Electric Elements

[chovain]

I'm going to start designing my future electric brewery soon, and want to see if anyone out there has any info on what can and can't be done.

HLT

The HLT, which is the part I'll definitely be doing seems pretty trivial to me:
* The bigger the element, the faster it'll heat.
* The better you insulate it, the less heat you'll lose.

The power requirement can be calculated given a heat loss, and the desired heating volumes and times.

Does anyone have any rough figures for how much heat uninsulated SS and Al will typically lose? I can get their thermal conductivity (W/m/K), but don't know how to convert that to a more practical unit given typical conditions (W/m^2 would be perfect). Any of the physicsy people have any pointers?

Anything I'm missing with this?

Kettle

I figure I'm unlikely to ever getting around to building an electric kettle, but I'm interested in going through the motions and designing one anyway. The kettle seems to have much tighter design constraints:
* The bigger the element, the faster it'll heat.
* A minimum power is needed to maintain a rolling boil.
* Too high a power density on the element will scorch the wort.

I figure the power requirement can be calculated once you've factored in heat losses again. Pick a desired evaporation rate corresponding to the vigorousness of the boil (L/hr), then multiply by the latent heat of evaporation to get the power needed to maintain that boil. Does that seem right?

The power density is one that is killing me. In my searches of HBD, someone says to aim below 25W/in^2 (37.5kW/m^2), while someone else says that 50-83 W/in^2 (75-125 kW/M^2) is a safe density. Does anyone have any practical experience with the power density that will start scorching wort?

 

[chovain]

I can get their thermal conductivity (W/m/K), but don't know how to convert that to a more practical unit given typical conditions (W/m^2 would be perfect). Any of the physicsy people have any pointers?

Ok - a bit of further research reveals that this is going to be way too hard to model, and that empirical evidence is the way to go. Anyone have any heat loss figures for their stock pots?

 

[damoncouper]

Mark, you might want to consider insulating Kettly too. I have found that once upto a roling boil I am only using about 1200-1400W for a 35-40L boil.

 

[mesa]

Hi Mark,

Does anyone have any rough figures for how much heat uninsulated SS and Al will typically lose? I can get their thermal conductivity (W/m/K), but don't know how to convert that to a more practical unit given typical conditions (W/m^2 would be perfect). Any of the physicsy people have any pointers?

Thermal conductivity goes up as the surface area of the pot increases and down as the thickness of the pot increases, hence the units are actually Wm/m^2/K which cancels to W/m/K, so you could take your conductivity multply by the area of the pot, divide by the thickness of the pot and multiply by the temperature differential between the outside of the pot and the inside.

Unfortunately as you appear to have already discovered the temperature on the outside of the pot is the hard one because its not just the air temperature. You've got to actually work out the thermal resitance/conductivity at the pot/air boundary. You can probably find some figures for this is you search hard enough, but ultimately I'd say just go the environmental route and insulate the heck out of it to minimise waste heat. A nice looking insulation job can still look good although not as nice as shiny things I must admit.

Alternatively you could do the experiment yourself with a smaller pot. Measure its total conductivity from water to air and normalise by the area. Calculate the conductivity of the small pot and compare it to measured total conductivity. My hypothesis would be that the total conductivity for a full pot is at least an order of magnitude less than the conductivity of the metal. If its not then at least you've determined the air/metal conductivity which you can use inconjunction with the calculated conductivity for your pot.

On the power density topic. I've used a kettle element before from a $10 kettle. I'm sure there are at least a few here others that do the same. I believe that the power density from this was high enough to produce "some" caramelisation (unfortunately I've not got enough experience to estimate how much). Personally I'd got for a reconfigurable network of elements so that you can produce styles that benifit from caramelisation as well as styles that don't, but maybe you'd rather use another vessel for this.

 

[chovain]

Mark, you might want to consider insulating Kettly too. I have found that once upto a roling boil I am only using about 1200-1400W for a 35-40L boil.

Yep - was meaning to repeat the insulation point in the kettle section. This leads to another question though: How easy is your insulation to remove and reattach? Alternatively, how do you go about cleaning your kettle?

I guess it's not so big a problem for the HLT, as I'd only ever need to do basic rinses. We have very soft water here in Sydney, so I'm not likely to get any build-up in a hurry.

 

[chovain]

Alternatively you could do the experiment yourself with a smaller pot. Measure its total conductivity from water to air and normalise by the area. Calculate the conductivity of the small pot and compare it to measured total conductivity. My hypothesis would be that the total conductivity for a full pot is at least an order of magnitude less than the conductivity of the metal. If its not then at least you've determined the air/metal conductivity which you can use inconjunction with the calculated conductivity for your pot.

That's a great idea. By getting a small pot, and testing the heat loss with various insulation configurations, it should be possible to work out how much heat is lost through insulation, bare sides, the base, and the top.

On the power density topic. I've used a kettle element before from a $10 kettle. I'm sure there are at least a few here others that do the same. I believe that the power density from this was high enough to produce "some" caramelisation (unfortunately I've not got enough experience to estimate how much). Personally I'd got for a reconfigurable network of elements so that you can produce styles that benifit from caramelisation as well as styles that don't, but maybe you'd rather use another vessel for this.

I'm probably going to go for one of Grimwoods' BSP elements if they're not too pricey, which will be driven by a nice big triac for variable power output. Does anyone know the power density of a cheapo kettle element? Alternatively, would anyone be willing to measure the diameter and approximate total length of their element for me? I can't get at the element in mine: it's one of those swanky flat bottomed ones.

Edit: As someone pointed out in another thread a while back, you can get the power density down by running 4 kettle elements: run two parallel sets of serial elements. Each element chews a quarter of its rated power (double the resistance in each of the parallel parts of the circuit halves the current, and each element only gets 120V). You get quarter the power density, with the ability to run at 1.2 or 2.4kW without the need for a triac.

 

[Yorg]

Mark, you might want to consider insulating Kettly too. I have found that once upto a roling boil I am only using about 1200-1400W for a 35-40L boil.

So what is your set up. I presume you have another element to get it to a boil?
Or do you use some kind of control?
Total watts?
Density, or description of your element?
Tips for young players on operating an electric kettle?

All would be very informative for someone (like me) contemplating going electric.

cheers.

 

[Thirsty Boy]

Yep - was meaning to repeat the insulation point in the kettle section. This leads to another question though: How easy is your insulation to remove and reattach? Alternatively, how do you go about cleaning your kettle?

I guess it's not so big a problem for the HLT, as I'd only ever need to do basic rinses. We have very soft water here in Sydney, so I'm not likely to get any build-up in a hurry.

velcro would be your friend. Get your swmbo to sew up a nice jacket for the kettle. Some sort of quilting with a bit of good tough vinyl/canvas etc... then just zip it up or velcro it so it can be removed and cleaned, and so you can more easily clean your kettle inside and out.

 

[kirem]

My brewery is all electric. there is plenty of inforamtion on ahb already.

use a control - sutronics burst fire on your kettle.

http://www.sutronics.com/acatalog/detail_bfm240_13.html

go to clarke rubber and get some insulation for all your vessels.

 

[chovain]

velcro would be your friend. Get your swmbo to sew up a nice jacket for the kettle. Some sort of quilting with a bit of good tough vinyl/canvas etc... then just zip it up or velcro it so it can be removed and cleaned, and so you can more easily clean your kettle inside and out.

Hah - she'd kill me for even suggesting it. SWMBO has been known to ask me to iron her clothes, and when I refuse, she just wears them creased .

 

[chovain]

there is plenty of inforamtion on ahb already.

But there's just about nothing on power density or actual heat losses, etc. Those two posts I linked from 90s editions of HBD were the only two specific claims about density that I could find on the net.

 

[kirem]

Mark,

Once you have gathered this information, what do you intend to do with it?

 

[justsomeguy]

Hi all,

I'm using a 2 element electric kettle at the moment. It runs one 1800 watt and one 2400 watt low density elements in the kettle. I haven't had any caramelisation problems on the elements and can easily maintain a boil with insulation and the 1800 watt element or no insulation and the 2400 watt element.

The insulation I used was an 8mm cheap foam camp roll that I wrapped around the kettle and held on with a webbing strap. Works a treat and really cheap. If it becomes too grotty then I just turf it out and get another one.

As to the heat requirements everyone has been talking about, well, it depends...
You may not have 240 volts into the house or at the outlet (it could be as low as 210 volts) and heat losses through the kettle are obviously going to screw things up to some degree.

The biggest factor I found when using my system is the heat loss due to the outside conditions. If there is a breeze blowing on the kettle that will have a big effect on the boil. The outside temperature didn't really have too much effect but any breeze did.

I'd recommend that if you are going to use two elements then make sure that they are of different wattages. That way you have more heat output options to use depending upon conditions.

I can use 1800, 2400 or 3600 watts. If I had two elements of the same value I'd only have two options. Unless you have some way of controlling the output to the elements, that is...

gary

 

[chovain]

Mark,

Once you have gathered this information, what do you intend to do with it?

Apart from the obvious (design and build), I'm hoping to put together a wiki article at least outlining the design constraints, or optimally detailing it right through to the design itself. This info is just about impossible to get your hands on .

 

[chovain]

I'm using a 2 element electric kettle at the moment. It runs one 1800 watt and one 2400 watt low density elements in the kettle. I haven't had any caramelisation problems on the elements and can easily maintain a boil with insulation and the 1800 watt element or no insulation and the 2400 watt element.

Any chance you know the density of those elements? Alternatively, can you measure the cross-sectional diameter of the elements, and each of their lengths (total length of the element, not penetration) so I can calculate it?

 

[Back Yard Brewer]

Hi all,

I'm using a 2 element electric kettle at the moment. It runs one 1800 watt and one 2400 watt low density elements in the kettle. I haven't had any caramelisation problems on the elements and can easily maintain a boil with insulation and the 1800 watt element or no insulation and the 2400 watt element.


gary

Ditto Here. But I normally have a 50ltr boil and on the odd occasion I turn off the 1800watt. I have used a camping mat and it does make a difference.

BYB

 

[hanzie]

Is everyone using submersable elements? How about 2 or 3 electric stove hotplates?

 

[0M39A]

Im just about to start building my electric kettle.

using a converted 50L stainless "vessle" and going to use 2 1800w kettle elements opposite each other in the bottom of the vessle.

insulate the entire thing with a camping mat, and install a ball lock tap in the bottom of it for draining.

hoping that using 2 elements turned on will bring it to the boil nice and quick, then i can turn one off, and a single 1800w should keep it boiling easily enough with the insulation.

will be using it initially for a couple of extract brews to get the hang of it, then move up to BIAB, and eventually end up with a 3 tier system.

sound alright?

 

[schooey]

I can use 1800, 2400 or 3600 watts. If I had two elements of the same value I'd only have two options. Unless you have some way of controlling the output to the elements, that is...

gary

Maybe I missed something here, or my maths is way off, but how can you achieve 3600W with 1 x 1800W & 1 x 2400W element? :blink:

 

[pbrosnan]

We're talking about the kettle right?

* Too high a power density on the element will scorch the wort.

I'd like to see that. Maybe if you boil it down to a paste ... or have an element you can plug directly into an electricity sub station.