Colin Königsberg

Benjamin Dinkel wrote:
The condensation that you're talking about will happen when you cool down hot (moist) air and will happen inside the tubes, not in contact with the backfill. So I don't see why it shouldn't work with heavy clay. It might actually be your best material.

Every single book/article I've read about these systems states 'heavy clay soils will not work because the condensation needs to be drained.' You use perforated drain pipe for that reason.

Anne Miller wrote:
My understanding of earth tubes is that they only work if constructed at deeper depth and level.

"Earth tubes" refers to a different type of system that's (mainly, IIRC) used for cooling, at least in greenhouse applications. They work on the (relatively) constant temperature of the ground at say 6+ feet down.

GAHT is a totally different architecture and works by taking excess heat generated during sunny days and heating earth below the greenhouse, and then pulling that heat back out at night.

Hi all:

I'm working on a 36' high tunnel with a GAHT system to help extend my season a bit in zone 5B.

I have most of it well sorted out but have some questions about backfilling around the tubes. The soil in this spot is nasty clay that doesn't drain worth $#@!, and I know that won't work as it needs to drain moisture that condenses out. So I am going to have to bring in alternate backfill.

As the GAHT pit is about 24x16', for each 6" of depth I am looking at 7 yards or ~10 tons of material which I'll have to buy and move 50-100 yards from my driveway to the building site as I can't get a large dump truck all the way there.

The gravel pits and quarries around here have a lot of different stuff available such as:

- Pond sediment, dead sand, or "silty fill" ~$8/yd
- "Dry screened state road sand" $17/ton (assuming this is just mixed size sand/grit of the kind they put on roads in winter)
- Washed native stone in a variety of sizes $19/ton
- Screened topsoil $30/yard
- River rock $80/ton

I have two questions:

1. Any comment on which of these would be good/better/best or a bad idea?

2. Does the fill above the tubes matter, or just what is below and immediately around them?

In other words, if I had a single layer of 4" tubes, could I go with a 6" layer of sand/gravel fill that encases the tubes, and then backfill with the existing junk on top of that? I could put a layer of filter fabric or something on top if infiltration was a concern.

I am also planning to build a slight slope into the pit with a drain tube at the bottom edge so that any condensate or ground water can easily exit.

I do have a small tractor and mini-ex so I've been doing the excavation myself. Depending on the amount of material I need to bring in I might look at renting a mini dumper or small loader for a day just because my little 1025R is good for about 1/3 yard per trip and I'd like to avoid having to make 100+ round trips with a little machine.

Anne Miller wrote:What a bummer.  I hate breaking light bulbs.

If that happened to me I would be looking for a new place where my seedling could get light.

Mercury contamination is only a thought when I break a thermometer ...

I don't have any indoor space that has really good, hard light, especially in February in New England. So artificial is kind of vital. Between upgrading my grow lights to good, really intense ones and adding a fan I am getting really nice, stout seedlings. I still have 11 tubes between the two fixtures, but after this I'm likely going to be looking at an LED replacement or some way to make sure the tubes can't just fall out.

I had to move my grow rack and in the process one of the fluorescent tubes fell out of a fixture and shattered on the floor. It was a great conclusion to an already frustrating and exhausting day /barf

I did the full hazmat treatment of closing the door, opening the window, and let the room air out overnight before going back in and picking up the remains without sweeping or vacuuming.

I did have one shelf full of ~1 mo old seedlings in there. Because I am sometimes paranoid about this stuff, I have to ask: is there any mercury contamination risk with the seedlings? Tomatoes, pepper, eggplant, and onions in case you're curious.

I am assuming that the risk from them being exposed to however much mercury vapor escaped is below the measurement threshold, but like I said, I sometimes overthink these things. And by sometimes I mean "most of the time."

Thanks in advance!

John F Dean wrote:I have a well stocked barn. I enclosed the ends of my high tunnel with a couple of storm doors and some storm windows.

How did you attach them to the hoop frame? Did you put a board along the bottom or anything like that? My tunnel does not have anything going across at the bottom of the ends.

Anne Miller wrote:Would something like this work:


source

Yeah, I was envisioning something similar to that. My tunnel already has a purlin tube so I wouldn't necessarily want to duplicate that with lengthwise beams like I see here. So my big question is around how I would attach the end wall frame to the hoops. I can think of ways to hack things together with U-bolts and some sheet metal or flat bar but I wanted to see what others have done before I reinvent the wheel, poorly :)

Earlier this year I bought a 14' gothic high tunnel kit from Farmer's Friend that I'm finally getting around to putting up. After it got delivered I realized I forgot to order prefab end walls and ordering them now would incur a hefty additional shipping cost. I'm a reasonably competent carpenter and fabricator so I'm considering building my own. I've googled around a little to see what other people have built but I haven't found much.

I don't need a completely paint-by-numbers guide but I'd like to know the right/easy ways to do it before I start buying materials and making mistakes. I can work out dimensions, cutting plan, etc. but I'm looking to see things like how people handle attaching the end wall to the tunnel frame, how people have built doors, attaching the film, etc. I do know that I want to build the frame to support installing a vent on each end above the door.

Thanks in advance!

Skandi Rogers wrote:For me it's a no go, since I need the extra heat the tunnel provides, even July nights can go under 10C here so it needs to be shut every night and then opened up by 7 or 8 in the morning to stop it roasting.

Thanks Skandi! Last season my plants did fine temperature-wise outside, so I think I'm safe on that front. It did dip as low as 6° C in late June but not for very long. The real gotcha here is that sometimes we will see a hard frost in early September, though last year it didn't happen until mid-October. In mid-summer my main concern will be controlling water since last year I got absolutely inundated--20" (so like 50cm) in July!

How much temperature gain do you get with your tunnel closed? Like, if it's 15° C and sunny, how hot will the tunnel get?

John F Dean wrote:I frequently leave my high tunnel unattended that long.  Of course, the devil is in the details.   In very cold weather, I check on it a couple of times a day.  

Thanks John! Do you have it completely closed all/most of the time, or do you ever leave it partially open?

My main concern is preventing it from overheating in the summer--as well as blowing away LOL. I'm less concerned about the colder season since I'd be leaving it closed then.

Hi all and thanks in advance for any wisdom.

I am in Zone 5B (western Mass.) and would like to try a small (think 25’ long) high tunnel for a little season extension and better irrigation control.

My question is whether it’s feasible to set this up so it can be left alone for 2-4 day stretches during the season. The site is a second home for me and I sometimes need to travel for work so I can’t be there 7/24.

I know I can set up drip irrigation (water is plentiful and cheap) so that is fine but I am wondering now about temperature management. My first plan had been to leave the sides partially rolled up and open the ends, but I don’t know if that’s asking for disaster with wind. My site is fairly sheltered and last year my gauge rarely hit 20 gusts even in storms. Usually the air is closer to dead still.

I know I could remove the cover completely but that would defeat some of the purpose. We got 16” of rain last July (2-3” would be normal) and that almost wiped me out.

Thanks again for any advice!