Combined domestic hot water and house heating system

[Lloyd]

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

[BruceM]

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.  

[Lloyd]

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 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
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

[mbryner]

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!?      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

[vdubnut62]

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

[Lloyd]

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

[mobile_bob]

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

[BruceM]

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.    

[BruceM]

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.

[Lloyd]

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

[BruceM]

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.

[Lloyd]

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
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.

[Lloyd]

How someone else designed a solution.

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.

[mbryner]

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

[BruceM]

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.