It's all Plain to Sea

mrhobbithhnet · Posted: Wed Oct 21, 2009 9:20 am Post subject:

Glad to hear one more person has a weetail to tell about polylock installs. It is too important to get wrong, easy to see when it is, and deceptively difficult to execute with any kind of ease... at first. After a few decades of watching the consequences of less than perfect installs unravel assiduously in front of me despite my best efforts, it is just one more opportunity to appreciate finesse in the workplace. If all the details in greenhouse building were so, there'd be a few more disappointed builders around. Thank goodness the rest is pretty much a no-brainer for reasonably experienced craftsmen.

Bubble roof greenhouses come to mind... what an incredibly fussy build those would be - ten times the fussyness of just an inflation roof. Imagine having to frame and seal perfectly enough to be air and water tight!
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randy · Joined: 02 Sep 2008 Posts: 51

The poly is installed on the roof, the south side wall and the west end wall. The east end wall piece is the wrong size so I'll have to re-order and hope the open east end will be OK for the time being. It took five of us most of the day. The day started out perfect but a breeze came up about the time we began fastening down the roof and made things a little scary.

Photos updated to show poly inflated. Note the very small inflation fan in the northwest corner. It does the job just fine.

mrhobbithhnet · Posted: Sat Oct 24, 2009 4:36 am Post subject:

I feel for you, having it so close to all wrapped up must put a damper on the scene. No worries till the planting starts. Hope you get a replacement in time. What's up, order wrong or ship wrong?
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randy · Joined: 02 Sep 2008 Posts: 51

I have re-designed the air distribution/control mechanism into/out of the SHCS. An earlier version was a complex assortment of els, tees, ect. The new version is a simplified 48" x 48" x 16" box.

The box will be divided into three 16" vertical sections and placed at one end of the pared 12" HDPE header pipes. The left section will accept air input from the greenhouse. The center section is divided into an upper and lower half, each at the end of one 12" header pipe. The top half of the center section has one normally open motorized damper on the left and a normally closed damper on the right. The bottom half of the center section has a normally closed motorized damper on the left and a normally open damper on the right. This configuration will direct air-flow into the upper level and out the lower level. Reversing the dampers will reverse the air-flow into the lower level and out the upper level. The right section will direct air output into the greenhouse.

Installation of these boxes will be the next step. I will use 1/4" thick polyethylyne sheet and 18 gage galvanized studs to construct the boxes.

mrhobbithhnet · Posted: Mon Nov 02, 2009 4:29 pm Post subject:

Randy,

Great idea you are working with, it has potential to maximize the heat sink differentials for both heating and cooling cycles.

One thing though, upon looking at your plan view slide of the SHCS layout drawings, I am not seeing how you can equalize the flows in the individual tubes.

I am thinking that if you were to blow in and exhaust out the same end of plenums like I think I'm seeing on the plan, the air will short cycle through the tubing closest to the fans, as it always takes the path of least resistance. Unless I am not seeing something (likely, I'm not there) the only way to get equal flows is to pressurize the plenums quite high so that all the 4" tubing sees relatively the same pressure on their inputs. The cost in fan energy to do this is has been very, very high for me and not really do-able with regular fans, but practical only with high pressure blowers.

Curious, fill me in on what I am not seeing here.

BTW, I am coming south through Idaho from Canada in a few weeks, would you entertain a visit? I'd love to come cheer you on...
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randy · Joined: 02 Sep 2008 Posts: 51

You are correct. There will be a short circut effect and I hope it won't be substantial. If I place the inlet and outlet at opposite ends the short circut effect would be elliminated but I would lose the ability to reverse the flow. My fans are Fantech FKD 12XL and will deliver 1423 cfm @0.75 in W.G.

I would be pleased to host a visit when you come through. I would certainly benefit from your experience and look forward to going over some of the details of my project. Not sure if the SHCS will be operational by that time.

mrhobbithhnet · Posted: Wed Nov 04, 2009 2:46 am Post subject:

I'll be in touch with you in the next week or so Randy. I should have some sort of an idea of when I'll be heading down your way by then. I appreciate your willingness, I think we'll have a lot to share. Looking forward to it...

I'll give your existing tubing arrangement some thought in the meantime, there might be a way to ensure equal flow with reversibility... it might involve reversible fans. Can you return the Fantech units still? The best fan options these days is to go with 1/4 hp 3 phase motors, blades, frequency controllers and your own assembly.

This gives you complete power curve control for speed and direction, computer controllable with a $100 PLC and a host of other benefits.

We've completely gone over to 3 phase freq controlled motors at Strawjet.com, dropping the old approach with single phase worked up with windings and more windings and condensors for your direction, starting torque and power curve needs. All that is history with brain dead simple 3 phase motors for all jobs. Plug em into a controller, set the speed, direction, ramp up/down time and forgettaboutit! If you plug a SHCS fan into a digital temp sensor or two you could easily program your fans to power up and adjust speed to the air temp and soil temp differentials, and reverse based on time or temp. Automationdirect.com
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randy · Joined: 02 Sep 2008 Posts: 51

Unfortunately a 3-phase power line is not available in my area.

mrhobbithhnet · Posted: Fri Nov 06, 2009 4:52 am Post subject:

Sorry, I didn't make that clear. You use 3 phase motors for sure, but you don't need 3 phase power, you run the motors from controllers that generate the 3 phases for you! All you need is regular 110 vac or 220 vac, what ever single phase you have. The controllers do all the magic for you. That's the beauty of it, we can set up any drive system we want, all with identical motors, and just send out appropriate controllers that do the translation in the locale we sent it to. You could never even think about doing that a few years ago, but the advent of dirt cheap controllers that can generate 3 phase from any input has opened up an entire new range of options for less money than conventional ways of creating variable speed, reversible, multi-torque drives. 3 phase motors are dirt cheap to supply and keep running, very, very efficient and will run forever if you put a few bucks into bearings. Take a look at automationdirect.com:

Controllers
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randy · Joined: 02 Sep 2008 Posts: 51

Uncovering the first of three SHCS manifolds in preparation for the installation of the air distribution box refered to in earlier posts. In the attached photo the upper and lower 12" manifold pipes as well as two 4" UACT are exposed in the excavation. The air distribution box will be constructed around the manifold pipes. The excavation measures 1.5' x 8' x 4.5', about three tons of silica sand.

mrhobbithhnet · Posted: Wed Dec 02, 2009 3:09 am Post subject:

randy · Joined: 02 Sep 2008 Posts: 51

I have just started monitoring the greenhouse temps outside, inside and in ground at 4' depth. This morning at 7:00 am, before sunrise, these temps were 7d, 26d and 50d respectively. The temp in ground remains constant. This is about the bottom of the silica sand and the top of the 20 mil pond liner. Beneath this is the drainage system and numerous soda springs. The springs surface at about 60d. The drainage system consists of drainage pipe seperate from the SHCS and 8" of coarse volcanic cinders. The floor remains uncovered silica sand and is dry and loose at the surface however, is moist several inches deep. The other day I moved a 4' x 8' sheet of poly from the floor to reveal satutrated sand, because of condensation on the underside of the poly. There is no ventilation inside the greenhouse and the SHCS remains unoperational. This indicates a significant heat flux between the ground and the greenhouse air. How much of this heat flux is do to ground moisture evaporating into the greenouse air (latent) and how much is do to conduction through the floor (sensible)?

mrhobbithhnet · Posted: Mon Dec 07, 2009 2:16 am Post subject: Re: Temperature observations

randy · Joined: 02 Sep 2008 Posts: 51

The first air distribution box is finished and ready to move to the SHCS. The following photo shows the box without the top and front panels. The four motorized dampers are in place.

This next photo shows the box in place at the inlet/outlet end of the header pipes. The top panel is absent and the excavation is ready to backfill.

randy · Joined: 02 Sep 2008 Posts: 51

I was fortunate to recieve a personal visit from MrHobbit. I had the opportunity to demonstrate my greenouse project as well as some of the local area features (outgassing CO2 and low grade geothermal springs). It is the combination of these features with SHCS which makes my project somewhat unique.

One of the subjects we discussed was split-night air temperature combined with root zone heating. This is an appropriate discussion along with SCHS because this heating strategy potentially maximizes the value of a SHCS and elevates SHCS into the realm of realistic commercial consideration.

The strategy involves accepting a lower night time air temperature (45-48 dF) while heating the root zone. In my case I will attempt to grow row crops (tomato, bell pepper, cucumber, etc.) commercially while only applying heat at the root zone. This will be accomplished using a hydronic heating system with 120,000 btu capacity. My potential greenhouse growing season will be March through mid-December, with seeding to begin February 1st. The remainder of December through February the greenhouse would be inactive, perhaps producing a few cool greenhouse crops for personal consumption.

References and research in this area are abundent, to name a few:
The Solar Greenhouse Book, James C. McCullagh;
The ABC of NFT, Dr. Allen Cooper;
ATTRA, Root Zone Heating For Greenhouse Crops, Steve Diver;
Crop Science, Crop Physiology and Metabolism, Mineral Nutrition of Tomato Under Diurnal Temperature Variation of Root and Shoot, Martin P. N. Gent and Yong-Zhan Ha;
Rutgers, Numerical Modeling of Greenhouse Floor heating, E. Ross, D. R. Mears, T. O. Manning, G. J. Wulster and A. J. Both.