Liquid Cooling
The alternative way to cool the building is to directly cool the temperature of a transparent Building Envelope comprised of multiple layers of low wieght (almost no mass) transparent coverin materials. The Sola Roof process, which is the most effecient system, uses a water based Liquid Cooling process. When the building roof and walls, which form the Building Envelope, are cooled down directly to the dew point temperature relative to the humidity and air temperature of the atmosphere within the building then the air will not overheat provided that there is a leaf canopy within the building that will absorb the majority of the solar radiation. Due to the Transpiration Condensation mechanism. This Liquid Cooling process can control the interior humidity and temperature very exactly and there is no need for ventilation as is required in the conventional buildings.
DISCUSSION
There are often questions about how we can "collect solar heat" using the Sola Roof and I would like to provide some background here - perhaps there is a good Page Name? that could be found or this could go to a Q&A section.
First of all I discourage the very idea of "heat collection",for example there is not much value to using the bubbles as a solar heat collection system - it could be done but it is not the most effective way to use the system. To provide capture of solar thermal gain it is much better to use the Liquid Solar process that operates by spaying (or distributes with preforated hose or other methods) a "cooling liquid" film over the inner skin. This cooling liquid can be the soap solution. With your large liquid thermal mass and since you are placing the soap liquid tank into the larger water reservoir plus using pipe coils within the water tank that the soap liquid will flow through - then you will have a very good set up to use the soap solution as the cooling liquid. Your soap solution will have the same temperature as the large water thermal mass. It will also transfer thermal gain to the larger thermal mass and so will be the "working fluid" for the controlled environment system. Circulating the cooling liquid will result in cooling the inner skin to a dew point temperature and the plants in the greenhouse will produce transpiration that will condense on the inner skin. The plant transpiration convert the solar radiation to "non-sensible" thermal energy that becomes sensibe, thermal energy that would warm the inner skin except that the cooling liquid is able to absorb this heat energy quickly and take it away to the large thermal mass system, where the temperature will change very slowly. Thus the inner skin will remain relatively cool and always 10C or so cooler than the air within the greenhouse.
The temperature will gradually increase by a few degrees over the whole day. In the Photo section of the Forum see Nelson Thermal Data?:
&.view=t&.done=http%3a//photos.groups.yahoo.com/group/solaroof/lst%3f%26.dir=/Nelson Thermal Data?%26.src=gr%26.view=tNow at night the bubbles give up slowly this thermal energy that is collected during the day. The inner skin remains at the temperature of the Liquid Thermal Mass system because the soap solution is thermally coupled to the reservoir temperature with the soap liquid in the coils of flexible non-preforated agricultural drainage pipe. Then when the bubbles are renewed at intervals during a cold night the inner skin is always at the temperature of the Liquid Thermal Mass system, while the outer layers of bubbles near the exterior skin give up the stored thermal energy captured by the liquid cooling process. We do not need any "hot" thermal storage. Cool to slightly warm is fine for even the coldest climate. Cool bubbles provide better insulation. Cool liquid collects the solar energy. Hot or warm liquid will not collect efficiently and also - most importantly - cannot condense the transpired moisture; cannot sustain the closed environment for growing with CO 2 enriched atmosphere; cannot regulate the temperature of the building within the limits for optimum plant growth; and will emmit thermal radiation onto the leaf canopy which is the opposite of a "natural growing environment" where the plants see a cold sky.
All previous greenhouses show the plant leaf canopy a "hot sky" because the radiative temperature of a glazing (or glazing and shade canopy system) is not controlled as it is with the Sola Roof process. In fact attempts to provide "shade" from the sun will normally reduce the Photosynthesis Active Radiation and increase the thermal radiation. The bubbles, when used for shading can remain cool because we can regenerate them from our soap solution which is at the cool temperature of the Liquid Thermal Mass system. But most importantly, during the winter or in hot sunny climate, the cooling liquid is also continuously chilling the inner skin and absorbing direct solar IR. The solar IR is absorbed about 20% by the thin film cooling and the bubble shading can absorb nearly 100 % while still remaining at a cool temperature because of the dynamic process. I expect that most of you on this list will understand that water has a high capacitance and that our thermal transfer rate can handle the solar thermal gain rate and can operate as a steady state system if there is additionally an energy rejection mechanism to keep the Cooling Liquid at a constant cool temperature.
But the typical process is to use a Liquid Thermal Mass of a volume that will provide a temperature swing from day to night. Let me emphasize that only the liquid components of the thermal mass are able to provide the capacitance and transfer that is necessary. The solid components of the thermal mass are not actively engaged and have almost no interaction with the thermal process. Therefore making special effort to link up more solid thermal mass has no payback. You have the soil and ground or floor of the greenhouse and I would not spend (waste) money to link to rock beds, soil or subsoil, or build any massive structural elements into the greenhouse unless it is part of a normal footing, floor or wall system that you would have in any case. Placing pipes into such subsoil or footings can be a big problem, because leaks are difficult to find or repare. I say this after building a 12,000 foot flooded rock bed floor as a thermal mass in the Calgary project that had continuous problems with leakage.
I love the shallow pond growing systems that provide all the thermal mass that a project could need. Liquid thermal mass in fabric tubing below benches is a good system. Below grade reservoirs and tower tanks are also an option. Putting the soap tank within another tank and using flexible fabric tanks is also practical and gives an immediate thermal exchange.
I mostly use the the term "thermal" rather than "heat" so that we can get used to the idea of cool running systems that work just fine. Our surroundings need to be cool because we are "hot bodies" - that is part of our synergy with the plants. They have a cooler temperature. How unlikely it would be if the plants in a multi canopy forest had a higher temperature then the animals! The plants themselves live in a relatively cool environment and are champions of rejecting waste thermal energy so that they and the atmosphere around them will not overheat. Biosystems and Biomimicry technology will run cool - while all our previous engineering concepts are dominated by high temperature and pressure. That is machine technology - fire, steam, the heat of a nucear reation - none of those concepts have a place in a biomimicry technology. Living systems operate at ambient temperature and humidity.
This is why the combimation of solar, plants and cold water resources is so important. Cold water is as important to ambient energy systems as is solar radiation. The difference with Sola Roof is that we use these concepts with some confidence and guiding vision so that the design result is optimum. For example the SWG has contradictions that decrease the effectiveness of the total system. We have a few people using the Bubble Tech and it is now a good time to give equal attention to the "solar controlled environment system" and the Liquid Cooling process which is well integrated with the Bubble Tech system and I would like to see more projects that are implementing this important aspect of the Sola Roof concept so that our projects are able to capture, use and reject the solar thermal "waste" energy. This is important because it also is a process for producing clean water in large quantity.
I hope that this explanation gives more background to understand how the Sola Roof is a total concept for "living structures". Maybe I have opened as many questions as I have provided an answer to what appears to be a simple system. If so, please ask so that everything is clear.
Regards, Rick