-demand propane heater coil and solar/woodstove coil I was going to use 2 coils each of 3/8" in parallel.   They would be running of circulator pumps anyway at lower flow ~1-2 gpm (assuming here, need to get data on the Laing and El Sid pumps, etc.).

@BruceM:

QuoteMarcus, (sorry Brett, I got your name here by mistake)-

No problem.   Figured you'd catch it sooner or later... :)

@FatCharlie:

Thanks for the tip about the tube bender!

Marcus

Edit: spelling and clarity

And, for those of you wondering about smashing the insulation: from the Rmax data sheets,  the compressive strength is 20 psi (= 2880 lbs/ft2).   Put in perspective, a 4 ft high column of water with a 1 ft square footprint is about 30 gallons or 240 lbs.

I am just curious as to how are you going to fasten your pond liner. Are you planning to line and insulate the inside top also?
The tanks around here are cast in halves, a top and a bottom with a seam around the middle, think mickey D's hamburger box.
Sounds like a good plan but I'm just not bright enough to cipher this one out. Pictures help! I'm a visual learner.
(8 x 10 color glossy pictures with circles and arrows and a paragraph on the back of each one telling what each one was)
Ron

In the immortal words of Miss Emily Litella, "Never mind" on re-reading your post I saw "The tank is poured first and then the lid is poured on top after the bottom and sides are solid."

Quote from: BruceM on January 25, 2010, 02:24:43 PM


Llyod- I don't think you really want composting peat- once it breaks down, how will you replace it?

Hi Bruce,

I don't want to try and convince anyone, but the idea has many merits. First one has to understand peathttp://en.wikipedia.org/wiki/Peat (http://en.wikipedia.org/wiki/Peat).

Unless there is a reason to remove the peat it could last thousands of years with just a topping off. It can be controlled by anaerobic process, it can be easily removed by a large shop vac.

I have an old Swed friend who said that the only way he could keep his underground pipes from freezing was to fill the pipe trench with peat.

It could even be a Methane gas producer http://www.peatnet.siu.edu/Assets/G.pdf (http://www.peatnet.siu.edu/Assets/G.pdf), which could be used as an additional heat source.

Everyone's gardens love the stuff, it can even be used as fuel to burn.

Ok that's it.

Lloyd

Sorry just one more link...I'm done
http://www.tsl.uu.se/UHDSG/Popular/Peat.pdf (http://www.tsl.uu.se/UHDSG/Popular/Peat.pdf)

Other uses:
Peat has also been used as an isolation material for construction due to the low thermal conductivity. Iceland, Ireland and many other places suffer from lack of major forests and had to use other construction materials. Peat was then used as an isolating layer between the outer wall and the inner wall or as covering material on the roof.

Here is a link http://www.pws.gov.nt.ca/pdf/GEP/13-Insulation-Apr04.pdf  (http://www.pws.gov.nt.ca/pdf/GEP/13-Insulation-Apr04.pdf)to a gov study on northern pipeline insulation issues....which may be a good resource for all insulation ideas.


http://www.vdh.virginia.gov/EnvironmentalHealth/Onsite/Regulations/FormsDocs/Documents/Eco-PureTypicalDesigns.pdf (http://www.vdh.virginia.gov/EnvironmentalHealth/Onsite/Regulations/FormsDocs/Documents/Eco-PureTypicalDesigns.pdf) It could also be combined to create a water purifier.

http://www.eco-purewastewatersystems.com/septicpumptanks.html (http://www.eco-purewastewatersystems.com/septicpumptanks.html) Eco Pure Poly Septic Tanks

Methods of Insulation http://www.freepatentsonline.com/6105335.html (http://www.freepatentsonline.com/6105335.html)

Peat Moss Insulating Panels http://www.kompass.com/guide/extraction-industries/peat-moss/GSENWW51010102_C11140.html
(http://www.kompass.com/guide/extraction-industries/peat-moss/GSENWW51010102_C11140.html)
Thanks,

Lloyd

Lloyd,

Well, I'm learning new things about peat.  Peat may be a great insulation material, but how would you use it around a wooden storage tank like most of the guys here are interested in?   It would make the wood rot and be wet all the time.   Also, it wouldn't work in my situation because if I do place a septic tank under the foundation of my house, the building dept will want it surrounded by non-compactable material, i.e. gravel, sand.

Anyway, I was all excited about this septic tank heat storage idea, thinking we had a novel concept.   Then I found another guy on the net who did it 30 years ago:

http://yarchive.net/ac/solar_heat.html

Still, it's pretty cool.

Marcus

OK, I feel stupid.  I'm finding more and more stuff about using septic tanks for heat storage online:

http://hearth.com/econtent/index.php/forums/viewthread/17752/P0/

When peat is kept dry and fluffy, it's insulative.  If damp, it rots, composts, decays.  Hay bale houses do the same.   If you want insulation, keep it dry < 20% moisture, otherwise it will decay.  You may get a little warmth from it's decay, but you then start loosing insulation that must be replaced. Same from the methane, too much work to try to get methane from your peat insulation, then you have to clean up the mess, and replace it.

Quote from: mike90045 on January 26, 2010, 01:57:11 PM
When peat is kept dry and fluffy, it's insulative.  If damp, it rots, composts, decays.  Hay bale houses do the same.   If you want insulation, keep it dry < 20% moisture, otherwise it will decay.  You may get a little warmth from it's decay, but you then start loosing insulation that must be replaced. Same from the methane, too much work to try to get methane from your peat insulation, then you have to clean up the mess, and replace it.

Mike,

You are for getting the anaerobic process, natural peat bogs are a direct result of being water saturated, which creates the oxygen starvation.

Quote from: mbryner on January 26, 2010, 01:12:39 PM
Lloyd,

Well, I'm learning new things about peat.  Peat may be a great insulation material, but how would you use it around a wooden storage tank like most of the guys here are interested in?   It would make the wood rot and be wet all the time.   Also, it wouldn't work in my situation because if I do place a septic tank under the foundation of my house, the building dept will want it surrounded by non-compactable material, i.e. gravel, sand.

Anyway, I was all excited about this septic tank heat storage idea, thinking we had a novel concept.   Then I found another guy on the net who did it 30 years ago:

http://yarchive.net/ac/solar_heat.html

Still, it's pretty cool.

Marcus

Marqus,

I think that the ply tanks are going to suffer rot in a very short time, the liner will trap the moisture. The only sure way to slow the rot will be to use pressure treated lumber and plywood.

All insulation material are subject to water take up and will eventually loose their insulating values...yes even the various of foam boards, especially if they will be used in the tank.

It might be possible to excavate a 2-3 foot  around the septic tank and back fill that with peat.

Lloyd

Marcus,

When I built my cabinet shop, the Old Swed who poured the slab put about 1 1/2 foot of  highly compacted peat down, then a layer of 6 inch crushed rock, then a 5' reinforced concrete slab, the floor stayed at near room temperature, and was warmer than room temp in the morning before the shop heater came on. After 20 years the slab has not failed, and shows absolutely no signs of hydrostatic pressure cracking.

Lloyd

Where do you get Peat for cheap?  I've never seen anything but very expensive bagged Canadian Spaghnum (sp?) peat moss here in AZ. It would make foam look cheap.

Foam board also works well under a slab, so it's also only a matter of cost and risk. Foam between slab edge and stem wall is also very important, thermally.

I don't suppose there is any data available on R value for peat moss at various compressions/density?

Hi Bruce,

My shop is a pole building, so no stem wall.

In Seattle at Home Crapo the good Canadian Peat goes for about $6.00 per bail...don't know the weight, but it is highly compressed, and the bail is about 36 x 18/20" square.

Which is way cheaper than insulation at the same store.

A good garden/farm store will likely sell it by the yard or truck load.

Lloyd

I'm still trying to find some R-value info for peat moss.  Any suggested links? 

Hi Bruce,

I'll have a look....Quick search turned this up, certainly worth looking at.


http://www.perlite.com/faqs.htm (http://www.perlite.com/faqs.htm)
Q. What about Perlite's insulation uses?
A. Perlite's R-value is nearly 3.0 per inch at 6-lbs./cu. ft. density. It registers 0,0,0 on ASTM's E-84 fire tests for flame spread, fuel contribution and smoke density. Water resistant, silicone treated Perlite is poured directly from the bag into cmu block and cavity walls. UL Design U905 shows that a 2-hour fire rated 8", 10" or 12" concrete block wall improves to 4-hours when cells are filled with water resistant Perlite insulation.

or this

http://seanmichaelbutler.wordpress.com/2009/01/05/your-home-is-garbage/ (http://seanmichaelbutler.wordpress.com/2009/01/05/your-home-is-garbage/)
A Bioblock with a one-foot thick EPS or peat moss core, on the other hand, achieves an R-value of 40.


http://www2.niles-hs.k12.il.us/jacnau/IJAS/Best%20in%20Category%20Winners%2706.htm (http://www2.niles-hs.k12.il.us/jacnau/IJAS/Best%20in%20Category%20Winners%2706.htm)
29. Which Filling Gets Top Billing?

Purpose

            The exhibitors are attempting to determine which of four selected materials, when used as fill in a burlap sack, performs best at stopping the passage of water.

Procedure

            The exhibitors assembled a controlled water flow device and filled burlap sacks with each of the four selected materials: sand, soybeans, diaper material and peat moss.  Using their controlled water flow device, the exhibitors tested the performance of each material in stopping the passage of water.  These tests produced substantial, reliable data from which to determine the efficacy of the fill materials in stopping water flow.

Conclusion

The exhibitors concluded with reasonable confidence that peat moss blocked the highest volume of water, followed by, in order, sand, diaper material and soybeans.  Peat moss was the most effective at stopping the passage of water.  The exhibitors noted, however, that the peat mossÕ lack of measurable weight would be a problem in actually substituting peat moss for sand in any burlap sack barrier, as pressure would have to be applied to keep the bags in place.  The exhibitors expect that a combination of sand and peat moss could provide both an improved fill material for any burlap sack barrier and a more environmentally-friendly option.

Bruce,

A definitive answer.


On the other hand, some tests carried
out by the National Research Council some years ago on a material
marketed as peat moss indicated a "k" value of 0.29 when placed
at 3.2 Ib./cu. ft. density.
http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/tn/tn222.pdf (http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/tn/tn222.pdf)

Quote from: mbryner on January 25, 2010, 11:39:53 PM

QuoteWhen I build my large heat storage tank I will depend on the heat stratification of the stationary hot water for additional efficiency.

Ditto.

ronmar, how would a flatplate heat exchanger work in a large tank?   Don't they have to have a counter-current set-up of transfer fluid and fluid to be transferred to?

Same as a copper coil would in a large tank.   Pump hot water thru a coil at the bottom of a tank of water, and the tank water that gets heated by the coil rises to be replaced by cooler water.  Add or subtract energy to/from the tank and you will have fluid movement.  Stop moving energy and the water will mostly stop and stratify.  I say mostly because you will always be removing/loosing energy.  

Since the flat plates thermosiphon so well, a vertically oriented flat plate heatex at the bottom of a tank, with the primary "loop" fed with a hot supply and cold return pipe, would induce thermosiphon flow in it's secondary "loop". A chimney pipe on the upper outlet of the secondary side would assist this flow and deliver the warmed water to the top of the tank.  This would also allow you to setup counter flow which would be more efficient and which is not really possible with a free coil in or at the bottom of a tank(see attached drawing).  This would be way easier to service than the coil in tank, cost less than the copper coil material for a given surface area, and be more efficient IMO.

Turbulence is your friend in heat transfer.  A coil in tank heats up, and the surrounding water absorbs this heat.  Since there is nothing really there to channel the water, it dosn't readilly move away due to eddy currents and friction.  As the warmed water slowly flows around the pipe it builds up laminar flow.  So you get a really warm layer right against the pipe skin, kind of like the water layer in a wet suit.  This warm water against the pipe, effectively lowers your Delta T which slows heat transfer.  It takes time for the heat to move thru this layer to dissipate into the surrounding water.  So you either need to pump your supply water slower to allow more time for heat transfer, or add additional surface area(copper) to compensate for ths fact.  The same thing is also happening on the inside of your copper pipe where the pumped fluid builds up a laminar layer against the skin of the pipe which insulates the warmer center flow from the cooler pipe skin.  Most of the Wort Chiller builders reccomend running a piece or two of bare copper wire(there is that "C" word again) inside the pipe to cause turbulence and help break up laminar flow.  The opposed herringbone pattern of the flat plate heat exchangers makes laminar flow all but impossible even at very slow flow rates.  That is the real key to their efficiency.

I believe this same configuration could be used for domestic water pre-heat.  Just put the heatex at the top in the warmest water.  As long as the water at the top of the tank is warmer than the feed water, it should cool the water which will flow downward thru the heatex secondary, same as the cooled water falls in a thermosiphon radiator...   My personal plan will have a little twist on this scheme with a pump that is controlled by a thermostatic switch set just a little higher than the electric element controller is.  As the water tank temp falls, this pump will draw cool water from the bottom of the domestic hot water tank and pump it thru the heatex to maintain domestic tank temp instead of the electric element cycling on.

(http://i270.photobucket.com/albums/jj85/rmarlett/th_storagetank.jpg) (http://s270.photobucket.com/albums/jj85/rmarlett/?action=view&current=storagetank.jpg)

Thanks Lloyd, alas I'm not able to convert that to a US R value for comparison. A K value is the same as the newer U value, I think.   R= 1/U if it was in US units, but I'm not sure to get it to an R value per inch thickness.  It does seem like an interesting material for some applications.

Ronmar:

That's an interesting idea.  All the flatplate exchangers on e-bay are pretty expensive though....   Where were you going to get them?

Some of the industrial flat plate exchangers are pretty expensive.  The one I am using is a brazed variety, stainless plates, brazed together with copper in an oven.  Search "brazed flat plate heat exchanger" on ebay  and you will see a lot of these smaller units engineered for domestic heating and lighter industrial applications.  I bought the one I use on my 6/1 from a wood fired boiler vendor for under $100 delivered.  5"x12", 10 plate, about 600 sq/in.  It quite easilly takes 195F engine coolant and delivers 120F domestic water, transfering about 18,000 btu/hr at full engine load...  www.flatplate.com has an online calculator to help you choose an appropriate sized heatex for your application.  

How bout this idea,

Take 1000 gal propane tank epoxy coat inside and outside, cut all the fittings in the top including a manhole,
dig a big hole fill the bottom of the hole with peat wet it out and use a jitterbug to reach a compaction required, set the tank, back fill with peat. Again wet  it out and compact to desired.

All the water used in the compaction will leach to the surrounding soil and reach a level equal, so as long as you place the tank in dry soil with a water table low enough. It will create an anaerobic environment that the peat will dry and not further compost

Put an access vault around the fittings/manhole (insulate the cover) and then trench and pipe to the building

Lloyd

I think you'll find that a 500 or 1000 gallon propane tank aren't cheap but they've been worse.  I just checked- near the fabrication plant in the US its $1200 for 500 gals,  $2200 for 1000 gals.  Elsewhere add for additional freight.  That's a very good price compared to when I bought some tanks 2  years ago.


Since we can't convert peat moss's k value to a US R-value, and also don't know the compacted value, it seems pretty "wild wild west" to me.  I guess we can assume about the same value as straw bale, for about the same density, that's between R 0.98 to 2.38 depending on density and moisture content.  Wikipedia says straw bales are R 1.5.

Compacted peat?? R 0.5 ???

The R-value when saturated is another unknown, and is important for an outdoor buried application. Most materials like sand and sawdust loose much of their insulation value when wet.  

Hi Bruce,

A quick google http://images.google.com/images?hl=en&client=firefox-a&rls=org.mozilla:en-US:official&hs=dlg&q=used%20propane%20tanks%20500%20gal&um=1&ie=UTF-8&sa=N&tab=wi (http://images.google.com/images?hl=en&client=firefox-a&rls=org.mozilla:en-US:official&hs=dlg&q=used%20propane%20tanks%20500%20gal&um=1&ie=UTF-8&sa=N&tab=wi) turned up many opp's for cheaper. These are certified for pressure gas, if you contact a propane distributor, and tell them you want a used tank that's not certified, it will be much cheaper. This surely looks cheaper than a septic tank.

http://collectiveknowledgellc.com/propane.html (http://collectiveknowledgellc.com/propane.html)
1000 gallon for $1,350.00
(sand blasted & painted add $200)

500 gallon for $595.00
(sand blasted & painted add $150)

250 gallon for $425.00
(sand blasted & painted add $150)

Now on to r-values for peat, I'm thinking your a little conservative, I'm estimating an r-value at about 4-5 per inch compacted to 6.2 bls. Peat by the yard here in Seattle is $6.45 per yard delivered, So assuming I put a 3 foot layer around the tank. I will have an extremely well insulated tank, cover with some water impervious ground cover, whether it be ground scape cloth or or cc slab. Now as long as you install in dry soil no moisture issues.

The 1000 gal tank is 16 feet long by 43 inches, so that's about 11 yards of peat, so let's go ahead and triple that for compaction, that's about $225.00 delivered, using a 3 foot compacted around the tank.

I think well a little research this might make a viable option for a tank that will serve a long life.

Lloyd

Well, since the co. building dept. is already making me consult a geotech engineer about putting a concrete septic tank under the basement, wonder what they'd do if I decided to put in a propane tank surrounded by peat moss!?   ;D   At least with a concrete tank and polyiso foam around it, there are known variables.  6" foam = R40.   Simple as that.   Lloyd, if you go dig in your backyard, put the propane tank in the ground and put that peat moss around it, then get us hard data, you may be on to something, and you may have quite a receptive audience.   :)   If not just for the novelty factor! 

Since last posting here, I found many examples on the net of using concrete tanks for heat storage.   Most people are putting the foam insulation on the outside, though.   Seems to me if the ground gets wet around the tank and insulation, then there's bound be quite a bit of thermal bridging, no?  Unless I put a water barrier completely around the outside envelope.  Someone correct me please if I'm wrong.   Any glaring reasons why not to put insulation on the inside and use EPDM liner, like the wooden tanks?  My contractor wants to put it on the outside, maybe just because he's used to putting insulation around block foundation wall perimeters.

marcus

Just cover the outside of your tank in good ol' Black Mammy roofing cement (tar) then add your insulation and wrap that rascal in black plastic. Shoot, under a slab, and with proper drainage, it will still be there long after the cockroaches have died out. That black plastic
will never decompose! An added plus is an increased heat storage capacity from the mass of concrete. They's more'n one way to skin a cat! ;)
Ron

ok people,

Let's stop for a quick second..... a wet basement is the result of "service water" (look it up on google), now just imagine a cc tank full of water...hydrostatic pressure alone will weep the tank dry, not to mention saturate the insulation, what ever it is.

An EPDM liner is only good for 140 degrees(not the most efficient hot water heating sys), it has a short life time if kept at 140 and above.

A good recovery, and thermal system; to be the most efficient needs a constant tank temp of 160 and above, by the time you allow for loss in the pipe to and from the tank, and efficiency in the thermal heat system.

A 1000 gal tank is going to take a good BTU delivery to be cost effective, most systems such as solar hot water don't get there now...maybe an evacuated tube sys might. The system we need think about is truly a Co-Gen, waste engine heat, solar, and maybe even a voltage dump from an MMPT, or dc gen once you pass the bulk charge stage(if you're lucky).

Marcus...my thought based on experience with a number of building municipalities, is that you wait until the house is permitted. I see no reason to obtuse the permitting process with something most bureaucrats know nothing of, and are only interested in abetting if there is something in it for them.

It might seem good to have the tank under the foundation, but I think that locks you in to all sorts of potential issues, it may(no it will) cost more to permit, and resolve, if a problem develops. My thought is that an underground tank adjacent is a much more efficient process overall, and I'm not just talking mechanical efficiency.

What if? What ever tank and insulation you decide on, and there is some sort of catastrophic issue, what would be the costs to unearth a tank under your home?

A tank under a garden shed, that also provided the support for a solar water collector, would in my mind solve many issues. The costs to trench and insulate the piping to and from the main house, is much less troublesome than any of the potential issues of a tank under the BIG HOUSE.

Lloyd

i can't remember,but i have it somewhere in  my collection of such a house with the tank under the basement
it iirc was built by MIT back in the 30's and has a ~27000 gallon tank under it
the tank is charged by solar during the warm/hot/warm months and heated quite effectively through the upper atlantic
states winters.

now i can't imagine how a listeroid/changfa or any other small engine is going to charge a 1000 gallon tank let alone a 27k gallon
tank.

Lloyd mention of using a dump load function from the electric side of the cogen seems most plausible, but i doubt many here will do
it,

after finding that my s195 based trigen operates at peak efficiency (as measured in BSFC/kwatt/hr electrical) at full load, it became apparent
that my loads need to equal the full capacity of the unit, either a single load, or a mix of loads makes no difference
if i cannot provide enough to max out the system, then i will be driving a resistive element heater to aid in heating my thermal bank.

i am thinking that something as simple as a hot water tank element mounted in a piece of copper pipe with water flow T's in and out
and well insulated would work very well for such duty. the controller system could sense and modulate the power to the element to use
any and all available surplus power generation to keep the unit operating at full output.

i guess i would have to do the math, and run some scenario's to determine how best to make something like this work, perhaps between
other loads being switched on and off line the heater could be brought on to fill those gaps?

bob g

Llyod, You lost me totally on this:  "I'm estimating an r-value at about 4-5 per inch compacted"

Closed cell extruded polystyrene, is about R6 per inch.  Urethane foam is about the same.  No way compacted peat is anywhere near this.  You sure haven't provided any data to support this.

Further, the notion of burying a steel tank surrounded by peat, and not having the peat get saturated from ground moisture... well, good luck on that too.

And lastly, a used propane tank is a nasty thing I wouldn't use for a heat storage; you don't want to run your potable water through toxic water in a single walled heat exchanger- that will not pass inspection or a sanity check.    

Marcus,   Gorilla glue or foam-in-a-can be used to seal the edges of foam board, so water infiltration isn't as big of an issue, but it is a mess to do.

 One advantage of insulation on the outside of the concrete tank is that the tank mass becomes part of your thermal storage mass.  Plus your tank just got smaller.

Handifoam is being on ebay  also check Tigerfoam.com.  It's running about $610 for 600 board feet (1" x 1 foot square)  at Tigerfoam- though I think Handifoam has better quality control (you get the board feet you pay for). The advantage of the sprayed foam is that it becomes integral to the tank.  The kits for this make it very easy to do.  It's hard in about 30 seconds, you would just go around the tank building it up a couple inches at a pass. 

I still like the foam and epdm on the inside, too.  Tough choice.

Bruce,

One of links above went to a site in Ireland that makes, insulation board from compacted peat, at 6.2 lbs, the listed u value was cross referenced at wiki to r-value.

Also one of the links above speaks to using peat as a water stopper. I think you are either not understanding real peat, as opposed to garden soil with peat, or some variants that are thought to be peat, many people call composted wood shavings, and other organics, peat, which it really isn't. Real peat doesn't rot as you call it, that's why people use it for the things they do.

Look at any propane/ag gas distributor and you will find that they bury tanks on a regular basis, after opening a man hole in the tank, prepping it for an epoxy coating inside is no big deal.

Industry runs caustic steam through domestic hot water recovery all the time, so I don't see that as a real issue either.

Service water is underground water at some pressure that causes it to move under ground. When a cc barrier is placed in front of it, hydrostatic pressure pushes it through the cc. So a curtain drain is the only answer, diverting the water.

Dropping any kind of a tank in dry soil is not going to be an issue, unless you allow water from the top, again that's not a hard solution. My point is you have to know with what the issues are and deal with them.

EPDM, from all I read at many pro solar sites is only rated for a service life below 140. Any kind of Insulation behind an EPDM inside the tank made of cc, that is then water proofed on the outside, will eventually take up moisture, and reduce it's r-value.

What are you going to do with all of the water vapor that travels from the tank in the basement up through the house..I see no effective way to stop it unless it was a pressure tank, which a cc tank isn't.

A 1000 gal tank with insulation inside is now only a little over 500 gals, so if you need a real 1000 gals your costs will double.

Lloyd

Llyod,
I found no link above that provides a US- R or U value for peat (or even the metric value), not even in manufactured boards, which would not be the same. 

You claim R- 4 to 5/inch is your estimate for compacted peat; as I previously stated, this seems unbelievable considering foam (blue) board is R-6/inch.  Is there some data somewhere to support your estimate?

Just because bagged peat moss can be used to stop water flow (like sand bags) doesn't mean that it won't get saturated and loose it's R value.   You misinterpret the test and seem to suggest that peat moss is a good waterproofer.  That would mean sand is a good waterproofer, too.  ::)  Any gardener knows both peat moss and sand absorb moisture quite well.  Both can be used as insulation, too, and will loose insulation value when saturated with water.

Hey Bruce,

As I said earlier, I'm not trying to sell anyone on anything. Define the issues and solve the problem. We all do as we choose to do, what we do.

So to that end everyone's solution is based on how they define and solve the issues. Options are just options.

Lloyd

http://www.missiongas.com/undergroundtanks.htm (http://www.missiongas.com/undergroundtanks.htm)
LPG tanks installed underground are required to be placed in accordance with provisions that are not common to above ground tank installations. The purpose of these provisions is for the safety and longevity of the buried gas tank. All safety provisions must be adhered to as required by NFPA 58, Section 3.2.9. Choosing an underground installation is aesthetically pleasing and is safe provided all requirements, codes, and rules are followed.

How someone else designed a solution.

http://www.quality-stuff-for-you.com/HYDRONIC/RC.htm (http://www.quality-stuff-for-you.com/HYDRONIC/RC.htm)

Heat storage

Radiant heat works better than baseboard system as radiant demands a much lower temp than the 165*f required for baseboard. For example I can hold 500gal at 195*f so that gives me 500gal at 30*useable before it reaches 165*f.  Radiant heat would yield 500gal at 100* of useable heat, before it reached 90*-95*f  over three times as much as baseboard.

I think that the 500 gal tank is beneficial for efficiency but the value of a larger tank for added heat storage would not be practical.

The tanks can be purchased use from scrap yards ($.13 lb) ($150) Tank is easy to insulate it is supported by a 1" rubber matt salvaged from horse trailer. Down side is cost of expansion tank ($350)

This has been a project I have enjoyed and am pleased with results.

So I've decided definitively to use the concrete tank under my house slab.   The geotechnical engineer evaluated our house site today and made recommendations to our contractor.   He wants a curtain drain all around the base of the tank, daylighting into the nearby slope (i.e. 6' deep trench from tank to slope).   It will have to have 3/4"-0 rock all around for about 2' and be *very* well compacted since it is close to the house foundation.    The tank will be casted with a square hinged locking steel man-hole lid, and 2" PVC pipes x 8 though the concrete lid for  the copper heat exchangers.    3/4" copper will go through the 2' PVC and sealed around with Great Stuff foam.   I'll use a tiny flex hose to vent steam to outside the basement.   1000 gallon tank lined with 6" of foam is closer to 675 gallons of water.   Easier to keep hot.

Also, because of the engineers rec's for scraping away a lot of clay, we will have to fill with gravel for about 1 foot thick before the slab.   He also recommended drainage tubes under the slab.   So, I'm going to make the tubes elbow up into the basement into a plenum, where a low wattage fan can then distribute cooler air into the house via ducts.   A low energy cooling system.   They are sometimes called "earth tubes".   I don't know how well it will work since the tubes will not be very deep (they should be 3-6 ft deep and mine will be ~18" deep), but it's worth a shot since I have to put the drainage tubes in anyway.   Just thought this group may find it interesting...

Link:
http://www.builditsolar.com/Projects/Cooling/passive_cooling.htm#Other

Marcus

Hi Marcus,
I had a friend who did earth tubes...and had to close them off after his wife and kids got sick from the mold.

Be very careful in design about how you will be able to clean the tubes- as condensation combined with airborne molds/bacteria/dust/dirt will grow stuff you don't want in your air supply.  

You have to look closely at your condensation situation- what is the air humidity in the summer, and what is the dew point, as well as your soil temperature (cooling tube wall temperature).  You may have to build in a drain/condensation system besides allowing cleaning.

Earth tube cooling systems are like solar hot air rock storage systems-  they get shut down when the inevitable mold situation becomes bad.  Only by designing in a cleaning system could earth tube cooling ever be sustainable.  

Another design factor that is rarely mentioned-  the earth around the tubes will become warmed the more the system is operated, so performance data from an infrequently run test setup is wildly misleading.  

I considered something like this for my Concho off grid property-  I have a big hill next to the house site and the soil temperature is 65F at 6 foot depth.  I considered a single bured tube, which would drop down the hill and  into the house floor via convection.  I abandoned this eventually due to too many difficulties in design (making it cleanable), a too tight budget, and not enough data at that time to do either a good design or predict performance.  

If you do design a system, please do bury thermisters connected by twisted pair so that you can collect performance data later via ohm meter.

My on-grid home is solar active hot air heated;  2 foot of rock storage under the slab floor (radiant slab)- the rock storage air is never drawn into the house.  It works well but the power requirements for blowers and the noise of same made me go hot water for my off grid home.

Lot of potential health issues with earth tube cooling as Bruce mentioned.  If I was going to earth cool, I think i would do it like the geothermal heat pump systems do.  Pipes buried and circulate water thru them.  Use a air to water heat exchanger(radiator) to transfer the dwelling heat into the water and ultimately into the ground.  Then you only have one condensation point to worry about maintaining cleanliness on, just like with conventional A/C...

My .02

Water and fan as Ron suggests wouldn't work for my location as the water temperature would be too warm (68F+). I do think Ron's approach is a good one and it's a lot safer than earth tubes.  It all depends on your soil temperature.  

Another cooling scheme for the right climate is using  in-floor pex for a cooling heat absorber.  (Assuming you're using it for heat already- as you should!)

This won't work in a humid climate, as dehumidification is needed, and you'd have wet floors.

The water temperature can be only a few degrees below the desired room temperature with this method.  Earth source is possible in some areas.  Since I'm in high desert, where it's almost always cool and dry at night, I was planning to use a night time water cooling tower (big bong cooler), and just run the cooler and in-floor circ pump at night to chill out the house. With mid 60's outside temps that would give me 50F water for ch-ch-chilling. Only a few hours of run time at night would be needed. (House is super insulated, can hold the cool through the hot part of the day.)

By doing double wall construction, R38 sidewalls, R80 ceiling, and other design features to increase interior thermal mass and improve thermal performance, it ends up that I won't need cooling at all. I can get away with less air exchange during hot summer days because of special interior finish/material selection. (No carpets, no latex paint, no synthetic materials even in furniture, no particleboard or plywood, etc.)

All good points.

I'm putting the perforated drain pipe under the foundation anyway.   Why not just have them elbow up into the basement?   If there are problems with condensation, I'll just cap them in the basement.   BruceM, what kind of climate did your friend live in?  The friend who tried earth tubes with poor results?   

Here in Southern Oregon the humidity is quite low in summer.   The HVAC guy thinks it will work great in our climate because I'll be taking maybe 30% humidity warm air and cooling it to 50%(?)-60%(?) humidity, without much condensation on the pipes.   Hope he's right...   At least he's not trying to sell me a heat pump or some other kind of energy ludicrous A/C system for my off grid house.   And since they are perforated pipe on a 2% downhill slope away from the house, any condensation *should* drain away or flow into the ground.  It won't be like the southeast where you would be taking 90% humidity air and trying to cool it underground, resulting in wet moldy drywall.    I think it will have some benefit in our area to increase the humidity, for both wood and humans.

Ronmar, your method is good, but then there's one more pump and controller.   With earth tubes, one can open an upstairs window and (hopefully) create a chimney effect to cool the house passively.


edit: spelling and readability

also:

QuoteAnother cooling scheme for the right climate is using  in-floor pex for a cooling heat absorber.  (Assuming you're using it for heat already- as you should!)

It would be wonderful to put in a radiant floor w/ PEX in a thin concrete pour, but there are budget constraints and I have to pick between the masonry stove (see www.heatkit.com) or radiant, and we'd rather have the masonry heater.   The rock mass of the masonry heater will help cool the house in summer, as long as the sun doesn't shine on it, which it won't because of the window overhangs upstairs and wrap around porch downstairs.   

Marcus

Hay Marcus,

I would think twice about the cooling tubes, if you think about it the tubes proposed are drains and thereby intended to have moisture, so that will raise the humidity of the house. One of the principle of a heat pump is that it also dehumidifies, thereby taking less energy to make the occupants more comfortable even at higher ambient temperatures, in summer, and lower ambient temps in winter.

It sounds to me that a water pipe exchanger cooling system would be smart. It's unlikely that you will be using that giant storage tank under the basement for heat during the summer time. So that can become your cold sink, then run a pump cycle at night time much like the ancient Egyptians did, and allow the heavens to provide the cooling. This will require a roof mounted cooling matrix.

Liang has some great 12 or 24 volt circ pumps, the pumps are designe to run off an PV & mmpt or bat bank, they draw low amperage, and are rated for 50,000 hours up to 212 degrees.

Passive design can also reduce both heating and cooling costs, so they are great. I designed and built a Solar Envelope house in the NW back in the early 80's. It was the first house that the county ever permitted that didn't require a mechanical heat source. We had to do a complete energy audit before they would issue the permit. The insulated basement was the cold/heat sink, it wasn't for habitation, there in lived a basement full of 4 man basalt rock.

We had to add mechanical dampeners to close of the envelope on the North side of the house connected to fire and smoke alarms. Because this was  a super insulated house, that was very much air tight, we had to add an air to air heat exchanger that also had a built in dehumidifier. This kept the air in the house and the basement dry, and fresh. In the summer the Solar Chimney design drew the cool air from the rock storage through the house, and in the winter the warm air was created and stored in the rocks, by the same design, just by closing the vents to the heavens.

just a thought.

Lloyd

He probably did.  I know from experience that 100f at 20% humidity is way more comfortable than 100f at 80% humidity...

Quote from: mbryner on February 05, 2010, 12:29:13 AM
I'm putting the perforated drain pipe under the foundation anyway.   Why not just have them elbow up into the basement?

Any radon problems in your area?

the only part of the statement i would disagree with is

in winter it is beneficial to have higher humidity because it will make you feel warmer
at a lower thermostat setting.

bob g

As a radiologist, you would think I would know about radon, but it's an entirely different thing, so here's a reference.   According to this website, http://oregon.gov/DHS/ph/rps/radon/county.shtml , average radon levels for Josephine Co. are 1 pCi/L.  That's about 4x lower than the recommended max in a living area.

I'm talking about taking in really low humidity air through dry gravel under a slab.   Do you guys really think it will cause that much condensation?   (I'm asking for advice not criticizing.)

re: the giant storage tank as cooling: yes, possible, but then where would I put the heated water from solar panels?   Maybe I need 2 giant tanks, 1 for hot and 1 for cold?   :)

Quote from: Jens on February 05, 2010, 06:42:54 AM

Quote from: Lloyd on February 05, 2010, 01:46:51 AM
One of the principle of a heat pump is that it also dehumidifies, thereby taking less energy to make the occupants more comfortable even at higher ambient temperatures, in summer, and lower ambient temps in winter.

Ummmm .... I am sure you didn't mean to say what you said ?????

I did mean what I said, just for the record. If you ever lived in the south, you'll remember running the air condition in your car, even when it's in the mid 70's, because of humidity. A house with a heat pump kept at 78 degrees is very livable, and your elec. bill will be less, than if you try to keep in the low to mid 70's.

In winter an easy experiment is set your thermostat to 68, then pull a shirt from the dryer that is about 90% dry, after cools try wearing it around the house, you'll soon learn that you are more comfortable in a completely dry shirt.

Marcus, I seriously doubt there will be any benefit to making all that hot water and storing it under your house for the summer, you can easily heat the water you need for domestic use and store that in a large conventional hw tank, just ad a summer valve. As a matter of fact you could add a hot water heat pump, get a heat bump to the water, dehumidifier bump, along with some cooling bump. I use to sell the E-Tech units, for res, and apartments. They were a great investment, which lowered energy cost from the gird, and made life more comfy. They were at that time one of the best return on investment, even comparing with conservation

In the early 80's I was quiet involved in the solar movement, but the market quickly flattened when the crisis was gone.

Lloyd

No way I would bring air into the house through rock or gravel.  Virtually very system that has done this has always resulted in health hazardous mold.  Even systems with just plastic tubes (like former work friend's Mesa home) have become dangerously moldy.  Good luck to the family that lives there, especially the wife and young children who spend more time in the home and may have a less robust or developing immune system.  

Even if the rock/gravel system is very dry, there are plenty of molds that don't need much moisture.  When I made some modifications to the down ducts in my existing solar hot air system, I found that while bone dry, the mold levels in the rock storage were very high.  Fortunately that air isn't brought into the home, it is just recirculated.  

As for condensation-  you have to find out weather data for your location, to find the typical humidity levels during the months and time of day of operation, and compare to the temperature of the soil at the depth of your proposed air tubes and dew point.  20% humidity is plenty of water, if dew point temperatures exist at the tube walls.  My friends house was in Mesa, AZ, with much lower humidity during periods of operation.  (He did not operate it during the monsoons.)  

I'll have to go take a look at some climate data for your county. 

I don't see running a heat pump for heating water as something I'd want to do for an off grid home; the impact on the power/battery bank/PV system size and cost is too great.  The battery bank is a significant ongoing operating expense.  Solar with propane backup seems more appropriate for most locations.

Quote from: BruceM on February 05, 2010, 10:46:20 AM
I don't see running a heat pump for heating water as something I'd want to do for an off grid home; the impact on the power/battery bank/PV system size and cost is too great.  The battery bank is a significant ongoing operating expense.  Solar with propane backup seems more appropriate for most locations.

Hi Bruce,

A properly sized unit combined with a solar water heater is going to be very efficient, and will not be a big load on the system, as it will be 1st supplemental...the amp draw is going to be on the magnitude of a small under counter refer, when it's running.

It could even be built with the new rolling piston design compressor, run on bat voltage or off a PV/mmpt.

Lloyd

Lloyd

I guess it depends on your perspective on the size of your off grid power/PV systems.  Here most people view their (high efficiency) electric refrigerator as a major load for their electrical systems. There are a couple folks systems that are so big they would laugh at such a load as insignificant.

A heat pump for hot water heating is a relatively expensive system;  I  don't see the value as a backup system to solar hot water, but I'm sure there's situations where it might be great as a primary system such as in a climate where solar isn't viable.

My backup propane hot water heater requires no electricity at all, and cost $350 at the local ACE hardware store. No trouble finding a local guy to service or replace it, should I get too incapacitated for that myself.

 

Heat pump for AC is out of the question.   Until we had to dig deeper for the foundataion.  I wasn't going to even have AC, because it cools down enough at night in summer to open the windows, and the thermal mass of the masonry heater should temporize temperature swings inside in the daytime.

Have to remember, our house is 2600 sq ft, w/ ~3000 watts of solar panels.   Every little load counts.   Every circulator pump, etc.   The fridge will be the major load as Bruce says.

If these tubes have perforations in them to collect drainage water and remove it from under the slab, I don't think it is a very good idea to use them for cooling.  Being from southern oregon, you have probably been in a lava cave/tube?  If the tubes you are burying have holes in them and are exposed to earth, the air that comes out of the tubes is going to smell like that which you find in a cave or in a house crawlspace...

Pumping air(you mentioned low wattage fan) and pumping air both cost energy...

Marcus-  I like the masonry stove as thermal cooling mass idea. The masonry stove might be an even more effective cooling mass if you could move air through it at night;  if you could put a fan to move cool outside air down the chimney and out into the house, that might chill out the masonry faster than blowing warm house air up. It's another situation where some buried thermisters might help work out the optimum design.  It might be less annoying with the fan up topside; fans at night can be bothersome depending on sound character.

Also-  5/8" sheet rock is a fairly cheap way to add a lot of mass throughout the house, while having nicer walls at the same time. (Stone or masonry is always nice but hurts the pocket book.)   It is "fast mass"- if you leave windows open when it's too hot or cold, it has a lot of surface and will dump it's heat/cold fairly quickly.  But well managed, mass is mass, and "fast mass" can be helpful for passive (windows open) night time cooling, it will cool off quickly if there is good air flow.

Hmm.  You guys got me thinking more outside the box again, especially Bruce with your last reply.   Thanks!    Since the masonry stove needs outside combustion air, what about taking the air from the cooling tubes into the air inlet of the masonry stove, in the normal direction and not just at night.  It would keep the stove cool all day to help keep the house cool.   The air wouldn't get into the living space; it would just go out the chimney.   The chimney could act like a draft tube.   Any mold that formed on the inside of the masonry stove would get burned out every fall at the first firing.   Wonder if that would work?   In winter the draft from the fire would suck air through the underground tubes and warm it a bit.   Probably negligible increased efficiency because of warming the air a few degrees for a 1000 degree firebox.

Marcus

That is out of the box thinking....and may just be a very good idea. If the fireplace will draw its own draft in the summer you'd definitely be on to something.

Thanks, Geno

Feeding combustion air directly to the firebox from outside is a good idea in general.  If you draw air from the building, that air has to be made up from somewhere else.  This happens by cold air being drawn in thru every crack in the envelope...

I had a wood stove, and changed it out for a pellet stove.  We were very dissappointed with it's initial performance as our main living space was far colder than with the woodstove.  After a little bit I figured out what was happening.  A pellet stove is a lean burn device and pumps a very large ammount of air out the exhaust.  What was happening in my drafty old house, was that drawing the combustion air from the home, pulled in as much, if not more cold air thru the cracks as I was heating.  You get around the doors and windows and you could actually feel the cold air moving.  I hard plummed a 2" air line to the combustion air inlet from outside.  The difference was night and day in room comfort... 

I was going to feed outside air through a 4" pipe for combustion anyway, this just makes a possible passive A/C out of it.

OK, now here's another idea building on the concept.   Geno, says:

QuoteIf the fireplace will draw its own draft in the summer you'd definitely be on to something.

Why not extend the chimney with uninsulated pipe about 6 feet or so higher than required.   Sunlight shining on the black flue pipe will heat it, heating the air inside and causing even greater draft, slowly sucking cool ground-air into the firebox and cooling the masonry.   What do you think?

Sorry to dampen the enthusiasm for this, but there's no way to pull colder, heavy air up out of the chimney by convection!  You'll have to use a blower.

there is if the stack is tall enough, and is painted black

look up thermal chimney

i have several books from back in the 70's and 80's that show illustration

my old 3 story victorian house would "thermal" cooler air from the basement hard enough to
blow my daughters hair back while standing in the doorway.

what was even with the attic stairs door closed!

when that heat rises, and if it has a runner to go up, it will draw up heavy cold air behind quite well
in my experience.

bob g

OK, I'll partially buy the big solar chimney concept.  The air coming out of the solar chimney must be substantially lighter than the column of cold air it's pulling up the shaft, which means you'll need a substantial thermal chimney.

The draft of solar chimneys can be very impressive...but they don't usually pull a column of earth cooled air through tubes. 

Plan for a fan just in case...

There's a solar chimney about 24" in diameter on a solar/green demonstration home nearby. The house is built into a south facing hill.  The summer airflow up the shaft  is very impressive, you can hear a whooshing sound and feel it near the opening.  I asked where is the air inlet for the house...they looked at me with blank, confused faces.  One tried to tell me it came down the center of the flow.  ::)  The only inlets for that tremendous flow up and out were leaks in the building envelope- I thought it smelled "earthy" ! 

Quote from: BruceM on February 06, 2010, 10:20:47 AM
Sorry to dampen the enthusiasm for this, but there's no way to pull colder, heavy air up out of the chimney by convection!  You'll have to use a blower.

I agree.

If the house was totally sealed and the underfloor pipes were open to the outside you could probably create a pressure differential with the heated chimney that would pull cold air up a small way above ground level but any volume of it would cool the chimney and destroy the weight differential of the column in relation to outside ambient. Denser air does not flow uphill. flow will only exist when the average density of the lift column is less than the average density of the other column . I expect you would have a short circuited convection current going on in the heated portion of the chimney. You could induce flow if the outdoor temperature were very cold and the ground tubes open to it though.. I saw this one argued to great length about someone wanting to duct from the ceiling and have hot air pulled down into his crawl space to  by the chimneys draught sucking the cold air up into the room and into the stove intake.

Yes, the principals of thermosiphon apply here.  It will take a lot of energy to create enough of a vacume to lift cold dense air.  Also a single wall chimney might give you creosote buildup issues when burning the stove.  Chimney fires are not a very good time... 

Duh oh, I forgot about the chimney liner- that would screw the whole concept, as it insulates the masonry from the flue. Thanks Ron.

Do the big European masonry heaters use flue liners?  That was what I thought Marcus was proposing since he was talking about large mass.

OK, you're all bursting my bubble here!!! :(   Yeah, I was wondering if the concept would have enough draft effect.   But, at least maybe it would work together with a fan to increase the draft effect?   Yes, the big Euro-inspired masonry heaters have a chimney liner, but the creosote is a non-issue.   The fire is very hot and short-lived, and the stove is designed to hold most the heat instead of sending it out the chimney.   The smoke going out the chimney is not nearly as hot as a woodstove.  If it wasn't burning so hot and completely I would indeed worry about creosote.   But, if I extend maybe 6-10 ft of unlined black stovepipe above where the completed chimney stops, I don't see how it could hurt and it might just cut the blower fan wattage?

All the regular thermal chimney use a water mist at the top of a "chimney".   The evaporative-cooled air falls into the house.  Totally different concept (reversed flow from what I'm proposing).

Again, this forum has got to be the coolest on the net.   Where else could we talk about diesel engines running all kinds of fuels, heat recovery from engines, house design, thermal storage, chimneys, earth tubes, etc. etc., doing real number crunching (or at least real experience) and talking to no-nonsense decent people from all over!   (And I can still be my Libertarian self but be "green" without labeled a "greenie wacko".  No offense to anyone, I've never been politically correct, and if you're here you're probably running a "polluting" diesel engine.   OK, now I'm just rambling.   Just took a nap and still waking up; it took a little while to get my 2 y/o daughter to take her nap and I went to sleep next to her...)

this place is sure nuff turning out to be greater than the sum of its parts!

and we got lots of parts!

bob g

Too bad the liner blows the air thermal exchange.  Still, passively the masonry stove will help as "slow mass", as long as it's in the envelope and the house airflow is managed to keep the house cool.

If you are going to close up a lot during the day in the summer, then you might consider improving indoor air quality by materials selection.  Carpet is by far the worst offender, next is particle board. If you have an insulated slab, tile is very comfortable and durable, the best for indoor air quality. 

The low speed generator, off grid living, and ways to save energy for your climate is all part of the same game for many of us.  Planning for and off grid living especially gives us a new perspective on energy and energy conservation. 

Quoteconsider improving indoor air quality by materials selection.  Carpet is by far the worst offender, next is particle board. If you have an insulated slab, tile is very comfortable and durable, the best for indoor air quality.

OSB is not eliminated from our construction materials, i.e. roof panels, but yes, we have thought of such issues.  The bedrooms will have carpet (wool if it doesn't cost too much in the end), the bathrooms get tile, the kitchen will have cork, and the rest gets reclaimed wide plank clear heartwood yellow pine (used to be gym bleachers for 40 years).  The only slab is in the basement (workshop and garage).

Why does the liner blow the air thermal exchange? 

for the disbelievers in the crew :)

http://en.wikipedia.org/wiki/Solar_chimney

of course the system has to be engineered correctly, but there is no reason that the hot air going up a solar chimney
cannot pull colder denser air right on up the chimney as well,
it just has to be heated.

the larger the heated chimney area, the more air it can pull of course.

there is much written on the subject

part of the passive solar cooling scheme

bob g

The ceramic flue liner will kep cold air from  direct contact with the masonry.  The surrounding airspace between flue liner and masonry may not be big enough for much convection- and may act as an insulator. A gap of at least 1"  is needed for convection air flow.

New wall to wall carpets are toxic hazards and don't belong in a healthy house.  Occasional batches are exceptionally toxic - there is still no regulation of this problem.  Vote with your wallet and say no to carpet.  There is "controversy" about this issue due to political manipulation by the carpet industry.  A google search of  carpet, health will show you the tip of the 'berg. 

http://findarticles.com/p/articles/mi_m1525/is_n2_v82/ai_19148779/

Having been disabled in a new sick industrial building in 1987 (also involving aircraft composites), subsequently developing MS and epilepsy, I have little doubt about which side has credibility and which one is a economic and political whitewash at the expense of the public. 

Wall to wall carpets create a huge surface area of plastics and unknown mixtures of volatile chemical out-gassing for the first few years, then are collectors of dirt, mold and bacteria that an never be removed. (Roll up an old wall to wall carpet and you'll see and smell.)   Why put the worst offender where you spend 8 hrs a night?   A cleanable natural fiber throw rug or two in the bedroom (or some slippers) solves the cold floor "problem".  A heated floor also eliminates the cold floor problem.

The flue liner is only for about 7 ft, after all the hot air (or cool air in this case) goes through the masonry heater passages.   Look at this link for examples:

http://www.heatkit.com/html/gallery.htm

I can't afford a masonry chimney all the way to the top of the ceiling, so there will be regular insulated pipe flue through the roof as per normal practice.   But, I understand what you are saying about limiting convection.

QuoteA heated floor also eliminates the cold floor problem.

Yes, but the listeroid and propane boiler are my big power sources besides the masonry heater.   Hydronic flooring, while admittedly a great heating concept and provides additional thermal mass, is quite expensive to install, especially on multiple floors.   Well, you'll say a wood fired boiler for the hydronic system is available.  Of course, but then I'll have to choose between the masonry stove and hydronic floors, and a boiler in the basement doesn't satisfy the need to look at the fire!

Carpets:  there are many alternatives to synthetics, like wool.

Marcus

P.S.  I don't think I've ever been so apathetic about Super Bowl Sunday.   I love football, but don't care about either team.   Guess I'll just record it on a PVR and watch it after it gets dark, at 2x speed.   Happy football cheering everyone!   :)

I dont think the refractory in your heater is going to like the moisture if you do manage to get flow through it from the underfloor tubes. There is usually considerable caution in first firings to gradually dry out the moisture the bricks absorb. I worked for several years at a lime kiln and the bricks were considered to be harmed by moisture. Of course "fire brick" is a very broad, catch all term.