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Greenhouse Insulation Questions  RSS feed

 
Jason Warren
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I have a 48 x 24 greenhouse with poured concrete walls. Heights: North wall is 9' tall and south is 4' tall. Entry way is 2' above footer. Everything will be back filled to 1' from top of wall except for the entry way which will be back filled to the top of the wall. We installed a 3' outside grow bed to insulate the south wall. The north wall has three 1200 gallon fish tanks built into it. I'm insulating all walls with 2" foam board on the outside attached to the seal plate. The complete fish tank / back wall system is on a 7 x 48 slab 12" thick and should act as a massive heat sink. My hope is to use the ground and concrete to help regulate the water temperature and therefore the temperature inside the greenhouse. I might use floating rafts aquaponics to help insulate the fish tanks further.

For the back walls should I turn my 2" foam board sidewise insulating 3' underground or turn it upright insulating 7' underground? Should I trap more heat within the concrete walls or exchange more heat with the underground soil?

I will have a french drain around the foundation which runs 50' underground to a pond. This drain is a minimum of 2' underground. I'm sloping the back fill away from the structure and capturing all rain from the roof, however the ground does seep water as is evident since its been opened. Does anyone want to guess my heat loss to the 4" outside exposed air column encircling the building or the fact that the ground seepage water will suck away some of my stored heat as it flows down hill through the drain?

Thank you,
Jason
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Greenhouse from entry way
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Grow beds
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South Insulation
 
Jason Warren
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7 foot it is

Hold more of the heat in the concrete block and concentrate it at the base of the fish ponds.
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Back Wall Insulation
 
Nick Kitchener
Posts: 477
Location: Thunder Bay, Ontario, Canada
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That's an interesting design.

Personally, I'd be looking to couple your thermal mass to the earth. I strongly suspect that your biggest issue will be keeping this thing cool in the summer rather than warm in the winter, and once all that concrete heats up, you're pretty much screwed.

Come to think of it, is there any situation where isolating thermal mass from earth is desirable? Maybe in permafrost regions??

In hot regions, you want the relatively cool earth to sink heat.

In cold regions, you want the relatively warm earth to provide heat.

The objective is to maintain an even temperature that is suitable for growing the types of plants you want to grow. Tomatoes like a different temp range that broccoli for example.
 
Adam Moore
Posts: 123
Location: Mansfield, Ohio Zone 5b percip 44"
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Here is an example of a passive solar home that also recommends insulating the outside. It's not a greenhouse but close. https://www.thenaturalhome.com/passivesolar.html
 
Jason Warren
Posts: 26
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Adam - thank you for the link. It looks like they are insulating down to the footer as well.

Nick - Time will tell on the concrete heating up too much, if it does I will have to cross that problem when I come to it, even if it means ripping out some of the insulation

Here are my thoughts:

Concrete to Earth: Three of the concrete walls are on a 3' wide x 1' thick footers that are not insulated, the back wall has 3000 gallons of fish tanks integrated into it and the whole fish tanks / back wall system is on a 7' x 1' thick slab also not insulated. The back wall is 9' high insulated 8' so the bottom 1' of wall to the outside plus all the footers are touching earth. The back wall which will absorb most of the heat is going to easily transfer the heat to the 3000 gallon fish tanks which will trade warmth with the earth through the bottom pad. Do you know how much earth you can affect radiating out from a slab?

Sun exposure: My ridge is almost in the middle of my greenhouse, 1' closer to the back wall. My north roof is insulated and my south roof is pitched at a 45 deg angle. During the winter months the sun is shining almost dead on the south roof with an expose profile of 18 feet. In the summer time, the profile reduces to 13 feet at a 20 to 40 deg angle to the sun. This reduced profile and angle to the sun in the summer was part of my design theory to reduce heat. In the summer the complete back wall and fish tanks should not receive any direct sun although the use of Solexx will disperse the light. The Solexx which disperses light and has a 2.1 R factor should gain and loose a lot less heat then a comparable single wall plastic hoop house.

Inside temperature should regulate one way or another between 50 and 100. So I don't think the concrete will warm much past 85 deg. At 85 deg, I don't think it will be detrimental to plants would it? I might change the weather from winter to summer so I can do cold weather stuff 5 months and warm weather plants 5 months. I plan on doing citrus and other plants that can handle a 50 to 100 deg swing between winter and summer. I can regulate the concrete temperature by testing the fish tank water and adjusting ventilation accordingly.

I thank both of you for your responses.
Jason
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Zach Weiss
pollinator
Posts: 296
Location: Montana
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Great looking project! The horizontal insulation would be advantageous, particularly in the summer, as it provides a larger heat buffer. However if you are going to heat the water then vertical insulation is preferable; otherwise you'll just be trying to heat the ground.

The Solexx should really help with overheating in the summer. I think that much like with earthships the toughest time of year for you will be the fall. The solar cycle is advanced of the season cycle. In the fall when temperature are still high the sun is quite low and structures like this can get really hot. What is your plan for ventilation?

Is the foundation concrete block or poured concrete? If it's block with a wall that high and groundwater you should probably have pilasters for the north wall to prevent damage from the force of the water and soil on the wall.
 
Jason Warren
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Thank you Zach,

The walls are 12" solid poured concrete. Rebar 12" horizontal and vertical. The back and front walls have two courses of rebar 12" x 12" four inches apart. The fish tank along the back wall is 4' high and has two cross section walls tying into the back wall at 16' and 32' adding additional support. I also placed a 4" drain pipe and 2' of drainage (round) rock so the water on the outside doesn't back up against the wall. Next spring after the fill dirt settles I will reconturing the landscape to slope away from and around the structure. I should also plant some water loving plants or shrubs along the north side to soak up water.

I'm hoping not to have to manually heat the water. Blue Talipia can survive down to 60 deg and with the earth temperature at 55, I hope to maintain my water temperature at 70 to 75 with the building staying above 55 deg in the winter. I have 3000 gallons of water in the fish tanks, plus I plan to use 8 x 300 gallons totes (2400) as rain collection and base supports for my aquaponic grow beds. Another 500 gallons of water cycling through my grow beds at any one time. 5000 gallons of water cycling through the structure like a large radiator, picking up heat during the day and redistributing it at night. I also plan on using a blown air system for my non aquaponic grow beds to reduce humidity and as a heat battery.

I'm thinking I would like to aerate my tanks from the air up high in the peaks of the building thereby capturing some heat into the water. I'm not sure how much air or heat transfer that will bring.

The south side has 16 2'x2' window openings. I plan on having two large windows and two smaller windows on either end. One of the two smaller windows in each peak will support a ventilation fan. If I have to use the fans, I'll close the big windows and open all the smaller ones, so I'll be bringing air in across the whole south side down low and exhausting out the top two ends. I'm hoping there will be enough cross ventilation to not use the fans and just open all the windows. I will use fans inside to keep the air circulating.

I appreciate all your thoughts.
Jason
 
Zach Weiss
pollinator
Posts: 296
Location: Montana
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Sounds like you have a pretty stout foundation. I also like the idea of shaping the back-fill to pitch water away from the foundation, this is what I do with my greenhouses. I love the idea of water loving plants along the foundation, I've also heard of people using different herbs such as mint as disease control.

What is the mean annual temperature where you live? In some climates the earth maintains a consistent 55 but in some climates this is warmer, some colder. The temperature below frost like is on average the mean annual temperature for a climate. So for Bozeman, MT this means that the earth temperature is 44 degrees F. At the Krameterhof this is 4.5 degrees C. If you look up the mean annual temperature for your location, or average the mean high and mean low temp, you will find the approximate earth temperature for your location.

So I think you made the right insulation choice. If you were more tied into the ground you would be looking at heating the water for your aquaponics year round from 44 to 70 to 75. That's a lot of btu's. I'm guessing by your glazing angle that your in a northern latitude. So maybe looking at a 50 degree mean annual temp. If this is the case then like all aquaponics systems I've seen you'll have to heat the water. I've seen perch growing in unheated water, but they are much less tolerant fish than tilapia.

Fortunately there are a plethora of ways to heat water in an eco friendly manner. If I were you I would do a big Jean Pain mound to heat the water for the tilapia. This is a perfect system to meet your needs (steady consistent hot water) and could also be used to produce CO2 and compost for the greenhouse.

Love what your doing with the water cycle as a whole for the greenhouse, I think that will help a lot. For a passive ventilation system I've read that you need 2/3 of the ridge line to be vents. I would suggest using earthtubes and ridge ventilation to help keep the greenhouse cool in the fall.
 
Jason Warren
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HI Zach,

Thank you for all your useful information. Your website and greenhouses look great. I wish I wasn't so far away for a visit. I like the idea of the Jean Pain Mound for hot water and it would create compost for my garden beds as well. I plan on building a set of earth tubes after my ground has settled and I recontour the ground next spring.

I'm in North Western WV close to Central OH and lower PA. Our Average Mean Temperature is 52 deg F. When you talk about having to heat the water due to ground temperatures does the ground consistently suck heat from the building? I was hoping during the summer my fish tanks would rise to 75 deg naturally, how much of the earth under my tanks would be 75 deg by end of summer? 1 to 2 feet? Would it help keep my fish tanks warm during some of the winter. It will be an experiment to track the soil, concrete, water, and air temperatures inside and outside to see how they all play together. If I keep my greenhouse between 55 and 95 deg with the mean temperature at 75, shouldn't the concrete and water stabilize at 75 without additional heat? In the winter that might drop to 65. I plan on raising Blue Tilapia which I'm told can handle water temperatures down to 60.

The whole south side will be 2' x 2' casement windows, the sides will be various windows. I'm not sure yet how many I need to have automatic openers for. I've only see automatic openers for greenhouse type vents. Will these work for duel pane casement windows as well? If I came across your website earlier, I would have gone with a series of earth tubes and ridge vents. I might look at retrofitting these in next year. For starters I will use my south wall vents and side windows with a 24" exhaust fan in the peak as a backup.

Thanks Again,
Jason
 
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