You may not need to vent at night, a lot depends on the shcs system and the climate. If you live somewhere that has scorching hot days everyday, cooling the shcs at night may not be enough to offset the daytime gains without using conventional ventilation.
With a standard 2 plenum shcs all you need to do is attach flexible ducts to the plenums to pull air in from outside and exhaust it outside (bypassing the greenhouse completely). If the plenums are located on outside walls you can use a box on each with two sliding shutters to reroute the air, open the shutters to the outside air and close the shutters to the greenhouse interior.
The static pressure shouldnt be above about 0.2", a few long tubes with high velocity airflow will need more fan power than double the number of shorter tubes, both having the same total combined length.
If you blow down a 50ft hosepipe as hard as you can, you might go a bit red in the face ;) if you cut the hosepipe into five 10ft lengths and blow down all five at once it`ll be very easy.
I upgraded from 10" to a 12" 870cfm duct fan which was around ã80 ($134). Unless your greenhouse is enormous you wont need a 14" fan, especially with a pricetag of $775.

This post was edited by hex2006 on Tue, Apr 8, 14 at 14:33

Hex2006---YOUR ROCK. WHOOPIEEEEEEEEE!!!!

Thanks so very much for the fan advise. What a huge relief. My hubby really thanks you, I scared him pretty good with the $$$$.

Also, now I understand about the venting to cool it at night. It makes a lot of sense and my hubby now can design what we need. My goodness you know a lot about this SHCS.

How hot are your temps in the summer and how hot/cool does your GH get? Is it dry or humid? Do you need to outside vent? I don't know your zone. We get very humid all summer....day and night, so that should work in my favor I think. It usually gets in the 90's in the day, but the humidity makes it "feel" warmer.

I liked your idea of having a place where we could track results with the SHCS in different climate zones. After I get mine up and running I'd be happy to add my info and I bet Anna will too. Curlygirl and Steve333 might join in and lots of folks here. I think it would be fun and helpful to create such a "database".

Blessings to you for helping this newbie. ( :

I`m in the uk so the climate is fairly moderate compared to other places, typical summer highs dont get much above 32C and winter lows maybe -8C. We dont use the zone system but its perhaps 7 ish. The shcs can keep the greenhouse temps within bounds in summer and frost free in wnter. I`m south facing with no tall trees or buildings to block low angle winter sun which helps.
I have passive vents all around the base of the greenhouse along with a single large vent at the top for venting stale air and bringing in fresh which is needed to replenish the CO2 levels. Your humidity is ideal for shcs, moist air reaches dewpoint much quicker than dry air.

Hi hex2006

You have a climate with which I am familiar. I lived in the NW for a long time. Less sun (by a long shot) than SC. The temps here are warmer, and with the humidity it feels much hotter. I have to be careful not to be in the sun too long in the summer or I feel like I am going to pass out.

I was hoping my climate would be ideal with all the humidity and sun. Thanks for telling me it is! I am, as they say here in the USA, in hog heaven.

Now, Hex, you have brought up something else with which I am unfamiliar. CO2 levels. I will have 4 top vents. Do I just open them? Or should I just have hubby cut holes in the walls with removable doors, that could alo be used later if I need to pull air in and out while bypassing the greenhouse to keep it cool enough? How often do the C02 levels need help? Daily, weekly???

I am amazed how many details there are to this and I must say I am impressed by how much you know about it. I am grateful to you for your help.

Greenhouses delayed again by chickens. ;-) Hubby and I have put up an additional chicken pen (10' x 10') with interior coop and may need to put up a second before work on the SHCS foundation. This fall is looking less likely.

Hi Curly Girl,

Just wondered how your project is going. I'd love to see some pictures. Mine is slow, but some progress. ( :

Blessings,
Waterstar

Hi Curly Girl,
I am also interested in your progress.

We are currently working on that second 10 x 10 chicken pen. (One of the ordered pullet chicks has turned out to be an aggressive cockerel. DH calls him Bitey and I tend to call him Dinner or Fricassee.) The only progress that I can report on the greenhouse is that the drainage in the existing dug area is sufficient to have no standing water the morning after over 2 inches of rain in one day (3 inches over two days and 4 inches over five days) with fairly saturated ground. The rain was such that it had filled the 10' x 10' hole that had been dug 8" deep in order to bury hardware cloth under the second chicken pen due to runoff from uphill. While we had not checked the greenhouse area, I suspect that hole was filled with over a foot of water as well.

My current goal is to finish at least the entire foundation, the west greenhouse and central shed by the end of spring. We will see if I meet that goal. ;-)

Finally started digging the foundation. 1 foot by 12 feet by 6 inches took 45 minutes (west edge). I don't want to know what that calculates as for all of it. Actually, the first six inches is the worst as that is where most of the rocks are (especially as there was a pile of rocks and asphalt in this location when the road was worked on before we bought the acre.. ;-) I will do a calculation after I get to the planned depth. I expect it to be much better than the current 6 cubic feet per hour. :-D

Edit: Geek that I am, I could not resist doing the calculations. 288 square foot area, 6 cubic feet per hour for the first foot and at least double that for the rest of the depth works out to 48 hours for me to dig the first foot and another 48 hours to dig the rest, not including either soil transport time or DH helping. Figuring a 6 hour work day is 16 days or 8 weekends of good weather. It is possible that we could be working on laying the foundation walls in March if DH can dig an hour or so on good weather days. :-)

Second edit: Dug 3'x12'x6" in the next 45 minute session and then 2'x12'x6" in a 35 minute session. My estimate above seems more realistic.

This post was edited by Annalog on Wed, Dec 31, 14 at 15:00

Still on track. DH and I are making good progress on the 12'x24'x3' hole; it is over 1/3 dug. Hoping to finish the hole by the end of February and start the foundation wall and subterranean heating/cooling system at the beginning of March. I need to redraw the plans for the size change of the central shed as it affects the tubing layout.
---
Update: DH has been a digging demon. It looks as if we will be starting on the foundation walls by mid February.

This post was edited by Annalog on Tue, Jan 27, 15 at 8:05

The hole for the greenhouse project is now over 80% dug. The hole will be 12'x27'x3' for the foundation containing the underground part of the subterranean heating/cooling system. Both DH and I are getting excited about putting in the foundation and filling the hole back up. :D

Some photos:

The yucca that needs to be removed.

West end of hole. The pipe and pole are the result of electrical work before the design was changed.

View from the house looking east.

Few questions about this system for my climate – low elevation (700’), Mid Atlantic, zone 7, MD. In my climate I’m probably more interested in the COOLING aspect.

My thought is that a subterranean system might be BETTER for cooling on sunny days than ventilation from outside air, once the outside air is over a certain temperature.

If the subsoil temperature is 60F (guessing) and it’s 95 in the GH, and the outside temp is 84, if I could utilize that cool subsoil temperature, could I cool more effectively than using a ventilation fan??

Also – would this system do anything about CO2 levels? Would CO2 levels change in any way from this system or would it be “neutral”?

Glad to hear to updates on this site. My hubby got suddenly ill, so our progress has been halted for now....but hoping to start it back up late spring or early summer. He has the concrete poured for the corners and the frame up, so the next step would be me adding some dirt to the bottom and laying the tubbing in. Even if he is still ill, he may be well enough to show me how to cut the holes for connecting the tubes. Blessings to all and I will be following your progress!

Waterstar, best wishes for your hubby's complete recovery. Glad to see the progress to date. :-)

Hairmetal4ever, my system is not in place yet but I am more concerned about cooling than heating. My understanding is that the most significant part of the heat exchange is due to the water phase change that takes place (water vapor condensing from the air when cooling the hot and humid air from the greenhouse while underground or evaporating water from the warm and moist soil when warming the cool and dry air from the greenhouse during the winter. This should be our first summer to see this work. :-)

Nbet, I am looking forward to answers to your questions. DH and I have been focusing on digging and I had put off looking for the hardware and controllers. It is probably time for me to be thinking about those. Like the photos and the idea of an early test. :-)

Does the system affect CO2 in any way?

If levels are low, does the soil replenish it, or, if you're supplementing CO2, does the soil absorb it out?

Either way, if you supplement it, I imagine you lose less CO2 cooling your GH with this system than you'd lose with traditional ventilation , where it is escaping or you're blowing it out through a vent, but you might face low CO2 levels more often if you do not supplement.

Progress update: I took the yucca out on Sunday and it has a new home in Tucson with a coworker. It is currently too windy to finish digging but DH has started buying blocks and is eager to start the next phase. :-)

Hairmetal4ever, rereading the threads led me to a post by Hex2006 that mentioned passive vents to exchange some of the stale greenhouse air for fresh outside air to reset CO2 so I expect that the SHCS itself has little effect on CO2 levels.

annalog_gw'

Keep those photos coming...very exciting to see your progress

Waterstar, I am away from home but will be back late Tuesday. I am eager to see what progress DH makes while I am gone. :-)

Thanks again, Hex2006. I am so looking forward to my first year (summer and winter) after the greenhouses are finished.

The digging phase is finished! Now come the more expensive phases.

So far, the hardware cloth under the outside beds is in place and we are started on the underground wall for the perimeter of the outside beds. This wall is not mortared and will be filled with sifted dirt. The inner wall will also not be mortared but will be filled with concrete where the blocks are not set sideways.

Perimeter wall:

Capstone blocks under the hardware cloth, concrete blocks over the hardware cloth, and water and electrical access:

DH made progress yesterday and got all the walls outlined:

Achilles, one of our roosters, comments:

Beautiful! What is the purpose of the hardware cloth? I mossed that. ( : Blessings, Waterstar

Waterstar, the hardware cloth is to keep out the gophers and other critters. When we were in the digging phase we saw gopher tunnels that deep and DH uncovered a gopher nearly that deep.

I will also have a layer of hardware cloth just above the top layer of tubes to try to keep the mice out of the system. I will make that layer removable.

• It looks as if the floor level in the central shed will be about six inches above ground level, assuming the north side is about the same level as the south.

I sewed the hardware cloth where the edges are not between blocks.

The east end needs only one more row of blocks to reach ground level.

Future electrical and water access.

Temporary stairs.

Hex2006, you wrote, "If you plan to use a differential thermostat dont forget to install a tube for the sensor before you cover the tubes." Is the tube for the differential thermostat sensor one of the ADS tubes, a smaller tube inside one of the ADS tubes, or a smaller tube in the soil? I cannot find the discussion group where this was discussed. I found Sunny John's FAQ page where it mentions a 30 degree F soil/air difference for turning the fan on so I would think that the sensor should be in a tube in the soil, probably near the exhaust. How far down should this be? Should it be centered between ADS pipes or near a pipe?

Since each greenhouse will have two separate systems, I might need four thermostats. I also may need to modify or build my own. A quick search showed one for $35 with a range matching the range stated on Sunny John's site. Certainly I will want to know the inside and outside bed temperatures for each greenhouse and the air temperature in each greenhouse, as well as the winter external hoop house temperatures.

Definitely switching from the manual labor stage to the thinking stage.

Hi Anna

Just a small vertical tube, open at the bottom and large enough for the sensor to slide down. If/when the sensor needs replacing you can just slide the new one down the tube. Its worth installing some extra tubes in different places and depths so you can check soil temps, dont forget to put one or two outside the greenhouse so you can compare outside soil temps at similar depths. You wont need a sensor for every test tube just a digital thermometer with an external sensor will do the trick.

A differential thermostat is the best way to control the shcs, it doesnt care what the temperature is, only the temperature difference between the two sensors (soil temp/greenhouse air temp). If its set for 20F, the air temp has to be 20F higher than the soil temp before the fan will run. Reversing the sensors allows the diff stat to operate in a heating mode, where the soil has to be warmer than the air (by the differential setting) before the fan will run. A basic thermostat would run the fan when the air temp dropped to the setpoint. even if the soil couldnt provide any heat ;)

I use a differential thermostat in conjunction with a basic thermostat, the basic stat controls a relay that automatically reverses the diff stats sensors (cooling/heating mode) based on what the greenhouse air temperature is, ie; below 5 degC the shcs is in heat mode and above 5 degC its in cooling mode. The differential setting then determines whether the fan runs or not in both cases. If the soil isnt warm enough to provide any heat, the fan doesnt run :)

With several zones. its a bit more tricky unless each zone has its own fan.

Here`s a pic of the homebrew shcs controller i used originally

Thanks Hex2006! I have a lot of pieces of pvc water pipe and end caps left over from various garden and chicken building projects. I can put those in place and cap the ones not in use.

Nice controller!

Outside bed underground block wall mostly in place up to greenhouse floor level. These will be filled with sifted dirt.

Holes cut in blocks for water pipes. There will be a spigot in each outside bed on either side of the central shed and one in each greenhouse. There might also be one in the shed.

We have made some changes to our construction plans. The block wall under the greenhouse will now be filled with perlite instead of concrete. The top course of blocks will be bond beam blocks placed upside down with rebar in the channel and J-bolts to connect the plastic lumber base for the greenhouses and central shed.

I have eliminated many of the underground plenums from my original design. The outside systems should only need inside plenums, one intake and two exhaust, and the same for the inside systems. I am trying to determine if the plenums can be entirely above floor level, even if inside interior raised beds.

The intake plenum for the outside system will have a total of six 4" tubes, two at each level. I think that all six could come out the bottom of a large bucket or barrel next to the center of the end of the greenhouse, go down to the appropriate level, and then through a hole in the wall. Three would go through the north outside bed and three through the south. Then the three tubes would come back in through holes in the wall and up to a smaller plenum that would either direct the exhaust up into the greenhouse or back outside through the side of the greenhouse. The tubes on the upper levels could curve back and forth a bit to make up for the shorter distance. All tubes would be the same length.

The intake plenum will have a total of nine tubes, probably 3" but hopefully 4". I will know after the 4" tubing arrives and I learn if the minimum radius curve will fit in the central shed. This plenum would probably be best with the tubes exiting the side of the plenum. There will be two exhaust plenums, one with four tubes and one with five. Again, I am planning on the tubes coming up into the plenum and then either exhausting into the greenhouse or out through the side.

Problems or comments about the changes?

Hex2006, I don't have time to read the posts right now, just check in briefly (busy with hubby's illness). I just want to again THANK YOU for all of your information. When I get to start again I will be using them for reference over and over again.

annalog_gw

Thanks for the info on the hardware cloth. Duh, I should have remembered that. I am blessed not to have moles, can you believe it?!!!!! Amazing. I have mice, but only growing dwarf lemons in ground, everything else will be in planters.

Blessings,

Waterstar

Hi Waterstar,

Glad to share the info expecially as John`s (plain to sea) shcs forum website and everything it contained has gone forever.

Anna,

No clue about 4" tube but the 3" tube will take a minimum 12"-13" radius bend on a warm day, if you assume 15" radius for the 3" you should be fine. You`ll likely find you have to balance the flow in the tubes even if they are cut the same length as a serpentine tube incurrs more losses than a straight tube of the same length. A handheld windspeed meter (anemometer) is useful for balancing/checking the airflow. I use a skywatch xplorer 1 which is still going strong and was reasonably cheap. Another option is to put a pc fan in the airflow path and measure the voltage it generates with a voltmeter/multimeter. The balancing process involves crushing/obstructing the ends of the faster flowing tubes to increase the flow in the slower tubes. It may take a few goes to get everything balanced. It doesnt have to be perfect but, by the same token, you dont want huge differences.

Hex2006, I will be getting an anemometer. With the tubes all going out of the bottom of a relatively shallow plenum, at least for the outside cooling system, it will be easy to adjust the flow with partially obstructive caps. Also the least serpentine tubes will be the lowest ones so that should be helpful for summer cooling here in Arizona. Having easily adjustable flow would also help if I find a significant temperature difference by tube level.

I haven't yet decided if the inside system will use a deeper plenum with the tubes coming out of the side at each level and no serpentine differences or the tubes coming out of the bottom of a shallow plenum and serpentine differences.

I will be seeing how the 4" tube handles the curves in the next few days.

DH has put in the faucets for the outside beds and the greenhouses and stubbed a line inside the central shed. The electrical outlet is now on a pole inside the central shed. I packed the holes cut in the blocks for pipe access with coarse steel wool as rodent deterrent.

We finally tested the 4" tubing for the outside bed systems against the underground walls and then cut one of the 50 foot rolls of 4" tubes into three pieces just under 19 feet long each. (Yes, the rolls were each actually nearly 57 feet long. :-) ) This was almost long enough for the bottom-most level pipes to reach the floor level (8" short at each end) so we will add fittings to each tube to reach the bottom of the plenums. The tubes sticking into the greenhouse space will turn up along the walls. The top level will have 90 degree turn fittings while the lower levels can have straight fittings. The top level will be the only one with much of a serpentine path. Greenhouse floor level will be about 8" above outside ground level.

I have decided to use the 3" pipe for the inside systems. This will make alternating the levels between the two greenhouses under the central shed easier. It should also let me use similar sized intake plenums for the two systems as the outside system uses six 4" tubes while the inside system uses nine 3" tubes.

While thinking of various ways to fill the half of the sideways blocks that won't have a tube, we decided to use two half blocks instead. Unfortunately, the center holes in the half blocks are just a little too small for the 4" tubes. Therefore, we will be cutting out part of one side.

DH has put pavers between the shed and the greenhouse to see how our estimate of parallel turned out.

I cut the rest of the 50' rolls of tubing in thirds and then sorted them into three groups: short, medium, and long. I'll use the longer ones on the lowest level and the shortest on the upper level.

After temporarily capping the tubes then we can fill the outer sections. We have already filled the sections in front and behind the central shed.

We finally have the tubes for the outside beds of the east greenhouse in place but we are not yet ready to fill those outside beds. Even after cutting out part of the side of the half blocks, I had to chip out a bit of the thicker end to allow the pipes to fit.

I needed to fill some of the blocks with perlite before finishing the wall as the blocks are below a block that will be placed sideways.

We used some of the cut pieces to hold the bottom level of pipe in place.

While the sections of the pipes on the inside are different lengths, they should each reach to the same level above the greenhouse floor. The upper two levels are currently propped above floor level until after the first level is refilled with the dirt removed.

We will verify the pipe placement before refilling with dirt.

Other life activities have delayed progress but today we finished filling the east greenhouse foundation wall will perlite up to floor level. The next step is to refill the outside beds on the east to ground level, remembering to place the temperature probe access tubes. The west end should go faster. ;-)

DH set up a trial of his idea for the temperature probe access tubes.

The inside diameter of the tubes is one inch. The support pipe in the first photo will probably have a 45 degree fitting on each end before it goes into holes cut into the blocks. I suspect that the support is unnecessary but will look nice. Each pipe ends at a different tube level.

Any suggestions?

Looks neat and tidy, the support is a nice addition. Have you decided where to install the differential thermostat soil sensor yet?

Not yet. We are putting 9 sensor tubes in for each outside system, three on the end in the ground near the intake and three each near the north and south exaust ends. Once we can fill in the outside beds, then we can build the exterior hoop house and put up some shade. It will soon be too hot to work outside here without shade except for early in the morning and after sunset.

Hi Hex2006,

My hubby is still critically ill, but I finally found 2 strong and eager young men to help me. The first thing I will have to do is to re-read this site and my notes so I may remember what the heck I'm supposed to do. I do have almost all the materials.

annalog_ It is exciting and encouraging to see how much progress you have made. CONGRATULATIONS! Is this the plan you are still using?

Hi Waterstar

Havent been by the forum for a while but i hope your hubby is now on the mend. A couple of strong youngsters is just what you need to deal with the heavy lifting/digging side of the shcs. Supervisors have to make the coffee ;)

Hi hex2006,

Hubby finally headed in the right direction, but will be months before he is really better. I am grateful he is headed in the right direction. He did all the hard work before he got sick, so cement posts are in and framing for the HF greenhouse is up.

I agree with the strong youngsters. Sad thing is I have to re-read my plans and make sure I've got it right. I know you told me what kind of fan I will need...so will dig through my notes to find it.

Looks like I will be learning how to cut holes in the large plenum tubing. Shouldn't be too hard..

Thanks for checking in on me. I hope I get to slowly start to work on this during the winter...here it is not too cold and the soil is workable and not much rain...ie mud.

Blessings, Waterstar

Good to hear things are on the up and up. If the plenum is a plastic drum.or barrel the best option is a holesaw. If you run the drill in reverse you`ll get a nice clean cut hole and no risk of spraining your wrist as the holesaw grabs the plastic. Another (less attractive) option is to use a heatgun and a steel can (same size as the duct) attached to a piece of dowel/timber ( a can on a stick). Heat the can and melt the holes, wearing a respirator is a good idea..

HELP ASAP PLEASE!

Hi hex2006, et al,

Well, I was certainly wrong on my hubby's recovery. He has been basically in bed with major surgeries etc. since Sept. 2014...almost 2 years now. I am still taking care of him and my elderly cousin and I go 24/7 and am mostly brain dead and exhausted. The good news is that there is a very good chance my hubby should recover, but it will take many more months and/or years. I have stopped guessing and am just thankful that our prayers have been answered and I am not a widow.

I was also wrong about the strong men. They never showed up. I have now had a large hole in the ground with huge mounds of dirt next to it for about 2 YEARS. My friends and neighbors think I am crazy, and they might be right. It will be nice to have the hole covered up!!!

Today got VERY SHORT NOTICE that my grandson is going to help me in TWO DAYS (I am donating $ for college) and so I need to finish getting my materials.

As a reminder: I am the gal in a humid 7B climate with full sun exposure, a 10x12 Harbor Freight GH that ended up being over a septic tank drain field, so I lost 1 ft of soil. I am using 4" corrugated ADS tubes placed into two plenums made of corrugated 12" ADS for the heat sink.

With the loss of depth, I may end up having room for only two layers of tubing, so guess I will put them less that a foot apart in depth. I will see how it goes and I figure anything is better than nothing at this point.

Hex2006, my plenums will be on the outside wall so that I can follow your advise to "use a box on each with two sliding shutters to reroute the air, open the shutters to the outside air and close the shutters to the greenhouse interior." (To help cool in our hot humid summer weather).

For the life of me I CANNOT REMEMBER WHAT KIND OF TUBING I am supposed to use for the intake and output tubing. HELP AND THANK YOU ALL ( :

Well, I regained some brain function and am embarrassed by my comment. I have the 12 inch ADS Plenum in place with the elbow coming to the top, where I will put an adaptor to step it down to a 10" ADS for the intake and outlet.

Does anyone know how far above the top laying of the 4" ADS tubes I can put my growing medium? I'll ask the question on other forums where someone my still be active. ( :

I'd imagine you would need at least the space recommenced between layers of tubes before adding your growing medium. The heavy soil around the tubes is the thermal mass. If you have a loose growing medium close to the top tubes it won't absorb energy well. Have you made any progress? I'm interested in doing the same in a 7b humid climate.

Hi Waterstar,

Arriving late as usual but hope you and hubby are doing ok.

18" of cover would be good if you cultivate in the ground. More wont hurt but try not to go any less than 12" as that will increase the coupling between the top layer of tubes and the greenhouse..

Hi all,

Waterstar, I also hope you and your hubby are doing OK and that he is still on the mend.

Since my last post in 2015, I have had other stuff on my mind. For the end of 2015 through the beginning of January 2016, I was training for and then completing the Dopey Challenge (running a 5K, a 10K, a half marathon, and then a full marathon [our first] in Disney World) with my daughter. We were successful and are both Dopey.

Then in early April my oldest granddaughter was a passenger during an auto accident and was thrown from the vehicle at 85 mile per hour. Many of her vertebrae were broken. I spent nearly two months away from home to help my daughter with my granddaughters. Somehow, she is not paralyzed and can now walk with a cane. My husband has also spent time helping when I was not able to be there. My grandaughter has constant pain that we hope that the surgery this Friday will help alleviate.

In early August my mom fell and broke her hip. I spent another couple months away from home while she was in the hospital and in rehab. She is now walking with the aid of a walker.

We were happy to see the end of 2016. However, now my father-in-law has sepsis and is expected to die soon.

Therefore, my husband and I have decided to get our home and acre ready to sell so that we can move closer to our families. We plan to be finishing the greenhouse by spring so that, hopefully, it and the raised bed garden will be selling points. At least I will get experience using it for the first summer. We will be looking for homes for most of the chickens. I am hoping that we can take our older hens and special needs hens with us. I will be simplifying the greenhouse system slightly by setting up both the inside and outside underground tubing to be used for inside the greenhouses. I will provide the information I have to the future owners so that they can continue to use the system as it will be done or so that they can add the exterior system if they want.

Sorry about your family analog. I look forward to the day when there are autonomous vehicles so many people are injured and killed by human error in cars (their own or another drivers).