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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: 11:08am 02 Aug 2021
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Todays results were mixed, with a great start but then a cold change came through late morning and cramped my style.
You can see the results on the chart of reducing Ld on the differential controller from 8 to 5 degrees ... the temperatures on the chart all appear much closer together.
The jumping castle fan is still being used. Cheers, Roger
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 11:18am 02 Aug 2021
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I do have a question that has been in the back of my mind ever since I started this project.
If I stand in front of an air conditioner outlet and its temperature is below say 24-25 degrees ... it feels like a cold breeze.
If the room temp is only 15 degrees, but I can pump in 20 degree air ... is that still beneficial ... or is it just too low to do any good and would be better turned off?Cheers, Roger
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 12:31pm 02 Aug 2021
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I had no idea those sort of things were available so cheaply ... or that they could be set up to do a task like this.
I found a manual for this unit or very similar and had a good read, though it will be a job and a half for me to work it out.
I do have a small three quarter or 1hp 3 phase motor off my saw bench from when I converted it from 3 phase .. and its 5hp mate.
Decisions, decisions!!!
Haha, I like to keep you guessing. Nah, it's one area that I don't have a lot of experience in and just trying to understand what methods are available, which is easiest to implement, and reasonably priced.
I have a feeling this will need more fine control than just letting it rip when the sun shines on the pv panel ... and despite all the runs so far, am not exactly sure what to aim for as far as temperature cutoffs etc.
Yeah, that was a revelation for me too, I had no idea.
Yes, just need to keep it simple to swap over ... and your remote control idea sound cool. Cheers, Roger
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 04:48pm 02 Aug 2021
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Moving air always feels Cool. That's why you can feel cooler standing in front of a fan that is only blowing ambient temp air. Also why AC will continue to blow air even when the Compressor is not running and the air is not being sooled.
You will also note that due to the cooling effect, the same AC on heat mode will only blow when it is blowing heated air not just running in fan mode like when in it's cooling function.
As long as the air was not blowing on you, it would still make the room warmer. If it was blowing on you even the warmer 20 o air may feel cool to most people but, if it was directed at the floor or roof and not causing too much Draft, Then the room in time would be much more comfortable at 20 than 15.
Obviously it's going to take more air at 20 than say 35 To increase the room temp and in practical terms, longer as there is more air to exchange but.... It will lead to a warmer room non the less.
The trick is keeping the airflow and draughts down which is easier with a lower airflow at say 35o than 20 but 20 will still be a 5o temp rise given enough airflow/ time.
In other words, what may take 30 Min at say 35 to get the air up to 20 might take say, 3 Hours with the 20O airflow to stabilise the room at 20.
I Guess it's like battery charging. More amps gets the battery charged faster but less amps will still charge the battery, just takes longer but the end voltage will be exactly the same.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 10:20pm 02 Aug 2021
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If the total heat input to the room is the same, the room temperature should rise by the same amount in the same time. With a bigger fan, the entering air temperature will be lower, but the volume of air will be vastly more. More air is better to circulate the heat into all the remote corners of the room, but beyond that, you certainly do not want to sit in a breeze that feels cold even if it isn't really. And noise will be a factor too.
Evaporative cooling of the skin is what mostly causes wind chill effect, but also still air makes a great thermal insulator. Moving air removes heat much more effectively. So sitting in front of a fan on a hot day can have a significant cooling effect as Dave says. Sitting in front of a fan on a cold day feels a lot colder too.
So there may me some advantage in being able to control the airflow with blower speed, sacrificing some actual heat gain and improving the perceived comfort level.
With the larger system and the blower you have now, the heat input will be at least three times as great, so what feels like cold air now may not be quite so objectionable. At this stage, probably best to go with the orange monster and the differential controller you already have, and see how it goes.
Altering blower speed is not going to be possible with the orange monster, but you can always throttle the airflow down a bit as an experiment.Cheers, Tony.
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 11:45pm 02 Aug 2021
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Okay, that makes sense, thanks. It's funny how some times when it's blowing 25 it still feels cool ... but if I've just come from out in the cold, even 21 feels warm.
Yes, I think that's where any resistance will come from, will be from the cold draughts, so I need to work out my outlets etc to minimise draughts where we spend most of our time.
Good analogy, thanks.
How are you determining 'total heat input' ... can you expand a bit on this please ... particularly in relation to when the temperature in the tubes is higher than the room, but not by a lot.
Okay, that makes sense. Reinforces that I need to make sure my outlets don't create too much of a draught. Maybe that's where having them in remote areas of the house is not a bad idea.
That had been in the back of my mind all the way through ... controlling blower speed to prevent too much draught ... but of course don't want to lose too much potential heat gain. Balancing act!
Thanks, at least that is something to look forward to with the big one.
Are you suggesting I use the orange monster on the big one too ... or just to keep using it on this one. I'm waiting for a 'good' day to see what the results will be ... but I don't think today is going to be one,
It has cycled a few times, but lots of rain and very grey skys.Cheers, Roger
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 01:17am 03 Aug 2021
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Total available heat comes from the temperature rise in the tubes, minus losses. Its basically solar radiation x the area of your heat collector.
If we had no blower, and the tubes were just left out in the sun, the tube temperature reached would just keep increasing until the losses equaled the available heat.
With only a very low airflow, the tubes will be cooled somewhat, and some heat would be removed by the moving airstream. But tube temperature might still be very high, and the recovered heat not as much as to might be.
If we keep increasing the airflow, the tube temperature falls, and so does the air temperature of the air coming from the tubes, but we end up recovering more of the heat that is available from the tubes.
If we keep going with an even higher airflow still, we get still more recovered heat, but the temperature of the massive volume of air we now have, plus the noise that goes with it starts to become objectionable. From strictly an engineering point of view its still working better and more efficiently, and raising the room temperature faster, but it may not be a very nice environment to be in.Cheers, Tony.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 01:33am 03 Aug 2021
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I am sure there will be ways around all of this, such as reducing the air volume when heating only a single room first thing in the morning. That will result in a higher tube and air temperature, but may be far more acceptable.
When heating multiple rooms later in the day, a much higher air volume may be desirable for highest efficiency.
Once a workable control strategy is worked out, mostly by trial and error, making the whole thing fully automatic should not be too difficult.Cheers, Tony.
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 04:30am 03 Aug 2021
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That is much appreciated thanks Tony, it's starting to make more sense.
My aircon friend rang back earlier and we were discussing ideal and acceptable temperatures ... and he was still keen to see 10 to 15 degrees headroom ... but that doesn't mean that a lower temperature can't still improve room temp.
Of course as you point out, it may not be ideal for inhabitants, but could still get the job done.
And I understand that my aircon mate wouldn't get away with the temp differences I'm trying to use because customers would complain bitterly if they didn't have that really noticeable difference.
Exactly ... all those things have gone through my head at various times ... and while I may work out a reasonable strategy for this experimental unit ... you can bet your bottom dollar that it will be different again with the new one.Cheers, Roger
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 04:58am 03 Aug 2021
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Yep, Like the battery Charging. Total amount of energy input will be the same if you charge the battery faster or slower however in this case, The amount of air required is what concerns me. I don't know the maths, You probably do but I get the feeling it's not going to be linear on lesser temps with the airflow. Probably going to be losses but even if it is linear, I know from my own AC which is a large one, If I have it turned to just a couple of rooms, the thing DOES feel cold for a bit and the vents do get noisy and draughty.
I have taken some of the baffles out in my office here as it was a bit noisy but then you get a draught. Pretty get that anyway with the baffles as the amount of air coming in a relatively small room ( for the airflow) turns the air in the room pretty quick which in itself causes a draft. Time the draft stops the room feels too warm.
Do you mean that from an automatic POV or are you thinking something else Tony? I run my castle blowers at lower speed with PWM controllers with no problem other than they Hum a Bit. Run them for many hours like that. The ones I have which appear similar to Rogers are Universal/ Shaded pole motors, I forget the differences but they are NOT cap start induction motors.
I didn't know if they would be OK so I did like most other things, Tested them to see if they would let out the magic Smoke. So far, been fine.
Roger, I was thinking about the air flow again and the need to let the exhaust air out if you are drawing from inside. What I would suggest when you have it all set up is to run the system and take a reading with your water pressure meter. I would then open a door or window and check. If the pressure drops you are in fact creating an air pressure resistance. The solution could be just crack a window at the far end of the house. That will let the excess pressure escape and also allow the warmer air to move towards said window which will have the effect of drawing the warmth through the house. May well take a while before the air is not all cooled on it's way through but it will be heat soaking a wider area on it's way thought and that's what you want. You could open a far window even if the pressure is OK which I have reservations about and the air will still flow that way to the path of least resistance.
Other thing I did years ago and I see they sell ( overpriced) kits for now is simply move the air from one part of the house to another in a loop . You could have one exit into your main living area and once that is warmed up, you could draw air from there and dump it back to a further end of the house. Could even put this on a cheap thermo board so it did it automatically and cycled.
Would really depend on if you are going to recycle the air or use outside air. After pulling air in from outside, that is what I would recommend.
Like you, Time we are out of lockup so I can get the parts I need to finish my oil heater and co-gen, it will be too bloody late to use them for this damn winter. Gone far as I can with both atm and need supplies I don't have. I'll make bloody sure I have them for next winter even if I do have to work on them in the hot weather which is difficult for me. That's why I left the things till I could get more of a feel and acclimatise to what I was doing... if that makes any sense at all.
The fan heater alone is starting to push up the temp in the main room. Been hitting 20 for a few days which is good. had a frost the other day but over all, the important min temps are starting to come up and they seem more important than the day max temps. Seems the heat loss is more important here than the heat gain or stabilisation.
Might try starting to think of some cooling Ideas now.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 06:35am 03 Aug 2021
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You are quite right Dave, but shaded pole motors are still a type of induction motor, they have the solid cylindrical rotor.
Now normally, you cannot reduce the speed of an induction motor motor by simply starving it of power, without causing massive overheating in the rotor. The one and only application where you can get away with it is driving a fan or air blower !!
The reason for that, is the cubed law power requirement of a fan. Every time you increase the rpm, the drive torque increases square law and the power cubed law. That means at very slow fan speeds it takes almost nothing to turn the damned thing. At x3 rpm, it requires x9 torque and x27 power to turn it, so the motor is only loaded significantly right up near full maximum voltage and rpm. Reduce the voltage and the speed falls off, and so does the load, so you can vary fan speed up and down quite successfully with phase control.
Not really surprised it hums a bit Dave, but put any kind of decent mechanical load on an induction motor at much reduced voltage, and it will very likely go into terminal melt down.
You could run full voltage to a blower and just strangle the airflow with some flow resistance. That will also drop motor current, and probably the noise too. That should work well, as long as you are not trying to reduce the flow right down to zero, but only by some reasonable percentage.
Thinking about it, those motorised dampers may have an application in not only directing the air from room to room, but limiting airflow to a particular room to raise the air temperature. I have zero experience with adjustable air dampers, never even seen one, and the motorised ones sound expensive ? But if you can scrounge or perhaps borrow one to play with from somewhere, it might offer some interesting possibilities. Edited 2021-08-03 16:39 by WarpspeedCheers, Tony.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 07:24am 03 Aug 2021
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Thanks for the heads up Tony.
I used to simply put a restriction on the inlet, usually a bit of stiff cardboard or some Tin over the inlet but I thought using a PWM was more " Professional". It's certainly easy to Dial up a number on the PWM to match to the Fuelling rate to get a set output but that said No reason a better restrictor plate could not be fashioned and marked to do the same thing. Couple of my blowers draw through the motor side and have a grille around it so I was reducing them just by laying some rag around them which was a bit heath Robinson even for me.
Might go back to showing the restriction concept in my next Vid with a power meter attached to show people that they DO reduce output when the flow is reduced.
A throttle body comes to mind that could be regulated on the intake for the conventional Blowers that draw through the centre of the impeller. I'll have to look up how they are Controlled. If there was an easy way to control their opening with a 0-5V signal or whatever they use, that would be good. Could use them intake or output.
Might be a bit small for Rogers application but then again, the wreckers probably don't even bother taking them off blown engines so should be cheap to get multiples thereof.
As far as I'm aware, the motorised AC dampers are pretty run of the Mill and not exy. Seen my mate Chuck out loads of the things. Rogers mate should be able to hook him up with some.
From memory, The things can be set to part opening mechanically to effect air balancing in a system. Ironically, I have done that in my house just by cutting out some bits of cardboard and sitting them up above the Grilles. They can't be seen unless you look for them, ( be even harder to see if painted Black) but they do the job just fine.
Not really controllable on the fly though. I usually have the spare room blocked off completely unless I am doing a shoot or someone is staying and then I just reach up, lift the grille and slide the cardboard out. Also tend to put some in Daughters room in summer to reduce the cold air flow so it maintains her preferred 30o c temp level.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 08:07am 03 Aug 2021
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This is all quite educational, I did not know such things even existed.
Its just a geared motor and a potentiometer, rather like a drive by wire automotive throttle. I can see that if such a thing were mass produced, it need not be all that horrifically expensive.Cheers, Tony.
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 12:52pm 03 Aug 2021
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I'm assuming you meant drawing from outside ... and if so you may be right ... but I suspect it will be leaky enough to accommodate quite a flow of air.
Between exhaust fans, downlights, aircon vents, doors and windows etc. Maybe it is more airtight than I think, but I would be surprised.
Ours hasn't been too bad here, we can go out and about again as long as we wear a mask and sign in everywhere ... so I can't use that as an excuse ... I've been dragging my feet as usual.
The aluminium tubing is due to be delivered tomorrow ... all 130 metres of it ... then the excuses are really gone.
My new thermistors arrived today so I fitted a couple to the data loggers so they can be more responsive and get a better view of what's happening. Will be interested to see the difference tomorrow night.
There's no doubt, a low overnight temp can undo a lot of the good work we've put in ... and it does take so much longer to get back to a decent temperature.
Haha ... I don't want to hear ... I'll get sidetracked and never get this thing finished ... though obviously now is the time to be planning that for yourself.
I didn't either until we moved here, our place has half a dozen and most have stopped working. We were quoted something like $240 each for new motor gearboxes for them ... and for once, I have not been able to fix them myself or find equivalent motors from China.
The motors have a built in gearbox with plastic gears and they have just been so hot that they go hard and brittle and fall apart or jam up. These also have a pair of limit switches so the motor stops and can reverse ... so while the tech is simple enough ... finding a replacement has been the issue.
Having said that ... I may simply be better off pulling out each complete damper assembly and fitting new ones with a different type of motor.Cheers, Roger
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 01:14pm 03 Aug 2021
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Here's todays results. Cold, blustery and intermittant showers ... but also intermittant sun.
Cheers, Roger
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 10:07pm 03 Aug 2021
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There is more now happening, and the temperatures are closer together, so the charts will look a bit mote tangled than earlier. But the overall slow steady heat gain in the house is definitely there.Cheers, Tony.
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 12:18am 04 Aug 2021
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Yes ... really have to look closely to see what's happening ... but the end result with a higher inside temperature is good to see. Always looking for more and quicker, but that's human nature.
I was a bit slow getting going this morning and the fan started before I got out there, trying to suck the blind through the duct!!! Lucky I know now that it wasn't going to burn up my motor ... and in fact it was saving power.
It was a joy to see the dataloggers respond quickly to changes, but I think that even the bulk of the heatshrink and the tiny bit of silicone on the legs slows them down a little bit ... but they need some sort of physical protection or they'll be wrecked in a week ... especially seeing they have to be handled a lot for checking and downloading etc.
My 'how can I save effort/time' or I like to call it my 'lazy' gene was trying to kick in this morning when thinking about the aluminium tubes.
I was thinking that because the tubes are going to be horizontal and with no real force on them ... why can't I just assemble it on the roof and simply glue them in.
If I used high temperature silicone, something like Selleys RTV ... that should be enough to hold in place and provide an airtight seal ... and it should be able to cope with the extreme temperature too.
When I did my apprenticeship, and they still used to fix stuff like that ... we used RTV silicone to seal the soleplates on irons ... and it coped perfectly well with high temperatures, steam and pressure.
Anyway, it's just an attempt to get out of what I know I need to do and that is weld them all in. The only way I can see to do it is to clamp them all together vertically ... then set up a platform or something so I can reach to weld them around the top.
It's going to be difficult enough to do the job without trying to do vertical welds ... I need to get them so the weld action is horizontal.
EDIT: I forgot to mention that I changed the data logger recording interval from 1 minute to 10 seconds. With quicker acting themistors, I want to be able to see the action that happens.
I think their main use is usually to record temps in shipping containers and things like that, so they don't normally need to be that quick and responsive.
Edited 2021-08-04 10:27 by rogerdwCheers, Roger
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 02:13am 04 Aug 2021
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I didn't either until we moved here, our place has half a dozen and most have stopped working. We were quoted something like $240 each for new motor gearboxes for them ... and for once, I have not been able to fix them myself or find equivalent motors from China.
Get onto your AC mate Roger. He should get them regularly from upgrades and probably just chucks them like my mate. Even new he should be able to buy the whole Duct for about $60 or so each wholesale.
All you do is untape them from the duct and put the new ones in. They are double layered, the inner duct that carrys the air, the insulation layer and then another duct to hold in the insulation that goes over the top.
3 turns of tape on each duct sleeve ( which your mate will have boxes in stock of) re connect the wires and that's it. They may have to start in the open or closed position for the controller but other than that.... Done many of them myself and it's an unskilled labour Job.... which is why my mate takes me along to help.... :0)
Whoever quoted $240 ea was having a big lend of you unless that was supply and fit but even then....
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 02:32am 04 Aug 2021
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That was how I imagined you'd be doing it all along. I thought you would do the frames, get that up on the roof then put the tubes in on the roof and couple it all up.
Alternately, How were you going to get the assembly up on the roof?
Can you get the tractor to the back of the house and lift it with that? If the bucket won't go high enough, You could easily make up a Jib crane for the 3 Point hitch.
I just put mine between the Top link on the tractor and the top link on a receiver hitch Frame I have so the thing is an offset Lever. Goes from horizontal to nearly vertical and with a bit over 3 M length, has some good lift height. Can make it even longer by just extending the boom. I just bought some of those weld on ball ends and put along where the Implement would pin and the other on the end to pivot on the tractor where the adjustable link normally goes. I used the adjustable link to measure out where the one along the jib goes. Spose if you brought it in closer the thing could get a bit more lift but mine is near vertical now and I don't want anything hanging over the top of me. I also thought to make up a bit of a dog leg so I can get more height and push the load back a bit but that's going to start taxing my little toy tractor over anything beyond about Hundred KG but might be good for lifting panels on the roof.
I don't imagine this is too heavy so should be easy enough for your tractor to lift.
Before I had the little Kubota I used an engine crane with an extended Boom. You have to counter weight a setup like that though so I just ratchet strapped a 44 on the back and filled it with water so that was good for as much as the thing would lift on the ram anyway. You'll need a smooth surface to roll it on though like plywood or something if you have to get back onto grass or pavers.
rogerdw Guru Joined: 22/10/2019 Location: AustraliaPosts: 852
Posted: 04:34am 04 Aug 2021
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I hadn't asked him about that but I will. The quote I got for the motors was from the company he works for. Sounds like all their scrap goes to that other mate of mine I've mentioned who has these great huge heaps of dead aircons at his place.
Now that I'm getting a better understanding of what sort of fan may work ok ... I'm planning on going back soon and digging through to see if there is something suitable there. May even be some scrapped damper assemblies.
Yes, that is what I plan to do. Drag up the basic frame first, then each set of 30 tubes, then the ducting sections and covers, and last the glass tubes.
My comments related to using Selleys RTV Silicone to glue the tubes into the centre duct ... rather than weld them in before I lift them on the roof. It was a dumb idea really, just being lazy.
Maybe if I blow too many holes in the tubing as I weld them in, I can use the silicone to fill the gaps.
The heaviest part will be the main frame, but if I was desperate, I reckon I could get it up there by myself ... but to save the paint on the gutters and risk to tiles and stuff, I'd be able to do it with an extra person easily enough.
The rest I'm sure I could also get up there safely enough on my own if need be.
I had thought about a front end loader, but mine is really old and doesn't have one. It does have a jib for the 3 point linkage, but it still wouldn't be high enough.
It's amazing what you can achieve with a bit of thought and planning ... though I can see why you might upset the safety sissies. Cheers, Roger
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