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Tool Talk Discussion Forum

what melts @ 72 for thermal mass

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circus

09-29-2007 04:55:21




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Would like to build a thermal mass to heat and cool my home but can't find a substance that phase changes (freeze/melt) at 68-72F. help




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buickanddeere

10-02-2007 21:59:52




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 Re: what melts @ 72 for thermal mass in reply to circus, 09-29-2007 04:55:21  
Some mineral salt solutions can be blended to melt or thaw at room temps.



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550Doug

09-29-2007 09:58:11




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 Re: what melts @ 72 for thermal mass in reply to circus, 09-29-2007 04:55:21  
I just learned 2 weeks ago that log homes built of Pine logs are very good for thermal mass. Apparently the pine resin changes state at about 72F and slowly release heat as it cools. Some log home builders are now forcing pine resin into logs to give an even greater thermal mass effect.



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phil lowe

09-29-2007 11:41:07




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 Re: what melts @ 72 for thermal mass in reply to 550Doug, 09-29-2007 09:58:11  
you must listen to CBC radio ,I heard the same show ,,and I was happy to hear the story as I have a PINE log home and have been told that Cedar is the preferred wood for log homes ,,
I like my Big ol logs myself ,so this story was fun..



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Coloken

09-29-2007 09:55:22




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 Re: what melts @ 72 for thermal mass in reply to circus, 09-29-2007 04:55:21  
Can't help with your question but think you are on the right track. Lots of ways to get energy, what we need is a way to store it. Off the wall question: to release heat wouldn't it be better if it was a little higher, like 78? Or to cool, like 60 be better? Years ago I saw where some guy had many old 30 gal drums filled with used motor oil. All so basement water cistern used to store heat.



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K.W.

09-29-2007 09:02:16




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 Re: what melts @ 72 for thermal mass in reply to circus, 09-29-2007 04:55:21  
Im not sure what your trying to do but there is some stuff called DMSO. It freezes and melts somewhere around 75 or 72 degrees. If that helps? Its sold at TSC in the equine section.



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mjbrown

09-29-2007 08:17:46




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 Re: what melts @ 72 for thermal mass in reply to circus, 09-29-2007 04:55:21  
I've never read of anything that phase changes at that temp except the butter chocolate examples given below. Something that does would likely be....
1. Exotic there fore very expensive

3. Unlikely to have the 1/80 ration that water has.



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Red Dave

09-29-2007 06:13:36




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 Re: what melts @ 72 for thermal mass in reply to circus, 09-29-2007 04:55:21  
How about butter, it melts at room temperature?


Seriously, why does it have to freeze and melt at 72 degrees? Most heat storage units I've seen use water as the thermal mass.



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T_Bone

10-01-2007 15:11:43




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 Re: what melts @ 72 for thermal mass in reply to Red Dave, 09-29-2007 06:13:36  
Hi Dave,

Water gives up 144btu/lb upon change of state from ice to water. This is the industry base standard that all other substances are comparred too.

If you have a room that contains 10000cft with a heat load of 2º per hour would require 4.16 tons of ice with a wall/ceiling loss of "0º".

A wall/ceiling gain/loss of 0º is not possible on any type of wall/ceiling construction. All other substances would require considerable more substance weight than ice.

Always use BTU's for computing heating gains/loss or your numbers will not be accurate.

Cold only occurs at minus 360ºk. All other temperatures are a absance of heat. This is a important mindset to learn.

T_Bone

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circus

10-01-2007 17:25:43




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 Re: what melts @ 72 for thermal mass in reply to T_Bone, 10-01-2007 15:11:43  
Think of it this way 120 gallons of melting ice equals burning one gallon of fuel oil @ 100% efficiency.



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Circus

10-01-2007 16:40:16




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 Re: what melts @ 72 for thermal mass in reply to T_Bone, 10-01-2007 15:11:43  
Your saying it would take tons of ice to cool a 35x35ft house for 16 hours or so. The real snag is that the temperture difference between the substance and the air would be so slight the containers surface area would need to be huge.



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T_Bone

10-01-2007 15:14:34




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 Re: Oop's in reply to T_Bone, 10-01-2007 15:11:43  
Sorry Dave, that should have been addressed to circus.

T_Bone



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circus

09-29-2007 07:32:59




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 Re: what melts @ 72 for thermal mass in reply to Red Dave, 09-29-2007 06:13:36  
the heat at melting or heat sink at freezing is 144 times greater (water) than normal. If a gel or something melts at 72F and the container has a lot of surface area, it would cool in the day and warm in the night with 1/144 the mass with no machinery.



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circus

09-29-2007 07:45:56




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 Re: what melts @ 72 for thermal mass in reply to circus, 09-29-2007 07:32:59  
correction 1/80 the mass.



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Gerald J.

09-29-2007 11:00:29




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 Re: what melts @ 72 for thermal mass in reply to circus, 09-29-2007 07:45:56  
Water has about the greatest difference a phase changes. Nearly every other liquid used for phase changes has significantly less heat capacity. I suspect some may have less heat capacity with the phase change than just warming or cooling water.

You can always shift the effective phase change temperature with a refrigeration/heat pump unit. I know some commercial intallations use water ice for storage, especially for air conditioning. Making ice with off peak energy, melting it to cool when utility prices are higher. As much as those installations cost, water probably proved to be more effective than any other phase change media.

Gerald J.

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