Ebo David

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since Feb 17, 2018
Washington DC area
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Recent posts by Ebo David

Mike!  Good to be back.  Lots on my end, but that is for another discussion.

I agree with Cristo.  I remember reading about a rare high elevation plant that daily survives freezing temperatures at night, and very hot during the day.   Very few plants can withstand that, much less food crops.  Realistically we need to help you keep the temp range down.
4 days ago
I thought I posted this a few days ago, but it did not show up in the thread, so here it is again...

re: minor air leaks in the system...

I remember reading that even very small air leaks can completely destroy your ability to keep the heat/cold where you want them.  In my readings I remember someone writing about how much cold air came into his house through the electrical plug boxes in an old house where the walls were either inadequately insulated behind the receptacle boxes.  Try sealing all holes you can with plastic, or however, and see if that helps. Maybe you already got that done, but...

re: thermal mass...

I forget how far down you went with your insulation along the walls.  But as you mention the mean annual temperature is ~40F in your area, and is why you did not want to go with a low grade geothermal like the Citrus In The Snow and similar greenhouses, and why you made a comment about a heater putting out 40F air, and the outside air being -20F then the house would not be 40F in the morning.  Ok, but also consider this -- if you did not insulate the soil under your greenhouse then you have a constant heat sink sucking the temperature in the greenhouse soil (basically in an insulated box) down to that temperature.  I remember reading about someone that built a greenhouse back in the 70's -- insulating just the underground perimeter walls and not the bottom.  They were hopping to keep the soil temperature high.  They found that all the heat was being sucked out of the bottom.  That said, this is part of what makes the climate battery and low grade geothermal work, or at least as I understand them.  So all of this said, I would be surprised if you could keep the greenhouse soil much above the mean temperature year around.

I also found the following: "The 24-hour cycle of air temperatures disappears at a depth of one-half foot; five feet down, ground temperatures lag three months behind seasonal air temperatures. The lag is six months at 15 feet. Soil temperatures are constant below 30 feet, and, incidentally, about equal to the average annual air temperature."  At first I thought the 12" to 18" depth was to little, but then read in the context of pumping the soil temp up makes sense.  That said, if you are growing plants in the same soil, they will get down to where your are heating the rootzone, and that might cause some issues depending on the temperature fluctuation.  But with a 115+F between inside and outside (as reported a -6F and +110F previous)I am guessing you really need a lot more thermal mass to stabilize.  I could be wrong.

re: changing the design from an arch to triangular/rectangular...

Take a look at Citrus In The Snow greenhouse <http://www.citrusinthesnow.com/>.  That profile might be a good compromise.

I need to jump back on my projects here.  I hope that all continues to go well on your end!  Thank you so much for sharing the details and allow us all to think along.
5 days ago
Just remember this.  Every sentence in the code was written because someone was injured, maimed, or killed.  Fundamentally, it is all about safety and then efficiency, and even efficiency can be about safety some times -- given the population and how areas population are expanding, if you do not make buildings more efficient  that you can have power outages, water outages, etc.

With rainfall collection, check your state and county programs.  In PG County, Maryland it is not only encouraged but they actually have a grant program to help you pay for it!  Take a look at Maryland's Rain Check Program.  Finding examples and explanations from other locals should help a lot.

As for other building codes.  I am surprised that you did not start with a LEEDS certified architect.  There is going to be a point where they are going to want certified drawings.  Hiring the architect up front will actually help with that.  They will be able to give the permitting folks what they need to OK you.  Also keep in mind what I said about safety before.  If someone is injured, maimed or killed in/from a building that they have inspected and signed off on, then they can be held legally accountable.

All the above said, I really do with you the best of success in moving this forward!
2 weeks ago
I would suggest getting the temp sensors up, or whatever other sensors you have, and running as soon as possible.  You may find that the information is useful, and also might run into a bug as it is collecting.  Better to find sooner than later.  Also if you are initially worried about the barrels freezing, only fill them 3/4 of the way.  If you have some temp sensors set up you can track the outside/inside air temp as a function of how much water you have in the barrels.  As a note, water stores a LOT of energy and can release it as it starts to transition to freezing.  So if you get enough solar gain to keep things just above freezing, the barrels will help with any dips in the night.
3 months ago
Please post data as you use the greenhouse.    If I recall you instrumented it.
3 months ago
@Brian, can you post some pictures of the beds you are referring to?  Are the ones you lined with pond liner for hydroponics, or are these fiberglass beds just plant beds, and if so why are they closed off?  Is there no drainage?

 EBo --
5 months ago
Very nice.  Thank you for sharing!
6 months ago
Mike, you are welcome.  I am glad it helped.

As for the flattening the glue problem... On thing that could be done, but it will be tedious to set up, is to use use screws or bolts as stops.   The basic idea is that you have something which adjusts the heights of different pieces in the assembly so that the only parts touching the truss pieces are the screw heads.  THe problem is how to adjust the head heights.  Probably a better way is to take one of the assembled beams, mark out where the glue joints go, carve/route a glue channel,m and then wax everything up so that glue drippings do not stick so easily.  That way you have flat pieces parts and no smushed glue berries.
7 months ago
Mike, if i am following you correctly you should be able to correct that by clamping the pieces in two planes -- if you clamp the piece from the wall sticking out, you can force the rib to lay flat against the jig, and the other one parallel to the wall to pull the two ribs and the spacer block against it.
7 months ago
Mike, your truss frame is inspiring ;-)  I am surprised that the trusses are not coming out flat with that setup, but maybe I do not understand the comment.  

I look forward to follow your progress.
7 months ago