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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
Posted: 03:40am 23 Jul 2021
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Thanks Tony, and yes I've bumped it up one degree for each ... Ld 11 degrees and HD 16 degrees.
With the room at 16.6 ... it turned off with tubes at 27.5 ... and the outlet was at 26.0 ... which is just about right. Much lower and the airflow feels a bit too cool.
Ideal day now for testing as the cloud comes and goes ... I see cycles every five minutes or so.Cheers, Roger
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 03:47am 23 Jul 2021
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Its now going to pull every last drop of recoverable heat out of those tubes, and that should make a big difference under marginal conditions.
Its the ideal time of year for testing.Cheers, Tony.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 07:51am 23 Jul 2021
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Imagine the output when you have the full set up!
With this automation, it is going to be very effective. Much like a GTI with a PV installation. gets whatever it can and gives you the best output.
The tubes getting to 110 is something. You'll be able to divert the output in summer and direct it to bake bread in an oven! Imagine what the consistent output in summer will be. You certainly could push the air through a water to air intercooler from fleabay and use that to do your domestic water heating or for the pool.
Getting and keeping the house at temp through the day without having to go though stacks of fire wood will also make a big Difference. I am very convinced of this after doing it. Mate said to me yesterday, is it just me or has this winter been bloody Freezing? He lives where it's on average 50+ warmer than where I am and in a unit block that also insulates him very well.
Usually me complaining of the cold but very different for him to be.
I am a bit surprised how well the floor is keeping temp. It is very consistent in the main room but the bathrooms which are tiled and away from the diesel are very different and much colder.
Maybe making something up out of PVC that blows the air along the floor will help warm it and store some heat? Just a bit of pipe with holes or slits to spread it over a meter or so should do the trick.
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 01:55pm 23 Jul 2021
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Yes, I hadn't appreciated just how much it would be able to snatch up any bits of heat ... then shut off until there was more to grab.
And being able to keep the fan on high speed so it pumps in more quickly is very handy as well ... and not having to worry that I'll forget about it and have the cold blowing in and undoing all the good work that's been done already.
I am going to have to make sure I keep an eye on it once the warm weather comes in ... maybe I'm going to have to find a heavy tarp to keep out the heat ... at least until I need it to dry some fruit or bake some bread or burn off some paint.
Yeah ... although a few days of proper wintry weather detunes my enthusiasm at times ... but when the sun pops back out ... look out!
I still haven't tried that myself. I've had a few days where I could have ... just so many things to try and so little time. Cheers, Roger
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 02:12pm 23 Jul 2021
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I haven't posted any charts for a while but thought it was worth showing how things look with the new differential controller looking after things. Thanks Tony.
Hopefully tomorrow's will be better again seeing it can be ready to go with the first sunlight ... assuming of course that we do get some.
And I really do need to pull apart another of the data loggers and fit the sensor externally, so I get quicker and more accurate readings. At present it takes 8-10 mins to catch up ... and if there are any wild swings it misses them altogether.
I might go out and modify one now ... and be ready for the morning. Cheers, Roger
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 02:14pm 23 Jul 2021
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Right now, we are at the shortest day plus one month, so it's probably about as bad as its going to get cold weather wise.
It might be interesting to log it over the next few days and see how much temperature increase throughout the day can be achieved. Multiply that by the increase in the number of tubes in your final design, should give a pretty good idea of the final potential.Cheers, Tony.
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 11:55pm 23 Jul 2021
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I don't know if this is a normal winter or not for us over here ... but I have been amazed at how many days the sun does shine at least for a few hours ... and how few days it is grey and overcast all day.
Another observation is that it doesn't seem to matter how cold the ambient temp is ... if the sun shines, we can pump heat.
At present I have 18 tubes and the new one will be 60 ... so potentially 333% higher ... plus being on the roof, will not be shadowed by the fence in the mornings and later afternoon.
It started off early this morning, soon after 8 am ... though I wasn't able to concentrate much on what was happening. Seemed like it maybe should have been allowed to build up more heat before it came on ... I'll have to look at the data tonight to see if it makes more sense.
I did crack open the logger that sits at the warm air outlet and drilled a hole so the sensor is exposed directly to the airflow ... so will hopefully be a bit more responsive.Cheers, Roger
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 12:11am 24 Jul 2021
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It does not need very high tube temperatures to work. As long as the tubes are warmer than the house, there will be heat to harvest. In fact, the blower will cycle and keep the tubes at a just sufficiently high temperature to work. That is excellent, because heat losses through the ducting will then be far lower if the warm air coming back to the house was at a much higher temperature. The whole thing will be much more efficient than allowing the tube temperature to get really high before turning on the blower.
The data logs will tell the story...Cheers, Tony.
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 10:19am 24 Jul 2021
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Okay, well I thought this mornings figures were a bit dodgy ... but while I had drilled the outlet data logger case to expose the sensor to make it more responsive ... and it does seem a bit better ... it still seems a little slow.
I might bring it right out on stilts into the airstream to see if that helps.
Apart from all that, it looks like the system is working very well
With the conditions we've had since the rain set in at lunch time, I normally would have just turned it off ... but like you suggested Tony, the system still managed to eke out half a dozen more bursts of heat that I would have missed out on.
Cheers, Roger
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 01:39pm 24 Jul 2021
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Looks very Promising! I'm sure the heat output was not a lot but the fact you got any is the takeaway here. When the clear days do come, going to be very worthwhile.
The controller seems to work with my solar PV belief, Get in early and keep it flat out long as you can. This is generating heat soon as the sun hits it and beyond and now you are able to take advantage of that. Will make a big difference to the total Kwh of heat you get in the house.
Multiply this by 3 Odd on the big array and will be impressive.
Weather here has been OK till about lunchtime and then turns to crap. That wouldn't be a total loss for your system though. If you got good sun in the morning, it would recover the house heat from the night possibly to carry you through 4 hours or so till late afternoon where the sun falls off quick anyway. The August winds have arrived here already and plenty of gales blowing up. I surmise the beauty of the tubes is they won't be affected by wind too much.
The tubes definitely have the capacitor effect so can be charged up with heat over time then that is dumped into the house. Brilliant.
I have been looking to see if I can find any cheap Tubes as this all has me quite intrigued with the things but so far all I have seen is what I would consider well over priced and none really local but they seem to be popular around Canberra judging by the number of ad's I'm seeing.
I am so looking forward to seeing what the big array will do in Summer. :0)
Is there a way to take output measurements In KW? Can you ( or the other smart people here) work it out on the temp through the outlet and the airflow which I take it is also Fixed?
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 03:35pm 24 Jul 2021
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Thanks Dave. It did actually start out very well because of the early sun ... and took the room from 16 degrees up to just over 20.
Then of course when the change came through and the outside temp dropped considerably ... the guts dropped out of it.
I need to address that data logger because I was getting away with its sluggishness before ... because it used to have time to catch up to the changes in temperature ... they were long slow changes ...
... but now that the temp goes up and down over only a 5-10 min cycle ... the device takes far too long to respond and reads 5-10 degrees too low sometimes.
If I could use my good meter to log the readings, it would look far better.
Yes, this is what Tony's been trying to get across to me all the time ... and now that I'm already seeing the effect, I'm a convert too.
Definitely hanging out for that, though hoping I'm making the right decisions.
We don't seem to have that problem here, though there are enough grey days to take the edge off the enthusiasm sometimes. Of course when the sun comes out and the heat goes up ... it's all smiles again.
It was funny this afternoon. I came in from sawing and splitting the last of our wood and it was already 4pm ... so normally it's all over by then ... but the tubes were hovering just one degree below where the fan would have turned on again ... 31 degrees.
As I said above ... I have no idea where the heat was coming from because it was 10 degrees outside and had been raining virtually the whole time since lunch.
I haven't looked since getting this big batch ... but I'd be ringing around to find out who installs them and get friendly with them ... or find out if any local plumbers regularly "uninstall" them because they can't make them work properly as water heaters. You seem to have that knack with pv panels, just work your charm on the plumbers.
Haha, me too.
For outputs in kWs ... I did use Tony's suggestion where I added an electrical heater in the outlet tube ...
... then once it was running smoothly on sun power and I had a consistent temperature ... then turn on the element and wind it up until the output temperature was exactly double.
Then work out what the element was drawing in watts ... and that is the same wattage the sun was providing.
I did use that for my early 6 tube setup ... but once I put in the 18 tube system it got pretty dangerous trying to run an element up over a thousand watts and all inside plastic.
There is a formula you can use and which I have quoted figures from.
I did post it once before and was told it was not correct ... but they couldn't provide the 'correct' one.
Airflow in meters per sec x
Outlet Cross Section Area (in sq meters) x
Specific heat of air (~1000 J/kg-C) x
(Outlet temperature minus Inlet temp)
= Output Power in Watts
So today, a higher output would have been around lunch time before the rain started.
Air Velocity 4.0 m/s x
Outlet Duct C/S Area = .01779 sq/m x
1000 x
The outlet temp was 37 degrees minus inlet of 21 degrees = 16 degrees
4.0 x .01779 x 1000 x 16 = 1,138 watts
Yesterday when I turned it on late in the morning and the output was 88 degrees ... minus the input at 16 degrees = 72 degree difference.
4.0 x .01779 x 1000 x 72 = 5,123.5 watts
Of course that was only an instantaneous reading because it very quickly dropped back as it removed the stored heat from the tubes ... but it was still pretty impressive standing in front of the duct pumping out that level of heat.
I like to imagine the new one at 3.3 times that output ... though that sounds almost dangerous ... but I'll be happy if it can be pumping out 3 or 4kW on a regular basis.Cheers, Roger
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 03:55pm 24 Jul 2021
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That all appears most encouraging. Even when the blower is cycling and the system struggling the temperature is rising.
If you can get a nice clear day, that should be really interesting.
With three times the power and some better weather ahead, this is showing some great future potential.Cheers, Tony.
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 04:20pm 24 Jul 2021
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Yeah, thanks Tony. Despite being the middle of winter we still do get some great days of sun, even though the wind can be biting. I can't wait for another of the good days to see how this new controller performs then.
I just went out and modified the data logger again and fitted the sensor fully outside the case. I think that is what worried me this morning seeing it still lagging behind the actual temperature ... and of course making the graph I showed look poorer than it should.
It's funny how different results can take the edge off the enthusiasm ... and then some good ones can bring it all back.
Thanks to you and Dave for all your advice and support, it really helps.Cheers, Roger
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 04:44pm 24 Jul 2021
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Wind and a low outside temperature should have little or no effect, the only real killer will be big black nasty clouds that block the sun.Cheers, Tony.
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 02:13am 25 Jul 2021
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Yes, that seems the case.
What surprises me most is it doesn't seem to need direct sun either ... just light ... though of course the output is not that spectacular until the sun pops out.
My modified data logger is working better than yesterday .... much more responsive ... though still 2 degrees below for a minute or so ... and finally as close as .5 if the fan runs for long enough.
Looking forward to seeing the chart tonight.Cheers, Roger
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 02:54am 25 Jul 2021
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If your logger uses thermistors, try getting some of the really small bead thermistors. These have a very short time constant, well under one second. In fact they are used in hospitals to detect breathing by sticking one up your nose. They are that fast and that sensitive.
Just a random thought Roger. The relay in your differential temperature controller will probably work fine for years, but the motor inrush current might eventually burn the contacts. If you fitted an external relay to switch the motor current, it would be a lot simpler and cheaper to replace if it ever does eventually suffer. A solid state ac relay would be the bee's knees.Cheers, Tony.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 03:55am 25 Jul 2021
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I'm wondering if an amount of Hysteresis in the sensors wouldn't be a bad thing? Stop the switching too fast but then again there is probably a very gentle ramp up and fall off within the thermal capacity of the system itself in the ducting as well as the tubes.
Have to Concur with Tony RE the relay. I have an analogue Timer I use for the fuel control on my burners. Uses one of those Mini relays. Supposed to be 10A bit every time I inadvertently short it for the briefest time and with only a strand of wire, blows the thing. Plenty of room in the case so I'm just using it to drive a proper relay.
Should be able to drive a FET from the board once I can work that out.
One thing Roger, Be careful with those Packaged SSR's. They are Chinesium quality or lack thereof at their finest. They might be rated at 50A but the dissections I have seen on YT show the actual mosfet is 10A. if that. I have some on a few things I have built, the Inverter fan controller was one and a Light sensor for turning on the Christmas lights and they worked fine on a high rated unit with a low load.
The white SSR's are popular and much cheaper than the original black ones but are optimisticly rated. ( what a surprise!) I shelled out for a couple of the good ones then didn't bother using them because I figured out how to run the Mosfets direct in the months they took to arrive.
Probably better for you to just use a well rated mosfet in the first place.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 04:08am 25 Jul 2021
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If the fast cycling is annoying, just set Hd a bit higher. It will then take longer to heat up and cool down, and cycle more slowly with only a slight loss in overall efficiency.Cheers, Tony.
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 08:39am 25 Jul 2021
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That's a great idea Tony, thanks. I did wonder about something like that but wasn't sure if I'd find something compatible.
They are a tiny teardrop glass looking device, all of 2mm in diameter by 4mm long ... a bit like a tiny christmas light globe out of its holder.
I did measure its resistance last night before I unsoldered it from the board at about 17 or 18 degrees ... and it was 124k. Dunno if that sounds like it can be replaced or not.
I've been spoilt by the thermistor I use on the Owon multimeter because that seems pretty instantaneous.
That makes sense, I'll give it some thought as to how I can go about it easily.
Once I get the big one on the roof, I hope to go with DC from a pv panel or two ... so may be able to go with mosfets
So far the switching has not been a problem. It certainly cycles with short periods when it starts in the morning but didn't take long and was on for an hour or so this morning.
I can just hear it from where we sit at our computers ... but I am atuned to hearing noises ... and my wife would only notice it if it was blowing cold air.
It's windy and chilly outside, but the sun is shining pretty well and temps are rising nicely inside.
Yeah, I agree that it hasn't bothered me so far ... in fact it has been rather handy for those reasons.
It's really the fact that it shows in the charts some readings that are nonsense ... and make it look like the control isn't doing what it is supposed to be doing.
I've never used them before myself, I have a soft spot for relays. Many years ago I built a device that used triacs for switching ... and I pretty soon regretted not using relays. Worked perfectly until a globe blew ... then there was a fair chance the triac would also fail. Didn't help that I didn't know anything about solid state switching and protection ideas.Cheers, Roger
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 09:44am 25 Jul 2021
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Here's todays figures. Was a nice day ... cool enough, but sunshine on and off all day.
Nice to see the lounge temperature go from 16 degrees up to 22 degrees.
The charts are certainly quite different to before fitting the differential controller, with the switching on and off until the sun is sufficient to allow the fan to run continually ...
... and then later in the afternoon as the sun reduces and it comes in cooler ... then the fan switches in and out again until it gives up for the day.
Another thing I should mention is that I have had the fan switched to high speed ever since fitting the differential controller. Just about all my graphs in the past were with the fan on the low setting ... except on really sunny days.
Something that seems odd is the temperature of the outlet into the lounge is higher than the temperature in the tubes during the middle of the day. Not sure how or why that is happening.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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