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paolometeo

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Posts: 13
Reply with quote  #1 
Hi everyone!
My name is Paolo. I built, with my friend Franco, a thermal solar collector with car radiator and simple materials in order to explore a DIY way for producing hot water from the sun. The collector works in Milan Italy since one year. Now we are making a new one with more recycling material, as sheep wool and used pallets. The name is "ARETHA Project":
The project intends to provide instruction to build a 5 sqm collector and to share experiences about it.
It is not for business, but for helping people to make solar thermal panel by themselves with low technical skill and poor materials.
We have also launched a funding campaign to build one ARETHA collector with recycled material in Sicily, see:
https://www.indiegogo.com/projects/aretha-project#home
I would like to discuss with you our project
thanks
Paolo

solardan1959

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Reply with quote  #2 
paolometeo,
   I like the idea of the radiator but I am not sure the fans would help much.  It would be interesting to see how much more heat is produced with the fans than with them turned off.  Another option would be to run them at a very slow speed and also in reverse so it draws the hotter air away from the glazing and across the radiator first before the cooling effects of the fan.

  Any drawings of what you visualize with the lambs wool and pallets?

Dan
paolometeo

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Reply with quote  #3 
Hi Dan,
The fan is placed behind the radiator to provide the right heat exchange between air and water, just how it happens in a car, but in a reverse way. The fan is switched on only when the temperature difference between air and water rises over a fixed threshold. A simply control system made with Arduino does it. The fan position inside the ARETHA box, should provide an air circulation in all the box volume. The glaze is made by a thick polycarbonate sheet that contributes to the thermal insulation. Here you can find some sketch and photos. In the photo you can see one of the pallets filled by the sheep wool and covered by 4 mm plywood.
Paolometeo
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solardan1959

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Reply with quote  #4 
Paolometeo,
   So you actually meant "sheep's wool", I thought it was just another name for rock wool or some other type of insulation.  Sheep are not very common over here in the U.S.
Quote:
The fan is placed behind the radiator to provide the right heat exchange between air and water, just how it happens in a car, but in a reverse way.


But that process is to remove the heat from the radiator generated by the engine.  I still feel the circulation will remove the hot water cooling the radiator and blowing air on it is detrimental.  You may feel you are taking the hot air from the collector and blowing that over the radiator increasing the heat in it but I doubt it really does increase the heat.  The heat would already be in the top of your collector and the sun would also be directly heating the radiator.  The fan would be taking the heat away from it.  It would be a simple test to determine if it helps or not.  More radiators in the open space at the bottom would also make better use of the collector but your real collector may have one down there also.

Dan
Garage_Hermit

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Reply with quote  #5 
interesting approach,

however, where is the air intake and exhaust ?  i.e. how does the air circulate ?

G_H

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SolarInterested

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Reply with quote  #6 
The fan would also be circulating hot air against the glazing promoting heat loss. Your double wall 'hollow sheet' polycarbonate would be better than single wall in this respect but heat loss through the glazing will still occur. This is something that we try to avoid in hot air collectors with baffles to keep flow away from the glazing.
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cwwilson721

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Posts: 303
Reply with quote  #7 
As I see it, think of the box they have designed as a "solar oven", no in/out for the air, and using the fan to circulate the 'stagnant' air thru the radiator (as a air-to-water heat exchanger), and continuing the analogy, the radiator is the 'food' being cooked.

It will work. However, greater efficiency would be realized if:
  • The air had a intake and exhaust port. This would allow fresh, cooler air to enter and get heated, then exhausted. The exhaust hot air could even be utilized for more 'air' heat, or for drying of foods for preservation, or other uses. As it is currently setup, it's 'stagnant', or just getting super hot in the box, wasting alot of heat that could be used for other purposes. The higher the heat inside the box, the more that gets wasted thru glazing/etc. You also risk the possibility of melting the glazing from too much heat.
  • If you have intake on the 'bottom', and exhaust at the 'top', the fan would work better if the radiator was 'tilted', using the full 'depth' of the box. Would be best if tilted 'upwards', thus letting the radiator also absorb more sunlight, plus all the air in the box would flow thru the radiator. In this configuration, the fan would be best used as a "pusher" fan, blowing from the back of the radiator, to the front, then out the exhaust port. You would get *some* heat loss thru the glazing like this, but a lot less than if the box were left 'stagnant'. *Best* use of the current fan, however, would be to detach it from the radiator completely, and use it in the exhaust port. This would even out airflow, and lessen (to a degree) the heat losses of air/glazing contact. If you're NOT utilizing the 'waste' hot air, however, the fan could be kept as a pusher, because the loss of heat thru the glazing after it goes through the radiator wouldn't matter.
The main advantage to the current parts/design is that's it's cheap, made of locally available 'waste' materials, and fairly easy to build.

With the minor changes I've said above, which would require no additional parts/expense to implement, it could provide hot water, hot air, and be more efficient. HOWEVER, the intake and exhaust would have to be sized correctly and the fan speed adjusted to allow the air to get hot enough for the heat to be exchanged to the water in the radiator, before flowing through the radiator, then being exhausted out the exhaust port.

But, with all that being said, the current setup will work.
paolometeo

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Posts: 13
Reply with quote  #8 
Quote:
Originally Posted by solardan1959
Paolometeo,
   So you actually meant "sheep's wool", I thought it was just another name for rock wool or some other type of insulation.  Sheep are not very common over here in the U.S.
Quote:
The fan is placed behind the radiator to provide the right heat exchange between air and water, just how it happens in a car, but in a reverse way.


But that process is to remove the heat from the radiator generated by the engine.  I still feel the circulation will remove the hot water cooling the radiator and blowing air on it is detrimental.  You may feel you are taking the hot air from the collector and blowing that over the radiator increasing the heat in it but I doubt it really does increase the heat.  The heat would already be in the top of your collector and the sun would also be directly heating the radiator.  The fan would be taking the heat away from it.  It would be a simple test to determine if it helps or not.  More radiators in the open space at the bottom would also make better use of the collector but your real collector may have one down there also.

Dan

Right, sorry for my english. Sheep are common in Italy and other countries, people use their milk, meat, but not wool.

The radiator in Aretha, works to exchange heat between air and water inside it. The fan provide a forced circulation inside the radiator pipe and inside the box. Of course a good insulation of the box walls is important and the polycarbonate, 16 mm thick, provides this. A small pump provides the water circulation between the tank and the radiator.Position of the radiator inside the box is an important issue, I think, so it would be interesting to test other positions. For example we could put the radiator in a tube, rectangular section, where air passes in. The concept remain the same. The radiator is a very efficient exchange device, small and powerfull.
Garage_Hermit

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Reply with quote  #9 
Paolo,

That fan and that radiator happen to work OK on a vehicle, because they were designed for that - working in an open circuit.  The circuit works as follows: cold outside air (static air) is converted to dynamic air ("ram air") by the fact of the vehicle moving through said air).  This movement causes a flow of cold air over the hot radiator, thereby cooling the radiator contents, which are permanenently circulating through the radiator and around the engine block, in the coolant system (which is a closed circuit, driven by a water pump).

So two instances of heat exchange take place: air-to-water (at the radiator) and water to metal (at the engine).  The engine block is cooled according to a regime determined by the thermostat.

When the HOT car is standing at lights, or in traffic, there is little or no ram air available, so to prevent the engine overheating, the (electric) fan takes over, controlled by a thermostat (heat switch).  The fan creates a dynamic air flow, using static air and an electric motor.  The dynamic air cools the radiatorr once again, until the thremostat decides otherwise, and another thermostat turns the fan off, or down.

However, your system looks suspiciously like a SEALED circuit - there is no outside air flow.  Yet a fan is designed to create air flow...  So it needs AIR...

There *will* be a tiny internal (turbulent) flow from the fan, but it will have no effect - it cannot carry heat, because it cannot evacuate heat - no flow... No heat exchange. The fan will suffer from system effect.

No flow = no heat transfer = no efficiency.

Sorry but IMO, the fan is actually contributing nothing to the system.

G_H

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(1)  "Heat goes from hot to cold, there is no directional bias"
(2) It's wrote, "voilĂ " unless talking musical instruments...
stmbtwle

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Reply with quote  #10 
I think it would work. The way I see it the heated air flows up in the front of the collector, transfers heat to the radiator, then flows down the back of the collector to the bottom where the process is repeated.

A large one might be easier/less expensive to build than a water-tube collector, if the radiator and fan can be had cheaply.

I think the fan would improve air flow and heat transfer through the radiator, but I have some concerns about it's life in that hot environment. Might be better if the fan we're located at the bottom, in the cooler part of the collector.

A black divider (corrugated roofing?) separating the front and back of the collector would control airflow and prevent mixing. Possibly a screen absorber could be added in the front part.

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