[Greenbuilding] [BULK] Evacuated tube collectors?

[Lawrence Lile]

There are a lot of fancy differential thermostat controllers for pumping
solar collectors. They have complicated thermocouples, wiring, and
headaches. They also have a miserable failure history. 

There is also a bonehead simple controller.  It consists of a solar
electric panel, maybe 10W, and a 12V DC pump.  If the sun is shining,
the pump goes.  If the clouds shade the solar electric panel, then they
are shading the water heater too and the pump doesn't go.  If you've got
50% sunshine, the pump goes at about 50%.  At night, the pump doesn't
go, when you aren't making any hot water.  Ingenious!  

Here is one place you can buy the pair:

http://www.solarsupply.com/Pages/DCPumps.htm

Search around and you can save $40 or $50 at the cheapest online store.


El-Sid and Shurflo both make good pumps that can handle this trick.  The
El-Sid pump is blindingly simple.  There is a sealed rotary pump unit
magnetically coupled to a little box that makes it spin.  There are no
moving parts other than the rotor inside the sealed pump. It is
lubricated with water so there is no bearing.  There are no brushes,
motor bearings, or anything else to fail. The little box makes the rotor
spin by switching magnetic coils on and off with electronics. The box is
replaceable with two screws, and you can strap on a bigger box if you
want more water. There are two wires.  Hook them up to 12 volts and it
pumps.  Wow, I am really impressed with simple, ingenious solutions and
this is one of them. 



Lawrence Lile, PE, LEED AP
Project Solutions Engineering
-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of Speireag
Alden
Sent: Tuesday, July 17, 2007 8:47 PM
To: greenbuilding at listserv.repp.org
Subject: [BULK] [Greenbuilding] Evacuated tube collectors?
Importance: Low

Hallo, all.

     The time has come to put in the first solar hot water collectors. 
These will eventually generate some amount of solar pre-heat 
year-round, with overcapacity through the summer, when excess will 
heat the ground around and under my earth-bermed house, AGS-style.

     The house is in west-central New Hampshire, so the system must be 
utterly resistant to cold temperatures, and it would be very nice if 
it could generate some amount of heat during December, when days are 
short and often cloudy.  So I'm interested in evacuated tube 
collectors.

     A bit of research turns up two types which seem promising:

     http://www.solarthermal.com/

     http://www.sssolar.com/

     Does anyone have any experience with these?

     Does anyone have other recommendations?

     I want to be pretty simple on controllers.  I'm thinking that 
I'll put one temperature gauge right where the pipe enters the 
ground, inside the insulation jacket, and another at the manifold for 
the solar collector.  Between them, I want to put a controller which 
will compare temperatures, and when the panel is warmer than the 
pipe, close the circuit on a solar-panel in-line pump hook-up.

     Although I like tinkering, I see no need to re-invent the wheel 
and I have plenty of other things to do, so I'm willing to look at 
off-the-shelf solutions for the control stuff, if someone can point 
me to them.

     Eventually, I will expand the system such that the hot water from 
the collector will be routed first to the house storage, and then 
when that is hot enough, to heat the interior of the house via the 
radiant floor, and when that is hot enough, to dump the heat into the 
ground around the house.  So there will need to be several sensors 
and switch valves.

     Can anyone guide me toward a good solution?

-Speireag.

-- 
Fill the molten glass.
Sit with singing summer frogs.
Think on Jack's wedding.

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