Bubble Tech - Introduction
Both the liquid and the air components of the Bubble Insulation? and Bubble Shading are reused within closed cavity spaces of the walls and roofs, using a method that recycles the liquid and air. No air outside of the greenhouse Cavity Space is required to blow the bubbles. For air pressure supported greenhouses some outside air is used to keep and maintain the static pressure that supports the outside film layer. A separate blower maintains this static pressure system and very little outside air is actually introduced into the cavity space since only the air loss through leakage needs to be replaced.
The air in the sealed cavity space will be clean since the soap liquid constantly washes it. The liquid also works in a closed loop with no possibility for contamination in normal circumstances. However, it is always best to have a filter in the liquid system. It is important to keep access ways into the cavity space closed so that insects and dust do not get in and pollute the soap liquid. Do not track dirt into the cavity space on shoes or clothing when entering inside the wall cavity. It is best to use soft water with neutral Ph and low mineral content. This will further inhibit growth of organic mater within the cavity space. The soap has a mild anti bacterial action and sometimes it may be necessary to use a biocide agent in the soap solution. Organic growers will probably want to avoid using toxic chemical agents although for practical purposes the soap liquid is always contained within the sealed Cavity Space and will not affect or come into contact with the crop.
The soap solution has good bubble generating results at a 1-3% concentration, which is typically a 10-30 times dilution factor from the concentrated soap. The basic foaming agent for the bubble greenhouse is sodium laurel sulfate, which is a common commodity in the production of shampoo and other products that are well proven as safe for use and are biodegradable. These materials are derived from oils, sometimes being produced from coconut oils, which are a renewable resource.
A machine called a Bubble Generator is required to mix the soap liquid and air that is drawn from within the cavity space to fill the entire cavity space with bubbles is located within the cavity space. The machine uses a blower component to provide the power to blow the bubbles and a liquid pump to deliver the soap liquid on a screen where the air and liquid are mixed and forced through the screan by the blower. A fan can sometimes be used where there is a low backpressure for the bubbles to flow and fill the cavity space. But for long flow paths, especially where the bubbles need to change the direction of flow the blower is able to continue to produce bubbles against a higher backpressure.
Our purpose is to be able to control the quality of bubbles in the cavity space, since they are not static but have properties that change over time. The natural gravity drain-down of liquid from the bubble walls causes the bubble walls to thin until bubbles collapse and break. Thus the bubbles dissipate over time. This also depends on the concentration of the soap solution and the presence of additives that can extend foam life. One such additive is glycerin, which can be used to make more persistent foam. I have also used Cocomide DEA as a bubble life extender. Not all additives that extend the life of bubbles (such as protein type additives) are good choices for the greenhouse application, because they may gradually cause some clouding and loss of transparency of the glazing or create foam that is too long lasting and is difficult to dissipate.
The bubbles that fill the roof and wall cavity space of the greenhouse must have properties that are of a good value for insulation and shading factor. When the bubbles dissipate and these properties degrade, then it is our purpose to be able to restore the original high quality of properties that were established at the time that the bubbles were first created in the cavity space. This is possible by the generation of new bubbles that replace the collapsing bubbles. the new bubbles from the bubble generators in the manifold (end wall) cavity will move into the roof and displace the old bubbles.
When the blower operates to regenerate bubbles it will take in not air, as in the first cycle of bubble generation, but rather the old bubbles will flow into the inlet of the blower. The blower can break the old bubbles thereby releasing the air to form new bubbles at the screen. The new bubbles are blown from liquid pumped from the Soap Solution tank and delivered on the screen by the nozzle system. The regenerated bubbles will have a temperature that is dependent on the supply temperature of the liquid from the storage tank. The liquid created from destroying the old bubbles will flow back to storage in the Soap Solution Tank. This liquid may be quite chilled and the return liquid will (on a winter night) cause the gradual lowering of the tank temperature. Or if the bubbles have been used for shading (on a summer day) the liquid formed from destroying old bubbles will be warmer then the tank temperature and will tend to raise the temperature of the tank. However, compared to the volume of Soap Solution in the Soap Solution Tank, the return liquid is a very small quantity. The tank temperature will therefore only change very gradually and is therefore a source of thermal stability and can be called a Liquid Thermal Mass, although it interacts with the Solar Controlled Environment space in a way that is very different than a conventional solid thermal mass systems such as rock beds or concrete walls and similar massive components that have been typical of Passive Solar Design?.
If some old bubbles remain in the cavity space (and are not renewed) then the system will fail to completely control the properties of these areas where the old bubbles persist. It is likely that the insulation value of these areas will be less than that of the area where the bubbles have been renewed. Collapsing bubbles will gradually consolidate into denser and wetter foam that will persist and be difficult to remove during bubble regeneration cycles. Neither will old foam that persists in the cavity be easily removed by the bubble destruction cycle. The bubble destruction cycle attempts to remove all the bubbles in the cavity space by operating the blower components only (no pump operation) so that the air/broken bubbles in the cavity passes through a dry screen, and of course no bubbles are made. This airflow has a higher velocity than the bubble flow because the dry screen has much lower backpressure and therefore the airflow will be higher. Thus the old bubbles that are in the cavity space are best dislodged and will be pushed/pulled into the manifold opposite where they will be destroyed as they pass through the blower.
For more specifics on each stage of the process, please see the following pages: