Paraffin heaters?

[Roswell Bob]

Is anybody using paraffin as a thermal storage medium?

 

[FilterGuy]

I have not even heard of it (but that does not mean much). Is the purpose to store heat for house heating? Water heating?

 

[Roswell Bob]

Yes. Store heat and retrieve when it is needed. Paraffin requires quite a bit of energy changing from solid to liquid and gives off quite a bit of heat when returning back to a solid. It would probably well-suited to be used with a solar water array. Heat it up during the day and you are good all night. I have a concrete slab on second floor that is under south facing wall. It does a fairly good job of collecting and storing heat. I also have a few tons of brick stacked around a wood stove I have in the first floor apartment. That also works well.

 

[FilterGuy]

I read up on it after I saw your post. It would take some doing to set up, but it is a pretty interesting idea to use phase-change to store the energy.

 

[Q-Dog]

I read about this in a solar house book I have that was published in the 1970s, but have never seen it in use.

 

[Roswell Bob]

Yep Old technology.

 

[WillyP]

I've certainly heard of it. But it seems like a very expensive solution to a problem that can usually be solved by heating water (or stone) instead.

 

[Mr.Michael]

Mass and insulation are the key. Paraffin probably works as well as oil or water until it becomes solid. I would assume heating up 1000 pounds of oil/water by 100 degrees would store about as much energy than 1000 pounds of paraffin. Water is obviously cheaper and non flammable but oil could potentially store more energy as water due to the higher boiling point. I think a liquid beats a solid like metal or stone, draw heat from the top and add heat at the bottom.

 

[FilterGuy]

Mass and insulation are the key.

Not necessarily.

The unique property the paraffin has is a phase change at a relatively high temp. When the paraffin melts, it gives off a large amount of energy. When the paraffin hardens (Freezes) it absorbs a large amount of energy. The phase change energy absorbed or released is huge and can exceed the thermal mass energy by multiple times. Consequently, you could get a huge amount of thermal storage in a small system. Water probably has a higher phase change energy than paraffin, but it's phase change temperature is inconveniently low for a thermal storage system. Paraffin on the other hand melts and freezes at a temp that is very good for solar thermal systems.

Having said that, there are also challenges. Not the least of which is that the wax cant be the solar collection fluid. You would have to have water or oil going through the solar heat collector and then use some type of heat exchanger in the wax. You would then use the same fluid and heat exchanger for extracting and distributing the heat.

There is little chance the system would ignite the paraffin, but if there was a fire from some other source, I could see where it could get bad... The system would have to be designed with this in mind.

Overall, I agree that the complexities probably out weigh the benefits in most situations, and that is probably why it has never caught on.

 

[WillyP]

Not necessarily.

The unique property the paraffin has is a phase change at a relatively high temp. When the paraffin melts, it gives off a large amount of energy. When the paraffin hardens (Freezes) it absorbs a large amount of energy. The phase change energy absorbed or released is huge and can exceed the thermal mass energy by multiple times. Consequently, you could get a huge amount of thermal storage in a small system. Water probably has a higher phase change energy than paraffin, but it's phase change temperature is inconveniently low for a thermal storage system. Paraffin on the other hand melts and freezes at a temp that is very good for solar thermal systems.

Having said that, there are also challenges. Not the least of which is that the wax cant be the solar collection fluid. You would have to have water or oil going through the solar heat collector and then use some type of heat exchanger in the wax. You would then use the same fluid and heat exchanger for extracting and distributing the heat.

There is little chance the system would ignite the paraffin, but if there was a fire from some other source, I could see where it could get bad... The system would have to be designed with this in mind.

Overall, I agree that the complexities probably out weigh the benefits in most situations, and that is probably why it has never caught on.

I believe you have that backwards. Paraffin absorbs heat as it melts and gives off heat as it cools.
While it wouldn't work as a fluid in a collector. It could work as a insulator around a storage tank. For example if the collectors heat a fifty gallon drum of water, then that drum is surrounded by wax, the wax would melt during the day, than as it hardens, it would give off that heat into the drum. Thus allowing the water to stay hot much longer.

 

[sunshine]

For example if the collectors heat a fifty gallon drum of water, then that drum is surrounded by wax, the wax would melt during the day, than as it hardens, it would give off that heat into the drum

I had to google: 1 kg paraffin = 40 litres water when doing the above.

 

[FilterGuy]

believe you have that backwards. Paraffin absorbs heat as it melts and gives off heat as it cools.

Oops..... your right, I got it backwards..... I am not sure how I did that.... Sorry about the confusion

While it wouldn't work as a fluid in a collector. It could work as a insulator around a storage tank. For example if the collectors heat a fifty gallon drum of water, then that drum is surrounded by wax, the wax would melt during the day, than as it hardens, it would give off that heat into the drum. Thus allowing the water to stay hot much longer.

Yup something like that would work.....A drum of Paraffin with a drum of watter inside of it.... but I would put insulation around the outside of the Pariffin drum as well. Once the paraffin melts it is probably not a very good conductor.

I was thinking some kind of radiator or loops of tubing in an insulating drum of paraffin, but the concept is the same

 

[WillyP]

Oops..... your right, I got it backwards..... I am not sure how I did that.... Sorry about the confusion

Yup something like that would work.....A drum of Paraffin with a drum of watter inside of it.... but I would put insulation around the outside of the Pariffin drum as well. Once the paraffin melts it is probably not a very good conductor.

I was thinking some kind of radiator or loops of tubing in an insulating drum of paraffin, but the concept is the same

I like the radiator idea. You could just lower it inside a steel drum, then fill the drum with paraffin. I am designing a system that will have two fifty gallon drums of water, that will be heated by vacuum tubes. That water will be used to heat underground tanks that feed my radiant floor heater. I'm trying to come up with a containment system for the paraffin outside the tanks.

 

[Roswell Bob]

Yes, it is the phase change that stores the energy. I have a large concrete slab (5 tons) on the second floor so I am all set. I have a ton or so of pavers surrounding the wood stove on the first floor so all set there. I was thinking along the lines if I had a small cabin the paraffin could moderate the heat overnight. If time of use metering becomes the norm then using electricity at off peak hours to heat the home may make paraffin storage worth the effort.

 

[FilterGuy]

If time of use metering becomes the norm then using electricity at off peak hours to heat the home may make paraffin storage worth the effort.

I would think the spread between peek and off-peak price would have to be pretty big to make a reasonable return on investment.