This is a very interesting variation on the PEX/aluminum collector with some good ideas to consider if you are going to make a large collector.
The collector is 24 ft wide by 8 ft high, and is built as one large single collector.
All the details are provided on Scott's site ....
Scott can also be found on the Yahoo Group Simply Solar -- which he founded -- its a great place to discuss new solar thermal ideas.
Scott also has a very nicely done Youtube video that gives a good overview of this project and his solar air heating collector...
I think that building the collector as one unit like this has a lot of advantages compared to building a bunch of separate collectors:
- It saves on materials and results in a good solid and simple structure.
- It looks good.
- It save some time and labor.
One of the nice things about building the collectors yourself is that you have the freedom to try things like this.
Ground mounting like this is a nice way to go and makes the construction easier.
This same one big collector approach can be used with the collector integrated into a building wall, as we did on the Solar Shed... Scott's approach of making one large, single absorber takes it a step further.
One thing that you give up with the very wide serpentine layout of the PEX tubes is that it would not work very well as a drain back collector. Each one of the horizontal runs in the serpentine would need to have about 4 inches of down slope, and you would end up losing a lot of absorber area due to the drops, but this is not an issue for the closed loop design.
This same kind of one big collector approach could be used with the copper/aluminum style of collector. From a flow point of view, such a collector could be feed at the lower left and lower right corners, with the return from the center top. This could be done as a drain back with each half of the collector pipe grid sloped down a little toward its return corner. With the price of copper having come down some, this would not be much more expensive on a dollars per BTU basis than the PEX collector.
I do have one concern. I think that this may well be pushing the PEX too far from a temperature point of view.
The moderate tilt may result in stagnation temperatures that are too high for the PEX and result in a short life. Since the system is closed loop, it will be under some pressure, and this will make life for the PEX a bit harder yet. I know that Scott is aware that he is on the edge here and as a dyed in the wool experimenter he is willing to take the risk of having to do some rebuilding of the absorber if the stagnation temperatures do result in a short life. If you are less adventurous than Scott, you may want to consider either going to the copper/aluminum design or going to a vertical collector. Anyway, it will be good to hear how the PEX does over the first couple seasons.
I think that Scott's design would also work very well as a vertical collector. For space heating applications, when you consider ground reflection, vertical collectors perform very well -- if you have a snow field in front of the collector, a vertical collector will do even better because it benefits from the high reflectivity of the snow. The construction would be even simpler if the collector were vertical. The stagnation temperatures in the summer for a vertical collector would be much lower. As an example, at the summer solstice, the day long radiation on a collector tilted at 65 degrees is about 1500 BTU/sqft, while a vertical collector sees only 610 BTU/sqft on the same day -- this helps keep the stagnation temperatures down.
As you can see, I am a big fan of vertical collectors for space heating :)
Anyway, this is a really nicely done design and installation with lots of good ideas -- thank you Scott!
Gary October 3, 2009