Thread: Shed heating ornament

Originally Posted by shedhappens

That does surprise me Dean, in the last house I built I put the tank as high as I could get it in the roof and put the solar hot water panels as low as possible, ie near the gutter, these also had to be lower at one end that the other, the lowest point being the inlet and the highest point being the outlet to the hot water tank, these panels were supplied with non return valves to stop the water cooling at night and during ###### weather.
Then when I fitted the water jacketed flu heater I also fitted non return valves but I had problems with the hot water in the tank cooling somewhat through the day during inclement weather when the heater had gone out, when I noticed this I put I put my hand on the flu heater and it was quite warm ? So why was the water circulating through ?
Because I was a tight #### and fitted el cheepo non return valves, so I replaced them with good quality vavles ($180) and added much more insulation to the pipes between the water heater and the tank, problem fixed.

Cold water falls, hot water rises, that is how a thermosiphon hot water system works.

I would be interested to know why your system doesn't require non return valves ?
I'm thinking that your slow combustion stove is always burning so this problem might not be evident ?

shed

The thermosyphon system works by, as you say, hot water rising and cold water falling. When the fire is burning the hot water in the jacket gets hot and the water rises up to the tank thru the upper pipe (inlet). This lift pushes the slightly heavier cold water down the lower (outlet) pipe and back to the jacket. The system needs to be hotter at the bottom for a thermosyphon flow to occur. If it is hotter at the top the hot water wants to stay there.

When the fire is not burning the hot water is all at the top so to speak so there is no lift to move water. The water settles according to density. Cold at bottom and hot at top.

Our stove goes out all the time. We get lazy, surprisingly enough. Early this week it went out overnight (we slept in). It was lit again that night and the water was hot very quickly, as in the hot water was cycling around.

I know that if the heat source is higher than the storage tank then non return valves and a pump is required. I have seen every mm of our pipes except for the 6mm in the ceiling (asbestos sheet) and I can tell you that there are no non return valves there. Also I installed the piping to this stove when it was installed. The pipe was already there but needed a bit of adjustment to fit the new stove.

I have started making some solar hot water panels (some years ago) based on plans from an Earth Garden book (self sufficiency magazine). There is no mention of non return valves. The only time I have seen mention of non return valves is when the storage tank is lower than the collector panels.

I do not know why your flue jacket was cooling the water.

Dean

Another point I just thought of is that the hot water storage tank is a thermosyphon system in itself. If the tank is full of "hot" water and the fire goes out and then some hot water is used

The remaining hot water will stay at the top of the tank
The new cold water fed in to replace the hot, will stay at the bottom.

Over time the temperature will even out but after 24 hrs we can have a shower and the water is still quite hot.

Dean

Its got me stuffed to, were i grew up we had a rayburn that supplied all our hot water, plus heat, cooking etc. In summer we generally had to light it every 3 days to get hot water, in other words the water definitely didn't cool by syphoning back into the jacket. The tank was on a stand directly behind the stove (In a sort of cupboard, great place to grow mushrooms), that way any heat loss from the tank went into house heating.....
My current solar hot water system is the opposite, pump driven with check valves and a fancy "soft" valve, it stops the thermosyphon but will open when the pump comes on.
Dean, way OT but have you seen this site? Solar Water Heating Projects and Plans

Of course the other thing to do with hot water from the shed stove is pump it to a radiator on the other side of the shed......

Cheers,
Ew

Originally Posted by Ueee

Its got me stuffed to, were i grew up we had a rayburn that supplied all our hot water, plus heat, cooking etc. In summer we generally had to light it every 3 days to get hot water, in other words the water definitely didn't cool by syphoning back into the jacket. The tank was on a stand directly behind the stove (In a sort of cupboard, great place to grow mushrooms), that way any heat loss from the tank went into house heating.....
My current solar hot water system is the opposite, pump driven with check valves and a fancy "soft" valve, it stops the thermosyphon but will open when the pump comes on.
Dean, way OT but have you seen this site? Solar Water Heating Projects and Plans

Of course the other thing to do with hot water from the shed stove is pump it to a radiator on the other side of the shed......

Cheers,
Ew

Thanks Ewan but I have seen that one and been through most of the designs. IIRC my design is represented in there. I have to get back to making those panels. It should save us having to light the stove in summer.

My grandparents had a Rayburn and our neigbours also have one. Both supplying hot water.

Some years ago SWMBO bought one cheapish. The top plate was stuffed. The rope grooves were rusted off. We did have some fun getting a Tiger Snake out from underneath it, on the back verandah while we had about 3 big pots of plum jam cooking up on various gas BBQ's etc. The jam did get slightly burnt.

Dean

Originally Posted by Oldneweng

I do not know why your flue jacket was cooling the water.

Dean

Dean there are a lot of variables when installing a thermosiphon hot water system, the position of heat source and the position of the storage tank are not always going to be perfect so you have to adapt and design your system around those problems.
Here is a document that can help explain "Reverse Thermosiphon" to you, http://solar1.mech.unsw.edu.au/glm/p..._flow_SE86.pdf
If you do go ahead with your solar hot water panels and want them to be efficient and reliable you will need non return valves, and no doubt frost valves if you have the problem of pipes and pumps freezing at certain times of the year.

shed

Originally Posted by shedhappens

Dean there are a lot of variables when installing a thermosiphon hot water system, the position of heat source and the position of the storage tank are not always going to be perfect so you have to adapt and design your system around those problems.
Here is a document that can help explain "Reverse Thermosiphon" to you, http://solar1.mech.unsw.edu.au/glm/p..._flow_SE86.pdf
If you do go ahead with your solar hot water panels and want them to be efficient and reliable you will need non return valves, and no doubt frost valves if you have the problem of pipes and pumps freezing at certain times of the year.

shed

I am going to have a considerable distance between the hot water tank and the collectors so I don't consider reverse flow to be an issue. It will probably be 3 to 4ft. I am lifting the storage tank above the roof, along with the cold water supply tank stand so we get better water pressure and because there will not be sufficient height between the top of the collectors and the storage tank. I have already got this one worked out. The storage tank will be fully enclosed and surrounded with lots of insulation. This all makes the solar design simple.

The article still does not explain why you were getting reverse flow as the temperature at the jacket would not be all that cold. At most ambient I would have thought.

Dean

Dean, how will you frost protect it? Well I pressume you get below zero there? Mine has a line of code in the controller (home made) that turns the pump on if the temp gets too low, feeding the collector's with water from the bottom of the storage tank, usually about 14 or 15deg in winter.

Originally Posted by Ueee

Dean, how will you frost protect it? Well I pressume you get below zero there? Mine has a line of code in the controller (home made) that turns the pump on if the temp gets too low, feeding the collector's with water from the bottom of the storage tank, usually about 14 or 15deg in winter.

Below zero is actually rare around here. It does happen a couple of times a year I suppose. I was going to look into the frost valves but I have't decided yet. Winter would not be much of an issue with solar hot water as we generally get all our water heating from the range. I could even drain the collectors. I will be fitting isolation valves at the connection points of the pipes near to the storage tank. The solar is only to provide hot water during the hot months.

Dean

Originally Posted by Oldneweng

I am going to have a considerable distance between the hot water tank and the collectors so I don't consider reverse flow to be an issue. It will probably be 3 to 4ft. I am lifting the storage tank above the roof, along with the cold water supply tank stand so we get better water pressure and because there will not be sufficient height between the top of the collectors and the storage tank. I have already got this one worked out. The storage tank will be fully enclosed and surrounded with lots of insulation. This all makes the solar design simple.

The article still does not explain why you were getting reverse flow as the temperature at the jacket would not be all that cold. At most ambient I would have thought.

Dean

G/day Dean, I think that the problem with my flue heater demonstrates that rules can be broken when it comes to thermosyphon, the pipes from my hot water tank had to travel about 7 mtrs before descending another 2 mtrs down the wall to the flue heater, that is roughly an 18 mtr round trip for the water.
When I noticed the warmth in the flue heater (when the fire was out) I got up in the roof and felt the pipes at the hot water tank that went to and from the flue heater, the top one was quite warm for a considerable distance and the bottom one was less warm, that is how I determined that I was getting reverse flow when the fire was out.
So why ? You tell me, I think that there only needs to be a temperature difference at the upper and lower pipes for the flow to commence, but why it would wanna flow backwards ? I don't know.
I am assuming/guessing that any heat in the flue heater from the water would cause a draft in the flue that might perpetuate the problem and "possibly" further cool the water in the heater to make it sink and thus drawing the hot water out the upper pipe, if, how and at what speed this could or would happen I don't know ? If at all. I would be interested on all theories of this phenomenon.
When I did all this there was no internet, the research that I did at that time suggested that I would need non return valves.
Maybe I didn't need to replace them with better valves, maybe I didn't need them at all because it could have been the extra insulation that I put on the pipes that did the trick ?
Why does yours work without valves ? Or are they in the stove or the hot water tank ? If not, then it shows that two systems that work on the same principles can act quite differently. Why I don't know ?

Here bellow is a cut n' paste from a gov dept about the requirements for a wet back or flue heater, I think that (b) iii relates to not using shut off valves, so you don't make a bomb, they don't mention non return valves, I broke a couple or more of their stooopid rules but ended up with an excellent water heater once the bugs were ironed out.
From what I have just read on the internet there seems to be a few different opinions out there.

7.4.1
Installation considerations
When installing a boiler as a booster, the following issues should be considered:
(a)
The heat source should be located below the storage tank to allow thermosiphon flow.
(b)
The flow and return lines from the storage tank to the boiler should:
i be copper
ii rise or fall in a continuous gradient
iii have no valves fitted to them
iv have no dissimilar metals in them
v have no elbows fitted to them
vi have a diameter relative to the length specified in Table 7.2;
vii connect separately from those lines to the collectors to prevent interference between
the two systems
viii be insulated to the required R-value so as not to be a hazard.
(c) The storage tank must be copper or stainless steel. Vitreous enamel tanks should not be
used as the enamel can dissolve at high temperatures.
(d) The system must be open vented to the atmosphere to prevent any pressure build up in
the boiler.
(e) Pressure/temperature relief valves must not be used.
(f) Boilers must not be connected directly to mains pressure storage tanks.
(g) A tempering valve must be fitted to the hot-water line to the house

That came from here and might be worth a look
http://ee.ret.gov.au/sites/climatech...ence-guide.pdf

Originally Posted by Ueee

Dean, how will you frost protect it? Well I pressume you get below zero there? Mine has a line of code in the controller (home made) that turns the pump on if the temp gets too low, feeding the collector's with water from the bottom of the storage tank, usually about 14 or 15deg in winter.

G/ay Ueee, the frost valves I had often started to dribble at 9.30 to 10.00 pm on a clear night, the water just run down into the gutter and back to the storage tank so it didn't matter. I had a tank up the hill that gravity fed the house so when the frost valves opened they not only stopped the solar hot water panels from freezing but also the exposed pipework from there to the house.

It got pretty cold there one night and the water jacket on the pilot motor of my D4 dozer was frozen up and split open That taught me not to be a tight #### and put the green stuff in

Made some more progress over the last few days...

The 'throttle' is welded in... the plate rotates via a pin which is plug welded to the plate on the top (as pictured) to a lever underneath.... a lesson learnt a while ago... attach earth clamp to the bits you want to rotate rather than the biggest chunk of metal, or it might not ever move again....

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I've attached a few legs made from 50 x 50 x 3 SHS. Here you can see the lever that rotates the plate inside. There is a bit of stuffing about here.... if you weld it in the wrong spot you might never really know what the plate inside is doing as you move the lever. When upright, this stove will be full open with the lever to the left and fully closed to the right... I think....

CIMG0493.JPG

I fished a couple of big slugs from one of the scrap bins and turned them into feet... I drilled the holes to bolt the stove down with a couple of dynabolts. If you look carefully you can see the 'pierce' and 'lead in' from the laser which I have filled with weld..... working for a laser cutting company is pretty good, but the dangerous part is there is an endless supply of stuff that 'might come in handy one day'.....
CIMG0485.jpg
CIMG0496.jpg

Attached the shelf for the cinder box and guides made from a bit of angle. The round plate is once again a big slug from the centre of a 5.0mm mild steel flange we cut for a customer.
CIMG0497.jpg


The base is now finished, just needs a bit of a cleanup with the grinder mounted wire brush and a chiseling of the stubborn weld spatter. Will probably paint the legs with VHT Engine Enamel and the hot bits with pot belly black.

Shedhappens, my stove pipes go straight up the chimney for about 2m and then about 5m across the attic on a slight rise, the top one a bit more due to different heights of connections. When me bought the house there was a different stove/wetback and no insulation on the pipes at all. I have added some and will cover all of it in the attic.

I am pretty sure there are no valves in the wetback or the hotwater tank. I have had the connections off both and if there were any valves they would have to be non-removable/repairable. Our hot water tank is about 60yrs old. I have poked stuff into the connections to check for silt etc.

The insulation would have some effect for sure but it is too complex for me.

So why ? You tell me, I think that there only needs to be a temperature difference at the upper and lower pipes for the flow to commence, but why it would wanna flow backwards ? I don't know.

I was hoping you could explain it to me. It is always good to learn about stuff like this in case it comes in handy. You are correct that a temp difference at the top and bottom pipes can cause flow. Hot water is less dense than cold due to expansion. This causes it to want to rise. It is a combination of hot water trying to rise and cold water trying to fall.

the top one was quite warm for a considerable distance and the bottom one was less warm, that is how I determined that I was getting reverse flow when the fire was out.

The top pipe on the storage tank is the inlet for the hot water. It goes in here. There is of course heat transfer to the water in the pipes and the top of the tank is always hotter than the bottom, unless the water is all boiling and rolling over. We have had that happen a few times.

I would suggest that there are some factors involved here that we are not aware of. My father built a hot water unit many years ago using a stove with a wetback, 1/2in copper pipe and a 44gall drum on a stand about 3ft high just outside. No insulation at all. As far as I remember it worked although it was for the seasonal workers hut so I did not use it myself.

Re the cut n' paste material, having valves and elbows tends to break up the flow. Not a good thing. Most is just common sense. Having a continuous gradient would be ideal but I doubt there are many around that have. I was planning on valves between collector panels for convenience in connecting, them as I was going to build them one at a time and just add them on as they are ready. I will probably put a valve on the ends of the top and bottom pipes to shut them off then remove the valves and connect the next panel with a compression fitting. The valves would also be attached with compression fittings.

Dean

Originally Posted by Gerbilsquasher

to try and avoid welding the mild steel plates to the cast iron brake drums... I wasn't sure how well they would mix!

so what holds and seals the middle section ( i guess its steel) to the top and bottom drum?

Great to see see your progress Gerbilsquasher. We had to keep ourselves entertained while we waited lol.

working for a laser cutting company is pretty good, but the dangerous part is there is an endless supply of stuff that 'might come in handy one day'.....

I am sure we can think of some ways to alleviate the Danger. We wouldn't want anything bad to happen to you.

Nice forge.

Dean