Attempting to build a passive year round greenhouse in Colorado at 9k feet

I'm attempting to build a greenhouse that I can grow out of year round in Colorado at 9k feet - and 'passively' (no mechanical heating assistance). I'd like folks ideas on my design below, specifically the following question:

- Will the window locations / sizes allow enough direct / indirect sunlight throughout the course of the year to allow the plants to grow?

Examples of current direct sunlight coming into the room in Winter, Spring/Fall, and Summer (see pictures)





Background:

Home location: Near Cotopaxi, CO @ 9k feet, south orientation, no shading

Greenhouse is a 16'L x 10'H x 35'W area within an oversized garage 50'L x 10'H x 35'W and 3' awning overhang (see picture below).

Heavily insulated / airsealed
- Triple glaze glass
- Insulated shutters that close at sunset and open at sunrise
- R60 in the attic, R30 walls, R20 under slab

High thermal mass
- Full concrete slab
- 3 concrete cisterns holding a total of 12k gallons of water

Hi Darin
Short answer is no. You will not have even close to enough light to grow food. I believe that you absolutely need some overhead sunlight to grow food indoors. Maybe you can grow a few leggy leafy greens, but they will not be particularly happy, and probably not very nutritious either.

I highly reccomend checking out CRMPI in Basalt. They have a website, crmpi.org They are masters of high altitude greenhouse design. I just came back from a weekend design course there, and the amount of understanding they have about passive solar greenhouses is incredible. Check out their info, and arrange a visit during one of their public tours if you at all can.

Greenhouse growing is awesome. I am a bit lower than you, but I grow food year round at 6200 feet, in an off-grid, totally passive greenhouse. It is wonderful. Thing is, there are far more ways to get it wrong than to get it right. It is great you are looking for solutions now, rather than fixes later. Keep up the good work, the results will be worth it, I promise. Good luck!

I was hoping against that, but had a feeling that might be the case....

If that's true my options are?
1) Put in some overhead windows (per normal)
2) Maintain the ceiling integrity and reflect light in with tiltable mirrors outside the window

I'll check out the site you mentioned, was not aware of that - thanks for the tip!

Hi Darin. I am an eco architect and working on building my own eco home with integrated greenhouse as we speak. Have you looked at the earthship design? They have a green house component, and I would say that is about the minimum over head glazing you can get away with before it is not enough. Simply put, at least 30-50% of your grow space needs to get summer sun and obviously that would mean it gets good mid season and winter sun also. You could get away with less, but remember, without direct sun, most plants will not thrive.

Have you looked at growing micro-greens? I have 2 an indoor shelf units that I grow micro greens and sprouts, mainly sunflower, pea, soy, buckwheat and wheat grass, mung beans and depending on if you can get a cheap bulk supply of other seeds such as radish, broccoli, then them also. The great thing about these is they don't need much sun, actually for 40-50% of the growth, no sun to indirect light. I supplement the sun with LED grow lights for a few hours a day towards the end of the growth which is, depending on the crop, 10-14 day growth cycle. Micro-greens and sprouts are pretty much the most nutrient dense foods per gram on the planet and great to keep you going over the winter months and supplement your regular diet. Also look at other plants like the New Zealand spinach that like half sun. If you have never grown sprouts or micro-greens, you need to do a little reading, as it is important to harvest them before they start using much of their potent energy to change to an adult plant. Try http://www.hippocratesinst.org/ for some light reading for a start. Also mushrooms are great for your situation at the back of your green house around the water tanks.

Hope that helps a little, keep on growing!!

Chris

adding to my last post, the ultimate would be an insulated retractable roof/awning cover that you can move depending on the season. Now that would rock totally!! Trick would be to make one cheap enough to warrant it.

Chris Jose wrote: Simply put, at least 30-50% of your grow space needs to get summer sun and obviously that would mean it gets good mid season and winter sun also. You could get away with less, but remember, without direct sun, most plants will not thrive.

That's great info. So if my 'grow space' as allocated in the design is 16'X35' then I would need between 168 to 280 sq ft of glazing overhead to meet that 30-50% number, sound right?

Chris Jose wrote:Have you looked at growing micro-greens?

Never had, and that sounds like a great option. I'll research into that further, thanks!

And in an original design with overhead windows I was trying to figure out how better to insulate them in winter months. The retractable insulated shades on the vertical walls works great, but with the snow I'm expecting they won't do for the roof I'm afraid (at least externally). I'll have to explore if that can be done internally under the glazing for the overhead sections, or maybe just a manual insulated panel for the winter months.

Great tips, thanks!

If you make it a little less passive, as in use shades and movable awnings instead of the fixed overhangs, you can do better. Insulated shades also reduce night losses, so they can be a double use.

Hi Darin,
i am not much help with greenhouse design, but you may want to contact Penn and Cord up near Westcliffe.
They live is a similar high altitude setting and design solar greenhouses. While they generally build standalone greenhouses, they may have some ideas that help you build on onto your garage.

Here is a link to their website: http://pennandcordsgarden.weebly.com/greenhouses.html

If you have lots of outdoor growing space and only want to use the indoor for seedlings to get an early start and not really require it to be fully productive during summer due to the out door crops, I would definitely make less than more with the overhead glazing perhaps enough to light up one 2 foot wide raised bed alone the very south edge of the green house. That is sort of a compromise, so it really depends on budget verse how much you really need the green house working for you. So hope that answers your glazing question.

Excellent thoughts and ideas, thanks again to everyone for their thoughts.

After reading more on the sites folks have linked, I've done a substantial rework to the design as seen in the picture below. I'd like again for folks comments on if this will function decently:


Special notes
- More of a typical 'slant' greenhouse integrated into the garage space. I 'superimposed' the greenhouse outline over the house framing that will be adjoining it for better understanding of the intended integration
- Blue indicates glazing, green is external framing areas, pink is internal framing areas
- Raised beds are 3' in height for ease of access and wider options for planting (root profiles)
- Glazing slant pitch is recommended 45 degrees for summer sun deflection, snow shedding, and better moisture deflection (less condensate on higher pitch)
- Upper area is essentially a 'chimney' leading to automatic windows triggered based on humidity or temperature
- Solar coverage on the growing beds will be 100% in winter, decreasing down to roughly 60% direct sun in the height of summer
- Minimizes the amount of glazing required which then increases the insulation levels (attic space is R60)
- Rolling insulated shutters on all glazing for insulation and security

To address some questions / comments on my application:
1) Intention is year round growing potential, I need to be able to have a reasonably productive garden year round
2) I understand there is overkill in this design (like the rolling shutters). But this house will be my residence for the next 4-5 decades and it's worth the additional consideration

Way to go at it Darin,
Here are my thoughts on the upgrade-

Ventilation is going to be a critical consideration. The ceiling chimney will not dump hot air fast enough, IMHO. It is very easy to fry your plants in a greenhouse. Cross ventilation from the two ends of the greenhouse is a key design feature that is almost always used.

Being able to open a door between the greenhouse and your house is a great way to moderate the temps. You can let warm humid air into your house in winter which is great. On cold nights you can keep the door open to keep your plants warmer. Problem is in summertime, hence the need for tons of cross ventilation.

Your back bed wont get enough light. The plants there will be stunted, leggy, and leaning diagonally toward the front of the greenhouse. The sun angle is one consideration, but overall light levels matter a lot too, and it will be noticibly darker in the back than the front. There is something critical about overhead light that seems to be a big determiner in the success of a greenhouse design. Windows alone rarely get the job done.

Having seen a lot of integrated greenhouses, there are a lot more ways to fail than to succeed. The tiniest differences can make the difference there. I would really reccomend copying a design that has proven successful for others, especially if you envision using this for decades. Attached greenhouses have the benefit of staying warmer at night, but often are solar ovens during the day, even in winter.

Finding ways to minimize the temperature differential from day to night, while allowing ample light levels, is the challenge of greenhouse design. Strategies like CRMPI's climate battery are genius for that.

Sharing a wall with your house is a good idea. I would reccomend having a polycarbonate south wall and ceiling. Have the north wall shared with your house. Keep your depth at 16 feet, that is a good dimension. South wall at 7 or 8 feet. Roof pitch anywhere from 4:12 to 6:12. Interior curtains are an excellent strategy for cold nights. Some shade cloth can be very good in the summertime.

Just some thoughts, sorry not super coherent nor concise. Hope they help.

Thanks for the thoughts and inputs, I've adjusted the design to try to allow better ventilation, light coverage, and light diffusion. Again, inputs are welcome!

Adam Klaus wrote:The ceiling chimney will not dump hot air fast enough, IMHO. It is very easy to fry your plants in a greenhouse. Cross ventilation from the two ends of the greenhouse is a key design feature that is almost always used.

By adjusting the pitch to a 5in12 I was able to increase the chimney window height to 2' tall and given this extends across the 35' width this seems to be a decent amount of airflow potential? Also increased the chimney size to 3' to further increase that airflow.

Adam Klaus wrote:Problem is in summertime, hence the need for tons of cross ventilation.

While difficult to tell, there will be awning windows in the lower vertical window wall to allow air inflow. There will be some similar ones on the east side wall. The west wall is connected to the house and for use in fall / winter when needed.

Adam Klaus wrote:Your back bed wont get enough light.

With the slightly lower pitch I've been able to extend the direct sunlight potential into the back bed. This combined with the opaque glazing to better diffuse the light across the space will hopefully address this?

Adam Klaus wrote:Finding ways to minimize the temperature differential from day to night, while allowing ample light levels, is the challenge of greenhouse design. Strategies like CRMPI's climate battery are genius for that.

The large concrete thermal mass, the 12k gallons of water, and the large adjoining open garage air space was intended to smooth temperature fluctuations - were you referring to something else or you don't believe that in conjunction with the ventilation is sufficient?

Adam Klaus wrote: I would reccomend having a polycarbonate south wall and ceiling. Have the north wall shared with your house.

I did update the slanted ceiling to twin wall opaque polycarbonate, but was planning to leave the lower vertical wall glass for the longer lifespan even though the higher cost ( comparison here) - I also need the vertical glazing to be able to have awning style windows for ventilation. Good plan? As for the north wall, that simply extends into the garage (see picture in initial post) to attempt to leverage the thermal mass in concrete, water and air.

Really, a lot of my thinking is just shooting from the hip based on experience, so take it for what its worth (a grain of salt). Greenhouse design does fascinate me though, so there is that.

Overall, something just doesnt seem right to me, and I think that is the ceiling height, which is determined by your front wall height. The distance from the ceiling polycarbonate to your plants is very small, and I think will result in fried plants. I think this is a major consideration. I think the front bed will cook, the middle bed will grow pretty well, and the back bed will be light starved.

I think there still is a ventilation issue. CRMPI and others have a formula about how much venting to glazing ratio there should be, I dont remember off hand, but definitely check that mathematical relationship out. I understand the lower air entry vents, and the upper chimney vents. But I think you should seriously oversize your venting capacity, especially since cross-ventilation is not possible with this layout.

Doing glass on the wall and polycarbonate on the ceiling is a decent combination. I would definitely use triple wall polycarbonate at the least for the ceiling, and at your altitude, I would go with the quad wall polycarbonate. The cost will be minimal as a proportion of total project cost. As far as the glass wall goes, your plants in the front bed are going to fry in the wintertime. Polycarbonate cuts 20% of the light, and diffuses it as well. But glass is super hot in terms of the light it allows into the greenhouse. In the summer, the sun angle will mitigate this. But in the winter, it will be a problem for the front bed, IMHO.

Just my three cents, there are definitely others with more expertise than me. Given the cost and importance of the project, I would really reccomend paying a professional consultant for a couple of hours of their time. It will be the best two hundred dollars you spend on this project.

I've reached out to CRMPI to do a review of the designs, hopefully a ounce of prevention is worth a pound of cure

Thanks for all the inputs from everyone, comments are always appreciated!

Hi again Darin, I am not sure if Adam is taking into consideration that the green house is a part of a total area 3 times bigger, so more air space to take heat away, so based on my initial thermal gain calcs, you shouldn't have issues with overheating or ventilation that is assuming you are leaving the greenhouse component fully open to the rest of the building. If you don't mind only having 2 out for the 3 beds properly growing in the summer months, I would keep with the first 6 in 12 pitch as it gives a little more protection, for a few reasons. 1. less solar heat gain in the summer (although I think due to the lower opening windows and the huge combined area of the garage etc which has huge garage doors for additional cross flow and that you have the entire 35 foot long upper vertical window exhausting, I really can't see any issues, worst case you can add a little shade cloth in the peak of summer); 2. less thermal lose in winter due to smaller glass area, and better pitch for snow clearing; 3. you will be between the 30-50% of the roof glazed which is closer to the ideal in extreme climates. You have lower temperatures at that altitude, so insulation is important. I am based in Kiev, Ukraine, summers average 30-35 C, winters average -10-12 C but can get as low as - 25 C so I have to have a rocket mass heater with pipes heating the beds. As long as the roots stay warm enough and the air in the greenhouse doesn't freeze, I am confident I can grow more than just kale, brussel-sprouts and broccoli during the winter .

This is just my opinion based on my extensive research, and as I said from the beginning, it is important to find a reasonable balance in extreme climates. Life and design is so much easier in mild climates.
Perhaps I will move south in the future.

Chris,
The biggest difference between Colorado and Ukraine is the intensity of high altitude sunlight. It is a force to be reckoned with. I am at 6200 feet, and the difference from here to 9000 feet is huge.