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This project page will be updated as work progresses. We wanted a large greenhouse that would be 3-4 season. Since we are off the grid, propane or electric heat is not possible. Instead we will use a combination of a wood burning stove and thermal mass passive solar.
To be honest, given our location and weather, we are more concerned about keeping the greenhouse cool enough in the summer than warm enough in the winter.
There are many designs out there for passive solar greenhouses. In fact, we had purchased several sets of plans for various designs. However, due to a sense of urgency to get the greenhouse built, we decided to order an 18' x 40' metal and polycarbonate kit. We will retrofit the passive solar aspects (insulated North wall and ceiling, Fifty Four 55-gallon drums full of water, solar heated raised beds) into the shell.
The first step of this project was to level a 22' x 44' foot pad. If it were not for the 3 stacked rows of water filled 55-gallon drums to be installed, being level would not be a high priority for a greenhouse. Living in the mountains, finding a truly level area of ground is almost impossible. The area we selected had been more or less leveled by the previous owner, but there was still a 14" drop from one diagonal corner to the other.
We started by using a lot of dirt/rock mix from the surrounding area to get a pretty level working area. Then we laid down metal stucco lathe across the entire area. This will prevent all the critters we have around here from burrowing into the greenhouse.
Then came the many tons of 3/4" crushed granite gravel. This was used to allow a final level of the timbers, as a thermal mass, and for drainage inside the greenhouse.
After the gravel pad was pretty level, we then laid out the true 4"x6" Douglas Fir timbers we had milled at a local saw mill. Douglas Fir is known as 100 Year Timber around here because of its durability without being pressure treated with chemicals.
The footprint of the greenhouse framework was laid out with the timbers which were then covered with 4"x4" flashing on both the exterior and interior side. In addition, we added 4" deep metal gutters to the exterior side of the long sides to channel rain/snow run-off away from the "foundation".
Below is a photo gallery of what is described above. Click on a thumbnail for larger view. This post will be updated as we progress.
Update Mid-December 2014:
The framework for the greenhouse finally arrived. We assembled the trusses in the shop and moved them out to the pad. It took a bit of work, but the framework is now up, plumb, level and ready for the polycarbonate covering.
We added 2 windows on each end and two large windows in the center front (south side). We have to build a couple of large vents for the upper ends that will have temperature controlled automatic openers.
Unfortunately, Winter has really set in here. Snow and below 0 degree temperatures. Hopefully we will have a few days here and there where work can continue.
More photos below. Just click on thumbnail to see larger view.
Update January 2015
We have had enough breaks in the weather to allow us to completely enclose the greenhouse with the polycarbonate sheets. Although single wall, the polycarbonate has a 10 year warranty against hail damage and lifetime warranty against yellowing or cracking. Given our location we are more worried about keeping the greenhouse cool enough in summer than keeping it warm in the winter.
With the addition of a wood burning stove we can work on the inside throughout the winter. (the stove in the photos below is for display only since it does not meet the stringent new EPA guidelines - it of course will be replaced with a fully compliant model before use).
There are a total of 6 large windows and the two 4' wide doors. A large automatic opening vent will be added to each peak of the East and West walls.
Now we can start building in the passive solar features. Next up is to insulate the entire North wall, part of each end wall and approximately 4' of the ceiling above the North wall. This is to prevent heat loss from the 38 fifty-five gallon drums of water that will serve as the main thermal mass.
We will build a solar heated raised bed along the entire South wall. The area of the raised bed exposed to the South wall will also be insulated. This will leave plenty of room for many additional beds in the middle area.
We plan to add as many vertical growing features as possible including some 8' tall hydroponic vertical tubes.
Update Mid-March 2015
Since closing in the greenhouse in January, we have been able to continue work regardless of weather. In fact, if the sun is shining, we have to open doors and windows regardless of outside temperature.
The next step was to install the insulation on the North, East, West walls and up 26" on the South wall where the insulated, solar heated raised beds will be installed.
For the insulation, we repurposed 60 4'x8' sheets of used 1.5" thick, foiled backed, radiant barrier poly iso insulation. None of it was in "like new" condition - but definitely good enough for this purpose. For the North wall, we ran 3 horizontal runs of 2x4 nailers that were screwed into the metal framework. We installed 3 layers of the poly iso giving us 4.5". Along with the dead air space between the poly iso and greenhouse skin - we have approximately a R-30 insulation factor.
We did the same for the part of the East and West walls that will be next to the drums full of water. A single layer of poly iso will be mounted above the drums. We may add a couple of layers of 1/2" thick bubble wrap on top of that if need be.
The heated raised beds are constructed from cedar 2x4's and standard corrugated 26.5" x 8' galvanized steel roofing panels. Since the main South wall beds will never be moved, we built the exterior walls into the framework of the greenhouse. The exterior walls are insulated with 4.5" of poly iso.
The long inside walls of the raised beds are staked in place using 30" rebar rods. The long beds will be divided every 4' with a piece of the galvanized metal to allow different soil mixes and to prevent the spread of disease, fungus and such throughout the entire bed.
Six island beds will be added to the long beds and have trellis from bed to ceiling running North to South.
The beds will be solar heated. 4" irrigation hose will be zig-zagged throughout the bottom of the beds. The top end will go to the very peak of the greenhouse where the warmest air will settle. The bottom end will have a suction fan attached. This will draw the warm/hot air from the top of the greenhouse through the beds where the heat will be absorbed by the soil. The heated soil itself will be a fair thermal mass and combined with the 2100 gallons of water in the drums, the plants should never freeze (but that's why we installed a wood stove for backup just in case).
There are two photos showing the platform for the thirty-eight 55-gallons drums. I used true 3"x8" Douglas Fir beams I had milled for this. I needed to make sure the 14630 lbs of water (plus the weight of the drums) would not shift or settle. The drums will be 19 abreast with two rows stacked. The drums are also used-once repurposed. We used heavy duty food grade liners inside the drums to prevent future rust and keep the water as potable as possible.
Updates April 1, 2015
Passive Solar Heated Raised Beds: We have pretty much finished the raised beds (except for mixing/adding the soil). This is the first major passive solar aspect we are retrofitting into the greenhouse besides insulating the North wall.
The previous update showed how the raised beds were insulated to the exterior wall and the basic construction. Once the beds were all put together, the next step was to add approximately 10" of compact straw to the bottom of the beds. This was done for two reasons: We won't grow anything in the greenhouse that needs 26" of soil and the straw also acts as an insulator from the cold that will migrate in from the ground/gravel.
Next, we added the 4" corrugated drainage pipe that will carry the heated air from the top of the greenhouse throughout the beds to heat the soil. Only the beds up against the exterior walls will be heated, the island beds will not. The 4" pipe was zig-zagged through the beds from both the East and West walls to the middle. The wall ends go up the wall and are routed to the peak.
The idea is to have a fan drawing air DOWN from the peak, through the beds will the heat will be absorbed, and out the fan housing for circulation. You want to pull air down the pipe instead of putting fans at the top because air will compress when pushed - but nature abhors a vacuum and will do anything to fill one. So if we create a vacuum (by sucking air from the lower part of the pipes, it will literally suck the warmer air from the peak.
I needed to fabricate something where I could hook in the two pipe ends, that was airtight (except for the top where the fan sits) and that protected the fan from debris and splashed water. This would be much easier if we were on the grid because I could use basically any fan. However, since we are all solar - I need a low-draw 12 volt fan. The solution I came up with was relatively simple: A drain sump, a roof vent and a very large computer case fan. The drain sump is airtight other than the top grate and is designed for easy connection of two drain pipes. The roof vent allows good air flow but is virtually rain-proof. The case fan draws extremely little juice. The large case fan fit almost perfectly in the round opening of the roof vent. I had to cut off the mounting tabs of the fan on one side. I used a hot glue gun around the perimeter to hold it in place and fill in the small gaps. I'll wire it with a low-voltage cool only thermostat (made for RV's). If I set the thermostat for 80 degrees, once the greenhouse reaches that temperature it will kick on the case fan. In the evening, as the greenhouse cools down and the inside air cools below the set temperature, the fan will automatically turn off.
NOTE: While the fan contraption worked well during bench testing, that was with only one pipe attached. After a test run once installed, I believe the fan will have to be upgrade to something larger with a much higher CFM rating. My first option to evaluate will be an electric automotive radiator/cooling fan. While they are designed to move a lot of air - they also draw a lot of power - so I may have to just go with another of the larger fans I'll be using for the powered vents. They are a bit pricey but the CFM/amps is outstanding. Of course either way, I will probably have to ditch the roof vent section and fabricate a different fan housing. Will update once testing and research has been complete.
Since the "soil" up here is only good for pinon pine, tumbleweeds and cacti - we have to make our own for growing food. For the greenhouse we used a mix of aged horse manure, coconut coir and composted forest soil and a final layer of Eco-Compost. We managed to get half the beds filled and added the trellises (made from galvanized cattle panels).
Update - June 2015 - Ventilation
Ventilation is crucial in any greenhouse for temperature and moisture control and the plants seem to do better with plenty of air circulation. We decided to employ both passive and active ventilation via large automatic peak vents and two 12volt high volume / low amperage fans.
A lot of greenhouses use the temperature responsive wax automatic openers on roof vents. Due to the construction of our greenhouse and the fact I've never seen roof vents that did not eventually leak, I decided to build some for each end (East and West). I knew they had to be very light weight as I intended to use the automatic openers in the entirely opposite way they are designed.
The automatic openers are basically a large spring loaded hinge with a wax filled cylinder/piston in the middle. As the wax heats, it expands and drives the piston out thereby opening the hinge. When it cools, the wax contracts and the springs pull the hinge closed. By design, the openers are supposed to be used to lift a vent up and to the outside and use the weight of the vent to help close it down again.
I wanted to do just the opposite - lower the top of the vents down and to the inside of the greenhouse. Otherwise they would have become great big funnels in the event of sudden rain. I researched but could not find any info anywhere about this "off label" use. I had to experiment with numerous mounting positions and angles to find the solution that would allow the mechanical mechanism to open without binding but still allow the springs to pull the vent back up to the closed position.
For the active ventilation, we purchased two 12volt fans that move a high volume of air but draw very little power. They are made for RV's and such. I built cedar frames for them and fabricated some sheet metal shrouds to protect them from rain/snow. One was mounted down low on the East side pulling air in and the other up high on the West blowing air out. The greenhouse has its own independent solar PV system with batteries wired to 12 volts. I put the vent fans on a low voltage thermostat (also made for RV's) that turn them on around 80 degrees and off again when the temp drops below that. The wiring of the greenhouse will be the subject of the next post.
The previous post covered the ventilation system to heat the raised beds but I left a note indicating the super large computer case fan was not creating enough vacuum to get a good circulation going. I solved this with the "push/pull" method by adding a 120mm case fan to the top end of each of the 4" drain pipes pushing hot air into the pipe. With those pushing and the central exhaust fan pulling, it creates a nice flow.
Update June 2015 - Wiring
We are completely off-grid. When we bought the homestead the house already had a decent solar PV system. However, there was no power in the garage/shop nor the chicken coop/garden shed areas. We added independent systems to both, each consisting of 390 watts of PV panels, 30amp charge controllers, four 6 volt batteries wired to 12v and inverters as needed.
For power to the greenhouse I debated back and forth whether to move the entire chicken coop/garden shed system out to the greenhouse and run a single 12ga wire back to the coop for lights - or run some very heavy gauge wire from the garden shed out to the greenhouse and go from there.
When a neighbor offered just enough used heavy gauge wire to make the run from the shed to the greenhouse, the decision was made for me. If the wire had been enough to string overhead and make the return drops I would have gone that route. However, it was just barely (and I mean barely) enough to make a straight underground run. So the first step was to dig a shallow trench and pull the heavy wire (imagine 55 feet of stiff automotive size battery cables) through conduit.
Once done, I had a good dose of 12v right inside the East door of the greenhouse. I could have installed a large inverter from there and used 110 volt fans, pumps, lights from there - but any time you convert electricity from AC to DC or voltage to a different voltage - there is a loss.
Since everything I needed to add to the greenhouse was available in 12v (think RV or camper) - I used low voltage / low amperage 12v for everything - although I did add an 800 watt inverter just to have 110v available for small power tools and the like.
Due to the fact that I have burned more than my fair share of wiring set-ups in vehicles by not having in-line fuses, I decided to go overboard here and added a main 100amp fuse between the batteries and the inverter / auxiliary wiring. This protects the entire "circuit" in case the inverter shorts or draws too much. From there I added a six circuit automotive fuse block which feeds six standard light switches that control each circuit. The six functions controlled by the fuses/switches include:
Lights: Four dual-bulb 12v incandescent light fixtures.
Vent Fans: Covered in the post on ventilation. The fans are also controlled by a thermostat (see note below).
Bed Heat Fans: The system that draws heat from the peak of the greenhouse through the raised beds and heats the soil. (also on a thermostat).
Fountain: I found a small 12v submersible water pump - so decided to add a water feature because - well because I wanted to.
Hose Pump: In the winter we'll move a 275gal tote into the greenhouse for both a thermal mass and to use to water the plants as necessary. The pump is a 10amp RV pressure pump that only comes on when water is called for.
Spare: Have one spare circuit for something or other - but at least it's wired and ready to go.
Note on thermostats: The thermostat for the bed fans/heat works perfectly because the fans are all extremely low amperage. However, for the first few days I thought the thermostat for the vent fans was defective. There was no rhyme or reason to how it was acting. I was having to "calibrate" it a couple of times a day. After installing a replacement with the same behaviour, it dawned on me to test them with an infra-red thermometer. I had my concerns about the 26ga wire used inside the thermostats when first installed. It tested out to be heating up with the draw the vent fans were drawing - enough to effect the bi-metal coil spring that controls the contacts.
I fixed (more or less) this problem by soldering some 16ga wire jumpers on top of the factory 26ga wire. This lowered the electrical resistance enough to let the thermostat to only heat up 2 degrees above ambient temperature. One day when I have nothing else to do I replace the 16ga jumpers with 14 or 12ga.
Late June 2015 - The "Real" Shade Cloth is Installed
In early Spring we finished installing the polycarbonate skin on the greenhouse. It only took a day to realize it would get way to hot inside to work without some type of shade cloth. Fortunately I had found a great deal on a repurposed used swimming pool cover that was just the right size to use as a temporary shade cloth until I had time to set up what we really wanted.
There were two "must haves" - we had to be able to easily adjust the shade cloth to cover or reveal the South side and always cover most of the roof. And, we had to be able to do this without bending down into the mud or snow depending on the weather (and our ageing backs). The design and size of the greenhouse made a standard roll-up set up out of the question (the South side is 40' long). It also could not be a single piece because the chimney for the wood stove would prevent enough adjustment room.
There were several issues to deal with to make this work. We have high winds up here and the standard edge tape and grommets would not last long. We've used those heavy duty plastic alligator type tarp clips before and knew they would hold up a lot better than grommets.
The idea was to pull the shade cloth straight down with the tarp clips and paracord, but then angle back up to a post about 32" tall - so we needed eyelets or similar to mount at the very base of the greenhouse to route the paracord down and through and back to the post. Because we had put 4" gutters along the base to channel run off away, there is limited working space which required something that mounted with screws instead of being larger like eye-hooks. We came across heavy-duty two hole picture/mirror hangers and bench tested one by hanging a 60lb vice from it. It survived the bench test so we purchased a bag of 100 for around $15.
Finally, it had to be easy to adjust the paracord without having to untie knots or unwrap from cleats. We didn't want it to become a 30 minute ordeal just to adjust the shade cloth. We found some self-clamping, instant release cleats made for pickup truck beds. You feed the rope through the hole that has a spring loaded notched clamp inside. This clamp allows the rope to easily pull one way, but tightens down pretty hard when the rope tries to move the other way. To release the rope, you just pull down on a lever that moves the clamp out of the way and the rope moves freely. Perfect!
So, the plan was to order three piece of shade cloth - a center one 4' wide by 20' long that would stay fixed running from the base, up over the roof and stop at the chimney. On both sides would be a piece 18' x 20'. The side pieces would overlap the center one by 6" or so and if pulled down to the base of the South side would still cover most of the roof. To reveal the South side, you simple release the ropes on that side and pull the shade cloth down the North side. Re-adjust all the ropes to take out the slack and you are ready to rock.
We already had some non-pressure treated 4x4's on hand along with some stain/sealer so after a trip to the local hardware store for a few bags of concrete and large lags bolts, we cut, assembled, stained and erected four 32" high posts. Two one each side, centered on the adjustable sections of the shade cloth.
Everything works like a charm and it takes less than 5 minutes to adjust the shade cloth to any degree of South side exposure needed.
For the actual shade cloth, after much research, we decided on Aluminet 60% cloth (a metal embedded woven plastic actually). It's kind of pricey compared to regular non-metallized cloth - but has many benefits that justified the cost.
Update October 2015 - 55-gallon Drum Thermal Mass
Its October 21st, its cold and raining, and while most of the warm weather plants have been pulled from the greenhouse the work continues. We finally have all the thermal mass in place. Most of which comes from 55-gallon drums (or barrels) filled with water.
We have learned two very important things about steel 55-gallon drums. First, there is no such thing as a standard size. We ordered 60 "used once" drums with plans to stack them three rows high, 18 barrels across. We assumed that while manufactured by different companies, such drums would be the same diameter and height - like gallon milk jugs or similar. In fact, we ended up with 10 different heights - ranging from 32" to 35" tall with a few slightly different diameters. So much for nice even rows.
Secondly, since the greenhouse project was put off for two years due to other unexpected (and very expensive) events - we learned that even almost new "used once" drums will surface rust badly if left outside for any length of time. Since the intended use was long-term storage of water as a thermal mass, we couldn't start out with barrels that were already rusting.
So the first step was to use grinders and rust-removal brushes to get the critical load bearing bottoms back down to bare metal and then paint with Rustoleum. Then, the entire barrel was painted with an exterior latex flat black for light/heat absorption - times the 40 barrels we ended up using. The salesman who sold us the greenhouse kit assured us the arched walls would give us the nine feet height we needed to stack three rows. When the kit finally arrived, the side walls were only eight feet tall - so we had to settle for two rows of 19 drums each. We added two more barrels next to (and directly connected to) the wood burning stove.
You can not stack barrels directly on top of each other - they are not designed for that. You have to use a layer of plywood between the rows. The next step was to measure all the barrels trying to find groups of four (for 8' lengths of 2' wide plywood) that would provide an even, stable base for the upper row. As it worked out, for the bottom row, we had groups of 4, 4, 3, 4, 4 - with the group of 3 being directly centered behind the wood burning stove, so we used the tallest for that group. The top row was a mish-mash of different heights.
Once the bottom row was in place we began filling them with water. Although the drums are coated on the inside with some type of waterproofing, we didn't want to take the chance of rust returning AND we wanted to be able to use the water for drinking/cooking in emergencies (like the well going dry again). So, we used food grade drum liners - basically huge garbage bags made with a food grade plastic. Although much thicker than normal trash bags, a friend had several bags fail when he used them for the same purpose, so we double-bagged. Even with that precaution, we had to redo several barrels when the double bags leaked (probably due to unseen debris in the drums).
We left the lids off the freshly filled barrels for a day or so to double check for leaks before sealing them up. Once the first row was in place it was simply a matter of putting the layer of 1/2" plywood on top (with a bit of trimming) and repeating the filling process again.
NOTE: After doing a test burn in the wood stove, we discovered the plastic liners melted where ever there was an air pocket between the barrel surface and the water. So, we removed the liners from the six barrels (three on each row) that were adjacent to the wood stove and obviously the two that are in direct contact with the stove. This placed the nearest barrel with a liner a safe 3' away from the intense heat. Also, we hope the two barrels that are directly connected to the stove (about 100 gallons of water) will absorb a lot of the radiant heat instead of letting the stove create an intense "hot zone" of air.
Also of note is that in the shop, as a test, I connected a drum of water to the wood stove using a method with much less direct surface area/contact and after a good burn, the water temperature in the drum (at least at the surface) was over 120 degrees. Just this 55 gallon thermal mass would stay warm for hours after the fire was history.
So, we have approximately 2000 gallons of water in the 40 barrels. As additional thermal mass and to be used for watering in the winter, we painted two 275-gallon food grade water totes flat black and added a 12-volt high capacity water pump to one. That added another 550 gallons.
By chance, we found some black 18-gallon plastic storage containers on sale and added 16 of those in the space above the second row of barrels. With 15 gallons of water in each, that added an additional 240 gallons. So we now have a total of approximately 2800 gallons of liquid thermal mass along the insulated north wall of the greenhouse. When the sun is lower in the winter, it shines directly on the flat black containers heating the water. At night, that heat is slowly released back into the greenhouse. And, if necessary, we can use the wood stove to not only heat the air, but also the eight barrels of water either connected to or in close proximity of the stove.