Any updates on data from those with SHCS greenhouses?

8 years ago

Ive gone through a ton of old posts regarding people considering the idea, in the process of building the idea out, and some completing. But most posts are years old. I feel at this point there should be a good amount of data to share. I have contacted VA Tech about their SHCS project but have not heard back from the folks currently running it (Roper is no longer a part) Seems sunnyjohns site is no longer.

So, for those who have done it.... questions for you:

1.) What zone are you in? What temps does the house get in winter, how about in summer?

2.) What medium did you choose for the heat sync, native soil, stone, sand? why did you choose?

3.) How many circulations of the greenhouse air volume do you have set up per hour? Why did you choose what you have and would you change?

4.) How many pipes/length of pipes? What ratio of total pipe length vs sqft of greenhouse? (or volume of greenhouse)

5.) What type of glazing are you using?

6.) Are you using any supplemental heat sync such as water barrels/concrete walls etc?

thanks!

Featured Answer

steve333_gw

8 years ago

Well I've had my SHCS GH up over a full year so I can give some feedback.

First a description: it is a 34' x 15' lean-to structure, with the N wall against an unheated barn. It uses square metal tubing for framing and twin wall polycarb for glazing, in the commercial GH style. It has a fairly standard sunnyjohn calculated subsoil heating system with a 30K BTU ventless heater as backup. 4" drain pipes underground with 55g plastic barrels as plenums. I used the GH to grow tomatoes, peppers and eggplants last summer, and it also houses some potted citrus and a fig tree.

Last winter was fairly typical, perhaps a bit less cold than average but also less sunny. I kept the heater set at ~50F to keep it above freezing for the citrus and one tomato which we kept alive and producing over the winter. This is zone 5a, so min temps in the -10 to -20F range (and it got there several times this winter). In hindsight, I probably did not place my plants in an ideal location for keeping them warm (tomato blocked the heat to the citrus), but everything made it thru with no freezing damage. I burned about 110gal of propane in the heater doing this, plus a small amount of electricity in some space heaters on the most cold nights. At today's prices that would be maybe $150-200 in winter heating costs. Were it not for the citrus, I probably would not use any additional heat, but the GH would go below freezing. In the previous winter, it got down to 27F without heat at about -20F outside.

To answer your questions:

1. Min winter temps ~35F with extra heat. Max summer temps 95F with ventilation (will be adding water misting this year).

2. I used local subsoil (decomposed granite, like coarse sand) around the heat sink tubes.

3. 5x as per John's calculator. I will be replacing the fan with one that can do roughly 2x the flow when the current fan dies, as I think the heat transfer below ground is not ideal.

4. I used the lengths/spacing as recommended by John's calculator (his site is down, but if you search for SHCS here, a poster has saved the calculator which you can download). I have not done enough testing of the subsoil temps to say whether or not this is ideal.

5. Twinwall polycarb.

6. No additional heat sinks, but supplemental heat.

A few thoughts/things I would do differently:

1. The ventless heater is problematic at really cold temps. When it runs a lot, it ends up putting too much moisture into the air. Not a problem at 20F outside, but over long cloudy periods with below 0F temps it keeps the humidity >90%. I may go to all electric heat on those periods to help control the humidity.

2. I have a smaller GH (8'x16'), also a lean-to which is on the S side of my garage. That GH has only touched freezing a couple of times in 14 years with no supplemental heat. Reason is (I think, have not run the numbers yet) that it uses the insulated garage as a heat sink during the day and pulls heat from it at night. It also helps that it is smaller and therefore has more excess heat to save.

I think my larger GH would do better if I insulated the barn it was attached to, but I suspect that even then it would not stay above freezing without supplemental heat. John C used to say in his workshops, that in our climate, a SHCS GH would extend the seasons in a larger sized structure, but not get it thru the winter above freezing without additional heat. Which is what I am seeing.

3. I will be adding additional venting and misting to help control summer temps. The SHCS does capture some heat (roughly a 30F drop in temp on hot sunny days air in to air out), but it is not enough to keep the GH as cool as I want it. I think a higher volume fan will help some, but in hot sunny climates additional venting/cooling is needed.

4. We just went through a 30 day period where it was cloudy and rainy/snowy. Quite unusual for us, and something I did not plan for. Again humidity became an issue a couple of times during this period. While I don't expect to see a repeat of this again, I probably need to think about adding a means of venting the GH, or something, to control humidity for these conditions.

In general, it appears the SHCS does provide significant heating to the GH. I can't put a $ figure on it, as I don't know what conventional GH heating bills run in my area. But from my testing, I am heating from a baseline of 27F or so rather than the outside temps.

I don't believe additional heat storage in the GH (barrels, water bottles, etc) would be that valuable. There is some venting of additional heat on sunny days during the winter, but by and large those are not the days that the heaters come on. Rather it is the cold cloudy spells which require supplemental heat, and more heat storage would not be all that useful for those times.

HTH

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Comments (73)

hex2006
6 years ago
last modified: 6 years ago
Hi Will

It would be hard to achieve 90F 90% RH in and 70F 40%RH out as the dewpoint (mass temperature) would be down around 45F, mine is never that cold ;)

The heat transfer numbers would be good if you could manage it though, i make it 21,176.6 btu/hr without the latent and 126,883 btu/hr with the latent.

btw, in my book its the revived "SHCS" calculator ;)
asimpson_gw
6 years ago
last modified: 6 years ago
My shcs greenhouse is finished, its 4200 sq feet and is working great. Will Lennox and the eco design team designed it. I am growing guava, banana, citrus, figs, avocado, star fruit etc in this greenhouse. It stays very warm, its like walking into a tropical rain forest, especially when you have 1000 tonnes of soil heated to 71F. The greenhouse regulates its temperature using the climate battery fans and the two vents plus a shade curtain. You can see one of my 30 inch exhaust pipes in one of the photos below. I am attaching pictures. I only finished the greenhouse in January so I still have a lot of work to do with the soil and finish grading outside but things are going well. My avocado tree has grown nearly a foot in a only 5 days. Im located in Southern Ontario on the zone 6a/5b border. Winter low temperatures here are generally between -10 and -15F
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hex2006
6 years ago
Looks great, 1000 tonnes of mass equates to a depth of about 6.6ft. Technically, you`ll have around 7% less as the 6-12,000ft of tubing displaces mass ;) You`ll find the mass doesnt heat or cool evenly so although its nice to think there is 1000 tonnes evenly heated to 71F, it wont be ;) With enough sensors in the ground you can monitor the heat movement.in real time.. Unfortunately, very few installations measure much more than the tubing inlet/outlet temperature and greenhouse air temperature. The most important measurement is airflow through the system, (not the fan cfm specification) as you cant calculate system performance without it.
asimpson_gw
6 years ago
last modified: 6 years ago
I have two climate batteries separated with each battery being 42 x 41.5 ft. Each battery has a 24" inch fan running at about 9100 CFM (18600 total) through 6156 linear ft of tubing. 3 layers of tubing, 162 total tubes with 38 feet between the manifolds. That should work out to mean that the air is traveling at 10.73 fps for the tubing and taking 3.54 seconds to exit the tube. My greenhouse has an extreme heat loss of about 221000 BTU/hr in the winter so I have a backup heater which is 250,000 BTU in case the climate battery cannot maintain my desired air temperature (sometimes we get polar shocks). I only installed the heater a few weeks ago so I haven't used it yet and I didn't use it this past winter.
hex2006
6 years ago
ADS tubing is the worst air duct in the world because it wasnt designed for air ;) I had some tested professionally in order to get the information because the manufacturer couldnt provide it and wasnt willing to do the testing which was reasonable. . Depending on bends and how the tube-to-manifold connections are constructed (worst case being just pushed into holes so the tubes protrude into the manifold) i would use the fans specified output related to 0.5 iwc for flowrate calculations.. For a large system, it would be worth having the flowrate tested as its the only way to know for sure but i expect it will be considerably less than 9100cfm.

I`m sure the system will work very well as it is a proven design. Its a shame you didnt install sensors to track the performance. . My system is much smaller and it has 26 sensors inside and outside. It was designed under John`s watchful eye and incorporates many innovative features that would likely have become standard in shcs design had John still been with us. For example, with the original shcs, the dwell time of the air in the tubing is dictated by airflow rate, (less flow, more time in the tube and vice versa). In mine these parameters are completely independant and fully adjustable. You may find humidity an issue especially at night when in heating mode, especially if the tubing isnt modified prior to installation to improve its drainage properties (the standard perforations are not ideally placed to drain all the condensate). On average, the air exiting the tube in heating mode consists of 60% latent (you can calculate this via measurement), which serves to increase the RH%, not the air temperature. Some have resorted to using dehumidifiers which isnt a good solution with relatively low air temperatures (colder coil temperatures needed for dewpoint)

Its always good to see a new shcs installation but it would also be nice to see the design being moved forward. True visionaries /out of the box thinkers (like John) are getting very thin on the ground..
asimpson_gw
6 years ago
last modified: 6 years ago
What type of tube did you end up using? I do have speed controllers on my fan so I can speed them up or slow the flow rate down. But I don't know under what circumstances I should do so. Ideally I think a fan designed to work at higher static pressures would be better than the HAF type fans I am using, but I don't know if there are any that would work. What innovative features did you end up incorporating? Im certainly curious.
hex2006
6 years ago
last modified: 6 years ago
I went with corrugated drainage tubing (perforated) as its the most economical option. The only hassle apart from having it tested was cutting full length slots partway through the corrugations to ensure drainage. I assumed you were using tubeaxial fans or something similar, HAF`s are much cheaper and use less power but they`re not designed to handle ducts ;) I`d recommend trying to get at least a rough idea of the actual airflow in the system, its the most important parameter of them all.

I use a speed controller in conjunction with 2 thermostats to control the fan. One thermostat controls the heating/cooling mode activation points (adjustable).. The other is a differential thermostat which monitors the difference between the air temperature and the mass temperature..This arrangement prevents the fan running if the mass cant store heat (in cooling mode) or provide useful heat (in heating mode)

A typical shcs control system consists of 2 standard thermostats which monitor air temperature only. The issue is the heating stat could fire up the fan at say 50F even if there isnt any useful heat in the mass. If the heat runs out while the fan is running and the gh is still below 50F,.it`ll keep on running ;)

If i set the differential stat to 5F, the mass must be at least 5F higher than the air temp or the fan wont run. In the event the mass temp drops below the 5F differential while the fan is running, it will turn the fan off. As the air temperature increases, the mass temp must maintain at the 5F differential which acts as an automatiic self-regulating energy conservation feature...It works the opposite way in cooling mode, the air temp must be warmer than the mass by the differential for the fan to run. As the mass gets warmer, the gh air must also be warmer (dictated by the differential setting) before the fan will run. This ensures there will be room for the heat. .

The fan speed control should be set to keep pace with the incoming solar gain. This maintains the greenhouse temperature using the least amount of power. Using an unnecessarily high flowrate will cost more in power (higher flow, higher losses) and result in a less stable gh temperature. If the system outruns the incoming gains, the gh temperature falls and the fan will cycle on and off.
PRO
Eco Systems Design, Inc.
6 years ago
last modified: 6 years ago
My associate Will Lennox just pointed out this forum to me, and I'm delighted to see this discussion happening, especially with some of our clients, Adam and Kyle, posting results. It was 2008 and 2009, when my partner Jerome Osentowski asked me to connect with John Cruickshank, aka Mr. Hobbit, to have him design the SHCS system for a student of Jerome's. John quickly taught me to use his calculator, and urged me to design it and run it by him. We got to do several greenhouses in this way, before he passed on. Much of that experience is detailed in Jerome's book, the Forest Garden greenhouse, and we continue to develop the methodology, project by project, learning more and more as we go. We did change the term to describe the shcs as a "climate battery", because we are storing heat and humidity in the soil, and because our clients and contractors had trouble remembering the original term.

I appreciate your long experience with your greenhouse, hex2006, and especially your willingness to share it with others. We are also hoping people interested and/or experienced with it, will be willing to use the blog we have set up on our website at ecosystems-design.com, to communicate with us and each other. We are developing tools and posting much of our own experience, including Mr Hobbit's original calculator and instructions, which another client found on an internet archive, so we now have it posted for anyone to use.

The only tubing material we use for our climate battery designs is corrugated, perforated tubing, either 4" or 6" diameter, and it is made by ADS. I would love to know what the difference between ADS tubing and what Hex2006 is using, as they seem to be the same. We just specify the tubing with the most perforations in it, for maximum transfer of humidity, for phase change and absorption in the soil. As far as our calculations go, we size fans to deliver between 10 and 20 air changes per hour, which Mr Hobbit himself was leaning toward, in the last projects he designed.

I see there's a word limit here, so I'll have to continue in an additional post, as I don't have time to edit this one adequately.

Michael Thompson

Eco Systems Design, inc.
PRO
Eco Systems Design, Inc.
6 years ago
last modified: 6 years ago
We have experimented with climate battery fans at either end of the battery, on the intake side (pushing) and on the exhaust side (pulling), and found the former to provide better performance, likely because of the positive pressure it provides, which would tend to push air through the perforations, to a degree. Corrugated, single wall tubing is most ideal, because it creates maximum surface contact for the air flowing inside the tubing, and for the soil packed around the outside.

We have also learned that "sticky clay", or the soil used to make pottery, is a very inefficient medium for a climate battery, because it absorbs humidity from the tubing, but it only migrates a short distance into the soil (we found a couple of good tests for clay on youtube). Sandy loam, or topsoil, is ideal, especially for a greenhouse with perennials, which will set roots deeper. We have used roadbase once, at the insistence of the client, and we found that it performs much better than high clay content soil, but with perennials in organic soil around the battery tubing, Jerome believes that we get more cycling of the soil moisture, when it is taken up by plant roots and evaporated back into the greenhouse air. Plant roots will not migrate into roadbase, made of sand and stone aggregate.

Our calculation methods are based simply on "delta-t" and "delta-rh", both between the intake and exhaust port of the battery, and between the indoor and outdoor climates. We are routinely experiencing outdoor-indoor differences of 45 - 50°F in winter, before backup heat is called for, and intake - exhaust port differences in every season, that depend, as mentioned in many of the prior posts, on how much heat is stored in the soil, and how well this is managed through the winter. Jerome likens this management to sailing. Like adjusting your sails to maximize propulsion from wind, he adjusts his climate battery carefully, to charge and discharge it according to sunny / cloudy / hot / cold weather patterns, to keep the soil "charged" with heat and humidity throughout the extreme seasons.

We aim to provide a useful forum, including design and calculation methods, for anyone to use on our website, and hopefully, an open-source forum to detail methods and performance results over a wide range of outdoor climates and indoor hardiness zones. A future of local food, good for health and economic well being of families and communities, will benefit from all our efforts.

MT
hex2006
6 years ago
The issue with large installations is they very seldom have sufficient fan power available to test anything but the prescribed greenhouse turnover rate.of 5-20 times per hour. My system was designed to provide a turnover rate of zero to over 60 times per hour to fill in the blanks..The advice on the website says:

when we are charging the battery, we need to run the fan
speed a little lower, to allow the air more time in the tubes to release
its energy into the soil, verified by a larger difference in temp and
humidity across the air ports

My advice would be to compare the outlet air temperature to the mass temperature and increase the fan speed to reduce the in/out delta T to ensure the full length of the tube (and mass around it) is being utilised. What you suggest will ensure the outlet air drops to the mass temperature in the tube which will happen long before it exits. The argument here is it will cost more power to increase the flow which is true for the long tube that is too long for efficient heat transfer at the desired flowrate. The counter-argument is to make the tube shorter, which reduces the loss and allows higher flowrate while ensuring efficient heat transfer over the full length of the tube. In both cases the flowrate and outlet temperature only needs to be sufficient to offset the incoming gains in order to maintain the greenhouse temperature. In this regard, flowrate will always trump the output air termperature no matter how cold it is. Imho, far too much emphasis is placed on the in/out temperature difference, these numbers always appear very impressive (to potential customers) until you add flowrate into the equation then everything changes.

I dont understand why asimpson_gw`s system is equipped with HAF fans, they are not suited to the task and wont deliver close to 9100 cfm in that system. If i`d put 12,000ft of tubing into the ground i`d know exactly what the flowrate was, right.down to the last cfm.
Will
6 years ago
We've had great success with HAF fans for many years now, in nearly all of our climate battery installations. I understand that they are not designed for ducting, but the back pressure in the system seems to be low enough that they function well, and have the high flow ratings we need without the extra expense/noise of ducting fans.

We would like to see further research around the climate battery, including different configurations of fan types and flows. In the meantime we're working off of our accumulated experience, making steady improvements as observed over the years.
hex2006
6 years ago
last modified: 6 years ago
Will,

Saying it "Seems to be low enough and have high flow ratings"doesnt instill a lot confidence in the thoroughness of the design process, you need the actual numbers before you can calculate the performance ;) Consider ducted air systems that are installed in houses have much lower resistance than
any shcs system but you`ll never see a HAF fan being used..

Advising folks to use no more than 10ft/sec is great if you can tell them where to find lossless 4" ADS tubing. If you cant then you should provide the missing information thats required to ensure they have 10ft/sec. If you dont understand what is missing you shouldnt be designing them.

Folks looking at the calculator will be unaware of the flowrate shortfall as the advice to reduce airflow to provide a large in/out differential leads them away from higher flowrates which is perfect.. A typical shcs will provide an output temperature equal to the mass temperature upto as many as 25 airchanges per hour. If the system only provides 2 airchanges per hour they will be none the wiser because the output temperature is still at exactly the same mass temperature and only a very small percentage of the tubing installed will be utilised. Feeling cold air from the tubing has a nice placebo effect but it wont be moving as much heat in the same time frame as the higher flow does.. Low flowrate limitations typically result in a system that cant store as much heat (because cooling provides the stored heat) or keep up with the incoming gains. It simply cant move the heat from the greenhouse fast enough.

You cant improve on a design when all the basic parameters of that design are unknown. You cant even be sure how the current design is performing.
asimpson_gw
6 years ago
How would you measure the actual flow rate?
hex2006
6 years ago
Try to find a certified TAB technician, he/she will have the appropriate test equipment and know-how. and provide you with a comprehensive report.. .

http://www.neudorferengineers.com/documents/NEUDORFER%20SAMPLE%20TAB%20REPORT.pdf
Will
6 years ago
hex2006, I am excited by the prospect of what I could learn from your experience, would you be willing to discuss directly? or over the phone? I would love to pick your brain more, and maybe you can help us to understand some of the finer engineering details that I've been working on figuring out.

our process thus far has been successful through experience with previous climate battery installations, repeating arrangements that have shown positive results based on plant growth, climate control, minimized inputs, and greenhouse owner happiness. as a student to engineering, it has been my personal goal to improve the climate battery technology by application of data collection, thermal modeling, and the engineering process. if you have significant data from your 8 years with your climate battery, would you be open to sharing what you've learned with me?
Will
6 years ago
you can reach me at wlennox07 at gmail.com or 7O7 Four78 9149.
hex2006
6 years ago
Hi Will

I`m not in the states so a call could get expensive ;) I have a lot of data from my system as it was designed with experimentation in mind and also to work with my non standard greenhouse ..The best way to learn about a system is to build one and monitor as many parameters as you possibly can. This should include temperature and humidity measurements inside at least one of the tubes, at regular intervals not just at the inlet and outlet plenums.. Temperature sensors located In the mass at the depth the tubes are installed and also below the system. You also want sensors in the ground at various depths outside the greenhouse.. Basically, think of all the questions first and then put monitoring in place that will provide the answers...

The cheapest way i`ve found to check basic temperature values in multiple locations is to attach the sensors to 12-way rotary switches, (12 sensors per switch) and connect the switch (or bank of switches) to a single meter. You can then switch through the sensors and record the data. The more you can monitor, the better..
asimpson_gw
6 years ago
Hex,

I would love to see some pictures of your greenhouse?
eciton
Original Author
6 years ago
last modified: 6 years ago
good discussion, its been two years since i posted it and I still havent broken ground. =/ such is life

thank you all for the additions to the thread.

-- Hex, if there were things you could do to improve your system what would they be?

-- Has anyone tried a fan at the intake and a fan at the outlet to try to push and pull the air through the system? would this improve anything over a larger fan at either end?

-- Does anyone have any experience with perennial/tree roots infiltrating the perforated tubing? Having done sewer/septic work for well over a decade I can only imagine tree roots filling the tubing system up in a matter of years if the pipes are not protected (I really like the idea of the compacted roadbase surrounding the piping)

Pictures/design plans are always appreciated!!
hex2006
6 years ago
last modified: 6 years ago
If you have to resort to a push-pull fan arrangement, you have the wrong type of fan or tubing layout ;) I did some root invasion testing with paulownia`s in big wooden troughs 3ft deep. Roots that found the tubes were air pruned before they could enter. The majority of the roots seemed to ignore the tubing altogether and head straight down. At the end of the season they were 8ft tall with a 4" thick root mat on the floor of the trough. I dont grow tree`s but i`ve never had any issues with roots in the tubing.

I designed my system to be as flexible as possible. If i had unlimited space, time and money (in that order).i dont think i`d change anything in the shcs. I would build another greenhouse because the one i wanted to build wouldnt fit in the space i have available :)
gregkn73
6 years ago
Hi all,

I am very interesting to make a SHCS or climate battery for my small green house, found very informative the page of ecosystems, but i am now a little confused, reading all that info here. i am glad , by reading real stories that shcs is something that works, but i now after reading the comments of hex, i dont know if the recomendations from ecosystems are totally correct. So Hex , the only change to their reccomendations, is using bigger duct fun? Since you have so many monitoring points at your system, can you supply us with some data, supporting your reccomendations?

Thanks in advance, Greg
hex2006
6 years ago
last modified: 6 years ago
Hi Greg

I dont know what the smallest installation Eco Systems has designed/installed but i guess its mainly large projects as the recommended 25-35ft tube lengths could be problematic for a typical domestic sized greenhouse. Some may conclude shcs isnt viable for small structures that cant accomodate a minimum tube length of 25ft. If that isnt the case (and clearly it isnt), you must ask yourself why 25ft is the minimum tube length ;)

You can learn a lot more about shcs from a smaller installation than a larger one.

I wouldnt recommend using a larger fan..unless the system is designed to handle the flowrate and there is a need for it. I also wouldnt recommend installing miles of tubing if the airflow isnt sufficient to make use of it. Consider small but important details that impact on performance, for example, ADS tubes pushed into holes drilled in a manifold so they protrude inside versus being flush with the wall or ideally radiused to provide a smooth transition.

I would definitely recommend doing simple experiments to validate information before deciding on the final system design. The same test equipment is required for measuring the system perfomance once its installed so you`ll need it either way..
gregkn73
6 years ago
"Consider small but important details that impact on performance, for example, ADS tubes pushed into holes drilled in a manifold so they protrude inside versus being flush with the wall or ideally radiused to provide a smooth transition"

As you probably have already understand english is not my native language, so i cant understand what you describe above. A picture or draw will help me lot to understand.

As far experimentation, except laying down the tubes and blow air inside them with a fan, i can not thinkof anything else before bury them. But the most critical point is the heating or cooling gain, which can not be tested without bury the tubes, so to what usefull experimentation you are reffering, before bury the tubes. If i bury them any experimentation will not help me at all, because i couldnt make any changes to the system. So please help me to what usefull experimentation you are refering to?

As far experimentation with shcs i have found only those 2 references, http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.504.5677&rep=rep1&type=pdf

http://wayback.archive.org/web/20110222100536/http://www.fao.org:80/docrep/T4470E/t4470e0c.htm

In the first one, they achieve very small cop ( 2-5) and in the second one, they early maturity tomatoes was only 7-10 days, and yield increase not at all significant at the end. SO the results from those 2 experiments, for me are not satisfying. Also another user https://www.youtube.com/watch?v=Ix1kRZjO91I abandoned his shcs, because of mold problems, as many users of earth tubes in houses, which is something similar to shcs.

So even i found brilliant the idea of not blowing hot air outside but down the earth and use it during the night for heating, i would like to find good answers and a sure plan , how to make them, before starting to digging soil, which is not......an easy work to do :-) So i would love Hex to see some of your data you gather all those years, and make to disaggre with the ecosystems palns and their huge experience they have installing not only one shcs. Thanks again for any answers and sorry for the long post. More success or failure stories, will also help me and others interested, if it is worth to dig or instead use some rows of barrels filled with water!
asimpson_gw
6 years ago
last modified: 6 years ago
Greg,

As I mentioned above I have a working shcs greenhouse designed by eco systems which is 4200 sq ft. I am in Canada (its cold here) and I grow avocado, tomatoes, citrus, star fruit, figs and bananas in the ground year round. My greenhouse stays warm. I think hex is suggesting ways that these systems can improve and other tips to test these systems to ensure we are getting the most out of them, but you have to have a plan for a working system to start from. The shcs is just one part of the whole system, you also need a greenhouse that is well insulated and vented and most commercial greenhouses need modification to achieve a balance between venting, glazing and insulation. Eco systems has many working greenhouses that have been in production for many years (at least two that are over 8 years old) and they are well documented with videos showing that they work very well. I can personally that they do actually work and theres no mold or other issues. When I built my greenhouse I didn't want to experiment and hope that it works, I needed to work from plans that had been tested and we knew worked in the field. Take a look at my pictures above or look at the video of Jerome's (eco systems) greenhouse here: CRMPI greenhouse

Maybe Hex has some input on this, but I would think that as the size of the greenhouse (and thus the size of the insulated climate battery) increases the losses from the edges would decrease. As the ratio of volume of air/climate battery to surface area of the glazing increases it should lower the thermal losses? One issue I have being in Southern ontario is that in the winter we can get weeks of little to no sunshine, and polar vortexes from the arctic so having a backup gas heating system is a good idea. A couple years ago we had one night where it was -20F!
hex2006
6 years ago
last modified: 6 years ago
Hi Adam,

Another way of looking at the greenhouse size is increasing the mass to glazing area reduces the solar gain so you can have too much mass and not enough heat to charge it ;) My approach would be to maximise floor area and minimise the volume which suggests a low profile greenhouse with a large footprint ;)

Perimeter heatloss increases with perimeter length, not forgetting that corners have greater loss. A perimeter that encloses the most area and doesnt have any corners is ideal, the most efficient shape is a circle ;)

The lack of information or vague statements about the reasoning behind a shcs design really bug me. You said you didnt want to experiment and hope it works, if you have AC or any forced air system installed in your house i hope you didnt settle for the same with those. Systems are designed to do the job, the designer/engineer doesnt just install ducts, fans and hope for the best. If he did he`d be out of business pretty quick ;) The problem with shcs is the hardware isnt standard (ie ads tubing for air ducts) so some of the information an engineer needs is missing or unknown. If you are in the business of designing systems you have to to know what these missing values are. I dont design systems but i still had the testing done, one because i hate unknowns and two because they dont have to be unknowns ;)

Some things are more universal (like physics and thermodynamics) which can be used to make at least educated guesses. For example, a 38ft tube running 52cfm would incur the same loss as 150cfm running through two 19ft tubes of the same type. The cost of the tubing, the surface area and the amount of mass the tubes are in contact with are identical in both cases. The difference is you get the option of moving 3x the air through the pair than the single. You can run 52cfm through each 19ft tube if you choose to (matching the 38ft system airflow). Fitting a larger fan is a simple upgrade for the 19ft system but it isnt a viable option for the 38ft system.

The tubing layout is fixed once you`ve buried it in the ground so its best to iron out any issues before you bury it. Making the design as flexible as possible can provide workarounds for potential issues you cant foresee ;).

Some things are more difficult to judge, such as tube spacing, closer spacing will bias towards heating, larger spacing towards cooling.

My solution to this dilemma was to incorporate both. The tubing furthest from the perimeter has a heating bias and the tubing closest to the perimeter has a cooling bias. The design i use provides the option of redistributing heat in the system, so i knew i could negate the bias if it didnt provide any benefit. I havent done much testing of the heat redistribution feature apart from confirming it does what its supposed to do.

If i had a massive greenhouse i would opt for multiple small systems with their own fans versus a single layout driven by a mega fan. Using multiple systems inside a single structure would offer more flexibility, better air distribution and higher efficiency. If no one wants to experiment and every installation follows the same format, the design will never move forward. It doesnt take much to dig a few temperary trenches, install some tubes and sensors for basic testing.. They could be useful as cloches/low tunnels with hoops 3.5ft wide x 1.75ft high ;)

Here`s a simple experiment you could try.

Sink a tube down to the depth of your tubing and install a sensor to measure the mass temperature. During cooling,monitor the outlet temperature of the system. Increase the fan speed incrementally to see if you can get the outlet temperature to climb above the mass temperature. An anemometer can be very useful here too. What you`re looking for is a velocity increase with fan speed. What you dont want to be seeing is the velocity stop increasing long before the fan is at full speed ;)
hex2006
6 years ago
last modified: 6 years ago
Greg

The installation in your link used 5 long tubes which to be honest isnt worth the cost or effort. https://youtu.be/sNIhxGjVcSM?t=276

Did you notice the RH% of the greenhouse at night? https://youtu.be/Ix1kRZjO91I?t=257
Although it was likely due to the aquaponics in that one, high humidity levels are common at night for most greenhouses. Its especially true for those with a shcs as the latent heat exiting the tubing increases the greenhouse RH%. You will need to think outside the box for a workable solution.
There are quite a few installations out there with some truely unbelievable design flaws. The worst one i`ve come across used 4x 180ft 4" ADS tubes (non perforated!). The tubes were arranged in a serpentine layout (in a single layer) buried 8ft deep.
gregkn73
6 years ago
Hex i think Ceres agreed with you about fun speeds :-) at their site they have an example of 12*20 solar greenhouse, using 2 levels of perforated pipes at 4 and 2 feet deep , with 2 duct fan of 120w each! So obviously they use much more air through their system than ecosystems designs, and they have a lot of experience also...

At their site a found also this photo

This is the smooth way for the tubes transitioned inside the manifold, you described me earlier?
asimpson_gw
6 years ago
last modified: 6 years ago
Greg

Looking at that picture I dont think that design will work as well. The intake and exhaust pipes are too small so youll need a lot of fan pressure. Manifold and tubes appear to be same diameter. Better to have a large intake and exhaust manifold pipe and a larger fan and have the tubes come off the larger manifolds. Hex did you take any pictures of your shcs during construction? That might help greg visualize the design? I have 3 layers of tubes and more of them per volume than that picture. Also that shcs isnt insulated around the perimeter which would allow you to isolate the solar mass more from the surrounding soil temperatures.
hex2006
6 years ago
Cere`s call theirs a ground to air heat transfer (GAHT) and charge $600 for a basic system design. That would be way too much even if the design was any good which it isnt ;) As Adam pointed out the manifolds are too small, they should be sized to carry the combined flow of all the tubes, not just one. Notice they did use wye connectors which is good but of no benefit in that layout. I suspect they used them to make installation easier than to reduce the system losses ;)

Their control method consists of the typical (off the shelf) two thermostat approach you`ll see in most installations. Below is a pic of the cere`s stats `n` stickers and the original control unit i made for mine as an off the shelf option didnt exist.
gregkn73
6 years ago
Thank you both for your comments. Something I can not understand, is why using 2 plenum. I understand one for the fan inlet, but why not exit each pipe outlet directly to greenhouse air for better air distribution ,instead of just one outlet?
hex2006
6 years ago
Greg,

You can do it that way but most folks opt to use plenums. The seperate exits will involve more work but, on the flipside, they do make balancing the system much easier due to providing direct access to the individual tube ends. Tubes that terminate into manifolds buried deep in the ground are very difficult/impossible to balance. The best you can do there is ensure the tubes are exactly the same length and install them as straight as possible.
gregkn73
6 years ago
Hex , why more work will involved for separate exits? Less matterials so less work I can think only.... If you make very light turns to the tubes, like snake for example , to achieve same length to All of them, the straight ones , compared to the ones with snake shape, will have a lot of air flow difference?
eciton
Original Author
6 years ago
last modified: 6 years ago
Anyone install one of these on the east coast? In Virginia in the summer it can easily be 96 degree and 95% humidity. Can the system handle that?

Mostly I'm concerned about mold build up, I don't expect the shcs to be able to bring the temp down to 80 degrees. At 96 I imagine all the vents open and fans/mister running to keep the plants from overheating. But that just adds humidity...

I plan on adding a considerable amount of drainage holes to the piping to help mitigate holding of water but I'm interested to know if anyone else has installed in similar conditions

Experiences?
hex2006
6 years ago
Greg

Even perfectly straight tubes can show variations in flowrate, thats why balancing is a good idea.

Eciton

You need to know what your soil temperature is ;) The greenhouse environment should be tailored to the plants, not humans. Its worth googling for information on vapour pressure deficit (VPD) before deciding on a target for the temperature and humidity levels.

Cutting a shallow slot part way through the lowest corrugations using a circular saw and simple jig will signifcantly improve the tubes drainage performance.
gregkn73
6 years ago
Hex or Adam thinking of manifold size. You wrote me that it should be a lot bigger than the separated tubes....thinking of irrigation systems , if the water pressure in the manifold is not big enough, then there want achieve evenly waterimg from the separated tubes. With low water pressure in the manifold, the first tube will take most water, while the last one nearly any! So isn't the same with air=fluid as water?

Hex do you know how sunny john , concluded to use such a big manifold diameter, with such small fans?

Also I still can not thing of any advantage of using a second plenum at the outlet! Only disadvantages! Extra materials, uneven air distribution because of few air outlets, extra air pressure because of extra tubing.....what is the reasoning of the outlet manifold?
hex2006
6 years ago
If the tubes are balanced they will all get the same amount of water. In your example, restricting the flow from the first tube would increase the flow in the second. By adjusting all the tubes (most likely several times) you would eventually have an even flow from all the tubes.

Adam uses 2 inlet and 2 outlet plenums which is much easier to deal with than 2 inlet plenums and 320 individual outlets ;) My plenum is different to most, but it does distribute the air very evenly. .
gregkn73
6 years ago
Hex i try to find pictures of your system, but because sunny john site does not exist any more, and because photobucket policy photos at this site are also not available any more. So if you can post again some , I will be grateful :-)
asimpson_gw
6 years ago
last modified: 6 years ago
In the messages above fruitnut mentions that his greenhouse temperature drops to near the outside temperature at night. I've noticed this is not the case with my greenhouse. For instance last night we had a low temperature of 7C (44.6F) but the greenhouse only dropped to 15.5C (60F) just around 6am, it took all night to reach that low. Now this is with no shcs running as I have my "heat on" stage set to 59F. So I wonder if there is some passive heat transfer from the soil that is keeping the greenhouse warm. Its 8:30am now and the sun is up and the greenhouse is back up to 75F even though its still 47F outside this morning but that's to be expected when the sun is up.

Hex what temperature do you find that you can heat the soil to in the summer? I've found that around 71F I cannot heat the soil anymore.
hex2006
6 years ago
The soil will passively transfer heat into the greenhouse as long as there is a temperature differential to drive it. Maximum soil temperature depends on how much sun you get and if you have insulation below the system or not. Again, the soil/greenhouse temperature differential will tend to limit how high it can go. .Mine has perimeter insulation but no insulation below and typically maxes out around 25c (77F). The heat definitely moves downward as well as upwards so some will move beyond reach. On the plus side, the average temperature below the system gradually increases (season by season) compared to ground outside at the same depth. It reflects the new energy balance created by sheltering the ground and actively adding/removing heat. In my case, the overall gain is positive (on average more heat in than out). In a cold climate it may swing the other way which is where insulating below the mass would pay dividends. It effectively fixes the volume of mass so you have to weigh up the pro`s and cons for both cooling and heating.

The night temperature drop depends on a lot of variable, the greenhouse glazing type, insulation and even the shape and framing materials. I designed mine to be as different from the norm as possible.
asimpson_gw
6 years ago
last modified: 6 years ago
Hex,

That looks great! Today I went and measured the airflow (CFM) at the exhaust manifolds. The airflow that I measured was very close to the CFM rating on the fans at the intake manifold. So I think the HAF fans are fine as long as the manifolds and area of the tubes are large enough that there is no a lot of back pressure.
gregkn73
6 years ago
Beautiful dome Hex. I will appreciate any photo from the construction of your hscs
hex2006
6 years ago
Adam

Its best to do a traverse of the duct as the airflow will vary considerably depending where you take the measurement. I originally used a skywatch xplorer windspeed meter and later upgraded to a fluke 922, no contest.

I personally would never use a HAF for shcs as they are the axial type which are touchy about flow, pressure and fan speed. If the fan ever sounds like its hunting, its not a good sign ;)
gregkn73
6 years ago
last modified: 6 years ago
My small greenhouse is 2m*6m, I saw some people use with great success water as an active thermal mass, by using car radiators, so since I have already an old car radiator and some EPDM liner, I'm thinking to dig a trench 0,5*0,5*6 exactly in the middle where is the walking path , insulate it, line the liner, cover it with wood panels and insulation, and by a small pump, fan and the radiator , heat my greenhouse. It will cost less both in money but mostly in digging, compared with shcs. The thermal mass of water in that way is 1.5 M3 , instead of 12m3 ( 2*6*1m) of soil with shcs, but I red that water is 4 times better than soil , as a thermal mass, and I will be sure that I will use 100% of the water capacity as thermal mass, while with the soil in shcs, i will not be sure that 100% of the soil mass is thermally used. Do you thing it is a good idea? Or I can't avoid digging 12m3 instead of 1.5m3? :-)
hex2006
6 years ago
Digging is the hard part but you should only have to do it once ;) You may not need to remove all the soil.. Undisturbed ground has more mass than disturbed ground, dig a hole and see how much of the soil you dug out will fit back in ;)

The soil will have upto 3x more thermal capacity than the water, simply because there`s a lot more of it. Soil is much better than water for this application, the reason is plain to see but easily overlooked ;)
gregkn73
6 years ago
Hex can you explain me please the obvious? Sorry but I can only seeadvantages using water instead of soil, as described earlier, so please point me to why soil is a better solution of thermal mass in my example. If I need more thermal mass in my mild climate, I can dig the trench deeper, to have more volume of water....
hex2006
6 years ago
The properties of soil can provide some useful benefits. The conductivity and diffusivity of soil allows the majority of heat stored by a shcs duting the day to remain within reach of the tubing and available for use that same night. When you mix water with water the heat will rapidly disperse into the entire volume.

In the winter you may have a very small window where excess heat is available so you need to move it from the greenhouse to the mass as fast as possible. The sporadic gains will increase heatloss so you are in a race to store it or lose it ;) With shcs this is a single step, low loss process. With your method you will need to push the air through the radiator to transfer heat to the water. Given the contact time will be very short (split second) you`ll need to move a lot of air. Once the heat is in the water you just need to convey it to the storage without losing any on the way. Digging seems a lot easier to me ;)
eciton
Original Author
6 years ago
last modified: 6 years ago
Has anyone done any testing on larger diameter piping for all the piping? ie, using 8" pipe vs 4" ads

Seems like you would get far more surface area, how does it effect air flow

I understand it's not likely a good economic choice, but I do have 180' of 8" pipe I was going to use as an earth tube system to try as a competing system to the shcs. Figured if i installed both then I could compare and I haven't seen any comparisons
hex2006
6 years ago
last modified: 6 years ago
Tubing displaces mass, if you have a fixed volume of mass larger tubing will replace more of it with air ;) Work out how much volume the 8" tube occupies and how much surface area it provides. Then work out how much 4" tube would occupy the same volume and calculate how much surface area it provides.

For those not good at math:

180ft of 8" (smooth) tube displaces 62.71 ft3 and has 377 ft2 of surface area. 720ft of 4" (smooth) tube will displace the same volume and has a surface area of 751 ft2.

Its the small details that folks miss that can make the biggest difference ;)

Looking at the average price of tubing, the 4" is also the cheaper option.
Solkraft
6 years ago
I've been investigating various ways to store solar energy in a new building I'm designing and just recently stumbled upon this thread. I'm building a small house with attached GH in Southern Denmark. The house is 27m2 (290ft2) and the GH is 23m2(250 ft2). The house will have a large solar collector for a hot water heating system, and from roughly Nov to Feb the warm from the GH will also be used to help heat the house. The rest of the year the GH heat will be used in the GH itself. Right now I'm planning to have two entirely separate SHCS systems, one under the house and one under the GH, both pulling warm air from and discharging back into the GH. The average winter soil temp here is 3 deg C at 1 meter so I will have insulation under the climate batteries. The GH glazing is only on the South side, at 25 deg from vert., and will be 4 m (13 ft) tall 10mm twinwall. The other roof and walls of the GH and the entire house will be well insulated.

There are some details I could use guidance or suggestions with, such as:

1. While SHCS systems dicussed here use perf. tubing, I have also seen systems such as the "Deep Winter Greenhouse" (U. of Minnesota) where the warm air travels under the floor through gravel. Their website has recently revised construction drawings of this system. Does anyone know of comparison testing or can explain the pros and cons of these two methods (air flow through tubing vs. through gravel)?

2. Soil at my site is heavy clay and does not perc, i.e. when it rains the water will not soak in. There will be a buried drain pipe around the outside of the building to hold the area dry but I worried about using this soil in the climate battery so I will probably buy some sort of fill material. I will grow at least partially in raised beds so I'll get good soil for that but what are pros and cons of various fill materials in the climate battery (for absorbing water/thermal mass/conductivity to the pipes)?

3. I've seen some warnings against having a house attached to a GH due to humidity problems (the connecting wall can become damp or moldy, ). But I've also seen even more sites that recommend an attached GH and list it's benefits. I like the idea of SHCS's ability to dehumidifying the air but I will also like to hear about other precautions I can take to prevent problems. In our damp rainy climate mold is often a problem even in houses without an attached GH.

All (kind) comments and suggestions are appeciated.
HU-47339220
4 years ago
Can anyone recommend sensors to use to measure temperature, humidity and flow?