For this solar water heating system either of these two types of collectors could be used:
The collector described below is the one that we actually built for our solar water heating system. Using the PEX tube collector version on our own system has more to do with just wanting to know how well it will it will perform and hold up over time than in believing its necessarily the best choice. If I was looking for something with less risk, and a little better performance, but somewhat more costly, I would choose the copper tube with aluminum fins collector.
This collector is a bit unusual because it had to fit within a specific area. Most collectors are taller than they are wide, while this collector is the opposite to fit under the window. So, the collector is about 12+ feet wide and 4+ feet high. The PEX collector uses a serpentine tube routing with a down slope so it they drains back OK. The 12 ft width seemed to wide for this approach, as a down slope over 12 ft would make the space between tubes to great on the downhill end. So, I decided to use two serpentine runs, each one 6 ft wide.
The construction of this collector is similar to the PEX collector construction described in detail here...
So, the material below does not go into as much detail, but still gives a good idea how this collector is different than the PEX collector prototype. See the above link on PEX collectors for more construction detail.
The collector is 52 sqft for two people. This is on the high side, and that is intentional. My thinking is that it is very little more work and expense to make the collector (and storage) on the generous side and to combine this with a tilt that is more optimized for winter collection in order to get a higher year round solar fraction.
Note that the size, shape, and layout of the PEX (two banks) is quite a lot different than the PEX collector prototype -- this is an advantage of doing the collector yourself -- you can make it fit the space you have.
These pictures show the side-by-side layout for the interior of the 12 ft wide by 4 ft high collector.
These pictures show the construction of the two absorber boards for the left and right sides of the collector. This is exactly the same technique as described in detail for the PEX Collector.
These pictures show the wide frame that accommodates both of the two absorber halves.
Frame with absorber mounted.
The galvanized EMT conduit provide support to the glazing.
The vertical EMT's run inside a corrugation, and
the long horizontal support runs just behind the glazing.
After the collector is installed, an extra wide sill (of synthetic wood) is installed on top of the collector frame to seal the top from weather and shed rain.
This picture shows how the PEX lines are brought out the back of the collector to be hooked to pipes leading down to the crawl space and storage thank just behind the collector.