DIY heatsink for use with earth/clay oven

[duncang]

Evening all!!

Been a while, but I am back in the saddle - some great conversations been happening on Green building though, so big pat on the back to those who contribute regularly.

For some time I have been planning the launch of a small artisan bakery in the Bath area. I am committing to looking at every aspect of the business and trying to make it as eco-friendly as possible. Also, in the current economic climate, I am having to be quite thrifty as every penny counts.

Our oven will be built from clay salvaged from a building site. I have put a couple of photos up on my website about this if you care to take a look.

The one I am planning on building for use in the bakery will be a LOT bigger, and will also have a chimney built-in to evacuate the smoke, which will be sent up a flue and out a chimney.

Here is my question: How could I make use of the otherwise-wasted heat from the smoke to help heat the hot water we will need for hand washing and washing up? I have a couple of ideas, such as a network of copper pipping in a box that you would make the smoke pass through, but nothing particularly clever...there must be someone with a clever idea out there?

Also, I would love to hear from anybody else interested in my project who can come up with some interesting ideas on converting a basic industrial unit into a working bakery, being as eco-friendly as possible. After all, this is just me having a go, I don't profess to know everything, far from it.

For those who do fancy getting involved, here is a video tour:

Here is a video tour, part one:
http://www.youtube.com/watch?v=kyeODrN77Ps
And second part of the video tour
http://uk.youtube.com/watch?v=OueKbkEFR6U

Loof forward to hearing from you,
Duncan

[growingthings]

Hubby and I have currently got a rather clever bod helping us to install our wood fuelled rayburn, and he was chatting about simple solutions for hot water is simply coils for the water within the fluepipes I'm not sure when he will be back but I can always ask him. He's unique but he really knows his stuff.

[duncang]

growingthings, thanks for that, yes sounds like the similar sort of lines of what I am thinking... could you get him to have a think about and pass on any thoughts he may have on this? Am quite handy, just don't want to do it for the sake of doing it, want to make sure I get it right if I can, so I don't waste anything!

Thanks!

[JulieSherris]

Duncan,

I have absolutely no idea about these sort of things, but we have a stanley range which does all of our cooking, heating & hot water....

Their website is brilliant, especially the technical section - if you're handy minded, this may well give you a few ideas to adapt to yur needs....
http://www.waterfordstanley.com/1332.htm I'd suggest the technical help & the installation pages.

Good luck with it, what a great project!
Julie.

[duncang]

I have been thinking about this, and reckon that, if there is a way to get hold of the thin piping that is on the back of fridges as part of the heat exchanger (without polluting by releasing the gas from them...not sure this is possible) and using a pipe bender to bend it into a coil, then that coil could be run through the flue, allowing the cold water input in the bottom, and output out the top. If that output is then sent (in my case anyway) to a British made instantaneous hot water heater, then surely the heat recovered through the flue will cut down the energy required by the instantaneous hot water heater to get the water hot.
(I plan on running the instantaneous water heater in conjunction with solar thermal hopefully down the line, so the water would go from solar thermal to heatsink to heater, or heatsink to solar thermal to heater.

Problems I am therefore facing:
- Sourcing piping from fridge thin/small enough to shape a coil, without polluting
- Figuring out how this can be bent into a coil
- How else to make this any more efficient (i.e this is relying on convection where the cold water comes in at the bottom of the coil, heats and works it's way through the coil to the top - maybe better with a pump?)

Look forward to hearing peoples' thoughts on this.

Best regards,
Duncan

[JulieSherris]

Duncan,

I've just had a long lecture from hubby about making a heat exchange.......

Anyways.... he says you can't beat thin copper piping - the fridge piping might not withstand the heat produced.
You have to make lots & lots of coils - with a pipe bender.... you'll also need bracing plates at each end because the heat will distort the copper piping.... then you have to make sure that there is enough force to keep the water going one way....

THEN he says.... if it's a commercial venture, you have to talk to the Health & Safety people before you go ahead, because of the Health & Safety At Work Act 1974....... He says it's a complete minefield & they may well have guidelines & rules & regulations concerning heat exchangers which work from oven heat....

Anyhow, he's also said that if you get thru that & still want to go ahead, then provide some info on size & running temperatures, he'll look at knocking up some rough designs which you can adapt to fit....

Julie

[duncang]

JulieSherris, thanks for that!!! Your hubby sounds like he knows his stuff!! I agree with it all completely, just wonder where you can get anything thinner than the standard copper piping used for plumbing...
I loved the idea of using piping from the fridge (provided this can be done without polluting as I said before) as it means using salvage material, which I am always a fan of instead of buying new...

Best,
Duncan

[duncang]

JulieSherris,

Actually, looking on ebay, I may have found what I need:
Click here to view ebay posting

The dimensions are 6.35mm diameter, with wall thickness of 0.71mm, so a LOT smaller pipe than then conventional domestic copper pipe...
Not that expensive either... what would your hubby think?
Tricky bit is finding a pipe reducer fitting to adapt this thinner pipe to the larger diameter conventional piping, and I don't seem to be able to find this as yet.

Thanks,
Duncan

[pureportugal]

we've got a wood-fired water heater and i'm wondering if you can adapt the principle to suit your needs. basically it's a firebox at the bottom with a central flue and a water tank around the flue. so rather than having water filled coils inside the flue you have a tall thin container of water around the flue. don't know how easy something like this would be to make yourself ...

[JulieSherris]

Duncan, hubby says you need 15 ml copper, else you won't get adequate surface area to heat enough water to make anything viable..... and no, fridge piping wouldn't be large enough either.....

He does know his stuff - he used to build & commission industrial robots when we were in the UK - nowadays he sits with a laptop & controls the robots from the warmth of his office Good job we have lots of projects for him to get his hands dirty at home

Julie

[chrisjs]

Hi,
I have successfully used a cast iron heat exchanger from a gas boiler built into the chimney of my pottery kiln. It heated 200gals of water per firing. If you do this make sure to include a pressure relief valve in the circuit and be carefull hot water systems can be very dangerous (they can boil and make steam!! which can lead to explosions!!)
Chris
www.ecodiy.org

[The Honk]

I looked into this recently and was told that the Building Regulations require various safety measures including installation by approved installers who are unlikely to go along with improvised solutions. I was thinking of microbore copper pipe wrapped around the outside of the steel flue with a pump and thermal store.

Other problems that could occur

1) Uncontrolled heating of water which will require a heat sink as well as safety devices.

2) Loss of buoyancy of flue gases due to cooling with potential for inadequate draw.

3) If the flue gases are cooled too much then condensation could occur resulting in damage to the cooker as the condensate will be acidic.

I have been quoted £337 (supply only) for an upgrade back boiler for my Esse wood burner but I'd much prefer to cobble something together myself as long as it was safe!

Anything that may supply free energy seems to attract much regulation and control in these days of obsene energy prices.

I was told that I needed a approved installer to fit my mains pressure boiler (electric water heater) but fitted the whole ststem myself last May and it has worked perfectly since. I was also told when I bought the esse that the flue had to be designed and fitted by a HETAS engineer so, after reading up on the basic requirements I installed it myself. This was a stainless steel flexi flue pulled up an existing chimney and fixed at top and botten with 6 self tapping screws and 3 fire cement joints and guess what.............it works perfectly

[grahamhobbs]

From my experience very little heat goes up the chimney from a baker's wood fired oven. Think about it, you want the heat to stay in the oven, not go up the chimney. The oven is built with a lot of mass to retain the heat, giving it out very slowly. The chimney is really there to take away the smoke when you are first firing up the fire, after that the doors should be shut as much as possible to keep the heat in. A single firing of a faggot or two, perhaps with a couple of small top ups, should be sufficient for a whole days baking.

OK some heat will go up the chimney but it is going to be very small, nothing like a wood burning stove (and most wood burning stoves with proper cast iron water jackets are not reckoned to be that efficient as hot water heaters).

[Nick69]

Hubby and I have currently got a rather clever bod helping us to install our wood fuelled rayburn, and he was chatting about simple solutions for hot water is simply coils for the water within the fluepipes I'm not sure when he will be back but I can always ask him. He's unique but he really knows his stuff.

Please dont do this, I am a Hetas registered installer and this is just the type of thing I have to rectify. It is extremely unsafe, the solder will melt within the flue and within 3-4m. Solder melts at 115 ish degrees Centigrade. The inside of a flue can and will reach at least 3 times at least.
Plus it will make sweeping the flue a nightmare as you wont be able to remove all the deposits, this iself becomes a Chimney fire hazard. A chimney fire will reach temps of 1000c+. As copper melts at around 1000c the pipes will give way and then you have another nightmare.

Now by all means consider a coil on the OUTSIDE of your vitreous flue but you still must watch the solder joints. Even better consider brazing a high temp joint.


No offense is meant by the above but the amount of installs I see with dodgy fitting 'Ad ons' etc is amazing and people dont realize how dangerous they are.