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Forum Index : Solar : Deciding if I should build this solar heater
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| rogerdw Guru  Joined: 22/10/2019 Location: AustraliaPosts: 852 |
I am inclined to agree with you on that Dave. I need to drag a spare pv panel out and start comparing. I guess I need to provide a load for it too ... otherwise it's no different to me letting the heat build up in my tubes ... and not blowing it out. Haha, I don't think we have one of those at all. I do have a couple of heat guns, but I'm not ready to canablise one of them yet. Should be easy enough to find an old blow heater I hope, just gotta go out and look. Cheers, Roger |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Dead easy in fact. Solar pumped hot water systems just use a differential temperature controller. As soon as the outlet manifold rises a couple of degrees higher than the water in the storage tank, the pump starts up. And then stops when the temperature gain falls to zero. It just cycles on and off on a marginal day, and runs flat out on a good day. Cheers, Tony. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Hey Roger, do you have any really big wire wound resistors in your junk box ? Cheers, Tony. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I suppose you could put an unmolested fan heater (or hot air gun) into a big box, and just let the air circulate within the box. Then feed your big pipe into one end, and have an exit pipe at the other end. No need to totally destroy anything to try that. Cheers, Tony. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Whoops ... and here I am thinking microprocessors, thermistors, digital displays, controls ...  I do have a few. What sort of resistance are we talking about? I also have 7 or 8 rolls of nichrome wire for diy if I get desperate. That's quite true and should work fine. Now I just need the cloud to go away ... or be totally consistant so I can get a shot at doing the test. This may be harder than I thought seeing it can change 3 degrees in one minute!!! Cheers, Roger |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
Yes, I did see that now you remind me. Is there a specific type of PCM you would use or is readily available? I looked into phase change a while back with regards to cold storage. Like you mention, Ice stores magnitudes more cold than the same volume of water and it does not matter how cold the ice is, as long as it's Ice, IE, Solid. It's the going from a liquid to a solid that is where the gains are. I am unaware of your home layout and available space but water holds a fair amount of thermal energy as well. That's why I suggested the Intercooler/ car heater core to blow the air through and transfer it to a tank. My suggestion with the storage would be to first determine the heating power you will have available. When the cold does come, you may be using it all keeping the house warm through the day or there is like 5 Kwh which may not be worth the effort. It's not the temp rise you get, it's the total power that counts. If what you generate is able to be stored in an old water heater or a Drum wrapped in insulation and plastic, no need to spend Big $$ on exotic materials just to have something a bit smaller in effect. No Idea how PCM works but seems to me the heat you will have will be low value or whatever they call it... Not Very high temps. In other words you will be trying to store the heat at low temps rather than being able to in the case of PV, have an element that keeps raising the temp of the storage medium to 80C or 150 or whatever. You may be trying to store large amounts of 30 C heat and there would not be any way to get more energy in through higher temps. Just might be a case of higher volume of thermal mass. Again, Don't know how the PCM works but maybe you'll be better off trying to heat water to say 30 O and drawing it down to 20 and using a supplementary heating method from there? |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
There are a number of commercially available products that can be bought at great price. There are some that come in big sheets with capsules of the PCM ... look like large versions of strips of tablets or capsules you get from the chemist. These can lay on the ceiling under the insulation, in the walls or under a wooden floor. Here's a quick visual plus an overview This article also suggests that "In Australia, expect to pay between $55 and $110 per square metre for PCM" You can also buy containers of the stuff ... like 860 x 470 x 27mm ... which can be stacked to create a large mass. Like large versions of our freezer cold packs. Some has been packaged into tiny plastic balls that can be used in concrete or in wall cladding. PCM's can be made from various salts, or paraffin wax, or even various mixtures of oils like coconut oil. Almost sounds like DIY ... but when you look into it, it seems either complicated or just expensive to buy the raw materials. And of course they frighten you with suggestions of fire risk and costs of doctoring it to make it safe. Yes, I think most uses for it are to keep things cool ... but it works exactly the same way to keep things/homes warm. I had a chat with a supplier in WA today and he was quite helpful. But he also pointed out that to use their 29 degree PCM in the plastic containers mentioned above ... that you need around 40 degrees of heat to 'charge' it to add the energy. Of course my results so far have only been up to around 30 degrees under good conditions ... so I may not have enough heat to use PCM. While discussing what I was doing, he suggested I may gain a lot higher temperature by simply slowing down the fan ... which does of course make sense ... ... and add to that, the fact that I want to use 18 tubes and not just 6. That must raise the temperature somewhat. It's a pretty big spread out house on a large block (4.5 acres), so plenty of room really to try a few things. While I agree that water or a pile of bricks can hold a lot of heat ... PCM can hold up to 10-12 times more energy. ... I recall reading where a one inch thick PCM wall cladding, can hold the same amount of energy as the same height and width of bricks 24 inches thick. From the link mmentioned above ... I'm also realising that I'm not really all that confident in my understanding of PCM either ... so I need to do some more study.  You are quite right, that is something I need to work out. I learned two things from experimenting today. After talking to the PCM guy I was trying to work out what sort of improvement going to 18 tubes would make. Could I get up to 40 degrees? Rather than trying to add another 6 tubes to my existing 6, I decided to cover over 3 tubes to halve my array and see what happened. The temp dropped from 26.7 down to 24.6 over about a minute. Then I removed the cover and it took three minutes to get back to 26.7 The second came after I did the school run and had the fan off for nearly 2 hours. At 4.48pm the temp in the outlet manifold with no fan on was (coincidently) 26.7 degrees still ... though at that time the sun was way off to the side and quite low. (this heat comes from the warmth rising from inside the tubes and hanging in the manifold) Turned the fan back on ... 4:48 ... 26.7 4:49 ... 53.3 ... took 1 minute to climb to this 4:50 ... 52.6 4:51 ... 47.5 4:52 ... 43.5 4:53 ... 38.1 4:54 ... 35.3 4:55 ... 31.4 4:56 ... 29.1 4:57 ... 27.3 4:58 ... 24.9 4:59 ... 23.1 If you check out the position of the sun at 4:50 ... clearly it can't be providing much energy to the array ... so all that heat that took 10 minutes to draw out must have been added over the previous 2 hours. The tubes are a great storage device. So to get higher temperatures, I need to add more tubes, slow down the fan ... or turn off the fan intermittantly to give the tubes a chance to catch up. Sun position at 4:50pm  Cheers, Roger |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
I got to admit, I'm having trouble getting my head round this stuff. A tank of water or a pile of bricks the heat can be directed into and then recovered. Lining ceilings with it and having to activate it at 40 o is escaping my comprehension atm. Yes, also what I was thinking and had in mind with regards to the actual KWH you can get out of the system. I can measure the flame from a match at 1000C but it's not going to do anywhere near the actual heating as a fan heater outputting 180o C but as a much larger total energy. To that end though, just using a thermostat may be all you need. Modern AC is variable speed on the compressor, the old systems just kicked it in or out and it ran flat out all the time. I'm thinking if you had a Thermostat probe strategically located, you could set the temp to say 25 and just have the fan kick in and out as the heat built up and then drop out when the temp fell off. Pretty much what I have been using the last week or so with a fan blowing the warm day air in. If it's not above 21 Outside, the fan does not run. When it is warmer than 21, fan pushes the warm outside air in. The only thing I can see with this idea is you'd have to have the sensor somewhere that could detect the escaping heat from the tubes or have something like a computer fan running inside the manifold to average out the air temp. As far as over heating the house, Maybe those solar controllers for water would work? Not sure exactly how they function but they list a high and low temp so that should work. If above this temp kick in. If above this temp on this sensor kick out. Pretty sure I have some bare Chinnah Boards that have this function as well and cost like $5-8. controller 1 Controller 2 More tubes will raise the temp for a given amount ( weight) of air. I think it would be far easier to control the temp by running the fan intermittently than trying to speed control it. That said, anyone knows of a reasonable cost controller to do that I'd be very interested myself. At this stage I'm still wondering exactly how you set it up to charge and discharge it as it were and how much heat you will have available to store. I'm seeing it a bit like Solar PV and Batteries. You have to cover your use and have spare to charge the batteries with. If you only have 3 KWH a day left over, then the cost of the batteries is not viable to recognise a ROI. Much the same as this. If you have say 15Kwh day you can store, you can do that at 45o in a 400L water heater tank you can probably buy from the local scrappy for $20. Not like you are going to otherwise need 3 1000L Ibc's sitting round. I'm mainly stuck on how one would set it up to store and then remove the heat relevant to your application. Given your testing numbers, seems in fact you can and with only 1/3rd the tubes you intend using. The question remains what is the total output going to be in KWH that you have to store. That's it! Switching the fans on and off I think will be the simplest and cheapest way to do it. The temperature ( voltage) can be increased letting the tubes accumulate energy. Adding more tubes will be the wattage you can get out of the setup. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Once you get some kind of electric heating element rigged up, you will then be able to get a meaningful number for actual solar heating power. Its then possible to see how much difference there is between low airflow/high temperature gain, or higher volume airflow at a lower temperature gain. I believe the high airflow solution might be better. Not only should the tubes give a slightly higher heat flow, there should be lower heat loss along the length of hot air ducting back to the living space. How about measuring room temperature, and comparing that with the hot air in your manifold, and run variable fan speed to maintain a low but fairly constant positive temperature difference. A controller for this should be pretty simple, once we can work out a control strategy after some testing. Cheers, Tony. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
I started to write an explanation but got in too deep ... I need to do more research and work out how to explain it better. Yes, I think that would work. It probably doesn't need to be too complicated. How has that worked for you. Is it beneficial do you think? As far as temp sensors ... I'll need to ... monitor my room temperature monitor the air outlet duct (to make sure the air I'm pumping into the house is warmer than what's in the house) monitor the air inside the outlet manifold (to know if it is worthwhile turning on the fan) If heat is building up in the tubes and floating out the top and reaches a certain temp ... then the fan will run and will need to monitor the air outlet duct temperature. If the heat peters out, then the fan will be turned off ... if not, it will stay on until the outlet temp gets lower than room temperature ... ... or possibly also until the room gets too hot. I spent a bit of time looking at those. I'm sure one of them woulld be a good starting point. To start with it quite likely would be ... but today I tried slowing the fan down somewhat ... and saw the temp go from around 25 up to 40+. Of course the airspeed drops accordingly ... but the temperature is very pleasant. I was thinking that amount of heat and flow would be perfect for under my desk to keep my legs warm. Maybe this might help. A while ago you gave a link to a thermal mass type heater which was literally a box of bricks with a heater element to warm them up overnight on a cheaper tarrif ... ... and that stored enough heat to be beneficial for the house the next day. All it does is to act like a hot water bottle (or a battery) and radiate that heat until it disipates. Now with PCM ... I could put a box in the corner of my lounge and fill with PCM modules and feed my hot air through them to warm them up. At night as the house is cooling down, the PCM will release its heat just like that box of bricks. You'll have to trust me for the moment that the benefit from a given size box of PCM will far outweigh the same size box of bricks (or tank of water). I also appreciate that if I don't have enough heat energy to pump into the house during the day, it won't really matter if I've got PCM or bricks or water. Yes, exactly right. Now I just have to wait for all the little goodies I ordered off eBay so I can get those numbers. To start with, yes. But I can see a point where having the fan variable could allow the system to attain a certain temperature before blowing it into the house. Leaving the fan too high and not having enough sun to replenish the heat being pumped out, will simply cause the temperature to drop to a point where the fan will have to be turned off, or otherwise will be pumping cold air into the house. Will be a balancing act between airflow and outlet temperature. A little bit at 40 may be a whole heap better than a lot at 25. Dunno, have to keep playing. Cheers, Roger |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Yes, as above, can't wait for all my new toys to arrive. Interesting you should say that. I reckon the guys with the more traditional type hot air collector boxes said it paid to keep the airspeed up and accept a lower temperature gain IIRC. Funny you should say that, I've been wandering around measuring various areas and rooms to see what sort of temperatures they are at present. Certainly getting cooler now. Yes, agreed. Once I've played with a bigger version I'll have more idea which way might work best ... or what things to try. Cheers, Roger |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
I'd have to say a reserved Yes. The days have been warm, 24-25 up untill you sent your SA gloom a few days ago, and the nights have not been that cold. Last night was wet but 15. I would say there is some benifit but not a lot. As you pointed out earlier, the floors are a massive heat sink and I don't think it's doing anything in that department. The furniture does seem to have slight temp variation but not a lot, couple or 3 degrees. Last few days I have been running a couple of fan heaters at about 1000W ea. One in the main Kitchen/ Dining/ small lounge area of about 85 SqM and the other in my small office. The main area seems to be keeping not cold withou being not warm either. The office I am turning the heater on and off because its warming up faster than the heat is leaking out to the main hallway. I think The heat for the area at the ambient temps is about marginal atM. Once it gets any cooler, it's going to start feeling cold. I have been maintaining about 19 in the main area and blowing in the warmer outside air surprisingly didn't change that much at all. Probably on the cusp of Critical temp i'd suggest. ... but today I tried slowing the fan down somewhat ... and saw the temp go from around 25 up to 40+. You can always slow the fans down with a PWN but if Tony can guide you with a Variable speed controller, So much the better. I didn't miss that! :0) So this stuff comes in different forms like bricks or something other than like flat Rolls? That was what I was trying to get my head around. The physical packaging as it were. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
That's good to hear it has some benefit. Well worth the experiment at least. Mmmm ... I imagine it will require a lot of energy to actually increase its temperature. No substitute for having lots of sunlight falling on it I guess. Got some big mirrors? Haha, I'm not even going to go there. At least you can manage your useage and feed a bit more back when you need to. I've been surprised at how low the temperature is in the house at present ... 15.0 in the coldest room and up to 16.6 in the best mid morning today. Makes my low 20's output from my contraption look quite useful ... and with potential for a lot more on better days, I need to get cracking and build a proper one. Yep, I'll be all ears when it comes time for that. Haha, yep I've got skinny legs and I feel the cold. Won't be long and I'll have to crack out the long johns. In this photo below I reckon these are the ones that are 860 x 300 x 27mm $30 each and supposedly good for 400 watts of stored energy. I did ask how long the 400 watts lasts for (as in Whr or kWhr) ... but that seemed like an odd question to him. Like it's not going to provide 400 watts forever, or a day ... maybe it is for an hour ... .4kWhr ??? I suppose 10 of them for $300 would then be 4kWhr ... and 30 would be $900 for 12kWhr If they are as good as I believe them to be, I'd pay $900 to try them out.  Cheers, Roger |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Was interesting this morning. Dull greyish day with pretty much full cloud cover, though not quite as dark as the other day. 9:40am and the array is covered in dew and still half in shade from shed, not that there's that much light. Ambient 12.0 and inside the outlet it was 14.1 I put my hand inside because usually you can feel at least a little bit of warmth near the mouths of the tubes, but couldn't feel any. I wasn't even going to bother turning on the fan but for some reason I did ... and was amazed to see the temperature come up to over 20 degrees. I thought the fan should be slowed so I didn't 'flatten' the tubes too quickly so wound the variac back to 120v. That is probably too slow as it doesn't move much air, so wound it up to 160v, which is probably half normal speed. Will be easier once I have an anemometer. Over a couple minutes it crept up to 23 degrees. So there's no doubt that the array had seen no sun this morning but was still able to pump out some heat. All very encouraging. Cheers, Roger |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
Not that bad actually. Over the past 5 days I have burned about 42 Kwh of power on the heaters. Before that I was making about 40 Kwh+ a day just from a 3 and 4 Kw inverter. I'm not sure how many panels I have up atm but it's not anything like I had thanks to " Remodelling the system. I'm about half way through the billing quarter and have used a net of about Nil power atm. I expect that to change soon and the cold will mean the solar won't keep up with the heating but I have the diesel heater for when that happens and still working on the waste oil system. I may have been overthinking that efficiency wise going to more trouble than I need so I think I'll build an Idea I have to test with and then build another improved unit incorporating the Mods I need to make from there. I have been surprised how relatively warm and stable mine has been. 18 Is the coolest I have seen last week when we had the 4o cold night but apart from that, the fittings and fixtures I have been temp Gunning are sitting at 19 or better which I didn't expect. Like I say though, the cold hasn't really heat here yet and mainly the days have been 22-26. I think that stops everything really cooling off. I have been looking out the window at night and you can feel the cold rolling down off them. I was looking out the front this morning at the pouring rain thinking the front wall of the house must be at least 40% window area if not more. Stupid it's not either double glazed or far less window area. Pain in the arse keeping all that glass even not so clean but not filthy. Me too! A very useful device I think! Getting my head round this stuff some more..... In this photo below I reckon these are the ones that are 860 x 300 x 27mm $30 each and supposedly good for 400 watts of stored energy. They appear to have hollow passages to circulate air though. That will be perfect for your application! First thought was to compare the amount of water it would take to store that energy at something remotely relevant to your purpose. It would take 10L of water to be risen from 20 ( which would be low as you'd want it) to 55o ( high as you would practically make it) to store 400 WH of energy. That seemed to make the PCM impressive. Then I worked out the area of the PCM and unless my usually dodgy mats is wrong again, I came up with a volume of just under 7L.... Which does not add up with the heat storage efficiency mentioned. I think My maths is correct and if it is, I can only assume the PCM advantage is more in it's heat capacity for it's weight rather than it's actual volume. I can see where it would be great to hang off a ceiling but if you have a pile of the stuff and a tank of water, the PCM would save about 30% in occupied volume. In most cases I'd suggest the weight would be a secondary concern. I Imagine it has a heat dissipation limit but that would also depend on things like if you were blowing air across it and what the temperature differential and volume of air flow was. Obviously going to radiate more slowly in static air than it would with a moving airflow. That's an advantage though. Very easy to put a fan on a cheap thermostat to blow air though the medium when more warmth in the room is required and if it has a gentle radiation it may only require very intermittent forced air although more as the material and the ambient air temp equalised. You are much less of a Tight arse than I am that's for sure! :0) For $900 I'll put a 200 drum of water in the corner and raise the temp 55o to get my 12 Kwh of storage. It would be good to verify my questionable calculations though. They don't seem to add up with the claimed energy density but again, maybe it's the weight that counts. If I could pack 12 Kwh into something the size of a shoe box, that would be significant to me but the weight is not so much an advantage from MY perspective. Just going to sit on the floor and the size difference isn't significant for the room I'd put it into. Might be different for other peoples needs and situation of course. The other thing though is no need to worry about a leak with the PCM but OTOH, I could use sand as the storage medium in a drum and take it up hotter and get the same or greater energy density. Not trying to berate the PCM in any way, It's very interesting and I'd be very interested to get some first hand info about it. I'm just making comparisons mainly from a $$ POV and comparing the advantages over my typical Low buck solution default mentality. Edited 2021-05-06 14:55 by Davo99 |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
That might even be half your answer at the moment for why your house is still reasonably warm ... all those windows letting the sun inside. We don't have a paricularly large area of widows ... and the bigger ones are on the south side of the house under a large covered outdoor living area. Yes, they could be spaced out inside a large box and have hot air pumped through them when it's available ... and at night, open up the box or have a seperate fan to circulate inside air through them to warm up the room. That's kinda out of my league, I'd have to do some serious study to work all that out. I think that's why I was so impressed with PCM when I read that a one inch thick panel can store the same energy as a 28 inch thick brick. Yes, exactly. Haha, maybe. Perhaps I've just been sucked in by the hype. That's why all the questions. I don't reckon I'd get away with a 44 in the corner filled with water ... though it could work in the workshop. Nah, I don't see it that you're having a go ... all good questions ... and I'm pretty close to king of the heap when it comes to being a cheapskate, so I've really got to be confident before I spend my money. I decided to ask the question over on the washing machine forum about how PCM works. Will be interesting to see if anyone knows about it and can explain in laymans term so I can understand ... or even better has some first hand knowledge. Cheers, Roger |
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Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648 |
There is some good info on the net if you google PCM. The way I understand it is that it takes a lot more energy to change the 'phase' (liquid to solid, liquid to gaseous)of a material than to raise the temperature of that same material by one degree if its in any of the 3 phases. So for heating you choose a temperature (say 24 degrees) where the material changes phases. The material is heated to just above that temperature (making it liquid) and as it solidifies when cooling down a lot of that stored heat energy is released. You could see a similar effect in your esky, it will keep cold a lot longer if a 1kg ice block at -1 deg C is put inside than if 1 liter of water at +1 deg C was in there. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
This is only going to work if there are fairly large REGULAR cyclic 24 hour temperature variations. In other words too hot for comfort during the day and too cold at night. It soaks up the excess heat, and then releases it at night. A simple brick wall can do that.... If its a bit cold during the day, and bloody freezing at night, its not going to be of any real value at all. Remember phase change is a zero sum game, this magic PC stuff cannot create heating or cooling, only store it at a very specific temperature, and not for very long. Once you get out of the happy day/night heat averaging zone, with either a few stinking hot days in a row, or a few brass monkey cold days in a row, its going to simply stop working. Pardon my cynicism, but I cannot get too excited about all this. I have seen too many rather expensive failed projects. Cheers, Tony. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
Being the strange individual I am, I woke up this morning to the sound of pelting rain and according overcast Skies. It was a bit chilly in the en suite, it's either 45o in there or 5o, and I thought of this idea. Not trying to skite or one up, but it did occur that solar would be useless and the combustion path which is my preference would be needed to make a difference and warm the place at that time. If you had left over storage would be OK but as you say Tony, get those cool days on the trot and this was day 3 of rain, the capacity would soon be used up. And also as you point out, have to be able to charge the heat bank to start with. I came into the office here where I have been playing with some small batteries hooked to some panels outside the window though various controllers and Noted that there was barely enough power being made to power the controllers let alone put anything into what should have been the grossly overpowered batteries. It was almost 9 am before the batteries started getting a charge and by that I mean ANY input sufficient just to raise the float level. They were already fully charged. I related how little heat any solar devise was going to be able to generate under those conditions. That said, they are not the main conditions one would have and I spose it's a case of getting ahead while you can and when you can to make whatever savings you can. For me, I'd need to know what the potential was and then play that off against how much power or solar panels or whatever could it buy me? I think that always have to be kept in mind otherwise you end up with the Home battery scenario where someone spends $15K to save $800 a year in power. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
No, not for the last 3 days, hasn't been any sunshine. Going round giving the furniture covid checks with the heat gun earlier tonight, I'm more convinced that 1kw fan heater out there is making the difference. It's rained the great majority of the day today so no outside thermal input. Despite that, everything was sitting around 19-20o.... it's gone up a degree. The place feels great, not chilly other than the unheated ensuite and far as I can see, only input is the little heater which has been going since about 6 when I got up. That would make it about 16Kwh input for today so far. Probably near what my full system would be capeable of on a day like today but not a lot on a sunny day where I'd be able to do over 60 Kwh this time of year with no trouble.... on a sunny day not a crappy one. Nah! You just use an Online calculator like I do! :0) I do have a very good practical Idea of energy and heat from playing around with it now and know what a KW looks like electrically and in combustion. I can relate it to the energy in hot water we use and how much heat a heater is putting out for the energy consumed.... and the effort required for a generator to make it. I relate that comparison to marketing hype. Despite first thoughts for what many that haven't looked into this fascinating area , Brick is not that energy dense. I know that off by heart. Looking it up, water is 4182 , Brick is only 840.... KJ/ Lb I think it was. Don't matter, in that equation, you'd only need about 5.5 inches of WATER to one inch of the PCM. Still favourable to the PCM but not nearly as impressive in real terms to the king of thermal storage for non exotic materials, water. I suspect the comparison to brick came from some sales hype because people would naturally think of brick as being dense and holding a lot of energy once heated. Water does better than Steel, aluminium, stone, sand and most everything else quite easily. Only way to beat it is go above 100oC but then you have to go a LONG way above to catch up on a volume/ weight basis. I am also getting a better handle on this PCM. It seems the different formulations have different temp ranges at which they function. That penny didn't quite drop before. Your input would have to be fairly specific to get it to function. You would also want to choose one that worked at a suitable " discharge" temp. Bit involved this stuff! And there are many questions I'd ask too. I hope I put some of the " Hype" into perspective above. There is no question the PCM is a more effective heat storage medium but for mine, the benefits and their importance should be weighed against the cost and particularly that of other storage mediums. Thats just the packaging. You could have an ordinary water heater tank outside and just duct the air through a heat exchanger from the tubes in the day and from the tank into the house at night. The question that comes to my mind is how and where you going to set up the PCM? Slabs of 800 x 300 or whatever aren't exactly small and Inconspicuous either so I'd suggest where you locate them could also be possibly used to situate a water storage tank even if it was bigger. Might be that you can get away with a 50L tank for the energy you will generate. The difficulty I see in all this is the energy potential is not at all constant. The energy needs won't be either so it's not going to be an easy equation to work out. Not meaning to shove my idea down your throat but I would suggest maybe using something like water may be a good idea initially at least till you work out in practical terms what you do and don't need storage capacity wise. No use spending more on PCM than you need or finding some other bug in the system that may bring up difficulties no one foresaw. At least with water you can get your numbers and then get the Right pcm you need and the right amount. Testing with the cheapest option to figure out what the final requirements are to me would be wise. Think about using water ( or sand or brick or whatever is cheapest) as a test medium to get your numbers and then spend the money on the final solution you know you need. That's only smart and Intelligent. The way I see it there are 2 parts to this system, the heat generation and the storage.... and maybe the distribution. In any case the generation and distribution will be the same regardless of the storage medium. Get the generation working first, measure it and get some Numbers then add the ( cheap) storage system, work out your numbers again and then build the final iteration from there Knowing you are close to the mark as you can be without spending the big bux. There is a forum for washing machines??? Geez, my life and proclivities don't seem so dull and strange after all! |
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