Off grid and a bit further

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Off grid and a bit further

Postby JRHill on Mon Apr 15, 2019 1:59 pm

We have a hoop cold frame, 5 years old, 32x48. I built the damn thing at no small effort. The upper ends are open and the whole frame is at a 15-20% grade. Originally I thought it would self ventilate to te upper end. NOT, its just too much heat to exhaust. In the summer it gets to 120f. In the winter everything freezes. From the wife we just need more venting and in the winter a woodburner. The structure is 75 yards from the nearest PV power. Even in the summer we don't have enough power for a vent fan for that structure. In the winter, it'd take more fuel to heat that than the house.

Now y'all have context. No, I'm not going to heat it in the winter. But what direct drive things have other folks used for ventilation in a similar circumstances where your creativity is being challenged by the boss? My gosh we love fresh produce but at what cost?

Best,
Jim
JRHill
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Location: South central WA
My RE system: -House: FM 80, VFX 3648, FlexnetDC, FlexWare xformer, Mate 3 / Hub, WattPlot/, 2925w SunTech 195, Trojan L16RE-B Batteries. Backup 1: Honda EU7000is w/2 wire auto start via FM80 aux, backup 2: 11kw Miller Bobcat;
-Well: Grundfos 11-SQF-2 pump, controller & AC switch (CU200, IO101), Tristar 45 Controller, 780w SunTech 195, Trojan golf cart batteries.
-All running since July '11 with various upgrades and workarounds.

Re: Off grid and a bit further

Postby raysun on Mon Apr 15, 2019 2:07 pm

Do you actually need all the insolation on summer? Besides excess IR, you could be collecting excess UV. Most greenhouse growers will shade their hoop houses in summer to keep things less "hot" at both ends of the spectrum. Strategically placed shade cloth may help substantially.

Genius idea to placate intransigent spousal units and feed your inner nerd: use flexible solar panel strips as shading devices and the PV harvest to run auxiliary vent fans.
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Re: Off grid and a bit further

Postby Kurt Lundquist on Mon Apr 15, 2019 3:09 pm

Hi Jim,

I have a much smaller 1/2 hoop house that I build on the south side of my house. I deal with the same issues and have yet to bite the bullet on a vent fan. I use reflective shade cloth in the summer and also roll up the bottom half of the plastic cover. The shade cloth is made out of some kind of foil type material that has held up well the past 8 years. This helps a lot but I still need a real vent fan in the top area to silence the wife's complaints.

I know of a chicken farm near me that is using these flexible modules to run fans/lights for some huge chicken hoop houses: nhttp://store.evtv.me/proddetail.php?prod=270wpanel. I don't know how they mounted them but it sounds like the system is working very well. Ideally, you can find a fan that runs directly off the PV output unless you think it needs to run when it is dark out.

If you have space adding thermal mass can go a long way to helping even out the temps year around. Get some 55-gallon barrels, paint them black, and put them around the beds you use the most in the winter. 1lb of water freezing releases 144BTU of heat (~42 watts). Adding a second cover/smaller hoop over those beds inside will help too. Adding smaller black tubes of water between the plant rows to go the extra mile. In the summer you can shade the barrels from direct sunlight and they will help keep the air warmer at night and cooler during the day.

A few years back I read a great write up about some greenhouse techniques used in Nepal. I did a quick search and couldn't find the same write-up but this should be useful: https://www.sciencedirect.com/science/article/pii/S1877705812047807

I'd love to know what you figure out in the end.

Cheers,

-Kurt
Kurt Lundquist
Renewable Energy Project Engineer
http://alphaenergy.us/
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Re: Off grid and a bit further

Postby JRHill on Mon Apr 15, 2019 3:59 pm

raysun wrote:Do you actually need all the insolation on summer? Besides excess IR, you could be collecting excess UV. Most greenhouse growers will shade their hoop houses in summer to keep things less "hot" at both ends of the spectrum. Strategically placed shade cloth may help substantially.

Genius idea to placate intransigent spousal units and feed your inner nerd: use flexible solar panel strips as shading devices and the PV harvest to run auxiliary vent fans.


Oh, I didn't mention-the 120 temps are with a 60 percent shade cover over the top... Dang, weeding sucks.
JRHill
Forum Czar
 
Posts: 547
Joined: Thu Feb 17, 2011 12:12 pm
Location: South central WA
My RE system: -House: FM 80, VFX 3648, FlexnetDC, FlexWare xformer, Mate 3 / Hub, WattPlot/, 2925w SunTech 195, Trojan L16RE-B Batteries. Backup 1: Honda EU7000is w/2 wire auto start via FM80 aux, backup 2: 11kw Miller Bobcat;
-Well: Grundfos 11-SQF-2 pump, controller & AC switch (CU200, IO101), Tristar 45 Controller, 780w SunTech 195, Trojan golf cart batteries.
-All running since July '11 with various upgrades and workarounds.

Re: Off grid and a bit further

Postby JRHill on Mon Apr 15, 2019 5:41 pm

Kurt Lundquist wrote:Hi Jim,

-Kurt


Kurt, I tried the barrels. I thought it would work better but not. So we try for cabbages and kales that can survive the cold nights. On this side of the Cascades we are in the rain shadow but it can get damn hot, esp with the drought that is 4+ years now. Thanks for the links so I can research further on the topics. Love the idea of the hoop within the hoop. Told the wife and she said: "Oh, yeah, I told you about that." Sigh.

Since we are in the forest there is wire fabric buried deeply around the perimeter of the cold frame and it goes to chix wire up higher. Even on productive years we feed the forest wildlife, esp out of the garden. Imagine the beautiful berries and tomatoes, all with at least one or two bites out of them... Mmmm

So the project continues. TY for ideas, in advance. Will update when I find the magic bullet and the right caliber. But, living in WA, I can't have the tool available when I need it. I could be prosecuted. But the bad guys and evil critters are free to run and pillage.
JRHill
Forum Czar
 
Posts: 547
Joined: Thu Feb 17, 2011 12:12 pm
Location: South central WA
My RE system: -House: FM 80, VFX 3648, FlexnetDC, FlexWare xformer, Mate 3 / Hub, WattPlot/, 2925w SunTech 195, Trojan L16RE-B Batteries. Backup 1: Honda EU7000is w/2 wire auto start via FM80 aux, backup 2: 11kw Miller Bobcat;
-Well: Grundfos 11-SQF-2 pump, controller & AC switch (CU200, IO101), Tristar 45 Controller, 780w SunTech 195, Trojan golf cart batteries.
-All running since July '11 with various upgrades and workarounds.


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