norm
New Member
"Work is the curse of the drinking classes" - Oscar Wilde
Posts: 18
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Post by norm on May 26, 2011 14:50:24 GMT -5
I'm in the (slow) process of putting together a solar arrangement for domestic water heating. I'm about to start the panel construction. The general scheme is described at: www.solarco-op.proboards.com/index.cgi?board=solarthermal&action=display&thread=44A couple of questions for those here who are experienced in these matters. 1. The double glaze unit which I intend to use (at least initially) is probably the heaviest component. (I will use it simply because I have it.) Is window glass any more heat transparent than, for example, perspex? 2a. Will need recommendation about some form of "filler" (GripFill?) between the copper pipe and the aluminium plate. Material which is reasonably stable at the temperatures likely to be encountered and which is a reasonably good conductor of heat. 2b. This may also be the preferred method of securing the panel thermistor to the panel. Some thought will be needed concerning the exact location of this thermistor on the panel. 3. I propose to paint the entire collector surface matt black. Any specific brand of paint recommended? Or not recommended? 4. For the first season I do not propose to use the system during winter. It will be drained. So no need for antifreeze this time. What about some detergent (washing up liquid) to lower the viscosity of the water in the loop and therefore increase pump efficiency. I'm sure I could find the answers myself by searching the forum here. Thanks - Norm (lazy sod)
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Post by cye on May 28, 2011 10:01:06 GMT -5
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norm
New Member
"Work is the curse of the drinking classes" - Oscar Wilde
Posts: 18
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Post by norm on May 28, 2011 15:33:43 GMT -5
Thanks for that, Cye, and for the email.
I had forgotten about galvanic corrosion between Al and Cu.
Plan B. I will attempt to surface etch the Al sheet with sodium hydroxide (caustic soda) solution. It reacts with aluminium and it happens that I have some here - used for clearing kitchen sink waste pipes.
Then apply a coat of matt black stove paint. Next drill holes to take plastic cable ties to secure the copper tube to the plate.
Then re-paint the areas around the holes and the "underside" of the copper pipe. Finally secure the pipe to the plate with the cable ties. Should be able to check for electrical conduction between the Al and the Cu as work proceeds.
Fill regions between pipe and panel with a roof sealing compound and apply more matt black paint.
I'll leave it to the testing stage to experiment with positioning the panel thermistor.
How does that sound?
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Post by cye on May 28, 2011 17:08:46 GMT -5
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Post by caveman on May 31, 2011 13:59:42 GMT -5
Norm, Thermistors are so cheap it might be worth putting three on the panel and exploring which one works best. As is often the case, performance at noon on a bright summer day is no test. Snatching heat from a brief show of sunlight, out of season, is where the devil lurks. Much will depend on how quickly the panel heats and what the losses are. Both of these factors are covariant with the temperature differences between the in/out flow and panel/air. What this boils down to is run a model on a computer or 'suck it and see'! I am a fan of the latter because I seem to learn best by osmosis and there is always more to it than I think there is. conor Dow Corning make a high temperature silicone adhesive/sealant. I do not remember any details as it was many years ago I used it to seal fire rope into a flue pipe join.
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norm
New Member
"Work is the curse of the drinking classes" - Oscar Wilde
Posts: 18
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Post by norm on Jun 1, 2011 13:54:41 GMT -5
Well done, CavemanConor. You have sussed me out! I would want to experiment with several positions for the thermistor. Happens that I already have a reel of 8-core "telephone" cable so having connections to all thermistors available inside the control unit will be easy. Indeed, an "unused" thermistor could be used to monitor the temperature at the panel.
Cye. Cable ties. Maplin do a variety rated at up to 105 degrees C. They will be around the copper pipe and I hope the temperature there will not get that high. But, that is something which will need to be examined during testing.
I have done one etching of the aluminium panel using sodium hydroxide - caustic soda. It has certainly dulled the surface. I'll post the photos of the method and resulting appearance in the thread detailing the construction. Will not be today!
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Post by caveman on Jun 1, 2011 16:10:04 GMT -5
norm, I have that 8 core cable running to and from all my bodgings. The outer plastic cover does not last very long in sunlight. it gets brittle, cracks and lets water in. Run it through a bit of pipe any where it is exposed to 'the big lamp' and it will do the trick. conor
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Post by cye on Jun 1, 2011 17:46:06 GMT -5
Cye. Cable ties. Maplin do a variety rated at up to 105 degrees C. They will be around the copper pipe and I hope the temperature there will not get that high. But, that is something which will need to be examined during testing. expect flat panel stagnation temps of at least 150c. higher for selective coating on pro panels. strongly recommend you skip the plastic ties. maybe risk ty-rap (conrad electronics)? rgds, cye
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norm
New Member
"Work is the curse of the drinking classes" - Oscar Wilde
Posts: 18
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Post by norm on Jun 2, 2011 1:54:48 GMT -5
Wow! Thanks. Cye. Had not anticipated that sort of temperature. Re-think happening here about securing the copper pipe to the aluminium panel.
Caveman. Thanks - that will be easy to incorporate.
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Post by cye on Jun 4, 2011 4:38:18 GMT -5
Norm, See attached description of a new zealander's homemade flat panel (alum and copper) which has lasted over 30 years. he uses lithium grease to counter galvanic corrosion. I'm thinking though that the grease method may work better with his 'double-sided clip fin' type collector design though, as the grease is effectively enclosed? Attachments:
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Post by caveman on Jun 5, 2011 10:43:28 GMT -5
Cye, Is that the blackgrease inside a CV joint? If so it is available in a cartridge as it is used to lub. the pins in diggers.
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norm
New Member
"Work is the curse of the drinking classes" - Oscar Wilde
Posts: 18
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Post by norm on Jul 3, 2011 16:01:06 GMT -5
The revised story :
Put a strip of PVC tape along track of pipe. Tried to secure the copper pipe to the aluminium sheet with copper wire along with its PVC insulation. I could not adequately round the contours of the holes in the sheet, the PVC got cut and a conduction path resulted.
Sorry to have to say, used nylon cable ties. Filled gaps between the pipe and the sheet with a roof repair compound. Painted all with matt black stove paint. I will be happy to re-do the panel at a later date if (when!) problems show up.
Got to quickly set up the panel and the control gear with a bin of water in the sun today. Some photos are in the main thread.
I will soon need to invest in the appropriate 12V water pump. I am using a car windscreen wash pump and they are intended for only very intermittent use. The one I have becomes very hot after continuous running for about 30 seconds.
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