Passive Collector for green house

[FrankG]

the link below is to the latest installment on the Green house project posted earlier in the spring... It includes 6 passive solar collector panels and more work on the hacked HVAC system...

http://www.theworkshop.ca/energy/grnhouse/3/gh3.htm

FrankG

www.theworkshop.ca

frank@theworkshop.ca

[Volvo farmer]

That's pretty neat Frank!

Since your goal seems to be to keep the greenhouse from freezing at night, I wonder if you wouldn't be better off experimenting with heating something more massive than air. If you could somehow heat 200 gallons of water or glycol to 100F during the day and store it inside the greenhouse, that water would radiate it's heat throughout the night and even out those temperature spikes you are seeing.

[wdyasq]

In the greenhouse I kept I placed several plastic barrels as shelf supports and filled them with water. I thought about putting a duct from the peak of the greenhouse to under the barrels but a small fan circulating the air down during the day - timer controlled, seemed to be adequate.

Ron

[Norm]

    Good use for pop cans....I was wondering

how much airflow in really strong sunshine...

does it compare favorably with the more common

passive collectors. I suppose I'll just have to

see for myself. I like the idea, you can just

keep making a couple of stacks at a time.

Thanks for clue ing me in on this.

  I was thinking of taping them together with

duct tape?

   The lost foam casting is a good way to cast

with regular sand, still like wood patterns and

synthetic casting sand as long as my 200 or so

pounds of the stuff last.

   Haven't done that for a long time my last

furnace was just some refractory bricks stacked

around a salvaged heating element from an electric

clothes dryer with a stainless steel mixing bowl

for a melting pot ...takes about half an hour or

longer ...but it's quiet....(wife didn't like the

one I had prior an oil burner unit).

               ( :>) Norm.

[FrankG]

Thanks all for the comments...

Thermal mass is definately the next step... There is a 5ft wide section of back wall that could house some sort of collector and storage tank. My first thought would be to employ some sort of convection siphon effect that would reverse in the evening...

Obviously I haven't thought too much about it yet, but will search the web for ideas before the spring.

FrankG

www.theworkshop.ca

[Gary D]

Frank, nice work on the collectors! As for thermal mass, might be a good thing to look for a solid load bearing wall(or add supports) before much weight goes in there. Water storage tends to be great but heavy... The wife might not like it if a wall or something "sags"  ;-)  Gary D.

[willib]

i agree on the need for a thermal mass

not much beats water ( or water with glycol) as a thermal mass

how about putting another collector ( the pipe style ) outside , insulated , and pumping glycol and water through storage tanks located inside

[Clifford]

Interesting design, and always worth experimenting.

In 1979 we built our "family house" experimenting with passive solar heating.  

City: Eugene, OR.  

Average Winter Temp:  30 - 40 Farenheit.  Occasionally teens and twenties.

Average Winter Cloudy Days 90% (well, that was a bit of an issue for us).

Note, the coldest days were often the clearest of days.

Unfortunately, some aspects weren't as efficient as we had hoped.  However, the basic design was:

45. degree south facing roof... skylights on roof (Total of 7 - 4x8 double panes) + attached greenhouse on one side with all glass greenhouse roof.
    
12. " Solid (relatively dark) brick wall down the middle of the house.
    
    

Before building "my house", I'll have to carefully consider the benefits and failures of my parent's house.  I think the basic design concept was fine:  Solar panels + "absorber"...  then moving the "absorber" away from the panels and using the space in the middle as living space.

The greenhouse was behind my parent's bedroom, and their complaint was that the bedroom would actually start getting warmer around 3:00 AM (the time for the absorbed heat to pass through the 12" brick wall).  I believe that we had a net gain in energy with the greenhouse and the brick wall behind it, but it would have acted as a 2-way channel, passing house heat to the greenhouse, and solar heat to the house.

Anyway, the greenhouse was great for growing things like cactuses, and as far as I know, it never actually froze inside.  I remember one winter day with snow outside, and 90+ degree temperatures in the greenhouse.

One note.

The brick wall is essentially always below 90 degrees.  So, no matter what, it will always feel cool to the touch.

So,

Back to the original issue:

I would add to the greenhouse design would be some kind of an absorber...  

Assuming we are talking about a permanent structure, consider a dark colored concrete/brick back wall (north side).  If it was freestanding, you might insluate the back of the wall.  However, in your case, you might want to radiate heat back into the house (or back and forth).

The question I would have is what to do with the floor of the greenhouse.  Would the benefit be realized from insulating it from the earth...   or perhaps utilizing the earth itself as a heat sink.  

With the idea of using the floor as a heat sink, you might have nearly equal performance by painting the floor black, or just make sure it is dark (at least in the winter), and using it as a natural heat sink.  The goal might be a lower "spike" in the daylight, but maintaining a higher average temperature difference.