This is to continue the discussion from the previous Subterranean Heating/Cooling System thread.
This post was edited by Annalog on Tue, Apr 1, 14 at 18:41
I will be interested to see what the folks say about your lay out plan. Hope you are on spot!
Thanks, Waterstar. I think this plan is very close. My biggest concern is now the tube crossings. I could eliminate the ones from a single greenhouse by adding one more exit plenum on the south side of the greenhouses, nearly matching the north but with only the south lines while the north exit plenum would have the center and north lines. However, then all three lines would need to leave the greenhouse space through a 16 inch space in order to make room for the additional plenum. But since that would be at nearly the same distance for all the tubes, maybe that wouldn't matter as much.
My plan to have 1/2 inch hardware cloth below and above the heat sinks was confirmed Tuesday when I turned the soil in the raised bed near the chicken coop -- two underground nests of field mice! I don't know if they moved in during the winter when the bed wasn't being watered or earlier when I stopped cultivating as much after planting a perennial on each end of the bed. It may be that the mice killed the perennials and not the early cold snap.
While the lower level of hardware cloth will be permanent, the upper level will be removable if needed.
I kind of like your idea of "...leave the greenhouse space through a 16 inch space in order to make room for the additional plenum. ...".
Sounds like you need a greenhouse kitty!!! ( :
OK, a drawing of the idea with the extra exit and no crossing tubes from the same greenhouse.Tubes from the two greenhouses do overlap but offset by 6 to 8 inches vertically.
You`ll be ok with the 6"-8" spacing. If the tube lengths and amount of bends differ a lot you`ll need to devise a plan to balance the air in such a way that the longer, more bendy tubes get a bigger share. If they`re all balanced equally, the longer bendy tubes will have a longer dwell time than the shorter less bendy tubes.
All the tubes in each system are planned to be the same length (inside system tubes are longer than outside system tubes). The bendy bits are exaggerated but are to allow the two tubes with the shorter paths be the same length as the one that goes around the other tube.
There will be separate fans for the inside and outside systems so at they can be operated separately or at the same time. Since the outside of the outside heat sink won't be insulated, I plan on only using that one for cooling. I figured that it would be OK for those tubes to be a different length than the tubes in the inside systems.
I am planning on movable baffles or adjustable openings to balance the airflow if necessary.
I am eager to get started digging when the weather is less windy.
Looks a lot better to me. I'll be interested to see what Curlygirl says about the ones just for cooling...
The easy way to increase cooling capacity during the season is to make provision to connect the inlet and exhaust plenums to the outside air. That gives the option of running the system at night to lower the soil mass temperature to increase the cooling capacity for the following day. You may never need to use it but its worth incorporating into the overall design just in case you do.
This post was edited by hex2006 on Sat, Apr 5, 14 at 18:56
Please accept my apology. I meant to say I was waiting to see what YOU had to say about the tubes just for cooling. ( : By the way, thank you for all of your posts in the past years, they helped me learn a lot.
Wow! Your comment is going to change my design. In my hot humid summers here cooling will be an issue. I will talk to my hubby today so he can figure our how to "to make provision to connect the inlet and exhaust plenums to the outside air." THANKS.
By the way, in some of your old postings you mention that your greenhouse is 154sqft. I'd love to see a picture of it.
I dont know if Curlygirl has her system up and running yet but it would be nice to hear how other operational shcs systems are performing in different climates.
You can see some pics of the greenhouse and the shcs install on johns old forum. The shape of the floor and roof didnt lend itself to the standard 2 plenum tubing layout so i had to come up with something different.
Hex2006, the tip to provide a means "to connect the inlet and exhaust plenums to the outside air" is a great one. I now remember reading that somewhere (probably on Sunny John's site) but it had not stuck in my brain. ;-)
I can see how to do that with the inlet plenums since they are in the north corners. The exhaust plenums for the outside systems are very easy as they are already outside and the exhaust could go through the wall or straight up. The inside exhaust plenums are a little trickier. I currently see three options. There could be additional holes in the foundation walls but I really don't want holes that near a corner. I could have the exhaust exit through the base of the greenhouse glazing. This is definitely the easiest. I could figure out how to use the foundation wall holes for the outside systems for the inside systems but I expect that will be too complicated and limit future flexibility options.
When I add a clear cover in the winter over the exterior frame over the outside beds and greenhouses (essentially putting the greenhouses inside hoophouses), this modification changes from cooling the inside greenhouses to heating the outside hoophouses. In the winter, the outside systems might be set to hoophouse air day and night while the inside systems could be set to greenhouse air during the day to capture heat and to hoophouse air at night to heat the hoophouses. So many ways to use the system. I love it!
Thank you very much!
P.S. Now I think I may want to insulate the ground around the outside beds. I am thinking of leaving the above ground uninsulated and adding nearly horizontal insulation underground below the walkways around the structure. Fortunately this can easily be added later. :-)
This post was edited by Annalog on Sun, Apr 6, 14 at 11:29
Hex2006, That link was great, I loved reading your info. Must admit tho..it gets over my head. I read it more than once and it still doesn't all sink in. Thankfully I will be able to get this SHCS in without totally understanding all of the physics, thanks to help from folks you, curlygirl, Steve, Anna and others. The info from Sunnyjohn, Roper and others is just so valuable, but I go brain dead off and on when I am reading all of it. Oh my. ( :
So, now I am confused about how to implement the summer idea of connecting to the cooler nighttime outside air to lower the temps during the day. If I put the intake outside at night to reduce the underground temps, then during the day it will be taking hotter air from outside, right? Wouldn't I want to intake the cooler inside GH air during the day? Are you talking about using 2 systems as vs. my one?
My GH will have the temperature controlled vent openers. The opening/closing temperature range is 59 degrees to 77 degrees, so I will be using them in warmer times of the year. Our temps here in both the summer and winter are usually about 20 degrees cooler at night than during the day.
Can I use the vents to control the intake and outflow of air? I was planning on having them open at night and closed during the day during the summer and then closed during the winter.
For further temp control in the summer I am putting up deciduous or annual fast growing vines outside the greenhouse on the west wall, but letting the sun hit the South and east walls so that my espaliered citrus trees can get light.
I just get so confused sometimes!!! DUH.
Anna, I'm sure glad mine is not as complicated to figure out as yours. ( :
Running the cooler night air through the shcs tubing removes some of the stored heat. The following day the shcs runs as normal, taking air from the top of the greenhouse and exhausting back into the greenhouse. A lot of the information out there is valid apart from the 5 airchanges/hr or 4ft/sec tube air velocity. Roper`s website advocates the 5 airchanges hr and
How do I take the air from the outside as vs the top? Just by opening closing vents? I hope so. We will return the auto temp opener/closers because they won't help up. Hopefully we can find some openers/closers that work on a timer (or are at least electric so hubby can modify them or hook them up to a remote control). I know I sound so ignorant, but that's because I am on this subject. ( : Sigh.
From your post on Posted by hex2006 (My Page) on Fri, Nov 6, 09 at 22:16 I figured my1,044 cu ft. GH would need about 1000 cfm after static resistance. But now I can't remember if that was based on 20 times...I guess I'll need to go back and refigure that. In the meantime though, I have used that 1000 cfm figure to estimate my fan requirements.
I chatted with a very good tech at Grainger and he says my static resistance is about .8-1 in. so that means I would need to get a fan that is 11-1200 cfm for baseline with target flow of about 1000 cfm at .8 to 1in static pressure. He sells one (14" though....bigger than I would like) for $775. (http://www.grainger.com/category/inline-duct-fans/duct-fans-and-accessories/hvac-and-refrigeration/ecatalog/N-lxvZ1z0qm1z)
I also chatted with a tech at Canarm and found I would have to go to thier HVAC devision to get on strong enough. He says the blades on his that Roper mentions are flat plastic at a set pitch and he is not convinced they will function well with a .8 static pressure. I have not priced this one yet...but will call Northern Tools and/or Farmtek? for a quote and will also research it more.
What kind of fan did you settle on? I know it is variable speed from what you said in some of your posts. I'm afraid to hear the price...but why go through all of this work and expense if it will not work right when I am done? I sure don't want 140F.
Thanks again for your kindness to help me learn.
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 ÃÂ£80 ($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.
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. ( :
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
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.
Earlier in the thread there is mention of what type of controller is used to manage the fan for these underground systems. Could I get some more info on that and the "differential thermostat' that maintains a set difference between air/soil temp. Can't find anything like that in stores. Tested out mine for the first time using a reversed shop vacuum, probably 500 cfm. Inlet was 84f/74rh, outlet was 53f/84rh. So it seems to be working. But I don't know the best way to control it.
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.
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. :-)
Brings back ,memories of the seemingly never ending digging phase :)
If you plan to use a differential thermostat dont forget to install a tube for the sensor before you cover the tubes.
A lot depends on the greenhouse, tubing layout, soil type, RH and other stuff but i`d say with a 35F air/soil temperature differential you should be able to acheive soil temp (60F) air from the tubing at upto 13 airchanges per hour. Educated guess based on my experiences suggest 64F air out at upto 25 airchanges/hr and 67F out at upto 45 airchanges/hr. Note that the differential temperature and RH wont remain constant due to the action of the shcs. The soilmass heats up, the greenhouse air cools down and the RH reduces.
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.
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.
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.
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.
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.
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.
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.
Glad to share the info expecially as John`s (plain to sea) shcs forum website and everything it contained has gone forever.
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.