Anotherpower.com Forum
Renewable Energy Questions/Discussion => Solar (heating or electric) => Topic started by: David HK on December 30, 2012, 05:03:44 pm
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I am posting two photographs one of which shows my own heater - the pipes are set up in a 'S' or zig zag fashion.
The other shows all pipes fitted into 'T' junctions so that cold water enters one side and exits the other as hot.
Does anyone have views on the pros and cons for each method?
David in HK
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Hi David.
One long serpentine path means the water will spend more time in the heater and thus get hotter for a given collector temperature.
It also means you get the greatest pressure drop, so high flow rates are a greater problem.
Conversely, the parallelled pipes will pass far more water with less pressure drop. In a perfect world, water would flow down each tube equally, thus a slower flow down each pipe and should heat up much the same - but without any way to control the flow rates, the reality is that it won't be even.
My personal view is that the single, serpentine path is likely to perform more consistently (but watch your construction and mounting orientation - it will be a pig to get the air out of unless you have cold flow in the bottom and hot out the top, and even then even small errors will see air trapped)
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Ross,
Thanks for the speedy reply. My own unit is the serpentine type which lies at an angle on the car port roof. Getting air out has never been a problem since the outlet is on the higher side.
Point taken about the other comments. May father lives in Spain and has a system which needs an overhaul so I am planning for a replacement of the existing pipework and replacement with new.
David in HK
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With the T-Style a graduated orifice metering system across all the parallel flow points is required with those nine tubes graduated up to open flow on the last tube. There are (were) open source plans on the internet using common materials to accomplish it. I'd probably think the serpentine split into two parallel runs would give the best flow with less compromise on heat gains.
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Just an observation wouldn't you want the water to fill from bottom up in a parallel design Ross?
This keeps the pipes full at all times
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Just an observation wouldn't you want the water to fill from bottom up in a parallel design Ross?
This keeps the pipes full at all times
Yes, but the original post said The other shows all pipes fitted into 'T' junctions so that cold water enters one side and exits the other as hot. and I was taking that at face value - vis, that the flow was "side to side".
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Ahh ok makes sense then Ross
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The note from DANG was most interesting. I was unaware that different size orifices allowed controlled water flow in paralleled pipes.
I wonder how many other people are equally unaware, and how many have built a solar hot water heater in blissful ignorance of flow orifices?
I shall stick with the serpentine, zig zag, or S method, because it's so simple and straightforward.
I have done a Google search for design features of paralleled solar hot water pipe designs and cannot locate anything mentioning flow orifices. If anyone does a similar search with success please post a link because it would be useful knowledge for all readers.
David in HK
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I'll never learn to use a less exact voice in these postings without links and citation!
The last layout design I studied up on had restriction discs, I'm betting someone took the time to calculate the flow rates through copper pipe circuits on that one. Can I find it again? Lost like spider poop dropped from the web.
You can bet having offset intake/outlet pipes would ease much of the imbalance but itd be like the long battery string where some units feel more 'draw' than others, I'd guess good enough for myself but for the highest degree rise per time unit the balanced collector would pay off - intermittent sun from rain or long pipe runs to the collector etc...
Apologies for not having references available, they may turn up yet :)
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I have spent and hour and more searching Google for everything I can find on solar hot water designs, pipe joints, reducers, orifices, and so on.
I have been through plumbers PDF's, pipe manufacturers sites, refrigeration, gas pressure, oil pressure and anything else I can think off and I cannot find any commonly available T type water pipe connector with different size orifices to control water flow. I can only conclude that one has to make it yourself to suit the application. If they were common items I can see that some worker would have a bad day and end up with a complete mix up of orifice joints at each side of a parallel tube set up.
Any comments?
David in HK
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ide go with a black base--the silver reflects the light[heat] away? [black absorbs heat]
never built one--just my thoughts................
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David---available, here anyway, are orifices designed to go in standard hose connections, for things like soaker hoses.
could be slid into the T before soldering. Not easily replaceable, if mayhem happens.
Some copper T's allow the copper to slide all the way through. Suspect cheaper ones. Using these, the orifices could be drilled
in the supply tube, T's slipped over, and soldered in place. But, again, not easily replaced.
Just a couple of things I've used in other applications.
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Thanks bj,
My existing solar hot water heater has performed flawlessly for seven years so I will stick with a proven design. Its simple and easy to construct - no hassle to maintain.
Do you have any photographs of the things you mentioned. I am only interested to the point of curiosity.
David in HK
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I would say that the serpentine style is more likely to get the water up to usable tank temperature than the parallel type of connection.
My swimming pool uses the parallel connection but its not looking for a very large temperature gain - it has 62 PVC injection molded manifolds top and bottom with 14 'spigots' that feed ribbons of neoprene pipe each tube being about the diameter of a pencil and 5m long. It takes a 1HP pump to push the water through at a decent rate. I reckon that the 50 sq m provides about 45KW of heat on a sunny day but the 1.6Km of pipe would only work in a parallel mode!!
Having said that, I've had the 65,000l of pool water up to 40C when I overrode the controller ;)
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Nice ;)
I'd love to see any results from tests or whatever comes of this... Heat is currently in my sights for the van and I'm thinking once its well insulated, a 5 gallon tank might be a useful addition along with a small collector up top.
Only question I have about what is above so far is... If the water is already hot, why do you need to heat it? :P
Steve
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Mad, I'm not sure 5 gallons is going to help you much, it's not a lot of energy storage at any reasonable temperature.
Do the math, ( equation found here)
http://www.engineeringtoolbox.com/energy-storage-water-d_1463.html (http://www.engineeringtoolbox.com/energy-storage-water-d_1463.html)
E = cp dt m (1)
where
E = energy (kJ, Btu)
cp = specific heat capacity (kJ/kgoC, Btu/lb oF) (4.2 kJ/kgoC, 1 Btu/lbmoF for water)
dt = temperature difference between water stored and the surroundings (oC, oF))
m = mass of water (kg, lbm)
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That I realize... That equation may or may not prove useful in my case, but I wouldn't even bother until I have the mega insulation done. I'll be picking up the pink foam tonight, along with some foam in a can, and see how that does.
Steve