Hi /diy/, i am about to invest ~$20,000 or less in building a commercial greenhouse on a virgin plot of land in Alaska.
it needs to be around 2,500 square feet. i'll be using automated fan systems attached to thermometers, coupled with well-placed ventilation in sides and roof to cool the greenhouse and provide adequate air flow.
my biggest design problem at this time has to do with heating and cooling. how to design the greenhouse so that i don't end up with pockets of hot and cold air? how to keep it uniform? once you get over a certain square footage, you cant simply blow air through the whole thing, the cool air heats up by the time it gets into the middle because its too big and hot.
i was thinking of making it very elongated, and instead of the exhaust fans pulling air in all the way down at the end, have them periodically spaced along one of the long walls and have vent opening on the opposite walls.
the only problem then is that i have to buy more fans, set up more thermometers, and use more electricity, upping my initial costs. not to mention ill have to frame those extra fans into something solid!
alaska provides an interesting challenge for commercial greenhouses because the summer season has nearly 20+ hours of daylight every day, and the winter has as little as three hours of daylight per day.
In order to induce flowering in my plants, i'll need to cover the greenhouse every day at certain points in the grow cycle during the summer.
i'll also have to use supplemental lighting and a furnace of some kind in the winter.
Most large greenhouses do what you're describing, with fans every 7 feet or so on the side walls.
For winter heating you'll probably want to go with something reliable. I've seen commercial greenhouses use basically oversized radiators stretched along the walls. Maybe work out something like that where you pump hot water into a radiator.
Alaska isn't the best place to greenhouse due dark/cold autums-winters-spring. The cooling part is somewhat easy, large commercial greenhouses uses evaporate cooling, which is cheap. You can buy these supercheap from alibaba.com
You may want to look into chinese style greenhouses
They use an earth or brick wall to the north that adds insulation and thermal mass, so you have a longer grow season.
They usually have automated isolation covers for the nights, so the temperature stays up.
You can supplement the thermal mass by adding water containers in front of the north wall.
Bonus point for using them to grow fish and establish a aquaponic system.
For heating and light, you have several options.
Energy from the grid will cost you big time.
Solar will be mainly there, when you have enough light anyways, so you would need a big battery bank, that will be expensive.
A small scale hydro electric turbine could supply you with sufficient, reliable electricity run a big number of grow lamps, if you have a suitable stream nearby.
A biogas reactor can supply a gas powered generator which in turn produces electricity for lights, heat and even CO2
You can also build a rocket mass heater and use wood for fuel.
Another possibility is building a passive solar greenhouse adding isolated thermal mass underground and heating it up by pumping hot air from the top of the greenhouse inside, whenever the sun is heating up the air in your greenhouse.
Your air inlet should be going through a long pipe buried underground, so the air is preheated in winter and cooled in summer by the ambient temperature of the earth.
I wish you all the best with your project! Keep us updated!
Do aquaponics or aquaculture. Then you have a massive amount of water ( ideally in ground) to act as a thermal mass in the g house.
This can help stabilize temps.
During winter, get some black pipe or whatever and run the water through it, letting the pipe coil somewhere to solar heat.
put some steel wool in a glass bottle and set up a magnifying glass to heat the metal-> water inside...rig that together somehow.
But aquaponics srsly.
You can increase thermal stability by adding mass into the space as suggested. Water for aquaponics is ideal because it will serve two purposes. And long floating raft trays for lettuce growth are cheap enough and easy enough to DIY together for very high profit margins.
Always remember to get ahold of your local agricultural extension office and network with other farmers and growers to tap into their local wealth of knowledge and experience.
If you go through with this, try and build business relationships with local restaurants, preferably in the higher end markets if they exist there.
I sell to six local restaurants and the farmers market. The restaurants, they're my bread and butter. They get seasonally curated veggies fresh daily for their menus and they provide regular income. My highest profit margin by far is my lettuce.
if things are warmer the deeper you dig into the earth
I wonder about building a subterranean greenshouse with vents on the top, since heat rises, and some mirrors and reflectors at the top to bounce enough light to the plants.
I also have no expierence with building and designing greenhouses, so Im sorry I can't be any more help.
what is a 'large' greenhouse to you? is 2500 sq feet large enough to need to space out fans like we are talking about here? ive seen some models that stick with the fans and vents installed into the ends rather than the sides for the size i am shooting for, which has me doubting...
the water and earthen north wall is a good idea, but only if my ventilation travels down the length of the greenhouse instead of across its width.
a radiator might be a nice idea, not sure. i'll look into it.
if i can do a gas-heated radiator that also produces co2, like >>1022390 mentions, that would be ideal. wood is too finicky for me, ill need to be able to move off-site during the winter. cant be in there all day and night tossing logs in and taking the temperature.
passive heating would be ideal, but i dont think ill have the sun for that when i need it most.
ill be in the south of the state, so it doesn't get terribly cold. im in probably the most temperate part of the state, fortunately.
thanks for the evaporative cooling tip!
i have been on the fence about aquaponics.
thanks everyone for your input, i will check back to this thread every once in a while and keep you updated as the project progresses!
>passive heating would be ideal, but i dont think ill have the sun for that when i need it most.
That's the beautiful thing with well build passive solar.
The underground thermal mass storage will -if designed and build properly- hold the heat for many months. You can heat your greenhouse in january with energy that you captured in august! And it will cost you just the energy you need for a fan and a few control systems.
Pic related goes into passive solar greenhouse design.
The greenhouse shown on the cover is located on 7000 feet in the rocky mountains