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Forum Index : Other Stuff : Cold storage "battery"
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renewableMark Guru  Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Yahoo, the idea was to store a form of energy cheaper than batteries with power that was normally going to waste (in summer excess PV production). Probably doesn't appear sensible on a small scale. Anyway I have seen your various efforts on home efficiency. How would you retrofit insulation into a brick veneer home that only has the concertina foil in there currently? This stuff looks like a good idea. Cheers Caveman Mark Off grid eastern Melb |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
I am away till tomorrow night. Give me a bit of time and I can give you a considered answer. brick houses with cavity walls are tricky. insulating the cavity can be a disaster if its done wrong. Storing energy as cold is doable but if the space is not great at excluding heat it will always struggle. People usually leap straight to insulation but that is number 4 on the list of priorities. I'm confused, no wait... maybe I'm not... |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
The " Noble" answer with any of this is always to improve insulation. That would cost 10's of thousands on this place, at least and probably mean tearing out walls and to be in any way effective, would also require the addition of double glazing to the over 40 windows and doors the place has. The place was built a bit over 20 years ago and is insulated for the standards then which isn't bad but probably not up to ideal now. While not the current flavour of the month, the fact remains using the solar I have to heat and cool the place will still be very much cheaper even in the long term than the considerable costs of Insulation I have severe doubts would even be mentioned come resale time. I'm paying under $1000 a year for power atm. If I spent even 20K to add insulation and somehow halved my power power bills which insulation would not do because there are other things than heating and cooling, then the payback time would be about double the time I give myself as a life expectancy. Of course I'm also thinking I'll be moving on from here in about 10 years or so thereby making the insulation investment even less worth while. If need be, I still have considerable roof area I could put panels on, not that I could ever see the reason to do that either. I was going to do an oil heater for this winter but never got round to it. Taking the heating off electric would give us more than enough power all year round anyway and make the bills as low as they could be. I don't mind paying for a service like power, I just want to minimise what I have to pay for the convenience. |
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| ryanm Senior Member  Joined: 25/09/2015 Location: AustraliaPosts: 191 |
I don't think salt would be a great thing to use as anti-freeze in this system for the same reason it's not used elsewhere. It's corrosive. I think at 24% solution by weight it would eat through even stainless and copper fittings. Plus so close to saturation there are going to be crystals forming in the solution which would make it worse with abrasion. Specific heat of water is 4.18J/g compared to a latent heat of fusion of 334J/g, so melting ice is approximately 80x more efficient space/volume wise. |
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| ryanm Senior Member Joined: 25/09/2015 Location: AustraliaPosts: 191 |
I currently have plans to make a unit like this, but I have more schemes than I do time so it's probably at least twelve months away. I've already sourced a couple of 2.something kW box units for the ice making. The thought is multiple smaller units will give redundancy. Before then I've got at least one F&P windmill planned. I have a slow, but reliable breeze that kicks in at 9pm with clockwork precision, so if the mill puts out enough power I'll just throw up a couple to run a small split system. I do have grid power as a backup as well. It's more the challenge than any potential savings that motivates me. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Yes, this might be a consideration and worth researching for it's effect on those materials. Perhaps it may be possible to replace the parts of the system that come into contact with the brine soloution with that hard plastic Pipe like air and water line tube? The other possible additive could be methanol. Not as cheap as salt but at 40% in water gives it a freeze point of -23 and at 50% is -36oC. Given the higher freeze point at 50%, it works out the same having 500L of 40% as the thermal energy storage with 500L @ 50%. The efficency of the cooling unit would I imagine be falling off a lot more at - 35 than - 20. Bought a lot of Meth in my Biodiesel making days so know where to get that, the price will be a factor however and it requires a lot more precautions in handling than salt that's for sure. I wonder if adding a lower amount of salt to the Meth would lower the freeze point some more? Copper may be a bit touch and go but I think stainless would be OK as it's used in acid applications. Something I'd have to check. I was planning to go a bit lower on the salt concentration, around 20% to hopefully stop any fall out forming and possibly crunching in pumps etc. And that as far as I can see is the only benefit in going to ice. A 500L fridge or Freezer, or 2 of them would not be an inconvenient amount of volume for me to accommodate. I was in fact thinking about using an IBC If I could get some coolroom panel or the thick construction foam blocks to insulate one with. I have a Number of IBC's around the house now and 2 where I would locate this system. All I'd have to do is lift one up and box it in with the foam/ coolroom panel. From what I have seen, commercial ice systems need a lot of heat transfer area in order to stop the melted ice insulating the cooling pipes and allow a fast enough melt to occur. By staying with a liquid the piping and a lot of expense and other complication could be eliminated. |
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| zeitfest Guru Joined: 31/07/2019 Location: AustraliaPosts: 375 |
There is development using liquid air as energy storage. The air is liquified using excess energy then stored in an insulated tank. When required the liquid air is then boiled using waste /ambient heat to drive generators etc. There are economies of scale too. It would be great here, instead of an aircon the liquid could simply be evaporated in the room where cooling is required. I think small liquifiers are feasible, a Dewar tank (like a large Thermos) might be expensive though the price has plummeted from what used to be. ed- Some cheap Peltier devices from the net could be used to regenerate a little power easily too. Edited 2019-09-03 20:28 by zeitfest |
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| ryanm Senior Member Joined: 25/09/2015 Location: AustraliaPosts: 191 |
I don't mean to be straight out negative, if you think you've got a new way of looking at a problem go for it, but air liqifies at -194.35C according to wikipedia. That is so far out of our (at least my) capabilities it may as well be a space laser. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Well, I for one would get throttled by my wife if another project this scale gets started, but here you go if inclined. https://www.instructables.com/id/Homemade-liquid-nitrogen-generator/ Cheers Caveman Mark Off grid eastern Melb |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
There is also the old technology of water ammonia absorption refrigeration. Back in about the 1930's to 1950's people were buying refrigerators powered by a gas or kerosene burner. This was after the old melting ice block domestic coolers and before the electric age and grid connection and mechanical refrigeration. Its basically a completely sealed system, without any moving parts, you heat one part of it with a flame burner, and it gets really cold in another part.  When I was a Technical officer working at the Victorian Solar Energy Council, we (the Victorian State Government) sponsored an experimental solar powered absorption airconditioning system. It worked quite well in a mid summer clear blue sky, but even the slightest cloud and it would stop working. It was also a very expensive installation, and was eventually scrapped as not working consistently enough to be practical. But it told us one thing. Something can be successfully engineered, but it may be just too expensive and too complicated to justify its existence. Cheers, Tony. |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 814 |
They are still using the old ammonia cycle fridges for caravans with 3 way fridges (240v/12v/lpg), but with modern soft-start fridges and solar panel/lithium batteries becoming the standard, they are being dropped in favour of 'standard'household fridges on inverters instead (I went to the Brisbane Caravan Show, and the number of vans there that are coming with lithium batteries and rooftop solar as standard is staggering, L/A is really only found on the 'povpack' base models now) |
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| ryanm Senior Member Joined: 25/09/2015 Location: AustraliaPosts: 191 |
Davo, Feasibility of implimentation aside for a moment. Here are my calcs on your methanol based idea using just a temperature deta and no ice. Actaully works out better than I thought it would truth be told. Some of the numbers I've put in might be a bit different in real life and I think getting even 70% efficiency out of the storage is probably a bit high, but at least it's in the right ball park.  |
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| ryanm Senior Member Joined: 25/09/2015 Location: AustraliaPosts: 191 |
Those old three way fridges are nifty. It nearly broke my brain when I was a kid and someone told me you could keep food cool using a fire. Doesn't really solve this problem though. You're still getting the cooling in the middle of the day when batteries aren't a factor. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
And this is the key point I try to bear in mind with my hair brained ideas. Does not matter how much better, more efficient, longer lasting whatever, if I can't build or complete it or if it requires more expense that just doing things the conventional everyday way, then it's no good to me. I know what I'm proposing is far from the best solution but it is something I believe is manageable and doable for me with my skill set and limitations. Also importantly to me, the setup I am thinking of is practical from the POV of where I can locate the thing and set it up with the layout of my Home. There are many Ideas for different things but putting them into action and setting them up to work with ones home layout is also an important factor to me. |
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| ryanm Senior Member Joined: 25/09/2015 Location: AustraliaPosts: 191 |
If someone were to pursue this idea I think the best way to get a cooler by far would be to find a secondhand glycol chilling unit of appropriate size from a pub or nightclub. Probably a bit tricky to find one available at the right price. If you had the skills you might be able to get one that is broken and harvest the heat exchange block out of it to use with another compressor. Excluding that there are already people rigging up DIY chillers for home brewing and computer overclocking. It doesn't take much effort to modify an old box type air-con into a chiller, example with lots of pictures . At least around where I am these type of air-cons are generally available for $50 or free if you come and get rid of them for the owner. Combine that with an old de-gassed freezer from the tip and it's a fairly cheap setup. Obviously if you have reliable access to grid power a cheap split system is always going to be the most cost effective option. Edited 2019-09-04 14:13 by ryanm |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
Hi Ryan, That's a much more scientific way of calculating things than I did it but still looks good. I thought my numbers might have been a bit High but then I saw you were working on a temp differential of 40 being -20 to +20 which would go a long way to explaining the difference. Mulling the idea over more, I have also had the idea to Bury an IBC for the storage tank. I have a suitable location in a presently disused garden bed I might just grow over with lawn anyway and if I inked the hole with coolroom panel or building foam block, that should provide insulation and lower the temp differential to outside the tank than if the tank were located above ground by a substantial amount. If I used the tank for heat storage in summer, then again the temp differential is for the most part going to be less than if the tank was above ground especially with the sub zero winter temps experienced here even less than a fortnight ago. Never know it today being over 25 and bright sun. Does highlight what I was talking about though, Miles of excess solar. I noticed your calc works on a 5.2 KW output. If I doubled that for 1000L capacity and added another 50% to allow for a 40o temp difference, call it 15 Kw Input, I still have power to spare well and truly above what the rest of the demands are in summer at least. To be remotely Viable in winter I would have to go to Diesel power for the compressor but that is not really a great issue either. A water cooled engine could be enclosed for sound Proofing and the excess exhaust and cooling heat fed back to the system for a very good efficiency. |
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| ryanm Senior Member Joined: 25/09/2015 Location: AustraliaPosts: 191 |
From what I've read of other people building chillers normal AC compressors start to struggle below -10. Still work, but are not very efficient. That's why I've used that figure. 15 on the top because if I'm going to all this trouble to cool a room I want it to be about 20C and still need to leave a few degrees differential. I intend to make a DIY version of this using scrap materials for pretty much everything except the copper piping, insulation and control circuitry. If you're looking to heat in winter burning firewood directly would surely be cheaper to run than a diesel generator? |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
That is the problem, the (COP) coefficient of performance drops like brick with reduced evaporator temperature. Many people have starry eyed ideas about using salt or glycol mixtures to reach lower chilled water temperatures. But the reality is, straight ice, and straight chilled water is still going to be the most thermodynamically efficient on the chiller side of the system. There is a very big difference in working out the cost effectiveness of a commercial system that is working near full rated capacity every single day, and the do it yourself hobby project that is only required to provide cooling during the occasional heat wave. Cheers, Tony. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577 |
The ice bear idea was what got me started on this. I think with solar it's a great way to go especially for people whom may not be at home during the day and want to offset their power usage. I get the idea the commercial product would not be a cheap investment however. I don't know about the ability of compressors to work below -10. My thoughts are it's got little to do with the compressor, it's more to do with the way the evaporator is set up but it's not something I'm knowledgeable in or haee looked up. A second thought is it may be possible to boost the cooling power if need be by playing with the internal pressures of the system. I would use LPG as the refrigerant and that only takes half the amount by volume roughly to achieve the same pressures as R-134a. I'm thinking car systems which are not designed to go to sub temps in the evaporator but certainly will ice up Which is undesirable in their application as it blocks the evaporator fins. Again, the only advantage is see with ice is the ability to store more thermal energy in a smaller space. as that is not so much an issue for me I feel the Fridge / IBC tank would be adequate for my needs. What sort of capacity are you thinking of building your Ice system? I was thinking of an indoor fire but it's aesthetically appealing and that's about it. My father has an indoor slow combustion fire and it's a right pain in the arse. It is VERY efficient though. I sweat when I'm dropping the trees and then taking the limbs off, I sweat when i'm lifting them with the tractor and putting chains round them, I sweat cutting the things into rounds, I sweat splitting the monsters he has, and I certainly sweat stacking up about 3 Cubic meters of timber at a time. The wood heater keeps me REAL bloody warm even when I'm 500M away and the thing isn't even Lit!! I think a diesel engine would work out more economical than electricity. IF I got it up to say a modest 50% efficiency with the waste heat and multiplied that by a factor of 3? for the EER That would be 10KW of power in a litre of diesel, halved which would be 5 x 3 would be 15Kwh of heating for say, $1.40. Power here costs me .30C Kwh so that would be the equivalent of $1.50 worth of power for the same heat factor so I wouldn't be any worse off. If I can get the efficiency higher, I'd be better off again. The thing is, I have been running vehicles and diesel engines on Vegetable oil for 16 years next month. That's free fuel so is rather efficient. None the less, you may be right and give me food for thought. I was intending to convert a 100Kw spa heater to veg oil and use that for heating. It does pose a bit of a problem in getting the output down low enough from the burner. 200,500Kw burner is a walk in the park, built loads of them. A 5 Kw burner which is around half liter an hour is a different thing. It's much harder to make something reliable and consistent and have the control although I I have been playing with that recently and believed I have cracked it. None the less, If I up that to 20Kw output, 2L an hour, it's much easier again. I could tap off an amount of heat to go directly to the house and have leftover to put in storage. Realistically, I could make the output anything I liked for more heat, faster reserve warm up etc. Fuel delivery is not a problem and as long as the water flow through the HE is sufficient then its all good. Quick calc shows taking 1000L of water from 25 to 85 @ 10Kw will take 7 Hours. Allow for inefficiency, lets call it 9L of fuel and round that up to 10. If I am diverting say 5 Kw to the house all day, that's 15L day of oil. Less than my vehicle uses on average per day so easy accommodated. Fortnights worth heating out of a 44 gallon drum. No problem at all. But I think that's way over kill as that 60o heat rise with 1000L of water is 66KWh. Given I'm I'm already heating the house during the day before I shut the burner down and the place will be virtually heat soaked in the walls, furniture etc, I'm going to be lucky to need half of that heat at night. Yes, this part too is very practical and doable and I think your suggestion of a direct burn rather than an engine is a good one. I was just thinking of a co gen setup but can't see I'd need it. With the heating load taken off the solar, my numbers for this winter just gone would suggest I could have more than enough power even if I leave the Hot water on electric. This is looking better the more input I get with it. Being able to use it " Reverse Cycle" as it were with a non electric heat source in winter would really be the icing on the cake over an ice system. Having the 1000L reserve would make all the difference. I'm also just thinking of where I would bury the tank. There would be some heat loss and I think this would keep the ground above warm. Perfect to throw a small greenhouse over and grow Vegetables over the winter. This really could be a VERY worthwhile system! Biggest single expense I can see here is Hiring the excavator to dig the hole for the IBC and as that will take about an hour if that, may as well sink 2 for good measure. actually easier than digging say a 1200 sq hole to dig one 1200x 2500 as there is much more swing for the boom arm to travel. With 2 ton of thermal mass, I probably wouldn't need much salt or booze in them anyway. 20 o heat difference on 2 ton of water is 27 KWh of cold storage. -5 would be about all I'd need to achieve. 60 o for heat would mean I'd probably only have to fire the Burner in winter every 2nd to 3rd day. I'm really liking this idea! |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
I have one of those 3 way fridges in my caravan, it works really well, the freezer section will make ice blocks just as fast as the home fridge will. It's amazing what a small flame makes it work, it's literally just as small as the pilot light in a gas hot water unit. There is an idea for a combo appliance, HWS and air con in one. That pilot light could be used to run the absorption fridge. Cheers Caveman Mark Off grid eastern Melb |
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