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Author Topic: Cold energy Storage MkIII  (Read 334 times)

glort

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Cold energy Storage MkIII
« on: August 29, 2019, 08:35:27 AM »

Following a couple of discussions of Cold/ Ice  energy storage, I have been doing some more head scratching and research on the idea.

Ice while very efficient as storing cold energy is also somewhat problematic on  DIY Basis.  There is the problem of ice expansion and transferring the cold in the ice through water which may make the melting process difficult and somewhat expensive with the amount of coils needed to be put through the ice.

I'm thinking of using excess solar power to create cold energy and store it for use on hot summer Nights.
Ideally the energy could be restored through the day so an 8 Hour cycle to take advantage of the solar available would be ideal.
The previous discussion looked at using a domestic chest freezer for creating the ice and as a thermally insulated container. There was doubt as to weather a freezer had the strength for filling with water and freezing it due to a freezer is not going to have the cooling power to freeze the water fast enough.

My thoughts are to use a chest freezer or an old refrigerator turned on it's back as a cheap storage container. The size I have in mind is 500L +.
 For cooling power i'm thinking of a car AC compressor and using the metering valve to not go into the normal densely packed evaporator tubes but rather a loop of stainless steel pipe running the length of the container. The AC compressor could be driven by an electric motor to make use of the solar power through the day. There would also be potential to drive it with an IC motor and add in a RX valve for heating in winter. The heat from the engine and exhaust could be used to increase efficiency by elevating the temps going through the Condenser.

Looking into something Bob touched on being salt in the water, it seems this could be a very viable solution to get around a lot of problems associated with having ice.
If we took a 500L frezer and added 120Kg of Salt ( about $50 worth here) the freezing point of the water now instead of being 0 Oc becomes MINUS 20 OC.  That means if we have 500L of salt water at -20 and take it up to Plus 20, we have a thermal storage of 23Kwh of thermal energy.
Definitely a worthwhile amount and sufficient to cool a decent area of a Home for one night. 

Being we still have water, a lot of problems with having ice go away.
We wouldn't need all the pipework as with ice for a start.  The water could be removed from one end of the freezer, Pumped through the HE and returned the other end of the fridge or freezer.  Perhaps some circulation of the water during the cooling cycle could be beneficial and a small pond pump or air lift could be used to move the water around to prevent localised Freezing.

To get call it 20 KWH worth of cold, I guesstimate  the input would have to be around  5-6 Kwh of energy.  There should be an EER of about 4x on the AC cooling side but there would have to an account for the inefficiency of the electric motor and belt drive and also an electric fan running through the evaporator.  Using brine as the working Medium, if more power was available and more cooling wanted, an extra fridge/ freezer could easily  be fitted with some pipes and used as an extra holding tank.

Astheticaly, these could be used as benches or even a table or stacked on top of one another for more compact packaging.

I don't think having ice is necessary for a worthwhile system.  While it might be more efficient in storing the energy, this could be made up for with solt water by just increasing the volume  fo the water whoci would be remain a very practical amount.  If one could get 20 or 40 Kwh of cold storage, to me that would seem as much as most people can use in a night and also as much spare power as a lot of people might have to generate the cold in the first place. If you tried to Freeze too much ice, firstly you may not be able to throw in sufficient power to get the phase change and secondly, are you going to need more stored cold energy anyway?  If you could get 40 KWH, that would be a good 8 hours on a large whole house ducted AC running flat out.

Also with the salt water system, you have the ability to store heat and elevate the temp of the water.  Not sure what temp the plastics would take but I also know that most people tend to grossly underestimate how hot plastic can get without deforming.  I have boiled a number of plastics and they just don't care about 100oC  and I don't think anything in fridge would be worried about 120 if you could get it that high.   Unlikely a lot of people will have much if any excess solar power in winter but if one were using an IC engine it would give the ability to run it in the day and shut it off at night.

Going to see if I can get a couple of car AC systems this weekend and give this a go.  I have a space at the end of the house that would be perfect to locate a fridge/ Freezer which is out the way and close to the power board  and also at the end where the main bedroom is which is what I really want to cool at night.

I'm having the 32A circuits installed for the solar next week so hopefully I'll have less problems with voltage rise and can get more power out my systems. In any case being able to run something like this will be good to use the excess power that pushes the voltage above what the inverters are comfortable with.

I  believe an AC compressor needs around 3-4 HP so I might look at running my 5KW 3 Phase Motor on 2 Phases and see how that goes.  I can start it unloaded then have a timer kick in the AC compressor clutch after 5-10 sec.  Failing that I have a 1.5 HP single phase up the back and I'll look at putting a small pulley on that to gear it down.  Compressor may not make as much power but I'll be able to kick the smaller load in earlier and out later on the excess solar that will cover it.  Either way I am not thinking that chilling the water fast enough is going to be a problem with the sort of energy a car AC compressor can generate which is the equivalent of a mid size household split.

the most difficult thing I see about this is plumbing the AC side.
Car AC fittings tend to be Bolt on O ringed aluminium fittings while  Domestic/ Commercial AC tends to be copper flares.

Other than that seems practical, affordable and doable to me.   :)







mike90045

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Re: Cold energy Storage MkIII
« Reply #1 on: August 29, 2019, 05:29:27 PM »
I recall there being a huge amount of energy in the phase change state, converting water to ice and back to water, at 0c.  Simply dropping the freeze point 20 degrees with salt, may not be enough delta to match the phase change energy.
I'm the electronics guy, and we pass all the thermal calcs to the thermal engineering department.

glort

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Re: Cold energy Storage MkIII
« Reply #2 on: August 29, 2019, 10:32:16 PM »

While there is a lot of energy getting the water to phase change, there is also a lot of problems in both Freezing and then re thawing the Ice to release the energy.
In practice, I don't see the point of going to the trouble to use Ice when you might only use half it's cooling capacity and therefore still have spare Solar power through the day you can't use because you have already filled your cold bank.

As I showed, It would not be hard or take a very large container to store 20Kwh of cold.  I think for a lot of places, that would be sufficient cooling especially at night when there was no sun and cooler than daytime temps. If a person had cheap off peak power, it may be better to recharge the system at night for use in the day.  In that case Ice may be better BUT, it's also going to be a lot more expensive and complicated than salt water.

Even if one wanted 40Kwh of cooling capacity, something the size of 2 large Refrigerators is not an overly large or Impracticaly large amount of containment to handle.

ajaffa1

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Re: Cold energy Storage MkIII
« Reply #3 on: September 01, 2019, 09:48:17 AM »
Hi Glort, I think you have very easily doable project there. Fridges/freezers are not designed to hold that amount of fluid, brace them with timber and run ratchet straps around them.

The trick to maintaining a comfortable home in summer is to turn on the AC early, when it is powered by your solar. It is much cheaper to keep a house cool than to try to cool it down when you get home from work after dark. If it does start to get too warm then you kick in your DIY air conditioning system.

Bob

glort

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Re: Cold energy Storage MkIII
« Reply #4 on: September 01, 2019, 12:36:08 PM »

Hi Bob,

I agree with the early theory entirely. I have been doing the same over winter with heating.  During the day I let the AC bounce of thermostat set 20oc.
In the afternoon I turn it up to about 23 Before  the temp drops too much.  Being a sad case that has no life I monitor Generation and use every day and found this used much less power over all than letting the place go cold and trying to warm it up.

I'm getting a couple of 32A Circuits put in this week for the solar so i hope to be able to pump the power back in and reduce the voltage rise I'm getting now.

Didn't get the compressors as I hoped this weekend but its definitely something I want to try. I have the perfect location and application for it so will be practical in application as well.  I don't really see a problem with filling them with water,  just the freeze expansion I think would have been a problem but I'm sure I can get a fridge or Freezer cheap from my friendly local scrappy to try. If one bursts, I'm sure he won't mind doing an exchange for me.  :0)

ajaffa1

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Re: Cold energy Storage MkIII
« Reply #5 on: September 02, 2019, 12:05:28 PM »
Hi Buddy, a trick known to every Pommie gardener with a fish pond in the back yard is to throw in a football in winter. The expanding ice crushes the football rather than busting the concrete/GRP pond liner.

Perhaps you should be lining your freezer tank with polystyrene or bubble wrap, might not be enough to cope with the expansion issues but adding one of those cheap inflatable swimming pool balls would probably be adequate.

Bob

glort

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Re: Cold energy Storage MkIII
« Reply #6 on: September 03, 2019, 12:28:27 AM »

I was thinking of some thing to take up the expansion but never thought of a Ball.
Perhaps a Bunch of something like tennis balls would be better given the volume of a Fridge Freezer.
Perhaps a soft inflated Basket ball that was submerged into the middle of the vessel would be good too and allow more compression area?
Other thing I thought of was those Pool noodles.  Styrofoam came to mind but I thought that would crush down and not return. The pool noodle stuff is very spongy.

Never thought about this before but having mentioned it, seems like I might have been lucky with the terra cotta bird baths around the place in winter. Then again, they only freeze about an inch on the top rather than right through.  Thank heavens for that!

dieselspanner

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Re: Cold energy Storage MkIII
« Reply #7 on: September 03, 2019, 08:51:35 AM »
If you can get down to -20c or so with a saline solution remaining liquid, how about burying an IBC container surrounded by re purposed polystyrene packing in the garden / under the garage / shed etc.?

Probably not the most efficient but you'd have a large thermal mass with no danger of it splitting and wouldn't cost a lot either.

Cheers
Stef
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glort

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Re: Cold energy Storage MkIII
« Reply #8 on: September 03, 2019, 09:24:38 AM »

That's a very good suggestions Stef. I was thinking about an IBC if I could get some cool room panel or some of that thick building foam to encase one.
An IBC would allow for loads of capacity and also give a good thermal mass for heating as well. Could get decent heat storage without the need to have the water too hot.

I have a bit of garden I could put the IBC in not far from where I was thinking to locate the thermal storage.  Would not be too far to run pipes and I could run them underground with no problems.

ajaffa1

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Re: Cold energy Storage MkIII
« Reply #9 on: September 03, 2019, 11:42:17 AM »
Very much like the idea of burying an IBC, should give a very good thermal mass for both hot and cold storage provided it is well insulated. It might be a good idea to ensure that you have sufficient space to increase the capacity by burying a second at a later date.

Looking forward to hearing how well this works.

Bob

AdeV

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Re: Cold energy Storage MkIII
« Reply #10 on: September 03, 2019, 06:53:36 PM »
...no danger of it splitting and wouldn't cost a lot either.

...and even if it DID split, all it's going to do is water a patch of the garden from underground  ;D
Cheers!
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glort

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Re: Cold energy Storage MkIII
« Reply #11 on: September 04, 2019, 10:46:57 AM »

...and even if it DID split, all it's going to do is water a patch of the garden from underground  ;D

It might be a good idea to ensure that you have sufficient space to increase the capacity by burying a second at a later date.

Good lord you two are Bona Fide, Died in the wool, goddam geniuses!

I'm doing the mental arithmetic on this, Dig a hole, maybe 1500x 1500 Sq x1500 Deep.  What a pain in the arse that's going to be to dig with an excavator that's going to cost me $200 to dig one lousy hole that -might- take me an hour .
 Bury 2 IBC's Bob suggests.
Well, that will certainly make digging the hole easier to dig one 1500x3000.  Much more travel for the boom on the excavator so I can get down easier and get the corners straighter.  Got to hire the machine for a day so makes it more worth while at least.

OK, now I have 2 Ton capacity.  If I crunch the numbers on that, If I only go to minus 5oC allowing a much reduced salt concentration and therefore less corrosive, and take it up to say 15oC so the air coming it is still reasonably cool, at least 10o lower than the ambient I'd want, I now have 27 Kwh of cold thermal storage! Now that's going to make for one nice cool house and burn plenty of myuy otherwise excess solar which is the holy grail since I started this obsession.

But I had another thought..... ( Yes, 2 in one day, MIRACLE!)
I thought of driving this setup with a diesel engine in winter for heat generation.  The engine powers the AC compressor that I put an RX valve in the system and use the cooling waste heat and that of the exhaust and feed that back in the system to get much better efficency.  I can turn the diesel off at night and run on the stored heat.

But why run an engine just for heat? I was going to convert a spa heater this winter but my roundtuit  must have got lost in the post so never got done.
One of the biggest obstacles I saw was making a burner to run reliably at about 5 Kw output.  I think I have cracked it but....
Why not just do a 20 Kwh burner which will be a boat load easier and divert say 5 Kw to the house and the other 15Kw to storage?

If I have 2000L of water sitting @ 25oC and I want to raise it up to 85oC and am throwing 15Kw at it, that gives a burn time of just over 9 Hours. Allow for inefficiency, call it 10 hours. A bit long but I believe I won't have to run the thermal storage right down and I can alsways crank up the burner harder to get a shorter burn time. No problem there.   I'm burning 2L an hour, 18L day, Pfft, less than my car uses, 2 weeks out of a 44 gallon drum, 2 IBC's for the whole winter, no brainer.

But there is a kicker. That 2 ton of water now sitting at 60O temp differential of what I want to pull it down to, now has a meagre 140Kwh of heat storage!! I use at worst 50 Kwh a day total and if I'm pumping 5 Kw into the house all day, it's going to be well heat soaked in the walls and furniture and I'm going to be real lucky to need 20 Kwh at night.
I can't see this needing to be fired up more than every 3-5 days!

Of course I wont achieve perfect insulation on my buried tanks. Some of that heat will escape into the surrounding soil and heat tends to rise... which will make the 600MM of earth I plan above it nice and warm.... and plants like warm soil... So remembering what Ade says about a garden, throw a little green house over the top of the buried IBC's and I have Summer Vegetables or whatever else I want all year round!

All sounds too good to be true so someone shoot me down to reality.

I can get the compressors and AC gear for nothing, I have the spare solar power, IBC's cost nothing and I think I have 5-6 sitting round now as water tanks, the excavator will cost me $200 for the day, probably the biggest expense, I have plenty of garden right at the back of the house that we were thinking just to grow lawn over so I won't need long Pipe runs, can locate the AC and the burner in an out of the way end of the house... I can't think of anywhere this idea becomes Impractical.

The only thing I have reservations about is finding the cool room panel or building foam at the right price to insulate the tanks.
I'm also thinking to line the hole with black Builders plastic to try and keep any water out and cap it over the top as well if I'm going to have a garden there. Might be able to put a second layer and turn it up like a catchment to hold some moisture lower down.

Now the final question is... is it all worth while? What's it going to save me, what's it going to give me, is the effort worth the returns?
That I might have to seriously ponder a bit more.  :embarassed:

dieselspanner

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Re: Cold energy Storage MkIII
« Reply #12 on: September 04, 2019, 02:26:00 PM »
As for the insulation, two thoughts.

First, there must be loads of polystyrene packing you you could break up small and use. the whole thing is going to be over the top as far as storage goes, so less than perfect insulation shouldn't be a problem, make the hole 200 mm bigger all round and throw in lots.

Second, when I did my barge I found an outfit in Wales that bought up all the damaged sheets of foil backed insulation from two of the big British manufacturers - Selotex and Kingspan, I think. As I only wanted it in small areas a palette load went a long way and was very cheap. There's got to be someone doing similar 'Down Under'

Cheers
Stef
Tighten 'til it strips, weld nut to chassis, peen stud, adjust with angle grinder.

glort

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Re: Cold energy Storage MkIII
« Reply #13 on: September 05, 2019, 01:33:21 AM »

Good suggestions Steph.

I did think of the foam boxes I see around that are used for Fish and other things that have to be kept cold. Mrs has been getting some for me I have been using to put plants in. One I put a 400W heater out of a fridge in and connected that to some panels. seems to have kept the soil nice and warm.
My only though with that was getting enough of the things., I'd want a triple layer at least cause the stuff is not too thick.

I looked at cool room panel and that's more than I would want to put into the project initially anyway.  Along the lines of your Idea, I did see and ad for a mob that remove cool rooms and dispose of the rubbish. I thought it might be worth giving them a ring and seeing If I showed up somewhere they were working if I could load up the trailer with the stuff.
They might have to dump it, they might re sell it but I couldn't find any ads for used cool room panelling.

Some years ago when my brother in law was managing a waste disposal company.  They had  masses of the stuff come in after there was a big remodeling at the main fish markets.  Was going to cost a fortune to get rid of and he was looking for a way to strip the aluminium off the foam. He managed after some time with the stuff sitting round to sell that to some mob in Indonesia.  I remember him specificly talking about how when the deal was done the guy he had been talking to got all smug and said something to the effect he should have pushed the deal harder, they would have paid more for the material.
My brother in laws Boss was there and said, I'm going to take him out to lunch for this anywhere he wants to go, we were looking at paying many thousands to have the stuff disposed of and he actually made us money out of it.

I think there is something with that polystyrene that makes it a difficult and unwanted waste product so they may be happy to offload it.

I saw last Night an ad for a company making sheds and granny flats out of the stuff. I though that would be insulation at a new level!
Turn on a heater or an AC for 10 Min and that's all you'd need for the day if you didn't go in and out a Lot.

I also remember seeing Sheets of the stuff stacked up at a factory somewhere that was left over packing. It was only about 10mm thick but it was is 2400x1200 sheets and they had mountains of it. Wish I could remember where that was.

ajaffa1

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Re: Cold energy Storage MkIII
« Reply #14 on: September 05, 2019, 12:43:55 PM »
Hi Glort, if I was still living in the UK I would be sitting my IBC on a 150 mm polystyrene base and then paying the local insulation company to fill the void around it with spay foam insulation. My understanding is that spray foam is very expensive here so I would be very tempted to collect as much polystyrene as I could, put it through a cheap garden shredder and use the resulting small beads for back fill. If you are concerned about the ground collapsing and crushing you tank vermicucrete might be the answer, this is a mixture of sand, cement and vermiculite. We used to use it for lining chimneys between the brickwork and the flue liner: strong, cheap with good insulating properties.

Bob