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Insulation under floor of water distiller

February 22, 2020 — BarryK

The saga continues. Here is the previous post in the gradual accumulation of what is intended to be DIY plans for a solar water distiller:

Now for the insulation under the floor of the basin. I was going to use fibreglass batts, after misadventure with using expanding foam with the previous prototype: that case, I had spread baking paper, which turned out to be a very bad idea. If I spray the foam directly onto the (slightly damp) plywood, it will stick and (hopefully) not lift off. So, decided to give expanding foam another go...

Before we get to putting in the insulation, there is the matter the inlet and drainage plumbing. Contrary to what you might expect, I put the inlet as a hole in the floor of the basin, not on the side wall. I also cut a hole for drainage. These two holes are at opposite sides of the basin, with the intention that water can be poured into the inlet and flow out the drainage hole, for periodic flushing of the basin.

Both holes were cut with a 16mm spade drill bit. Silicone tube is then inserted into the hole and sealed with black silicone sealant. I want the tube to bend 90 degrees, so I bought two Norma brand 13mm elbows:

...these are for automotive use, and the plastic will work up to 120 degC. Cost a bit more than trickle irrigation elbows from Bunnings though, AU$4.97 each.

These are attached to a short length of silicone tube, and I did use a cheap Bunnings trickle-irrigation plastic pipe clamp:


...the silicone tube could probably have been bent 90 degrees without needing an elbow, without kinking, and maybe with some channel to prevent it from flattening. Anyway, I went for the Norma elbow.

Next, it was glued into the basin floor, here is the underneath view:


...there are some pieces of wood placed to hold it in place while the sealant sets.

Here is the underneath view when both inlet and drainage pipes are fitted:


...notice the two blocks of wood in the top-middle. They are just some scrap pieces, placed there to give the bottom plywood something to screw onto.

The bottom plywood is two pieces. I won't give measurements, as it is easy enough if you build this, to measure and cut the plywood. It is the same 6mm marine ply that I used for the floor of the basin, cut from the same original 810x1220mm sheet purchased at Bunnings. Here is what the two sheets look like when fitted:


...16mm holes were cut for the tubes to stick through, and filed to allow the tubes to come through at an angle.

About those little holes in the above photo. 12mm holes. I had the idea of screwing on the bottom plywood sheets, then use those holes to inject the expanding foam.

Ha ha, that stuff has a mind of its own! Yes, I did try that idea, injected the foam, but it built up enormous pressure, and the plywood bowed out. I needed to have screwed it down more firmly in the middle. I had reasoned that the excess would come out of those holes, but that didn't happen ...perhaps the holes should have been bigger.

Aborted that. Took the plywood sheets off, bought another can of expanding foam and, the next day, after a spray of water, spread the foam all over the surface, as best I could anyway. This snapshot is just after spraying, it did expand some more afterward:


...baking paper was wrapped around the silicone tubes, with sticky tape, not that I really expected the foam to stick to the silicone tube, just being paranoid.

Waited another day, then used a large wood saw for most of the cutting, then a hacksaw blade to finish off, got it reasonably flat:


So, what's next? Obviously, any water placed into the basin is just going to run straight out of the pipes in the floor. However, the drainage pipe will have a tap attached and the inlet pipe will bend up and be attached to a funnel.

This means that there will be water in those pipes, and you might think that will mean heat loss. However, water is quite a good insulator, and mostly any heat loss would be due to convection, hot water rising and thus the water circulating -- which won't happen in this case, as the hot water is at the top.

Actually, this is an experiment. I will measure the water temperature where the pipe comes out the bottom of the distiller, very interested to find out just how much it will heat up. 

Shopping list (prices in AU Dollars):

Norma elbow 13mm x2
2x $4.97
6G 16mm wood screws, 40pk
Expanding foam, 750ml (Bostik)

* I used two 500ml cans, however, that was due to a misadventure. A single can should be OK, and probably it will have to be more than 500ml. 

Tags: nomad