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Forum Index : Solar : Deciding if I should build this solar heater
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Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648
Posted: 04:05am 23 May 2021
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Altronics sells a fan like that which runs of 12V, it shifts 30cft/min. The 12V marine bilge blower fan I have here is rated about 100cft/min but takes much higher current.
I will get one of these Altronic fans (~$27)and see how it runs off a small solar panel. The plan is to build a solar hot air heater too .
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 04:15am 23 May 2021
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I bought a 100mm e-bay 270 CFM bilge blower, ten amps I think it was, and it really did put out a measured 270 CFM too. It is noisy flat out, but at reduced power it still blows pretty hard.
If its running off a solar panel, ten amps should be no sweat, 130 watts or something.Cheers, Tony.
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 09:12am 23 May 2021
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That's cool, join the club. What sort of device are you planning?
I can see a 12 volt bilge blower fan being the go if I end up using a solar panel to run my system ... I'm only using these 240 volt ones to do some experiments because I've got them ... and I wanted to run them together to compare different setups.
I still haven't got used to the units. Sounds like most use cubic feet per minute ... but the formula I've been using for power requires cubic meters per minute ... and it's awkward to be constantly changing between metric and imperial.Cheers, Roger
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 09:44am 23 May 2021
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Well it could be worse, U.S. gallons per fortnight or something.Cheers, Tony.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 10:10am 23 May 2021
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If it's a US measurement it will be in " Football Fields". From the US made Docos I watch, seems to be the universal measurement they all understand no matter what it is they are describing.
For those wanting to push air through any length or resistance of tubing, I'd be going for the Scroll type Bilge Blowers rather than the fans myself.
Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648
Posted: 12:43pm 23 May 2021
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I looked for those evacuated glass tubes on ebay - too expensive for me. So I will try 50mm x 1.6mm alu tubes, anodised black, which should be easier to use than those zillion drink can contraptions seen on Youtube. The tubes, having each end open, allow the air to flow through rather than in and out.
More details when I get going, have to order one of these temperature loggers you have too.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 01:35pm 23 May 2021
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I take it this is a DIY method rather than something commercially Produced? In out would certainly be easier.
Is there an advantage to having tubes ( Like the ally or cans) over having a flat back backing in a case with transparent material over the top?
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 01:43pm 23 May 2021
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Haha, yep always learning something new. Today it's airflow and velocity and tomorrow it'll be more 'brazing' of aluminium tubes with those fancy alumweld rods.
Klaus have you seen the plans for the collectors using aluminium flywire ... almost looks like they are the best performer ... and also the easiest and cheapest to make.
From the examples I have seen, I keep wondering if they would outperform what I have so far!!!
In fact, today I realised that I have to aim for the highest input temperature I can get ... to provide the highest output ...
... and that is not necessarily from the room I'm trying to heat.
In fact, our laundry gets to 25 degrees or so just from the sun ... so my thoughts were to draw air from the ceiling in there to get a head start on the lounge which might only be 19 or 20.
Then I was thinking, I should build a solar collector on the outer north wall to feed my evacuated tubes ... and of course to do that I would definitely build a flywire mesh collector.
Bit over the top I suppose, but if my input could be 25 or 30 degrees, which should be easy ... then the tubes should get it up another 10-15 degrees much more easily and for longer periods.
And the added benefit of introducing fresh outside air and pressurising the inside to push air out any leaks.
I don't know if they are the best loggers, but certainly cheap enough and work well ... and provide insights that I might normally miss.Cheers, Roger
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 09:17pm 23 May 2021
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That is an excellent idea. If you use more than one air blower, and arrange suitable differential temperature controllers, you could try quite a few interesting things.
Each blower might need a swinging trapdoor to prevent unwanted back flow, but that is easy.Cheers, Tony.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 10:50pm 23 May 2021
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Is your laundry separate or just where the manhole is?
I had this idea a couple of years back. We have a tin roof with sarking underneath and batts (badly) placed on the ceiling. In summer it's insufferable up there so I thought I'll just bring that heat down with a fan. Unfortunately in winter, it's barely warm so I can't see much benifit.
The other thing is when I get up there dropping cables for new power points or putting in more downlights, I start Coughing and have a hard time. I don't know if it is the fibres from the batts or dust or what but suffice to say, It's not good!
I would first put a logger up there and see what temps you are getting maybe half way up a bearer for an average reading. I would also consider a filter on your air Pickup. Pulling air from up there you are going to increase air movement and may disturb dust and whatever. You don't want to be pumping that into the house. I'd get an AC filter and housing ( they aren't expensive) and put that over the end of the pickup to be sure. At very least You'll then be pushing any dust out the house rather than in.
Definitely put a data logger up there (for a few days) before you do anything else so you at least get an idea of what the roof temps are doing. Might be very worthwhile or might be otherwise but at least you'll know and can commit fully if you do go that way.
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 11:35pm 23 May 2021
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Thanks Tony. Never even thought of having selectable inputs, though should be doable.
The laundry is on the same wall as the where the collector is now ... but having just glass as its wall and door, gets a lot of sun thru onto the tiles. Always noticeably warmer in winter (and stinking hot in summer).
My thoughts were to put a vent in the ceiling and the duct from there to the input of my contraption ... so no problems with dust in the ceiling cavity.
... and this is for when I put it on the roof ... only a short duct from the ceiling of the laundry and up through the tiles to the inlet.
That has always been in the back of my mind too ... in fact that's why I did the system in my workshop, ducting air from upstairs.
I have exactly the same issue and certainly would fit a filter if I was to extract air from the ceiling ... but you're right, I do need to monitor the temps up there for a while to see if it's worthwhile.
I imagine right up near the peak would be best ... though with a tiled roof, a lot more gaps for it to escape.
There was a thread in a forum years ago discussing this idea and some really crazy opinions as to why it would be a terrible idea ... people went really mental.
I was going to go up there yesterday and just check the temperature, but got sidetracked.Cheers, Roger
Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648
Posted: 04:55am 24 May 2021
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Its DIY Davo99. The lot will be in an insulated sealed glass fronted box and I could have a reflecting or black or fly screen mesh at the back as well. The idea is to blow in the air from the top, it gets warmed up as it travels down to the black tube openings and gets further heated on its way up inside the tubed (they will have a twisted strip 'twirl' insert) to the hot air outlet on top.
This is still at the development stage though I'll get a fan soon to see how it runs of a solar panel. The tubes come in 6.5m lengths so buying 4 and cutting each into 4 pieces will give me 16 x 1.625m tubes. Just enough for a box made from a standard 1.2m wide plywood sheet.
Should be an interesting project but I doubt it will be ready before the next Winter .
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 03:07pm 24 May 2021
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I learned a few things over the weekend about these tubes and positioning in relation to the sun.
All the systems you see sold as water heaters have the tubes lined up as if pointing to the sun ... and my air heater is the same.
Since assembling my current test heater I've had a number of tubes just lying on the ground next to the shed ... some lined up like the heater and some at 90 degrees to them.
For some reason I checked the temperatures inside and found the ones at right angles to the sunlight, were on average at least 20% higher.
That led to putting together two sets of three tubes and comparing two different setups ... one set up like my existing heater but horizontal and at 90 degrees to it ...
... and the second one the same, except I hooked them up to have air blow through in 'series' rather than parallel ... hoping to have each tube add heat to the previous one ... but expecting to have next to no volume of air.
That's pretty much how it played out ... the standard setup working like normal and the series setup generating much higher temperature but with very little airflow.
To have a better crack at the series arrangement, I reconfigured the second set to be the same as the first ... and hooked the output of one to the input of the other.
At about 10:20 this morning I turned it on with my dataloggers attached ... one at the output of #1 and the second at the final output. The ambient temperature was quite low at about 15 degrees.
You can see the result on the chart and seems to be a very worthwhile temp gain ... though the airflow was still restricted somewhat because of just three tubes.
My thinking is that say 8 or 10 tubes in parallel feeding into another 8-10 tubes should have a lot less restriction to airflow ... but a double crack at adding heat.
First photo show the series setup to the right. Very rough and crude, but didn't expect a practical output, though the temperature rise was impressive ... around 20 degree gain over the input ... but pity there was not much air blowing out.
Second photo shows two lots of three tubes hooked one after the other. Cold air input on left and final output on right. The brick was to help deflect the wind from blowing into the output coz it was pretty blustery.
This chart is of the two stage setup from the last photo.
Cheers, Roger
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 10:11pm 24 May 2021
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Probably more overall efficient to go for lower overall temperature rise and greatest airflow.
Higher temperatures at reduced airflow are of no real advantage heating up a whole large living space.Cheers, Tony.
Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138
Posted: 11:05pm 24 May 2021
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Warp is correct, from having build and played around with solar water heaters in the past; it is way more efficient to have less temperature gain with a higher flow (air in your case). All the tubes should be in parallel not series, set your temperature differential switch to say on at 5 degrees and off at 2, compared to the air temperature inside the house. If you don't want to use a differential thermostat, then a PV panel could drive the fans directly, if there is sufficient sun to make the fans start, then there is heat to be gained to pass into the house.
Cheers Mike
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 12:23am 25 May 2021
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Are you guys serious ... lol ... and I thought I'd discovered the holy grail of home heating.
Oh well ... thanks anyway ... save me a lot of time wasted pursuing it.
Still, from the chart, it seems to reinforce the idea of having my intake air at the highest level as possible ... so not a total waste of effort.
I'm thinking a 'conventional' solar air heater on the outside wall feeding the input of my evac tube collector. That can have as high an airflow as I like, so shouldn't hold back the final result ... and I like the idea of introducing outside air to put a little pressure inside.
Then I'm left with what to do about the direction of the tubes. 20% is a substantial difference ... though that will be probably be better around the middle of the day and less pronounced perhaps in the morning and afternoon.
Though again, the 20% differences I measured were around mid afternoon. Maybe I need to take notice of them at different times of the day.
I can see the water heater systems needing the tubes the way they are ... but no reason an air heater couldn't have them horizontal ... just turn the whole thing 90 degrees ... but of course then I am limited to the number of tubes in a row because the roof is obviously wider than high. Mmmm!Cheers, Roger
InPhase Senior Member Joined: 15/12/2020 Location: United StatesPosts: 178
Posted: 01:23am 25 May 2021
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How about a series/parallel arrangement? What if you put say 3 tubes in series for a high temperature, and put them in parallel with another set of 3 in series for increased flow? 3S2P in battery nomenclature.
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 02:49am 25 May 2021
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The difficulty with individual tubes being in series is that the airflow is limited to what air I can force down a tube only 30mm in diameter ...
... then feed that into the next and the next ... and while the temperature increase is awesome ... there's such a tiny amount of airflow it is useless to heat a room.
Having had time to think about this more, my next question is ... if I find that the sun comes out and the temperature coming out the outlet rises to 35 degrees ... I should just ramp up the fan so that the heat is pushed out faster ...
... and then slow it back down once the output temperature gets down to ??? ... the room temperature I'm looking for ... say 20 degrees ... or a couple of degrees higher? What are your thoughts?
Edit: I see that Mike is sort of suggesting the range between 2 to 5 degrees above my desired room temperature.
Thank you, that does make sense.
It is a little difficult to do that exactly, because you need to turn on the fan for a while to see what temperature is going to come out ... so I probably need a seperate sensor in the manifold that indicates that the temperatrure is high enough to warrant turning on the fan ...
... then watch the output temp to decide to leave it running or turn it off ... at the degrees you suggested ...
... and then some smarts to decide whether to ramp up the speed or throttle back.
I'm not fussed either way really ... I could create a smart controller of sorts to do all this ... though there is a definite attraction to having it automatically run just from the output of a normal pv panel.
Of course I'll have to sort out a dc fan first ... so time for a visit to the wreckers.
I have an additional two dataloggers now, so a bit easier to monitor more parameters.
One of them should probably go inside the manifold. Edited 2021-05-25 12:54 by rogerdwCheers, Roger
InPhase Senior Member Joined: 15/12/2020 Location: United StatesPosts: 178
Posted: 03:12am 25 May 2021
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With a single set, yes. But if you had several sets of series tubes in parallel the resistance would be less. Imagine them as a 3S2P battery system.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 03:12am 25 May 2021
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To begin with just couple your blower straight up to a solar panel and see how that goes. If your collector temperature gain is very high, you need a bigger blower.
In most vehicles you can select either outside air or recirculated air for the heater/blower. Recirculated air gives the fastest warm up, as you have already worked out, sourcing the warmest air gives the greatest heat gain.
However, recirculated air (in a vehicle) may become extremely humid and add to the problem of window demisting. So if its cold, and your clothing is wet, outside air will be far better if you hope to see out of the vehicle.
In a home, humidity and cooking smells, may sometimes build up if the inside air is continually recirculated. Its normal in heating/airconditioning applications to add a proportion of fresh dry outside air to possibly humid stale recirculated air.
You mentioned earlier that the laundry gets nice and warm through direct solar gain. That would be good, unless you are doing a lot of washing, which may cause a humidity problem.
Some means of sourcing either inside air or fresh outside air, or an adjustable mixture may at times be very welcome in different situations.Cheers, Tony.
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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