Plastic Shipping Container For Hot Water Storage

[Tom Reed]

EDPM sheet is what you're thinking of.

[rcavictim]

Have you considered using good condition 200 gallon oval steel home heating oil tanks?  You should be able to acquire these with a bit of searching for in the ballpark of $50 each.

[LowGear]

All EDPM is not created equal.  I've seen it used for roofing and for water features.  Not the same stuff exactly.

But let us return to the original question.  275 gallon totes and their ability to store hot / warm stuff?

They sell for around $100+ in the Seattle area in nice shape.

How hot is hot? 

How many BTUs are in a gallon one degree above ambient? 

How many degrees above 70 (a nice room temperature) do you have to be in order to harvest heat from your stored water? 

Isn't a floor heated to 120 degrees pretty warm?  (What was the label warning about temperature?)

Do you need to consider that one of these puppies weigh (275*7.5=2,062) or a clean ton?

Can we get the water cold for use during the summer?

Casey

[DanG]

A 4x4x8 box of water weighs just under four tons...

and stores the energy of 6-1/2 gallons of gasoline (787400 BTU) if you raise the temperature 100 degrees from a 55°F ground-water temperature.

I think that much water needs more than 2x6 framing.

[LowGear]

The thing to keep in mind (I think therefore I make mistakes) is that it takes no more strength to hold back four foot of sea than four feet of bathtub.  That comes to less than 2 psi at the bottom foot and something like .43 for the top foot.  You have seen how flimsy above ground pools are and they have no top straps.  There are far better trained minds than mine that can explain this phenomena.

6.5 gallons of gasoline.  100 degrees?  Nearly 1000 gallons of water.  This is starting to sound feasible.  So to raise one of the totes (slightly more than 1/4th the volume) to 140 degrees is looking like 1.5 gallons of gasoline or less?  How many BTUs in water heat does his engine put out?  Capture-able exhaust heat?

So back to the basic questions:

How many BTUs are in a gallon one degree above ambient?

How many degrees above 70 (a nice room temperature) do you have to be in order to harvest heat from your stored water?

Isn't a floor heated to 120 degrees pretty warm?  (What was the label warning about temperature?)

Do you need to consider that one of these puppies weigh (275*7.5=2,062) or a clean ton?

Can we get the water cold for use during the summer?

Casey

[Ronmar]

So back to the basic questions:
How many BTUs are in a gallon one degree above ambient?

That depends on what your starting point or ending point is...  1 BTU will raise 1 pound of water 1 degree F.  So to get that 1 gallon of water to warm 1F above it's starting point(ambient temp?), you expended 8 BTUs...

How many degrees above 70 (a nice room temperature) do you have to be in order to harvest heat from your stored water?

It depends on your heat transfer method and time available.  heat transfer is mainly about temp difference, flow rates and time.  A large heatex needs less time and heat difference to move a given ammount of heat than a smaller heatex.  In-floor radiant heating for example has a large surface area, so uses a much lower transfer temp, perhaps 90F or even less depending on other structural factors such as sealing and insulation.  Small baseboard heaters have less surface area, so need greater temps to heat air, say in the 110+ degree range

Isn't a floor heated to 120 degrees pretty warm?  (What was the label warning about temperature?)

from what I have studied, 120 would be way too hot to feed a radiant floor...  You use a tempering valve to mix hot source water with returning cool water to maintain as constant a floor loop temp as possible...

Do you need to consider that one of these puppies weigh (275*7.5=2,062) or a clean ton?

water is heavy:)

Can we get the water cold for use during the summer?

cooling is a whole nother can of worms with it's own engineering challenges.

Wayne
  As for the tank, your best bet for integrity is to go round.  the 1500 gallon above ground pool I set up each year has no 2X4's or heavy plywood...  it just has a continous band spreading the outward force evenly to the other side.  I will be building my own tank also and it will be round as that is the easiest structure for me to make self supporting.  you also need to consider the weight per square foot.  What sort of structure is this much water going to be setting in/on?

Jens alluded to one of the issues you will run into with the engine feeding the tanks.  it is going to cycle as it gulps cold coolant.  The problem this makes, particularly with series tanks is it will be circulating cold water right on top of the hot water in the tank, with the engine burping pockets of hot water in there as it cycles.  You will end up with the heat spread out throughout the tanks, instead of heating the first tank first, then working on down the line.  What you need is a thermostat in the secondary loop to only let out a desired temp of water.  IT, no flow till the water gets warm, or only warm water leaves the engine heatex.  This is what I do on mine and it works very well.  It only outputs 120F water from the engine heatex(engine runs at 195F).

[WStayton]

Jens:

 Do you think that a box constructed out of 2"x4"'s which is 12' long by 4' wide by 6' deep will be structurally sound?  I was afraid that the top would slowly spread apart until something finnaly gave and dumped the whole 2200 gallons of 180 F water in the middle of the space filled with a generator, an inverter, a bunch of batteries and lots of 120/240 AC running around - making the ORIGINAL vert big mess!!!  I thought of putting 3/8" threaded rods across every four feet or so, to contain this spreading but, since these are going to be in a hot wet environments, they would need to be stainless adding still more cost.  My plan that I thought might (!) work was to build it out of 2"x6" studs on 16" centers with 15/32" Plywood on the inside and have every fourth side stud stick up six inches above the tank and then run a 2"x4" across it to contain the spread. But, if I build it out of 2'X6" and 15/32" ply, and make it waterproof I have already got more money in it than the $100 per 320 gallon tank the other way.

 One other point - after some reflection, I thought that it was better to have several containers, in series, so that I could be assured of having enough 150F water to heat domestic hot water, etc., etc. - If I have 2200 gallons of 85F water, I have kind-of missed the temperature boat.  I'm trying to design something that works for when I have lots of waste heat AND for when I only have a little.  If I create something that only serves one end of the spectrum, I have missed the boat!!

 About insulation:  I have noticed that some closed cell foam, especially the environmentally friendly stuff that is made out of soybeans, etc., has a max operating temperature of 180F.  I have also noted some petroleum based foams are okay up to 250F.  Note sure what happens if you insulate your attic in Phoenix with the soybean stuff . . . well, actually, it probably melts and makes a mess!  <grin>

rcavictim:

 I thought about the steel tanks, usualy ex-fuel oil tanks, around here.  One problem:  If assembling a heat exchanger is a PITA through a 10" hole, it is REALLY a PITA through a 3" diameter fill-port.  With steel tanks I would either have to 1) Take a gas hatchet and cut the end out of the tank, or at least a BIG access hole through it or 2) scrap the idea of assembling heat exchanger's from domestic heating finned tubes and just use smooth copper formed into a circle.  I figured it would take a LOT of smooth tube to equal the heat transfer of a finnned tube!  Not undoable, but I think that the cost of four or five times as much smooth tube as finned tube, which I figure to get used finned tube pretty reasonably, would be a not insignificant item for a tight-wad like me! <grin>  Also, the fuel tanks wouldn't let me lay a whole array of finned tubes side-by-side.  Not sure how much they will stratify, temperature wise, and thus I would, maybe, have some finned tubes 30F warmer/cooler than the one on the other side of the array.  The possible problems overrode my cheapness, in this case!

LowGear:

"How many BTUs are in a gallon one degree above ambient"  1 gallon = 8 pounds = 8 BTU per degree F for pure water - adding antifreeze degrades the capacity by 20'ish %, for a 50:50 mix.  Since I would use pretty much straight water in the holding tank, and I'm thinking to use the 320 gallon ones filled to 300 gallons, so I've got 2400 BTU per degree per tank.

"Isn't a floor heated to 120 degrees pretty warm? "  I think that 110 is recommended to unde floor just so that uyou don't burn your tootsies.  I was thinking to use baseboard heater's with the same finned tubing in them that I was talking about for a heat exchanger.  Baseboards are more accepting of higher temps, though 180F water does make them creak and groan when the water is first turned on and they grow thermally and creak across all the metal suports.  Silicone spray lube helps, but still doesn't cure the creaking from very hot water.  I CAN live witha fedw creaks and groans, however!  <grin>

Weight:  They (300 gal) are 2450 pounds +/-, counting the container.  My slab is 5" concrete with one layer reinforcing mesh in the middle of it.  I would be happier if it had some rebar in it, but it was poured before I arrived on the scene, and, in its previous life, it wasn't really expected to take much of any load since the space doesn't have a door big enough for a vehicle and was built by an amish guy who doesn't/didn't have a vehicle, anyhow!  My SWAG is that it will probably crack a little, but since my load is a one time thing, not repetative, the cracks will probably be okay.

"Can we get the water cold for use during the summer?"  Um, this is upstate NY - it hits 90 about three days a summer and I'm VERY coldblooded, so I'm not planning on any AC, at all! If it gets hot, I'll just open the window and if it gets into the 90's, I'll use a box fan, that's it! <grin>  It only take about three ice cubes for my martini and I like my scotch neat, so I don't see having a big cold storage reservoir! <grin>

DanG:

 "I think that much water needs more than 2x6 framing."

  Actually, I think 2'x6" is enough if you solve the spreading apart problem, but I would rather have several smaller containers anyway, so it kind of a moot point.

LowGear:

"So to raise one of the totes (slightly more than 1/4th the volume) to 140 degrees is looking like 1.5 gallons of gasoline or less?"  Gasoline???  Huh?  I'm planning on a diesel - the only gas will be in a can in the corner for the lawn mower and maybe to mix with the WVO for viscosity control! <smile>

" How many BTUs in water heat does his engine put out? "  I figured that the engine would be at a 20 kW average overall.  A diesel engine rejects about twice as much heat as it turns into work - figure an amount equal to the work in the cooling water and a similar amount in the lube oil and exhaust.  I'l be able to recover all of the cooling heat and about half of the exhaust-heat/lube-oil heat becuase I have to leave engough heat in the exhaust that it doesn't condense any where in the system - also, my marine wet exhaust probably isn't all that efficient since their objective was to make the exhaust system cool enough that it didn't catch anything on fire not to extract every last BTU of heat.  So, I've got about 30 kW's of heat to use as I see fit.  1 kW-hr = 3414.4 BTU, so I have about 100,000 BTU per hour to play with.  For my six hour run time, I will have 600,000 BTU - so my four each 300 gallon tanks, with 1200 lb of water,  will increase about 60F.

 In summary - I'm pretty convinced that I should use several small tanks instead of one large tank in order to ensure that I have at least some water with useable heat when I only have solar heated water as the source and have a couple of cloudy days.

 I WILL get a tank (though probably not in the next two or three days! <grin?) so that I can see if 1) I can, indeed, insert the 1/4" liner and 2) after heating for at least 30 days it doesn't spring a leak or three.  If I can't put in a liner, or, if it leaks, I will have to go to something like a metal tank like rcavistim suggested.

  I'm pretty comfortable with the amount of heat storage that I will have, since, in the winter, I will have a pretty reasonable heat load - the domestic for a 30' x 40' building with R-11 in the walls and something like R-22 in the ceiling.  I probably will increase the ceiling R-value  but even with R-22 the heat flow should be manageable. And, I will be able to have as much additional through wood fired boiler, as I want.

 Remember, I'm only planning on running the engine for two six hour sessions a week, in the winter, once a week in the spring and autumn and not at all in the summer.

 Of course, EVERYTHING is subject to change when, after I get it installed, I discover that I need more or less electricity than the solar electric panels are delivering - the solar electric panels are what really drives everything electric, with the generator just doing pick-up duty for the solar electric panels when they can't handle the load.  If I find that I need more solar panels in the long day times, there is room and I will do that, which would also increase the electricity in the winter, but I can't imagine a system that just meets my needs in the long day periods, would be able to meet it in the winter.  I will have some significant electrical loads in the winter that won't be there in the summer - namely running the circulator for the dwelling baseboard heating.

 For heat, the heirarchy is First) Heat from solar panels, Second) Waste heat from the generator and Third) Heat from the wood burning boiler.

 My SWAG is that in the short days of winter, the solar will meet the domestic hot water needs ONLY - domestic heating will have to come from the diesel and the wood boiler. I think that the diesel waste heat will be enough for domestic heat on the days that it is running and the wood fired boiler will have to cover the other five days a week.

 The diesel thould burn about a two gallons an hour at 20 kW output - so if it also cover the domestic heating load, I will be heating with twelve gallons a day - fuel oil burned in a furnace is about 140,000 BTU per gallon - so if I burned twelve gallons per day in a furnace, could I heat the 1,200 sq ft dwelling?

 I'm planning for a wood burning stove in the living room, BTW - so at least one spot in the place will be warm! <grin>

Thanx, everybody, for the input!

Regardz,

Wayne Stayton

[mike90045]

here is a link to the TANK part of the Solar Shed. http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/Tank/Tank.htm

A pretty good article, worth the read for the whole thing.

"decided on a plywood tank with an EPDM liner.   These tanks have been successfully used for quite a while, and are reported to have a life of 10 to 20 years and more.  They can be built to fit the space you have available.  The tanks are easy to build, but the tanks must be structurally up to withstanding the fairly large loads from the water -- 500 gallons weighs 4150 lbs."

[DanG]

I've been collecting pieces for a solar DHW tank for a while and am interested in your project. I'd not be worried about the 'catastropic' failure, it'd be watching the slow-motion train wreck of a wooden tank relaxing over time that would kill my buzz. The 100-year-old Minnesota cellar here is too damp for plywood. Just having the tank down there un-insulated would make this house much happier, it averaged 52°F all winter and has now just warmed up to 57°F. Makes 1st floors floor cold and I hate cold floors.

300 gallons of hot water in a wire cage sounds like a recipe to have tote plastic look like magnum sized bubble-wrap after a heating season. Adding slats between the rods and wrap-insulating the outside sound do-able, beware the thermal expansion heave & shrink of the plastic where any bulkhead fittings go through, a little loose so it can move might dodge some grief.

[WStayton]

mike90045:

  Would you please make your posts in 24 point type from now on, so the big dummy (ME!! <grin>) will see them right away and notice them.  While the rest of us have sort of run around looking at the pennies and nickels dropped on the ground you have, again, hit upon the $1,000 bill!!!!  I had previously read some of Solar Gary's stuuf, but either had forgotten that he had a tank, etc. in his system, or completely missed it on my way by.

  I had not thought, at all, about  EPDM liner material - not sure why - just negligence, I guess. That does, indeed, look like the correct way to line the tank(s) - no problems with temperature capability and I hadn't realized that these were fabricated by lapping the uncut corners up to form a "pleat' and thus eliminate any possibility of having a leaky seam.

  Although Solar Gary doen't specifically refeernce any thing like it, aren't there some special fittings for installation through a wall lined with the EDPM material that have big bases with a seal to eliminate/reduce leaking problems?

  Disregard all previous references to "storage totes" those ideas are hereby relegated to the scrap heap!

  Thanx for pulling my head out of my A$$, AGAIN, mike90045!!!

Jens:

  About size of container vs a vs structural integrity:  I'm thinking that if I built the tanks out of 1 and 1/2 a sheet width, for height, and made them on  4'x4', L X W, with 1.5"x1.5" around the bottom exterior edge, instead of 1.5"x3.5". I would have 450 gallons each with a fill depth 5.5', leaving room for interconnections that don't go through "under water" and thus reduce the leak chance, and used 1" of polyisocyanurate on the inside, to cover up screws heads, etc., etc, for liner "health".  I was planning on my "containers" being insulated by 12" of R-7 foam, and I see no reason to do anything different with these boxes.  The only change that I really envision making, besides slightly altering the dimensions, is to make the "encircling" mechanism out of laminated 1"x4" stock, alternating the corner laps, thus making the weakest part of the "encirclement" a bit stronger and a bit easier on the eyes.  (Who said that engineers make everything with a chainsaw, and ugly?  <grin>)   I'm not sure if it should have a vertical "stud" up the middle of each side or not, but it is far easier to put one in and not need it that to build it without one and, later, have a "flood".  I would use a 3/4" ply "scab" of 8" x 3/4" marine ply over the joint between the bottom 48" width and the top 24" width of the side material.

  Another thing I see that I would do differently is seal and paint with good, oil based, exterior grade paint.  Not sure why Solar Gary didn't do that with his, since it isn't a lot of money for a great deal of water proofing and, again, its a little easier on the eyes!!!

   I'm not sure if I am wild about that 4' square "box" being unsupported in the middle of the box, though in Solar Garys design I suppose he could have cut the underlying foam to fit in it and not shown that.

"I would suggest at least three tanks in your system - one small tank, an 80 gallon steel hot water tank for example, and then two large 4*8*4 tanks."  If I use four 4x4x6 tanks built as above and make one end of the daisy chain hot, shading the temperature to the other end, do you still think I need the small, 80 gallon tank for "HOT" water.  I'm thinking that the first tank would be hot enough, even when only getting solar heating to have a reserve for three or four days of cloudy weather.  If I have 450 gallons of water, I will have 2700 BTU per degree stored in there - which means that I could draw 3,600 pounds of hot water, warming it 50 degrees and still only have to draw the temperature of the first container down by 50F. So if it was at 180F before my "cloudy" period, it would still be at 130 at the end of it.  Why the little tank?

About the temp of the hot water finned  tube domestic heating:  I only suggest that 180F will work, since that is what my dad had in the house that he built in about 1958.  The oil fired boiler came with a large package that contained the tempering valve that mixed the recirculated water with reheated water to give you whatever temp of circulating water you selected.  My dad looked at the box full of various valves and sensors and only saw yet another way for something to screw up, so he installed the system without the tempering valve AT ALL.  It worked just fine, but, as elucidated previously, cracked, snapped and popped on start up due to thermal growth over all of the supports.  My mother b!#$%@d and moaned about the noise, so he siliconed everything, several times, but that only attenuated the noise, it certainly didn't eliminate it, though it eliminate the noise from my mother!!!  <grin>

  I intend to pull the "hot" water for domestic baseboard heating off of the bottom of the coolest tank - at least until experience demonstrates that that won't work! <smile>

"I am almost willing to bet that you are not going to see that "  What do you doubt?  The amount of heat rejected by the engine?  How much of the waste heat will be absorbed by the water storage bank?  Some other part of the analysis?  Please elucidate - If I screwed something up, I would much prefer to know about it now, rather than after it is built and trying to operate?  I'm expecting to make mistakes - the last guy that didn't make any mistakes, wound up with his feet nailed together, and I'm not, it goes without saying, in that league!  I'm hoping that if you see something that you think is "hinky" you will wave a red flag and scream!!!  I'm a little slow, to grasp the whole meaning, but if you scream loud enough and long enough, I WILL come around! <grin> So, speak, PLEASE!

Thanx for the input, guys and mike90045, especially - once more I, and my bank account, have been led back from the precapice(sp?)!  <smile>

Regardz,

Wayne Stayton

[Geno]

I don't know how they'll be affected by heat but bulkhead fittings are commonly used at depths greater than 4'

http://tinyurl.com/3mrsz6q

Thanks, Geno

[WStayton]

Jens:

  About holes in the liner:

  My thouight was to only fill the tank to within 6" of its top, and then make the connection through the middle of this six inches, so the centerline of the hole would be 3.0 in above the liquid level - but, AGAIN, I think I am inventing a $500 solution to a $5 problem!

  I was thinking about how to close the tank with a lid, which fit tightly, without having it interfere with tubes/pipes coming out of one tank and going into another one.  A much better solution would be to make the adjoining sides 1.0" to 1.5" shorter than the other sides and just come up and over the 4.5" to 5" of tank side that is above the liquid level.  I am a little wooried about being dependent on siphon action to accomplish all of the fluid travel, since if enough air gets trapped in the "loop" over the adjoining sides, it won't siphone anymore, but where is the air going to come form, anyway?  I guess the worst case is that a little air will be in solution and come out of solution in the tube and then rise to the top of the loop as a bubble, but if that bubble is smaller than something like 20% - 30% (? - worst case?) of the volume of the loop exposed above the fluid level, it will simply be swept away by the next fluid flow through the loop.  Not MUCH air is going to come out of solution, since I don't have an aerator in any loop, anywhere, and every loop discharges under the surface of the water, so, relatively soon, most of the dissolved air will escape and thier won't be any significant bubbles in the loops.  The one hitch may be when the fluid sits quiessent (sp?) for the whole summer, with all the fluid flow coming from/through heat exchangers and the bubles can collect for four or five months, but even then, I don't THINK that they will be big, problem causing bubbles.

About joining sheets:  If I do it with an 8" wide, 3/4" thick, "scab" that is glued with resourcinol, the joint will be stronger than the material it is made from, so if the sheet of 3/4" marine plywood is not in danger of breaking open, the joint should, likewise, not be in danger.  I was thinking that screwing the joint together so that is adequately "clamped" while the resourcinol cures will be a little tricky, in that I don't want to have screws sticking out to potentially pierce the liner material, but if I use 1.25" screws and insert them from the inside of the tank and put the 1" of foam inside that Solar Gary recommends, I shouldn't THINK that I will have a problem.  Of course cutting out the 3/4" x 8" slot in the uprignt suports, to go over the "scab", will be a PITA, but, in the scheme of things, it will be a lot less PITA than assembling 36 pieces of finned tubing through a 10" access hole!  <grin>  Just put the dado blade set in the table saw and keep-on cutting!


About having the 2"x4" bottom cleats on edge rather than on their sides: 

  Again, I am planning to glue them with resourcinol, so the joints should be stronger than the wood.  For construction pine the strength is something like 6400 psi to the elastic limit.  At the bottom I will have 5.5 feet depth x .433 lbs/ft = 2.3815 psi.  Since the pressure is less than 2.38 psi everywhere except at the very bottom, the 5 psi is larger than the "real" load will be.  I will have a 1.5" x 1" glued joint holding each 1" wide column of water, so the load on the wood joint is 5 / 1.5, or a little more than 3 psi.  This load is WAY less than the strength of the material, and the joint is stronger than the material, so it should be safe by a large safety factor.  Of course clamping/curing will be critacle for the joint to have anywhere near this ultimate strenght, but I think that if I through screw it with 3.5" screws every 3" along the length of the joint, from the bottom, that will be sufficient.

  I intend to glue/screw the corner joints and the verticall 2" x supports in a similar fashion


About your lack of confidence in the amount-of-heat/temperature-of-water:  I did a few numbers (engineer's favorite pass time!  <grin>), and something is wrong somewhere!!!

If your engine is turning out 20 HP, it must have rejected/unused heat of something like twice that.  Since don't think that you are capturing exhaust heat and lube oil heat and certainly not heat radiated off of the block, you SHOULD be getting about half of the waste heat, or another 20 HP worth of heat.  Since you put all of this heat along with the electricity generated back into the storage container, you should be putting something like 40 HP worth of heat into the vessel.   Since 1 HP = 2545 BTU (you can argue about European vs US horsepower, but that differance is only about 1.5%, so for purposes of this discussion, nevermind!), we should have something like 2545 BTU x 40 Hp x 4 hours = 406,400 going into the fluid storage container.  If we have 240 gallons in the container, at 8 lbs/gal, we have 1920 pounds of water.  Adding one BTU to one lb of water raises its temperature one degree F, no matter how you transfer the BTU to the water, so we should raise the temperature of the container 406,400 BTU / 1920 lbs = 211.67 F!!!!  You report that your water heats an average of 75 F, so where in H#$L did the other 254,000 BTU go!!! <puzzled frown>  Even if I make some assumptions about the amount of HP your making (Like you are off by 10%) and there is some loss from abient radiation and conduction and natural convection (Maybe another 10%) there is still close to half of the heat that is produced that is MISSING!!! <REALLY puzzled frown>

  Energy can be neither created or destroyed, it only changes  it "shape/form". like from the heat in a oil fired boiler flame to the energy contained in steam - so where it has gone, here, I have no IDEA!

  That an internal combustion engine only puts about one-third of the fuel's energy into horsepower produced by the engine, is well established for about the last century.  That the non-work energy is split roughly 50%-50% between cooling water and "other" is, similarly, widely held for about the last century.  You can get p!$$y and argue that the thermal effeciency of an IC engine is not exactly 33%, and yes, you can find specific IC engines that are anywhere between 20% and 45%, but for a small diesel engine, I don't think that you will find a range larger than 30% to 40%, at the absolute outside limits.  And, if your engine is a spark ignition engine, it efficiency is WORSE than a diesel, so there is still, yet, more, already, energy missing.  I have absolutely NO idea where the answer to this is!

  I can ask a lot of questions about how many amps at how many volts, yada, yada, yada . . . but I'm pretty sure that you know, at least to within 10%, how much energy your engine is putting out, so, help me out here, guys, what am I failing to see?  There has to be a LOT of energy going somewhere - where is it???

  If I take worst case examples and assume 10% error on all the measurements, there still is half of the heat from the engine missing!  <frown>

  On that question, I'll rest my convoluted case! <grin>

As always, thanx, eveybody for the input!

Regardz,

Wayne Stayton

[WStayton]

Jens:

  Ok, so we are not making 20 HP, here but 9200 watts.  1 HP = 746 watts, so you are actually making 9200/746=12.33 HP.  If you capture all of the cooling water heat and half of the rest  of the heat, and turn the electricity into heat,, you have a total load over four hours of 12.33x2.5X4 hours=123.33 hp-hr of heat into the thermal holding tank. At 2545 BTU per hp hr, you have 313, 861 going into the tank in four hours.
At 240 gallons x 8 lb/gal, you have 1920 lbs of water.  Since your waste water heats up 75 F during the four hours, you have 144,000 BTU being stored in the water - that only leaves 169,861 BTU to be accounted for!  <grin>  You state that the the cooling loop loses about 5F between where it comes out of the engine and where it goes into the tank - do you have any idea what the flow rate is when this happens?  Also, do you have any idea what the temperature loss of the tank is, per hour, after you shut the engine off, with the tank just sitting there?

  Also, you say " loss inside the house is irrelevant " - well it may be irrelevant in terms of heating the house, but in terms of accounting for the heat discharged by the engine it is VERY relevant. 

  Since the tank is not insulated,  the heat transfer from it is probably pretty significant but by far the easiest way to estimate this is to know the heat loss for an hour.  If you make any sort of heat transfer estimate you have to make some estimate of the R value of the tank, liner, etc. and if your just shooting in the dark, as I am, your apt to make as many bad guesses as good one's.

   Anyhow, I'm still confused as to where a BUNCH of heat is going, but your descriptions have pointed out where it might be.  At least we now know, with some degree of confidence, what the total heat rejection by the engine is.  It is true that you can argue about how much of the exhaust heat is really transferred to the water tank, but guessing that is half of the available non-water jacket heat, at least gives a place to start.  It may be 45% or 55% of the non-water jacket heat, but that 5%, or even 10% is relatively meaningless in the greater scheme of things since we are trying to guess at a lot of other values.

  If you have any idea about the temperature decline in the sitting tank, and about the rate of coolant water flow, I would, VERY MUCH, like to hear it - just as a matter of intellectual curiosity! <grin>

Thanx of reading, guys!

Regardz,

Wayne Stayton

[Ronmar]

Wayne, the direct conversions don't work out quite right here as they do not take into account generator and drive efficiencies...  Because of that I think your numbers are actually conservative:)  At any rate, running a listeroid myself, and having done some pretty carefull fuel use measurements, .125 gallons per KW/HR is a pretty close estimate for fuel consumption in a listeroid on diesel fuel.  At 9.2KW of electric load, Jens is probably burning close to 1.15 gallons of fuel.  That at 140000 btu/gal is around 161000 BTU/HR consumed.  1/3 of that into the cooling system(something I have also confirmed out of my cooling system heat exchanger) is around 53,666 BTU/HR.  Half of that from the exhaust heatex is another 26,833 BTU/HR.  The 9.2KW of electric heating elements works out to around 31,408 BTU/HR for a grand total of around 111,907 BTU/HR.  Over 4 hours by my figuring, that is 447,628 BTU into the water...

But having been in on a few discussions IRT Jens system isssues, the numbers have never added up:)

[Crofter]

I see you have fallen in love with the notion of making joints in the ply sheeting; I think Jens gave you good advice there.

The figures are quite likely correct for the strengths of Resorcinol glue on wood under ideal conditions; theoretical values that do not take into account field condition effects of dimensional changes from moisture, heat, uneven and out of line forces that lead to spot loading and thus incremental failure. Bonding to one face layer does not engage nearly the potential tensile strength of the whole thickness. Progressive failure; divide and conquor!

A scarfe joint or a double sided scabbed joint would have mechanical advantages but  is way more complicated than the nature of the job warrants. Going to a larger tank has some apparent advantage in volume to perimeter ratio, but the strength in the whalers gives very quickly diminishing returns re. lateral deflection.

Also you cannot consider liquid in a tank to be a static load based on calculated pounds per sq. in. Vibration from traffic etc. is a very real and magnifying effect. I have been party to several shit outs of formed concrete. Someone apparently forgot about vibrating.

I dont feel the construction you have in mind would fail but it does have some potential negatives labor wise and there is some benefit in having your eggs divided between two baskets.