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gregkn73

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Reply with quote  #1 
Hi, Since I am very satisfied with the heat gain of my sunspace, and because I have one radiator in my living room that I am keeping it always closed, I am thinking to make a new collector to heat water and distribute it to the unused radiator and if aretha is too "productive", i may later replace radiator with a fan coil. I have almost decided to make a Aretha type collector to heat water, due to the simplicity, relatively good efficiency and also because I have a spare car radiator. The winters are not very severe in my place , so I am thinking to make a close loop solar thermal system. I had many questions for the Aretha that Willie answer most of them, but I have one for the closed loop that I can find an answer. The most expensive part of the close loop system I can source locally, is the circulator. I found in eBay cheap circulators , like this one https://www.ebay.com/itm/12V-Solar-Hot-Water-Pump-Circulation-High-Quality-Food-Grade-212-F-w-Coupler/381005463497?hash=item58b5b1ffc9:g:vnAAAOSwq7JUIoLW Since it will be a close loop system, the circulator don't need to be big , but I don't know how reliable are similar to the above circulators! Did anybody use one ,like the above ?

stmbtwle

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Reply with quote  #2 
That pump should do well, it's about the same as I use and about the same price. If it works for you order a spare. You CAN burn them out.

What are you planning to power it with, an ac/dc supply or solar?

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
gregkn73

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Reply with quote  #3 
Hi all,

I haven't done anything yet, because the pump from china was lost , and received the new one 2 weeks ago. So since I have free days at the end of the week, I went earlier to find parts to connect , radiator with pump and to the rest pex tubes. But the pex tubes are 1/2 in, as the input out putof the pump, but the input out put of radiator are 1 1/8in! So I couldn't find any parts to connect them :-( Willie do you have any close photos of your project , to understand, how you proceed. Also should a 10A 12v power supply , be enough for the car radiator fan?

Thanks in advance for any help.
stmbtwle

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Reply with quote  #4 
Sorry Greg not much in the way of pics. 

1-1/8" is about the outside diameter of 1" CPVC pipe, so I'd bush the 1/2" fittings up to 1" and make the final connection with a short piece of radiator hose. You can also try nylon-reinforced clear vinyl hose from Home Depot, it will take the heat.

Yes a 10A power supply should be plenty.  Just about all radiator fan motors seem to be rated at "80 watts" which is about 7 amps on 12v, though my experience is that depending on the size of the fan blade itself, the fan motor may draw a lot less.  My little 7" fan only draws about 3 amps at full speed.

You can get a manually adjustable speed control on ebay that works well, or you can modify it to make it automatic. See my thread "cheap and easy speed control".  The basic model needs a snap switch or solar panel to turn it on, the Arduino model is full-auto. They do NOT use the same temp sensor.  I'm in the process of putting up diagrams in the next few days, or I can send them to you.  Good luck


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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
gregkn73

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Reply with quote  #5 
2 days ago I finally finished the project. A closed loop system wasn't as simple as I thought when I started. I needed ,except a closed expansion box, a auto water fill of the system, keeping the pressure in the close loop ,around 1 bar. That causes a minor lick from the tap of car radiator, which I haven't solved yet :-( any ideas will help me a lot.
The collector is 2*2.35*0.15, is placed in the south side of my hoop greenhouse , tilted at 75-80° , so I sacrificed minimal space in the greenhouse. I insulated externally only the back side, and since it is in a greenhouse I cover the front side with clear plastic, remaining of the greenhouse, instead of polycarbonate. I use a car radiator from a Nissan sunny 1.4, and used moscuito net, as a screen. I circulate water with the small circulator mentioned in previous post, and send water to one unused radiator , double pane with double fins 1.4*0.6*0.1, total water volume of 7 lt. The total volume of the close loop system is only 10.5 lt.

Unfortunately I expect better performance. Both days , which wasn't tottaly clear, achieved Max T 44,5°C, exactly as my sunspace. I thought with that dimensions of collector and only 10.5lt total water volume and just one radiator to export heat, to achieve at least +10-15°C ,compared to sunspace. The sunspace ,this time if year, in a tottaly clear day achieve Max 54-55 °C, while in December and January 44-46°C. Radiator with 55°C water T, produce enough heat, but with 45°C minimal. I am thinking, if I add 8 PC fans 10mm ,at the bottom of the radiator , if I can gain any more hear, a kind of fan coil.

Any thoughts of increasing my collector efficiency, radiator efficiency with current T, and solution for car radiator tap lick, due to system pressure, will be greatly appreciated. Following photos



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stmbtwle

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Reply with quote  #6 
For the radiator cap, cut a piece of rubber gasket material to fit under the cap, then put the cap back in place on top of it.   That should stop the leak.

If I understand it your Aretha is inside the greenhouse, and covered with only a single sheet of film.  What is the temperature inside the Aretha and what is the temperature in the greenhouse?  I suspect you're losing a lot of heat through the plastic into the greenhouse. There's also the loss due to the greenhouse film.  The air temperature in the Aretha needs to be substantially hotter than the water coming in, or you won't get much in the way of heat transfer through the radiator. You could try is a second layer of plastic film, about 2cm above the first, this would give an insulating layer of air.

If you have a way to measure it, what is the air temperature in the Aretha before, and after it goes through the car radiator, and what is the water temperature before, and after?  There should be a substantial drop in air temperature, and a rise of only a few degrees in water temperature.  

It's possible that the house radiator is already using all the heat the Aretha can produce, and is returning cold water to the Aretha.  You will only get a few degrees rise in a single pass through the Aretha. You can get a higher water temperature by reducing water flow, but unfortunately this won't do much for actual heat transfer.

Do you have room for good air flow in and out of the Aretha radiator?  

I do not understand why you need to keep the system under pressure. Without a way for air to escape the system one or another of your radiators may become airbound.

The pc fans on the house radiator may help, depending on temperature.

__________________
Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
gregkn73

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Posts: 49
Reply with quote  #7 
Thank you Willie for your suggestions.

The Aretha is inside the greenhouse. On Saturday which has milky clouds , the higher T in Aretha was 44 °C and in the greenhouse 32. Since there is not big difference , I cover Aretha just with a clear plastic. If I had it outside, I would choose polycarbonate, as on sunspace. Do you thing that this is the reasons I can not achieve higher T? With just 10,5 lt volume water of the close system ,4,7m2 of collector surface, and just one medium radiator to export heat, I would expect 10-15 higher T than the sunspace, which has 10,5m2 collector surface and a 1200m3/h fan, exporting heat. According too your experience with Aretha , what should be the difference in higher T between the two collectors?

Unfortunately, because it is a close system under pressure, I can not measure waters T. Also I haven't a second sensor to measure T before and after car radiator. But when the T was 44 inside Aretha, I measure air T at top of home radiator, it was 44! So I think Aretha , transfer effectively heat to the water. The problem is I can not achieve higher T inside aretha, at least as I expected. On the other hand I might had very high expectations :-)
I am not sure if mosquito net , is adequate as screen to increase enough the T inside Aretha and if black soil cover cloth will be better as a screen ? also because car radiator is very close 1 cm from the plastic, and the fan is strong enough, if adhering a small second piece of plastic, directly in front of car radiator, can increase efficiency?

The reason I understand close loop systems need some pressure to work ,is to eliminate air inside the systems. We open a small manual valve at eachhome radiator at the beginning of each season , to extract any air.
stmbtwle

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Reply with quote  #8 
Greenhouse 32C, Aretha 44C, radiator 44C.  Your Aretha IS working.  "milky" clouds WILL greatly reduce your performance.  I would reserve judgement till you get a clear day.

The house radiator heats the room by cooling the water (just as in your car) and the water then cools the Aretha.  Too much cooling and it will never reach desired temperature (just as your car), too little and it will overheat.  You could try closing a valve partway to restrict flow. This won't make much difference in the heat output but it will raise the temperature.
I do not think you will ever get the output you're used to with a furnace.

I think your mosquito screen is the same as what we all use, and everyone is pretty happy with it.  Your photos look quite "black" which is what you want. I can't comment on your collector as I really can't see it. Some of the air-collector guys might be able to help.

Having more space between the radiator and the plastic will help "breathing" and you need to try to keep the air flow off the plastic, that is lost heat.  However in a collector as thin as yours that will be difficult.  You might try something like this:  https://simplysolar.supporttopics.com/post/show_single_post?pid=1294959228&postcount=41&forum=282856

Another method would be to move the radiator out of the collector entirely: 
https://www.facebook.com/307885346030194/photos/a.308184936000235.1073741828.307885346030194/592557564229636/?type=3&theater   (this is the inventor in Italy)

This allows for a better air flow in a thinner collector.  I always put a piece of metal as a deflector between the radiator and the plastic to deflect the air.


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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
gregkn73

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Posts: 49
Reply with quote  #9 
I will try to find a thin piece of metal, to use as a deflector in front of radiator, or can i use an aluminium foil sticked in front of the plastic?

Also the screen, if it is not totally streched, can it affect the efficiency?

And since I use the original fan of car radiator, it draws significant energy, while I red you use PC fans.if I reduce the rotation of the fan, by reducing volts supplied, will I reduce radiator efficiency?
stmbtwle

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Reply with quote  #10 
I always like a bit of a gap between the plastic and the metal deflector. In the ZP model, the deflector is inside the outer screen as well. In your case you simply don't have the room. I'm not too sure what to do. You could try the foil. Paint the outside of it black before you stick it on.

What you MIGHT try is to remove the plastic and build up the sides of the collector with wood, maybe 3-4 cm, depending what is standard lumber size in your area. I think it will give you room to work and better air flow.

In my experience the more air flow you get through the radiator the better, so reducing the fan size may not be a good idea. In mine the two pc fans are not quite enough and it runs hotter than I like. I would keep the radiator fan you have. What you can do is install a 12v speed control like this one. You don't even have to open the collector. Then you can play with it till you get the best speed.

https://www.ebay.com/itm/12V-40V-10A-PWM-DC-Motor-Speed-Controller-with-Knob-LW/182304262165?epid=1175122397&hash=item2a722e4815:g:94sAAOSwPCVX9dHY

The air-collector guys seem to like a tight screen, but how tight I don't know. I doubt floppy-loose is good.


__________________
Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
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