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JoeK

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Reply with quote  #11 
scott, I need to catch a few Z's since I'm working in a few hrs but check out "hugelkultur" (sp?) and sheet mulching. both highly reccomended for raised beds. active compost under your sprouting seeds will speed germination and give a few extra degrees soil temp throughout the first growing season. then next year you will have a very productive rich composty soil. First year will perform stellar as well but certain elements need to be in balance. mainly Carbon and Nitrogen ratio. More on that later.
I've also buried manure in between the raised beds, underneath pathways, in the space pictured which generates additional heat. Most effective at the beginning/end of the growing season as the exothermic stage of the compost is relatively short lived.

Ky-Jeeper

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Reply with quote  #12 
I have 5 30'hugelkultur beds and love them. Thought about running pex through the beds for a longer growing season via a solar batch water heater.
SolarInterested

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Reply with quote  #13 
http://www.appropedia.org/Hugelkultur

Interesting - thanks for mentioning them.

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Both temperature rise and airflow are integral to comparing hot air collectors
JoeK

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Reply with quote  #14 
Thanks for the feedback, everyone.  Glad you've enjoyed my postings. Finally a bit of an update. I'll asnwer a few questions I received.
I do not have any experience with data logging, but I would LOVE to set something up if it could be done for a reasonable price.  I am actually planning to move from this property in just a few months though so the operation of the greenhouse will have to be turned over almost immediately to someone else... have another amazing project to move on to and no time to hang around, though I've lived here for 4 yrs now and absolutely love this place.

 The system in my thread will be using a fan sized as follows.  According to my latest calculations the volume of air above the ground to be fairly close to 1,000ft^3, plus around 2-300ft^3 worth of subterranean ducting. That's for 4" nominal ID and average 15-20ft lengthx 14 pipes, plus most of two barrels @ 7.5ft only adds 15ft. Accounting that there's a big water tank in there taking up ~45 ft^3 and soon enough a bunch of plants I like the easy American math provided by just approximating at ~1200ft^3 total air volume in the system. Calculation gives 5 changes per hour to require just 100cfm airflow. 200cfm gives the full reccomended 10 changes per hr, recycling the air every 6 min.  I will likely put a well oversized fan in there and run it on a variable speed control to dim it.

I'm hoping to find some sort of a meter, like a handheld kestrel or the like, to measure actual windspeed in real time. I know one of the experts on these systems uses one that measures temp and humidity at the same time as air speed.  Any input, advice, or reccomendations on handheld or stationed measuring/datalogging equipment or techniques would be welcomed warmly into my vacuous brain cavity.

Fan will be controlled via thermostat to  run whenever temps rise or fall out of range ~55-75* or similar. The designers of the systems just use two industrial thermostats, one sets the high point and the other low.  I will have a tiny system by their standards, and a tiny fan requirement, but I found a controller for 22$ on ebay called Digital STC-1000 that should do both functions if I'm reading it right. I'll have one in my hands soon enough and find out if its all I need. Will want to upgrade to something a bit more sturdy soon though as cheap chinese electronics are not known for dependability.
The system absorbs or releases heat accordingly as cooling or heating is needed. Relatively warm air at 50*+ comes out of the soil during cold winter nights, while relatively cool air comes out in the high sixties or likely in the seventies during hot summer days. And much of the time this mass buffered system should be able to maintain the inside air temps pretty darn stable in the desireable range. Hopefully near 70* a lot, you know, tropical [smile] It'll be a grand success if it can at least stabilize in the broadly happy zone of 50-80*, most of the year at least.
Time will tell, since I haven't actually tackled any real calculations of total system gain/loss, though I know I probably should! =0

The link I posted on page one contains within a link to a chinese study where some data logs including soil and air temps can be viewed. Limited windows of data are published but its something.


  If soil temps can (hopefully) remain in this speculative range much of the year it should be a raging success of plant growth. Will wait until the kinks are worked out a bit before planting any high value perrennials like a cold hardy ,dwarfed avocado tree, pomegranates, figs and maybe a dwarf citrus too. Also have another small space for a dwarf or fig etc.on the new porch, more on that later [wink]

The insulation is indeed to slow the heat loss to surrounding soil. probably a minus in summertime when dealing with cooling needs, but I think it will be worth it for the gain in winter.  Convserving as much heat as possible in winter is straightforward, but its a bit more tricky in summertime, and I'm not honestly sure how it will all operate until its up and running. I do think the system will need to be run at night, exposed to the cool air, in order to vent heat accumulated during the day. Likely desireable to vent heat directly out during the day as well during the hot months of summer. I think I have fresh air vents layed out well enough for both purposes. There will be a long, low, passive intake vent along the North wall near the soil surace, 8x3ftish, two of the small windows along the bottom of the East wall are on hinges, as well as another, smaller vent 1x5ish along the west wall below the subterranean intake riser. A sort of small passive heat vent will be located at the top of the East wall to vent heat directly out during hot summer days, probably should have bigger vent for this purpose...but I think I can incorporate a hot air panel on the roof as well to provide heat via active fan in winter and possibly power a second heat vent out the top along the ridgeline in summer. If the panel were designed slightly differently it could be allowed to vent heat off via convection only and use no active power input. with a Fan assist at hand if needed. Gaining heat from it in winter will need a fan for sure though.  I have an 8x4" used hot air panel, commercial unit bought used for 50$, seems to operate fine, needs a coat of paint and a replacement gasket for the glass though. this will go on the roof to boost the heat as soon as possible! the growing season will be on in this thing about as soon as I get it finished, hopefully have it running before the ides of march...
 Fully half the structure on the Northern side will be covered with galvanized siding/roofing sheets and insulated as well as possible. This should provide a lot of shading and heat reflection/deflection from the high sun of summer. I was out there yesterday and today, february 19/20, and it was still allowing 100% of the low angle sun in at this time of year. The Eastern wall is glazed in used (free) double pane windows from when some friends upgraded to new extra high efficiency windows in their home. For reference to the exposure aspect of the structure,  long axis lies ~15-20% West of south according to both apps on my phone.  I think sun parameters are going to work out well enough. I intend to put siding up on the inside as well to reflect precious winter light and heat off the interior N. wall towards the growing plants, and the heat mass they are planted in.
Extra heat mass inside as well in the form of a 300gal water cube located near East wall glazing and air return from subterranean duct. Dreams may include switching tank to a hot tub in future...

here's where it stands today after getting half the West wall up before snow flurries came around yesterday.



JoeK

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Reply with quote  #15 
Think I finally got this round of pics sorted...showing overview of site and exposure. trellis on top of fence will be removed soon.  During the shortest days the rising sun enters the East wall and then moves to the S. glazing during the early morning hrs, then it is intermittently shaded by those pine trees during mid-day with a short clear window again near the end of the day. Sun will start clearing those trees completely again in a couple weeks, but then it will soon begin moving higher in the sky enough to be shaded by the Northern half of the hoops more and more as summer enters full swing.  2-20-14-3.JPG Feb-20-14-2.JPG 
2-20-14-4.JPG 2-20-14-5.JPG

JoeK

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Reply with quote  #16 
West wall is getting a little sun in this photo, but that only happens for maybe 30-60min. a day, otherwise it is shaded by the neighboring studio apartment (its part of the property too.)
Feb20-14.JPG 2-20-14-6.JPG 
Feb20-14-1.JPG 2-20-14-7.JPG 
Since the west gets a lot of sun on its interior side, I think I'll mount at least one pallet full of greens on the inside. Something like this. This shows a sneak peek at what is going on against the N.Wall of my recently constructed back porch sunspace off the big house. I'll make a seperate thread for that some other day...
2-20-14-8.JPG 2-20-14-9.JPG

mattie

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Reply with quote  #17 
Hello Joek
i have some questions if you dont mind.
if you use the SHCS to store energy in the soil which is surrounded by insulation underneath and at the sides but not on top, is the heat not left to escape through the greenhouse structure during winter months? unless the structure is designed to ensure a high percentage of it remains inside or is the constant cycling of air enough to capture a large percentage of the heat gain in the soil.What happens on cooler nights when the energy stored in the soil is fully released? You do have the sensible and latent heat difference with the dew point met in the pipes.The energy stored in the air will also change with humidity levels.(A bit vague for anyone interested look up relative humidity)

If the temperatures get really low outside and then to add to this there isnt a lot of solar gain, might it be posssible to take advantage of the constant temperature at depth like in the case of the walipini? A secondary loop deeper in the ground perhaps that could be turned during prolonged cold periods? Or is the depth here great enough to take advantage of the constant year round temperature(somewhere like 50 to 55 f to 10 or 12 c)

I suppose a lot of this is down to in what way the plants respond to jumps in the internal climate and how long it takes to see the negative aspects of this,if its a short period then there is some timeframe allowed for a new day to kick in and the temperatures to start rising again.(After all plants do live outside sometimes too [smile] )

This turns into an additional question in the summer months.As you mentioned yourself , the insulation in the soil is a two sided coin; on one hand you get to capture the suns energy in the soil on the other you limit its cooling capacity.There has to be some general ratio here, dependent on location, greenhouse volume,soil type etc.(apologies if this has been dealt with allready the sunnyjohn post i have not had time to read all of it yet).

Regards Mattie
mattie

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Reply with quote  #18 
Hello Joek
Regarding data loggers and sensors im sorry i can not recommend any .There seems to be a massive jump in price between the chinese versions on ebay and the more professional looking models.I had seen one for humidity and temperature on ebay though that had the option of recording the data to an sd card which is a handy function, although once more i cant state how how long it would last or how well it would work.
However as there is limited data regarding the performance of a system over time i do feel it would be worthwhile doing.If you dont not want to invest all your cash in sensors and data loggers perhaps kickstarter would be somewhere where people could donate to allow you to do as the information gathered is of value to many others.

Regards Mattie
mattie

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Reply with quote  #19 
Here is some of the instrumentation used on the greenhouse with heatsink post.http://www.roperld.com/science/YMCASolarGreenhouse.htm#instruments

There is also some monthly data recorded on that page for a similar type of system.http://www.roperld.com/science/YSGHData/

Regards Mattie
JoeK

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Reply with quote  #20 

Hi Mattie and everyone,
            In answering those question I'll go ahead and provide some further site info and construction details. Bear with me if I seem to ramble around before i get to the point.

In reference to insulation on the top it is almost always true that the glazing is the weakest thermal point in a greenhouse. It certainly should be. There's only so much one can do to slow the heat loss at nighttime.  I can look it up, but I think the 10mm twinwall polycarbonate I'm using for glazing is about R-3 or so. It cost ~350$ just for the 3 panels on the S side.  The N and W-walls will be insulated as well as possible under the plywood and galvanized siding. I just looked at a chart that showed cardboard about as good as fiberglass or denim batting per inch...haven't settled on insulation yet but need to decide soon. I did put up some R-13ish polyiso board on the West wall already, and just picked up a big roll of reflectix bubblewrap sheeting for 8$ at the ReSource yard.  A pallet planter filled with moist soil affixed to the interior W. wall will absorb a lot of BTU's during the day. That spot gets some of the best exposure year round. When it radiates it back out at night it will help moderate the temperature drop out in the central planting area.  I'll have to find something heat tolerant to plant in it for the summertime when it's still is going to see a lot of sun.  Maybe some Rosemary could make a go of it.  The water mass above ground on the E. side will perform similar function. The old windows are decent, but nothing like the insulated wall on the West.  The triangle shaped glazing around the sides of the windows actually consists of two layers of the twinwall polycarbonate seperated by a 2x4 width (actually 3.5" i think). So those are much better insulating than the old windows are, but do transmit less light. The 330gal Water cube can hold ~2750lbs of water though so its a MUCH more significant mass. When I installed the cube on its used fencepost supports before winter I dug a pit a couple feet down below it and filled it with donkey manure and worms.  Instead of worms though it could be filled with a "hot" compost pile with plenty of nitrogen to add some heat to the equation in October/November just as winter starts to show.  The pathways under those boards are similarly trenches filled up with compost, and were it done purposefully would radiate heat effectively to the surrounding grow beds.

Regarding insulation of the heat mass, Yes, The hope is also definitely to benefit from the sheltering effect of the earth that closely surrounds the greenhouse.  The North sloping sight was leveled only just enough to fit the structure in. Thus the S & W sides have significant earth sheltering for the underground heat mass.  On the N & E walls the exterior grade is much lower due to the original slope of the site. I placed an additional 4" layer of earth that surrounds the insulation boards on these sides.  It is held in place with some scraps of plywood, metal roofing, and a couple used siding panels that were donated by my neighbor.  I'll put a couple pictures up that show some the earlier construction and the extra buffer of dirt surrounding the insulated heat mass. The buffer is actually exposed inside the structure right now, but I'll cap it well with insulation when I do the wall, which itself will conceal the buffer layer. If I left it exposed to the interior it would provide a thermal bridge for the heat to circumvent the insulation and be transferred more easily out the N sidewall.
  Frost line lies somewhere in the 3-4ft range around here depending on microclimate and how fast you hit bedrock.  I'm expecting the greenhouse itself to create a significant "thermal island" and the frostline of the directly adjacent soil to be affected such that the 4ft. insulation boards will reach easily below that line. I don't know if it will be enough to tap into the average 50* temp of deep soil or not, I think you'd have to be deeper.

Overall the system is designed to build up and carry a big load of thermal energy into winter, and slow its loss as much as possible. It is as well insulated as possible at every turn.
In order to maintain the underground storehouse of heat as long as possible the idea is to only use the fan to draw heat out of the ground during cold nights just enough to keep certain parameters. Allowing the heat that simply radiates up from the mass to suffice whenever possible.  For example keeping the air temp above 32* shouldn't require active transfer until the temps really drop outside. Keeping active draw to a minimum should be able to maintain its thermal inertia fairly well, at least I hope. The temperature tolerance required for dwarf trees and other perennials is two fold. Generally plants can take colder air temps for a short period if their roots do not get too cold. For many trees and "mediterranean" climate perennials, like figs and pomegranates, as long as the roots stay around 25* they can handle temp dips down to the teens while in a state of dormancy for the winter.  This means the temp of the heat mass (soil/roots) is as important to consider as the air temp. Probably more so.  I think this greenhouse will at least be able to keep the heat mass up to 25* without trouble. If i can get that hot air panel mounted on the roof securely, I have no doubt it will at least be suitable for figs and other "mediterranean" plants. I've found nurseries claiming citrus and even avocado varieties that can survive down to 20*F or so. An avocado tree would be amazing. Might even be room for that and a citrus. they'll need regular pruning and maintenance to keep under the cieling of just ~7ft or so, but I think it may be workable.
Don't plan to plant any expensive trees until its performance has been evaluated for a winter or two, but may have a go with a pomegranate or a fig right out of the gate.  I haven't decided if the little fig I got from Jerome will go in the ground out here or just in a big container on the back porch, where it would definitely be fine.  Kale outside survived -17* below and several days that never saw temps above 0* in November. There was a blanket of maybe 2 inches of snow covering them during that.  Other hardy winter crops should also survive easily inside this thing year round. The short days of december/January might not provide enough sunlight for them to really grow much, but they should remain harvestable during this time.

I have no doubt the interior airspace will heat right up on a cold sunny day in January, but I don't have much clue numberwise just how efficient the transfer to heat mass will be.  BTU captured vs loss, or the common % used for panel collectors would be cool to figure out someday...

The hoop structure is a good shape to minimize exposed surface above ground to sub zero winter temps and also withstand frequent high winds. It also sheds snow well and importantly it will match the existing architecture to which it is adjacent.  Did I mention it was easy, quick, and cheap to frame up? Used 5/8" rebar as the hoops @ ~10$ each 20ft stick. Got all of them erected in just about an hr. Should have bent them a little more precisely, but my neighbor and I just bent each one as it went up. First one end was clamped in place, each hoop end anchored to another 4+ft piece of buried rebar with 3 steel clamps and ~8" overlap. The attachment points were pre-bent to approximately match the final curve. Then my neighbor Bob pushed from the free end while I stood in the middle (marked w/tape) and made sure they went up straight and bent evenly, almost. They really bent quite easily. I could have corrected the variance better had I realized there was an issue right away. They are all pretty close though and I didn't realize how out of phase the panels were joining up until I would have had to dismantle too much to get back down to the "skeleton". The bit of variance isn't really any issue on the insulated half and where the two glazing panels join out of phase there is a strip of special tape that manages to bridge the small gap OK. By the time the ridge"pole" of 2x4's and the two 4"x6" endposts got bracketed it really felt strong, and now, almost all the way covered, it hardly even flinches when the high winds howl.  It's got just enough room inside for 1 or perhaps 2 dwarf trees or similar large perennials like a fig or pomegranate.  I hope it will stay cozy inside, but it will definitely be a constraint on what plants are gonna fit in.

In regards to summer cooling, You bring up the excellent point of adjusting designs to suit the locations dependent variables. This one is located in a semi-arid, cold winter climate, with a very short (~90-100)day frost free summer growing season. Site is in Colorado's Rocky mountains @ ~7kft elevation, ~40N Lat.  Steep grades and many microclimates are found in the mountainous canyon lands surrounding.  Avg yearly precip around 15-18 inches or thereabouts.  Ponderosa Pines predominate amongst junipers and a few other species of conifers.  Patches of aspen are a local attraction for the fall colors. Lots of wild roses and currants in the understory. a few types of Cactus are seen on drier, usually S facing locations. As mentioned I recorded -17*F during that early cold spell back in november and last month saw the season low hit -22* while frequent sustained winds of 30-40mph pummeled what seemed like non-stop for several days at a stretch. A friend on the sunny side of the street (across the canyon) says his monitor records gusts at 100mph 2-4 times per year average. Feels like a wind tunnel often enough. In this context you can see why "winterizing" is primary concern, and summer cooling not so much. The shading from the N wall should be sufficient to mitigate any serious overheating potential.  Around here  Most houses with decent design do not need any cooling in summer.  Just open the windows at night and we might see temps drop to the low 60's or even 50's after a scorching summer day at 90-100+*F. Daily fluctuation of 40+* is common in exposed areas. The sun can really get cookin up here.  I'd love to see what irradiance measures in real time under clear skies.  Certainly the typical estimate of 300btu/hr/ft^2 is a very conservative number at this site.

We benefit from ~300  days per year with sunshine, about half of those considered "clear" days, and the other half "partly sunny". Colorado is certainly known to have great conditions for solar.  PV panels are very much "In" fashion statewide.  I found a calculator http://www.degreedays.net/ that says ~7,400* heating degree days typical in this area for a base temp of 65*.  But that's suitable for a home. For a base temp of 45* the heating requirement is reduced to ~2,600*. A base temp of 32* requires just 987*days. The low insulation of the glazing would probably raise those numbers a bit, but I think overall it will be good to go.  On a typical cold winters day, under sunny skies, temps often stay somewhere below freezing, but above zero. Of course they drop much lower during the occasional cold spells, winter storms and such. Its unusual for significant cloudcover to linger more than a couple days at a time though. On most days the solar gain should be easily able to get the internal temp up to a comfortable range, and I suspect some extra heat to suck underground for storage even in mid-winter.  I do plan on installing that 4x8 hot air panel on top just N of the apex too which will definitely result in some excess for storage.  Any excess heat stored during the day will radiate at night from directly below the plants.  This will create a rather significant microclimate at soil(and below) level even without any active draw from the fan.

Whew, sorry if that's a dense reply, but please do let me know what you think. Happy to hear more questions, they really help me to consider all the different angles.

Joe





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