Help needed for solar water heating panels project

[stevesteve]

I have been sitting looking at the gas bills (with a proposed 14% rise prices next year) and thinking that I really should set up some panels to add to our system.

I had found a local scrap metal merchant and decided that I would look for some copper sheet. I could cut down some old hot water tanks or ideally I wanted to get hold of some roofing copper.

The metal yard was a real treat. Lots of old motors (rewinder heaven but I haven't the space for a big tower) and when I asked about copper he said "you could look around... unless you'd be interested in that" pointing at a half used roll of roofing copper!





The copper sheet is 7.4m(24')long  x 0.6m(2') wide x 1mm(1/25").

I am at a latitude of 52 degrees north in the UK and did a couple of tests yesterday. Bare copper left in the sun reached a temperature about 51C (124F). Assisted by my daughter we set up a simulated panel using some children's paint to blacken the surface. An old blanket to insulate the back and a piece of double-wall polycarbonate sheet to cover the front. The thermocouple went on the back this time so that it was not directly exposed to the sun.





This configuration reached a temperature of 85C (185F) at 3:30 in the afternoon.

QUESTIONS:

The main questions concern the copper tube... what diameter to use? The sizes I have available are:

8. mm (1/3")
   
10. mm (2/5")
    
15. mm (3/5")
    
    

I will solder these to the sheet... probably the front surface so that the tube contact area conducts heat from the plate and the other side of the tube is facing the sun.

I also need to decide the spacing between the tubes.

I also need to decide whether the water should run in through one inlet and then up and down the panel multiple times then out of one outlet, like this?





Or should it run in parallel through multiple tubes like this?





Does anyone have experience of constructing panels like this or does anyone have commercially built panels that I could copy a configuration from?

[whirlybird]

Greetings Stevesteve

Its not often that i feel enclined to respond to posts but it seems to me that you are on the right track with your solar project.

I have built several (in fact many) solar water heaters in the past years,all of which worked to one degree or another (pardon the pun).

Without preaching there are a few things that you must do to get good results.

1. the water must flow in the base of the heater through a manifold, that balances the flow and then out the top the same way.do not use the up and down method even if you install a circulating pump.
   
2. It is a good rule to use the largest thinest pipe you can afford
   
3. The right paint on the surfce is of prime importance we have a chemical that will oxidise the copper and when its been in the u/v for a while it wont turn grey it just gets blacker
   
4. Pollycarbonate is not good for heat retention.
   
5. Try to make double glass sheets with some silcon sealer etc,
   
6. A wooden frame or box works better unless you are carefull with insulation.
   
7. Wet insulation = no insulation you need to pay attention to drainage there will be lots of condensation in your climate.
   
   

Well thats my rant, I hope it helps and by the way good luck.

Also the pipes on the front is a good way to do it and also a little heat sink paste under them will help

I put my pipes through a small roller and flatten them(use soft copper pipe)make a small mandrell to re shape the ends .

All the best

Whirlybird.

)

[PaulJ]

   My commercial system has 2 panels each approx 1m by 1.8m, mounted at about 30* to horizontal - I'm at latitude 37.

   Each panel has 13 risers of 1/2 inch copper pipe in parallel, connected top and bottom to 3/4 inch pipe. The panels are connected parallel as well.

   The panels are filled with an antifreeze solution, this travels to a heat exchanger which I assume to be a pipe-in-pipe type. It's the same length as the panels and is mounted next to them.

   The tank is mounted horizontally above the panels/heat exchanger. The system works entirely by thermosyphoning, i.e. no pumps or additional control mechanisms required apart from a pressure relief valve of course.

   Don't underestimate the importance of the pressure relief valve, even if you're making a low pressure system. A good solar hot water system could reach boiling point and above on a hot day; the resulting steam explosion would probably destroy your house (and everybody in it). If you have any doubts at all about this ask a licensed plumber or whatever your local equivalent is. At the very least a failure to comply with local regulations will probably void your insurance if something goes wrong.

   A tempering valve to limit the maximum temperature of the hot water coming out of your taps is a good idea too, particularly for the bath/shower if you have young children.

   We're in a pretty sunny part of the world, our system supplies all our hot water for 8 months of the year and most of it the rest of the time.

   Paul.

[Sri Oracle]

me and my girlfriend just finish a solar/wood heat thermosphion system.  Here is the website where we got some great diagrams.  

http://www.green-trust.org//2003/fireandwater.htm

For the solar array we used 14 - 1/2 inch copper pipes with an old glass door panel and 2x4 box.  Make sure to use copper tee's and not elbows for the array.

i think the website will help alot!

good luck

sri  

[GaryGary]

Hi,

There is a lot of information on build-it-yourself solar collectors at my site here:

http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm

and here: http://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm

As was mentioned above, don't ignore the other essential components in a water based solar collector system -- expansion tank, pressure relief valve, the right kind of circulation pump, air purge valve.  If you use antifreeze, make sure its the non-toxic vareity.  Reading the "Basics" articles listed at the links above would be a good investment of time.  The water heating basics articles listed from HomePower are very good, and mostly free downloads.

I think that polycarbonate is a good glazing material -- its good up to about 270F and as long as it has the UV treatment on the outside it will last a long time.  Don't use Acrylic or PVC glazings -- they won't withstand the high temperatures.  I've built a couple of collectors with single wall polycarbonate, and they performed well.

Good Luck!

[windyknight]

Hi Steve

Just arrived at stage you were when you posted this back in Sept. and was wondering how things worked out?

keith