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Post by chrisz on Oct 3, 2011 14:16:08 GMT -8
I'm looking to build a brick rocket heater similar to Lars'. I'm also looking to add a coil on the top of it for hot water.
I've noticed from other sites wood stoves and a masonry heater web page, they seem to like 3/4" as a good size. Any thoughts?
Any thoughts on how many bends to put in (the top of the heater is roughly 18X22)?
I am thinking of taking the brick rocket heater, and on top of the top course I was going to pour a cap with the coil in the cap. If the heater itself has a firebrick top, I should be safe casting another top from "regular"concrete? any thoughts?
thank you
cz
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Post by canyon on Oct 5, 2011 20:32:06 GMT -8
3/4 inch is the minimum size in my opinion and be sure to put a pressure relief valve where the coil exits without the possibility to isolate it. You can do concrete there but you also can avoid the concrete and do claycrete or clay/sand mortar and have a chance at breaking it apart someday without destroying the copper.  |
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Post by chrisz on Oct 12, 2011 6:12:04 GMT -8
ok, I'll check into those other "mortars" to use. Can anyone point me in the direction to be able to figure out how much heat I'll be able to collect form this coil, so I can size my water storage tank accordingly.
One other thought I had was to go a bit more trial and error, and hook up a scrounged tank, and hook more in series if I realize there is more heat to be taken.
Thanks
cz
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Post by endrunner on Oct 20, 2011 19:26:17 GMT -8
In order to compute the amount of heat you can collect, you will need as a starting point, the temperature of the air there, also any clue what the air speed is. Heat exchange is a function temperature difference and the rate of velocity of the two different mediums, ie what is your water change speed as well. Surface area of 3/4 pipe is easy to compute but velocity and air vs water are the larger factors.
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Post by wedgeman on Nov 30, 2011 16:54:39 GMT -8
this may (or may not be relevant) to the question at hand.. factors: - heating water in a simple tube can be erratic and lead to scalding issues or steam/explosion factors.
- there is not enough mass to keep consistent
- adding thermal mass to the stove will take longer to heat but will result in consistent water temps.
therefore: I might suggest incorporating a water tank in the top area, and putting the water pipe IN that tank. the water will regulate the temperature a bit, so you have more thermal reserve AND prevent runaway heatrise (steam/scalding/etc).... just a thought.... |
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Post by mintcake on Dec 13, 2011 10:36:17 GMT -8
I might suggest incorporating a water tank in the top area, and putting the water pipe IN that tank. the water will regulate the temperature a bit, so you have more thermal reserve AND prevent runaway heatrise (steam/scalding/etc).... just a thought.... I'd like to second that idea. And even then, I'd want some VISIBLE sign when things aren't working properly, maybe a thermometer/pressure valve on the tank or similar, and a level gauge wouldn't go amiss either. Of course an over-pressure relief valve or a thermal expansion pipe, since the thing probably doesn't need to any degree. Half my lifetime ago I was a student in a house with a coal burning cooker which had a boiler on the back. We never did get it hot enough to really cook on, but it heated up water for the bath OK. One day, we'd had it burning and the water didn't seem to get very hot. Next thing we knew there was a strange sound of water pouring in the attic space. It seems that the so-called plumber had plumbed the little back boiler directly to the water inlet/outlet pipes to the hot water tank, rather than using a proper loop. So the nice high-lime-scale water was constantly depositing its lime-scale into the boiler, and being topped up with fresh. Boiler eventually blocked... The rushing of water was the steam forcing all the water out via the thermal expansion pipe, he'd remembered that, thankfully, or I'd probably be dead. Just because it works fine for a year doesn't mean it always will, and you really don't want a steam explosion demolishing your house. |
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Post by mintcake on Dec 13, 2011 11:03:12 GMT -8
Back to the original question, Are you planning to run radiators/floor/bench heating, etc from this, or a steam engine, or ??
Assuming you want to heat another room and this to work from convection, without a pump, then the pipe should be big. - the bigger the better - otherwise you'll not have enough pressure difference to move the water through the pipes (OK, you will when it starts boiling, but...). Also you should be thinking of nice smooth pulled bends rather than solder-joint ones, not to mention making sure the pipes going up are hot and the ones going down are cold.
You're going to need to work out the total effective length of your system (adding distance for corners, 'T's, etc ), work out the pressure available (density differences & heights) and see if you get enough litres of water flowing to move the heat you want to move.
If you've got a pump, then you need to look at surface area of copper, etc, but you can get away with using smaller pipe (easier to bend). It depends on your pump's pressure/flow rate graph as well, in extreme cases.
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Post by chrisz on Dec 28, 2011 7:46:00 GMT -8
My plan is to build this in the garage on the "floor level" ( I also have an attic with storage space up there). It will heat the garage/shop end of the garage. I am thinking of adding the water coil set up to help heat the water for the house. I was initially thinking of running a pump system to move the water to the basement in the house where I'd run a heat exchange tank to my "house" hot water.
There are many options to go with, as far as placing a water tank above the heater, adding radiators in the garage attic for heat up there also, I suppose I need to work on a few basic things like getting it in first and know that I can add water tanks/coils on top of it later if I want to.
cz
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Post by panbreaux on Jan 16, 2012 9:10:47 GMT -8
when i was building my experimental water heaters i ran into a physics major working in the plumbing dept at lowe's. he conveniently calculated the efficient tubing length for my project. i'm a bit lacking in the "alphabet math" dept but i think his formula for calculating the length is, tube ID X circle D X rise length X 2 X Pi. using the 28.5" tube length he calculated and dividing by Pi, then 2 then 9 (rise), then 4.5 (rocket chimney OD) i came up with .32" which is the ID of my copper. someone better at math might be able to see if i calculated it wrong.
he explained to me that it needs to have a full ring wrapped top and bottom with the rest of the length spread between the two for the best efficiency. after a few experiments i've found that as long as you have two wraps and spread the "rings" apart 2 times the diameter or more it will seldom steam up if tank is aligned 4 feet or less away for every 6 foot of rise. the speed of the water cycling through helps to make up for the shorter coil length not collecting as much heat per pass.
on an enclosed and/or pressured system i'd also recommend lots of safety gadgets. personally i think these types of water heaters are better suited for vented, as needed, small batch use due to safety and hair pulling issues. fixes for one thing tend to affect other balances negatively.
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