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Forum Index : Other Stuff : Cold storage "battery"
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renewableMark Guru  Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Hey guys, just came across this youtube clip Now in my case the battery is chock a block full by early to mid morning and all the excess power generated from the 10KW array is wasted. What I was thinking of was a simplified system of that youtube clip. Basically 1 big chest freezer like this 300L unit then run some refridgerant lines into the house where a small radiator was fitted with a fan. ATM I don't want to buy more batteries, but being able to store cooling for the hot nights much cheaper than batteries/air con seems appealing. If you were paying for the power it wouldn't stack up, but in my case during summer probably 5-7 hours of production are not utilised and wasted. Has anyone ever done this small scale? Is it a waste of time small scale? BTW it was just planned to operate in a small bedroom that doesn't absorb the cooling from the rest of the house that well. Cheers Caveman Mark Off grid eastern Melb |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
I tossed this idea round last year with some people on another forum. A few points in no particular order that are in need of consideration.... Domestic Freezers have fairly small Motors, around 300W so aren't going to make a lot of use of the excess power you have available. As they are low powered, they won't freeze their Volume in 12 Hours which is the most you would want and preferably less. Looking at the machine linked and deciphering the Chinglish I take it this one has a 205W motor. With my off the top of head guestimate of thermodynamics, I'd say that one is going to take several days to freeze it's capacity. Water has a LOT of latent energy and 205 W is not a lot of power to throw at that amount of water. If you were heating it, that would be days, maybe a week if the thermal losses were nil which they never could be. For me I'd rather something that did 3 Kw than 300W but that's not going to be affordable or most likely of any practical size for the purpose. . It may be possible to get a commercial freezer with a Higher power motor but then you would probably be up for a lot more $$. I am not sure if it is possible to install a larger motor in a freezer because as I understand it, all the tubes, condensers, capillary etc need to be proportioned as a complete system. We questioned if you could fill a freezer full of water and freeze it. The consensus was the expansion could destroy it. As such you would probably have to use tanks of some sort, preferably somewhat flexible and put them in the freezer to give the water/ Ice room to expand. You would need a LOT of tubes inside the ice because once there is water in contact with the pipe beyond a Cm or too, the heat transfer from the Ice to the water can be very slow. I take it that is why the tank in the Vid had such a High concentration of tubing. Other commercial systems work on a Flat plate Heat exchanger system where the ice and the water used as the thermal transfer medium in in alternate closely spaced wafers. Freezing the water is easy, getting it to thaw quick enough to release the energy at a satisfactory rate is more the trick hence the need for a lot of tubes or wafers. One would need to use antifreeze in the transfer water because if the water in the tubes froze, which it would otherwise, the whole system would have to be defrosted to clear the tubes. The thermal energy in ice is some huge amount, 300X? More than in the same Volume of water at 1 oC. The temperature of the Ice is irrelevant, It simply must undergo the phase change from a Liquid to a solid. Once that is achieved, the thermal ( cold) storage is magnitudes greater than if the medium remains liquid. It's an interesting concept and one that for once would be able to make use of excess solar put toward something that was useable and appropriate for when you had it. I don't think it's as simple and straightforward as we would like but I'd sure like to figure out a way to make it worthwhile! |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Its x334 http://www.splung.com/content/sid/6/page/latentheat I have decided to just run with a small battery, and any excessive airconditioning demand comes off the grid. For me at least, doing anything else is just not going to be cost effective. Using say 10Kwh to 30Kwh at night for perhaps three or four nights per year, when we get several 40+ Celsius days in a row (in Melbourne) does not work out all that expensive. Cheers, Tony. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
Where I am, 40-45O days are far from unusual. The nights however tend to drop into the Mid 20's. The days are still quite bearable up until about midday then things start getting warm when everything inside and out heat soaks. I tend to run the AC flat out all day when there is plenty of solar to try and cold soak the place as much as possible. at night if the place is still too warm, opening the windows and pulling air in isn't uncomfortable. Sometimes I wonder about insulation. It can't keep heat out forever but once a place does heat soak it just makes it harder to get out. My first house was a Fibro Box that had ceiling batts retro fitted. It still got hot but was easy to quickly cool. No thermal mass as such and all retained heat was quickly removed. The back and North end of this place cops a LOT of summer sun and I'm going to look at having awnings installed to keep the direct sun the brickwork off which I think will make a difference. You can go out at Night and feel the heat radiating back out of those walls. although insulated, some of it has to be going inside as well. Also thought about a Chiller type system where water is sprayed on a radiator with air being drawn through and the hopefully Chilled coolant then pumped into the house through another radiator and fan. Not sure what the temp drop potential is, I think it is only a few degrees. That said,Last year I put Micro Mist irrigation sprinklers in front of the condenser of my AC. That seems to help a lot. Instead of the air coming out the other side hot, it's just warm so must be easier on the system and more efficient as well. Another hair brained idea has been to use the 3000L Tank on the shaded side of the house and recirc water through a radiator from there. I'm sure would be OK for a While but once the water heats up, how much heat will it loose again at Night? it's one of those tall skinny tanks so the surface area isn't bad, maybe a fan on that would help and or a water spray as well. The other thing I did was put radiator fans over the manhole which is in the laundry which blew air from outside up into the roof cavity. I can't say I have any idea if it helped anything or not. Every thing I have read says keeping the roof cavity cool helps a lot and my mate in AC also thinks the same and he's not one for believing in fantasy. The roof space is Definitely cooler with the fans which I power off a couple of old solar panels. The air exhausts at the highest point of the ridge capping which has a gap in the insulation which I take is intentional to allow the escape of Moisture and maybe hot air. As the panels are not suitable for my arrays, the fans I got for nothing and running them is free, I figure it sure isn't hurting even if it's not helping. Right now I have those fans at the end of the house blowing the days warm air in through a window which does warm the rooms which get no sun now but will be too hot in summer. If it wasn't so bone dry here for months, I'd say having the good airflow would help prevent mold and Mildew as well which has been a problem in other places I have lived. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Yup. We seem to be in agreement on a great many things Dave. I live in a very old weatherboard house in a wealthy snobby area. My home is about the oldest and crappiest in the street. But its VERY well insulated, and low thermal mass. Even the interior walls between rooms are insulated. I have four airconditiones and six gas space heaters, so I can selectively heat or cool whatever room(s) I am occupying. Even the back shed has a heater and airconditioner. It has a pitched roof with flat ends, so its very simple to ventilate the ends and let the wind blow straight through the roof space. That is very effective. I feel really sorry for my neighbors that live in brick ovens, with a pyramid style roof, and often very dark roof tiles.  Cheers, Tony. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
Yeah looking at the ability for the freezer to re freeze a large mass it doesn't look like it's a workable idea. Kind of thought that as no one else does it. Cheers Caveman Mark Off grid eastern Melb |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
At least this place has a Light green roof, faded even lighter. My neighbour next door just had an extra layer of insulation put in his roof and then had the tiled roof re painted Charcoal. First thing I thought of was about 2 ton of thermal mass sitting at about 80oC in summer. Good job it's the roof but I think that extra insulation won't go astray. He has a pretty small wood fire inside which he clearly loves and burns the thing flat out. Seems to be a thing with people with wood fires. They like to keep the winter temps the same as the summer temps they would Put the AC on to cool the place down! I know several people that do the same. Warmer in winter than what they would have the place in summer. This place has over 40 windows. I'd never have a place with so many again. Cleaning them is a pain to start with but being all single glazed, the heat loss or entry is ridiculous. I tried insulating some on the hidden shaded end of the house earlier this year with Bubble wrap but the Mrs threw a hissy and said she wassn't having the house look like a shanty and ripped it all out. I'd like to get onto a cheap source of perspex so I could fit that to a lot of the windows. Having them double glazed would be out of the question. It would be 20K Minimum and that will go a long way to heating and cooling at the rate I get billed for power. I like trying alternative low cost heating/ cooling solutions but I also live in a very upmarket area in a "fashionable" house and it is not easy to incorporate these things without detracting from the look of the place. There really are some Lousy design aspects of the place. If I built a place there would be many things I'd incorporate into the design the first one being a "Plant room" like my mate has were all the pumps for the pool and central heating boilers, HWS and everything else is located. I'd have a co-gen system to provide heat and power. Pretty surprised my mate hasn't put in a back up genny given how reliant his place and home business is on having juice and that he is well in the back blocks. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
It's certainly done Commercially and seems to be a growing tech given the availability of solar. Thinking about it, not that I know much, but every powerful freezer I can think of uses cold air to freeze things in a cool room. I don't know where there would be much call to freeze large amounts of water other than in an ice works. Perhaps a better way to go would be to have something like an upright freezer and have say a 44 in the thing with the coils running through. You'd at least get round the expansion problem. It may be possible with a bit of mucking round to fit an extra motor or a commercial compressor and fan unit. I think it is workable, just not particularly simple or straight forward. I was thinking about the expansion as well. If you didn't fill the freezer, it may be OK. You can fill an ice cream container with water and it does not split, tends to freeze from the outside in and push up rather than out. I haven't run the numbers on cold water. Rather than Ice, there may be a reasonable amount of thermal energy in 3 or 500L of just chilled water. Might be a lot easier to cool that than turn it to ice. If you have the compressor from a car AC, you should be able to run a long loop in an old chest freezer as the evaporators are normally set of tubes running back and forth with fins to make the thermal transfer area more compact. Once you get past the capillary every thing behind that is not critical. With a Car Compressor you could simply belt drive the thing with a 2-3KW motor and pump a decent amount of thermal energy into the water. I set up a Diesel Driven AC like this a few years ago before I had so much solar and it worked fine, it's pretty straight forward. all one would need to do is drive the system from an electric motor rather than an IC engine. I might see if I can find some tables somewhere that give the thermal energy stored in cold water and see what sort of volume would be needed to give a decent among of energy like 10KW or a bit more. I could easy divert 2 KW for 6 hours so 10 Kw would be good. In reality, for my setup, 3 KW would probably be better. Have to see how much cold water that would give me. Only thing I can think of with cold water ( and I think you could get it colder if you added salt) would be the need to stir/ circulate it to prevent localised freezing and a boundary layer around the circulation pipes. A Fish tank pump should handle that or an air pump in a tube with an angle to form a lift pump. I don't think it would need much, just to keep the water moving. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
That was easier to find info on than I thought! If we have an old freezer with a 500L volume and we have a temp difference of 20o C which would be water taken from 1 Oc to 21OC, that would give us a thermal capacity of 11KW. Quite practical and worthwhile. And this would still be water and easier to deal with. But it could get much better. If we add 120Kg of salt to that water, ( 6 bags of Pool salt @ $7 a bag roughly = $42) our freezing point is now MINUS 20Oc. If we say Minus 15 and take it up to 20Oc, we have a 35O difference which now gives a thermal capacity of a very nice 20Kwh. If we allow to go to 25 Which I think would start getting inefficient as the less the difference between the temp you want and the coolant the less heat transfer you get, that gives us an extra 3KW but it maybe hard won. Given we would need maybe 25KWH input from our excess solar as nothing is 100% efficient and we'd need to run a fan on the condenser as well, I think that would be all the excess most people would have anyway so whether we have ice or not is irrelevant. We would need a large Compressor unit to get that much power however so it would have to be the car AC electrically driven or probably a commercial Size refrigeration unit. The car compressor would I think be the easy to aquire and less costly option. The other thing that comes to mind is this could be fairly compact. Given the temp differences, I'd suggest something more like a car heater core than a radiator would do. That would allow the plumbing to be in 3/4 hose and the evaporator to be much more compact. A car heater core and fan would do Nicely. I would think it wise to incorporate a temp sensor on the evaporator for the same reason they are on AC units. If you were pumping Minus temp coolant through the heater core, you would easily freeze the core with condensate and therefore block the airflow. AC is usually set to get an exhaust temp of 2-5OC to prevent this. When the evaporator gets too cold, the Compressor Kicks out. The air warms the core again and when it reaches whatever temp, the compressor kicks in again. In this case all we would need to do is switch off the coolant pump, let the core re warm and off we go again. Simple, easy and cheap to do. The salt water setup would solve a lot of the problems and could easily be done in a conventional chest freezer although the thermal energy stored would be MUCH lower than if one used an AC compressor from a vehicle which from memory is usually around 3-4 Kw depending on the actual compressor size of course. It may be possible to run a 200W compressor for 8 Hours but that would only be an input of 1.6 Kwh and hardly worthwhile from any perspective. I think I'll grab some AC systems and give this another go. Pretty sure I have a 2HP single phase motor up the back, I can always gear it accordingly to prevent overloading even if the compressor is not going flat out. My 5Kw 3 Phase running on 2 Phases may also be up to the job. Edited 2019-08-28 21:23 by Davo99 |
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mackoffgrid Guru Joined: 13/03/2017 Location: AustraliaPosts: 460 |
Can someone check my logic. Just hypothetically, If I freeze a 100kg of pure water to cool a room at night. The energy from the phase change is 100 x 334000 Joules = 33,400,000 joules If I run a small split air cond it may consume 500 Watts to maintain comfort. That aircon may have an EER of 4 so lets say its equivalence to ice is 4 x 500W = 2000W To compare the block of ice, I divide by 2000, then to get hours of use I divide by 3600. Equivalent hours comparing 100kg ICE to aircond = 33,400,000 / (2000W x 3600 sec per hour) = 4.64 hours Does this sound right? Cheers Andrew |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Some useful definitions and numbers: https://www.nwnatural.com/uploadedFiles/ConnectToGas/StepsToGetGas/FAQ/FAQs_The_Definition_of_Cool.pdf One kilowatt-hour (kWh) of electricity contains 3,412 Btu. One ton is equal to the amount of heat required (288,000 Btu) to meltone ton of ice in a 24-hour period. A one-ton air conditioneris rated at 12,000 Btu per hour Cheers, Tony. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
If I understand what you are comparing Correctly, 100Kg of ice is 9.3 Kwh. Running The AC with an effective 2000W cooling capacity for 4.64 hours would give 9.28 Kwh of cooling capacity so Yes, the figuring as I understand it is correct. The thing of course being that in fact over that period you would be using only 2.3 Kwh of electric power. |
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| mackoffgrid Guru Joined: 13/03/2017 Location: AustraliaPosts: 460 |
Thanks guys, now that you mention it I have heard of the one ton air-cond. Nice to see the back of envelope math wasn't too far off. Night time cooling is important to me as I can be a poor sleeper. In Brisbane, I finally put a little split into my bedroom last season and I generally slept very well. (I used to leave the big lounge Aircond running through the night, it did a poor job and costs heaps) Night time air conditioning is obviously a problem at my off-grid property. So some years ago I did ponder about freezing Ice for night time cooling but my lack of knowledge in the area persuaded me to drop it. I'm hoping that if I do a conversion of a car to electric that the batteries would be big enough to run a couple of small splits over night. If some one works out how to do the Ice thing then its just a matter of adding more solar panels to run more compressors ..... Cheers Andrew |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
Like I pointed out above, I don't think for this application going to ice is necessary. 20Kwh would be a decent amount of cooling if one is looking at it from a Night time perspective. I'm not sure how the cooling side works efficiency wise. It was mentioned above it has 4x EER and if that is so ( I know heating has more output than input) then to get to 20 Kwh cooling one would only need about 5Kw of panels on the job to produce what should be about a 6X KWH ratio to give 30Kwh a day. If you threw 10 Kw of panels at the problem, then you have 40Kwh of Cooling and with that you can open a cold stores facility! The way I see it Ice while giving higher storage density is fraught with problems from A diy perspective. Using Salt water however and the ability to take it to well below zero would make for a less compact but still very workable storage. Large 500L Freezers are not uncommon and certainly not overly bulky and with the addition of around $50 worth of salt as a once off, would provide a good amount of cold storage. Just looking on Gumtree I found Units of 500, 600, 700 and a couple of 1000L commercial size freezers so the unit size is available. No reason why 2 Smaller units couldn't be plumbed together either. I also found a stack of fridges. If these were laid on their backs and the drain hole sealed with some silicone if they were frost free models, no reason these couldn't be used as well. I don't know if the insulation is any better on a freezer but I'd suggest any difference isn't going to matter in this application. Wouldn't be hard to get some of that thick sheet construction Styrofoam and build a box of that around the unit and increase the insulation dramatically. Every time I go past a scrap yard there are stacks of fridges and freezers there so I'd suggest that acquiring a suitable unit shouldn't cost more than $20 as that would be miles above their scrap price. Not like it needs to be running. You could cut the Motor out and leave that at the yard and the thing would only be worth $10 For the cabinet which is all one would want for this idea. One other thing came to mind, If you used a fridge on it's back and it had a freezer section, if the cold brine was kept on the larger fridge size, there would be enough cold to make the Freezer section at least a fridge. If you just ran a loop of pipe and sealed it from one side to the other, you'd probably have enough cooling for a freezer again long as you didn't raise the brine temp too much. Unlike solar heating that has the lowest availability when you want it, solar cooling allows you to make use of the energy in a way that you have the most when you want it the most. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Or you could just use a small electric start petrol or diesel engine to run an automotive airconditioning compressor directly. Hook that up to the indoor half of a split system. It could all probably be done with secondhand parts quite reasonably. Cheers, Tony. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
Yes that was what I did before and it wasn[t hard and worked well. Just used LPG for the gas and measured the pressures rather than the weight and it worked well. For this setup I wanted to make use of the excess solar I have in summer. Could just run the Ducted AC but I can't offset one leg of the 3 phase with that and this would be an interesting and practical project which I could probably learn a lot from. One thing with the engine driven version would be the ability to make a very efficient Reverse Cycle setup for winter. One could use the waste engine heat and exhaust heat through the condenser to elevate the ambient temp and get a much better output. Would only require a reversing valve to be added in and some ducting for the heat from the engine. Shouldn't be all that hard to do the setup and then have an IC and an electric motor and have them each side of the compressor so all one had to do would be change a belt. Could use clutches as well but simpler, easier and cheaper just to move a belt given how infrequently it would need to be done. I don't know about that. Talking to my fridgy mate recently about my Ducted system, he was telling me it all had to be matched, including the fans on the condenser. I wanted to put extra fans to push though more air and get better efficiency but he was very cautious and said If I pulled it down too hard and got Liquid coming back to the compressor it would blow the snot out of it instantly.... which makes sense. That said, from what I have looked up, car compressors are pretty close in output to mid size AC units so it may be just a matter of matching the compressor to the rest of the system. I Imagine varying the gas pressures could allow for adjustment as well but that calculation is well beyond my knowledge. I'll ask him when I see him next but he's a bit hard to get info out of like this. He makes a LOT of money and doesn't see the point of any DIY or hackery being far more " Just go and buy a split and be done with it." type. Some people have no sense of adventure!  We are very far apart on outlook of things. I'll cobble something together and it works and I'm happy no matter what it looks like. He has to have everything working AND looking like a Million bux as well. He has said many times, You do things that everyone says wont work and it works perfectly but Geez it looks like sh*t! I'm trying to improve the aesthetic aspect of what I do. Yes, very much so. I'll try and pick up a compressor and the evap and condenser out of a car this weekend. Getting the condensers out is always a pain but I'll see what I can find. I had the setup working before but I tossed it all out when I came here. Made a LOT of mistakes throwing what I should have kept and keeping stuff I now wonder why the hell I did! The only thing I can see may give a bit of difficulty/ Cost is the hoses. Automotive tends to use bolt on O ringed flanged where Domestic AC tends to use flare joints or Soldering. Copper is easy to run and I'd guess much cheaqer than flexible hose but marrying up the fittings may take some working out.... or it might be really simple. Just thinking that everything I see on Automotive AC is aluminium which does not braze up well to copper. I was just looking at replacement Refrigeration Compressors. Firstly they are not cheap. I think $500 would be a minimum for the size to be near useful. That said, they don't seem to specify current draw on single phase units that I could find instead of going by LRA which doesn't say much about what they are pulling. I also saw they specify 3/4 HP etc but I'm not sure if that is the Current rating, 754W or the cooling capacity or..... Probably out of the price range anyway. If I had to spend $500 I'd spend another 500 and just buy a split and set it to Freeze during the day and be done with it. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Refrigeration compressors are outrageously expensive, and a split system with a dead sealed unit compressor would be worth only scrap value secondhand. As you say, automotive compressors are about the right size for a mid to large sized domestic unit. How about belt driving an automotive compressor direct from a fork lift dc electric motor ? Cheers, Tony. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
I can get any amount of those I want from my mate whom owns an AC company. He has an area at the back of his property where he strips the things for Recycling. It really is like a scrap yard with what he gets especially the big industrial stuff he does so much with. I very much like the idea, not sure of it's viability in practice. I have been tipping Blackouts here in NSW/Sydney this and coming summers. It would be great to have an ac unit I could run from solar. That said, setting up for what I think is going to be 48V would be a pain as I'd have to parallel connect a LOT of panels. The other thing would be driving the motor from 240 To run at night. I'd need a forklift battery charger to supply enough current for that as well. I have not priced forklift motors but I'd be very surprised to find any in the bargain category rather than the "Sorry, HOW Much did you say " department. Then there would be the problem of switching which I'd probably need something from a forklift to handle. 5KW is only a bit over 100A @ 48V but the voltage would probably make relays expensive. Might see if I can remember to look some places up and give them a ring tomorrow and see how much they laugh at my silly questions. |
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| renewableMark Guru Joined: 09/12/2017 Location: AustraliaPosts: 1678 |
You can get PM treadmill motors in 2HP, they are often 180v DC like this Cheers Caveman Mark Off grid eastern Melb |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
He probably thinks you are completely wasting his time on pointless rubbish.  My experience tends to agree with that, I have fitted an inverter split system to a house for $500 and with intelligently installed insulation that does not heatsoak we got the space holding 22 C @ less than 250 watts on 40+ days. It was a case of more thinkin and attention to detail and researching house design rather than just bunging a cooler in. there are techniques and tricks to get that under 100 watts but you have to manage the liquid to water vapour phase change on both the evaporator and the condenser. That takes some science on the condenser side that is out of my comfort zone. It looks very similar to distilling booze but in a closed cycle and with water. I'm confused, no wait... maybe I'm not... |
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