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Forum Index : Solar : Solar hot water and Rayburn
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| Taswind Newbie  Joined: 13/12/2012 Location: AustraliaPosts: 31 |
Hi all As well as the windmill I am working on , I am also going to install a second hand solar hot water system . Have a Beasley flat panel system with a 300 litre stainless close coupled tank with a heat exchanger between the panels and the cylinder , I have also purchased an old Rayburn slow combustion stove . Now the fun bit , I want to connect these together , so my question for today is 
Has anybody or does anybody know ?????? Can I run the rayburn through the heat exchanger and open vent it with a top up tank mounted above it . The heat exchanger as is , is a closed system , but has a bung on the top of it , which I was thinking of removing and running into the top up tank , which in theory should allow it to vent into it and then top up any fluid lost due to boiling of the system . The panel and heat exchanger also run on a glycol , water mixture system , but have read that you can also run this through wetback woodstoves. Anybody got any experience with this ?? Big ask I know Will post up a pic later |
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| MOBI Guru  Joined: 02/12/2012 Location: AustraliaPosts: 819 |
Hi Taswind, I built my own home about 8 years ago now and put in a system similar to yours. I have a slow combustion lounge room heater (with oven and cook top) fitted with a wet back. Also on the roof, I have two solar collectors which feed into a heat exchanger coil in the water heater tank. It is of course a closed loop using a vegetable based anti freeze/boil compound. It works off thermosyphon as the water heater tank is gravity fed to the house and vented to the air. The wet back in the wood heater thermosyohons the actual water through inlet/outlet in the top and bottom sides of the tank. I don't think the wet back can withstand more than a few metres head. Mine is about 4 metres which gives me enough pressure for the shower. We are in the south east of south oz and have never run out of hot water - also, being on solar and wind only (no grid), we don't know what a power bill is nor for that matter a power failure. Can you do up a sketch of what you propose? david m David M. |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Yeah, traditionally wetbacks were run directly coupled with the hot water tank with a header tank and a steam/vent tube at the highest point on the roof (above the header tank level). I would be guessing here but I cant see that anything has changed, the HWS needs to be open to the atmosphere when it is heated with a large heat source that is not controlled. It can get a bit freaky if the stove gets the water real hot, when a tap is switched on the pressure drop will let the water boil in the tank and blow hot water out the vent tube. I would be interested to know what the maximum possible head is, the Beasley HWS in my house is Circa 1963 and the owners manual is long gone. Comes to that, so is the wetback Carmichael stove, my parents sold it for $90 in 1972. I'm confused, no wait... maybe I'm not... |
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| MOBI Guru Joined: 02/12/2012 Location: AustraliaPosts: 819 |
The unit I have in the roof (Solar Mio) is nothing more than a copper vessel inside an insulated galv iron container. It couldn't withstand any internal pressure other than that wich develops when the vessel is full. The wet back in the heater (Metal Dynamics - gourmet)look fairly solid and can handle more pressure, at least the head from roof height to lounge room floor. I don't use hot water pumps to cycle the water only thermosyphon - I like to keep things as simple as possible (less to go wrong when we are away). david m David M. |
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| Taswind Newbie Joined: 13/12/2012 Location: AustraliaPosts: 31 |
MOBI , when we sold our house on 50 acres a few months ago that was our plan too , was buying 100 acres of bush and going to build an off grid home , somewhere in between though my wife talked me into moving back closer into town  .
Is not too bad though ,is close to everything and still have a few acres to play on , but I have all this stuff I have been saving up for the off grid house , so am putting all to use here  in the hope of knocking my power bills down .
yahoo,The hot water cylinder runs on town pressure , not low, so I cant feed straight into that , so I need to run a heat exchanger , and vent that . The system that I have has a heat exchanger on it already for the glycol section , to stop it freezing down here in the cold , so I was hoping I could tee into this and run the wetback through it as well as the solar panels and it would transfer heat to the hwc the same as the panels . But I will have to vent it , it is sealed currently , on the pic below you can see the cylinder and the heat exchanger , what I would like to do is to tee into the lower pipe and then take the cap off the top of the heat exchanger and connect it to a header tank to mount above it for it to vent out of? Any ideas folks ? Will it work 
My main two concerns are is this heat exchanger going to be big enough ? or is going to be continually boiling , I am hoping that the heat the hwc is always sucking off it by thermo syphoning will be enough , works with the solar panels??? Also if I tee into it , will this somehow make the solar panels thermo syphon ,when I am using the woodstove in the cooler months drawing warm water into them and cool the hot water off , am hoping because the water in the panels is colder it wont be drawn into the heat exchanger ??  |
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Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
I dont think you need to make a closed loop system into a open loop system just to add a solar collector. But the problem of thermosyphon in reverse is a issue you need to address in the design, as for example in a loop system with no directional flow control the hot water at night will travel backwards to the solar collector and dissipate the water heat to the air temp...... not good. Just view it as a one way circulating system and design to only permit a one way flow. (use check valves in the system) Pete. Psst, i thought the grass was greener in Tassie, but all i see is dead leaves and brown grass?  Sometimes it just works |
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| Taswind Newbie Joined: 13/12/2012 Location: AustraliaPosts: 31 |
Pete , The grass was green about 2 weeks ago , but a few hot days and the wind has been blowing steady and it is brown now , will be a bad year for fires down here this year , have had plenty of growth and now it is dying off quick and no rain |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Well all i can say is "watch your Butt" [punt intended] as it might prove a bad year for fires. Its not a lot better here local either. Pete. Sometimes it just works |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Be careful about closed systems with solar and combustion heating. As there is no thermostat to turn off the heat it can boil quite a lot. You may have seen the Mythbusters episode where the deliberately disabled the safety valves on a hot water system. The result was extremely destructive to the building around it, if anybody was near it they would have been very severely scalded by the steam. Watch this if are tempted to use a closed system. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Taswind Newbie Joined: 13/12/2012 Location: AustraliaPosts: 31 |
G,day Madness It will be an open system when I change it , will work just like a normal heat exchanger and be topped up from a small header tank , which it can also vent through. You can buy a heat exchanger for wetback connection to mains hwc that work exactly like this , but I already have this one which should work the same way am hoping , at worst , if it doesnt work , I will have to run two heat exchangers , the one for the solar input and one for the rayburn input . Am just trying to do it all on one heat exchanger . Stage one is complete , I have the solar system up and running , but the Rayburn wont be added until a bit later as I want to change the kitchen around to fit it in . |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
So long as the wet back can thermo syphon to your existing heat exchanger it should be no problem. Would probably help to have something in the heat exchanger that to raise the boiling point such as automotive coolant additive. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| MOBI Guru Joined: 02/12/2012 Location: AustraliaPosts: 819 |
Have you seen the "In Flue" type of heat exchanger where the bottom section of flue is removed and replaced with a stainless sleeve with inlet and outlet fittings. Just like a wet back but doesn't take up fire box space. They are fairly effective but not quite as much as the true wet back. They don't look too unattractive especially if the mesh sleeve is used over them. David M. |
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| Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
Do they have any issues with creosote build up? There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| MOBI Guru Joined: 02/12/2012 Location: AustraliaPosts: 819 |
I've never used one, just seen them in the "Slate and Fireside" shop. I did ask at the time I was shopping around for hot water systems when we built our house but wasn't made aware of any problems. I thought that they were overly expensive. Anyone with basic welding skills could make one for a lot less. I suppose, if you use dry, seasoned hardwood, even though it is a cooler section of the flue, it shouldn't be any worse than an ordinary flue secition. (Opinion only). David M. |
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| MOBI Guru Joined: 02/12/2012 Location: AustraliaPosts: 819 |
I thought I'd put up a couple of pictures of the wet back heater we have. As you can see, it has a generous cook top and an oven which is great for baked dinners and making cakes. A bit tricky for bread though. The wet back system is open loop to the header tank in the ceiling through 1" copper pipe up the wall cavity. No, it doesn't have a slope, Ilean. 
David M. |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
I have had a look around at a few wetback units since we last chatted about this. It looks to me that they are deliberately designed to transfer a very small amount of the heat available from a heater, not like a boiler at all. I find it hard to believe that there is not an off the shelf relief valve that would easily hold this system at a set low pressure, 10 PSI?. I do notice that companies like solaradiant recommend fitting a heat dump to prevent "stagnation" with their large systems. If it could be run at low pressure with an expansion tank and relief valve it would solve a lot of problems. http://www.radiantcompany.com/system/ I'm confused, no wait... maybe I'm not... |
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| MOBI Guru Joined: 02/12/2012 Location: AustraliaPosts: 819 |
When I built the farm house about 23 years ago, I had an old low pressure copper barrelled hot water system which had exactly what you are talking about. 23 yearsw isn't that long, so surely the LP valves it had are still around. They didn't look much different to the modern day ones. Perhaps one of the new ones can be adjusted?? David M. |
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