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[split] New Firebox Construction (Pond loop & components discussion)
The house has central air ducting, and I'm using a central air airbox for the recirculation. So air movement isn't an issue. Also, this takes care of the condensation as the unit is built with this in mind already. Condensation collects on the coils, runs down to a catch pan that dumps the water outside.

I agree that the pond water can heat up, this is one reason why I'll be planting shading plants around the pond. I'll have a fountain that will help with heat discharge. I have a larger pond (about 35Ft x 80Ft x 5-8Ft [depending on rain]) that has varying temps. The first few inches of the water can be hot, walk a bit further in down to the knees and it gets a lot cooler at the bottom. The deep sections I'm sure are even cooler and this pond has direct sun all day long. So the shaded pond shouldn't have much of an issue getting rid of heat.

Taking 80F air and dropping it down to 72F is a lot cheaper than trying to take 90F air and dropping it down 72F. That is why I don't mind doing a pre-cooling using the pond. Even if the air temp doesn't drop all the way down, this allows the secondary cooling system (if needed) to function better. Which, that unit has a secondary cooling system on the coils as well (another topic on this)

I had worried about the tote getting soft or degrading over time. But these are the types of totes that are commonly left outside in the sun to store all kinds of fluids in, including food grade liquids. But, they are made of HDPE:
Quote:HDPE or High Density Poly Ethelene plastic has an amazing temperature range, and is considered safe for short periods up to 248°F (120°C) or for long periods up to 230°F (110°C.) Since boiling water never gets above 100°C, this means that anything boiling and below is safe for a food grade bucket.
So I doubt temperatures will be an issue here.
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You still do not want HDPE outside, as UV can degrade it.

Your best bet would be black HDPE with a white paint on it.
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These IBC totes are regularly stored outside for years at a time with all sorts of chemicals in them. Everything from oil at refineries, gas depots (for fleets or farm), and farms and more. Considering these are regularly stored outside as that is their designed function, I doubt UV degradation is a problem. Maybe they have a special coating sprayed on the outside, or infused with the primary HDPE plastic, I don't know.

So far, after having these totes outside for 3 years, the only thing that has degraded was the plastic screw on cap that is not made of the same material. The tote plastic itself is still very strong, flexible and the same color as it was before.

I do appreciate all your concerns, though Smile

As far as painting it, the best reason to do so is to keep algae from growing in it. The one tote I'm using as a test medium was sitting for over 6 months about 1/3 full of water. It had algae growing in it even though the lid was on top. Considering the hole is only about 10 inches in diameter, it's kinda hard to get in there to clean it out. Before I put this thing in full production, I'll need to get some kind of scrubbing brush to clean it out and add a little chlorine to the mix to help keep algal grown down or out completely. Should only need about 1/2 cup for the size of the system.
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Why paint, when its insulated its dark also, but algae does not need sunlight to grow.
Algae is capable to make its own oxygen, but not his own nitro oxygen(N2).
As long if there is oxygen and some nitrates(NO3) there will be algae.

So there was something to eat in the water or tote, one leave is enough for 6 month of algae.
When you close (and put some psi in it) your system, they will disappear like smoke in wind force 6.

I agree on chlorine, it will clean algae and dissolve as a gas over time, if you can get pure chlorine.
I think you mean: Sodium hypochlorite.
But what is the effect on pvc and copper.

I think you would be better of with lye.
Or stupid as it may sound, throw some iron piece in it, and let it rust!
But when you have copper pipe(s) in your system, it will also disappear.

Fun fact about algae, they can create hydrogen to fuel a car

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I did a little reading on various epdm and hdpe pe and pp plastics
As far for the hdpe plastics there are various degradations, but most have a uv protection material melted in them.
The thing what concern me the most, is that most, so not all, hdpe plastics can handle 90C.
Some can handle for short time 100c.
Tyleen plastics seems to have there eutectic point at 70C.
There must be a triangle embedded somewhere on your tote, that triangle will give you some abbreviations and there is a number in it.
Just to make it yourself sure.
I have barrels hdpe with a 1 or 2 number in it.
They hold some chemicals, like lye, acids, oils ect, some are for food some are not.
It surprises me that there is so much variance, between "just" hdpe and "just" hdpe.
Again most, if not all, have uv blockers, and can handle temps up to 90c and short amount of time 110.
I think your fine with your tote, i knew you would be lucky Tongue , like i stated a few post back.

Now the trick would be to keep the water below boiling point, if you don't want or can't to pressurise your system.
Please keep in mind:
A pump wont put pressure into your system.
Water starts bubbling at 85c, boiling at 100c, you really want to keep the h and o together.
I strongly suggest:
or stay below 85c
or increase the boiling point by adding additives 
or fill it with oil 
or pressure!
With those 4 choices your system will stand or fall.

How far are you with your "hot" side?

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Yeah, "just" hdpe and "just" hdpe can be huuuge differences. Kinda stinks that there aren't more visual distinct differences in the name

I figured the hot side will only get to about 60-70C. I don't want any steam forming at all in the tank.

When I talk about pressure side, I'm only referring to the output side of the pump, not the input. There will be some pressure on that side, no matter how little. If there wasn't, there'd be no flow Tongue
I'll have a pressure gauge on it anyways just to monitor it, as that will also tell me if the system is getting too hot and starting to steam.

I haven't built anything other than the part of the box. However, I will be changing my design. I'm going to go the route of a double barrel heater setup. Basically two iron 50gallon (189.27L) barrels that have a 6" flue pipe connecting them together, and the smoke flue is at the opposite end of the top barrel. The fire is built in the bottom barrel. The dbl barrel setup allows for a lot of heat collection both radiantly and directly with the coils. The top barrel can also be setup to be a cooking oven, too.
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I would advice this for savety, set it on 80c-84c and let it switch on a separate/extra pump if it gets at 80-84c to cool off a bit.
Heat up the house, would give a problem with your cold side, or run a line into one of your ponds.
Or a extra radiator outside in the shade, just for comfort and safety then.

Also for safety, IF your iron barrels have a good coating at the inside! dissolve salt, 15-20 grams a litre.
It will dissolve by time, you don't have to boil or aggravate and than add.
Salt will dissolve with flow from my experience without tricks just flow, up to 30 grams a litre.
I must admit i don't know what the long term risks are on copper or at those temperatures or amount.
Pvc, hdpe and most plastics no problem for sure.
After 6 gram a litre there will be no algae/plant life possible, or you must get salt water plants.

My pond contains 6 grams salt per litre water, i have a bucket, where i throw in the salt with a small pump running water on to it, 50 kilo at one day, gone!
My system is running for 20 years now on salt, no problems, no leaks.
Inox, copper, pvc, pe, pp and epdm, no problem! But below 30C.

With my experiments that i have done, and the knowledge i have gained plus with what i've read, please consider this:
You don't want the trouble and problems of water, with or without additives.
We are talking about a low pressure (flow only) system, with low temps.
If i was you, i would do oil, but this is to my knowledge, i really hope someone will chime in on this, for a good medium to use.
Baby oil, 5w15 motor oil or similar.
You want the heat in the storage, and transferred quick when you need it: imho: oil, sorry Blush

ps, the water in my profile pic: i was running out of salt for my pond and waiting for 200kg delivery.


This is now, those algaes are adapted/resistant to salinity levels up to 5 gr per liter, they are dying by the way.
that area is approx 1.60 deep, the fish is approx 1,55 meters.
Selling everything at marketplace.
Like it. I thought you had moved when I started reading, firebox, Florida, lol. You need to go on holiday/vacation to somewhere really cold, lol.

Stay away from oil for heat circuit/reservoir, it's more expensive than water, holds less heat per unit volume, you can't sell it easily (for a good price) after use and any leaks can prove to be rather expensive and not just from the fire as cleanup involves soil removal or heating. You need something in the water to prevent it from becoming a Darwinian experiment on the creation of life.

Phase change, per unit volume of space compare to water, still very difficult to make sense as the cheapest phase change material is wax, but that has issues over thermal conductivity so you end up having to have a tank of wax with iron rods/rebar to transfer heat more effectively or the coil has to be wound into an through the tank. Water is difficult to beat.

Blocks/chunks of iron are more energy dense but the weight poses issues on the design as a half ton of steel stacked in a little box makes for reinforced floors or a sinking heat storage unit. I have some 10kg round billets I experimented with (250kg) which also make good for various other experiments, like dropping from heights....

LPG tank for the flue, nice. I had to fill mine with water before I dare cut into it...

My design (still on paper, but I have the cylinders) was to use 3-4 cylinders stacked. Lower cylinder is the firebox, next cylinder is a heat exchanger like the design in a steam engine but vertical and using scaffold poles with two end plates, next 2 cylinders are then just a flue. Lower cylinder is then wrapped in rockwool with a thin sub 1mm sheet wrapped around to keep the rockwool in place.

If the flue is longer you get more updraught which increases the fire temperature with the additional airflow and then reduces the size requirement, but the trade off it having to top it up more frequently and the size of material you burn.

To regulate the fire, reduce the air intake and not the flue would be my preference. Eliminates any gaps from becoming a new flue with heating and carbon monoxide which is generated when the fire is choked by a reduced oxygen intake.

Peltier/thermal generators, still way way too expensive to make sense unless your a space ship with a radioactive heat source and a million miles from home.

IBC units are cheap enough and resiliant so the only issue for the sun exposure is an introduction to Darwin, unless....... you combine the heating system with a fermenting in the tank the first part of the year and then when you need heating for the house, instant distillation system..... hoooo har.
If you can't quantify how much they cost, it's a deal, I'll buy 5 of them for 3 lumps of rocking horse ......
Thanks for the inputs. I'll take the suggestions into consideration.

Just to clarify the water loop will be a closed system. And it won't come into any contact with the water in the pond. It's just going to flow through piping in coils at the bottom of the pond.

I haven't done a gauged temperature reading of the pond, but after several weeks of direct sun, the 3Ft of water currently there isn't even warm. I walk in it barefoot every few days just for relaxation and the ground is always cool at the bottom. So when the pond is full, about 6ft (2m) deep, there should be plenty of heat transfer available.

I will be using water for the loop primarily because I get it for almost free. We have very good well water here. The only thing it really has is a higher concentration of calcium than most like. Iron content is very low.
Chlorine/bleach will be introduced to help with algal growth. Even if the tote is closed in insulation, some light will still be able to reach the water. I doubt I'll be able to fully block the light out unless I build a shed around it, which I hadn't planned on. At least not right away.

The flue isn't an old LPG tank, it's old bladder water tank. So no chance of exploding Wink

I had thought of creating steam with flue coils and use that to turn a turbine for power. But that's for another thread.

I think I need to draw up a diagram of what I plan on doing to make things a lot clearer to understand.
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Lpg tanks are pretty cheap over here.
So to weld up some tanks, they come in different sizes, is for someone very good to do and for others not.
BUT his safety rule to fill the lpg tank first with water, is very good, there are a lot of people that don't understand that a empty gas tank is not empty.
Often results in: gas tank/darwin award, 0/1

5% bleach/Darwin, 1/0.

But wax, never heard of that solution.
Al the commercial systems has oil or propylene glycol(coolant) in it, there are even central home heating systems with oil in it.
All synthetic oils most silicon based.
Granded oil is more expensive than water, it heats up a little slower than water, but hold the heat way longer than water.
And it not so easy to cool down, because there is more mass, its also more steady than water.

Now if you want to go the professional route, you can mix with 50% water 50% propylene glycol.
Or cheap 80% water/20% propylene glycol.
To get it cheap, go to some car graveyards, car demolition ect, here in Holland if you now the good ones they wont do difficult.
Don't forget to filter it, ~ to 200-300 micron.
And it is saver for a occasional cold night.

But i am very curious about wax.

Peltier element aren't so expensive anymore, i was surprised, i ordered 10 (15 amp) to play with.
Mind you, i more a Scottish guy when it comes to money Big Grin, you will understand!
The trick with peltier is very good insulation between the hot and cold side, and to get rid of the one you don't want.
The better you separate the hot and cold side, the better they work. But i will make a seperate thread on this.

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