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Old 10-22-2007, 06:54 PM   #1
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Running cost of an oven

hi all

i am going to try and roast a chicken at 60 degrees celsius for 4 hours (ref: heston blumenthal: search of perfection) and see if it really does taste better than cooking if to 1 hour at 150 degrees.

But before i do that i was just wondering if the oven would use more electricity cooking longer on a much lower heat?!?

Cheers

Aaron

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Old 10-22-2007, 08:16 PM   #2
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Have you roasted chickens at 150C (302F) for only 1 hour before? That seems a bit low for only one hour in the oven. Most recipes advocate at least 350F (176C) for one hour, or until the internal temp is 165F (73.8C).

To roast a chicken at 60C (140F) for 4 hours is an interesting idea akin to smoking foods at low temp. The long slow cooking time causes the meat to be fall off the bone tender and perhaps juicy, but you’ll not get a crisp skin that way. It will probably look like it was steamed or boiled.

Chicken doesn’t need long and slow cook times like this, and is often better done fast (an hour or less) at higher temps to sear the bird and give it color. Still, there’s no harm in experimenting.

Personally, I’ve grown to dislike smoked chicken due to the texture. Long slow smokes impart good smoky flavor, but chicken cooked long and slow is a but mushy for my tastes. Even when I do Beer Can chickens, I up the temp and decrease coking time because I prefer the texture of the meat that is produced with higher heat and shorter cook times. Low and slow for chicken is rather pointless IMHO.

But, now that I have digresses into uncharted territory, lets look at your original question about energy use! It really depends on your oven, especially how well insulated it is. To get the oven to 60C will not take much time at all, so your initial start up time will be fast and use less energy. To keep the oven at that temp, it will need to cycle the elements on for a set amount of time to add more heat to the oven (heat will slowly dissipate during the cooking).

In theory, the shorter “on time” of the elements required to get to 60C and then maintain 60C for 4 hours should be about the same, but possibly slightly higher than running the oven at 150C for one hour. But again, it depends on how well your oven retains heat. I’d wager that a 4 hour cook at 60C will use slightly more electricity than a 1 hour cook at 150C, but now a substantial amount! Certainly no enough to make you notice it in your utility bill.

For maximum efficiency, do NOT open the oven during the four hours of cook time. This ensures the heat remains in the oven and the elements don’t have to turn on to maintain the heat as often (thus less electricity used).

I’m curious though as to why you’re concerned about this aspect?

After you have tried this, try cooking the bird at 500F (260C) for 15 minutes, then drop the temp to 350F (176C) for an additional 25 to 30 minutes, or until the internal temp is 165F (73.8)
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Old 10-22-2007, 08:47 PM   #3
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Yeah - sorta' what keltin said. It depends on how many watts (or kWh - 1,000 watts/hr which is probably how you electricity is billed) your oven pulls at 60C and 150C - and the insulation ... aka the efficiency of the oven to mainain a certain temperature over a given period of time - and how many times you open the door.

I doubt it will double the amount of electricity ... but I just checked my electric bill and I pay 13.87 cents/kWh ... so if I used 1 kW at 150C for an hour and at 4 hours at 60C used twice as much electricity - it would cost me about 13-14 cents more.
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Old 10-22-2007, 08:54 PM   #4
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Quote:
Originally Posted by Michael in FtW View Post
Yeah - sorta' what keltin said. It depends on how many watts (or kWh - 1,000 watts/hr which is probably how you electricity is billed) your oven pulls at 60C and 150C - and the insulation ... aka the efficiency of the oven to mainain a certain temperature over a given period of time - and how many times you open the door.

I doubt it will double the amount of electricity ... but I just checked my electric bill and I pay 13.87 cents/kWh ... so if I used 1 kW at 150C for an hour and at 4 hours at 60C used twice as much electricity - it would cost me about 13-14 cents more.
Exactly, and not knowing the element type, the wattage needed, the resistance of the elements, etc, its hard to give factual numbers since you cant run the equations without them. But a sheer guesstimation says that at most it would only double (if that depending on how well insulated the oven is), and even that is only pennies.

But good god man, where do you live????? You're paying 13.87 cents per kWh?????

I just calculated mine again, and it has risen since the last time I checked, but were only paying 7.12 cents per kWh! It's up from the 5.7 cents per kWh I checked last year.
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Old 10-23-2007, 03:57 AM   #5
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i know the skin wont by crispy but i am going to give it a quick fry with ground nut oil to brown up the skin. My dad has a chinese restaurant and they do the same method as wel. They roast the chicken for ages and deep fry it for 30 secs to give it an ultra crispy skin. Do you think it will be cheaper doing it in a gas bbq instead since no electricity is needed?
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Old 10-23-2007, 04:25 AM   #6
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Hi Keltin - Don't mean to Digress but what are Beer Can chickens???
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Old 10-23-2007, 10:06 AM   #7
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Quote:
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Hi Keltin - Don't mean to Digress but what are Beer Can chickens???
Its when you prop a whole chicken on top of a 1/2 to 3/4 full beer and then roast it, usually with indirect heat and wood smoke....but it can also be done in the oven. Heres a pic of some.

And chicouk, that recipe sound pretty good. I like the idea of the deep fry at the end! Very cool. But as was discussed earlier, doing it in the oven will not cost that much more if at all.

Oh, and gas for your grill is way more expensive than electrcity for your oven! It's definitely far cheaper to run an oven for four hours than it is a gas grill.
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Old 10-31-2007, 09:35 PM   #8
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hello chicouk,
Based on the information you provided, you will probably spend approx. 25% more electricity when cooking the chicken @ 60C for 4 hrs.
This is based on the calorimetric equation Q: c m (Tf-Ti),you can find this in any physics manual if you need to do other calculations.
I hope this helps you.
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Old 10-31-2007, 10:05 PM   #9
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But - aren't you making the assumption that there are no other heat losses in the system, wysiwyg?

I'm sure keltin and I, and a couple of other members, would be most interested in how you arrived at this conclusion, from the given information, to solve for Q.

Can you show your work? I'm not doubting you .... I'm curious about what you got that I overlooked.

I was thinking that in calculating for Q in Q=mc(Tf - Ti) any heat loss would be lineary - not variable. How did you calculate the variable heat loss fluctuation - (both the range and the cycles) to determine fuel consumption?
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Old 10-31-2007, 10:55 PM   #10
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Hello Michael in FtW,
There will be oven heat losses and oven heat efficiency issues for both cooking methods.
However, they will affect both processes in similar way (I will explain it at the end)

Q is the amount of heat the oven will transfer to the chicken. Q1 for the low temperature cooking, Q2 for the high temperature.
Since C (Constant of proportionality) is specific for each material, in this case a chicken (LOL) will be the same for both processes.
Similar thing applies to m (mass of the body), it should be similar for two chickens cooked using the different methods.
Relative to Tf, it will be 60C and 150C for each method and Ti is 20C (ambient temperature in C)

The amount of heat per unit of time transfered from the oven to the chicken will be
Q1 (Joules): C . m . 40C
Q2 (Joules): C . m . 130C
since Q1 will expose the chicken for 4 hrs longer...
Q1 (Joules): C . m. 40C . 4hs and simplifying C and m from both equations, we get:

Q1 (Joules): 40 . 4 or 160
Q2 (Joules): 130

These are not the actual amount of heat, they are just the relative values (I don't know C for the chicken)

160 is approx. 130 + 25% therefore, process 1 will transfer more heat to the chicken.

Relative to oven heat losses: There will be losses that will affect both processes. In process 1, the extended period will increase the oven losses. However, process 2 requires a higher temperature, that will result in higher losses than process 1 but since it is shorter, I assume the differences cancel out each other.
Similar can be said relative to the oven efficiency to produce heat. It will be more efficient for process 1 since temperature is lower than process 2, but since it will work four times longer, I assume oven efficiency will be roughly the same for both processes.

I hope this is clear, I tend to overexplain things sometimes (I am an engineer by trade)
Let me know if you have questions.
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