Energy Matters Forums

[MichaelB]

I just published up a news item about an entry in the U.S. Solar Decathlon. As well as an 11 kW solar power system, the Cube House includes goodies such as:

phase-change material in both walls (paraffin) and ceiling (salt hydrate)

... anyone know what that is about?

[Gordon-Loomberah]

Phase changes are good when trying to store energy! It generally takes quite a lot of heat added to a system to change the substance from solid to liquid or liquid to gas, which occurs at a constant temperature. That energy, aka latent heat, can be regained when you go gas to liquid and liquid to solid.
Think of water boiling- you need to add stacks of heat to vapourise (boil) it after it reaches 100C, but it all happens at the boiling point, and the temperature wont increase while the boiling is happening (if you keep it all stirred up sufficiently). If you then condense that steam to water, that process also takes place at the boiling point, but the latent heat is released into the surroundings. Melting ice takes quite a lot of heat from its surroundings, but it all happens at 0C.
Paraffin has a mp of ~53C and a latent heat of fusion of 184kJ/kg, so a lot of heat can be added to the system and the temp will rise to and remain at 53C until the wax is all melted. Then when you draw out hot water, the incoming cold water is heated to ~53C (assuming you have a good arrangement so that the heat can easily conduct to the water) until all the wax is solidified, after which the temperature starts to drop again.

Gordon

[munter]

Phase change materials are an interesting topic and are pretty well described above. They could have some potential for contributing to thermal control of residences in the future though I'm reluctant to get too excited about them yet though as I think there are significant steps forward that can be taken with existing materials and superior design before you start to need semi-liquid ceilings and wax-cored walls.

[Martin]

PCM technology has come a long way in the last few years. PCM waxes operating at various temperatures are encapsulated to convert them into solid particles and are available as milk-like dispersions or powders. We call these "microPCMs". MicroPCMs operating at, say, 25oC can be added to standard building materials e.g. wallboards, ceilings etc to provide "intelligent thermal mass", working to absorb excess heat thereby helping to regulate internal temperatures within a comfortable range. Other PCMs operating at 60-70oC can be used for storing solar thermal energy. Products are available now and others in development, if anyone is interested....

[Tracker]

Products are available now and others in development, if anyone is interested....

Martin, I for one am really interested.

One of the silly things that I am thinking of, is storing heat, either solar heat, or electric-heat, generated during the Off-Peak power periods, for heating use at night.

And again - just the concept of storing "Cold". Build it up at night, and use it during the PM Electricity peak?

Do you have a link to suitable information.

[120ThingsIn20Years]

Products are available now and others in development, if anyone is interested....

Martin, I for one am really interested.

One of the silly things that I am thinking of, is storing heat, either solar heat, or electric-heat, generated during the Off-Peak power periods, for heating use at night.

And again - just the concept of storing "Cold". Build it up at night, and use it during the PM Electricity peak?

Do you have a link to suitable information.

Did you ever learn any more about this? Just trying to revive this thread as its of particular interest to me. Im very interested in what kind of material undergoes a change at 25 deg C. That would keep my fishies and wife happy



(yeah I know I said I wouldn't be commenting for a while because I'd be reading old posts, but I hate it when I get all excited about a thread that turns out to be a dead end )

[Gordon-Loomberah]

Not exactly 25C, but pretty close!

http://www.cryopak.com/products/gel-pac ... 2-20-24d-c

[gully]

Both air conditioning and evap. cooling use the phase change / latent energy (of refrigerant or water, respectively) in order to cool. Coupled with insulation, it seems feasible to have energy tanks to store a medium (hotter or colder) than the surrounding environment, for a period of time.

[120ThingsIn20Years]

Not exactly 25C, but pretty close!

http://www.cryopak.com/products/gel-pac ... 2-20-24d-c

that is one very useful product!

I'm making a suit out of it

[120ThingsIn20Years]

Do materials that do phase changes at humanly pleasant temperatures all take similar energies to nudge them over the edge? ie when ice-cream melts, is there a similar % energy difference tween solid and liquid similar to say paraffin?

I'm struggling to even ask the question here.

if it takes x energy to complete the shift from wax to melted wax (from the point where the temperature remains constant even when energy is applied), does it take the same energy for ice-cream, or does it take the same % increase? Or do various materials just do whatever the Great Pumpkin says?

I hate not being able to even pose the question.
I should have paid attention at school
I also hate it when I cant make my spell checker understand even a ballpark notion of what it is I'm trying to write

hang on Ive got it...

If I had a substance that did a phase shift at 25 deg C, would it require exactly the same energy to make that shift as a different substance that just happened to also undergo a phase shift at 25 deg C.

thanks in advance if you mean to reply/sorry for the confusion if you have gone numb

-120things