Greenhouse Build

[Specialkayme]

Yankee hailing from North Carolina over here, and I specifically became a member because of the carnivorous plant greenhouse build experience on this site, for what that's worth. I'm not sure I can agree that my friends on the other side of the pond do many things better than us, but you sure have greenhouse growing down pat.

So my nepenthes collection has grown to the point that it isn't feasible to keep them under grow lights in my living room. Plus I want to try and expand into some hydroponic vegetables and herbs, and do some year round growing, so I'm planning on building a greenhouse on my property. I'm looking to build a passive solar greenhouse, and provide as little supplemental heat or cooling as I can (although fans are an absolute must). I'm targeting the ability to grow intermediate to "lower highland" type nepenthes, which would give me a good range of temps to accommodate most other types of vegetables I'd want to grow with it. I'm shooting for day temps no higher than 85F/30C and no lower than 70F/21C, and night temps no higher than 70F/21C and no lower than 60F/15C. I'm expecting my target high (day and night) to be for the summer, and my target low (day and night) to be for winter. I'm Zone 7b, so we get some hot summer days (mid 90'sF/34C is not uncommon), but our winters are usually mild (typically the lowest it gets is the mid 40'sF/5C for extended periods of time). We occasionally get snow, maybe a few mm at a time, maybe 2 or 3 times a year. And usually it's gone the same day. Humidity in the summer is usually an issue though.

I've been inspired mostly by this guy Sweet Gum and Pines and this guy Merck's Greenhouse. Both live in comparable environments to me. The first has been operating growing nepenthes about an hour away from me for a decade. He definitely uses more electricity, by using an evaporative cooler and a propane heater. The second is able to do things much more passively, by using water barrels as heat batteries. That would be a much more preferred option. I'm then partially stealing a design from here.

Electricity and water will be run to the space, which isn't an issue.

So here are my plans and thoughts:

1. The footprint will be 16 feet long, and 10 feet wide.

2. The "foundation" of the walls will likely consist of either cinder blocks, or landscaping timbers, and the structure will be secured using ground anchors. A 4x4 pressure treated post will be driven into the ground and concreted on either end, extending 12 feet high. A third will be in the middle. A 4x4, 16 foot beam will act as the ridge resting on the 3 posts.

3. The center posts will be off center. The longer side (8 feet) will be facing south. The shorter side (2 feet) will be facing north. The shorter side will have a 10 foot wall, made of 2x4's, insulated with rockwool, with sheathing on the outside (painted). The longer side will have a 45 degree roof slope, covered in Triple Wall Polycarbonate. The walls on the long side will be ~3.5 feet high, and also covered in polycarb. The shorter side will have a roof that's either shingled, or with tin roofing material. 

4. The roof trusses will consist of 2x6x12' pressure treated posts, 2 feet on center.

5. For air movement (and cooling), a 2'x2' air intake shutter will be on either side closer to the ground, set to open at 75 degrees. On the long wall, another passive shutter will also open at 75 degrees. Hopefully that will create a chimney effect (like in Merck's Greenhouse). A separate 20" 3400CFM Exhaust Fan will be positioned above the door, set to turn on at 80 degrees. If I need to, I'll insert another air intake on the door on the opposite side of the greenhouse. 

6. I highly suspect I'll need to get some Aluminet Shade Cloth to cut down on the light and heat in the middle of the summer. But I don't know how much until I get it up and running.

My plan is then to install a heat battery. I've seen plenty of designs that use 55 gallon water barrels, and the math indicates I should need 700-900 gallons. They'll be stacked in the right hand side of the greenhouse, in the 2' section to the right of the door. I may try to just put a 4 foot high, 2 foot wide, and 16 foot long "pond" in there with some aquatic plants and some koi instead, which should provide 950 gallons of water. 

But I'm not sure if I should put in a subterranian geothermal battery system, like this guy did. I've seen plenty of people do this in northern climates to me (Idaho, Canada), but not many that have done it in warmer climates like mine. If I do put it in, I'd have to dig in all the pipes before I put the walls up, so a decision needs to be made on that. If I did it, I'd try to dig down about 3 feet or so to install the tubes, then fill with dirt and some gravel.

Whether I use the geothermal battery, or the water battery, or both, hopefully I can hit my target temps. If not, I can always get an evaporative cooler to help drop temps and install it on the west wall, or an electric heater, or take the hit and install a split level HVAC unit. That I can figure out after I build it and observe the temps. But the subterranian construction I can't . . . 

If I need to, I'll add some supplemental LED lighting, but I have no plans on it currently.

So for those that have built and maintained greenhouses for year round CP growing, what are your thoughts? Should I do the subterranian battery system, or skip it? Anything I missed?

 

Edited July 23, 2021 by Specialkayme