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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 |
Ouch ... sounds painful. I was kinda shocked once I woke up to this ... I've said before I usually walk around with my eyes half shut ... but the sun never got high enough to fully cover the array. At the best point the bottom 10 inches was still in shade ... ... and now I know why the results fall off the chart at 4:15 or so ... I thought it was because the sun goes behind the trees on the other side of the road ... but it's probably more to do with the fact that even if the sun is shining ... it's only the top 18 inches of the array that actually gets any of it. Duh!!! Nah, I only got the fan and motor. The guy wasn't all that helpful ... though he did give it to me for $25. I found an article that describes these fans and housings here ... And that gives the formula for housing dimensions which is really helpful .png) I had the brilliant idea of seeing if I could swap the DC motor over for the AC motor in my Blauberg fans ... but unfortunately the car fan motor has a D-Shank shaft and the Blauberg has a threaded shaft ... so that's unlikely to work. Looks like I'll need to build a housing. Yeah ... probably correct. According to the forecast, today was supposed to be similar to yesterday and 1 degree colder ... so I was not expecting much at all ... but I would say it's probably been a copybook day ... best one I've seen yet for this system. And especially now I realise I have to either dismantle my fence or chop down some trees ... just kidding ... but I can see how I can improve it more by addressing these things. My plan of course is to put them flat on the tiled roof ... but with the reduced angle I may lose a bit of efficiency. If they were more upright, like the stand they are on now ... I'm really confident some decent reflectors could add a lot of extra power as well. That's great. Best way to find out is to try a few things to see if it pans out and proves your ideas on not. And from what you described, you probably don't need to throw any money at it ... just use what you have lying around. If it starts to look good, it's easier to justify a few bucks to take it to the next stage. Yes, That keeps crossing my mind here too ... our ensuite is as cold as, and pumping some heat in there would make a good thermal storage unit. Cheers, Roger |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
Can't see why it wouldn't work? How would you control the staging or would it be a manual setup? |
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Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648 |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
With regard to blower housing dimensions, Dave is quite right, all you need is a rectangular box with a round hole to match up to the inside dimension of the rotor. Mount the rotor and motor inside the box, and provide a suitable air exit hole for your ducting. A very carefully proportioned scroll is only required for very high speed rotors running at very high pressure ratios, where the aerodynamics then become a critical factor of how it works. For moving bulk amounts of air at low pressure, as in ventilation, any old thing will work just fine. A few years back I was really into air blower design and carried out a few back to back tests myself at home. I compared a very well proportioned commercial scroll housing to a bloody great oil drum housing using the same 500mm diameter rotor and motor. Measured flow and pressures were identical. I still have a lot of pictures of the various blower housings I tested around here "somewhere" on an old hard drive. You only need to collect the air being thrown off the rotor all the way around its circumference, and then direct it towards a suitable exit. All the theory about accelerating the air to very high velocity in the rotor, then turning kinetic energy into pressure energy, through smooth deceleration in a scroll shaped volute is perfectly true, if you are trying to generate a very high air pressure. For just moving bulk air around at negligible velocity and pressure, a very simple and ugly air collector box is all that should be required. Cheers, Tony. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Yeah, that was my first thoughts too ... I could see it being easy enough to build with cardboard or some flexible plastic. I'd really love to just put them on the other side of the fence ... totally uninterrupted position (and still our property) ... but the difficulty is running vents across the path. Would have to go overhead ... ugly!! and would also be very lossy. I think it's the roof or nothing. It's amazing what you can find that's normally just thrown away I know my thinking is probably wrong ... but I see it that if I can warm that up because of the thermal mass ... it's less heat that is sucked out of the rest of the place. And now you tell me ... lol. I spent all last evening sorting out my fan.  Very useful info thanks Tony, I'm sure this wont be the last fan I have to sort out. I know I said earlier that I couldn't see a way to adapt the 12 v motor to my Blauberg fan assy ... but I was looking at the 8 inch version. When I pulled apart a 6 inch one it looked more do-able. Then when I went scrounging through my junk to find suitable material, I found a clear perspex disk that was perfect for the job. 10mm thick and had been turned in a lathe with a stepped lip. I tapped that into the duct and it was a snug fit. Used a hole saw to accommodate the neck of the motor ... then cut another disk from an old cutting board ... and then a smaller piece to clamp the motor in place. Only thing that annoyed me was the threaded rod I had was not metric ... should have been 6mm but was quarter inch something!!! I forgot to mention ... the original Blauberg fan was a perfect tight interference fit pressed on the new motor shaft. I 'stuck' it on with some silicone in case I need to get it off again. Can't wait to try it out this afternoon ... and wait till you see how it fits in place of the old one ... magic.    Cheers, Roger |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Oh that is really nice Roger, very well done. It looks like a bought one.  Cheers, Tony. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Thanks Tony, very kind of you. I thought I should put up yesterdays results seeing they were very good ... and followed by todays which were down a bit ... though understandable because it got down to -4 overnight and cooled everything off. After some family stuff I'll update on the DC fan. Results from Saturday 29/05/21  Results from Sunday 30/05/21  Cheers, Roger |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Okay, well I left it a bit late this afternoon to try swapping to my DC fan ... and you know the saying about pride going before a fall ... ... well I went to swap it over but it wouldn't fit!!! An identical model number Blauberg fan has a 5mm bigger diameter body ... and a much bigger fan!!! ... though the final ducting is for 150mm duct on all ends. Anyway, it wasn't hard to change the complete fan over and try it out. I had doublechecked the airspeed with the AC fan on high ... and it was 3.5m/s. Unfortunately the shading for my 250 watt solar panel was too much to even start the fan ... so I hoisted it up on the bin and leant it against the gutter on an angle towards the disappearing sun. I still couldn't work out why it wouldn't start, until I realised I was creating a shadow on it. Once I got out the way it took off. Not used to pv yet! I called my wife to balance it in case it dropped off onto my tubes and went in and checked the airspeed. Over the minute or so I monitored it, it varied between 2.98-3.4m/s. Pretty incredible that it was so similar to the AC fan. I then propped the panel up fairly flat to avoid shading and the fan ran fairly slowly ... but was still pumping out pretty reasonable heat. Of course I'm keen to see how it goes in the morning, whether it self starts too early or too late. Because the sun is getting lower and lower, the fence will shade the bottom of the pv panel early in the morning and from about mid afternoon ... so I placed the panel over the fence where there is no shading and hooked it back up. I do wonder if I might need two panels side by side ... but with one facing NE and the other NW ... so it has enough power in the morning and later afternoon ... but then afraid it might have too much during the middle of the day. Will see what happens tomorrow. This is how I was supposed to change my fan over ... Would certainly make maintenance easier for anyone working on aircon and exhaust systems.     Edited 2021-05-30 21:30 by rogerdw Cheers, Roger |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Its probably a bit late in the day to get a good indication, tomorrow should be interesting. Cheers, Tony. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
I sold some panels to a guy about a year ago. He was complaining the panels weren't doing near their rated output when he tested them by dead shorting them with an amp meter. I pointed out it was an overcast day and they would do better if his daughter wasn't standing directly in front of it leaning it on herself holding the thing up. He thought he knew ALL about PV so I wouldn't feel bad if I were you Roger. No Idea how much time I have spent chasing faults in things I have b uilt because I didn't switch them on or connect a wire to the power. Gives me the heeby geebys just thinking about the occasions I can recall! I have noticed with fans and Pumps, the things will do like 50% output at 20% power. They are not linear. Going to the other end, dropping 20% power results in a 40% output drop. Don't know what it is but noticed it for many years with many different things. Like the pump I use for collecting veg oil I made. Uses a 12V scooter motor. On 12V will do about 60L min and runs quiet. On 24V it dies 80L a min and makes a noise and gets hot fast. On 30V does about 90L min so it's not maxed in the hose size etc at 24V. A setup Tony has mentioned which I think is brilliant is to have the panels east west at 60 O . I have done that and works great. Gives you the best spread of power across the day and avoids that Midday spike. That said.... I don't think trying to even the power output is best for your setup. You really want the ramp up and fall off so the PV output matches the heat generation of the tubes. That's kinda the idea of having the Solar powering the fan so it automates the fan speed to the heat generation of the tubes without having to have electronics and more complication. The panel needs to be seeing the same input from the sun as the tubes so their outputs correspond. -IF- You did need to go to 2 panels you would want them on the same plane as the tubes otherwise you could well get the fan blowing too hard outweighing the output from the tubes and Cooling the place. When the PV is falling off, so will the heat the tubes are generating so you would want less air to avoid it getting too cold. Similarly, when the fan is going flat out, the heat from the tubes will be at max as well so all you would really need to do I think is balance that. Restricting the inlet if it gets too cool may be best because at lower ends all you would possibly do is get a bit less flow but higher temp air and that's OK. In reality as the fan moves less air the restriction becomes less or irrelevant anyway. You have done a great job on all of it Roger. The testing is often the hardest bit because everything is Built Temporary. when you know how it has to be and can build it permanent you don't have to worry about leaving things so they can be swapped. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Haha, yeah. I even got up early and put out the dataloggers at 7am. Yep, same here ... and even worse is when I blow something up and it costs me money for parts and more of my time as well. I haven't had much experience with that, but am surprised at how much airspeed I get with this fan at only 5 volts. Sounds like it may be similar with this. You are probably correct. I was more concerned that the motor would need more power to actually start running ... but what I am seeing so far, I don't think that is going to be a problem. Yes, exactly right. Yeah, I guess I was worried that it might not be linear enough ... but it has to be a heap better than waiting for me to decide to turn it off or slow it down. Thanks Dave, I appreciate yours and Tony's support and keeping me honest ... along with the others who ask questions from time to time. I'm not posting because I'm trying to bignote myself ... it's to have you guys as a sounding board rather than wasting too much time doing stuff that will never work ... and also to keep a record of the progress for myself and anyone who comes along in the future with the same questions I have had. So for a progress report. I am rarely outside before 8:30 or so ... so was interested to see if this thing would fire up like we hoped. Clearly the sun is getting lower all the time ... and when it appeared around 7:25 on the PV panel I wondered how long before it would have enough grunt to spin the motor. At the same time I realised that the evac tubes array was still fully in the shadow of the fence ... and yet the PV panel was in the clear on the other side. Hardly a fair test if it did get going. I hooked up a voltmeter to the panel so I could see what it was doing ... and about 7:50 I heard the fan start running ... quite quickly too. I checked the airspeed at 1.75m/s ... and a few minutes later was at 2.09m/s. Should have gone out to read the pv volts. For reference, the airspeed on the AC motor was 3.5m/s on high, 3.0m/s on low and 1.5m/s on 140V (on low) which I often used when there was little sun and not enough heat in the tubes. Note that by this time the sun was hitting the evac tubes ... but only the top two feet ... the rest was in the shade! Of course with the fan running and so little sun on the tubes ... it was blowing in COLD air ... 13.4 to start with and only very slowly rising. It was fascinating to check the airflow to see that it had stopped or sped up ... and I ended up positioning the meter so I could read it from inside the window at the inlet position so I could get an idea of what volts were needed for what airspeed. This part looks like it will be perfectly ok ... probably better than I expected. Obviously I have to get the tubes on the roof because it's never going to make any sense while they are shaded so much ... which will only get worse as the sun gets lower and lower over the next few weeks. Until now, I only ever turned on the AC fan from 9am onwards ... and most days there was already a store of heat in the tubes from the earlier sun. And today is one of those days where there simply isn't a lot of heat available. While it started off reasonably clear, it went to 95% cloud cover pretty early ... so the thing is not going to work for today. Luckily my wife had already gone on shift, so I left it running so I can catch the ups and downs on the dataloggers later ... and I'll let the fire rip later this arvo to try and catch it up a bit before she gets home. In fact I will get it going again now to try and stem the downward spiral.Cheers, Roger |
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| Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648 |
Hi Roger, a few questions about your ducting if I may ask as I'm about to go shopping for that stuff. I assume you are using 150mm PVC tubing? Does that need insulating outside or have you some of that alu ducting inside the PVC? Or nothing? The sharp bend of the flexible tubing, does that affect the airflow much? I assume that alu flexible tubing comes in standard sizes, do the PVC tube end fitting match closely or are you using adapter fittings? Since I do not have your super efficient heat tubes I'll need to reduce losses as much as possible. Thanks. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Hi Klaus, the top two tubes across the top are 160mm OD and 152mm ID pvc. Picked up from scrap yard for $10. The end caps I bought from Bunnings and were just under $10 each. I haven't insulated it for this testing but definitely plan on having it insulated for the final unit. I have measured up around 28 degrees on the outside of the outlet duct, out in the weather ... so it must lose a lot of heat from that. I'm sure it does, though because my airflow is fairly tame, I don't think it is that bad ... ... but again in my final unit I will make any bends as wide and smooth as possible as per the recommendations for ducting systems. Yes, it appears you can get 100, 150, 200, 250, 300mm flexible ducting ... and probably more. The 150mm wouldn't fit on my 160mm tubes ... so I cut a couple 100mm lengths of the 160mm tube and cut a strip out of each so I could collapse them and slide them inside as a coupler. Then they fitted well and a bit of tape over holds it all together with no leakages. Yes, that makes sense. Because I was chopping and changing all the time I didn't worry about all the little things to make it as efficient as possible ... though will definitely address them all in the final build. You can buy insulated flexible ducting ... just the ordinary duct with a wrapping of insulation 'wool' and with an outer plastic wrapping. I will definitely use some of that on my heat outlet with the new one ... though if I can't find some easily, I can't see why we couldn't wrap the normal stuff with insulation blanket and tie it on or find something to wrap it with. Cheers, Roger |
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| Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648 |
Thanks Roger, you and this topic are a mine of good info. I'll go to Bunnings tomorrow and see what I can find there. Hopefully I only need very short PVC tubing bits for making couplings - I should have some scrap here somewhere  .The plan here is to get the intake air from the under roof space (old concrete tiles). That means I have to cut two round holes into the fibro walls (60 year old house), that should be the only tricky job. The whole unit will sit on my flat garage roof which abuts the house. The collector faces due North there and is somewhat protected from out SW gales here in the West. Max ducting length to the passage way ceiling outlet is about 3.5m, almost all of this above the ceiling, under the roof. Easy to place insulating batts over the ducting. My bilge blower fan outlet is only 80mm diameter but at full throttle the thing wants to take off unless held down. I think I settle for 150mm ducting, that looks a good compromise. The 3 speed fan control I posted above seems to work (with a bench power supply) but the zeners shown are wrong, they should be between 4V7 to 5V6, 1W for a 12v DC motor and 400R coil relay. I just ordered a PCB for that. |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Thanks Klaus, though I do feel I'm blundering my way through all of this. I'm just thankful for all the help and pointers I'm getting. Like Dave said the other day, I've always wanted to experiment with that in the house. We have black tiles so there should be some warmth up there. I need to put a logger up there for a few days to get some idea. Good on you for giving it a go. Only way to find out is to give it a try I guess. Can't see why it wouldn't work. Glad you got your circuit working ... I was trying to work out just what values you needed, though thought you could have been using 5 volt relays. With 12 volt relays I can see the zeners needing to be lower. Cheers, Roger |
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| rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Well here's my summary for today. Not sure what to think. Was certainly partly successful ... but it was cold and gloomy pretty much all day, despite it starting with a bit of promise.  Cheers, Roger |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Another panel in parallel would definitely be worth trying next. Meanwhile, something like this might be worth getting: https://www.ebay.com.au/itm/121917535737?hash=item1c62d9f5f9:g:iE0AAOSwyjBW3mP- Edited 2021-06-01 08:15 by Warpspeed Cheers, Tony. |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
Interesting! Quite against what I presumed would be the potential problem of the fan pushing cold air. Seems the Tubes are some significant way ahead of generating heat over the PV generating power. Perhaps Tilt has something to do with it? If the panel were flatter on a gloomy day may kick in better. I would have assumed a 250W panel would have been enough to move the fan though. Been overcast all day today and my solar generation is lousy as is the way. The panels that were power the inverter fan have been put on the charger for the battery running the diesel heater and have been able to bring it up to charge and float it with the heater running which I kicked it at 2 Pm due to the house temps falling after a cold night and then no sun today. The panels ( 2x 175w) are pretty flat and facing SW not that it matters today but doing well for the conditions. Perhaps playing with the angle of your panel may help Roger? Paralleling 2 Panels will be interesting. In the sun they will really make the fan howl because they should have easily enough power to overpower the fan and push the voltage High. The question to me is if there is actually enough heat in the tubes on such a day to be worried about? If it took some hours to build the heat you got and pulled out for 15 Min, is it worth worrying about in the first place? To get it seems you either have to go to some electronic control or add another panel but I have a strong feeling that you may over cool the tubes then but all just guesswork. Only other control I can think of is the pulsed Capacitor dump I made for a water heater. Might just need something to let the panel come up to it's curve and then a jolt to overcome the motors initial inertia. But again, even if the thing is running, if you get 200 or 500Wh out of it, is it even worth any heating value what so ever and going to make a scrap of difference in the house? I think we all want to get what we can with our endeavours but by the same time, we also get to the thing I term as urinating on a bush fire where the action is just irrelevant in it's impact on the outcome. |
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| Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648 |
Well, if one considers that the incoming solar radiation is on average around 1KW/ sq meter so if one gets 500W out its running at half its theoretical max capacity. In my case I'm fully aware that such a project is unlikely a money saving idea but it definitely has, IMO, 'feelgood' value. Urinating on a bushfire has more of a 'feel relieved' value but also makes one feel good afterward. Its a hobby and money spent on it is never wasted. |
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