Solar Hot Water Collector

Evacuated tube, that is...  There are two basic kinds of solar hot water heaters out there (besides your typical garden hose in the sun), a flat panel collector, where you have a circuit of copper tubing running inside an insulated flat chamber, and evacuated tube.  The whole tube is not in a vacuum, but actually the outer shell of the tube is a double walled tube, and between those walls is an evacuated tube.  In the middle, there is a fin mechanismn that picks up the heat (trapped by the vacuum and the fact the glass is thermally opaque, so it can't effeciently radiate its heat back through the glass).  The fins transfer the heat to the copper tube in the middle, which contains a little bit of a working medium, which boils and evaporates, becomes superheated, and then transfers the heat to the top of the tube, where the copper tube is exposed to the insulated manifold header, where the water runs across, picks up the heat, and takes it back to the storage tank. 

No, I didn't invent this thing... I just bought it, and I think it's really cool.

There is, of course, a raging debate over which type of panel is better, but bottom line, the flat panel is normally cheaper, and the tubes are more...not for me, though, because I don't buy anything the normal way.  In our climate, we could have easily used either, but we chose the tubes for these reasons...

1.  Cool factor (yup, vanity)

2.  Higher operating output

3.  Much higher temperature output (not more heat, but more "temperature voltage")

4.  Higher resistance to hail

5.  Modular... Broken tube, change it out.

6.  Easier installation (perhaps)

7 Higher resistance to freeze

8.  Availability

I could go on...

Anyway, 30 tubes in all, have the potential to produce about 38,000 BTU/Day, or the same as 11.3 kWh per day, which at our utility rate of about 12 cents/kWh that translates to about 41 dollars per month...average.  Payback in my opinion is instant, especially if we ever had to sell the house.  There are other advantages, with tricky accounting, and I would never go into those here ;-)  Suffice it to say I have a 1.2 million pound heat storage device ;-)

OK, so here is a little experiment, moring haze, with no load on the panel, so the pipe can't get rid of it's heat, hooked up a thermistor to my non contact temp gun.  The big number, 67F, is the temperature of the grass, and the little temperature is the heat pipe, 200F and climbing fast.

Then off to check out the progress on the tile.  Most of which is now laid in the "fields", mainly they have to do the ridges and then tidy up around plumbing and flashed walls, neither of which is going to happen anytime soon, as I need to line those guys up...

You can click on these, which make them big, for much better color...  It rained in the night a little bit, which washed away a lot of the tile dust, so the color was even better than before without all the "dusty rose" powder color on things.

Starting the Master Bath tile, which was about the last thing to go.

Then, off to my regular warehouse hardware store for something to build a frame to hold the solar collector.  Of course, with a normal house, and a normal person, you could have just mounted the thing on a 5/12 pitch and about averaged out the use between summer and winter at this latitude, and on a shingle roof you wouldn't have to do much for flashing other than a little silicone...  But, we are on a tile roof, so the collector doesn't sit on the tile, it sits on the deck below, and has to be suspended up above the tile.  So here is my solution...  1/2 inch pipe fittings.  I have also decided I want to optimize the panel only for the winter season... Why??  Because the rest of the year I am trying to maximize the use of the desuperheater (which makes the GSHP run more effeciently).  To make a short story long, the solar panel with run us a chance of overheating things in the summer, because between the desuperheater, the solar collector, and low demand for hot water, we could easily cook the water past the boiling point (at atmospheric pressure, anyway, which of course we have in excess of 50 PSI which significantly raises the boiling point)...  regardless, by optimizing the panel at a higher angle in winter, there is less angle of incidence in summer, and the panel can't produce as much heat as it otherwise would in the summer....hopefully causing us to not have a boiling event which causes the pressure relief valve to let go.  In addition, it gives me more effeciency (though with less sun) in the winter, when I need the heat more.  Additionally, in the middle seasons, I am also closer to optimum when there is less chance of the desuperheater being in operaiton... Bored YET???

This is a closer look at the header, which is an extruded aluminum piece that holds the copper manifold and accepts the evacuated tubes, as shown...  They just sit in there, nothing magic.

Nifty little plastic widgets at the bottom pop onto the rail, and then allow you to tighten and push up on the tubes, holding them in position on the collector.

Another view down the row of 30 holes... 

Any why the upside down and backwards h shape?   Because I wanted the frame to have some resistance to the shear effect of having the collector being fairly heavy, and the pipe brackets being fairly small.  This makes the thing much harder to "twist" and makes it a lot stronger.  I honestly don't think you will see any of this from the ground, which is all under the collector tubes, but, I painted them anyway... brown.

So, my strategy for installation...  Tomorrow I am hoping to get the vertical supports actually mounted to the roof deck (the only place not tiled in) and then they can actualy drill holes in the appropriate place for the tile to slide over the pipes.  Then, I will have them tile the field under the collector completely, but leave a perimeter at the sides and bottom.  The copper lines coming through the roof have to wait for a special piece of flashing I ordered (later in the week), but after than happens, I can pierce the roof with the copper and then solder on all the fittings, as well as run the wire to the thermistor (temperature sensor for the controller).  I can then mount the collector frame and header.  If you mount the tubes dry, repeated heat cycles aren't good for their health...