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# Using paraffin wax in thermal accumulators

Member Posts: 15,012
at
http://www.solarnetix.com/index.php/58-Solar-Storage/View-category.html

He is a dealer in Ontario that handles the Latento tank. He knows a lot about this technology. Last I checked around 5 grand for that tank.

hr
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream

• Member Posts: 22

Anyone hard about using paraffin wax in a thermal accumulator to increase its heat storage capacity?

John Siegenthaler has an article in the HPACmag where he describes some of the new accumulators that he seen at an European trade show. One type off accumulator includes paraffin wax with water. The wax floats on top of the water and as it goes through the phase change it either accumulates or releases signifant amount of heat. I find this quite interesting.

Luc
• Member Posts: 18
Paraffin wax must have significant latent heat value

I remember watching a TV show in History, or Science Channel about the development and design of the Lunar Rover. The batteries needed a cooling system, and they couldn't add any substantial weight to the design. Their solution was to use paraffin wax as a heat sink. It apparently was quite efficient at absorbing the heat, and then gave it up when the batteries were not under stressful use. So, if NASA used it as a heat sink it MUST be good. Right?
• Member Posts: 22

Thanks hotrod for the input.

Any other manufacturer that use this technology? Presently, I am looking for an accumulator for a wood boiler appplication.

Luc
• Member Posts: 210
Heat Storage Capacity of Paraffin Wax

If you do the math, the Latento with 20 Kg (44 lbs) of paraffin wax, will store or release about 4,000 Btu when a liquid - solid phase change occurs. This occurs at a constant temperature (the melting point).

The heat of fusion of paraffin wax is about 90 - 95 Btu / lb and the heat capacity is about 0.64 Btu / lb / *F. With water the phase change to ice is at 32* F which is OK for cooling systems but not heating systems. The heat capacity of water is of course higher at 1 Btu / lb / *F.

So you can store more heat in a smaller space with paraffin wax at its melting point than you can with water at the same temperature.

Paraffin wax is used is heat sinks because it can absorb this heat at constant temperature when it melts, and slowly release it later when it freezes.

Doug
• Member Posts: 22

Thanks doug for the info.

What is the phase change temperature?

Siggy talks of 131F for the paraffin wax in his article and they say 65C(149F)for the Latento in the specs.

Is it because the latent material is a composition of paraffin and other material?

I have an application with baseboard. Would it be worth it if the phase change is bellow 140F?

Luc
• Member Posts: 236
Wax vs Water

Wax doesn't make a lot of sense in my estimation. Check out this plot of the storage capacity of a tank filled with wax versus a tank filled with water. Not a huge difference. You're better off adding another water tank. The melting point depends on the exact wax. From what I found on the internet, it looks like it melts anywhere between 117°F and 147°F.
• Member Posts: 210
Paraffin wax

Paraffin wax is not a pure compound with a specific melting point, but it is a mixture of straight chain hydrocarbons with 20 to 40 carbon atoms per molecule, with a broad melting range. You can choose different mixtures with higher or lower melting ranges.

Then they use additives to change the properties even more and to formulate the desired melting temperature range. So you have some choice of melting ranges - depending on the formulation. Melting range could be formulated anywhere between 115* F and 150* F as required to suit the application. You would have to find this out from the supplier.

This is what accounts for the melting ranges of 131*F for the paraffin wax in Siggy's article and the 65C(149*F)for the Latento in the specs.

It is a nice technical concept that works - store energy now and release it later - all at a certain design temperature.

In my earlier post I calculated the quantity of energy that could be stored and released by a Latento as 4,000 Btu for each temperature cycle. Please check my math. That is not a lot of energy - maybe 5 cents worth.

The best application would be storing free energy now, for use later to displace expensive energy. I don't see much point in storing and releasing energy which all has the same price. You could do it, but I don't see the point.

The Latento seems like a way of making the storage tank smaller.

Suggest you try to figure out how much energy you can actually save with such a system.

While I don't want to throw cold water on any idea to save energy, storing energy with other structural heat sinks such as concrete or stone - or using water tanks, may be more cost-effective.

Doug
• Member Posts: 22

Thanks Andrew for the graph. It really give me a good idea. I will do the math for my specific application.

Luc
• Member Posts: 22

Thanks again Doug. I will do the math for my specific wood boiler application. It might not be worth it because of the big storage tank.
• Member Posts: 236
Thermal Conductivity

One other thing is that I believe the thermal conductivity is fairly low for the wax, and there will be very little convection going on in that wax while the block is melting. I really think that water is a much better storage medium when that is taken into account.
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