DIY solar pre-heater

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DIY solar pre-heater

Postby 120ThingsIn20Years » Sat Jun 26, 2010 2:03 pm

Does anyone know of a product like corflute thats made of anything else?

coreflute.JPG


I'm in the "yet another leak" stage of making a DIY solar pre-heater.

I'm attempting to use corflute as the collector. The collector will be under glass and it will use a solar siphon (passive convection) for circulation. Corflute is that hollow plastic stuff they use for signage for things like real estate, and political campaigns.

I realize corflute is a poor conductor but its cheep (free) and has a massive water holding surface area, and I can just make my collector bigger if need be (I live on a farm so huge is fine). Anyway its thin so should work at least as well as black hose.

This isn't my idea but something I read a few weeks ago when researching different methods.

The plan is to split a hose length ways and glue it onto each end of a sheet of corflute. Like this but with the corflute sheet placed not quite so far into the hose.

IMG_1202.JPG


The problem I'm having is in the gluing, and with the general strength of the products involved. Corflute hates silicone, and black hose hates hot glue. Also, even though this will run at ambient atmospheric pressure, the corflute is a little weaker than Id like it to be.

I could probably get away with the corflute if I could glue it better. The glue cant be anything like superglue as it needs to be a filler as well.

So, to summarize..... (thanks for reading this far :) )

Can anyone think of a corflute-like product that might work instead?

Can anyone think of a glue that would act as a filler but that isn't silicone or hot glue?

Can anyone think of a method to prepare the surfaces so they might like the glue better eg some kind of primer or something?
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Re: DIY solar pre-heater

Postby Gordon-Loomberah » Sat Jun 26, 2010 2:57 pm

It really, really sounds like you are setting yourself up for a permanently leaky system, I would expect if it ever heats the water up enough to make the corflute soft, then even more leaks will appear.

I think you would be way better off using coils of inexpensive black poly pipe of the type used in garden irrigation systems. A big flat coil of 13mm in a glass fronted box should work ok.
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Re: DIY solar pre-heater

Postby bpratt » Sat Jun 26, 2010 6:29 pm

Corflute also gets affected by the UV, and over time it goes hard then brittle, and as Gordon said you will end up with a lot of leaks. :(
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Re: DIY solar pre-heater

Postby 120ThingsIn20Years » Sun Jun 27, 2010 7:18 pm

Points taken.

I'm going with poly
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Re: DIY solar pre-heater

Postby Gordon-Loomberah » Mon Jun 28, 2010 5:53 pm

120ThingsIn20Years wrote:Points taken.

I'm going with poly


20m of 13mm thin walled poly is $3.97 at the big B, if you are trying to do it on the cheap, it doesnt get much cheaper than that! :)
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Re: DIY solar pre-heater

Postby Billc » Wed Jun 30, 2010 11:38 am

Re: using black poly in a solar collector. Tried using cheap 10 mm black poly last summer in a home solar collector & the heat caused the plastic to taint the water (both taste & smell). May work OK if you can get a better quality poly.
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Re: DIY solar pre-heater

Postby wt29 » Wed Jun 30, 2010 2:15 pm

I've used Corflute (Correx etc) to build model aircraft - cheap fun.

Gluing it is an artform. I use Bear Brand Gel (not liquid) Contact cement after clean of the production oils (from the extrusion process) and it seems to stick well. Don't know what will happen once the temperature rises. UV could be an issue too.

These guys - http://www.spadtothebone.com- have worked out dozens of ways to glue and work Corflute. You might get some ideas here.

Cheers
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Re: DIY solar pre-heater

Postby friendlyfisho » Wed Jun 30, 2010 3:09 pm

I think you have a good idea there, as corflute is a readily available , cheap and ideal material to use as a solar radiation collector and heat exchange - and it has a much higher WAF (Wife Acceptability Factor), much better than a coil of poly tube on the roof.
I have translucent corflute which has been UV treated on my greenhouse, so I don't see why a panel with a coat of black paint should experience UV problems.
I would suggest you forget about the glue and fill sealing method and instead develop a mechanical seal. One that comes to mind is a bit like pushing an irrigation fitting with a nipple into a hole lined with a rubber grommet.
Try using 50mm HD PVC water pipe, rout a straight channel whose length is the same or a tad longer than the width of your corflte, and using a bit of appropriately shaped rubber strip, make an oval shaped grommet to line the edges of the channel. If you have calculated your dimensions correctly, you should be able to slip the corflute in between the rubber edges and form a water tight seal. Tip - use soapy water as a lubricant.

I have used translucent corflute to double insulate my clerestory windows in Tasmania with fantastic results.
A tightly fitting sheet of corflute with the open ends taped over is placed just inside the window architrave and held in place with a few brads for the winter, makes a huge difference in heat retention overnight. What you end up with is a sheet of glass (original window) a 50mm or so air gap, a sheet of acrylic,a 5mm or so air gap and another sheet of acrylic - effectively triple glazing !
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Re: DIY solar pre-heater

Postby BigB » Wed Jun 30, 2010 3:50 pm

Dear120thingsin20years, dont let the nay sayers put you off. Coreflute comes in various grades , materials and colours. Talk to the boys at Corex in Dandenong they have some magnificent strong, robust, and UV stabalised grades for you to use.

Ask them about their co-extruded 5mm thick 1500 GSM coreflute that comes in black which would be magnificent for solar collection. You could make top and bottom end tanks out of PVC tubes and mill a slot in it slightly smaller than 5mm, wedge in your coreflute and plastic weld it with a filler rod of similar plastic. Try some off cuts of the PVC pipe cut into strips and melted onto the join with a soldering iron.

Have a go and let us know the results. Jeff Court is your man at Corex. Jeff Court [Jeff@corex.net.au]

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Re: DIY solar pre-heater

Postby Z6CHAS » Thu Jul 01, 2010 4:09 pm

This sounds like a good idea.
A few tips.
1. Nothing glues poly tubing and it is too flexible. You can only join it with barb fittings or highly skilled
heat application.
So for the top and bottom tubes use strong, rigid PVC or metal (copper or stainless steel).

2. Use "ViSe" Supergrip Polyurethane Glue or any Polyurethane glue available from Bunnings to glue and
seal the joints.

3. Paint the coreflute surface with flat black paint (chalk board) to protect it from UV and increase light
absorption.
I repainted a corroded, leaky solar hot water panel about 10 years ago and it is still going OK.
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