Author Topic: Want to build a gas fired deck oven. Any plans available and suggestions?  (Read 31446 times)

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Offline Sqid

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #125 on: August 27, 2012, 11:32:50 AM »
A conveyor oven would be loosing so much heat, being open on two ends, that two burners must be essential.

I envisage the upper burner on my oven to only kick in occasionally when the door has been open for a long time.  Maybe only use about 30,000 btu and keep 120,000 btu below.

Shuboyje mentioned that a manual control would be suitable for the upper burner.   I think I shall probably wire it in to a separate automatic thermostat controller.  Also I think I shall be using a normal thermostat rather than a PID as the work load on the oven is so variable.


Online Chicago Bob

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #126 on: August 27, 2012, 12:33:16 PM »
"Also I think I shall be using a normal thermostat rather than a PID as the work load on the oven is so variable."

Is that not the advantage of the PID....able to better control variable situations?  Hmmmm......
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Offline Sqid

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #127 on: August 27, 2012, 11:12:44 PM »
Hi Bob

My understanding is that a PID uses fuzzy logic to learn from past experience what to tell the burner to do in order maintain a constant temperature.

This is great for heating when the parameters are relatively constant i.e. different times have fairly regular ambient temperatures and fairly regular demands for heat.

With an oven.  We are generally in need of more burner activity at supper time which a PID would learn and be able to burn the gas accordingly.  Occasionally the oven sits there doing nothing for 2 hours and at 3.50 pm is called on to cook 25 pies.  I don't think a PID would cope so well in this situation.

I think the above would just about fit on the back of a postage stamp!    

Online Chicago Bob

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #128 on: August 27, 2012, 11:35:18 PM »
Oh OK Squid, thanks.
I thought the PID was more sensitive to changes and can react faster than a normal thermostat.
btw, what does..."I think the above would just about fit on the back of a postage stamp! "  mean?
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Offline Sqid

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #129 on: August 27, 2012, 11:49:47 PM »
Your correct in that a PID can keep a temperature more constantly adjusted.   It doesn't exactly react faster but it does predict what will happen.  For instance a thermostat would turn on the burner at 290 to get the temperature to the desired 300.  When it gets to 300 it will turn the burner off.  Quite possibly the stone will keep on transmitting heat after the burner is off and the oven will heat up to 303 before it evens out.  A PID would know this and therefore perhaps only turn the burner on 'till 298.   It would also know that if the temperature is dropping that it doesn't need to wait until 290 to turn the burner on.  It might give a short blast of heat at 295.

btw, what does..."I think the above would just about fit on the back of a postage stamp! "  mean?

I know next to nothing about what I'm writing ;D

Online Chicago Bob

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #130 on: August 28, 2012, 12:09:24 AM »
Dang..'ol PID pretty smart...
And I think you have much more to say than a postage stamps worth, thanks!
btw, why would PID not apply for your situation(humor me please)  ;)
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Offline Sqid

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #131 on: August 28, 2012, 12:23:54 PM »
Now I'm really just winging it.

Generally I understand that a PID can vary the power depending on how far away you are from the desired temperature.  If you only open the oven door once or twice it could tell the burner to blast at 1/2 power for 2 minutes.   If you are constantly opening the door and the temperature is dropping rapidly the PID would recognise what is happening and tell the burner to run at full power until you are near to the desired temperature (set point SP).   This sounds great but the switching mechanisms for the burner on/off that I have come across only do on or off.  I think if I start delving into variable gas flow mechanism I would really give myself a headache.

The other problem I see is that you have to dial in the parameters yourself and then it will learn from there.   So you tell it the SP (desired temperature) and temperature difference where it has to start working.   It will learn to keep the temp. at your desired 300 C within a degree or 2 but once you start putting different loads on the system it will be turning on and off just as many times as a normal thermostat.   Don't really see its advantage here.   If you were curing pepperoni in a closed fridge then it could maintain the humidity very constantly.  But once you start opening and closing doors erratically then it has no real benefit.

That was fairly long winded without saying an awful lot.  If anyone can confirm that I'm not talking bo##ock$, please do! 

Also if you're reading Scott, what do you think about the aluminium plate and warping?

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #132 on: August 28, 2012, 01:00:21 PM »
Gotcha Squid, thanks. I guess it just sounds like an additional unnecessary expense (and something else that can burn out :))
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Offline shuboyje

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #133 on: August 28, 2012, 08:54:51 PM »
A PID and the thermostat do the exact same thing.  They turn something on and off to control temperature.  The only difference is how they decided when to turn it on and off.  A thermostat generally has some sort of set point as to when it turns on and when it turns off.  For instance it may turn on when the temperature is 5 degrees below the set point and turn off when it is 5 degrees above.  Nothing fancy.  A PID uses computer algorithm's to determine when to turn on and off to maintain much more accuracy.  Where a thermostat is static, a PID essentially learns based on the effect of it's past functions.  The longer it is used in a system, the better it will get.  Huge changes in load, like one day deciding your deck oven doesn't need a door might give it fits until it has time to readjust, but small changes would be no problem.  The mass in the oven acts to stabilize the temperature and would only help the PID to function even better.

The big reason I mentioned a PID in the first place was cost.  Task specific oven thermostats are pretty expensive here in the states, but a PID is $30. 
-Jeff


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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #134 on: August 28, 2012, 08:58:35 PM »
Thank you Jeff   ;)
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Offline Sqid

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #135 on: August 29, 2012, 04:06:22 AM »
Thanks for clarifying that Jeff

Here is the burner I had made in Bangkok

Offline Sqid

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #136 on: August 29, 2012, 04:07:29 AM »
Close up of the 2mm ports

scott123

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #137 on: August 29, 2012, 05:43:03 AM »
Richard, I wouldn't put any thickness of aluminum that close to the burner. Is steel plate really that much more expensive than aluminum?

That's a pretty nice burner, btw. I think the holes need to be closer together- like double the number you have now.  That might help it light a bit better.

Offline Sqid

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #138 on: August 29, 2012, 07:45:14 AM »
Hi Scott.  How ya doin?

That's a bummer!  I thought I was going 'cutting edge' oven design with an aluminium plate. :'(  Trying to avoid getting hot spots in the oven.
Steel is cheaper 6mm.  About $7 sq ft
Stainless 6mm.  About $19 sq ft
Different thicknesses are available.

Is there any major advantage to using SS rather than normal steel and would 1/8" be suitable for both?
Maybe steel, then aluminium, then firebrick hearth?

The burner ports are 8mm apart.  If I double the number of holes they will be very close - 3mm.  Does that sound about right?

buceriasdon

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #139 on: August 29, 2012, 08:18:20 AM »
Richard, I assume the burner was copied from a similar burner, correct? Also you will be using natural gas? How long before you can trial fire the burner? Curious to see how far natural gas can push a flame.
Don

Offline Sqid

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #140 on: August 29, 2012, 11:34:35 AM »
You're probably right Don, that I had said previously I was using natural gas.   I assumed that because this country is so rich in gas deposits that it would be a taken.  Alas, again I am mistaken, we are in fact using LPG

I had fired the burner up this afternoon for the photo sesssion but I don't have high pressure at home and the flame was barely visible.  That was my first attempt at posting pictures on the internet so feel encouraged to have another go!  I shall get some pics tomorrow.

Offline Sqid

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #141 on: August 29, 2012, 11:38:19 AM »
Oh and the burner wasn't copied from anything.   The place that did it had never used SS before and had never made an H design.  Funny thing though, the guy who was actually doing the work was Burmese. 
« Last Edit: August 29, 2012, 11:44:41 AM by Sqid »


buceriasdon

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #142 on: August 29, 2012, 12:46:22 PM »
Richard, I know you will have problems with an even burn from one end to the other with such a long burner. The size of tubing limits the amount of gas that can be pushed along evenly to the end. I assume first off you used a LPG(smaller) orifice not a NG size jet.  How much pressure does your LP regulator allow? If you still find poor combustion at the opposite end of the gas inlet, and I think you will, you may have to enlarge the holes slightly in the problem area or add a manifold that supplies gas along it's length. I wanted to wait until you had tested the burner, although looking at the photo left me with doubts. Sorry to be such a wet blanket. :( I await further test then with greater pressure.
« Last Edit: August 30, 2012, 07:08:39 AM by buceriasdon »

buceriasdon

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #143 on: August 29, 2012, 05:41:28 PM »
Richard, I have to apologize here as I must have missed you saying the H burner was running the length of the oven area. What I had envisioned were several shorter H burners run off a main gas feed line and running perpendicular to the oven. I would have sent up a red flag had I fully understood what you were describing, but I didn't. However the more I study your burner the less confindent I am about it's workability. If anyone wants to jump in and say, Don, you're full it, by all means be my guest. Scott posted a picture of what I thought was being discussed at post No. 79
Don
« Last Edit: August 29, 2012, 06:04:38 PM by buceriasdon »

Online Chicago Bob

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #144 on: August 29, 2012, 06:43:23 PM »
I have heard where another gas inlet was added on to the opposite end when a pipe run was too long for the original single inlet to provide enough umph. Is this what you are referring to Don?

"or add a manifold that supplies gas along it's length."

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Offline Sqid

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #145 on: August 29, 2012, 10:46:54 PM »
Don - Could you explain what LP and NG stand for?

There doesn't seem to be a problem with the evenness of the flame.   Even though it is 3'6" long, the gas is piped directly to the middle of the H and from there goes to the 4 extremities (only a distance of about 2').  

Several shorter burners running perpendicular to the gas pipe supply line would heat the deck more evenly.  This is the configuration that all the Thai locally made ovens use and the confiiguration that the manufacturer suggested and have experience with.   The big difference is that I want to make mine light automatically.   Without having a burner running parallel to the face of the oven it becomes complicated to light 4 burners.

I very much like the configuration posted by Scott at reply 79.  I prefer the jpg image to the Blogett but availability and  ignition pushed me to an H design.   It's along the same lines that Marsal explain is superior to there competitors U shaped design.

As it is, I'm not satisfied with the burner now.   Still looking out for better.   I may well try increasing the number of ports as Scott suggested; which not only will help with reliable ignition but will increase the Btus.

Bob.  The idea of two gas inlets is a new one to me and worth thinking about.  Thanks.  

And Don:

Sorry to be such a wet blanket. :( I await further test then with greater pressure.

I read this several times and thought no problem with the wet blanket bit but waiting for further failed test with pleasure is a bit sadistic!  Eventually I realised I was misreading 'pressure' as 'pleasure'. :-D.
« Last Edit: August 29, 2012, 10:49:28 PM by Sqid »

scott123

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #146 on: August 30, 2012, 12:23:25 AM »
Hi Scott.  How ya doin?

That's a bummer!  I thought I was going 'cutting edge' oven design with an aluminium plate. :'(  Trying to avoid getting hot spots in the oven.
Steel is cheaper 6mm.  About $7 sq ft
Stainless 6mm.  About $19 sq ft
Different thicknesses are available.

Is there any major advantage to using SS rather than normal steel and would 1/8" be suitable for both?
Maybe steel, then aluminium, then firebrick hearth?

The burner ports are 8mm apart.  If I double the number of holes they will be very close - 3mm.  Does that sound about right?

Don makes some good points about the length of the run and pressure. I'm recommending double the holes based upon the tight hole formation in weber grill burners and the ability of those burners to stay lit.  If you have the pressure, then I'd say drill out more holes.

Heat accelerates oxidation/rusting in steel, so theoretically, very thin steel plate might rust faster in the deflector role you're considering for it.  I believe 'aluminized steel' is made to counteract that.  This being said, I really don't see 1/8" or thicker steel ever rusting through at these temps. Any good design should give you burner access, so, with that access, you should be able to check deflector wear as well. If you do see any rust, go with ss next time. For now, though, I think you'll be perfectly fine with regular steel.

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #147 on: August 30, 2012, 12:45:37 AM »
Don makes some good points about the length of the run and pressure. I'm recommending double the holes based upon the tight hole formation in weber grill burners and the ability of those burners to stay lit.  If you have the pressure, then I'd say drill out more holes.


More holes is a good thing...they should stager at an advantageous/opposing angle though. Still gonna need fuel coming in at the a$$ end ..too long of a run no matter how much psi you present on the front end..IMHO of course..
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Offline Sqid

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #148 on: August 30, 2012, 12:48:08 AM »
At optimum gas flow.   Flames are about 1"

Offline Sqid

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Re: Want to build a gas fired deck oven. Any plans available and suggestions?
« Reply #149 on: August 30, 2012, 12:49:52 AM »
At maximum gas flow.   I don't know what pressure I have but I know it's not very high.
You can see that the flame is blowing out in places.


 

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