Great Presentation! We definitely needed more data to help us with our own decisions on building more of these. Thank you for sharing so much of your hard work for our benefit!!
@@arkadiuszlee407 Hi Arkadius! Air infiltration still occurs and has been more than enough. For air circulation when the main fans aren't operating, you should use a standard HAF for greenhouses. HAF stands for horizontal air flow.
@@phillipk2490 I did not do a third webinar. That would be a good topic to do someday. I hadn't focused on that in the presentations, because it wasn't particularly innovative. In fact simpler is best for reliability in regards to the controls. I'm a proponent of simple analog controls for the fans because I don't consider it an acceptable risk for crop failure when a digital controller fails due to corrosion. If you have something in particular you need to know, you can email me. My address is at the end of the presentation.
With regards to the pony wall, you could replace the doors with clear glass slider windows with screens. That way you would get the light down low and still have the windows as vents.
Since moisture cools, would it make sense to try an dehumidify the air that goes into the battery during cold days? Or is that a battle that cannot be won and the pipes would get wet but just after a longer while? Not neccessarily electric, maybe just a mesh on the intlet that is able to catch the water and collect it or redirect it to the soil. Im also thinking of catching more of the sun, like a massive black backwall that fully contains the inlet. Can always block the sun with screens for heat prevention (glassfront and black wall), but must store as much as possible in december. Great data and presentation, thanks.
Dehumidification is a very energy intensive process to actively do. There are several methods: blowing air over a cold coil (like in your house, basically an air conditioner) or using a dessicant system that uses heat to burn out the absorbed moisture. The climate battery itself is a dehumidifier, just not enough to prevent condensation on the glazing surface because it is still a very cold surface. Using an insulating blanket to increase the r-value of the glazing at night or a thermal curtain inside could help some without a lot of energy costs. However, I haven't had any problems with plant disease in the last few years related to the humidity. I have had some minor cases of edema in a few solanaceous plants for short periods, which isn't a disease, just not visually appealing on the leaves.
A dessicant dehuey is the only realistic choice for cold air as it doesnt rely on dewpoint but would be expensive to run. If you have a tall south facing fence close to your greenhouse you can make a large flexible solar air heating panel to attach to it over the winter moths. In the spring you simply take it down, roll it up and store it in the shed. The idea is based on the "Solar Flume" flexible (inflated) solar collector which was around a very long time ago, maybe 15 years. I couldnt find any links sadly but the basic idea can be found in this patent: US20080017499 Edit, Wayback machine archived at least some of the original website, solarflume dot com
When you were talking about heat exchanger tubes the diameter of the manifolds needs to be bigger than the runs between them. For example the manifolds and the pipes running from the manifolds to the surface should be 6 in. , while the runners between them should be 4 in. , this will give you better efficiency and air flow throughout the thermal battery. It will also allow your fans to work less hard, saving electricity and saving fans. I am not a master physicist or anything but i know basic physics. The air flow is pushing back on your fan if you place a 6 inch fan reducing it to fit into a 4 inch pipe. Also, if it is all only the same diameter then the air is only really flowing thru the first run, it will take path of least resistance and since they are all the same size it takes the first one closet, mainly. But with a bigger manifold(on both ends) AND the pipes feeding those manifolds to the surface, it will distribute more evenly thru all runs. It is a pressure/vacuum thing, you are building up too much back pressure/vacuum(depending if you are pushing or pulling) at the manifolds being too small to get free flow and even distribution. You need the air to freely get into the manifolds this way it will fill the manifolds evenly and therefore flow thru the runs more evenly.
Yes, the manifold diameter I used was 6" due to availability. 8" would have resulted in much higher airflows or even larger, like 10" would be great, but it is spendy and harder to get.
Thank you for sharing your data and design considerations for a greenhouse such as yours. Did you consider thermal mass heat storage such as stone wall on the north side of the greenhouse or water storage barrels on the north wall? Thank you, again.
Has anyone done a coefficient-of-performance analysis to determine if the energy input (fan kwh) provides a net benefit in output? Basically, is the COP above 1?
Yes, I had a graph of measured COP vs. fan speed at 1:00:30 It ranged between 5 - 50 depending on the air-ground temperature difference. These values are in line with other research papers I've read on the topic.
About 5,800cuft. I know some folks suggest 4-5 ACPH (air changes per hour) as a rule of thumb. However, that is a tool sometimes used for architectural design of spaces for human comfort and not a great rule of thumb for a heat exchanger. The optimal airflow rate should be based on how much solar gain the structure captures and the efficacy of the heat exchanger. I have some plots showing efficacy of this system at various airflow rates, but I cut it out so I didn't bore folks. Hopefully I can do some short in-depth webinars/videos sometime to provide a better guideline for folks.
@@waywardspringsacres I recommend designing the system to handle at least 20 air changes per hour, more is better if you have hot summers. Very few installations have the tubing layout or fan power required to test the higher turnover rates. I purposefully designed my system for 60 air changes per hour (12 years ago) to test this grey area and incorporated some additional features to enhance the system efficiency.
@@JohnGuest45 I recently did a webinar with the UMN Extension and shared some nice plots of the impact of higher airflow rates based on numerical analysis/CFD. I don't think the recording is available online yet. I will post a link on my Farm Facebook page when it is available.
@@waywardspringsacres I watched that one and it was refreshing to see your recommendations broadly follow my own. i`ve been trying to save folks from making the mistake of installing long tubes for many years as the only remedy is to dig them back up. I was a little disappointed you didnt mention the role that humidity plays but i understand the need to keep things simple as physics and thermodynamics are not everyones cup of tea :) I think its important that folks understand the plants are an integral part of the system because an empty greenhouse with a system installed will perform woefully compared to one full of plants. If you have overhead misting in your greenhouse you will have noticed the effect it has on the heat transfer. Something i would recommend in larger structures is to use multiple systems for greater flexibility and efficiency. A single fan in a large installation involves massive flowrates starting at a single point which makes it difficult and expensive to achieve an even air distribution and control the losses. Keep up the good work.
With a geothermal greenhouse, is there any benefit in insulating horizonally above the perferated tubes, especially if you are not growing trees direct into ground. I was considering doing this.
Question. Why don't you have water stored under the floor or soil for heat storage? Is it because of your severe climate and risk of water freezing and cracking your foundation? If you had water 1 or 2 meters deep in tanks under, won't convection of heat in the water reduce heat transfer escaping down through the soil? Also, I am aware that storing heat in water might need a different approach. Like a "radiator" with a fan blowing air through a car radiator and a water pump to pump the warmed water away. Did you not use that approach because it is too complicated? I live in a milder climate (Victoria BC Canada) and I am only allowed a 107 sq ft greenhouse and I did it DIY. So just over 8 by 12. I use 80 mm computer fans to blow air under the soil and they run directly off a solar panel. I insulated the north wall of it after seeing your video and others this winter. I have about a foot of water (contained by pond liner) under one planter (north side) and a rain barrel under the other one. Some of my heat storage is in the water. (I use water because we have really dry summers, sometimes 3 months with no rain). I have a pipe that brings air under the water level, and a syphon to remove condensation from that pipe.
I am growing in the soil, so want to make sure my plants/trees have plenty of root zone area. I didn't go the water route because I wanted to achieve the simplest system possible. Water is definitely an option, but requires more components/complexity/cost.
What a great idea! Thanks for all this research. My only question is do you have any problem with critters being drawn to the warmth and chewing into the tubes? An initial layer of hardware cloth or something like that would prevent that...?
I used iMonnit because of the diversity of sensor types that can be on the same network, which makes it good for research. However, it would likely be overkill if you just want to measure a couple things.
Been watching the different videos on this project and am impressed with the data. Thanks for all your work and data collection. Good stuff. Question about the perforated pipes. My worry would be that since dirt would get in those holes and maybe clog them over time. In your implementation where you put the soil back in place it seems like a fine soil (as opposed to gravel) would clog. what about using a sock on the perforated tubes to prevent the clogging. Also when connecting the distribution tubes to the manifold, do you need to seal that connection so dirt doesn't get in there? How did you do that since I think the manifold pipes were corrugated. Maybe just some caulking? I think you may have said foam in the video? One other question. How many fans (4?) and what type of fans did you use? Thanks again for all your work on this. Kind regards, Mike
Hi Mike! I don't think sock is necessary from all the research I've found on the topic. I've been running 3yrs now without issue. I used spray foam in a can to keep out the backfill. I have four PrioAir 8" fans.
@@waywardspringsacres I didn`t use sock and have had no issues. Sock may be necessary if you have pure fine sand but thats highly unlikely in most cases. With hindsight, i would recommend using non perforated tubing as the location of the perforations are as useful as a chocolate teapot. Cut a straight shallow slot part way through the corrugations (using a simple jig + circular saw or router) and locate the slot at the bottom during installation. Drainage tubing is designed to let water in via the perforations but not out. A drainage tube that doesn`t carry the water away isnt very useful.
Thank you Mr. Mutschelknaus! These two seminars have been great! I am beginning construction on my backyard 14.5x48 hoophouse style with climate battery up here in Western Massachusetts. Similar zone, a little less sunshine. Hoping for the best! QUESTION: Can you point me to a good thermostat option? I am having difficulties finding something that will control the four fans to turn on over a certain temp AND under a certain temp. Would love your advice! thank you!!!
That`ll teach me to edit a reply and lose it all lol. I`d reommend using a differential thermostat as they take account of both the air and mass temperature. A standard thermostat will turn the fan on/off based solely on the air temperature. If the mass isnt warm enough to provide any useful heat or its too warm to store heat efficiently, the thermostat will still run the fan. A differential thermostat doesnt care what the actual temperatures are, just the difference in temperature between the air and the mass. I had to make my own differential thermostat because i couldn`t find one with the right features at that time. With the advent of arduino etc. i guess it wouldnt be too difficult to make a comprehensive control system assuming you know how to code it to do what you want.
Hi Tara! In order to recommend a thermostat, I'd need to know more details about what kind of fans, voltages, fixed speed/variable speed that you want to use. Feel free to email me. shannon.mutschelknaus@gmail.com
How crucial do you think it is to get the air intakes up high? I'm using barrels as manifolds and the fans sit in the intake barrels (2 separate systems). My concern with raising the height of the intakes is the amount of shade they will cast.
It is not crucial at all if the fans are sized properly. When sized properly they will be moving enough air to prevent hot air stratification (hot air stuck at the ceiling).
@@cherrytreepermaculture756 I used a 5ft x 5ft sheet of 2mm to make a 5ft x 18" diameter clear intake. If you link some long cable ties together you can adjust the diameter click by click to ensure a nice straight tube before gluing the overlap.
Did you ever consider using an insulated floor slab below ground as well as the walls ? This action would have stopped any cold bridging through the ground and a better result for stored heat. The other question is ; did you ever consider using water to both store and collect the heat ? If your north wall had a vertical layer of underfloor heating pipes, encapsulated in a concrete wall, then these could have heated a buffer tank of water. I accept that in the summer the air temperature neeeds to be reduced in the greenhouse in order for the plants to survive.
I considered that, but chose not to. In hindsight I see that was a good decision, because in late Dec. & January in my climate, I no longer get enough sunlight to keep up with demand. At that point the system acts like a low grade geothermal consuming the natural ground heat. Insulation would have prevented that.
@@waywardspringsacres Insulating below the tubes effectively fixes the volume of mass. This could lead to having a fully charged mass long before autumn and you`ll be forced to vent the excess instead of allowing it to migrate below the system. The majority of the heat cannot be recovered but given how much heat it takes, even a small percentage returned is a lot. As the deeper mass warms, the temperature differential driving the heat transfer reduces, so it offers similar benefits to physical insulation without the disadvantages of fixing the volume of mass.
@@waywardspringsacres It takes a phenominal amount of heat to increase the temperature of the mass below the system, if you have sensors down there you`ll notice the average temperature increasing gradually over a period of years before stabilizing to a new norm compared to virgin ground outside the greenhouse at the same depth. Its getting harder to draw conclusions these days as the seasonal highs and lows are becoming more extreme. We had all time record temps of 40.3c (104.5F) this summer which was challenging, especially as it hit at the end ofJuly when the mass was already pretty warm. The night temps were over 29c so there was no opportunity to dump heat from the mass overnight to increase the cooling capacity for the next day. A combination of fogging to increase the greenhouse RH% and running very high turnover rates was enough to keep the greenhouse below 90F during hottest part of the day without resorting to shadecloth. I cant wait to see what the winter brings.
Is session 3 of this series available for viewing? We are in the planning stages to install one of these this summer and are currently in the design and material sourcing phase. Really looking for insight and recommendations for thermostats, in-line fans, and all electrical equipment. Thank you for the amazing presentation and sharing your knowledge @Shannon Mutschelknaus!
Tavin, there are only two sessions for this presentation. Shannon's contact information is included at the end of the video if you would like to reach out with specific questions.
Multi-span greenhouses with low energy consumption will become the direction. We can produce tomatoes, cucumbers and peppers in winter without heating in all greenhouses (light radiation conditions must reach a balanced value)
Do you cover the pipes in the ground with clean stone, and if so, how deep ? That leads me onto another question which is if you used stone would you then use a membrane to stop soil fallin through into the gravel ?
@@billleete3125 Not really more efficient. It is mostly more convenient for wiring and to have them up off the ground. Creating positive pressure in the tubes also assists push out condensate.
A 10" manifold would be optimal when using 4" grid. It's a matter of volume using pipe cross-sectional area.... pi r squared. 6" is way too small and 8" is too small. If you have more 4" pipes than go to 12" manifold.
You are correct. The price of 10" is many times the price of 6" as well as it is much less available. I have found that this works well enough to prevent freezing on zone 4. But you are right that there is a lot of room for improvement yet, which is exciting!
The optimum manifold diameter will also depend on its length, the type of pipe used and how the 4" tubes are connected to it. Air handling systems are relatively easy to design if the duct specifications are known, infortunately ADS tube wasnt designed to carry air so the relevant data is not available from the manufacturer. If you are planning to install thousands of feet of ADS it would be a good idea to buy a length of smooth bore pipe for some side by side testing to gather the missing data before you finalise the design.
@@JohnGuest45 The necessary losses, heat transfer coefficients, etc have been characterized. They just aren't available from the OEM of the pipe or in textbooks/ASHRAE manuals as it's more of a niche application. If you need, I can send you research papers with the necessary info.
@@waywardspringsacres I have come across research related to non perforated land drainage tubing but nothing for the perforated variety. If the info had been available when i installed mine i probably wouldnt have skipped the practical testing i did but it would have been interesting to see how the actual results compared to the predicted results. In the end i decided a combination of corrugated perforated tubing and smooth bore non perforated tubing was the best choice. I didnt have to worry about the silly cost of large diameter manifold tubes, no manifolds in the system.
@@waywardspringsacres he basically does a hoop house with 2 ~400ft lengths of 4' irrigation tubing under it with a nice fan that blows through them. He then puts 2" rigid foam in the back half and it keeps tomatoes alive through the winter in idaho. He also does double layer of greenhouse plastic with an inflator fan between them.
he did a 2nd one that does gravel under the ground with 10 tubes that come in from one side and go down to the 4ft below, and 10 more 1 or 2 feet above those but not connected where the air goes out. So he pushes the air through the rocks kind of indirectly. That keeps things a little warmer, but he doesn't recommend it because it's so much more expensive
@@josephlarsen The University of Minnesota Deep Winter Greenhouse utilizes a rock bed storage system. A rock/gravel bed can store slightly more heat, but unfortunately adds cost to an already too costly system. I plan to do further research and demonstration of some potentially lower cost methods.
I am building a 10x12 harbor freight we geo lines and wells from the old house unit what is the best size lines and floor, we were thinking gravel floor 3 ft deep with 10 55gal barrels in the floor 2 ft in with 300 of 3/4” line & a large radiator and fan. Can you please help we live in SW Missouri Thanks
Yes, there would be many ways to store more heat, water being a good one. However, the real challenge is how to move the heat fast enough into the storage system so that it doesn't overheat during the short intense sunny periods. I found that the soil had plenty of unused capacity because I wasn't moving the heat fast enough. The best way to improve this would be spacing more tubes, closer together to increase the surface area in contact with the air blowing through the heat exchanger.
@@waywardspringsacres If the system is already installed you can use an overhead misting system to increase the relative humidity of the greenhouse air. This provides direct cooling for the greenhouse air as the process requires sensible energy. The cooler air can absorb more (sensible) heat as it makes its way to the inlet. The secondary benefit is the increase in dewpoint temperature which serves to increase heat transfer efficiency inside the tubes. For example, air at 90F and 50% RH has a dewpoint around 68.9F. Air at 90F with 70% RH has a dewpoint around 78.9F. The condensate increases the specific heat capacity of the mass close to the tubing as wet soil can hold more energy than dry soil. Before you install the tubes its important to create a straight shallow slit part way through the corrugations to ensure the condensate can drain fully. The drainage holes or slots in perforated tubing are designed to allow water in but not out. Its easy to overlook small details that can make a big difference :)
that curved glazing has forced the design to be bit off optimum. better to use a flat and vertical south wall (that will optimize winter sun collection)- then ONLY a couple of operable skylights in a conventional roof for only a little summer sun and most importantly for summer ventilation. the low front vents are good. also only a small amount of east glazing for summer sun and no west sun. and use a mass floor- insulation under it IF you in the higher latitudes- and the north wall should be all mass (insulated on the outside). and moveable insulation for all the glazing areas.
Great information. I see you've been active here quite recently Shannon, so hopefully you'll see these questions as well :) 1) Are your construction drawings available somewhere? (I found the umn-page with the DWG 2.2, but I don't think your is there) 2) I notice your greenhouse is quite tall. Is that because you want trees in it, or is there another reason? (i.e taller = more volume that needs to be heated, although that might not matter too much - i.e it is probably the square footage of the walls and glazing that is the most important) 3) Do you think a thermal wall would be helpful as a climate battery? My location (near Oslo, southern Norway) doesn't has as much sunlight as you do, but the temperature is somewhat higher (pluss less wind and more snow, i.e insulation), so I would need to rely more on a climate battery for long-term energi storage and not too much on "refills" on sunny days during the winter (although our coldest month, February, does normally have more sun than the rest of the winter)
I don't have construction drawings, largely because I consider it a proto and plan to make a lot of changes to the structure for my next model. I do have a 3D pdf that I could probably share via email if you wanted.
I would not do the clerestory format if I were to build it again. Mostly I was concerned about the vent doors opening successfully when having several feet of snow, but they would be better positioned in the north roof.
I'm not sure about the thermal north wall and if it would end up being redundant with the climate battery or not. If you don't get enough sunlight to charge both, it may not be worth the cost, but it would need a deeper dive into the climate, day-length and thermal mass of the two systems to say for sure.
@@waywardspringsacres Thanks for the replies. That makes sense - moving the vents to the north wall would make an easier build as well :) In my location I would probably need more thermal mass to get me through winter, can't really rely on much heat for the sun :(
Thank you! years later - I am here to adapt your info to New Brunswick, Canada.
Great video. Thank you for making this video available.
This was an excellent presentation. Thank you for all the great information!
Excellent video. Many thanks for sharing your experience!
Thank you! I will be working on more videos in the future focused on specific aspects of solar greenhouse design.
Great Presentation! We definitely needed more data to help us with our own decisions on building more of these. Thank you for sharing so much of your hard work for our benefit!!
Whooley-Dooley, this post was a year ago; has there been no interest since then ? Shows the focus,or lack thereof, of the main population!
Wow, great, useful and applicable info. Very detailed and impressive data gathering systems. Thank you!
Thank you for the feedback!
@@arkadiuszlee407 Hi Arkadius! Air infiltration still occurs and has been more than enough. For air circulation when the main fans aren't operating, you should use a standard HAF for greenhouses. HAF stands for horizontal air flow.
@@SDSUExtension Is there a part 3 where you go over the medium, fans /blowers, and controllers?
@@phillipk2490 I did not do a third webinar. That would be a good topic to do someday. I hadn't focused on that in the presentations, because it wasn't particularly innovative. In fact simpler is best for reliability in regards to the controls. I'm a proponent of simple analog controls for the fans because I don't consider it an acceptable risk for crop failure when a digital controller fails due to corrosion. If you have something in particular you need to know, you can email me. My address is at the end of the presentation.
I have been waiting for this video!
With regards to the pony wall, you could replace the doors with clear glass slider windows with screens. That way you would get the light down low and still have the windows as vents.
Yes, that is a reasonable upgrade. Glass or a PC door would have a fraction of the insulative properties, but worth it for low growing plants.
Great video. Thank you. Why do you not coil up one 6 in. pipe from one corner to the other? Why do you need 4 in. runners.
Thanks for sharing
excellent!
Since moisture cools, would it make sense to try an dehumidify the air that goes into the battery during cold days? Or is that a battle that cannot be won and the pipes would get wet but just after a longer while?
Not neccessarily electric, maybe just a mesh on the intlet that is able to catch the water and collect it or redirect it to the soil.
Im also thinking of catching more of the sun, like a massive black backwall that fully contains the inlet. Can always block the sun with screens for heat prevention (glassfront and black wall), but must store as much as possible in december.
Great data and presentation, thanks.
Dehumidification is a very energy intensive process to actively do. There are several methods: blowing air over a cold coil (like in your house, basically an air conditioner) or using a dessicant system that uses heat to burn out the absorbed moisture. The climate battery itself is a dehumidifier, just not enough to prevent condensation on the glazing surface because it is still a very cold surface. Using an insulating blanket to increase the r-value of the glazing at night or a thermal curtain inside could help some without a lot of energy costs. However, I haven't had any problems with plant disease in the last few years related to the humidity. I have had some minor cases of edema in a few solanaceous plants for short periods, which isn't a disease, just not visually appealing on the leaves.
A dessicant dehuey is the only realistic choice for cold air as it doesnt rely on dewpoint but would be expensive to run. If you have a tall south facing fence close to your greenhouse you can make a large flexible solar air heating panel to attach to it over the winter moths. In the spring you simply take it down, roll it up and store it in the shed. The idea is based on the "Solar Flume" flexible (inflated) solar collector which was around a very long time ago, maybe 15 years. I couldnt find any links sadly but the basic idea can be found in this patent: US20080017499
Edit, Wayback machine archived at least some of the original website, solarflume dot com
Plant talk starting at 1:20:00 technical design talk before that
When you were talking about heat exchanger tubes the diameter of the manifolds needs to be bigger than the runs between them. For example the manifolds and the pipes running from the manifolds to the surface should be 6 in. , while the runners between them should be 4 in. , this will give you better efficiency and air flow throughout the thermal battery. It will also allow your fans to work less hard, saving electricity and saving fans.
I am not a master physicist or anything but i know basic physics. The air flow is pushing back on your fan if you place a 6 inch fan reducing it to fit into a 4 inch pipe. Also, if it is all only the same diameter then the air is only really flowing thru the first run, it will take path of least resistance and since they are all the same size it takes the first one closet, mainly. But with a bigger manifold(on both ends) AND the pipes feeding those manifolds to the surface, it will distribute more evenly thru all runs. It is a pressure/vacuum thing, you are building up too much back pressure/vacuum(depending if you are pushing or pulling) at the manifolds being too small to get free flow and even distribution. You need the air to freely get into the manifolds this way it will fill the manifolds evenly and therefore flow thru the runs more evenly.
Yes, the manifold diameter I used was 6" due to availability. 8" would have resulted in much higher airflows or even larger, like 10" would be great, but it is spendy and harder to get.
Thank you for sharing your data and design considerations for a greenhouse such as yours. Did you consider thermal mass heat storage such as stone wall on the north side of the greenhouse or water storage barrels on the north wall? Thank you, again.
with a geothermal Greenhouse is there any benefit in insulating horizonally above the heating tubes?
Has anyone done a coefficient-of-performance analysis to determine if the energy input (fan kwh) provides a net benefit in output? Basically, is the COP above 1?
Yes, I had a graph of measured COP vs. fan speed at 1:00:30 It ranged between 5 - 50 depending on the air-ground temperature difference. These values are in line with other research papers I've read on the topic.
What’s the air volume of the greenhouse & what is the optimal number of times to exchange that air for heating & cooling?
About 5,800cuft. I know some folks suggest 4-5 ACPH (air changes per hour) as a rule of thumb. However, that is a tool sometimes used for architectural design of spaces for human comfort and not a great rule of thumb for a heat exchanger. The optimal airflow rate should be based on how much solar gain the structure captures and the efficacy of the heat exchanger. I have some plots showing efficacy of this system at various airflow rates, but I cut it out so I didn't bore folks. Hopefully I can do some short in-depth webinars/videos sometime to provide a better guideline for folks.
@@waywardspringsacres
I recommend designing the system to handle at least 20 air changes per hour, more is better if you have hot summers. Very few installations have the tubing layout or fan power required to test the higher turnover rates. I purposefully designed my system for 60 air changes per hour (12 years ago) to test this grey area and incorporated some additional features to enhance the system efficiency.
@@JohnGuest45 I recently did a webinar with the UMN Extension and shared some nice plots of the impact of higher airflow rates based on numerical analysis/CFD. I don't think the recording is available online yet. I will post a link on my Farm Facebook page when it is available.
@@waywardspringsacres
I watched that one and it was refreshing to see your recommendations broadly follow my own. i`ve been trying to save folks from making the mistake of installing long tubes for many years as the only remedy is to dig them back up. I was a little disappointed you didnt mention the role that humidity plays but i understand the need to keep things simple as physics and thermodynamics are not everyones cup of tea :) I think its important that folks understand the plants are an integral part of the system because an empty greenhouse with a system installed will perform woefully compared to one full of plants. If you have overhead misting in your greenhouse you will have noticed the effect it has on the heat transfer.
Something i would recommend in larger structures is to use multiple systems for greater flexibility and efficiency. A single fan in a large installation involves massive flowrates starting at a single point which makes it difficult and expensive to achieve an even air distribution and control the losses.
Keep up the good work.
You wouldn't bore me; it's perhaps the most important bit of information with regards to geothermal systems.
With a geothermal greenhouse, is there any benefit in insulating horizonally above the perferated tubes, especially if you are not growing trees direct into ground.
I was considering doing this.
It would reduce the amount of passive heat transfer between the thermal mass and the greenhouse air.
Question. Why don't you have water stored under the floor or soil for heat storage? Is it because of your severe climate and risk of water freezing and cracking your foundation? If you had water 1 or 2 meters deep in tanks under, won't convection of heat in the water reduce heat transfer escaping down through the soil? Also, I am aware that storing heat in water might need a different approach. Like a "radiator" with a fan blowing air through a car radiator and a water pump to pump the warmed water away. Did you not use that approach because it is too complicated? I live in a milder climate (Victoria BC Canada) and I am only allowed a 107 sq ft greenhouse and I did it DIY. So just over 8 by 12. I use 80 mm computer fans to blow air under the soil and they run directly off a solar panel. I insulated the north wall of it after seeing your video and others this winter. I have about a foot of water (contained by pond liner) under one planter (north side) and a rain barrel under the other one. Some of my heat storage is in the water. (I use water because we have really dry summers, sometimes 3 months with no rain). I have a pipe that brings air under the water level, and a syphon to remove condensation from that pipe.
I am growing in the soil, so want to make sure my plants/trees have plenty of root zone area. I didn't go the water route because I wanted to achieve the simplest system possible. Water is definitely an option, but requires more components/complexity/cost.
What a great idea! Thanks for all this research. My only question is do you have any problem with critters being drawn to the warmth and chewing into the tubes? An initial layer of hardware cloth or something like that would prevent that...?
I have not encountered that issue.
@JohnGuest45 but on the other hand, in the extreme hot and extreme cold, wouldn't it help maintain a more constant temperature underground?
Not really because the heat will be able to move down below the system
What data logging sensors andprogram do you use
I used iMonnit because of the diversity of sensor types that can be on the same network, which makes it good for research. However, it would likely be overkill if you just want to measure a couple things.
Been watching the different videos on this project and am impressed with the data. Thanks for all your work and data collection. Good stuff. Question about the perforated pipes. My worry would be that since dirt would get in those holes and maybe clog them over time. In your implementation where you put the soil back in place it seems like a fine soil (as opposed to gravel) would clog. what about using a sock on the perforated tubes to prevent the clogging. Also when connecting the distribution tubes to the manifold, do you need to seal that connection so dirt doesn't get in there? How did you do that since I think the manifold pipes were corrugated. Maybe just some caulking? I think you may have said foam in the video? One other question. How many fans (4?) and what type of fans did you use? Thanks again for all your work on this. Kind regards,
Mike
Hi Mike! I don't think sock is necessary from all the research I've found on the topic. I've been running 3yrs now without issue. I used spray foam in a can to keep out the backfill. I have four PrioAir 8" fans.
@@waywardspringsacres
I didn`t use sock and have had no issues. Sock may be necessary if you have pure fine sand but thats highly unlikely in most cases. With hindsight, i would recommend using non perforated tubing as the location of the perforations are as useful as a chocolate teapot. Cut a straight shallow slot part way through the corrugations (using a simple jig + circular saw or router) and locate the slot at the bottom during installation. Drainage tubing is designed to let water in via the perforations but not out. A drainage tube that doesn`t carry the water away isnt very useful.
Thank you Mr. Mutschelknaus! These two seminars have been great! I am beginning construction on my backyard 14.5x48 hoophouse style with climate battery up here in Western Massachusetts. Similar zone, a little less sunshine. Hoping for the best! QUESTION: Can you point me to a good thermostat option? I am having difficulties finding something that will control the four fans to turn on over a certain temp AND under a certain temp. Would love your advice! thank you!!!
That`ll teach me to edit a reply and lose it all lol. I`d reommend using a differential thermostat as they take account of both the air and mass temperature.
A standard thermostat will turn the fan on/off based solely on the air temperature. If the mass isnt warm enough to provide any useful heat or its too warm to store heat efficiently, the thermostat will still run the fan. A differential thermostat doesnt care what the actual temperatures are, just the difference in temperature between the air and the mass.
I had to make my own differential thermostat because i couldn`t find one with the right features at that time. With the advent of arduino etc. i guess it wouldnt be too difficult to make a comprehensive control system assuming you know how to code it to do what you want.
Hi Tara! In order to recommend a thermostat, I'd need to know more details about what kind of fans, voltages, fixed speed/variable speed that you want to use. Feel free to email me. shannon.mutschelknaus@gmail.com
How crucial do you think it is to get the air intakes up high? I'm using barrels as manifolds and the fans sit in the intake barrels (2 separate systems). My concern with raising the height of the intakes is the amount of shade they will cast.
It is not crucial at all if the fans are sized properly. When sized properly they will be moving enough air to prevent hot air stratification (hot air stuck at the ceiling).
@@waywardspringsacres Thanks, that was my thought as well. I'm also using a couple of pedestal fans to promote air mixing.
You can form clear intakes from thin polycarbonate sheet.
@@JohnGuest45 Nice idea!
@@cherrytreepermaculture756
I used a 5ft x 5ft sheet of 2mm to make a 5ft x 18" diameter clear intake. If you link some long cable ties together you can adjust the diameter click by click to ensure a nice straight tube before gluing the overlap.
I heard that someone asked about the growing space. But I didn't hear what the Sq ft of the greenhouse was.
About 500sqft
Did you ever consider using an insulated floor slab below ground as well as the walls ? This action would have stopped any cold bridging through the ground and a better result for stored heat.
The other question is ; did you ever consider using water to both store and collect the heat ? If your north wall had a vertical layer of underfloor heating pipes, encapsulated in a concrete wall, then these could have heated a buffer tank of water. I accept that in the summer the air temperature neeeds to be reduced in the greenhouse in order for the plants to survive.
I considered that, but chose not to. In hindsight I see that was a good decision, because in late Dec. & January in my climate, I no longer get enough sunlight to keep up with demand. At that point the system acts like a low grade geothermal consuming the natural ground heat. Insulation would have prevented that.
@@waywardspringsacres Insulating below the tubes effectively fixes the volume of mass. This could lead to having a fully charged mass long before autumn and you`ll be forced to vent the excess instead of allowing it to migrate below the system. The majority of the heat cannot be recovered but given how much heat it takes, even a small percentage returned is a lot. As the deeper mass warms, the temperature differential driving the heat transfer reduces, so it offers similar benefits to physical insulation without the disadvantages of fixing the volume of mass.
@@JohnGuest45 Exactly! That's a bit tough to clearly explain to general audiences. Maybe I'll make some content illustrating that sometime.
@@waywardspringsacres
It takes a phenominal amount of heat to increase the temperature of the mass below the system, if you have sensors down there you`ll notice the average temperature increasing gradually over a period of years before stabilizing to a new norm compared to virgin ground outside the greenhouse at the same depth.
Its getting harder to draw conclusions these days as the seasonal highs and lows are becoming more extreme. We had all time record temps of 40.3c (104.5F) this summer which was challenging, especially as it hit at the end ofJuly when the mass was already pretty warm. The night temps were over 29c so there was no opportunity to dump heat from the mass overnight to increase the cooling capacity for the next day. A combination of fogging to increase the greenhouse RH% and running very high turnover rates was enough to keep the greenhouse below 90F during hottest part of the day without resorting to shadecloth. I cant wait to see what the winter brings.
Is session 3 of this series available for viewing? We are in the planning stages to install one of these this summer and are currently in the design and material sourcing phase. Really looking for insight and recommendations for thermostats, in-line fans, and all electrical equipment. Thank you for the amazing presentation and sharing your knowledge @Shannon Mutschelknaus!
Tavin, there are only two sessions for this presentation. Shannon's contact information is included at the end of the video if you would like to reach out with specific questions.
Multi-span greenhouses with low energy consumption will become the direction. We can produce tomatoes, cucumbers and peppers in winter without heating in all greenhouses (light radiation conditions must reach a balanced value)
Do you cover the pipes in the ground with clean stone, and if so, how deep ? That leads me onto another question which is if you used stone would you then use a membrane to stop soil fallin through into the gravel ?
No stone was used. I back filled the same soil that was excavated. Hauling in rock/gravel adds a lot of unnecessary cost.
Are your fans on the intake tubes or on the Exhaust tubes of your climate battery
Intake
Is the fan More efficient on the intake or is there some other reason for choosing the intake over the exhaust position?
@@billleete3125 Not really more efficient. It is mostly more convenient for wiring and to have them up off the ground. Creating positive pressure in the tubes also assists push out condensate.
@@waywardspringsacres Thanks for your insight.
A 10" manifold would be optimal when using 4" grid. It's a matter of volume using pipe cross-sectional area.... pi r squared. 6" is way too small and 8" is too small. If you have more 4" pipes than go to 12" manifold.
You are correct. The price of 10" is many times the price of 6" as well as it is much less available. I have found that this works well enough to prevent freezing on zone 4. But you are right that there is a lot of room for improvement yet, which is exciting!
The optimum manifold diameter will also depend on its length, the type of pipe used and how the 4" tubes are connected to it. Air handling systems are relatively easy to design if the duct specifications are known, infortunately ADS tube wasnt designed to carry air so the relevant data is not available from the manufacturer. If you are planning to install thousands of feet of ADS it would be a good idea to buy a length of smooth bore pipe for some side by side testing to gather the missing data before you finalise the design.
@@JohnGuest45 The necessary losses, heat transfer coefficients, etc have been characterized. They just aren't available from the OEM of the pipe or in textbooks/ASHRAE manuals as it's more of a niche application. If you need, I can send you research papers with the necessary info.
@@waywardspringsacres
I have come across research related to non perforated land drainage tubing but nothing for the perforated variety. If the info had been available when i installed mine i probably wouldnt have skipped the practical testing i did but it would have been interesting to see how the actual results compared to the predicted results. In the end i decided a combination of corrugated perforated tubing and smooth bore non perforated tubing was the best choice. I didnt have to worry about the silly cost of large diameter manifold tubes, no manifolds in the system.
@@JohnGuest45 Good Points! I wish I was more of an engineer myself. Very thankful for folks here in the comments to learn from.
i'd love to see a conversation between you and ldsprepper discussing the best options
I haven't seen much of his work. Just one video.
@@waywardspringsacres he basically does a hoop house with 2 ~400ft lengths of 4' irrigation tubing under it with a nice fan that blows through them. He then puts 2" rigid foam in the back half and it keeps tomatoes alive through the winter in idaho. He also does double layer of greenhouse plastic with an inflator fan between them.
he did a 2nd one that does gravel under the ground with 10 tubes that come in from one side and go down to the 4ft below, and 10 more 1 or 2 feet above those but not connected where the air goes out. So he pushes the air through the rocks kind of indirectly. That keeps things a little warmer, but he doesn't recommend it because it's so much more expensive
@@josephlarsen The University of Minnesota Deep Winter Greenhouse utilizes a rock bed storage system. A rock/gravel bed can store slightly more heat, but unfortunately adds cost to an already too costly system. I plan to do further research and demonstration of some potentially lower cost methods.
@@waywardspringsacres you should chat to ldsprepper, he's got the system down pretty cheap.
I am building a 10x12 harbor freight we geo lines and wells from the old house unit what is the best size lines and floor, we were thinking gravel floor 3 ft deep with 10 55gal barrels in the floor 2 ft in with 300 of 3/4” line & a large radiator and fan. Can you please help we live in SW Missouri Thanks
My email address is on the last slide of the ppt.
Water storage could it help store heat too?
Yes, there would be many ways to store more heat, water being a good one. However, the real challenge is how to move the heat fast enough into the storage system so that it doesn't overheat during the short intense sunny periods. I found that the soil had plenty of unused capacity because I wasn't moving the heat fast enough. The best way to improve this would be spacing more tubes, closer together to increase the surface area in contact with the air blowing through the heat exchanger.
@@waywardspringsacres
If the system is already installed you can use an overhead misting system to increase the relative humidity of the greenhouse air. This provides direct cooling for the greenhouse air as the process requires sensible energy. The cooler air can absorb more (sensible) heat as it makes its way to the inlet. The secondary benefit is the increase in dewpoint temperature which serves to increase heat transfer efficiency inside the tubes. For example, air at 90F and 50% RH has a dewpoint around 68.9F. Air at 90F with 70% RH has a dewpoint around 78.9F. The condensate increases the specific heat capacity of the mass close to the tubing as wet soil can hold more energy than dry soil. Before you install the tubes its important to create a straight shallow slit part way through the corrugations to ensure the condensate can drain fully. The drainage holes or slots in perforated tubing are designed to allow water in but not out. Its easy to overlook small details that can make a big difference :)
For market
that curved glazing has forced the design to be bit off optimum. better to use a flat and vertical south wall (that will optimize winter sun collection)- then ONLY a couple of operable skylights in a conventional roof for only a little summer sun and most importantly for summer ventilation. the low front vents are good. also only a small amount of east glazing for summer sun and no west sun. and use a mass floor- insulation under it IF you in the higher latitudes- and the north wall should be all mass (insulated on the outside). and moveable insulation for all the glazing areas.
Yes. The glazing arch is not optimal. It was reused from a prior greenhouse.
Great information. I see you've been active here quite recently Shannon, so hopefully you'll see these questions as well :)
1) Are your construction drawings available somewhere? (I found the umn-page with the DWG 2.2, but I don't think your is there)
2) I notice your greenhouse is quite tall. Is that because you want trees in it, or is there another reason? (i.e taller = more volume that needs to be heated, although that might not matter too much - i.e it is probably the square footage of the walls and glazing that is the most important)
3) Do you think a thermal wall would be helpful as a climate battery? My location (near Oslo, southern Norway) doesn't has as much sunlight as you do, but the temperature is somewhat higher (pluss less wind and more snow, i.e insulation), so I would need to rely more on a climate battery for long-term energi storage and not too much on "refills" on sunny days during the winter (although our coldest month, February, does normally have more sun than the rest of the winter)
I don't have construction drawings, largely because I consider it a proto and plan to make a lot of changes to the structure for my next model. I do have a 3D pdf that I could probably share via email if you wanted.
I would not do the clerestory format if I were to build it again. Mostly I was concerned about the vent doors opening successfully when having several feet of snow, but they would be better positioned in the north roof.
I'm not sure about the thermal north wall and if it would end up being redundant with the climate battery or not. If you don't get enough sunlight to charge both, it may not be worth the cost, but it would need a deeper dive into the climate, day-length and thermal mass of the two systems to say for sure.
@@waywardspringsacres Thanks for the replies. That makes sense - moving the vents to the north wall would make an easier build as well :)
In my location I would probably need more thermal mass to get me through winter, can't really rely on much heat for the sun :(
This website is all very technical, why not just move to Queensland, sorry, New Mexico or Arizona and build a nice earth-sheltered house ?