[Greenbuilding] [BULK] Re: Solar Water Heater architecture

[Lawrence Lile]

>Lawrence,

>The Tote sounds good; where might I find them (what is a boneyard?) It might even fit in the place I have available for the tank.

A Boneyard is a building materials recycling store.  Usually they have misordered windows and doors, frieght salvage, that sort of thing.  "totes" are a specific type of drum used a lot by chemical and food industries.  Handy to move around 500 Gals of stuff with a forklift, more efficient than 50 gal drums.  You can buy them new, probably for about ten times that figure.  Look for high density polyethylene, it  can handle the heat. 


> Watch the head on your El-Sid pump.  

>Right, I have about 25 of head.

In a closed loop system, then going up part is counterbalanced by the coming down part.  The head pressure is set by the piping run and the pressure drop through your solar collector and heat exchanger.  The capacity of the El-Sid in GPM is probably also small for this system.  Your collector MFR will have recommendations for minimum flow rate, double check this.  


> That's a whole lot of storage.  Most domestic systems start at 50 gals 
> for two people, 80 gals for four.  But hey, if you are running, say, 
> radiant floor heat you might want 500 gals.

>Most domestic tanks have lots of heating all day long.   My heat 
requirements, on a cold day, run about 15000 BTU/hour, at 100º temperature differential, that is 450 gallons.

So it is a space heating, not just domectic hot water system! Yep, you need 500 Gal. 



>That sounds interesting, but given that it is an open tank, it would seem that thermal expansion and evaporation would make it less sensitive than I would like.  Plus, I most want to detect a leak in the glycol system.

Good point.  Two colors is a good idea.  


>Food coloring is hard to detect in small concentrations.  Someone on this list mentioned a dye noticeable in parts per million (billion?).

I'd like to know about it. The only thing that comes to mind is radioactive tagging, not really something I'd have a part of.  

>> Best method of building the tank (and ensuring that failures don't
> result in a flooded basement?
>
> Buy a tank. Plastic Tote.  Or buy ten 55 gallon plastic drums and 
> build a foam box around them. Avoid steel, and avoid homemade tanks.

>I was thinking more of a catchment system under the tank.  I don't trust any tank, home built or purchased.

That's for sure.  We've used agricultural feed troughs as secondary containment pans, they are cheap and available in many sizes at your local feedstore. Which is another good way to make a big cheap tank.  Float foam balls on top to insulate it.  Don't use really small beads, they clog up everything. 

>> Control systems?
> Don't bother.  Put a PV panel on your pump, and you are done.

>I would like the following:
1)  Pump running the solar loop whenever there is heat to be extracted (this may be possible with just the PV panel.

You can buy a packaged differential thermostat if you want to get fancy. 

2) Pump running the floor heat whenever it is cold in the house, there is heat in the tank, and it is daytime (so there will still be heat in the tank for DHW).  This can perhaps be done by a programmable thermostat in series with a thermostat in the tank.

These should be available with your floor heat system.


3) Pump or release valve to keep the tank from getting too hot.

Two considerations:  Emergency overtemp and heat dump. 

The emergency overtemp can be a standard Pressure and Temperature valve as on a water heater tank, on the glycol side.  Don't send it to the drain, send it to a bucket.  You also want a P&T valve on your tank.  Or you can just have an open line to the drain, just above the high water line, since it is not a pressure rated tank.  

A heat dump cycle.  This will help your glycol last longer, maybe other equipment too.  If you have good, efficient evacuated collectors you may have to worry about heat dump. I have cheap, inefficient collectors and they probably won't get that hot.   It can be run from a simple thermostat, and can divert the water coming out of your collectors to a heat dump exchanger under the eaves, then back to the tank cooled off. Requires one solenoid valve and a thermostat.  If you decide you need to go to such complex lengths, I think they sell these.  If you are a hacker like me, salvage the heat exchanger coil out of a dead air conditioner unit.  

--Lawrence Lile