Heating Help

solar sand box

Going to the wall again for help.  I need to know if this pumping arrangement will work.  The application is a 700  square ft garage with little DHW use.  The radiant floor is a 2 ft deep insulated sand bed with a 4" concrete slab o top  with the tubes buried in the lower part of the sand.  Most of the solar heat will be directed to the sand storage.The idea came frome Bob Ramlow. 

add a 3 way

zone valve at the bottom connection, return to the collector.  Then use a solar controller with dual outputs.  It covers the DHW load first then moves additional heat to the sand bed.  This way you have control over your DHW temperatures and additional solar goes 100% to the heat load.

hr

Sand Bed Systems Debunked

If you haven't already built this garage, you may want to rethink it.

Sand beds aren't that great for houses:

http://www.builditsolarblog.com/2011/01/sand-bed-heat-storage-for-solar-home.html#comments
http://www.builditsolar.com/Projects/SolarHomes/SandBed/RamlowSandbed.htm

Kevin,

On one of the links that you attached, there was comment regarding a gent name Starr. You said that he deserves and award for his work in lowering the cost of solar/space heat application. I do hope that you understand that his basis of design is an open loop system for both space heat and DHW. In my professional opinion, his system design should be outlawed (and have actually attempted to make it so, but lost out to very well funded counter interests).

These systems are Legionella incubation machines, and I don't care how much "flushing" and or "purging" you do, the fact still remains that these systems CAN be deadly to certain people (ill, immune depressed systems) under certain conditions (house has been empty for a week, and it has been warm outside, like summer vacation).

I'd be careful of what you (I) say about it, because he is a VERY litiguos person. Numerous posters on this board have been issued Cease and Decist orders from his legal team when they questioned his practices. He also has a lot of political sway and influence.

Thought you should know.

ME

I neeeed more storage....

I liked what Daycreek did - sand below w/ tubes and tubes in concrete above, just hedged his bets and gave him greater design flexibility.  I think Gary's math on buid-it-solar demonstrates a greater practicality in using water for storage as opposed to sand.  I agree that the waters ability to be heated to higher temps AND provide a more rapid extraction of heat as needed AND the ability to uncouple the heat source against over heating convinces me to use water. 
I'm still waiting to see if someone comes up with a more dense phase change storage medium that can easily discharge or uncouple as needed, in order to reduce volume storage size.  The ole' wax rods immersed in water are the closest thing I've seen to this. 
AB Solar

sand beds I've done

I've done a half dozen sand beds, and they've all performed exceptionally well.
Half the battle is the building you put on top of the sand bed.

we have one (actually the first one we did) that is a 3000+ sf house (all above grade) with lots of windows and stuff, very normal looking house, that has been using 2 chords of wood per year in the sealed combustion fireplace insert.  that's in a 8000 Hdd area.

the other one is a 2800 SF barn/workshop that gets no lower than 50 F with no additional input.  but it's well insulated and has minimal windows.

I'm not going to argue the "seasonal heat storage" claim that others make as I don't think the numbers are there, but high mass systems are cheap and easy to put in, have minimal operating costs and few failure points.

the other saving grace is that there are minimal heat exchange inefficiencies in the system.   we typically use 1800-2100 ft of 3/4" pex in the floor, and get solar operating temps in the winter of 90 to the collector and 110-120 coming back from the collector.  those sorts of operating temps are not often seen in the flooded tank systems where the solar fluid is separated from the boiler/storage water by one or more heat exchangers. 

add in the $0 operating cost for most systems, grid independence, stable house temperatures and costs in the 3/4 of a more complicated system, and they can be a real winner.

Whether a particular system is a viable option is due to many more variables than can be presented in this forum, but I think high mass systems definitely have great potential for many many applications. 

My $.02

update

So this system was put together as per the diagram.  Not shown in the diagram is an expansion tank before the solar loop circulating pump. 
The idea was that when required, the DHW tank could supply heat to the floor.  Shut off valves can isolate the solar loop.  Right now, with the solar loop closed, the DHW tank energized, and the floor circulating pump on, no heat gets pulled out of the tank and put into the floor.  What is wrong here?

Needs purging

Purging the air out is required. Get out the old bucket, a gallon or so more collector fluid, and pump.

After a few weeks, more air will come out of solution and might airlock the pump again. It helps if your pump is at a low spot also. Most closed systems have air removal accessories.

airlock

OK. One other thing I thought might be a concern is that because the expansion tank is located by the solar loop circulater, the floor loop would have no access to the expansion tank when the solar loop is isolated from the floor loop.