Just charged and pressurized the solar heating system for the greenhouse, at 25 psi, which is good for a small drill pump. I've posted about this before, but here's a quick recap—

I found two flat-plate collectors in a salvage yard, one with cracked glass and another that appeared to have leaks. Swapped the glass and pressure tested the good one: bingo! Mounted it on a pole, angled for low winter sun. Plumbed it with PEX tubing and sharkbite joints. With good sun, the inlet temp can get up to 140°F. A small DC pump is driven by the 20W solar panel, at the same tilt as the collector. When the collector gets enough sunlight to heat up, the pump runs at a corresponding rate.


Because our winters are extremely cold (-40°F) the loop is charged with a 50% glycol solution. The inlet goes through a temp/pressure gage and down into coils through a 400 gal. livestock tank, the primary heatsink.


The water in the heatsink can get up to 120-130°F.


An AC pump (Taco, used for fishponds, etc.) circulates the warm water (more efficient for heat transfer than the antifreeze solution, where freezing isn't a problem) through a maze of PEX tubing under the greenhouse floor. That's two heat-conducting loops. I don't start the AC pump until there's a 10°F difference in the temps of the tank and the sand floor. I try to keep the floor at 55°F or above through the winter.


The insulated foundation goes down about 3 ft. Inside is a layer of 2-inch foamboard, 6 inches of gravel, and a fill of coarse sand. I installed a drain, but no water has ever come out. Having water held in the porous floor increases the heat retention.


There's a chipboard floor over the heatsink, with black rubber matting. The walking area is capped with dark pavers. The outer beds, sand, hold black containers for tomatoes and peppers, while the center bed is filled with soil, for cukes, beans, greens, etc.


Started up in 2010, with very few problems since. Last year, the DC pump failed, the collector boiled and ruptured the PEX tubing, and the antifreeze blew out. But I fixed it and it's working fine, let us hope for another ten years.

@subarctic That's quite the project Chip. Looks like a lot of thought and engineering went into the design.

Chip, I am in awe of your greenhouse system!

You have a world class deep winter greenhouse design, Chip. Bravo.
Bruce

A fine set up, Chip. Happy winter growing!

Besides our savage local climate, another factor in the design was that it be fairly self-contained. The only connection between the floor heating system and the home power is the AC circulation pump, which could be replaced by a DC pump on a solar-charged battery. But since our home power comes from a grid-tied PV system, it's all solar anyhow.

Same goes for the quartz radiant heaters on the ceiling, which are on a thermostat. For extreme cold nights, I use a small propane heater hooked to a portable tank outside.



The water source is four 75 gal. tanks, also passive heatsinks, which get filled with the garden hose, so— no plumbing connection! The water stays mostly at 60°F or above, which the plants like better than our 50° well water. It's nice to puzzle something out and have it actually work.

Chip, I salute you on the engineering and the rehabbing of the collectors! Very well done, all the way around!!!

-40F -40F -40F -40F -40F -40F -40F
...no, in so many ways.....no, for this ol' south Alabama boy who shivers a tad walking out in our current 56F temperature with a tee-shirt on.... -40F

Intheswamp said:-40F -40F -40F -40F -40F -40F -40F

Having gotten used to the metric system while working as a field scientist, I learned that -40°F is also -40°C.

One of those cool facts.

The only time I can remember it getting down to -40° here was way back in the mid 1970s; I had a 1975 Buick Skyhawk and when I drove out to go to work in the morning, when I turned onto the paved road from our gravel private road a couple of the tires came away from the wheel rims due to being so cold.

And this is why I continue to be so impressed by Chip's GH!

It's not frequent. Hasn't gotten that cold for a few years. We usually have a few nights at -30°F each winter.

Coldest I've ever had was -55°F when I was in a high camp in the Wind River Range in December. We had trouble keeping the stove lit, to melt snow for water and cook. Hunched up in our sleeping bags with our parkas , down vests, and all draped on top. Long night for sure.

I was younger (and tougher) then.

subarctic said:

Having gotten used to the metric system while working as a field scientist, I learned that -40°F is also -40°C.

One of those cool facts.

You're wrong. That's not one of those cool facts....that's a COLD fact!!!!! <BBBRRRRRRRRRR>

Quick update. The soil temperature at 8 AM today was 33°F. The soil temperature inside the greenhouse (same thermometer) was 58°F. With the floor circulation pump off, the water in the heatsink was 99.5°F. I'll turn on the circulation pump tonight. The greater the difference between the heatsink and floor temp, the more efficient the use of electricity.

marry me? lol. this is awesome.

I get it, but man, this makes my head hurt to consider all the details that had to go into planning this.

Like others i'm blown away by your design and fabrication of such a complicated system. All i can say is great work Chip, you done good.

Actually, it's just applied physics. No high pressure or temperature. Two pumps, one solar DC and one AC. Thermally driven vents. Lots of passive stuff such as the wall tanks.

I had to light the propane heater last night, with -20°F. With that on the LOW setting and the ceiling radiant heaters, it stayed in the mid-40s inside. The tomatoes look fine.

Chip, you've probably discussed it somewhere, but since I'm too lazy to search for it... do you use supplemental lighting in your GH during the winter?

We have clear air and sunny winter days. I've used 200W coil fluorescents, but didn't see a great difference in the plants. I still use lights on seedlings, to keep them from getting too leggy.

Took the last shadecloth off the roof. Recharged and pressurized the solar collector loop. The wee digital thermometer for the heatsink (400 gal. stocktank under the floor) has a dead battery, so 'll pick one up in town tomorrow.



The combination temperature and pressure gauge (old photo) on the collector loop is running at 25 psi and about 130°F midmorning.



A soil thermometer shows 60°F for the thermal mass of the floor.

The 13th winter for the greenhouse. So far, so good. 10°F last night. After a few sunny days, the solar collector loop had the water in the heatsink up to 94° and the floor up to 58°. When there's no sun, I leave the snow on the roof as insulation.



Thinned out the indeterminate tomatoes to let in more light. They don't produce as well in the dark of the year, but there's always a few ripe tomatoes to be had. The greens in the center bed sprouted nicely and are looking good.



We're eating the Bibb lettuce. The thick patch is radishes, arugula and spinach, ready to thin for sprouts. Also bush beans and lettuce seedlings.



The heirloom Moskvich tomatoes do well in cool conditions. Night temps inside stay in the 40-50° range, with ceiling-mounted quartz radiants and a small electric heater to supplement the retained heat of the floor.



Another heirloom, a Roma-type called Peasant, goes on producing through the cold months.

Chip, love the greenhouse and the fact you are growing with those temps outside. Now, make sure you post more pics this winter, not only to make us jealous but so we 3 season greenhouse growers can dream!