Puppeteer

Author Topic: Cold energy Storage MkIII  (Read 4525 times)

guest22972

  • Guest
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

  • Mendocino Metro
  • Hero Member
  • *****
  • Posts: 1594
  • Mmmm BBQ
    • View Profile
    • Mikes Solar PV page
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.

ajaffa1

  • Hero Member
  • *****
  • Posts: 1725
    • View Profile
Re: Cold energy Storage MkIII
« Reply #2 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

ajaffa1

  • Hero Member
  • *****
  • Posts: 1725
    • View Profile
Re: Cold energy Storage MkIII
« Reply #3 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

dieselspanner

  • Hero Member
  • *****
  • Posts: 726
    • View Profile
Re: Cold energy Storage MkIII
« Reply #4 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
Tighten 'til it strips, weld nut to chassis, peen stud, adjust with angle grinder.

ajaffa1

  • Hero Member
  • *****
  • Posts: 1725
    • View Profile
Re: Cold energy Storage MkIII
« Reply #5 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

  • Administrator
  • Hero Member
  • *****
  • Posts: 659
    • View Profile
Re: Cold energy Storage MkIII
« Reply #6 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!
Ade.
--------------
1x Lister CS Start-o-Matic (complete, runs)
0x Lister JP4 :( - Sold to go in a canal boat.

dieselspanner

  • Hero Member
  • *****
  • Posts: 726
    • View Profile
Re: Cold energy Storage MkIII
« Reply #7 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.

ajaffa1

  • Hero Member
  • *****
  • Posts: 1725
    • View Profile
Re: Cold energy Storage MkIII
« Reply #8 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

dieselspanner

  • Hero Member
  • *****
  • Posts: 726
    • View Profile
Re: Cold energy Storage MkIII
« Reply #9 on: September 05, 2019, 02:21:07 PM »
I've just had a delivery of Land Rover spares from the UK and the voids around the little boxes, in the big box, was (were?) filled with polystyrene packing 'beads', the things that look almost edible. They have to be cheap, surely........

Bob, as for crushing, once the cubes are filled with water they will be ok, our septic (sewage) tank is poly and around 6 M3 (room for ribaldry at my expense here, lads!) and we are always warned not to leave it even partially empty after cleaning.

Leaving the IBC (s) in the cage would give peace of mind.

I like the garden shredder idea!

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

ajaffa1

  • Hero Member
  • *****
  • Posts: 1725
    • View Profile
Re: Cold energy Storage MkIII
« Reply #10 on: September 06, 2019, 10:16:49 AM »
Hi Stef, always knew you were full of Sh1t,  :laugh: I know those polystyrene beads can be bought in bulk and cost next to nothing, if you have a local arts and crafts shop they generally sell them for filling cushions/bean bags and etc.

I have to get the local sewage pumping company in to pump out my septic tank, guess my Wife and I are also full of it!

Hi Glort, that is why I am watching what you are doing. If there is a fault in the logic you will find it at your expense, I will learn from your mistakes and try to avoid making the same mistakes.  :)

If you are going to fit a cross over switch you will need to get your sparky to fill in the necessary online paperwork with Essential Energy and then wait a month or more for approval. Your sparky will have to either do the work or supervise the work and sign off on it, this could be expensive. When I put my cross over switch in I found that they cost around $200 here but could be bought from the UK for around $50 including delivery for single phase, expect a three phase cross over to be much more expensive. I suspect that you could do the job using a high power three phase motor contactor/starter relay. It won`t be legal but it will do the job, 240 volt relay will drop out on mains power failure, easy to fit a switch giving you control.

Bob



Old AC units are a dime a dozen, scrap yards across Australia are full of them, 2KW might be a push as I think they start at around 3KW but an older lower power unit would probably be more user friendly with regards to servicing.