Hello
My name is Ryan and I live in Central Michigan where we have what I would say to be mild winters. I built a 10' x 16' greenhouse with "3/8 plexiglass sheets and double walled with plastic. The ground however i dug down 3' and dug 13 yards of material out then insulated with "8 of poly iso foam insulation on floor and walls makeing a tub with an r value of 44. Then refilled with 12 yard of Morgans Dairy Doo compost top soil. Now I heat via hydronic threw pex lines through the floor. I can heat the soil to water I what and would like to keep as warm as possible without killing plants so what would be okay in the winter as far as root temps? By the way I've heated the soil to over 90 degrees before very easily. Below are pics

This is really fabulous Ryan! You should post photos of your great set up on the Greenhouse forum. I bet a ton of people would love to see your set up. If my GH was not so large and old (it was built in 2003 and is 48 x 36 and now fully planted as a tropical jungle) I would have done something like this

You don't say what you are growing but most plant roots like temperatures of about 70F (+ or - 10 degrees) . Soil microbes start dying after 90F. My greenhouse is heated with solar hydronics but I have a concrete slab with the coils under the concrete. I had to add more tubes to one wall to keep my plants totally happy (its a lean-to so more coils to the house wall). I'm just trying to keep the air temperature above 55 - 60F. It seems to me by making the soil your heat sink, you may cook some roots to keep the plant canopies happy.

I hope you have a way for the foundation to drain, otherwise, you will have a swamp.

PS: You can 'Suggest a Change' to move this thread to the Greenhouse Forum or ask @Calif_Sue to do it for you. Its great to hear from someone who is doing the same thing I am.

Gina1960 said:This is really fabulous Ryan! You should post photos of your great set up on the Greenhouse forum. I bet a ton of people would love to see your set up. If my GH was not so large and old (it was built in 2003 and is 48 x 36 and now fully planted as a tropical jungle) I would have done something like this

Thank you Gina and I will do that and im sure after a few years of running it ill find things I wish I would've done different. But that just how you know trying cause can't make a greenhouse mistake with no greenhouse. Best of luck to you this season

DaisyI said:

You don't say what you are growing but most plant roots like temperatures of about 70F (+ or - 10 degrees) . Soil microbes start dying after 90F. My greenhouse is heated with solar hydronics but I have a concrete slab with the coils under the concrete. I had to add more tubes to one wall to keep my plants totally happy (its a lean-to so more coils to the house wall). I'm just trying to keep the air temperature above 55 - 60F. It seems to me by making the soil your heat sink, you may cook some roots to keep the plant canopies happy.

I hope you have a way for the foundation to drain, otherwise, you will have a swamp.

PS: You can 'Suggest a Change' to move this thread to the Greenhouse Forum or ask @Calif_Sue to do it for you. Its great to hear from someone who is doing the same thing I am.

Thank you for the reply and I did put drains in down below so the water could evacuate. And thank you for theinfo I was unaware of the microbes at 90°. And your setup sounds much larger but sounds to be an efficient way to heat. I did forget to post up what I plan to grow. I have numerous dwarfe fruit trees and alot of strawberries along with many other vegetables, herbs and flowers.

Hi Ryan and welcome to the forum!

Very impressive setup! Unless I missed it, how are you heating the water you are running underneath?

And, you are very right. After running your greenhouse for a while, you will find things you wish you had done differently. We all have! But, that's part of the fun of a greenhouse. I am always tinkering with ways to improve upon what I started off with. Enjoy and learn.

Jim

MoonShadows said:Hi Ryan and welcome to the forum!

Very impressive setup! Unless I missed it, how are you heating the water you are running underneath?

And, you are very right. After running your greenhouse for a while, you will find things you wish you had done differently. We all have! But, that's part of the fun of a greenhouse. I am always tinkering with ways to improve upon what I started off with. Enjoy and learn.

Jim

Thank you Jim its been a long time preparing but I heat with a hydronic setup otherwise known as radiant heat. I use a on demand hot water heater on propane to heat a mix of water with a tiny bit of aintifreeze

Lienpainters2 said:
Thank you for the reply and I did put drains in down below so the water could evacuate. And thank you for theinfo I was unaware of the microbes at 90°. And your setup sounds much larger but sounds to be an efficient way to heat. I did forget to post up what I plan to grow. I have numerous dwarfe fruit trees and alot of strawberries along with many other vegetables, herbs and flowers.

What kind of fruit trees? Tropicals will appreciate the warm feet but anything Prunus or Malus will not.

Here are a couple photos of my floor (2014) before concrete and now. My greenhouse is 6 feet wide and 23 feet long. I am growing tropicals, mostly orchids, on the east end and cactus on the west end. The side faces south.

I just LOVED your pictures and GH heating project, Ryan.

I think the on demand type gas heaters (which have gotten fairly affordable these days) are well suited; their usual durability problems are all associated with open systems and water minerals; for a closed system like yours that's a non-issue and it should perform well for a long time without descaling.

Because of the HUGE losses at night from the glazing, you may have issues air temp issues, (more likely just with gas consumption) though at least you have a fabulous lack of loss to the earth, which by reported data accounts for 1/3-1/2 of the thermal loss besides the upward/outward loss through the glazing for typical GH's.

I'd love to see you tackle the glazing loss via some method(s) such as insulated panels or soap bubbles. It's a difficult task that few have tackled. You clearly have the right stuff for it.

I'm a retired EE/CS guy, and appreciate the technical side of things more than most. I say BRAVO to you and your GH project!

BruceM2 said:I just LOVED your pictures and GH heating project, Ryan.

I think the on demand type gas heaters (which have gotten fairly affordable these days) are well suited; their usual durability problems are all associated with open systems and water minerals; for a closed system like yours that's a non-issue and it should perform well for a long time without descaling.

Because of the HUGE losses at night from the glazing, you may have issues air temp issues, (more likely just with gas consumption) though at least you have a fabulous lack of loss to the earth, which by reported data accounts for 1/3-1/2 of the thermal loss besides the upward/outward loss through the glazing for typical GH's.

I'd love to see you tackle the glazing loss via some method(s) such as insulated panels or soap bubbles. It's a difficult task that few have tackled. You clearly have the right stuff for it.

I'm a retired EE/CS guy, and appreciate the technical side of things more than most. I say BRAVO to you and your GH project!

Thank you Bruce!
I feel theres a unspoken connection between individuals who have an affinity for something and those are the connections we don't just learn from we actually prosper and thrive on.
My biggest battle right now is heatloss going up and out because even though double wall insulated with plenty of circulation the R value is just not there.. so even though the soil reads 60 degrees at the floor the air could be as low as 35 degrees. I have no auxiliary heat so my plan is to buy a water to air heat exchanger and blower to heat the air itself. But with that said right now my soil temp 3 ft down is 91 degrees which is required to hold 60 degree top soil temp.

I'm not sure any of the rest of us are welcome in the conversation anymore but just thought I'd mention Insulating Bubble Wrap before I left.

""right now my soil temp 3 ft down is 91 degrees which is required to hold 60 degree top soil temp"

Ouch, that's a healthy delta T over 3 foot of soil dept. Thanks for sharing your data! In studies I've read, reflective overhead curtains in standard commercial greenhouses cut losses by half (and don't have your earth insulation) , so some inexpensive experiments with mylar space blankets taped together, draped over rope or wire might provide some very interesting data.

Bubble wrap is a good mention; it's used in small greenhouses here in fall early winter and adds roughly another R of 1 added to an R of 2 for double wall. Helpful for a modest improvement. My favorite local GH vegetable grower uses external insulating panels in winter for all the sloped S glazing. (A passive solar design- heavy perimeter insulation, R19 insulated North wall and 3/4 of the roof area.) The removable outside insulated panels are lots of work every day but are effective. Exterior insulation is also good for extending the life of the GH structure; the structure stays warmer and doesn't ice up at night. It's difficult to implement in an automated, low labor fashion.

A water to air heat exchanger with fan as a unit are pretty common and reasonably priced last time I checked, and a good value considering the engineering for efficient fan/motor, fin tubes. Again, with a sealed hydronic system, long life and little trouble. I think it's a good idea in trying balance your soil and air temps.

Living in the mountains at 7600 ft/2300 m, I decided to build a four-season greenhouse that would collect and store sufficient heat to winter tomatoes and such.

I began by digging out a 1 meter hole, then pouring footers and using foam-insulated forms for the walls of the foundation. The base was 2-inch foamboard covered with Reflectix roll insulation. It was filled halfway with pea gravel and then with a layer of coarse sand. I laid drainage pipes, but no water has ever drained.



It was partly framed using lumber from the shed that I tore down to clear the spot. The roof is 6-wall poly (R 3.8) and the sides are 3-wall. The flate plate solar collector was salvaged and fixed. It's plumbed with PEX tubing, charged with a 50% glycol solution (it gets down to -40° here) with a PEX coil through a 400 gallon stock tank, filled with water, under the floor. The collector loop is pumped with a Laing EcoCirc DC pump driven by a 20W PV panel set at the same angle as the flat plate collector. When there's not enough sun to heat the solution, the pump shuts down.



The water in the stock tank is circulated with a Taco AC fishpond pump through a maze of PEX tubing in the floor. It was then filled to grade with coarse sand. Even in the coldest weather the floor maintains about 55-60°F, which helps to heat the inside air.



Beds were framed with recycled plastic lumber and I added black brick pavers in between. Above the heatsink, the floor is chipboard covered with black rubber shop mats.



The other passive elements are four black plastic wall tanks, which absorb solar heat and radiate about 8-15° each cold night. They're filled with a garden hose and are the source for watering plants etc. So I didn't need further plumbing.



The active heat is partly AC electric. I took apart one of those radiant patio heaters and mounted the 500 watt tubes on the ceiling, to warm the foliage, activated by a thermostat. For extreme, extended cold, I hook up a small propane tank outside and run a Buddy duckblind heater on low. I also put foam blocks over the corner vents, which leak cold air.

I'll cover the ventilation in a further post, if anyone's interested.

I really appreciate your writing about you greenhouse, Chip. It is a tour de force of deep winter greenhouses, given your elevation and latitude, and a very thoughtful design using affordable flat panel collectors, in floor heat and water storage to maximize solar and minimize power use. Do you have some data on your supplemental AC heating cost and the SF of the greenhouse?

Are you using supplemental lighting as well? The number of cloudy days with cold here is often a problem in late Dec through early Feb; vegetables just go dormant. Takes them 4-5 days or so to get going again during a sunny/warmer stretch. I'm wondering if your approach with warmer soil temps might help combat that dormancy.

I hope others will forgive my enthusiasm for more technical greenhouses. Those producing with a more keep it simple approach also have my respect, but as a retired engineer I really enjoy technical challenges and seeing how exceptional folks like Ryan and Chip have tackled them.

The quartz radiant tubes total 1500 W. The thermostat is set on 45°F. To calculate the power use, I'd have to log how many hours they're on each night, which varies from 1 to 10. But since we have a 4.4 kW PV power system, it's all solar. The PV setup was installed in 2011 and paid itself off two years ago. At this time of year we have banked power and our bill is about $32 per month for line charges.



There are also CFL grow lights on a timer, that I've not used his year, just to see if they make a big difference.



The aim of the design is to render the greenhouse as self-sustaining as possible.