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Old 06-08-12, 04:30 PM   #41
Snail
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Another point about burying the timber inside the insulation is that it will dry out even further than kiln drying can achieve. This doesn't directly reduce strength but may cause cracking around the fasteners, which is worse if anything.

With design of timber structures, strength is not the only consideration. When the load is continuous, as it is here, long-term creep becomes the critical design factor. Unfortunately, the timber design code rules are mainly concerned to keep this creep to very low levels for aesthetic reasons in buildings. We can be a bit more relaxed for tanks, but I am not sure how much. Does anyone here have long-term experience?

Because timber inevitably moves a bit, the liner must be able to accommodate this movement. A few years ago I had a very bad experience with a paint-on coating on a timber deck. It was not extensible enough to take the movement and cracked after only a few years. Needless to say, I went back to the good old sheet Butynol after that. Possibly an outside environment, even in a mild climate is more severe than this one, but, on the principle of never buying version one of anything, I'd not be happy with any liner that wasn't backed up by a lot of years of successful experience.

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Old 06-08-12, 08:42 PM   #42
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Quote:
Originally Posted by Snail View Post
Another point about burying the timber inside the insulation is that it will dry out even further than kiln drying can achieve. This doesn't directly reduce strength but may cause cracking around the fasteners, which is worse if anything.

With design of timber structures, strength is not the only consideration. When the load is continuous, as it is here, long-term creep becomes the critical design factor. Unfortunately, the timber design code rules are mainly concerned to keep this creep to very low levels for aesthetic reasons in buildings. We can be a bit more relaxed for tanks, but I am not sure how much. Does anyone here have long-term experience?

Because timber inevitably moves a bit, the liner must be able to accommodate this movement. A few years ago I had a very bad experience with a paint-on coating on a timber deck. It was not extensible enough to take the movement and cracked after only a few years. Needless to say, I went back to the good old sheet Butynol after that. Possibly an outside environment, even in a mild climate is more severe than this one, but, on the principle of never buying version one of anything, I'd not be happy with any liner that wasn't backed up by a lot of years of successful experience.
Hi,
The EPDM lined tanks of both lumber and metal go back to the 80's and have a good track record. They last longer than most commercial tanks, cost a small fraction of equivalent commercial tanks, and when the liner finally does go out, it can be replaced for a few bucks for another 20 years. They seem like a great all around value to me.

On the lumber at high temperatures, most solar heat storage tanks don't spend very much time above 150F, but I agree that it does add another good argument to insulating the inside of the tank.

I guess the one caution I'd offer is that its important to build a good structural design, and if you are not up on structural design and sizing techniques, its best to stick closely to one of the designs that have shown that they do work well.

Gary
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Old 06-08-12, 09:32 PM   #43
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Hi Gary,

I certainly would go for EDPM, if I can get it, when I finally finish
enough of my other projects to get onto the heating. It's the paint on type of liner that I was questioning.
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Old 06-09-12, 05:16 PM   #44
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Hi Gary,

I certainly would go for EDPM, if I can get it, when I finally finish
enough of my other projects to get onto the heating. It's the paint on type of liner that I was questioning.
Yes -- I think the paint on ones are still an open issue. The other Gary did his large tank with a paint on lining as described here: Paint on Waterproof Liner For Solar Heat Storage Tanks

I emailed him to see how his liner is doing, and his response was that after 2.5 years its still doing fine -- no problems. So, that's a start on a track record.

Gary
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Old 06-09-12, 05:31 PM   #45
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Hi Gary,

Thanks for the very interesting link. BuildItSolar is a jewel.

You note that the "other Gary" has built an exceedingly robust timber structure. So the reduced costs of the lining must be partly compensated for by the more expensive support. It all depends on relative material costs whether this is worth the potential extra risk. Of course repair costs could be low, provided that you detect any leakage before you get water damage to timber and insulation, which may not be easy.

menaus2 seems to be trying to minimise costs for both liner and structure, whilst also using a water-susceptible insulation. Seems a bit risky.

Peter

Last edited by Snail; 06-15-12 at 05:58 PM.. Reason: Mistaken attribution of this thread to Daox instead of menaus2.
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Old 06-15-12, 10:52 AM   #46
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uggh decisions, decisions. I'm looking at the Grundfos 15-58, but all the ones I can find have an integrated check valve. I'm thinking this would be a problem, because you want the vertical section of pipe inside the collector to be able to backflow through the pump to prevent the water that section from freezing. Anyone have experience with this issue?

(edit): Just figured out the check valve is removable (duh!) Anyways, I like the pricepoint and flowrate flexibility. I figure 2 of these should do the job nicely.

Last edited by menaus2; 06-15-12 at 11:06 AM..
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Old 06-25-12, 10:21 AM   #47
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I ended up getting the 2 Grundfos 15-58's, and a 500' coil of 1/2" pex-al-pex from pexuniverse.com and am excited to see how they end up performing.

As far as the timber tank debate goes, I think the elimination of thermal bridging compensates for the higher price with increased performance.

I've also been thinking recently about low cost tank options that are a lot faster to put together. Sure the framed tank is cheap but it's very labor intensive and time consuming. I'm interested in using large plastic water tanks as a more durable and ready to go option. It could rest on a foamboard base, a simple exterior enclosure (foamboard? maybe a woven plastic bag or cheap framing and drywall?) and fill the walls with blow-in insulation (fiberglass probably if moisture could be an issue). The result could be a tank with little warping, a cheap thermal barrier with no thermal bridging, potentially longer lifespan (?), and faster construction time.
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Old 06-25-12, 11:02 AM   #48
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I have both heat exchangers tied into the house plumbing like this. You can see the two ball valves to the HX with the bypass ball valve between the two. On the far right is the check valve to protect the city supply.



Painting the treated 2x4's for the collector frames.



Part of the South facing wall before starting. Looks boring with all sorts of solar radiation being pissed away as heat into the surrounding environment. Stupid! Let's fix that...



After some finagling with the level and some screws here and there, the right collector frame is up.



Both up.



A different angle.



Friend and I put up the insulation and OSB. We used 2 layers of 1/2" poly iso board against the siding, and 1/2" OSB screwed in over that.



The same on the left collector. The reflection of the sun off the foil backing was starting to cook us. We got the OSB on fully, but didn't take pictures of that yet.

Next: insulating the inside "sidewalls" of the frame, and installing the collector plumbing!
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Old 06-25-12, 03:41 PM   #49
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so did you just screw right into the siding to hold the foam and OSB into place?
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Old 06-27-12, 02:08 PM   #50
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Subscribing....read every word, and there's too much really good info here for me to miss.

Thanks to all involved,

Mark

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