Bubble Tech Insulation and Shading System: Changing microclimate to reduce climate change
Ross Elliott, Homesol Building Consultants
Lively Up Winter Harvest, RR #1, Mc Donalds Corners, Canada
(613) 278-0467

CLICK HERE to see a slide show presentation of the Lively Up Greenhouse

Key Points

  1. Why greenhouses don't work in very cold or very hot weather.
  2. How bubbles provide summer cooling
  3. How bubbles provide winter heating.
  4. Other applications, Open Source technology

Introduction

Fresh, unprocessed, locally-grown organic produce should be at the heart of an environmentally-sustainable food system, yet a typical Canadian meal has been transported over 2000 kilometers from producer to market, consuming vast quantities of fossil fuels in the process. Growing food in winter greenhouses is often uneconomical due to the low thermal resistance of glazing systems and the rising cost of fossil-fuel heat. Conversely, greenhouse overheating is a common daytime problem, and excess solar gain is generally vented rather than stored for later use in winter, or deflected with shading systems in summer. If a way could be found to produce food locally in cold seasons using only captured solar energy, this would reduce reliance on long-distance transportation of fresh produce, lower carbon dioxide emissions, slow climate change and increase food self-sufficiency. Use controlled environments to reduce greenhouse gases and produce fresh, local, organic food...Finite fossil fuels threaten global food security...

Materials and Methods

We built the 1500 square foot Lively Up Winter Harvest solar greenhouse prototype to research the use of soap bubbles to create a replaceable and removable layer that allows shading or R-30 insulation as needed. This layer prevents overheating by collecting and storing excess solar gain, reduces the Design Heat Loss of the building dramatically at night, while allowing maximum light availability for optimum plant growth during short winter days. A series of mist sprayers between the two glazing layers cool interior temperatures while collecting solar heat in 20,000 liters of water. The Bubble Tech Insulation & Shading System should eliminate the need for fossil-fuel heating or powered ventilation to maintain optimum growing conditions year-round in any climate. This is the first operational Tunnel Structure? of this kind in the world. Results of this research will be applied to creating a 9000 square foot gutter-connected commercial greenhouse operation, as well as many other projects currently planned or underway worldwide. All results will be published as Open Source technology with commercial users invited to Pay It Forward. For further details see www.solaroof.org

Results and Discussion

The greenhouse was completed to the first layer of plastic by the end of 2001, at which point further construction was suspended due to the onset of winter. Crops of lettuce, mesclun, coriander , swiss chard, parsley and beets grew vigorously all winter long under row covers, while the constantly circulating 42,000 lb. liquid thermal mass within the insulated foundation reached a low of 5C and kept the soil from freezing. This was without any bubbles or even a second layer of plastic, so we assume there is geothermal heat at 5' below grade maintaining the greenhouse at this temperature. A 4 channel data logger continuously records the greenhouse environment. The completed system was commissioned in April of 2002 and has been operating continuously since, while producing crops of peppers, tomatoes, cucumbers, edible flowers, herbs and salad greens. Various issues have been identified as needing further attention, and we will be making changes to the system in the spring of 2003 to optimize the greenhouse for extreme cold. Ultimately we plan to take this technology to the far North, where communities import all their produce, as well as to cold countries facing famine such as North Korea and Mongolia.

Conclusions

Preliminary results show that the greenhouse works as planned through the hot summer, shading and cooling crops as needed with dramatic results. Mid winter operations in 2002 resulted in no frost damage to the crops even at - 30C out side, although supplemental heat was needed at times due to technical glitches with the sys tem. Further research needs to be completed and we welcome financial support from government, industry or individuals for further investigations into agricultural and residential applications of this Bubble Tech technology.

References

Based on work first published by inventor Nelson, Richard (1994) "Results of Prototype Operations and Operating Principles of the Thermactive Systems Technology", and his subsequent collaboration with us on this project.

1 Shamim, Tariq, P.E ., Mc Donald , Thomas W. , Ph D ., P.E . (19 95) "An Experimental Study of Heat Transfer Through Liquid Soap". ASHRAE Transactions: Research

2 Modeled using HOT 2 XP? ver.2.104 (2001), Natural Resources Canada software, 85% reduction in heat loss @ 20C interior temperatures / -13C exterior temperatures. Zero purchased heat needed to maintain above freezing interior temperatures even at -30C exterior temperatures.

Lively Up Winter Harvest: Basic Principles of Operation

The Lively-Up Winter Harvest greenhouse is constructed of standard twelve-foot high aluminum greenhouse hoops 4' on centre bolted to the inner foundation, covered in greenhouse plastic. The vertical end walls extend 2' higher than the hoops. The outer foundation is spaced 30" from the inner wall, forming 3' deep trenches for soap solution storage down the two long sides, joined to each other with 4" pipe. This holds a total of 20,000 liters (41,700 lbs.) of thermal mass, which is solar heated in the winter, and the water is kept in constant circulation with a 20 gpm. submersible pump. The ridge member at the peak is a lightweight aluminum, open web parallel chord Solar Joist that spans from one end wall to the other. The ridge joist is 2' in depth, with the top chord used to attach the exterior plastic sheet. The interior and exterior sheets of plastic are spaced apart to create a roof/wall cavity space on each side of the joist. The outside sheet is stretched outward by pressure created in the sealed Cavity Space by a small blower that provides static pressure and compensates for any leakage of air-pressure. The outer plastic sheet arcs to the exterior wall of the footing, where poly-lock holds the sheet continuously. Thus the double plastic covering along each side of the center ridge forms two arching cavity spaces separated by the ridge beam air barrier. Typically the greenhouse will be oriented with the ridge pointing east/west. This means there is a South facing roof/wall and a North facing roof/wall. Bubbles are created by water-driven high expansion Bubble Generators connected to a 40 gpm. pump. There are two Bubble Generators, one at each end of the ridge joist near the end walls. The Bubble Generators are mounted on the joist - through the openings in the web members - with one unit facing into the North roof/wall and the other facing into the South roof/wall . Air can pass through the body of each generator to move from the one cavity into the other.

When one of the Bubble Generators operates, it takes air from the opposite roof/wall and transforms this air into bubbles that flow into the cavity. The bubbles will fill at a rate of about 2000 cfm taking little more than a couple of minutes to flow along the 50-foot length of the roof/wall, filling it to the peak. As the bubbles flow into the North roof/wall, air in the cavity has to move into the South cavity through the body of the soap generator at the opposite west-end of the ridge joist. If both Bubble Generators operate at the same time they grab the air from the opposite side roof/wall and both cavity spaces fill with bubbles at the same time. When the bubbles fill to the end and up to the peak (the high expansion bubbles have almost no weight and show no tendency to slump down) the bubble generating cycle is finished. The Bubble Generators are shut off and the bubbles will remain for hours in place in the cavity. The liquid forming the bubbles will gradually drain down and they will become thin walled and almost transparent before they dissipate completely. As the bubbles dissipate they can be re-supplied by operating one or both of the Bubble Generators.

The operation of the bubble cycles can be automatic, using simple electronic controllers. Shading can also be accomplished with the soap solution, collecting solar gain while protecting the plants from excessive heat and eliminating the need to ventilate for temperature control. A series of mist sprayers along the ridge can be utilized as needed to cool interior temperatures or remove soap bubbles while collecting solar heat, which is stored in the insulated thermal mass containment system for later use. Previous research has shown the interior temperature of the greenhouse will be the same as the temperature of the thermal mass when the bubble generation system is in effect. Irrigation is provided by a built-in rainwater collection system which pumps precipitation into a raised 1500 liter plastic tank inside the greenhouse. This water creates additional temperature-stabilizing thermal mass that keeps the BubbleGenerators? from freezing while providing gravity-feed irrigation for the plants.


Excuse my ignorance: "gpm" means "gallons per minute"? Can you give additional info on the pumps etc? If I go shopping, what do I ask for? Thanks! Lucas Gonzalez

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