Author Topic: Phase Change [heating with solar]  (Read 3279 times)

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Bruce S

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Phase Change [heating with solar]
« on: August 16, 2017, 12:30:37 PM »
With winter just a few short months away, the plants I have growing in pots will begin their annual back into the green house. The blue & black barrels can hold a whole lot of heat , but there's no real way for me to slow the heating without going into full insulation of those barrels ( very space constrained at this point).

I've been looking into different ways of storing more latent heat from our water barrels.

Being that my wife happens to be a chef, I also know first hand how well beef fat stores heat ( I've made a few tallow candles even). Tallow seems to be close to paraffin in heat/cold qualities, being that I can get it free thought I would try it first.
 
I went searching our forum and found that Madscientist267 had done some Phase change tests (for cooling) with salt water. I also saw where dnix71 has a link for Phase Change materials.

I'm wondering if anyone had thought about using the latent heat holding abilities of fats to slow down the cooling effect of the water or rather allowed the solar heating time to melt the fats to a liquid then release the heat while it converted back to a solid.

My thoughts are to use cases of canning jars, stacked in various arrangements,while sitting down in the barrels full of water; to absorb the heat from the water, melting the fats , then during the night the fats revert back to their solid state warming the water backup keeping the area warm. It may just be better to burn the tallow candles than all these other steps. BUT this seems to be a better cyclic route.

Any thoughts?

Thanks
Bruce S

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Amish_Fighter_Pilot

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Re: Phase Change [heating with solar]
« Reply #1 on: August 17, 2017, 09:09:00 PM »
That is an interesting line of thinking. Its sort of the opposite of the way some cooling systems are being designed now, and yet works somewhat the same way. They make ice at night and let it thaw during the day.

I would strongly recommend separating the fats from the water completely if possible. They should be able to share heat across a radiator or something, but mixing them together is a recipe for unwanted anaerobic bacteria(and the smell associated with it).

MattM

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Re: Phase Change [heating with solar]
« Reply #2 on: August 17, 2017, 10:42:46 PM »
Is this to hold thermal heat from the day-time into the night?  (Because sunlight is already at a premium during the day on quite a few winter days.)

It would probably work through the fall until the real cold sets in and then you can burn the fat when sunlight isn't so abundant.

I can't help but to think getting heat into the system is much easier than a recovery system.  Once the cooled down grease coagulates and shields the remaining liquid from exchanging heat, then what?

Amish_Fighter_Pilot

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Re: Phase Change [heating with solar]
« Reply #3 on: August 18, 2017, 12:13:22 AM »
They make blender blade attachments that fit right on jars. Maybe he can rig some of them up as low-speed agitators?

electrondady1

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Re: Phase Change [heating with solar]
« Reply #4 on: August 18, 2017, 06:13:26 AM »
your making the supposition that animal fat can retain its heat energy longer that an equal mass of other material ? how does that work?

mbouwer

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Re: Phase Change [heating with solar]
« Reply #5 on: August 18, 2017, 07:01:26 AM »
Bruce,

It's not so easy to store heat for a long time.

I gave my green house 3 layers of glas with a big cavity between them.
Even in high winds and at severe frost a 60 watt lamp ensures a pleasant temperature inside.

Regards Rinus



DamonHD

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Re: Phase Change [heating with solar]
« Reply #6 on: August 18, 2017, 07:05:10 AM »
This is the way I would choose to store heat, with phase change, if possible:

https://www.sunamp.com/

They're also up to about 30,000 cycles of the storage with no loss of capacity so far.

Rgds

Damon

Bruce S

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Re: Phase Change [heating with solar]
« Reply #7 on: August 18, 2017, 09:30:08 AM »
mbower1:
Keeping the green house warm can be an exercise in futility  :o.
Where I'm located we can get weeks of -12C weather during the coldest parts. AT that time any plants that are not in the house will be put in the composter. The green house was an inexpensive one and setting it up for extended winter projects will take some time.

elecrtondady1;
Not really sure what you mean about equal mass, however in side by side tests with tallow, tap water and salted tap water each at 500mL ALL warmed up to 150F , the tallow will hold it's heat 2x longer than either waters. This I did just in our kitchen using room temperature at about 78F. Along with using a no-touch infrared temp gun with the fluids being held in glass canning jars. I'd would've really like to have had a constant temp monitoring going on with all three.

IF by equal mass you mean the same amounts in weights, then no I did not test it like that.

DamonHD:
 that stuff looks a lot like the stuff we get for sore shoulders, they can be reused a bunch of times. I'll certainly be reading up on that stuff.
 
MattM;
Yes this is to grab any heat the sun can provide, setting up those beer can heaters are pretty easy, this is kinda like that , but in the water barrels it heats up the water instead of just air. Works pretty well, the green house keeps the wind and snow/ice stuff off of them and when the sun shines, the inside can get toasty ( not scientific term but,,, ).

Having the candles to burn could help, but I'd be a little worried about the fire ( I could always have my local FD engine house come by and give me tips  8), but then they would want to stay , hang out, drink my coffee  ;))

Another issue I'm worried about is the expansion rate of the tallow, since I do not want this and the water to mix, I need to keep the containers air tight.

This idea may turn out to be more work than it's worth :-(.
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Amish_Fighter_Pilot

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Re: Phase Change [heating with solar]
« Reply #8 on: August 18, 2017, 10:52:07 AM »
I still think the idea has merit, but your choice of material may need some revision.

Bruce S

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Re: Phase Change [heating with solar]
« Reply #9 on: August 18, 2017, 12:29:50 PM »
I still think the idea has merit, but your choice of material may need some revision.

I agree, but , this is why I post these things here. More than just starting a journal, beginning a test phase then spending loads of time or $$$, I can get very honest useful input.

Tallow, until humans become totally vegans (NOT in my lifetime I'm sure) will be around. A visit to a farmer's market only 10mins away can net me 20Kg for far less than buying paraffin.
The candles are neat to burn, and much much cheaper than making soy candles. Plus as an added bonus they're easy to burn in the chimney.

The Phase change link DamonHD sent is an interesting one too.

Cheers
Bruce S

 
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OperaHouse

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Re: Phase Change [heating with solar]
« Reply #10 on: August 18, 2017, 02:18:26 PM »
SUNAMP.......

Companies like this drive me nuts.

 It takes the storage capacity of a giant hot water tank into an appliance around the size of a domestic refrigerator.

Well.............How big is that water tank?

Weighs 50% than the same amount of water.

Doesn't exactly sound exciting.  Of course there are advantages, but they won't tell you anything till you talk to a salesman.  There is a new Australian PV to water heat box.  A lot of fluff in their video, but they couldn't tell me anything about how it worked when I asked, like how efficient is it when the panels are only putting out 20%.  It does make sense.  They are trying to market to the uneducated.

DamonHD

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Re: Phase Change [heating with solar]
« Reply #11 on: August 18, 2017, 02:50:13 PM »
I know Sunamp and its CEO reasonably well.

A huge virtue of the Sunamp solution is that is is far more compact and has far lower losses than an equivalent tank of water.

One version can take diverted power from PV, but other versions can be used as thermal stores for heating and hot water with other heat sources such as heat pumps.

Rgds

Damon

Mary B

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Re: Phase Change [heating with solar]
« Reply #12 on: August 18, 2017, 07:33:36 PM »
SunampPV price... GASP 1,800 pounds??? yikes! This page has some heat storage rates for various materials(no fats though...)

http://www.engineeringtoolbox.com/sensible-heat-storage-d_1217.html


Amish_Fighter_Pilot

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Re: Phase Change [heating with solar]
« Reply #13 on: August 18, 2017, 09:06:08 PM »
I think since the tallow gets so hard to work with and non-conductive as it freezes into a solid that what you should do is run coils of pipe through the jars and circulate the water through that. Its a fat radiator, only the radiator is radiating in to the fluid instead of out because of the temperature differentials. The water doesn't change phase, so make the water the thing that moves, not the fat.

MattM

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Re: Phase Change [heating with solar]
« Reply #14 on: August 19, 2017, 06:30:38 AM »
If the fat is mixed with something like used engine oil, would it be easier to transfer heat?

Solidified fat just doesn't migrate well.  I fear pulling heat from the fat will clump fat around the condenser and leave most of it uncooled.

MattM

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Re: Phase Change [heating with solar]
« Reply #15 on: August 19, 2017, 06:39:43 AM »
SunampPV price... GASP 1,800 pounds??? yikes! This page has some heat storage rates for various materials(no fats though...)

http://www.engineeringtoolbox.com/sensible-heat-storage-d_1217.html

I had no idea iron had such potential.  Railroad track scrap used to be easy to come by and they paid me to take it.  It would have been easy to bury several tons - and I mean TONS - and run PEX in contact with it.  Its a damn shame I don't have the 20' flatbed around any more.  If I'd only knew its other potential other than as a quick buck.

DamonHD

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Re: Phase Change [heating with solar]
« Reply #16 on: August 19, 2017, 10:05:02 AM »
A significant problem is the amount of insulation you need around it to stop heat leaking away too fast...

A nice feature of the Sunamp gear is its vacuum insulated panels.

Rgds

Damon

Amish_Fighter_Pilot

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Re: Phase Change [heating with solar]
« Reply #17 on: August 19, 2017, 10:13:13 AM »
Yeah, it would either have to be vacuum panels or aerogel. Nothing else is likely insular enough.

dnix71

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Re: Phase Change [heating with solar]
« Reply #18 on: August 19, 2017, 08:56:02 PM »
His idea of storing low grade heat in a sealed phase change box for compactness is a great idea, esp. the part about making it portable, so it doesn't have to be piped.

There are refrigerators that do the opposite of this, Eutectic fridges 'store' cold in a phase change.
This will allow for operation without a battery in many cases.
http://www.ozefridge.com.au/

Bruce S

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Re: Phase Change [heating with solar]
« Reply #19 on: August 22, 2017, 08:57:23 AM »
As a test before I go mainstream.
I'm going to make a few of these tallow units, I'll either seal it up in tin cans or beer cans. Beer cans will swell easier and let me know if how much to put in the cans that will allow the heating. For the water container I'll be using the large 1.4Kg Coffee containers that will also be painted black. These I get for free from work and will get hot enough to cook the roots of the plants that are (or were) growing in them.
The cheap $1/can black paint cans will cover about 2 containers with two coats that have lasted 2 years now outside.
Some of these have worked out nicely sitting inside in the southern windows of our grow room. This is where I also found the roots getting cooked from all the extra heat. The African violets didn't mind, but the basil flat out died.
 

I'll get pics as I go. I have just enough tallow ready for about two 350mL beer cans.

Cheers
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george65

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Re: Phase Change [heating with solar]
« Reply #20 on: August 25, 2017, 12:32:54 AM »

I'm not exactly sure what you are planning to do in the actual application here ( put jars of fat in a drum of water to slow heat release?)  However, whatever it is, be aware that using fat ( or oil ) will LOOSE you heat capacity.

You mention you are space limited and it would seem you want all the thermal storage you can get. By replacing water with fat or oil, the total BTU capacity of your system will be decreased for the same Volume. Fats and oils have significantly lower thermal capacity than water. Water is in fact one of the best thermal storage mediums with common materials and is hard to beat in Practicality.
If say for instance you are storing 5 Kw of heat now, You may only be able to stores 3 Kw depending on how much fat you use.

The advantage of a fat or oil over water would be in elevated temps over 100oC. At that point water will boil  but you could take fats or oils to 200oC . Be on the edge and they would be smoking at that point but they would do it.  Of course then you need the containers and piping etc that will handle that.  For the sort of temps you are going to want, water will be the best medium by far.

I want to do a greenhouse before next winter and will look at water storage and burning oil. This will elevate the co2 levels and provide heat. Unlike what many think, oil can be burned perfectly clean and even set up to provide constant heat with a simple controller.  There is around 10Kw of energy in ever litre of veg oil ( I imagine fat would be similar as it's a fraction higher in energy content than oil but would vary) so you wouldn't need a lot to heat a decent greenhouse I'd Imagine. In any case a decent restaurant would have 100L a week or so which would be more than enough.

I'm just going to build a real simple 2 stage burner to start with, Idle and heat. With a simple thermostat, once the heat is needed a fan will kick in and a valve open and the thing will ramp up. once it is at temp it will go back to the standby idle mode. That will provide some heat in itself anyway.
Co2 could be monitored and exhaust Vented in or out.
I'm thinking to make just a little baby 5Kw burner or at least program one to that and see how it goes. The variables of the thermal properties of the greenhouse would be infinite but 5 Kw would  easily heat any enclosed space backyard greenhouse size and would kick in and out as needed on the thermostat.

I'll try a direct heating setup first and see how that goes and if the Co2 is too high then I'll look at a hydronic  setup.
I think you'd be far better off burning the fats than trying to use them as a storage medium.

frackers

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Re: Phase Change [heating with solar]
« Reply #21 on: August 25, 2017, 05:09:27 AM »
I'm surprised nobody has mentioned supersaturated sodium acetate solutions as used in heat pads. Uses the heat of recrystalisation to store energy.
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DamonHD

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Re: Phase Change [heating with solar]
« Reply #22 on: August 25, 2017, 03:40:37 PM »
That's what Sunamp is doing, and their secret sauce is keeping the reaction under control.

Rgds

Damon

Bruce S

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Re: Phase Change [heating with solar]
« Reply #23 on: August 28, 2017, 07:03:55 AM »
Georeg65;
Because I'm hardheaded and I like a challenge  :o. That is what I'm trying to do.
I knew that displacing the water by the sealed glass or tins of tallow would lower the amount of heat by the volume of displaced water.
Since I'd also like to extend the growing season into the freezing months (squash, beets, turnips, Kale, etc) I also need to thing about freezing issues.
Likewise, burning the oil directly could be a nice solution, but then I have to stay around as a just in case the burn gets out-of-hand.
I have tested the floating candle thingy, and cute and practical. I have some chicken-of-the-sea tins that I'll be trying this out with.

Frackers:
That is intriguing, I do have couple of those snap heaters, but thought it would be too pricey even for me to try out.

Damon;
I wonder if they use a membrane to keep the solution regulated. Like Mary B said: At $2Gs per it a little out of my greenhouse range.

Cheers
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OperaHouse

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Re: Phase Change [heating with solar]
« Reply #24 on: August 28, 2017, 06:38:57 PM »
I'm surprised nobody has mentioned supersaturated sodium acetate solutions as used in heat pads. Uses the heat of recrystalisation to store energy.

I have one of those and it is a pain in the ass to use. You would need a load of cells and magic twangers to start it.  Do  they stop id a temperature is maintained?

DamonHD

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Re: Phase Change [heating with solar]
« Reply #25 on: August 29, 2017, 02:07:36 AM »
AFAIK, yes.

Bruce S

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Re: Phase Change [heating with solar]
« Reply #26 on: September 12, 2017, 09:47:48 AM »
It's been a little while since my last post.
I thought I would post a short update.

Here's a pic of the Tallow donors (but don't tell them  ;) ).
For my French friends,, YES these are those lovely tasting Charolais cattle.
   
After reading the suggestions here and doing more online research , I've decided the idea of Phase change might be do-able, but using the tallow as a fire would be better while I test the Phase change method.

I did some research on using the tallow along with Paraffin based candles to keep the green house warm for a much longer period without the worry of fire or spillage.

The real interesting setup is to use the paraffin based candle to buffer the tallow. I'll also setup the internet sensation (using clay pots as radiant heat) instead of merely a fire that could burn something.

More to come
Cheers
Bruce S
 
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