Heat Battery

Hi guys. It was suggested to me that I share my experience with phase change materials with this group so I’ll tell the story. (Hope I posted this in the proper group)

About 10 years ago I decided to experiment with running a car on waste vegetable oil. Bought a Mercedes diesel and the fun began. It appeared necessary to heat the fuel tank and fuel lines—especially for winter operation so I used the cooling system for the engine to provide the heat.

Winter came and I was working second shift at a factory, leaving work at 11:30 pm and it was cold. One night the temperature was about –10F and, for the first time, my car failed to start (using regular diesel). Even though I found that 3 of the glow plugs were burned out, I vowed this would never happen again, and set out to build what I called a heat battery.

The heat battery consisted of a steel box, approximately 4 feet wide, about 2-1/2 feet tall and about 8 inches from front to back. Inside it were stacked horizontally, 3 modular radiators that were about 6 inches square by 3-1/2 feet long, lying on top of each other. The steel box was filled with molten paraffin. The radiators were plumbed in series so that hot coolant from the engine entered the bottom radiator and exited from the top radiator, pushed by a small 12 volt pump.

I installed a timer that would energize the pump at 11:20 pm so that the heat would flow from the top of the heat battery, through the fuel tank and fuel line heating lines, through the engine cylinder head, then back into the pump to cycle again.

Don’t recall the exact paraffin I used but the phase change occurred somewhere around 145 degrees if memory serves. Work was 18 miles from home and I would watch the engine temperature gauge as it “charged” the heat battery. Seems like after 5 miles or so the temperature would begin to climb above 60C which is about 140F and reach normal operating temperature shortly thereafter.

When I got off work, a glance at the engine temperature gauge seemed to always read 40C or about 104F before I cranked the engine no matter how cold it was. Needless to say, my engine started instantly as if it were summer.

The heat battery was heavy—I’d guess somewhere around 150 lbs and I would install it in December and remove it in March. My goal was to be able to store about 2kw of heat but never measured it. The tank was insulated on the bottom with several inches of R-Max (the foam with foil), the sides and ends were insulated with a couple of layers of fiberglass with foil, and the top with R-Max and fiberglass.

I used this for about 8 years until I retired. Did not notice any degradation in performance during this time, and needless to say, my car always started in the winter. Hope this will be helpful to someone.

Bill Fox : This is interesting, thanks for posting. Am I correct in assuming that your heat battery just set on top of your Diesel fuel tank?
You didn't mention any other plumbing involving the Paraffin ! This seems like a good place to post it ! For the good of the Craft .
Your comments/questions are solicited and Welcome, Think like fire, flow like gas, Don't be the Marshmallow ! PYRO - Logical big AL !

Interesting idea. Thanks for posting!

The weight must affect the efficiency of the car. (Surprisingly, cars aren't getting more efficient---they're getting lighter. But that's another story.) Did you notice any significant difference in fuel economy?

Also, running an engine cold causes wear. Which side of the thermostat is this plumbed into?

Big Al: The heat battery sits vertically behind the main fuel tank of the car which is also a vertical tank that is directly behind the back part (not where you sit but where your back rests) of the back seat. The bottom of both tanks rest on the floor of the trunk and both extend to just below the rear windshield. The heat battery barely touches the top of the wheel well which is just to the rear of the heat battery (the spare tire sits horizontally). The WVO fuel tank sits to the left side of the wheel well and almost touches the left rear fender on the inside. This tank is homemade, irregular-shaped, and sits above and down inside what some would describe as a small vertical wheel well.

There was no plumbing involved directly with the paraffin. The idea being that while paraffin is a good heat storage medium, it is a poor thermal conductor, hence the idea of immersing the radiators in the paraffin so that the fins give more area to conduct heat.

Bill

K. Nelfson: Really didn’t notice much change in fuel consumption. This car would average 27.5 mpg on diesel and only slightly less on WVO. I did have better traction when it snowed.

The engine in this car is a 5 cyl diesel and it has several threaded plugs in the cylinder head. I tapped into one near the rear of the engine for heat. The return line connected to another hole near the front of the head. On a cold day, it was noticeable for the first 5 miles or so that the heater wasn’t producing super hot air but I’d rate it as better than warm. These cars also have an electric circulating pump for the heater and defroster and that line taps into the rear of the cylinder head and returns into a hose running to the radiator.

In thinking about the amount of heat needed to recharge the heat battery, if it indeed could store 2kw, that is only 6826 btus. If a gallon of diesel yields 140,000 btus and I get 27.5 MPG and this engine were 50% efficient, the waste heat would be on the order of 2545 btus per mile. I am sure my numbers aren’t exact but I think you get the idea.

Bill

Bill Fox wrote:
In thinking about the amount of heat needed to recharge the heat battery, if it indeed could store 2kw, that is only 6826 btus. If a gallon of diesel yields 140,000 btus and I get 27.5 MPG and this engine were 50% efficient, the waste heat would be on the order of 2545 btus per mile. I am sure my numbers aren’t exact but I think you get the idea.

I think the theoretical efficiency of an internal combustion engine is 30 % or so. Anyhow, I get your point.

Could you use a large water tank to achieve the same goal?

I'm impressed an your initiative. Most people would shy away from such a project.

Outstanding idea! I've considered phase change materials for long term refrigeration during a power outage before (tested several concentrations of saltwater in an attempt to keep frozen items frozen for a four day long period, using only an off the shelf 'extreme' type cooler. Four days because that is the longest power outage that I've ever experienced.)

This, however, would be a boon for a rocket mass heater! Imagine a heat mass bench that used phase change materials! Please, if you can remember or rediscover, what type of parafin wax did you use? It would be great if it was the basic candle type, as the mass could be as simple as an old gas-type water heater filled with wax instead of water. Perhaps with the outer insulation removed, laid on it's side and the bench built around it. Normally, a full ton of mass is required to regulate the heat output of the RMH; but using this technique would permit that mass benches could be lighter and/or smaller. Considerations would have to be made for heat expansion of the liquid wax, as well as prevention of oxygen getting into the tank.

Bonus if regular candle wax can be used, as a relatively cheap source of wax would be all of the half used candles for sell in the summer yard-sale season.

K Nelfson: I'm not quite sure what you are asking about using a large water tank to achieve the same goal--if in a car, probably not because of the weight. If not in a car and it is well insulated, sure but: If you are thinking of using paraffin, keep in mind that it conducts heat poorly and you will need lots of radiators or square area to be able to transfer heat to and from the paraffin. I got this idea from the company I retired from. In Germany, I think, they were working on a heat storage device to help lower engine emissions by warming the engine up sooner. Of course this was a much lighter weight heat battery and they wouldn't tell me how it worked.

As far as my initiative, consider it stubbornness. When my mind is made up, I research 'till I'm crazy, then won't stop 'till the project is completed or hit a brick wall.

Bill

Creighton: One of my interests is to be able to live a nearly normal life if there were a longer than normal power failure and refrigeration is at the top of my list. I’ll give you my slant in two words: Ballast and insulation. Studied this a couple of years ago and this will be from memory but think that with 50-75 lbs of ice (other storage mediums are better) + I don’t recall how many pounds of food in a deep freeze (chest style, not upright) at zero degrees F, insulated to R50, and the lid was not opened, with a ambient temperature of 70 degrees, the thing would stay below 32 degrees for nearly a month. To really make this workable, the compressor and condensing coil would be in a remote location. In this manner, a generator running an hour or less per day would more than compensate for opening the lid and keeping the temperature more stable.

I don’t recall the type of paraffin that I used. I may be incorrect but it seems to me that what I used had a higher melting point than candle wax and I may have paid nearly $1 per pound. This stuff is much heavier than you may think. As far as expansion, I let the system heat up to its fullest with the plug removed from the top of the tank before closing it. Don’t know if oxygen would be a problem or not, paraffin is a petroleum product.

I don’t recall the thermal capacity of the paraffin I used but I either bought 50# or 100# in an attempt to capture 2kw of heat. Keep in mind the heat transfer problems with this stuff. Doubt that I have the info on what I used but will post it if I find it.

Bill

Creighton Samuiels wrote:
This, however, would be a boon for a rocket mass heater! Imagine a heat mass bench that used phase change materials! Please, if you can remember or rediscover, what type of parafin wax did you use? It would be great if it was the basic candle type, as the mass could be as simple as an old gas-type water heater filled with wax instead of water. Perhaps with the outer insulation removed, laid on it's side and the bench built around it. Normally, a full ton of mass is required to regulate the heat output of the RMH; but using this technique would permit that mass benches could be lighter and/or smaller. Considerations would have to be made for heat expansion of the liquid wax, as well as prevention of oxygen getting into the tank.

Bonus if regular candle wax can be used, as a relatively cheap source of wax would be all of the half used candles for sell in the summer yard-sale season.

It doesn't really matter. If you look at different paraffins, you will find that, for example, a paraffin with a melting point of 52C has a heat of fusion of 147kJ/kg, and one with a melting point of 65C has a heat of fusion of 183kJ/kg. So for every degree you bump up the melting point, it increases the storage a little less than 3kJ/kg. (source here) That's not much on a percentage basis, a 2% increase for each degree.

If you really wanted to store a lot of heat, you would figure out a way to take one of those cylinders of roofing asphalt and stuff it in your rocket mass heater. But be prepared for all your friends to stay away until you have that permanently, for sure, 100% hermetically sealed.

The other thing to realize is that this heat battery doesn't store all this heat unless the temperature goes back and forth past the first-order phase transition temperature. What non-chemists call the "melting point". Which means you probably want to have your heat battery for your rocket furnace melt at anywhere from 100-140F. I'll give the engineer's "thumbs up" OK to your idea of putting any old wax you can find into a water heater tank.

The low heat condutivity of wax would be a problem, using a standard water heater tank as the container. What about an aluminum box, the kind that are often custom made for boats, usually as fuel tanks, with "baffle" blades running through it every few inches? The tank could be relatively shallow to start with, and be elevated above a "heat bell" space with supports, and absorb the heat of exhaust through the bottom of the tank.

This would quickly become more expensive than a normal mass bench made primarliy out of cob, but it might still be a useful idea in homes that don't have the structural support capable of holding up a one ton cob bench.

I just had another thought. Now I wonder what the heat limits of a standard waterbed "mattress" might be. Perhaps a thin one would be best, such as a futon thickness. A couple thin, 'twin' sized mattresses, so long as the plastic of the container wouldn't melt also, laid atop an otherwise normal but short mass bench (perhaps with a thin layer of copper as a heat spreader) and then an insulative/pillow layer on top of that to both protect users from excessive heat as well as slow down the distribution of heat into the living space?

Hmmm. More research is required.

Thanks for sharing. That is an elegant solution to the problem you were facing.

If nothing else, a pound or two of candle wax inside one of those boil-in-bag ziplock bags, sitting in a spare cookpot on top of the heat riser surface until bedtime; and then placed into a soft, insulated wrap would be a great gift idea!

Would also work inside of a microwave using this kind...

http://www.packitgourmet.com/CookIn-Bags.html

Another idea. Used glass jars. Clean the labels off, fill about 90% up with wax, jet some nitrogen into it as you close the top (to limit the amount of oxygen available for combustion, and then use it as a space filler in your cob bench. Easy peasy.

Alternatively, if a type of wax that can be found with a melting point around 70 degrees F, use this technique to build directly into the walls of a structure. Much like the glass jars used as bricks to build small buildings with natural lighting without windows; jars that contained a paraffin that melts around 60-70 degrees would have a much better temp stabibility over the course of the day and night. Would make for a great way to heat/cool a chicken coop, as an example. Or a tool shed. Wouldn't be nearly as hot in the late afternoon when you're digging through it looking for your rake, nor would the chickens be as likely to freeze to death in the cold of winter.

EDIT: Even better; fill the jar up to the top while melting the wax (double boiler, maybe). Once the jar is just about full of melted wax, screw the top on and set aside to let it cool. This will take a while, but the cooling will draw a vacuum and suck the pop-out on the jar top down. Whatever oxygen is left in that space is likely to be inconsequntial, and the vacuum should (obviously) prevent an overpressure condition as the wax melts and expands while in use, since the wax and jar were sealed at an atmostpheric balance around 220 degrees F (boiling point of water, from the double boiler). Going above 220 will certain increase internal pressure, but not likely significantly. I can't say as to whether or not a RMH could get the wax to it's ignition temp, which if there is any significant amount of oxygen trapped inside the jar, might result in a mini-explosion, which might break the jar. I really need to try it and see what happens.

Here's a pure candle wax with a claimed 160 degree melting temp. It's intended to be down blended into a softer wax for candlemaking, but for our purpose it would be perfect just as it is.

http://www.candlewic.com/store/Product.aspx?q=c49,p525&title=160-Melt-Point-Wax---5560

And with a bulk buy cost of less than $90 for a 50# caseload, this might just be something worth trying while the petrolem products are still available. It's not like we would be burning, or otherwise consuming, the wax. Since it's a petrolem product, it shouldn't ever rot, and should last at least a lifetime in service.

Mr. Elliott-
Would you be willing to run the numbers comparing the heat storage capablities of a one ton cob bench to that of wax with a melting point of 160 degrees? I'm not an enginneer and wouldn't even know how to start that one. I think that it would be a very useful data point to know how much of such a wax would have a heat storage capacity comparable to a full sized cob bench. I.E. how many pounds of wax would be required to replicate the heat regulation capacity of a full ton of cob (or other heat mass material, excluding those with extreme qualties for mass, such as soapstone). From what I can tell using Wikipedia, wax has a phase change heat density about two-thirds that of water-ice; which if I'm correct in that rough guess, is outstanding and should permit a huge reduction in mass requirements, and a lesser reduction in space requirements, for a RMH storage bench; so long as the heat transfer issue can be managed.

Creighton Samuiels wrote:Mr. Elliott-
Would you be willing to run the numbers comparing the heat storage capablities of a one ton cob bench to that of wax with a melting point of 160 degrees? I'm not an enginneer and wouldn't even know how to start that one. I think that it would be a very useful data point to know how much of such a wax would have a heat storage capacity comparable to a full sized cob bench. I.E. how many pounds of wax would be required to replicate the heat regulation capacity of a full ton of cob (or other heat mass material, excluding those with extreme qualties for mass, such as soapstone). From what I can tell using Wikipedia, wax has a phase change heat density about two-thirds that of water-ice; which if I'm correct in that rough guess, is outstanding and should permit a huge reduction in mass requirements, and a lesser reduction in space requirements, for a RMH storage bench; so long as the heat transfer issue can be managed.

OK, let's figure this out. One ton of cured cob should have a specific heat of 850-1000kJ, meaning it takes that many kiloJoules to bump it up one degree Celsius. (Engineering data table here) This is about the specific heat as a ton of water, but since cob is denser than water (say a density of 2.5 compared to 1.0), you need a smaller volume of cob, something only 40% the size.

Studying the table a little more, we see wax - 3.43, paraffin - 2.9, and beeswax - 3.4. These are solid specific heats, or the amount of heat that they will store on their way up to the melting point. Let's say three times as much. So 350 kg of these materials would have the equivalent heat storage capacity as one ton of cob, until you get to their melting point. At that point, as they melt, each kilogram of melting wax will take around 200 kiloJoules to melt, or put another way, melting 5 kilograms of wax (11 pounds) takes the same amount of heat as raising a ton of cob one degree. Looks like your 50 pounds of wax is going to act as quite a ballast to soak up heat.

I'd say 50 pounds is a good place to start and maybe you can cut the amount of cob down to a couple hundred pounds -- just enough for a nice veneer over everything else.

Creighton Samuiels wrote:If nothing else, a pound or two of candle wax inside one of those boil-in-bag ziplock bags, sitting in a spare cookpot on top of the heat riser surface until bedtime; and then placed into a soft, insulated wrap would be a great gift idea!

Would also work inside of a microwave using this kind...

http://www.packitgourmet.com/CookIn-Bags.html

That's a good idea. Another one would be to use the 2 liter soda pop bottles that are so ubiquitous. One man's trash is another man's treasure!

John Elliott wrote:

Creighton Samuiels wrote:If nothing else, a pound or two of candle wax inside one of those boil-in-bag ziplock bags, sitting in a spare cookpot on top of the heat riser surface until bedtime; and then placed into a soft, insulated wrap would be a great gift idea!

Would also work inside of a microwave using this kind...

http://www.packitgourmet.com/CookIn-Bags.html

That's a good idea. Another one would be to use the 2 liter soda pop bottles that are so ubiquitous. One man's trash is another man's treasure!

Wouldn't the soda bottles melt on their way to 160 degrees? Should be okay with soy wax, at a melt point of 122 degrees though.

John Elliott wrote:

I'd say 50 pounds is a good place to start and maybe you can cut the amount of cob down to a couple hundred pounds -- just enough for a nice veneer over everything else.

This is outstanding news. In my particular case, my new house has an unfinished basement over top of a 2500 square foot ranch, with an old concrete block fireplace & chimney dead center. It's ugly as hell, and has been cut off at the floor of the living level as it does not extend through the home. (the house was moved from another location and placed over the basement of a house that was torn down, the basement doesn't quite fit, but it's close enough) So I was seriously considering sealing up the fireplace section, which has been used as a dump for old bricks for a long time, seal the outside of the block with a plaster veneer or something else that can take the heat and keep the exhaust inside, and use that entire mass as a masonary 'bell' for a zaug built rocket stove. But with this new info, I'm going to add a number of recycled pickle jars full of 160 degree wax into the fireplace before I seal it up. With this new info, I won't really even need to build a cob bench at all! Even so, I think this new information will prove profoundly useful to others who don't have the space or the structural support required to build a full sized bench. Done correctly, 50# of wax might fit inside the downdraft section of a typical 55 gallon drum 'riser' of a rocket mass heater, offering a completely different method of achieving the same goal.

Thank you, sir; for your expertise and time.

hmm. This is getting VERY interesting. This could be a heat sink for a water heater, too. That will store a lot of heat right at the right temp for a water heater.

The preventing oxidation and fire are still a concern, though. Maybe they need to be in a water bath to prevent overheating.

R Scott wrote:
The preventing oxidation and fire are still a concern, though. Maybe they need to be in a water bath to prevent overheating.

That's why I mentioned sealing the wax up in old glass jars. When the wax cools, it'll seal itself inside without much oxygen to speak of. What remains would be consumed the first time it hits 400+ degrees. Since the tops are usually pretty thin, it'd be wise to paint them with woodstove paint to delay corrosion; but so long as the seal remains intact, there should never be any additional oxygen available to react with the wax. If the jars are, themseves, encased into the cob walls (rather than directly exposed to the exhaust flow) the caps should never corrode anyway.

R Scott wrote:hmm. This is getting VERY interesting. This could be a heat sink for a water heater, too. That will store a lot of heat right at the right temp for a water heater.

The preventing oxidation and fire are still a concern, though. Maybe they need to be in a water bath to prevent overheating.

Wax is pretty unreactive. And it has a high ignition point. The only thing I can think of less reactive with a higher ignition point is asphalt, which I mentioned jokingly upthread. I think if you seal these up good, and leave some headspace to take care of thermal expansion, it should work very well.

John Elliott : Sometimes I surprise myself, like now, I'm surprised how long it took me to make the connection! SO, you're saying that the LaBrea tar pits ---- !!! BIG AL !

Creighton Samuiels wrote:

John Elliott wrote:

Creighton Samuiels wrote:If nothing else, a pound or two of candle wax inside one of those boil-in-bag ziplock bags, sitting in a spare cookpot on top of the heat riser surface until bedtime; and then placed into a soft, insulated wrap would be a great gift idea!

Would also work inside of a microwave using this kind...

http://www.packitgourmet.com/CookIn-Bags.html

That's a good idea. Another one would be to use the 2 liter soda pop bottles that are so ubiquitous. One man's trash is another man's treasure!

Wouldn't the soda bottles melt on their way to 160 degrees? Should be okay with soy wax, at a melt point of 122 degrees though.

The melting point of Polyethylene terephthalate is 250 degrees celsius, or 482 fahrenheit, so soda bottles should be ok. I'm not so sure about the cap.

The question as to wax container.  .  as silicone is used for cooking containers, muffin tins for example,  finding some kind of silicone container should remedy the who expansion and burning point issue.

Derrick Reid wrote:The question as to wax container.  .  as silicone is used for cooking containers, muffin tins for example,  finding some kind of silicone container should remedy the who expansion and burning point issue.

Welcome to Permies, Derrick!

Possibly even just a silicone lid... there are silicone tops for Mason jars for fermentation. It would depend on whether the jar was confined within a cob bench (expansion space would need to be within the jar) or if it were a "hot water bottle" style warming device, where a flexible lid could bulge out when heated.