Solar water heating

[Stanley]

Thanks to all of you who have taken the trouble to send your thoughts.

On the question of a pump, I really think gravity would struggle to pull water through the matrix of 10mm pipework in the Solar Panel so I would use a pump. I think the normal central heating pump would be a bit beefy and cost a bit of power to run. (Must take a look at the rating of such a pump.) I also had not thought of the rate of flow of the coolant to maximise tha temperature when it reaches the tank. More controls to think about.

I quite liked the idea of a solar panel (electric) to power the pump. Would it be powerful enough? Depends on pump.

Personally I would use UPVC or similar for the box on the wall rather than wood as it would not rot.

I have still to sort out the sensor question though.

Thanks again.

[Set Square]

Er, but as someone has already pointed out, when the sun is low in the sky, its rays have to travel through a lot more atmosphere - with the result that a lot more energy is absorbed before it reaches you. The intensity felt by the panels is much less - even if they are at right angles to the rays!

[N. Thornton]

Purely for interest, its also possible to use a 2 stage system: decent solar panels direct on the HW tank, and a simple polythene covered blacked domestic radiator to prewarm the incoming cold supply to the tank. With a rad you need a few valves, and must remember to bypass and drain the rad when its going to freeze. So its a summer preheater.

Whether this is worth doing I dont know.

Or if you want £45 solar, theres the old coiled hose collector, pump and thermostat.

For the more serious options:

Crossflow heat exchangers on your shower drain/ shower cold feed typically payback in about a year.

Also solar space heating is a better payer than solar DHW, as theres no plumbing cost, and the total heat captured is greater.

Regards, NT

[Mike]

Mine is equally recycled. Plan is to fit a new (condensing) boiler next year, this will require replacement of the cylinder (building regs). It will also preobably mean replacing some radiators. Plan is to reuse these for the solar heating.

What do building regs say about solar heating?

[G&M]

Totally exempt - apart from making sure it doesn't fall on somebody. In fact if you are solar heated you can also ignore a lot of part L insulation as well.

[G&M]

I considered making one of these myself but how do you get round the building regs requirement that the outflow is not restricted ? You won't get much heat transfer from a 32 or 40 mm pipe and need to go down to 10mm or so I would think.

[Pete C]

Hi,

If you can make a kit or know someone who can, there is one available here:

[N. Thornton]

Do you know of a link that goes into a bit more detail about this?

Regards, NT

[N. Thornton]

use 32mm copper, 2 to 3 feet long, and wind microbore round it for the cold feed. Slobber in place to improve heat transfer. Ideally wind 4 microbores round it in parallel and put them into a 22 or 28mm manifold.

When they come out in the sheds I'd expect them to use a jacket with

1/2" connectors, but that would not be nearly as easy to make at home.

NT

[IMM]

When they come out in the sheds? Are they mainstream in Home Depot in the USA yet?

[Tony Bryer]

Where do you get this from? If you have solar panel assisted water heating this is taken into account when calculating the SAP Rating and Carbon Index and if the Carbon Index of a new dwelling is 8.0 or more this establishes compliance. But you'd be unlikely to be getting this sort of number unless you were building something insulated to a reasonably good standard, and even if you go down this route there are maximum U-values of 0.35 and 0.7 for roofs and walls respectively.

SAP-2005, draft currently out for consultation, does make additional allowances for solar panels and photo-voltaics but won't come into force until Jan 2006.

[Tony Bryer]

The area through which heat could be conducted would be fairly small. The way I'd do it would be to make something like the condensers we had in school chemistry but out of copper tube - a 32 or 42mm pipe running through a length of 50mm with branch and one end reduced tees either end with the end stop on the reduced end filed out

HH HH HH HH HHHHHHHHHHHHHHHHHHHHHHHH WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW HHHHHHHHHHHHHHHHHHHHHHHH

[G&M]

From the EU directive on energy efficiency. Overrides UK law. Note that I said a lot of part L insulation, not all of it, and meant to say fully solar (or other green non carbon generating source). Key thing is one can go single glazed.

But the basic outside structure still has to meet the required U values.

I presume this incorporates the above directive.

[N. Thornton]

its what was tested and it worked.

sure, but a lot more fab work, especially with differential expansion to take into account..

NT

[Pete C]

Hi,

Why not build it in parallel with the wastepipe via a kind of trap. Arrange it so the grey water will go through the heat exchanger but in the event it gets blocked will divert though the waste pipe instead.

cheers, Pete.

[G&M]

Thanks. That meets letter of the regs. My traffic warden, oops I mean BCO, doesn't seem to realise the approved documents are just one solution to a problem.

[Rick Hughes]

I did a number of posts on this about 7 years ago ... try a search on archives.##It is simple to make a controller all you need is a simple opamp set up in differential mode and use a pair of IN4148 diodes as the sensors .... when one pipe is warmer than other ... use it to trigger a relay to operate a pump ... simple and reliable, and you can set the differential level yourself ... 10 degree would be a good starting point.

A colleague at he time made up a number of these circuits and was selling them in a self contained plastic box in Exchange & Mart. His name was Robin Paine and I lost touch when he moved to Mansfield ...... you could try some goggle searches, bound to be loads of differential circuits on-line.

Rick

[Rick Hughes]

No the difference is what you want .... irrespective of temp of DHW tank .... if panel is warmer you want the heat, if you use a single stat, you are limited to only getting solar heated water when it is above the stat temp .... when what you want is solar heating any time it is warmer than DHW tank.

A differential controller can be made for less than a fiver.

Rick

[Rick Hughes]

Yep ... Grundfoss .... use a standard CH pump.

Rick

[N. Thornton]

it does. it also makes no sense. The full flow full width 3 foot unit harvested well.... doubt I've got the link anywhere, but lets look.... no.

NT