I thought hard about the issue of gable vs roof vents. I should also mention here that I relied heavily on the book "Greenhouse Gardeners Companion" when building this greenhouse. IMHO it is the best book written on the subject of home greenhouses. It is written by Shane Smith who is also accessible on a greenhouse bbs (kinda like this one!). His advice on the vents was that there was no discernable difference between the effectiveness of gable vents vs roof. I decided that the gable vents were much easier to engineer and maintain and I didn't have to worry about leaking.
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Greenhouse
- Thread starter TonyC
- Start date
- Views: 4578
Okay, Twinkle Toes...I'll take them one at a time!
Okay, you win, I did cut a few corners...but I didn't scrimp!
There's more than one school of thought on orientation. I have the long wall (on the right in the photo) facing true south (perpendicular).
It is heated by a vented 25,000 BTU propane greenhouse heater. This size is borderline for this size greenhouse. It should be bigger. Active solar requires solar panels, batteries etc. I wasn't getting into all that. Passive solar is probably what you mean. The most effective use of solar passive solar heat in a greenhouse is black drums filled with water. This has been determined by folks that are more scientific with me using reasonable materials (rocks, bricks, water etc.). I do this somewhat to augment my heater but it clearly has limitations, especially at night. If it's 22 degrees outside at night, black drums will not ever get it to 55 degrees.
On the covering, glass has several disadvantages. Single pain is not efficient enough in cold weather. Double pain is extremely expensive. Also, glass can break and is especially vulnerable when used as a roof! A single hail storm would take you right out. Poly is not cheap but much more affordable at $56 for a 4X8 sheet. It is somewhat flexible and extremely resistant to breakage. It insulates well. The only real disadvantage is that with twin wall, it is not clear looking like glass so the greenhouse may not be as "pretty", but it does let through 95% of the suns rays. I added an old window to the south side to offset this, sacrificing some heat loss in the process. I do cover it with poly in the winter though so I haven't lost much. Besides glass and poly, there is corrugated fiberglass like they have at Home Depot. It blocks more of the sun's rays and is a poor insulator. It also breaks down in the sun. Poly is good for 10 to 15 years or more.
Triple wall costs more but insulates better. Living in Virginia I didn't consider it a necessity. It just depends on how cold it gets where you live and how warm you wish to keep the greenhouse. Keeping it at 40 degrees is a lot easier than keeping it at 55. How much sun your area gets in the winter is also an important factor in this decision. You can find this out by going to http://lwf.ncdc.noaa.gov/oa/climate/online/ccd/avgsun.html
The misting system is for cooling the greenhouse in the summer and not for watering the plants although they do pick up some moisture from it. If it is 102 degrees outside, all the fans and vents in the world will not get it under 102 inside. By putting misters in the ceiling with a very fine mist, the ventilator fans will pull the moisture through the air and out the vents, cooling the air inside somewhat. There are more complicated and more effective ways to do this but I opted to leave them for a future date if I felt it was necessary. Covering the greenhouse with shade cloth helps a lot too but it also reduces the amount of sun that's let in. The shade cloth comes in a variety of densities which are chosen based on what you intend to grow. Some folks don't even grow anything in there during the summer.
I am a FIRM believer that plants do much better with rainwater than tap water. That is why I collect it and use it for watering. I'll take some photos of this and post them next week.
Automatic controls: I have a large ventilation fan that is on a thermostat. At the opposite end of the greenhouse are motorized louvers that open only when the fan kicks on. I also have window vents with temperature sensitive openers. These work all year round but are most useful during the transitional season when it's not too hot and the fan isn't running. If it's 20 degrees outside and the sun is shining, you don't really want that fan kicking in and pulling freezing cold air in there. I cut if off in the winter and let the window vents gently let heat escape if it needs to.
As you can see, it is a very complex proposition if done properly. Not complicated to do necessarily but good planning and research are wise. If you go to www.sundancesupply.com you will find a wealth of useful information as well as excellent pricing on most of what I have mentioned. I bought a lot from them and highly recommend them. Make sure you download their design guide at http://www.sundancesupply.com/DesignGuide.pdf
I hope this helps! If you guys are interested I will post a few more detailed photos.
Okay, you win, I did cut a few corners...but I didn't scrimp!
There's more than one school of thought on orientation. I have the long wall (on the right in the photo) facing true south (perpendicular).
It is heated by a vented 25,000 BTU propane greenhouse heater. This size is borderline for this size greenhouse. It should be bigger. Active solar requires solar panels, batteries etc. I wasn't getting into all that. Passive solar is probably what you mean. The most effective use of solar passive solar heat in a greenhouse is black drums filled with water. This has been determined by folks that are more scientific with me using reasonable materials (rocks, bricks, water etc.). I do this somewhat to augment my heater but it clearly has limitations, especially at night. If it's 22 degrees outside at night, black drums will not ever get it to 55 degrees.
On the covering, glass has several disadvantages. Single pain is not efficient enough in cold weather. Double pain is extremely expensive. Also, glass can break and is especially vulnerable when used as a roof! A single hail storm would take you right out. Poly is not cheap but much more affordable at $56 for a 4X8 sheet. It is somewhat flexible and extremely resistant to breakage. It insulates well. The only real disadvantage is that with twin wall, it is not clear looking like glass so the greenhouse may not be as "pretty", but it does let through 95% of the suns rays. I added an old window to the south side to offset this, sacrificing some heat loss in the process. I do cover it with poly in the winter though so I haven't lost much. Besides glass and poly, there is corrugated fiberglass like they have at Home Depot. It blocks more of the sun's rays and is a poor insulator. It also breaks down in the sun. Poly is good for 10 to 15 years or more.
Triple wall costs more but insulates better. Living in Virginia I didn't consider it a necessity. It just depends on how cold it gets where you live and how warm you wish to keep the greenhouse. Keeping it at 40 degrees is a lot easier than keeping it at 55. How much sun your area gets in the winter is also an important factor in this decision. You can find this out by going to http://lwf.ncdc.noaa.gov/oa/climate/online/ccd/avgsun.html
The misting system is for cooling the greenhouse in the summer and not for watering the plants although they do pick up some moisture from it. If it is 102 degrees outside, all the fans and vents in the world will not get it under 102 inside. By putting misters in the ceiling with a very fine mist, the ventilator fans will pull the moisture through the air and out the vents, cooling the air inside somewhat. There are more complicated and more effective ways to do this but I opted to leave them for a future date if I felt it was necessary. Covering the greenhouse with shade cloth helps a lot too but it also reduces the amount of sun that's let in. The shade cloth comes in a variety of densities which are chosen based on what you intend to grow. Some folks don't even grow anything in there during the summer.
I am a FIRM believer that plants do much better with rainwater than tap water. That is why I collect it and use it for watering. I'll take some photos of this and post them next week.
Automatic controls: I have a large ventilation fan that is on a thermostat. At the opposite end of the greenhouse are motorized louvers that open only when the fan kicks on. I also have window vents with temperature sensitive openers. These work all year round but are most useful during the transitional season when it's not too hot and the fan isn't running. If it's 20 degrees outside and the sun is shining, you don't really want that fan kicking in and pulling freezing cold air in there. I cut if off in the winter and let the window vents gently let heat escape if it needs to.
As you can see, it is a very complex proposition if done properly. Not complicated to do necessarily but good planning and research are wise. If you go to www.sundancesupply.com you will find a wealth of useful information as well as excellent pricing on most of what I have mentioned. I bought a lot from them and highly recommend them. Make sure you download their design guide at http://www.sundancesupply.com/DesignGuide.pdf
I hope this helps! If you guys are interested I will post a few more detailed photos.
TWINKLE_TOES
Veteran Member
- Joined
- Sep 3, 2000
- Messages
- 1,366
Tony,
Thanks for taking the time to provide such an excellant resonponse to my questions/w3tcompact/icons/smile.gif I am in the Pacific Northwest and don't have to deal with the temperature extremes that perhaps you do. I squared a deal sometime ago for a bunch, (24 pieces of "patio door glass" tempered 34" x 77') and my plan was to build double pane panels on the south wall. I also planned on passive solar as primary heat. I need to do some more reading, thanks for the links.
Al
Thanks for taking the time to provide such an excellant resonponse to my questions/w3tcompact/icons/smile.gif I am in the Pacific Northwest and don't have to deal with the temperature extremes that perhaps you do. I squared a deal sometime ago for a bunch, (24 pieces of "patio door glass" tempered 34" x 77') and my plan was to build double pane panels on the south wall. I also planned on passive solar as primary heat. I need to do some more reading, thanks for the links.
Al
dummy
Platinum Member
- Joined
- Jul 31, 2001
- Messages
- 730
- Location
- Southern Maryland
- Tractor
- Ford 1220, John Deere 770, Case 580E and Allmand TLB-35
Don't know about the rest, but I would like to see some more pics. of your project / site. What about construction time and crew size?
The "construction crew" was my wife and I. She handed me tools and I built it. It took about six months to build but if course that was part time and interrupted by bad weather and life in general. I stayed at it pretty steady, though. Needless to say, it's slow goin' with a one man crew. The entire structure is put together with stainless steel screws which adds to the cost and the build time but I thought it was worth it. There's not a single nail in the place! I will take some more shots of it tomorrow and post them.
scruffy
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TonyC, the only BAD thing about that one-man crew, is you can't fire the joker when he goofs off! /w3tcompact/icons/laugh.gif (Due to other influences) i.e. when the wife wants to go somewhere. (Mine doesn't drive, or go out of the house unless I take her.)
dummy
Platinum Member
- Joined
- Jul 31, 2001
- Messages
- 730
- Location
- Southern Maryland
- Tractor
- Ford 1220, John Deere 770, Case 580E and Allmand TLB-35
But the really good thing is, no one else to blame when things go wrong. Besides, look at all of that good quality time you get to spend with the wife that way. I might get mine to help once her nails are dry, but then she would need a hand and power tools 101 lesson. (yes dear, sometimes a drill is also called a screw gun I don't know why, just hand me the @%&^ thing.)
scruffy
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I must admit, my wife has been quite 'handy' when it comes to working projects with me. Even if she DOES wake me at 0dark30 on Saturday morning to work on a project she wants to get done!! /w3tcompact/icons/smile.gif At least she's 'up and attum' with me! Of course her timing is exquisite, she makes it out about the time I get finished....you know,those household 'chores'. /w3tcompact/icons/wink.gif
PaulInMi
Silver Member
Looks great Tony. I too would like to some more pictures.
Paul
Paul
