Author Topic: Ice air Con/ energy storage.  (Read 558 times)

glort

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Ice air Con/ energy storage.
« on: January 17, 2019, 03:15:28 AM »


This was brought up by Bruce a while back but the recent heat wave here has spiked my interest in the idea again.
I see there are a few different commercial systems being offered for this now, mostly industrial scale.

My original concept was to freeze a chest type unit full of water. The reason I rejected it initially was that I could not find a freezer with sufficent power to freeze it's capacity in 12-24 hours.
I have had a rethink on this as I can see that while it may not be possible to cycle a unit in perpetuity, It may provide some days off offset cooling.

Here even in summer the AC is not required every day and this would give a chance for a unit to take the time to freeze to solid and the invested energy to be used when needed. Even if it did not see through an entire hot weather event or only supplied cooling some days it would be advantageous.

So Bruce et al, I'd like to get some ideas and feed back.

First thing I am unable to find ( despite a variety of search terms in google) is how much energy in kwh is in a Litre of water when frozen or ice, whichever the correct paramater would be?  I saw something that suggested that the energy storage was less than I thought, about 46.5 KW in 500L of Ice.  that would be 1-2 Days cooling here.
If I can figure the accurate amount,  I'll have a much better idea of cooling capacity.

Looking at some freezers, I see the small ones seem to have the same motor power as the larger ones... at least on some brands.  Wondering about the tradeoff here. Would it be better to try and freeze a smaller amount of water faster or have a larger reserve that takes longer to recover? Spose that would depend on what the cycle rate may be. Ideally having multiple smaller units would effectively invest more power into a given amount of water than one larger unit.

 My other concern is that ice expends when it freezes. If I fill a freezer up or to say 80%, will the expansion go up to the vacant area or will it push out the sides and push the freezer unit apart?  I'm thinking up from freezing ice cubes etc but not sure that freezing and amount of water from the bottom up to a couple of feet will be the same.

Finally, How would the brains trust suggest setting up such a unit?

My thoughts are to have some coiled pipe ( NOT copper because I simply have an aversion to every Fker on YT using a copper coil as a HE!   >:(  ) but something like that plastic water pipe for home use  PTFE? or having a look at cutting an expansion coil out of a large  AC unit my mate has a stack of with say 1/2" to 3/4 in/outlets or a car heater core or 3 which are also 3/4".

Through this I would run an antifreeze/ Brine soloution so the exchange medium did not freeze and stop the show in it's tracks.  From there I'd have a circulation pump and send the chilled water through a radiator/ heater core and back to the Freezer HE.

I'm wondering if anything special would have to be done to ensure good convection and cold transfer to the HE in the freezer unit. Minds vision is the internal HE would be frozen in the ice and as the coolant is circulated the internal HE is warmed melting the surrounding ice and the water then surrounding it is chilled by the ice.  Question is of this would take place quick enough with something like heater cores or a long length of Tube would be needed to give a larger melting area.

I can see the HE at some point being surrounded by  many Cm of water before there is any actual ice and wondering about the transfer of water through said water.

Anything to be aware of or alternative setup suggestions?



Next idea would be how to set one of these up?

ajaffa1

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Re: Ice air Con/ energy storage.
« Reply #1 on: January 17, 2019, 06:57:43 AM »
Hi Glort, I was also interested in the post by Bruce. I found the flowing on Wikipedia:
Ice-based technology
Main article: Ice storage air conditioning
Several applications are being developed where ice is produced during off-peak periods and used for cooling at later time. For example, air conditioning can be provided more economically by using low-cost electricity at night to freeze water into ice, then using the cooling capacity of ice in the afternoon to reduce the electricity needed to handle air conditioning demands. Thermal energy storage using ice makes use of the large heat of fusion of water. Historically, ice was transported from mountains to cities for use as a coolant. One metric ton of water (= one cubic meter) can store 334 million joules (MJ) or 317,000 BTUs (93kWh). A relatively small storage facility can hold enough ice to cool a large building for a day or a week.

In addition to using ice in direct cooling applications, it is also being used in heat pump based heating systems. In these applications the phase change energy provides a very significant layer of thermal capacity that is near the bottom range of temperature that water source heat pumps can operate in. This allows the system to ride out the heaviest heating load conditions and extends the time frame by which the source energy elements can contribute heat back into the system.

Thinking about your concerns for finding a chest freezer that would freeze half a ton of water in a less than 24 hours, I don`t think it could be done, I also doubt that the freezer would have sufficient strength to hold that much water. However second hand chest freezers are cheap so you could use a setup with several freezers containing less water. A simple timer circuit could be used to switch between them when your solar power is available. Small motor valves could be used to switch between them so that you only drain them one at a time.

Another thought is that adding some salt to the water you are trying to freeze will lower it`s freezing point and  presumably increase the energy required to freeze it and thus the energy stored.

I wouldn`t recommend using brine in any heat exchanger unit as it will very quickly corrode the unit unless it is stainless steel. I think automotive anti freeze would be a better bet.

The expansion of ice during freezing is a major problem which would split a chest freezer in two. I wonder if someone like Clarke Rubber sell rubber bladders or kiddies swimming pools that could contain the water/ice and HE coil, keeping it away from the walls of the freezer.

I`ll try to think of some more ideas,

Bob




Oiler

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Re: Ice air Con/ energy storage.
« Reply #2 on: January 17, 2019, 07:09:20 AM »
Do you need a solid block of ice? Why not use a water/glycol mix in the freezer? You won't have to worry about expansion.
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ajaffa1

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Re: Ice air Con/ energy storage.
« Reply #3 on: January 17, 2019, 09:03:19 AM »
Hi Oiler, I had thought about that but I think the freezing takes the water to a different energy level increasing it`s storage ability. Water has some strange properties, there is something called the triple point of water (0 degrees centigrade at sea level) where it can be a solid, a liquid and a gas all at the same time.  ???

Bob

oldgoat

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Re: Ice air Con/ energy storage.
« Reply #4 on: January 17, 2019, 10:34:39 AM »
The term you are looking for is "Latent heat of fusion" and Ajaffa has done the calculations for you The ice changes from a solid to a liquid and releases the energy which you had put into it to turn it to a solid.

ajaffa1

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Re: Ice air Con/ energy storage.
« Reply #5 on: January 17, 2019, 10:51:37 AM »
Hi Oldgoat, got to confess I did not do the calculations, I just did some research and posted my findings.  :embarassed:
That said the latent heat of fusion is what captures and later releases the energy stored in the system. I still think that adding some salt will reduce the freezing point, increasing the energy storage potential.

Bob

glort

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Re: Ice air Con/ energy storage.
« Reply #6 on: January 17, 2019, 12:59:22 PM »

As I recal from previous posts Bruce made which I cannot find now, the phase change from water to ice even if just a hand full of degrees increased the stored energy  Many many times over.  I also seem to recall Bruce saying that the actual temp of the ice being -5 or -50 had little bearing on the total thermal capacity, what was important was the phase change from liquid to solid.

I'm sure Bruce will reiterate the correct key points when he sees this.

I thought of something like some non absorbent  rubber/ foam to line the freezer with.  I think they mainly have the coils on one side of the cabinet so if this was left clear and a couple of payers were glued around the other sides of the unit, there should be enough compress ability in the foam  to take up the expansion and stop and stress on the uint walls.

I'm sure Bruce would be able to tell us the expansion of ice so we would work out how much foam/ runner would be needed to allow for this expansion.

Thinking about it, it would seem logical that the rate of freezing the water would be inhibited the same way as thawing would be in the problem I forsaw in the water around the coils having to pass the cold from the outer layer of ice back to the tubes to be carried into the house.
There is no doubt a Freeze thaw rate at play here as well.

This would be very battery like far as I can see. There would be a given capacity and also a charge and discharge rate. In this case instead of the electrical current in charge or discharge being limited, the rate of heat exchange in freeze or thaw would be the limiting factor.  I'm thinking that the coil in the ice may have to be fairly dense so as to limit the distance between the water surrounding the coils and  the still to be melted ice.

Ideally I can see something like the cores of a heat exchanger through the ice being the best soloution with the cores being hollow water filled passages through the ice itself which cooled the water as it melted and had no thermal water barrier.
The cooling rate would then increase the more the ice melted what as with pipes or tubes of metal or plastic the thermal transfer rate would diminish the more the ice melted and the water jacketing  the pipe increased.
Not too practical to make Ice heat exchanger cores though.

BruceM

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Re: Ice air Con/ energy storage.
« Reply #7 on: January 17, 2019, 04:51:55 PM »
Bob has it right, it's the enormous energy in phase change, from liquid water to solid ice that allows the Ice Bear systems to work in a reasonable size. 

https://www.ice-energy.com/wp-content/uploads/2016/03/ICE-BEAR-30-Product-Sheet.pdf

Much of the engineering has already been done...it would be foolish to not look closely at what they have done and assume that there is a good reason for their design choices.  These systems weren't designed by fools.

Freezing a huge block of ice from the outside isn't done...instead there are coils or refrigeration copper throughout the the tank.  This is because ice will act as an insulator of the much colder evaporation coils, so we don't want thick ice which will block efficiency.

The process would also be vastly more efficient with a ground source loop for cooling the condenser side of the compressor, or an evaporatively cooled air exhanger, as Glort has previously experimented with.  But that is irrelevant to the ice block energy storage end of things. 

The cold extraction side of things is also being done with lots of small coils in parallel. I suspect the heat transfer rate needed requires this.  It takes time for a block ice to melt in a pot of boiling water- so lots of surface area is needed to make the ice block a better thermal battery.  Again, lots of small diameter copper is used...copper is great for thermal conduction.   I don't know the details of the Ice Bear system but they may run the "cold withdraw" side using refrigerant at pressure for compatibility with the existing AC system. 
A DIY system might put a large truck radiator into the AC airstream, with fan only operation.

It will take a massive amount of PV and inverters to run the AC during the sunny part of the day AND run similar or larger sized refrigeration unit to freeze ice.  Most commercial systems in the US currently are using bargain rate power late at night to do the freezing. 

A chest freezer is a slow poke, and could never freeze it's volume of water in a useful period for exchange, nor is it mechanically sound enough for the water pressure at the bottom, nor the expansion during freezing.  An EPDM then foam lined supporting structure (wooden hot tub with springs in the supporting steel bands that can flex with the expansion is my first thought, but again, I'd look long and hard at what the commercial systems are using. I'd run and ad on Craiglist or such and pay someone to let me come and look through their ice storage unit carefully.  It's SO much cheaper and faster to steal the fruit of someone else's hard learned development work.





glort

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Re: Ice air Con/ energy storage.
« Reply #8 on: January 17, 2019, 05:24:15 PM »

Seems the freezer idea is not Viable then.
Never easy to put excess solar to work or store energy.

BruceM

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Re: Ice air Con/ energy storage.
« Reply #9 on: January 17, 2019, 05:32:21 PM »
True, that's why I adjust my "big" power use to sunny days only.  I can't afford to throw money at it, ala bigger batteries or deeper discharge. 
Mostly sunny today, for a change, so I need to pump water to the tank and then do the monthly equalization charge all afternoon.  It's overdue.

glort

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Re: Ice air Con/ energy storage.
« Reply #10 on: January 17, 2019, 06:05:59 PM »

Going to be sunny here today.  44oC predicted.  Was 30 yesterday,  Still 37 when we went out for my Daughters birthday at 7:30 Pm and 30 when we got back at 9 Pm. Very Humid still too.

Place we went to had these water misters going outside. Weren't doing a thing other than adding to the humidity.
My Bald brother in law was complaining to the staff that the humidity from the sprayers was going to make his Perm Frizzy.

One over amply endowed young lass my nephew was checking out with great interest for her empty glass collecting talents told us she would go see the manager on duty and see if he could turn it down for my BIL thus once and for all proving the theory of the relationship between blondes, Chest size and IQ.    ::)

I'll have the water sprayers going on the condenser unit of my AC today. They seem to make a big difference to it's performance.  Got the draw down to 1Kwh per hour on the mains so pretty economical although I'd like to get it down more.
Balancing the input to the draw seems deceptively tricky however.

With the predicted temps, not going to worry. Will be very interesting to see how the grid holds up.  The energy authorities are predicting shortage of reserve supply so might be smart to get in early and get the house cool in case there is no power when the real heat hits.

Maybe a freezer I can make buckets of ice with I can sit in front of a 12V solar powered fan on days like this might be an asset we are reduced to.

ajaffa1

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Re: Ice air Con/ energy storage.
« Reply #11 on: January 18, 2019, 04:47:05 AM »
What about using an international freezer shipping container, they are insulated, run on 3 phase and pull about 32 amps flat out. A 20 foot container would hold a lot of ice, might take a couple of days to freeze but would store a lot of energy.

Bob

glort

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Re: Ice air Con/ energy storage.
« Reply #12 on: January 18, 2019, 05:21:34 AM »

Could be bit of a logistics problem there Bob.
I could not be too Critical if the mrs wasn't real happy about a 20 ft long freezer in the back yard.
$6K price tag might be a bit hard to get across the line as well.

Even at 16A x 3 phases, might be a bit much even for my solar proclivities.

That said, I could get another 3 Kw worth of panels on a 20 Footer.   :laugh:

ajaffa1

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Re: Ice air Con/ energy storage.
« Reply #13 on: January 18, 2019, 07:53:42 AM »
Sounds like that might not work then. Have you considered digging a large hole in the garden and creating an area of permafrost? This might sound mad but it would be cheap and the technology is proven to work. I believe they are using it in many places to form waterproof holding tanks to store oil, contaminated waste and etc. If you want to be very flashy you could create two, one hot and one cold, by pumping the heat out of one into the other. You could then have cold for summer and heat for winter.

Bob

glort

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Re: Ice air Con/ energy storage.
« Reply #14 on: January 18, 2019, 11:35:08 AM »


If one were motivated enough it's not a bad idea at all.
Be very easy to dig the holes, Put a membrane like pond liner in over a layer of insulation  and even drop in something like IBC tanks.  Be out of the way, naturally insulated all year round if you drop them below 6ft and be a cheap storage Medium.

I was thinking if I did a new Shed i'd look at putting a water tank underneath.  Might be more worthwhile than I though of.
even a decent ground loop would be worthwhile.  18 o here is warm in winter and cool in summer.

I was marveling today at the heat pickup just in the garden hose.
Had to wash something and the water was way too hot to put ones hand in.  I thought sitting there for hours in this sun, no wonder. Took a while to cool right off I noticed as well probably for the water to actually start coming from the mains.

The real amazement was when I went back 15 Min later and the water was again probably to the point of getting uncomfortably hot for a shower.  This really spun me out.  Sitting in the sun for hours is one thing but 15min in a light grey not even black hose and it's that hot??? Amazing.