Output 2

Subterranean Heating

And Cooling System

Demonstration at the

Love Creek Center For Permaculture

By Gabriel Bridges

February 22^nd, 2011

Core Elements:

Output Specification                    

Introduction and Background    

 Main Report                                

Conclusion and Next Steps        

Output Process Reflection         

Support Elements                                           

Evidence                                                          

Pathway Reflection                                        

Learning Journal Excerpts                           

Resource Review                                            

Evidence of Outcomes                                   

Evidence of Participation                              

Digiphon                                                           

This is my project on Subterranean Heating and Cooling Systems.  It fits in with my learning pathway of leading by example.  As far as I know it is the first of it’s kind in the region.  I have successfully incorporated the demonstration of a technology that is easy to create and is more appropriate for a solar economy.  This output packet is presented in order with appropriate photos, videos, charts, and links to resources along the way.  Payback calculations can be found in the appendix.    I will first tell of my introduction to the system and my experience up to date with the system.  I give a brief description of the technology and offer links to more information.  I will show how the greenhouse technology has worked on two separate greenhouses at the same location thus far.  I walk through the design and payback calculations. I have offered my own insights into the system from my own experience in using it so far. You will find photos along the way to give you visual connection to Subterranean Heating and Cooling Systems.  I will introduce you to some of my mentors and the collaborators. I will explain the uses of each greenhouse, compare them and then include some possible next steps for myself.

            Following is my own spiral-learning pathway up to date with Subterranean Heating and Cooling Systems.  My pathway starts from my introduction to the system to installing my own system and managing it at the same time my dad installed a system that he manages, both on the same site.  I will lead you on my pathway of discovering the system, wanting to demonstrate the system, building the system, my initial discoveries when using it, and the next possible steps of my involvement with the system.  Demonstrations of the technology at the Central Rocky Mountain Permaculture Institute and design plans from Going Concerns Unlimited helped guide the project.  Their examples have also inspired me to help make this technology available to all that may need it.

            Subterranean Heating and Cooling System (SHCS) has also been referred to as a climate battery.  I was first introduced to it in the midst of my UC Davis student career.  For an independent study course I went to the Central Rocky Mountain Permaculture Institute (CRMPI) to take a Permaculture Design Course in 2005.  I was drawn to the course at CRMPI because they were to highlight strategies to use in high altitude, dry climates, these are some of the characteristics of the site at the Love Creek Center for Permaculture (LCCP), the site where I grew up and have been developing a permaculture demonstration site since 2001.  I showed up a week early for a partial work trade for my PDC.  During my stay there I was introduced to how their greenhouses were heated and cooled.  For part of my work trade I helped install some of the tubing and build the garden beds that went on top of the tubing.  During the PDC we looked at the system in depth.  Two of the pioneering collaborators of this technology were teachers of the PDC, Jerome Osentowski of CRMPI and John Cruickshank of Going Concerns Unlimited.  They used technology researched by the Canadian government, also recently studied by the Chinese government, John Cruickshank explains and has links to this information on his website.  It is a pioneering approach to heating and cooling that requires a fraction of the energy that it takes to run a conventional greenhouse.  I was inspired by the ability to grow figs, bananas, vanilla bean, perennial peppers and more at 7000 feet in Colorado.

The system is explained in great detail on John Cruickshank’s website, SHCS explained.  The system works by taking warm humid air in the greenhouse, and pumping it through a set of perforated drain tubes, which are buried in the subsoil, eventually exiting back into the greenhouse minus some heat and moisture.  It is based on the phase change of water, from water to vapor, back to water and the cycle starts again.  This amazing technology is fueled by the power of the sun.  The sun heats up the greenhouse causing evaporation and evapotranspiration from plants.  When the heat of the greenhouse reaches a certain temperature that is set by the manager of the greenhouse, a thermostat will turn on the fan.  The air and water vapor are pumped into the cooler soil where the water vapor condenses.  The condensed water holds much of the energy that it took to lift it into the air as vapor.  This technology allows us to use the thermal mass of the ground as a storage tank for surplus energy.  At the same time the SHCS is storing heat in the soil it is also cooling the greenhouse, the daytime cooling aspect.  There is another thermostat that will turn on the fan at a low temperature chosen by the manager.  This will take the stored heat in the soil and transfer it to the greenhouse, the nighttime heating aspect. The system needs a summer of heat storage to run optimally.  It allows us to run a greenhouse at a relatively constant climate throughout the year. Having been tested mostly in cold winter regions, it has been tried and true for a heating and cooling system in cooler regions. But for using in a warmer climate where the cooling capacity of the system may be more important there has been little experimentation.  John Cruickshank has suggested the idea of burying the tubes outside of the greenhouse to use the SHCS strictly as a cooling technology.  The site where I am working with this system is more similar to where it has been tested but in very close proximity to warmer climates, I hope to be able to experiment with the same technology in adjacent climates, testing it in colder climates as well as warmer climates. John Cruickshank has been kind enough to make the knowledge of this technology available on his website, The Land of Hobbit House and Company.  He highlights the physics of the system and how it works.  He explains where the heat storage is, how it accomplishes daytime cooling and nighttime space heating. He not only makes the knowledge available, he has created a calculator to help people figure out how much tubing is needed to install, the size of the fan needed to run the system, how much it will cost and how long it will take to pay you back in terms of energy stored.

            When I returned to California to resume my studies at UC Davis I knew that I eventually wanted to work with the SHCS technology.  At the intentional community that I was living in there was a greenhouse that was in need of a cooling system.  I had proposed the idea to the community, but alas with little firsthand experience and the arrogance of some that were engineers the technology was never adopted and a swamp cooler installed instead.  This only reaffirmed that I wanted to eventually have a SHCS so I could demonstrate the technology.  After graduating from UC Davis in 2007 I moved back home to Love Creek where I continued working on a permaculture demonstration site and started my business, the Love Creek Center for Permaculture.  I planned to eventually install the system there.  One of my main intentions for adding this technology to the Love Creek Center For Permaculture is to increase the amount of sustainable technology models.  It compliments Dave Holmgren’s Permaculture Principle #2; Catch and store energy, as well as others.  I’ve seen it in action and I know it is important for people to see it.  I would like to see others adopt it for their own use.  I also want to increase our own food production capabilities on site. 

            There is one greenhouse on site that has been used since 2004; it does not have an SHCS as of February 2011.  It is not uncommon to see the temperatures dip into the 20s in that greenhouse on very cold nights.  This limits the ability to grow some plants, only frost hardy greens and herbs and some over wintering of other perennials.  I want to be able to do more in the cold winter months. With the inspiration of seeing the technology first hand it was finally time to install my own SHCS.  In 2009 we constructed a small greenhouse attached to our woodshop, we’ll call it greenhouse 1(GH1).  This was to be the future home of the first SHCS at the Love Creek Center For Permaculture, it was a retrofit as the greenhouse was already in use.  In the fall of 2010 we built another greenhouse on site that had the SHCS in place before the greenhouse was in place.  I will now show the progression up to date of each greenhouse and then show a chart that shows the differences and similarities.

Greenhouse 1 is attached to our woodworking shop and has been in use for over a year.

I have used it to over winter tender perennials and start seedlings for the market garden.  It has worked very well in the past year, allowing me to start tomatoes in January and every other garden vegetable, so I can have them ready to transplant in the ground once the timing is right.  Even though we have experienced no frost in this greenhouse I still wanted to see the SHCS in action in it.

The first thing I had to do was make sure I was doing everything right.  John Cruickshank’s website, The Land of Hobbit House and Company, has several links to all of the details needed.  Before I knew how much tubing I needed to install and how big of a fan required I needed to run some numbers.  I needed to find out the square footage and the volume of the greenhouse.  I came up with 108.6 ft² for the floor and 648.6 ft³ for the air space.  So I plugged these numbers into the calculator that John Cruickshank provides on his website.  Step 1 gets you to calculate the greenhouse volume and all of its dimensions.  When I enter the numbers in the

correct spot, things begin to change on the calculator.  Entering square footage gives an estimation of how many feet of tubing I’ll need.  Entering the volume of air space gives me a ratio of cubic feet to square feet and comes up with a recommendation for the

size of the fan, measured in cubic feet per minute (cfm).  Step 2 entails entering either the calculated fan size or a fan size of your choice.  The recommended fan was 54 cfm, but since we had one on site that was 50 cfm, we decided to use it.  I plugged in the cfm of the fan used and was on to step 3, where we calculate the underground air circulation tubing (UACT).  Here I began to run

into some problems with the calculator.  The estimation of tubing was 144 feet.  However when I plugged those numbers in, the tubing air speed of feet/second didn’t fall into the recommended range of 2-4 ft/second.  I wasn’t sure what to do.  When I changed the number to half of the recommended tubing, the air speed was in the correct range.  I tried to contact John Cruickshank through the email on his website, but no reply.  I contacted a colleague, who recently installed the system, to see if he could help me.  He didn’t know.  I’m thinking the small size of the greenhouse might have influenced the numbers.  So, the learning is the doing and I just went with the numbers that looked right.  I went within the recommended range of airflow and buried 4 tubes at two levels in the

ground. Now we go to step 4 where we plug in the costs for the system hardware.  My total will be around $230 after I order the thermostat controls.  Then on to step 5, which is the payback calculation.  I changed the numbers for the cost of energy and for the number of days I expect to get a 1ºF rise in soil temperature.  Since it is working so well in midwinter I expect at least 200 days where the air temperature will reach at least 90ºF.  After I plugged in all of the numbers I am very pleased.  It is saying that it will only take about 1 year to gain the energy equivalent of the cost of the hardware, very nice.  And from then on I will be gaining the

energy equivalent of my investment every year.

            I bought the perforated tubing and plastic culverts used as the plenum and the ADS tubing at local hardware stores.  I was able to use a fan that we had around that pumps 50 Cubic Feet per Minute, which was close enough to the recommended size from

Hobbit House and Company. In the fall of 2010, after almost a year of using GH1, my intern, Jack Smith, and myself began digging the trench for the tubing.  The tubing and fan were added soon after.  I built the permanent bed that runs the length of the greenhouse with lumber we had on site.  Soon after finishing the bed-frame I planted it with starts that were already on shelves in

the greenhouse.  I planted dill, bunching onions, arugula, mustard greens, peppers, galangal, lemongrass, and prickly pear.

Looking at the progression of the system from one end of GH1, the exhaust is at the far end.

Looking down at the exhaust.

The first day of operation for the fan in GH1 was January 14^th 2011, the soil temperature in the morning read 41º F.  While the greenhouse had been in use and relatively frost free, there were significant improvements in the soil temperature.  Before the SHCS we were seeing soil temperatures in the high 30’s or the low 40’s.  By the time noon rolled around the air temperature was 99ºF, this was already common, and the soil temp had risen by two degrees, not too common as the sensor is 3 feet deep.

A month of sun in January and February helped us catch up with some heat storage.  Within a week of getting the fan running we saw a temperature increase of at least 13ºF, the soil temperature had risen from about 41ºF to about 64ºF in the daytime and 54ºF in the night.  Three weeks later we were seeing highs in the soil above 70ºF, lows were hovering around 65ºF.  Plant response was very good.   This was due to about a month of sunny weather we had in January and February this year.  Cloudy weather would have resulted differently.  After about 1 month of sun we had a week of cold, cloudy and snowy weather.  With four feet of fresh snow there was at least one night where the SHCS could have been used for nighttime space heating as the air temp dropped to 36ºF, but the ground temperature had only dropped to 52ºF.  I haven’t installed thermostats that would turn the fan on in the day or night so I’ve been turning the fan on in the daytime manually, to charge the soil.  I still haven’t used the SHCS for nighttime space heating and it is doing very well, even on the coldest winter nights it is frost-free.  I’ll be ordering the thermostats soon to automate the system.  I’m very exited to say that GH1 is fully functional and in production 24/7/365.

            We fabricated a hoop-shaped greenhouse out of wood that is freestanding; call it greenhouse 2(GH2). GH2 was built in the middle of the main house garden at the Love Creek Center for Permaculture.  This greenhouse is to serve the needs of the main house and will include 2 citrus trees and an olive.  This greenhouse was put together mainly by my dad but there were several collaborators that came to help bury the tubing.  Collaborators included a Amelia Parisian (a Gaia U. associate), Craig Saydhur (RDI intern), Zach Wallace (local landscaper), Clinton Betts (Bret Harte High School student), Zach Knutson (artist), Chad Holbrook (brother in law), my brother Josh Bridges (Photographer) and my dad Rocky Bridges (coordinator for GH2).

My dad did all of the calculations for GH2, I won’t go into the design and payback calculator for this greenhouse but will talk more about the structure and it’s function.  This greenhouse has 8 tubes in a single layer in the ground.  The tubes were buried in pea gravel rather than soil and has more mass per volume than soil does.  It has insulation in the ground surrounding the outside of the greenhouse footprint.

            Greenhouse 2 sat for several months with no cover while we waited for fair weather to install the greenhouse plastic. The ground temperature sat just above freezing until we finally put the skin on the greenhouse on January 24, 2011.  Two weeks later, with lots of sun there was a significant increase in the ground temperature.  It approached temperatures of 54ºF.  We did notice that the lack of plants in the greenhouse might change the effectiveness of the system.  It was much slower in heat gain than GH1, one factor being the lack of plants yet.  Without the evapotranspiration that plants provide, the system lacks the humidity in the air needed to absorb the heat that can be transferred to the soil.  I assume a dramatic increase in soil temperature once plants are established in GH2.  Summer will provide plenty of excess heat to be stored as well.

  The ground temp. on this day was just above freezing with frost on the ground; notice the snow in front of greenhouse 1

  Just 5 minutes before the above picture was taken; the top is the air temp. and the bottom is the soil temp. GH1

 This picture was taken about 10 minutes after the above picture in GH2; top is the air temp. bottom is the ground temp.

Three to four feet of snow in 4 days plus roof shed buried the both greenhouses on February 17^th.  We got another foot of snow that night.  A few more cloudy days and then sun with clear cold nights put the greenhouses to the test as outside temperatures reached into the low 20s at night.

On February 22^nd the air temperature in GH1 reached down to 35.8ºF, while the soil temperature was down to 50.4ºF.

  GH2 was a frigid 24ºF inside with a soil temperature of 46ºF.

It is clear that SHCS technology can work well in the locale of the Love Creek Center for Permaculture.  The two that have been set up at LCCP have responded well with little time to charge up.  I will expect them to have a lot more heat stored and perform better in a year from now once they go through a full summer of charging.

            So far it has been an exiting learning spiral.  My initial contact with the system gave me great enthusiasm and now with my own SHCS I have been rejuvenated with more enthusiasm for it.  I am eager to get more familiar with the system through my experience.  I plan to promote the technology through educational workshops and my own demonstration. I’m exited to bring the technology to the region and I look forward to it being adopted locally.   Collaboration with local nurseries, other businesses, or homeowners on installation may be in the future.

            We hope to maximize the production of the two SHCS greenhouses we have on site.  A retrofit of the older greenhouse on site is necessary as it does freeze inside on occasion.  There are other integrations in the system I would like to explore.

            It would be nice to have an automated recording of the temperatures in the greenhouse.  A graph of the temperature fluctuations would tell a lot more than what I’ve provided in this report.  It would be nice to compare the fluctuations inside the greenhouse to the temperature fluctuations outside of the greenhouse for a whole year.  I know someone who has a weather station and is a computer expert; I will inquire him about the hardware needed. 

            In GH1 we are going to install another fan and thermostat that will take excess heat that the SHCS can’t handle and pump it into the building that the greenhouse is attached to.

            After attending an aquaponics lecture I’ve been inspired to combine the two technologies by simply adding an aquaponics system to the inside of a SHCS greenhouse.  I will possibly be collaborating with another Gaia University Associate on the combination of the two technologies this summer.

This process has given more meaning to my chosen project.  The project alone was exiting enough to engage in, but having to document my learnings and presenting them made the whole project much more rich and meaningful. Once I got started on implementing the project it went very smooth.  The only holdup was the contradicting calculations I came up with.  When I finally felt confident enough about my decision, I went forward and everything has worked very well.  I could have easily done the output on one greenhouse but having two made it more interesting and I learned more about SHCS.  I look forward to refining my skill of output packet design on the rest of my pathway design.  One thing I might do differently next time is to include more media.  I really like stop motion videos to show progression over time.  Photos, videos and other forms of media that I’m not as familiar with will be further integrated into my outputs.  I would like to explore creating an output packet with a different format completely.