thermal storage tank progress

[sunspot]

Three years ago (seriously!) I started building a storage tank for water to be heated by solar panels and a woodstove. Here it is:



This week I moved it from my shop to the space it'll occupy hereafter. There's angle iron, repurposed bedframe, along the bottom edges let into the fir framing with rebar welded between. The tank is deep and I wanted to build in plenty of strength to resist the water pressure.





The concrete slab where the tank sits is far from flat. I grouted the sleepers in after shimming the framing level and poured additional concrete between the sleepers for bearing.

There are two rows of whaler running around the tank, double 2x4" on the ends and double 2x6" on the long sides. The corners are bolted using timber washers.



Tieing the long side whalers together front to back is rebar to which I welded coupling nuts. The rebar ties to angle iron outboard of the whalers. Since I couldn't reach the bolts on the back side I tack welded them to the angle.



Fiberglass insulation was added wherever possible as things went together.





The inside is lined with 3/4" fir plywood and 2 3/4" polyiso.





The one wall exposed to the rest of the room was insulated and sheathed in 7/16" OSB before the whalers and bolts/angle went on.





The tight space made the getting the tank set up a challenge. I couldn't get the plywood through the door and over the tank sides so I had to move it into the tank before the walls were complete and temporarily hang it (in the order opposite to which it was needed) out of the way on screws. I'm happy with the results so far though.

The inside measurements are 61" x 40 1/2" x 66 1/2". Assuming it gets filled to within a couple of inches of the top that's 92 cubic feet or 2,610 litres (690 US gallons).

The lid will be permanent with an access hatch and I plan to line the tank with fiberglass and vinylesther resin. So if you're interested in that phase of construction check back in say, three years :-0

[randen]

Nice work!!!
Free heat from the sun you will enjoy that. Maybe with your renewed momentum you may finish the project quicker than 3 yrs.

Randen

[sunspot]

Originally Posted by randen

Nice work!!!

Thanks! I'm glad to have taken a step towards getting the system up and running. The 1" pex rough-in plumbing is in place. Now to finish the tank and sort out the collectors.

[randen]

How many collectors will you be installing? Which method will you employ to distribute the heat? Will you roll your own collectors? Drain-back?

Randen

[Mikesolar]

yes, nice tank. You had questions before about whether to build or buy collectors. What did you decide? Is that PEX O2 barriered?

[sunspot]

The system will be drain back. Heated by a water loop in the woodstove (wood is currently our only source of heat) and solar panels. DHW preheat will be one load. Space heating will be via old cast iron radiators I found at auction (heavy!). I had intended to build my own collectors but the tank alone has taken me three years and counting. So I asked for recommendation here and Mikesolar pointed me to Thermodynamics Ltd.. I've spoken to them and they seem happy to quote on custom sizes as well as the their standard ~ 4' x 8'. I have to decide where to put them. I have two options. A roof slope eyeballed at ~ 6/12 or a south facing wall. The roof has more area available but it adds ~ 6' of head and the angle is less than ideal. The wall is problematic with window penetrations, soffit overhang, and odd dimensions.

And yes, the PEX is oxy barrier ;-)

[sunspot]

And thanks for attaching the pictures randen. I've been following your projects. Very inspiring.

[randen]

Sunspot
Your investing a lot of time and energy to a new system. I would humbly suggest to educate yourself in the low temperature heating methods. One of the best is in-floor heating. There are others with larger surface area, heat exchange surfaces with a small fan force.

The solar hot water panels can be quite effective as we have actual success with our system. One full day of winter sunshine equates 24 hrs of space heating for us. Even at minus 20 Deg. weather. FREE
But without a good method to distribute that lower temp heat this may leave you a little dissatisfied.

The old cast-iron radiators are the old tech. that require very high temp water to offer any sort of comfort. They will work with a wood fired boiler but you will be kept warm with the constant wood cutting hauling and loading of your boiler. I understand you will have a huge heat battery but you will have issues with trying to keep it at temps around the 80Deg.C plus temps.

Growing up my dad installed a Newmack combination wood/oil boiler. Having a home with three strapping boys to help with the wood cutting, splitting, stacking, filling the boiler etc. It worked, but we now know how to do it better. That thing (boiler) only heated the home at a boiler temp 80-100 C deg. Problem baseboard radiators.!!! The convection needed very high temps and it took a lot of wood. All of us really got tired of dealing with wood. (except for one brother "The youngest") He still likes fire!!! We'll see how that will go as he just turned 50 yrs.

If you employ the lower temp methods the solar will work extremely well and the wood boiler can be used as your back-up when the sun isn't around. You will need only a small fire heating the large heat battery to 40-50 Deg.C

Heated floors are amazing. Check out the Uponor product with a nice tile on-top. The niceties for in-floor are it won't occupy any floor space or leave marks up the wall from the convection over a radiator. A beautiful tile floor is the actual functional attribute for heating. The heat is so uniform. The cat will sleep anywhere on the floor in the room and not just next to the rad.

DO NOT EVEN entertain the idea of between the joist heating loops with spreaders.

If you have forced air ductwork installed you could use an oversized air handler on a low speed setting so the house doesn't feel drafty.

The amount of solar collecting area is important. For flat plate (if you planning space heating) Min 10% of your floor space. But to be totally sufficient 20-30%
You had mentioned about your wall space area. The collectors work better vertical for winter heating. Increasing the total area of collector is totally worth changing a window to a long narrow (floor to ceiling) renovation.

Its a lot of work!!!! But, so is cutting wood. I'd just prefer to do it once.!

I can't do the explanation justice, of coming home after work, knocking the shoes off and feeling the warm tile floor with your feet. But to further know the sun, at no cost, no work had provided that heat FREE!! NIRVANA!

Randen

[SDMCF]

Originally Posted by randen

The old cast-iron radiators are the old tech. that require very high temp water to offer any sort of comfort. They will work with a wood fired boiler but you will be kept warm with the constant wood cutting hauling and loading of your boiler. I understand you will have a huge heat battery but you will have issues with trying to keep it at temps around the 80Deg.C plus temps.

It seems common to run radiators at 80+C, but I really don't understand why systems are designed to require that. The temperature at which you run the rads will depend on how well your house is insulated, and how many rads you have compared to the space you need to heat. Our house mainly uses a mixture of cast iron and flat panel radiators, powered by a GSHP. The water coming out of the GSHP never comes anywhere near 80C. Even during the coldest winter it never gets above 55C. Most of the time it is significantly less. For example, today it is -3C outside and the GSHP is pumping out water at around 35-40C to maintain a comfortable indoor temperature. So rads can operate at lower temperatures in a decent situation. If this is possible in our house, which dates from the 1890s, and in our climate, it should be possible most places.

I agree that underfloor heating is a more desirable solution but in a retrofit situation I can certainly understand why radiators would be a more attractive proposition.

[AC_Hacker]

Originally Posted by randen

Sunspot
Your investing a lot of time and energy to a new system. I would humbly suggest to educate yourself in the low temperature heating methods. One of the best is in-floor heating. There are others with larger surface area, heat exchange surfaces with a small fan force...

randen,

Excellent notes on low temperature heating!

I checked out a page on solar insolation for various parts of North America and South America.

Sunspot didn't say what part of BC he's from, but there's a good chance his solar gain potential is somewhat more modest than yours.

But at the same time, his location is such that his Heating Degree Days will almost certainly be lower than yours.

I just took a guess as to his location (guaranteed to be wrong) that his location is Victoria, and if that's the case his severe months HDD would be maybe half of yours.

But a low temperature approach to installing radiant would still mean more days on stored solar energy, and less wood to chop in the periods of lower insolation.

Best,

-AC