Questions from a newbie

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Re: Questions from a newbie

Postby Gordon-Loomberah » Sun Sep 09, 2012 9:14 pm

Dono2012 wrote:Can anyone tell me where the wetback might connect based on the diagram I posted earlier?


If that is a mains pressure tank without a separate circuit/heat exchanger inside it that is open vented for the wetback circuit, it can't really be used with a wetback.

With the next diagram, what does the red box above the stove represent? The main tank in that diagram appears to be low pressure, so it could be connected to the wetback without the need for a separate tank, but would still need a pump if at ground level. Heating a pool sounds a bit optimistic though! The tank would need to be rather large, with a large evacuated tube array connected for any significant amount of slab heating too, unless the wetback was of very high output and was always running when slab heating was required.
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Re: Questions from a newbie

Postby Dono2012 » Mon Sep 10, 2012 7:26 am

Thanks Gordon,
I was hoping someone here would have a system like the one I am trying to put together ie solar/wood with lpg booster who can tell me how their system connects together.
I'll keep looking on the web.
Cheers
Dono
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Re: Questions from a newbie

Postby Gordon-Loomberah » Mon Sep 10, 2012 8:43 am

I run a similar system- 78 evacuated tubes for hydronics heating and a separate 30 evacuated tube system for hot water. I've written about it and posted pics a few times in the forums. One of these days I'll hook the wetback up to the hydronics system via an open vented tank in roof space, and a heat exchanger connected to the hydronics tank.
I have a heat exchanger that can transfer heat from the hydronics system into the hot water on its way to the house, if the water isn't hot enough after a few days of cloud and rain. I don't run any sort of gas or electric boosting, and I'd suggest that you wouldn't need to either, if you have enough evacuated tubes and the wetback.
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Re: Questions from a newbie

Postby Cherokee Solar » Mon Sep 10, 2012 8:25 pm

Hi Dono,

I never get any email updates about this thread and so think it is dead, when it is very much alive and kicking! :D

What you are asking about is the exact system that I have and use here.

Gordon is spot on. The tank must be open vented and sit above (or close to above) the wood heater (with the wet back). My 400L tank sits in the roof cavity on a platform of 120x45 KDHW timber (sitting in a drained galvanised steel tray). Easy.

Don't be tempted to run a pump between the wet back and the 400L tank, because the pipes and wet back can get very hot and if the pump ever packed it in... A thermo-siphon is the best design as the water circulates by convection from the cold water in the 400L tank in the roof to the wood heaters wet back and then back up again into the 400L tank (gradually heating it). The plumber here who was excellent in such matters tested this arrangement out at another house in the mountain range to see what would happen and the results weren't good!

You can add solar hot water panels too so that when the sun is shining and the wood box is not operating, you get free hot water (and hydronic heating via radiators in the house)! ;)

The 400L tank provides hot water for the house (via an 18m copper coil that sits inside the 400L tank) and also hydronic radiators. Plus the wood box has an oven and hot plate combination which I use all of the time. When the wood box is going I bake a loaf of bread in it every time, plus the house smells of baking bread. YUM! ;) Not to make you jealous, but there is a loaf of bread in there right now - check the photo!

Wood Heater.jpg
Wood Heater.jpg (98.86 KiB) Viewed 6089 times


It is a really simple and effective system. The plumber added a small LPG booster too which operates on the days when it is warm and cloudy (ie. no wood heater and no sunshine) so that you have hot water regardless.

The 400L tank is really well insulated and it takes a few days to lose its heat. The water at the hot taps is much warmer than what you'd get in a new house these days (which I'm very happy about)

The wood heater was made by an Australian company (I think in Albury) - Thermolux (Gourmet cooker).

It was supplied as a total package including solar hot water panels by a company in Melbourne (and also Geelong) called Pivot Stoves and Wood Heating.

Check out their website as there is all of the information you need.

Give us a yell if you have any questions, like how does it work in the real world?

Glad to be of help!

Regards

Chris
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Re: Questions from a newbie

Postby Tracker » Wed Sep 12, 2012 7:14 am

Gordon-Loomberah wrote:You must not run a wetback stove into a pressurised tank- it must be open vented. You mention a pressure relief valve, so I assume it is high pressure water?


How would you go building a heat exchanger for the wet back.
Fit a pipe from the lower to the upper ports on the tank. This sits in a big and insulated Cu tube, with a second tube through it for the vented wet back system. Oil filled or glycol :-)

Would this not give you the best of both worlds.. :?:
..
.
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Re: Questions from a newbie

Postby Gordon-Loomberah » Wed Sep 12, 2012 8:36 am

The tank connected to the wetback has to be open vented- you could just run a long length of coiled Copper pipe with the high pressure water in it, sitting in that tank, or else a radiator style heat exchanger- much more surface area in a compact volume, that is designed to take high pressure, so a car radiator wont do if connected to the mains, but is fine with a 6-8m head pressure tank, as might be found in rural areas.

IMO, you would not want to fill the tank/wetback with Ethylene Glycol or oil, as they have less specific heat capacity than water, and you need a high concentration of Ethylene Glycol to get any appreciable increase in boiling point, which leaves you with 2 disadvantages- less heat capacity to shift the heat from the wetback, and a temperature that might heat the water sitting in the high pressure side of the pipe to over 100C- and when that is released it will explosively boil if significantly over 100C :!: :o

So, I'm not sure which worlds you were thinking of, but I might stay away from them! ;)
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Re: Questions from a newbie

Postby Cherokee Solar » Wed Sep 12, 2012 9:34 am

Tracker wrote:How would you go building a heat exchanger for the wet back.


Hey Tracker,

The heat exchanger sometimes can simply be a coil of copper pipe wrapped around the heater flue. As long as the water can travel consistently upwards it should be OK. Flues on wood heaters get pretty hot and are usually also considered to be part of the available heating.

In my case, the heat exchanger replaces some fire bricks inside the wood heater at the back of the combustion chamber. It is a steel (cast I think) box with an inlet and outlet pipe going through to the back of the heater and from there up the wall and into the 400L hot water header tank.

That tank must be open ventilated as you really can't afford to turn your hot water system into a pressure boiler. If the wood heater is run for 2 days solid here, and you don't run the hydronic heating or slow the combustion down on the wood box, you can hear the water in the 400L hot water tank rumbling away. The system has a controller which releases excess heat into the solar hot water panels if the temperature exceeds 80 degrees.

Incidentally, the other thing I have learned and observed at other peoples places is to not be tempted to purchase a wood heating box with too big a combustion chamber. The reason for this is that the larger the wood heating box, the more timber that you will use. I've known people who have had to go through a tandem trailer load of firewood every week and it doesn't have to be that way.

It is kind of like watching the television show Grand Designs when an owner or builder is banging on about how sustainable the house is, when the house is in fact 700m2! There is no possible way that large houses can be even remotely efficient. I guess if you say it often enough...

Regards

Chris
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Re: Questions from a newbie

Postby Dono2012 » Wed Oct 17, 2012 10:16 am

Hello,
Havent been here much lately...working on our building project.
Our system has been working well and powering our tools and running our fridge.
The small metal shed I am using for our solar control gear does get hot though...over 30 somedays...and the regulator fan kicks in to cool it down...the inverter doesnt seem to mind the heat so much and the fan kicks in when i boil the jug or run the microwave.
I am planning to run a pedestal fan but was wondering if I could run a small airconditioner in that shed from the 3000W inverter?
Any thoughts anyone?
Cheers
Dono
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Re: Questions from a newbie

Postby Gordon-Loomberah » Wed Oct 17, 2012 10:24 am

You certainly *could* run one, but there are passive measures you should take first!
Trombe walls would help a lot- just use sheets of plywood spaced off the existing metal walls by 70mm (mounted on edge-wise vertical 70X35 timber works well, thats what I use), and painted a light colour to keep the walls at ambient, rather than solar heated and much hotter. That made a huge difference to the internal temperature of my power shed on hot sunny days. I also added a roof-top ventilator, which also made a noticeable difference, and if you wanted more- you could add some insulation inside the walls.
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Re: Questions from a newbie

Postby Gordon-Loomberah » Tue Jan 22, 2013 9:45 am

Hey Dono, are you still with us? How is your system going? I hope you didn't suffer any damage from the Wambelong fire on your building project.
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