Element Sizing For Electric Kettle

[pbrosnan]

Hi all,

I'm thinking about going up to a larger system, may be 100L. I thought I saw somewhere some information about sizing electric elements for a given volume of liquid. Anyone have an insights?

cheers

Patrick.

 

[MaltyHops]

I did some calculations in this Element Fitted To Pot, Can I Use A Burner Too? ...
post relating to water heating which, if correct, would mean that if you used two
2200w elements, heating 100L of water from 20C to 100C would take over two
hours (and that's assuming there's no heat loss).

But I guess you're probably more likely to go from 20C to 70C for the strike
temperature for mashing which might take around 90mins. Once mashing is
over, you'd probably be going from about 60C to 100C to start boiling which
might take about 70 mins or so.

Each 2200w element would be drawing close to 10A so using more powerful
elements and dual 15A power circuits would speed things up.

T.

 

[Thirsty Boy]

I can just barley get a double (50l pr-boil) batch to work with 1 x 2400W element, if i am very patient. I'd say you will need significantly more than 4800w for 100L if Yu are intending to brew batches that size regularly (i only do it occasionally so i am willing to do the waiting around)

From a raw figures point of view...

Say you have a pre-boil of 100L, assuming you intend to stick within normal brewing parameters, you will want to boil off 10% of that during your 1hr boil. So thats 10L.

So you need to shove in enough energy to vaporise 10L of water. The latent heat of vaporisation of water is 2257 kj/kg and the density of water is 1kg/L so you need 2257x10 = 22570kj = 22570000J to boil off your 10L and you need to do it in an hour which is 3600sec. Watts are j/s so the number of watts you need to do the job is 22570000/3600 = 6269.4W

And all that is without any inefficiency or heat losses, and it doesn't say anything about the rates of change you will get, although we can work that out too.

So lets say you insulate your kettle pretty well etc etc and your heat losses aren't too bad. You can probably do it on two 3600W elements. Now that is 7200W and reverse engineering the maths above it means you'll evaporate a maximum of 11.5L per hour, which is a perfectly acceptable % of your 100L pre-boil. And now we know how much power you have and your volume, we can work out the maximum rate of change in temp.

Water's specific heat is 4.186J/g and wort is usually a little less than that, so lets say 4.0J/g. You have 100L of wort at say 1.050. So thats 105kg, so to raise its temperature by 1 you need to add 105x1000x4 = 420000J of energy. You can add 7200J of energy per second with your elements, so to raise the temp by 1 will take 420000/7200 = 58.33s

So without taking into accont any heat losses etc you could build a system with 100L of pre-boil capacity, install 7200w worth of elements and expect the system to give you an 11.5% evaporation rate and just slightly better than 1/min rate of heating. And i would call that more than acceptable.

With care to your insulation and process, your actual performance shouldn't even be all that far away from the theoretical maximums. For instance on my system, the 2400W should give me a maximum evaporation rate of 3.8L per hour and i actually get about 3.3L per hour or 87% of the theoretical max. So maybe give yourself a bit of extra grunt just to make sure, and some ability to dial it down as needed, but it shouldn't be too far off.

Hope thats helpful, and if my maths etc is awry I'm sure some helpfull AHBer will put it right fairly quickly.

TB

 

[matho]

pbrosnan,

attached is a spreadsheet i have been working on, the top part is to size an element and gives you temp rise per minute it works on the percentage loss E7.

the bottom part actually works out the loss thru the top of the pot and gives you the time between temp steps, add the required volume in the top right and element size and then add the temp steps and down the bottom put in you pot diameter. Its not perfect but give you a good idea just how much heat is lost thru the top and supports thirsty's idea of floating something on top to increase boil vigor.

View attachment element_sizing.xls

cheers matho

 

[pbrosnan]

Thanks very much gentlemen. This is why AHB continues to be a valuable resource. I'll let you all know how I go if I continue with this project.

 

[QldKev]

I know not directly answering your question, but I run a 100L batch from LPG no problems at all. I like to have way too much power, rather than not enough. I have 2 Nasa burners under my 140L pot (100L BIAB batch) and I can get the water to strike temp in about 15mins if I run the burners hard. The great thing is I have infinately adjustable heat, so once I get to the boil I can drop them back to a good strong rolling boil. I have a couple of videos on my website(link in sig) under burners and also 100L BIAB pages.

As Thirsty Boy has shown the maths for electric above, you would need as a minimum 2 x 15amp power points (or 3 x 10amp), not the type of thing the average house has spare. That was calculating on 100L of water, if you wanted 100L final vol, then you may need a larger starting vol to bring up to temp.

Also I'm not sure if you are looking at BIAB or 3V. With 3V you only need to heat a smaller amount of water up front for the mash in, and while it is mashing you can bring the sparge water up to temp. Also if you want to run any heat exchanger herms/rims you need to allow more power there. With BIAB you bring the full vol up to temp initally. Once the lot is in the kettle there is no real difference.

With my 3V I building (almost finished, but its been over long period lol) will allow up to a 100L batch.
A 140L pot for the kettle with 2 x Nasa
Mash tun with 2400w RIMS
82L HLT with just a 2200w element.

I plan on heating the initial strike water in the kettle using the nasas, and transferring that to the mash tun.
Then while I'm mashing I can heat the sparge water in the kettle, transferring that to the HLT for holding. (or I'm even thinking of using a lpg burner under the HLT) The little 2200w element in the HLT will only need to maintain the temp of the sparge water ready for when I need it.

This means I can run the entire system on 2 x 10amp power points.

QldKev



QldKev

 

[pbrosnan]

I know not directly answering your question, but I run a 100L batch from LPG no problems at all. I like to have way too much power, rather than not enough. I have 2 Nasa burners under my 140L pot (100L BIAB batch) and I can get the water to strike temp in about 15mins if I run the burners hard. The great thing is I have infinately adjustable heat, so once I get to the boil I can drop them back to a good strong rolling boil. I have a couple of videos on my website(link in sig) under burners and also 100L BIAB pages.

As Thirsty Boy has shown the maths for electric above, you would need as a minimum 2 x 15amp power points (or 3 x 10amp), not the type of thing the average house has spare. That was calculating on 100L of water, if you wanted 100L final vol, then you may need a larger starting vol to bring up to temp.

Also I'm not sure if you are looking at BIAB or 3V. With 3V you only need to heat a smaller amount of water up front for the mash in, and while it is mashing you can bring the sparge water up to temp. Also if you want to run any heat exchanger herms/rims you need to allow more power there. With BIAB you bring the full vol up to temp initally. Once the lot is in the kettle there is no real difference.

With my 3V I building (almost finished, but its been over long period lol) will allow up to a 100L batch.
A 140L pot for the kettle with 2 x Nasa
Mash tun with 2400w RIMS
82L HLT with just a 2200w element.

I plan on heating the initial strike water in the kettle using the nasas, and transferring that to the mash tun.
Then while I'm mashing I can heat the sparge water in the kettle, transferring that to the HLT for holding. (or I'm even thinking of using a lpg burner under the HLT) The little 2200w element in the HLT will only need to maintain the temp of the sparge water ready for when I need it.

This means I can run the entire system on 2 x 10amp power points.

QldKev



QldKev

Thanks for the info Kev. How much gas are you going through per brew and are you on bottles?

 

[raven19]

Just to add to some excellent posts above:

My big electric kettle (110L capacity) can get preboil of triple batches (80 - 90L) of wort up to the boil with 2 x 2400W ceramic bobbin elements, but it takes a little bit of time, along the lines of Thirsty's excellent post above.

I find leaving the lid on till it starts to boil helps along with some camping mat insulation.

For 100L I would be definately thinking 2400 + 3600 as a minimum, but you may as well go 2 x 3600W as per TB's post above.

At least when you start transferring your wort to kettle the temp of the liquid should be in the 70+ degree range, so you are only lifting it a further 30 degrees to get it up to the boil.

You will then need 2 x 15A circuits as a minimum for the above. Maybe get one more, so you can dunk an immersion element in there too to help get things boiling quicker then remove it once up to the boil.

 

[QldKev]

Thanks for the info Kev. How much gas are you going through per brew and are you on bottles?

I use the normal 9kg bottles, I have a bottle per burner. One bottle would probably run both the burners, I just like the flexibility of having seperate controls with the adjustable reg per burner. I use about 4 to 5kg of LPG per brew, but allow that at the moment there is no electricity in my current brew. (except the temp display) Once I'm at the boil 1 burner running hard seems to be more efficient than both burners runnings dialed back; but I run both burners as they are a lot quiter once they are turned down. Also currently I don't have any heat shroud around the burners so I'm probably loosing/wasting some heat.

So for cost thats about $10 to $12 per brew.

Electricity is cheaper. 7200w of elements at 25c kw/h is $1.80 per hour. Allow say 1hr to get to strike temp + 1hr to get to a good rolling boil + 1hr boil = $5.40.

To me even if LPG was $10 dearer, I only brew this size say 10 times a year, so it's not really a huge cost to factor in for great beer. It is still cheap compared to commercial beer too.

The downside of the electricity is it will take about an extra hour on brew day, or longer if you go smaller on elements. Also I don't know if you rent or own your house, be a bugger if you put in power points and have to move.

Elec systems are nice and quite, sometimes that would be great. If I had a 10,000w or more source for power I would seriously look at swapping over. 3 phase heating elements :wub:


QldKev

 

[Zizzle]

The downside of the electricity is it will take about an extra hour on brew day, or longer if you go smaller on elements. Also I don't know if you rent or own your house, be a bugger if you put in power points and have to move.

Elec systems are nice and quite, sometimes that would be great. If I had a 10,000w or more source for power I would seriously look at swapping over. 3 phase heating elements :wub:

Well time wise it depends. Electric HLTs are easy to put together and automate -- set a timer and wake up to strike water at temp, who cares how long it took to get there.

One good thing about the US is that most laundry rooms have 240V 30A sockets. No need for extra work by the sparky.

The brewbot has a 4500W element for 10 litre batches - complete overkill but it was a cheap low density element so I run it at low duty cycle via a SSR. Works well.

The other important factor here in cold country (it got down to -30C the winter past) is that electric doesn't have the same ventilation requirements as burning gas.

 

[QldKev]

Well time wise it depends. Electric HLTs are easy to put together and automate -- set a timer and wake up to strike water at temp, who cares how long it took to get there.

One good thing about the US is that most laundry rooms have 240V 30A sockets. No need for extra work by the sparky.

The brewbot has a 4500W element for 10 litre batches - complete overkill but it was a cheap low density element so I run it at low duty cycle via a SSR. Works well.

The other important factor here in cold country (it got down to -30C the winter past) is that electric doesn't have the same ventilation requirements as burning gas.

I've though about the idea of the 'set a timer' but sometimes if work is quite I knock of at lunch time and go home to brew, so zero prep time. Sometimes if brewing on a weekend then the timer would rock.

I'm not intrested in automating my rig, sitting around drinking beer and brewing with your mates is something I enjoy doing. If I enjoyed electronics it would probably be different.

Geeze, if I had a 240v 30amp socket available it would change a lot of things.

Good point about the ambient temp, it it was really cold I woudn't want to brew outside. Here, I always brew outside and the Nasa burners do warm up the environment, so much so I've moved from brewing on the back patio to the carport down the back, as it was heating up the house too much. The last thing here you want is excess heat building up. We are in the middle of winter and having a cold spell, Weatherzone shows it just 21.9c right now. So the heat would be great today, but most of the year it is a bad thing.

I guess it is like anything in life, take all the info from here and apply it to yourself and see what is best for you.


QldKev