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Forum Index : Solar : Deciding if I should build this solar heater

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Davo99
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Posted: 06:06am 17 May 2021
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  rogerdw said  

Yes, I have been pleasantly surprised at how well the temperature is being maintained even with a fairly low input.


I suppose it is only the lost temperature be replaced but I would have assumed my place at least was looking a lot more than a KW or so.
If anything it makes my oil heater build more difficult.  Getting the brun down to a KW will be most challenging.  Maybe just have the thing going at 10 KW and regulate the temp by leaving a door Open!  


  Quote   but it's great to see this air heater take over for the day and bring temperatures even higher  ...  especially knowing it's only costing the running of a 40-50 watt fan.


One thing I have been observing and am very surprised with is how even the house seems to be keeping.  I was thinking with the oil heater I'd have to still run the ducted fan and that's a KW on it's own.  I have been running the fan heater in the office here a bit which is at the other end to the diesel but so far, does not seem to be any cold spots that noticeable at all.  May as well run the heater for the KW and get some heat out of it as burn the KW just moving the air around.


  Quote  If it's too comfortable in the house, it's hard to get motivated to get back out to the workshop or go do some work in the yard.


I just went and replaced some crappy old 180W panels with some new 270W ones.
I'm going to have to go change my shirt from the sweat. I don't mind working in the cool provided it's not windy. I hate wind and it makes me crook every single time.


  Quote  

It sounds really useful and obviously with a bit of thought you can get the best results without just running it flat out and burning through all your diesel.


I am a bit surprised at how well it is working actually. Not a single complaint from the women of the house, only the odd compliment which is a bit thing. Might be calling it a bit early, seems winter still hasn't truly hit here but the deeper we can go into it and the sooner we can come out of it without having to throw massive amounts of power at keeping comfortable,  the happier I am.

I am wanting to experiment with the Veg oil because although I had a windfall with the diesel, I'm sure as hell not going to be that lucky too often although I will certainly keep my ear out and even try to chase some up from now on. The veg is virtually limitless and free so If I can run 50%, even if I have to buy diesel it's still making it a lot cheaper and far cheaper for the heat I get than buying power.

  Quote  Sounds a bit like what I'm trying to do here with adding heat during the day  ...  and then burning wood during the night when my air heater can't work. I'm confident I can save 30% of the wood I burn with my experience already.


30% is a good saving. I have a very clear picture in my mind what 30% of the wood I cut for my father would look like. That's at very least a Cubic meter, probably 1.5.
That's a good half days work at least for me.

I was out before thinking of the benifits of a heater like yours. Warm day in the sun but still a bit chilly when not working hard.  I don't want to use the solar too much because I'm pushing to make half the KWH I did in summer and  falling behind even with the diesel and I don't want to run the diesel stupid hours above what I already need it for. They are not meant for what I'm doing with it already so even if the fuel is free the running hours have a cost.


  Quote  

I'd never really thought much about the furniture and cupboards etc  ...  really just the tiled floor, but that does make sense. When we re did the Kitchen 12 months ago I emptied all the cupboards and packed the contents away  and removed all the old cupboards, benches etc and appliances carried it out. I brought timber and plaster in to move walls and carried all the demolished materials out. I brought in all the cement and the half ton plus of tiles.  I brought in the majority of the new flat pack kitchen and by geez that wasn't light.

The little asian blokes that brought in the full size granite sheet we needed for the Island and then the bench top were all thanking me and my mate for helping them bring it in because they were having nightmares of doing it on their own. That was over 300Kg all up.  Then there was the new stove, fridge, dishwasher, range hood and all the other miscellaneous bits and pieces BEFORE we packed all the boxes of crap back in and none of that was light either.

Easily got to be way over a ton in there, I'd suggest closer to 2 than 1 actually.  
It's a lot of thermal mass.


  Quote  
Yes, correct. When I talk about what I'm doing to anyone, friends, family or technical people, I want to be able to put real and honest numbers on things, that I can back up  ...  not some exaggerated, made up BS that makes me look totally dishonest.


I just need to know myself to understand if all the stuffing around is worth it and what I'm really getting out of the exercise. Just because I'm not good at maths does not mean I don't like to know the numbers. :0)

  Quote   A bit similar to what I'm looking at except the added part of seeing what changes with the PV output as it heats up or cools down.


To me this will be like Co-generation with engines I have played with. Many newcomers look at it as getting bonus heat from the electricity you are making.
The better way of looking at it is the bonus electricity you get when making heat.
It makes a difference if you keep that in mind and given the maybe 20% efficiency of panels in making power, the same thing definitely applies as it does to engine co gen.

  Quote  I don't know if you have any temperature data loggers, but they are certainly handy to have so you can sit back and look at the whole picture at the end of an experiment, rather than rely on notes taken during the event. I need more of them myself.  


No Data loggers but many thermometers.  Even with data loggers, I am not skilled enough to translate what they told me into numbers I could understand which for me in this case would be daily kwh.
 
rogerdw
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Posted: 11:52am 17 May 2021
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  Davo99 said  Maybe just have the thing going at 10 KW and regulate the temp by leaving a door Open!


Haha, yeah. I suppose the start up process is a bit fiddly  ...  you can't just have it turn off for 5 then turn back on again.


  Quote  Getting the brun down to a KW will be most challenging.


With electronics it's usually the other way around, okay at low power levels but difficult at high.


  Quote  May as well run the heater for the KW and get some heat out of it as burn the KW just moving the air around.


I had assumed I would use our ducted aircon on fan to distribute the hot air once I have a system on the roof  ...  but if I could direct the output into just two of the cold spots, I reckon that's all I'd need.

Where I have the existing one through the window, it has really helped that end of the house. My wife has mentioned a couple times just how warm it is up there  ...  so it's making a difference.


  Quote  I just went and replaced some crappy old 180W panels with some new 270W ones.
I'm going to have to go change my shirt from the sweat. I don't mind working in the cool provided it's not windy. I hate wind and it makes me crook every single time.


You make it sound so easy just swapping them around. I've got soft in my old age and prefer not to work out in the weather, but do occasionally if I have to. Need to be protected though.


  Quote  Not a single complaint from the women of the house, only the odd compliment which is a bit thing.


That's a big plus.  


  Quote  30% is a good saving. I have a very clear picture in my mind what 30% of the wood I cut for my father would look like. That's at very least a Cubic meter, probably 1.5.
That's a good half days work at least for me.


I reckon it's at least that much here. We always seem to get through a lot, though the house is always warm.


  Quote  They are not meant for what I'm doing with it already so even if the fuel is free the running hours have a cost.


I did wonder what their life time is likely to be  ...  especially running every day on high for a few hours. Still, sounds like they're not all that expensive even if you do eventually wear one out.


  Quote  I just need to know myself to understand if all the stuffing around is worth it and what I'm really getting out of the exercise.


Good point, I didn't even think to mention that, but it is the most important to me as well, so I know which way to head or to give up and try something else.


  Quote  Even with data loggers, I am not skilled enough to translate what they told me into numbers I could understand which for me in this case would be daily kwh.


Fair enough, though the ones I bought are surprisingly simple to use. In fact I ordered another couple today.

You install a simple program on your PC  ...  then plug in a datalogger and the program recognises it. You can set the parameters for what you want it to do, eg record temp in C at 1 min intervals  ...  and it's ready to use.

Then on the device you hold down the play button for 5 secs and it starts recording.

When you want it to stop, press the pause button for 5 secs.


To see the results, make sure program is open on PC and plug it into usb socket.

The data automatically downloads, and if you click 'graph', you get a graph of the days data.

It's also available as a spreadsheet etc. but the graph tells me all I want to know at the moment.

You can select multiple files to display together, which is what I use to display the data, though I add a third line using a graphics program. Won't have to do that once I have another logger.


These are the ones I've got.
Cheers,  Roger
 
Davo99
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Posted: 08:37pm 17 May 2021
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  rogerdw said  


You make it sound so easy just swapping them around. I've got soft in my old age and prefer not to work out in the weather,


Weather wasn't bad but it wasn't easy, that's why I was sweating.  Took 8 panels down, carried them up the back and put them on a pallet and then bought 7 of the new ones down.  Roof was low but I had very little clearance between the edge and the garden wall I built there a few years back.  Had to shove them up on my own then hold them from sliding off while I clipped the cables together then screwed them down.

They actualy look better than the old yellowed ones with the big Diamonds in the middle and they are putting out more power. The verandah is east west so I might throw another array up on the other side to give better all day charging.
Also want to move the couple of panels on the diesel heater battery.  They are more south facing than anything and I have room more northerly facing atm so I'll move them round. Just not quite getting the battery up where I want it atm.

Since loosing weight I have lost a lot of strength and these panels that didn't bother me handling them 25 at a time are now bit of an effort. Probably need to handle more to build myself back up again.

I want to replace what's on the shed which is about 40 odd panels and that's going to be an effort!


  Quote  

I did wonder what their life time is likely to be  ...  especially running every day on high for a few hours. Still, sounds like they're not all that expensive even if you do eventually wear one out.


Info on the net seems conflicting.  From what I can gather how hard you run them seems a big factor. The Failure point seems the fan. It's really the only moving part and  pretty much everything else is serviceable or replaceable.  I'm not sure if the fans are.  I have noticed though, a complete heater is worth about 5X it's price in spare parts, if not more.


  Quote   but it is the most important to me as well, so I know which way to head or to give up and try something else.


There are nearly always alternative ways of doing things.  I have seen over and over again particularly with different money/ energy saving ideas, It's often better just to do things the conventional way because the savings in any aspect you want to look at are negligible or don't exist despite the Hype.  Take commercial home batteries for instance. People buy them to save money but they cost a lot more than buying power from the grid.

That's why I did the calcs on the diesel heater. May have been more exy to buy fuel  than power so I needed to know which one was cheaper. Also looked at LPG but that is fractionally more exy than Diesel. Cheapest of course is still solar but I know it's difficult to produce what I need in winter despite the stupid amounts of power I can make in summer. I'm trying to balance the 2 heat inputs so I can use the available solar I have and make up any shortfall with the diesel. Veg heater will be the real answer though. Unlimited free fuel and I can have the place as warm as I want. Trick will be not having it too warm.


  Quote    then plug in a datalogger and the program recognises it. You can set the parameters for what you want it to do, eg record temp in C at 1 min intervals  ...  and it's ready to use.


Might be worth getting a couple to measure as you are, out and inside temps.
The house seems to have cooled a fair bit this morning which is unexpected. Mrs had the oven on last night which warmed out there appreciably but it's Cooled off this morning. Might be I went to bed early and turned the thing down sooner.  I don't think it's particularly cooler than it has been. 4o Atm so not warm.

Really does take a LOT of energy to keep this place warm.
 
rogerdw
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Posted: 08:09am 18 May 2021
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I didn't worry about an update yesterday, though I did keep the data.

Today was awesome, so wanted to share the results.

Forecast was for fog in the morning, then partly cloudy with a top of 20.

I noticed the sun out at 8:15, but didn't want to change the routine and logger charts, so hung off until 9am to turn them on.

If the tubes see much sun while the fan is off  ...  they seem to build up a lot of stored energy  ...  and once the fan comes on, we get a huge inrush of heat until it is depleted. That is clear in the chart below.

Rest of the details are in the image below



Cheers,  Roger
 
Warpspeed
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Posted: 08:30am 18 May 2021
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Great stuff Roger.
Its going to work a lot better with more tubes too.
Cheers,  Tony.
 
rogerdw
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  Davo99 said  Had to shove them up on my own then hold them from sliding off while I clipped the cables together then screwed them down.


Amazing what you can do on your own when you have to. Good job.


  Quote  Since loosing weight I have lost a lot of strength and these panels that didn't bother me handling them 25 at a time are now bit of an effort. Probably need to handle more to build myself back up again.


I haven't lost any weight, but I certainly have lost a lot of strength in the last couple years. I really need to do something about it, if its possible. Maybe some weight training.


  Quote  I want to replace what's on the shed which is about 40 odd panels and that's going to be an effort!


Sounds like a massive job. Good luck with that.


  Quote  The Failure point seems the fan. It's really the only moving part and  pretty much everything else is serviceable or replaceable.  I'm not sure if the fans are.  I have noticed though, a complete heater is worth about 5X it's price in spare parts, if not more.


That makes sense. I imagine it would be worth keeping one on hand if they aren't too expensive  ...  though the parts are where they make their money if the price doesn't stop you buying a new one. Either way they win!


  Quote  There are nearly always alternative ways of doing things.  I have seen over and over again particularly with different money/ energy saving ideas, It's often better just to do things the conventional way because the savings in any aspect you want to look at are negligible or don't exist despite the Hype.


Haha, yeah, though this forum is full of people who just wanna do things different  ...  even if it doesn't save much money or work any better. We're a strange bunch.  


  Quote  Might be worth getting a couple to measure as you are, out and inside temps.


Yes, they are really handy in showing info you might otherwise miss.

eg today I had a fantastic output from the device and for so much longer than previously  ...  yet when I went to compare the previous highest output temp, expecting new highs  ...  today wasn't as high as a couple days ago  ...  yet temps outside were higher and ran longer than the other day.

I would really love to have an irradiance meter logging the sun to compare that as well  ...  coz it's not just temperature that warms up these tubes.
Cheers,  Roger
 
rogerdw
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Posted: 09:01am 18 May 2021
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  Warpspeed said  Great stuff Roger.
Its going to work a lot better with more tubes too.


Thanks Tony, I'm getting more confident that this is all worthwhile.

In my head I worked out how to put up a system three times the size with 54 tubes  ...  and if I can get triple todays output on good days  ...  I'll be looking for ways to throttle it back.

The next three days are forecast for the same as today but 1-2 degrees warmer  ...  so looking forward to seeing high outputs continue.


In thinking about summer and having to cover the tubes to stop them getting ridiculously hot for no reason  ...  I wondered if I could use the hot air through a heat exchanger and use it to heat the pool. Though that would be a little tricky with the exchanger on the roof  ...  I'd still have to run the pump to get the water up there  ...  which I do already with the existing solar heater.

Pity I didn't start with a water heating system and forego the air heater  ...  though I suspect I wouldn't have started if that were the case. Still feels a bit tricky.
Cheers,  Roger
 
Warpspeed
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It should be possible to just switch it on and off with a room thermostat like any other kind of space heating.
The more heat you can gain earlier in the day the better.

Its going to make a big difference to the cost of heating, even if on some really gloomy days its not terribly effective. Like your pool pump, it should chug away in the background doing its thing, requiring very little attention.
Cheers,  Tony.
 
Davo99
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  rogerdw said  I really need to do something about it, if its possible. Maybe some weight training.


Putting on Muscle is a Very difficult thing when you get older.
My wife has lost a lot of weight and the one thing the Doc has been watching carefully is that she did not loose too much Muscle because she said ( as has been confirmed by others) that putting it back on for her will be near impossible.

Went and had lunch with my health Nut mate the other week and his energiser Bunny girlfriend.  She has been sick and put on a lot of weight and is loosing it again but he said it will take a long time for her shred the fat and build the muscle back up again.  Mind you, she is 60 and before she got sick she would have picked me up  by the belt in one hand and my equal size mate in the other and carried up up a flight of stairs like we would have carried a couple of drink bottles.
She is bit of a freak not only of nature that one but of incredible will, stamina  and determination.


  Quote  I want to replace what's on the shed which is about 40 odd panels and that's going to be an effort!


  Quote  Sounds like a massive job. Good luck with that.


Actually it's pretty good because it's a flat roof. Nothing like near as difficult or exhausting as doing the 35o house roof.  Yes, it's a fair few panels but once you have them up there, positioning them and connecting them up is no where near the effort, strain and stress ( of not falling off the damn roof) as the house ones.


  Quote  

That makes sense. I imagine it would be worth keeping one on hand if they aren't too expensive  ...


I was just looking at some parts on the web. Glow plug, gaskets and vaporisers.  Basic stuff you need for a clean out with the GP just in case. Add in the fuel pump and other things that seem to fail and I was thinking I may as well just buy another unit and the 10 gaskets for $10 and be done with it. As you say, in event of a failure, just swap the thing out and repair it without a rush.  

  Quote  

Haha, yeah, though this forum is full of people who just wanna do things different  ...  even if it doesn't save much money or work any better. We're a strange bunch.  


Maybe but no other group I rather be with when the unspeakable smelly stuff hits the rotational air moving apparatus. I think of that with my 2 good Friends. Both certified Geniuses and very hands on problem solvers.  Between the 3 of us there isn't a lot we couldn't fabricobble together to survive comfortably. I know the low end stuff that is beneath them but would fill in some gaps.


  Quote  
I would really love to have an irradiance meter logging the sun to compare that as well  ...  coz it's not just temperature that warms up these tubes.


An irradiance meter just sounds like a solar cell that has a small load and a data logger for the output to me. :0)
Edited 2021-05-19 01:46 by Davo99
 
Davo99
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  rogerdw said   I can get triple todays output on good days  ...  I'll be looking for ways to throttle it back.


Don't waste energy! Just open a window at the far end of the house!! :0)

  Quote  

In thinking about summer and having to cover the tubes to stop them getting ridiculously hot for no reason  ...  I wondered if I could use the hot air through a heat exchanger and use it to heat the pool. Though that would be a little tricky with the exchanger on the roof  ...


You know a car heater core would take all the heat those tubes could dish out about 10x over?  Motorbike radiator the same.  They are air to liquid HE's and the amount of thermal energy they can sink is huge. You could not need a very big he at all and no reason you couldn't bring the hot air down and put it through the HE.


  Quote   I'd still have to run the pump to get the water up there  ...  which I do already with the existing solar heater.


I think if the water is in a Circuit, coming down and going up, the energy required will not be a lot.  If the HE is down on the ground, same thing. I know a lot of those solar water heaters use Circ pumps which have virtually no head because the weight of the water coming down is the same as going up so really all they need to do is overcome frictional and any restrictive losses.

  Quote  Pity I didn't start with a water heating system and forego the air heater  
  Quote  

Did you read ANYTHING we wrote at the start..... or several times over??  :0)

  Quote  ...  though I suspect I wouldn't have started if that were the case. Still feels a bit tricky.


I thought what you did was going to be tricky but you managed that with seemingly little trouble.

Still convinced that you would not need an in/ out with water. The way I see it, as long as the open end is up, the heat will rise one way or the other. Has to. If it's stagnant in the bottom of the tubes it will get to boiling point. when it does that a gas bubble will rise and then be condensed by the sub boiling temp water and give up it's energy. That and probably stir the fluid in the tube and allow the water liquid to rise back up.  Other thing I see is thermosyphoning within the tube.  Hot water will rise to the top along the length of the tube drawing colder water in and the hot water will stick to the top of the tube and flow out.

I think a steady water flow across the top of the tubes and it would sort itself out.
 
rogerdw
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Posted: 12:19am 19 May 2021
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  Warpspeed said  It should be possible to just switch it on and off with a room thermostat like any other kind of space heating.
The more heat you can gain earlier in the day the better.

Its going to make a big difference to the cost of heating, even if on some really gloomy days its not terribly effective. Like your pool pump, it should chug away in the background doing its thing, requiring very little attention.


Yes, it should be quite controllable and I can either keep it really simple or try and build some sort of intelligent control with variable speed fan. That wouldn't be needed on the brighter warmer days, probably only to get the most out of the gloomy days.



  Davo99 said  Putting on Muscle is a Very difficult thing when you get older.
My wife has lost a lot of weight and the one thing the Doc has been watching carefully is that she did not loose too much Muscle because she said ( as has been confirmed by others) that putting it back on for her will be near impossible.


While we're fit and healthy it doesn't seem to matter too much  ...  but if ill health kicks in it can take a real toll. And aging just seems to creep up on you.


  Quote  Actually it's pretty good because it's a flat roof. Nothing like near as difficult or exhausting as doing the 35o house roof.  Yes, it's a fair few panels but once you have them up there, positioning them and connecting them up is no where near the effort, strain and stress ( of not falling off the damn roof) as the house ones.


Glad you've got it worked out. I'm a bit nervous about mounting panels on my shed roof. It's pretty high and a reasonable slope, plus I've never fitted panels on a roof before, so need to get confident about doing it.


  Quote  I may as well just buy another unit and the 10 gaskets for $10 and be done with it. As you say, in event of a failure, just swap the thing out and repair it without a rush.


Yes, it doesn't feel right having to throw away a complete unit for want of a couple parts  ...  but when those parts are almost the cost of a new unit, it virtually forces you to replace it.

  Quote  Maybe but no other group I rather be with when the unspeakable smelly stuff hits the rotational air moving apparatus. I think of that with my 2 good Friends. Both certified Geniuses and very hands on problem solvers.  Between the 3 of us there isn't a lot we couldn't fabricobble together to survive comfortably. I know the low end stuff that is beneath them but would fill in some gaps.


Yep  ...  never ceases to amaze me how little most people know or understand about practical things  ...  and we wonder why they talk so much crap about everything else. A lot of them don't have any clue about non practical things either.

  Quote  An irradiance meter just sounds like a solar cell that has a small load and a data logger for the output to me. :0)


I did wonder exactly how I could measure irradiance (cheaply) and a solar cell did come to mind  ...  I'd just need to buy a datalogging multimeter as well.

Datalogging irradiance meters are all over $300 and I kinda baulked at spending that much. Temp meters can be used in lots of applications, so I justified those to myself  ...  especially seeing they are only $30 something each.


  Davo99 said  Don't waste energy! Just open a window at the far end of the house!! :0)


I suppose  ...  that would definitely work.  


  Quote  You know a car heater core would take all the heat those tubes could dish out about 10x over?  Motorbike radiator the same.


Great idea, never thought about one of those.


  Quote  I think if the water is in a Circuit, coming down and going up, the energy required will not be a lot.


Hopefully by then I'll have finished my Warpinverter and have a roof full of panels so running the pump wont be so expensive.


  Quote  Did you read ANYTHING we wrote at the start..... or several times over??  :0)


Haha, yeah good point. Though I'm sure there must be some deep seated childhood issue lurking around there somewhere in regards to leaking pipes or flooded houses. That's my excuse anyway.


  Quote  I thought what you did was going to be tricky but you managed that with seemingly little trouble.


Thanks. I find that if I can think through and understand a complete process of building something  ...  then I have a chance  ...  but once there's a part that I don't know how to do  ...  or feels too difficult for my skills level, I come to a screaming halt.


  Quote  Still convinced that you would not need an in/ out with water.


You are exactly right. It was only half way through this project that I realised that some systems did actually use "water in pipe" systems.

I thought that they all used heat pipes.

I also discovered there's a third method, having a copper tube carry water into and then back out of the evac tubes to pick up the heat. A really tight 180 degree bend at the bottom of each tube.

I had considered that for a while to start with, but the quantity of copper tube I would need was going to cost a fortune  ...  and on an unproven idea I wasn't going to risk it. Of course I later discovered it was a method used for real  ...  though couldn't find any data as to the efficiency compared to the other methods.
Cheers,  Roger
 
Warpspeed
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Water in a pipe can be a real problem if you are in a frost prone area.
Boiling in summer can be pretty interesting as well.

For what you are hoping to achieve, I think just a direct air heating system is definitely the simplest, lowest cost, and least trouble prone solution.
Cheers,  Tony.
 
Davo99
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  Warpspeed said  Water in a pipe can be a real problem if you are in a frost prone area.


Forgive my ignorance but can frost only  be at ground level and not higher up on a roof?  I imagine if the temp is zero it's zero but I don't know much about frost.

We sure get it here and sub zero temps and I was looking to put fans  in on my garden to try and keep some of the more seasonal Veggies alive but looking it up I was unsure
if moving air stopped frost or the fans they use in orchards brought down warmer air from above Ground level.

Built a veg oil heater to blow some warm air around but it seemed better just to let the thing radiate. was going to put some tube on the sides and blow warm air along the ground but Mrs wanted to reclaim garden to pave it so never got that far.

I imagine the amount of water would be significant but I wonder what amount of alcohol would be needed to meet the lowest temps Rogers area saw? 20L of Metho or Methanol isn't that expensive.

Other thing is if just turning the pump on when the temp hit say 2 o to keep the water circulating may stop freezing to a point at least.  I believe that's what they do in parts of the US and Europe.  Water is always circulated through the mains  and has a return to stop in freezing when stagnant. In any case the water at night would have some temp left in it and the tubes are not going to radiate anything only the plumbing and if that was insulated.... Should get through the night OK.  would want to get to at least 20 in the day before the heating for the home came in so would have that reserve for the next night.


  Quote  Boiling in summer can be pretty interesting as well.


Good point and may be the bigger danger.  Alcohol in the system would lower the boiling point as well.  I wonder if the system was drained and left open if the water boiling off in the tubes would be a big deal?  May be quite gradual.  as the weather warms up the water may boil off gradually in the spring so once the real hot days come, the tubes are already empty. Blowing some gentle air through the pipes may help  drive off the water slowly.

OTOH, if an ammonia solution was used, the steam could be used in a refrigeration cycle for cooling!  :0)



  Quote  For what you are hoping to achieve, I think just a direct air heating system is definitely the simplest, lowest cost, and least trouble prone solution.


True but then the versatility/ benefit factor comes into play. If the system can be used to heat the pool after the house heating is done, the cost and effort factor I would deem to be amortised through it's extended utilisation.
 
Warpspeed
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  Quote  Forgive my ignorance but can frost only  be at ground level and not higher up on a roof?  

Frost is a very big problem with solar water heating, both pumped systems and thermosyphon systems.

There are two methods used to overcome it.
A pumped system can briefly run the pump if solar panel temperature drops to within a very few degrees of zero. That circulates hot water through the panel, just enough to prevent it from freezing.

Thermosiphon systems can have a frost protection valve at the lowest point.  That opens and dribbles water out of the system, drawing in hot water into the top of the panels, which again keeps the panels just above freezing temperatures.

Swimming pool heaters using black plastic pipe it does not matter if it freezes.  The plastic pipe just expands a bit to accommodate the ice.

Copper pipe must be used for domestic hot water heating panels because of the much higher temperatures, and maybe even have to withstand full mains hot water pressure, may split if the pipes freeze.

They are both problems you would be better off without.  Much less to fail or go wrong.

You could always direct hot air (from a second air blower) to a ground mounted heat exchanger fitted into your pool pump circulating loop.
Cheers,  Tony.
 
Davo99
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  rogerdw said  

Glad you've got it worked out. I'm a bit nervous about mounting panels on my shed roof. It's pretty high and a reasonable slope, plus I've never fitted panels on a roof before, so need to get confident about doing it.


I procrastinated and thought about doing the house roof for literally 6 Months or more.  I was thinking of using cherry pickers and brick elevators and all sorts of things and it seemed a real Dilemma. I started getting up there to make measurements etc and then someone said get those Dunlop Volley tennis shoes because they grip well. And they certainly Do! Mrs even calls them my solar shoes. Only time I wear them. I got up there a couple of times and just sat up there admiring the view. I remember one afternoon I was up there and the neighbour and his Grandson cam out and were playing with a helium Balloon on a long string.  I sat up there for over an hour watching them  and just enjoying the peace and calm. Neighbour said later I looked very comfortable up there. I said it was very nice and a simple pleasure I thoroughly enjoyed.

I was going to get a mates safety harness but the day came I wanted to put the things up and he had it on site so I got some Unistrut, welded the door striker  from a car on it and  got on the roof ridge, unscrewed 4 Bolts, put the uni strut  there and screwed it down. I had got some thick rope and made an abseiling type rig that went through my crotch and around my waist and that was it.  I was pretty confident in any case if I did fall, All I had to do was land feet first because it's about 3 feet at very best between the height of the roof and the height of me and less if I'm tearing the guttering off on the way down! Long as I didn't land on my head and crack the Pavers, all good.

In the end, it was a complete walk in the park and 100X easier than I had imagined in my worries.  I was doing the BIG 420W panels as well so I started with the hardest panels I'd ever done but I didn't have one slip, mishap or single close call. Yeah, took my time, thought my moves through and looked for potential problems and what would happen but it was just a non event which I was happy for.  

Looked a HELL of a lot harder from the ground that it did  once I was up there.

I put a short novel about it here:

Panel install

Re done the array in the first pic on the back of the house now 3 times and haven't bothered with the rope sice the first time nor had any concerns.  Put on my solar shoes  and sunglasses and I'm good to go.  Only safety concern I have is that my daughter when helping me does not stand under where I'm working.  If I slip and   a Panel ( or I) come down, will come down fast and I couldn't give a flying about a wrecked panel ( or me that much) but she is another matter. Long as she is clear, all good.

  Quote  I
Yes, it doesn't feel right having to throw away a complete unit for want of a couple parts  ...  but when those parts are almost the cost of a new unit, it virtually forces you to replace it.


No, it never feels right to me to throw thing away that could be repaired but that's probably why I have so much damn crap around the place.  I'm trying to fight a loosing battle against things that are purposefully designed to be disposable.
I got stuff up there that is just badly or cheaply made I have repaired many times over the years. Under rated components that are impossible to upgrade but not hard to swap every few years and when you know why something has stopped the repair is even easier.


  Quote  
Yep  ...  never ceases to amaze me how little most people know or understand about practical things  ...  and we wonder why they talk so much crap about everything else. A lot of them don't have any clue about non practical things either.


Oh don't even get me started. Like that other place we know of infected by a 99% population of people that I think are hard pressed to tie their shoelaces and probably get the person in the shop to thread them initially when they buy them.

I get it some people have their knowledge in other non practical areas and that's fair enough.  Some people are just completely inept and have no skills in anything at all though. They always blame the government for not doing enough when they are hard pressed to change a light bulb themselves.  

  Quote   Temp meters can be used in lots of applications, so I justified those to myself  ...  especially seeing they are only $30 something each.


Don't know it would give you anything more than an indication but what about replacing the temp sensor with an LED or 3 to give an input based on the light levels it sees? Would tell you when it was brighter and darker at least.

With what you said before about getting more power on not so bright a day, Welcome to the world of Solar!
Seen this so many times with my Pv. Kinda hazy day  then a bright clear perfect day and you make less power.  Matter of fact, I prefer a few clouds than none at all, long as they don't block the sun.

I don't know what wavelengths panels work on, never looked it up, but it's sure as heck not just the visible spectrum alone, that I can say for sure. Probably their sensitivity spans into the UV and IR ranges as well and the Tubes are probably similar. What we see is only a tiny part of the magnetic spectrum so more than possible when the Visible spectrum goes down the other wavelengths go up depending what part of the spectrum they are in and what the panels/ tubes are sensitive to.  Being black, they probably have a pretty wide range actually.

Just like your phone can see the IR emitted from security camera's but your eye can't.


  Davo99 said  
Great idea, never thought about one of those.


They are compact and will sink a lot of energy.  Even a decent cabin heater core can pull 20KW and I'd say that's on the bottom end of the range. Get one out of a Mercedes or BMW or other Euro " 6 months of snow on the ground at home" built vehicle and Id guarantee they will do 50kw from my experience.

There are Liquid to air HE's on fleabay  etc as well all set up with fans and some have thermo control's as well. All you do is connect them to power and a hot water supply....or cold if you have a Chiller.


  Quote  

Hopefully by then I'll have finished my Warpinverter and have a roof full of panels so running the pump wont be so expensive.


Circ pump I just bought has 3 settings from 60 to 120W and will do up to 6M head so plenty of lift and would need about a kilo of power a day unlike my ducted fan doing a tad over kilo an Hour!


  Quote   must be some deep seated childhood issue lurking around there somewhere in regards to leaking pipes or flooded houses. That's my excuse anyway.


It's a fair one. To overcome it have all the plumbing outside and just have the warm air coming in the house. That's the way I intend to appease my similar concerns.


  Quote  ]

Thanks. I find that if I can think through and understand a complete process of building something  ...  then I have a chance  ...  but once there's a part that I don't know how to do  ...  or feels too difficult for my skills level, I come to a screaming halt.


Yes, I am similar. I have to have a pretty clear idea of how I am going to go about a task and what parts I' going to use to do it before starting. Not to say I don't get into it and then say "Oh ohh!!" a lot of times but....
My pet and repeated infuriation is planning plumbing and thinking I'll use this piece here and that there and drawing up a list of what you need  then going to get  them and no one around has that one fitting you need. You then need to completely re design the lay out in your head in the shop with an additional 17 pricy fittings to compensate for the one that every vulture has sold out of. Ugggh!


  Quote  

You are exactly right. It was only half way through this project that I realised that some systems did actually use "water in pipe" systems.


There you go. I thought they all had the heat tubes as well but 00% opf my knowledge of the things come from this thread. Just the same, couldn't see why they wouldn't work reasonably well at least just letting the heat bleed off as long as the water is moving.

Actually, if the design was a non pressure design and the HE was at the top of the manifolds which had a slight rise to the top like a gentle Inverted V shape,  the heat would thermo syphon and probably wouldn't need circulation at all.... Much like one of those heat tubes work.  


  Quote  I also discovered there's a third method, having a copper tube carry water into and then back out of the evac tubes to pick up the heat. A really tight 180 degree bend at the bottom of each tube.


Seems to me that would still be basically an air to liquid system if the tubes are not liquid filled. Also seems that would  leave a lot of heat on the table in the tube but maybe not.  Don't even see why one would need the return line?  Have a manifold with even 1/4" down pipes going to the bottom of the tubes and let the hot water flow out into the main manifold. One could run into the other and any thermal transmission between each side would be irrelevant because it would all end up in the same place anyway.

If the tubes in a single manifold with water going by is going to work, why go to any more effort and significant trouble and expense?
 
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  Warpspeed said  

That circulates hot water through the panel, just enough to prevent it from freezing.


Was just thinking... with these Tubes being evacuated, I'd expect them to be the last things to freeze. They are little thermos flasks after all and that's their whole claim to fame, no heat loss.

The danger to me would seem to actually be in the piping to and from the tubes.
They wouldn't be hard to insulate so may not take much heat in the system at all to keep it out of danger with the occasional circulation depending on the temperatures experienced and for how long where they are installed. Might only drop to freezing for a few hours like here and not be enough time to freeze them up.

I remember 2 winters ago fetching the mop bucket outside at 11Am and it still had an inch of ice on the top.
 
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The vacuum only really slows down conducted heat.
Radiated heat will go straight through a vacuum.

The suns radient heat gets here without any trouble at all through 186 million miles of vacuum. An inch of vacuum will do nothing to prevent your black surface becoming very cold indeed at night.  It depends what it can "see".  Relatively warm cloud overhead, or the sunless terrible cold of deep space.

A black surface exposed to the near absolute zero of space on a cloudless night will radiate all its heat very readily. Frosty nights are always clear nights.

Cloud blocks thermal radiation.  Cloudy days are usually cool, but at night the clouds prevent the extreme heat loss you will get with a clear starry night sky.
Edited 2021-05-19 16:03 by Warpspeed
Cheers,  Tony.
 
rogerdw
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  Warpspeed said  Water in a pipe can be a real problem if you are in a frost prone area.
Boiling in summer can be pretty interesting as well.

For what you are hoping to achieve, I think just a direct air heating system is definitely the simplest, lowest cost, and least trouble prone solution.


Yep, I like simple, low cost and least trouble. I can always aim higher later on once this is finished and my inverter project is up and running.



  Davo99 said  I started getting up there to make measurements etc and then someone said get those Dunlop Volley tennis shoes because they grip well.


Thanks for the advice there, I'll have to look out for some.

When we had the workshop built here and gutters put on the shed, the builders used a couple of scissor lifts. They were awesome.

I took the opportunity over the weekends to use one to change all the fluros inside the shed, because I have no way of getting to them otherwise. Shed's too high.


  Quote  I was going to get a mates safety harness but the day came I wanted to put the things up and he had it on site


I'll definitely be using something to help prevent disaster. I do know where a safety harness is, I might see if I can borrow that. The roof is high, gutters are at 14 feet.

 
  Quote  Looked a HELL of a lot harder from the ground that it did  once I was up there.


Awesome, I hope I can say that when I'm finished. I enjoyed your short novel and do recall reading it before. Great job.


  Quote  No, it never feels right to me to throw thing away that could be repaired but that's probably why I have so much damn crap around the place.


Sounds like my place. But then I invite people to drop off stuff to be fixed. That's my job.



  Quote  Don't know it would give you anything more than an indication but what about replacing the temp sensor with an LED or 3 to give an input based on the light levels it sees?


That's an interesting idea. Had certainly not thought of that. I had thought about buying a datalogger multimeter and jerryrig some sort of light meter to feed into it  ...  but the ones I found on ebay have to come from China, so potential big delay.


  Quote  With what you said before about getting more power on not so bright a day, Welcome to the world of Solar!


Haha, yep. I already had noticed something similar with the pool pump really zinging along on days where I expected it to struggle  ...  but being quite mediocre on bright sunny days. Never seemed right.



  Quote  It's a fair one. To overcome it have all the plumbing outside and just have the warm air coming in the house. That's the way I intend to appease my similar concerns.


Yes, that's what I'd have to do for peace of mind. I'll still have plenty of tubes to play with, so maybe aim for water with the next lot.  
Cheers,  Roger
 
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  rogerdw said   The roof is high, gutters are at 14 feet.


Wouldn't want to bounce off the ground from there. I think the big thing is the angle of the roof. Steepest pitch on the shed is 8o . it's nothing. Most is 5o so even less.  The house is 35 and there is no walking round on that. Need a hand hold of some kind at all times.

The roof battens are 1M apart. I take the roof screws out, out in a solar bracket and then can hold myself or use them as a foot hold.
I started with a panel along the lowest line of screws near the gutter.  Pushed that up from the ladder and screwed it down. Then got on the roof and used the panel as a foot hold. Pulled the next panel up, manoeuvred that into position and Daughter screwed that down. Once the lower row was done I could walk along those ( pretty much laying sideways on the roof)  and used a strap with a hook my Daughter connected to the lip of the panel and dragged it up over the gutter, across the lower panels and into position. It was not elegant or graceful but it works and now we have done it so many times don't even think about it.

If your roof is less steep the Job will be exponentially easier. From what I understand a lot of homes are built with 22o roofs. That would be nice! Must have been expecting snow round here to make mine so steep!



  Quote   I had thought about buying a datalogger multimeter and jerryrig some sort of light meter to feed into it


Might be as simple as connecting some LEDS to a datalogging Multimeter. The LEDS will generate a current when exposed to light so all you need is a way to record the input.

[QUOTE I'll still have plenty of tubes to play with, so maybe aim for water with the next lot.  

Might be interesting to set up half a dozen to test as water heaters.
Could use the pool as the reserve and tap off from the pump to circulate the water. wouldn't need much flow.   Wouldn't change the pool temp but you could easy put a temp sensor in each end and measure the in / out temps.
 
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  Warpspeed said  The vacuum only really slows down conducted heat.
Radiated heat will go straight through a vacuum.


Very enlightening.
I am certainly learning a lot from this thread.

Thanks Tony. :0)
 
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