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EcoMotive

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Reply with quote  #1 
This is a project that I really WANT to get started. IF and WHEN are different stories.

These are my plans for a passive solar greenhouse that will hopefully be built in place of my existing traditional European style greenhouse. When I built my existing greenhouse I had no idea what a passive solar greenhouse was and I just built what I had in my head as a greenhouse. I really want to be able to grow greens all year long and this new greenhouse will be the key.

While designing the frame I paid particular attention to avoiding water penetration. The eves extend out over all four walls especially on the south side where the glazing is. The glazed wall is framed with 2 by 4 studs but has a 2 by 6 top plate and a 2 by 4 bottom plate. The glazing will butt up underneath the top plate but then run over the bottom plate. The glazed wall is also flanked by 2 by 6 studs to prevent water penetration from the sides.

All solar greenhouse plans that I've seen so far have a simple butt joint between the glazing and the peak of the roof. This leaves me puzzled about how water can properly run off of this joint.






The roof pitch is 4:12 which is almost exactly the angle of the sun on Dec. 21st. The glazing is at a 90 degree angle to the roof which simplifies framing and puts the glazing at an almost perfect incident angle to the sun on Dec. 21st.



I will insulate between the studs and rafters with fiberglass batts and then cover everything over on the inside with 1.5" polystyrene. This will give a high R value, eliminate thermal bridging and provide a draft proof vapor barrier.

Ventilated soffit will be installed on the North and South edges of the eves. Foam baffles in each rafter cavity will channel air between the North and South sides.




In this picture you can see the glazing roughly added to the south wall. Every other surface on the structure will be sheathed and then covered with siding or shingles... whichever is appropriate.  The door will be a pre-hung exterior door 32 by 80.

I would like to take the short knee wall under the glazing and make a small trombe wall out of it but unfortunately it will be obstructed by the planter beds in front of it. If anyone wants to use these plans for their own greenhouse, I suggest you also consider a trombe wall.



In this picture you can see the existing greenhouse and it's close proximity to the solar heater on my garage. The North edge of the new greenhouse's roof will be just over 18 inches shorter than the existing one. This will mean that very little of the garage's heater will be shaded by the sun on Dec. 21st. The sun will come close to shining on the entire absorber, leaving only the baffle in shadow.

Like I said, this project may never materialize but that doesn't mean nobody can benefit from these plans. If anyone wants a digital copy (a Google SketchUp file) of these plans just eMail me and I'll send them to you.

Lance in Newfoundland



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solardan1959

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Reply with quote  #2 
Lance,
   Seems looks a great plan and would work great for you and your current garage heater.  Does seem like a bit of a waste of your current great greenhouse.  Any chance you can move or reuse it somewhere else even if it is a neighbor who gets to use it?
  
That's a lot like the sunspace I'd like to build on the back of my garage.  I know you commented once in the past about using that space on the back of my garage.  In my case I would use my existing three foot eve, have a slightly more slanted angle more around 60 degrees, and doors on both sides.  It would be about 16 foot wide and should also be used to help heat the garage.
Dan
EcoMotive

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Reply with quote  #3 

I just done up a sketch of what the greenhouse should look like from the outside when completed.



I have several ideas in mind of what I will do with the materials from the existing greenhouse. It shouldn't be a huge waste of materials. Worst case scenario is I might be able to give it to my neighbor since she has always admired it and often goes in there to look around at the plants. The only thing is I have no idea how I could move it. We might need a backhoe I guess.

Lance in Newfoundland


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SolarInterested

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Reply with quote  #4 
Lance thought I'd post this link in case you hadn't seen it. Form follows function.

http://www.builditsolar.com/Projects/Sunspace/LowMassSunspace/Greenhouse1.htm

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solardan1959

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Reply with quote  #5 
Solar Interested,
   The one exception to me is I would not insulate the floor, or at least would put a sheet of insulation under a stone floor probably consisting of patio pavers.  While Gary is saying he does not want mass in the greenhouse so the heat goes to the invisible house in his case, I would want to retain heat in the greenhouse to keep my plants warm at night.  The pavers or cans of water would help the plants survive the cold nights hopefully.  I'm not sure how well this will work in the dead of winter up here but it will definitely help extend the season by 4 or 5 months.  And I could still add a blower to pipe excess hot air into the Garage for additional heat there.
Dan
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Reply with quote  #6 
Good point Dan as Gary was optimizing it to be a "low mass sun space" to collect heat for "the invisible house".
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Castlusion

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Reply with quote  #7 
From my readings and my 8*16 solar shed there are a few things that are constant in this type of "solar greenhouse" the length (south/north walls) is twice as long as the width east side and west side walls) water storage for mass is 2gallon per square foot minimum and up to 5 gallons per square foot maximum.This testing came from Canada for the maximum but admitted the difference between four and five gallons per square foot of glazing was not much. I chose 240 gallons because i have four 60 gallon barrels i am using. but i am also in Cincinnati OH so i am further south then most all of the test done in US or Canada.FYI i am a geek that crunches numbers for fun The solar green house book edited by James C. McCullagh has a wealth of information in it. for us number cruchers it looks like a great building wish i had  talent like that.
EcoMotive

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Reply with quote  #8 
Thanks Castlusion for posting the design guidelines for the passive solar greenhouse. I had seen these before but unfortunately I had to stray away from many of them. For example, the footprint of my passive solar greenhouse will be 10 by 14 feet instead of the nominal 7 foot depth with my 14 foot long south wall. The reason for this is that I will use the existing foundation from the existing greenhouse, the dimensions of which were chosen to maximize square footage while minimizing wastage of polycarbonate glazing.

I have 200 gallons worth of plastic drums that I will use as thermal mass. This works out to about 2.38 gallons per square foot of glazing. I know it's towards the low side especially where we get long periods with no sun here in Newfoundland. I am actively searching for more barrels and if I find them I will try to get it up to the maximum 5 gallons per square foot or even more.

I might have to go with corrugated polycarbonate as the glazing material instead of the recommended twinwall. You can't buy twinwall on the island and instead it has to be freight shipped in from Toronto. I ordered a large quantity for my existing greenhouse which made the shipping costs worthwhile. I also received several damaged sheets and got free replacements while keeping the damaged ones. I used the extra sheets for my pex-al-pex space heating collectors. I have lots of extra twinwall to use but in lengths that are too short for the passive solar greenhouse. I'm currently brainstorming about how I'm going to rig up a set of automatic electronically actuated thermal curtains to help cut the heat loss from the glazing.

The glazing is tilted a bit steeper than it should... for several reasons. One is that in order to simplify framing I wanted the glazing to be at a 90 degree angle to the roof. I wanted the roof to be a maximum pitch of 4:12 (about the sun's angle on Dec. 21st) so that it doesn't aggravate my shading problems with the garage collector. The tilt is about 70 degrees which also maximizes the solar intake at Dec. 21st; not necessarily a bad thing. The last point was my second reason behind the high tilt. This makes the greenhouse most effective in the dead of winter and borderline useless in the summer. That's fine because I'm only ever going to grow salad greens in it. Small greens (spinach, lettuce, etc.) don't need a whole lot of light and prefer cooler temperatures so in the summer they should do a lot better than if the glazing had a lower tilt.

I'm also expecting the greenhouse to need supplementary heat. I have a small collector in the works that will hopefully help to charge up the thermal mass during the day. I'll probably place it beside the greenhouse on my back lawn and circulate tank water through it. I'm looking for any excuse to get rid of the grass so I'll build a raised planter bed around it or something. The only downside is I would have to use a closed loop system which I am quite frankly terrified of having to build and maintain. I have a collector in the works now that I will probably use for the greenhouse.



Lance in Newfoundland

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 “Only primitives & barbarians lack knowledge of houses turned to face the winter sun.” 
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EcoMotive

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Reply with quote  #9 
Just a thought... Since the roof is 90 degrees to the glazing wall it might be possible to use an overhead garage door as an automatic thermal curtain. The dimensions of a 12 foot wide and 7 foot high garage door are just about perfect for my greenhouse and it would be relatively easy to install an automatic garage door opener and control it with some simple electronics. Garage door weatherstripping is readily available and should provide a good air seal. Hmmm....

Lance in Newfoundland 

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 “Only primitives & barbarians lack knowledge of houses turned to face the winter sun.” 
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