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.
In one of the recent discussions with a company that designs Greenhouses in WNC, it was discovered that one of the designs use 1000 gallons of water to store thermal mass. It was mentioned that this thermal mass allows them to keep the temperature within 60F to 85F range.
ReplyDeleteWe basically used this range for selecting PCM22P (having a phase change temperature of 72F) and found that we could store the same amount of heat in 1/7th the volume.
The cost of the freed up space outweighs the cost of PCM and the installation can be as easy as replacing 60% of the water with PCM filled capsules.
Now, more analysis is required to know the hourly temperature profile to see if temperature and it's duration are adequate for charging and discharging the PCM.
So, each project will have to be evaluated individually.