The Eden Project

   Last week, a friend of mine who lives in England, sent me a link to this outrageous park in Cornwall, called the Eden Project.  It’s basically an elaborate construction of domes (Yes, I’ve fallen in love with dome sturctures) transformed into gigantic greenhouses that sustain a global collection of plants; some, very peculiar.  It is a multi-purpose park that holds gardening and educational courses for all ages to music festivals, theatre productions, art exhibits, etc.

   These biomes sit on a foundation of granite.  Eden’s plan is to build the UK’s first geo-thermal power plant  utilizing the heat from the radioactive decay in the granite, deep inside the earth’s crust.  Although, drilling a hole 3 miles deep into the Earth must have an outrageous cost, the park experts are estimating that Eden, itself will need only a quarter of the green power generated.  The other three-quarters would feed back into the local community/National grid and possibly, supplying 10% of England’s future electricity needs.

   I wasn’t able to find information about the actual construction of the biomes or how they maintain suitable temperatures for plants and people.  And having no knowledge of power generation, I don’t know if there is even a need for thermal energy storage  in such a park that’s powered geo-thermally.  But I’m sure the power needs for Eden are immense and they seem to be headed in the right direction.

http://rgees.com/index.php

dome, di dome, dome

     I’ve been looking at a lot of greenhouses.  I’ve decided my favorite ones on the market are “Growing Spaces,” created by a couple in Colorado who began their venture 20 something years ago.  These greenhouses are beautiful.  They are essentially dome structures, well built and well insulated.   I assume the majority of people who own these greenhouses are using their indoor pool of water as their thermal mass to store the sun’s heat.

    So, I was recently reading one of the articles on their blog and someone asked what winter temps the dome would be able to endure if one were to install solar water heat exchangers.  They answered that with the solar hot water addition, the inside of the greenhouse could maintain temps 50 degrees (Farenheit) warmer inside than out.  This is truly significant when you’re talking about growing plants and veggies.  Think you can’t make this any better?  But you can.

    Regardless of whether you feed the hot water into piping underneath the dome or back into the indoor pool itself, using PCM in the hot water tanks can store the heated water for longer periods of time and you could probably downsize to smaller storage tank as well.

    This is how it would work.  Your solar hot water heat exchanger heats the water during the day when the sun is out.  I’ve seen solar collectors that follow the direction of the sun to receive optimal light.  But as soon as the sun goes down and the water cools, there is some kind of backup generator that switches on or other alternative heating source to keep the water warm in order to heat the greenhouse.  If you put PCM of an appropriate temperature  into the storage tanks, it will conserve the sun’s heat for a longer duration.  And to top it off, you’d be saving money and fuel due to less usage of your backup heating source.  Again, totally advertising here, but this basic idea of utilizing PCM to store heat is feasible with ANY solar hot water system.

    Check out these geodesic domes.  Wish I had an extra $15,000 laying around…

    This doesn’t have anything to do with greenhouses although I’m sure you could use some of his micro-houses for the purpose of a greenhouse (heat storage would still be an issue).  This guy’s clever.  Goes to prove, you can pretty much recycle anything.  

Derek "Deek" Diedricksen featured in the New York Times gives a tour of his “gypsy junker”.

storing the sun's heat...

    I recently developed a personal interest in Greenhouses which led me into a world of structural, glazing, binding, and sealing materials.  Not being much of the builder/designer type, I then, gravitated towards the thousands of different kinds of pre-fab kits.  Most curiously though, my on-line research of greenhouses, directed me straight back into my area of work, which is, thermal energy storage using phase change materials or PCM.
   
    My desire was to build our greenhouse on Mom’s property in Haywood County that currently flourishes with tasty veggies that grow from Spring to early Fall.  So, I thought “how great would it be if we could grow tomatoes and other summer edibles during the cold months”.  I found that if you’re in an area with mild enough winter temperatures and can get away with just a passive solar system, you still need some sort of thermal mass to keep the warmth through the night.  A greenhouse is just a big solar collector.  And as with all solar heating systems, they share the same problem.  How do you store the sun’s heat for later use at night?  PCM based thermal energy storage systems is the answer, of course.  Back to greenhouses.  Savvy gardeners have been successfully using all sorts of materials for thermal mass; the most common being, barrels of water, rocks, concrete, bricks, tiles, wet dirt and basically, any mass that stores heat.  These materials are all heavy, bulky and take up a lot of the greenhouse space that could be utilized for growing space instead.
   
    If I were not a small business partner of a company that produces PCM, and just wanted to build a greenhouse for my family, I would probably ask such questions as:

--how does the PCM store thermal energy?
--how much PCM is needed?
--what temperatures would be appropriate?
--what is the cost?
--how is it installed?
--what are the advantages and disadvantages of PCM next to the other types of thermal mass?

    There are many factors and variables to consider.