Heat Loss Question

[Ian9365]

Hi
Any scientists out there, I want to work out a heat loss figure in watts for my kettle. I can measure degrees lost over a given time period but a formula to convert that eludes me ?

 

[Clint]

Why?

 

[Ian9365]

Sorry wasn't quite exact enough in what I'm asking. I'm trying to work out how much heat energy in watts I need to apply to my stainless kettle to balance heat loss at mashing temps in typical ambient temps, say 18C for example

 

[Cwrw666]

Wouldn't it be more accurate to put some water on to heat and measure how long it takes to raise the temperature by one degree, preferably around mash temperature as I would assume it will take longer the hotter the boiler is due to increasing effect of heat loss. Then if you've lost say 3c during your mash just put the boiler on for the required length of time.

The problem with the way you want to do it is that you may well have a 2.5Kwh element in your boiler but you'd have to measure it exactly to work out anything sensible as I'd be highly surprised if the figure for the wattage is exact.

 

[Clint]

Ah right. Insulate it....wrap it up...

 

[terrym]

Sorry wasn't quite exact enough in what I'm asking. I'm trying to work out how much heat energy in watts I need to apply to my stainless kettle to balance heat loss at mashing temps in typical ambient temps, say 18C for example

There are too many variables and too many unknowns about your system to calculate it accurately. I suggest you fill your kettle with water heat it up to mashing temperature and allow it to slowly cool. Time the temp drop say over a 5*C range. In that case the rate of heat loss would be (Mass of kettle contents x Temp Drop/Time interval in hrs) in what ever units you want which can then be converted to an approximate power . Being an engineering dinosaur I would work in Btus/h so others will have to convert that to joules or kw and all those new fangled units.

 

[Ian9365]

Uhh yes ok but not an answer to the question

 

[Ian9365]

Sorry that was an answer to Clint

 

[Clint]

If you have an element in your kettle...wrap it up and connect it to Inkbird...that will cycle the element to keep your temp...I know not the answer but it'll keep your mash warm!

 

[Chippy_Tea]

Any scientists out there,

I don't think any members here are scientists, if the answers already given are not the answer maybe there isn't a definitive answer.




answer.

 

[Ian9365]

Sorry Clint wasn't being sarcastic, it does read like that but wasn't intended. I'm just interested as a technical excercise. I'm always trying to dream up ways of automating the process. Bit like sledge hammers and walnuts I suppose but there we are, I enjoy the challenge.

I could just buy a Grainfather or similar but wheres the challenge in that

 

[terrym]

I don't think any members here are scientists, if the answers already given are not the answer maybe there isn't a definitive answer.

In a previous life, a long time ago, I used to carry out heat transfer calcs on industrial heat exchangers and with the information available here there isn't a calculable answer. The only way you will find out is to meaure the heat loss on the unit and go from there. @Clint has the most pragmatic solution

 

[IainM]

Some of us are scientists!

My answer to the question is... don't bother. What Terry is missing from his equation is the heat capacity for the contents in the numerator, which would be different for a mash than it would be for water, and would vary according to mash thickness. Further, the heat loss rate won't be constant, as it would vary with external temperature and air circulation. Plus, the very notion of mash temperature is misleading. If it isn't well insulated then the centre of the mash will be considerably warmer than the the parts nearest the wall. If you heat from below with an element, then the lower part will be hotter, perhaps much hotter. To get it even you will need to recirculate like an all-in-one system, and the rate of recirulation will also affect the rate of heat loss, and the rate of recirculation depends on mash thinkness, grain crush, the pump and how much it is throttled. You'll never balance the heat going and coming out with an equation, which is why all commercial and home-brew electronic setups that keep a constant mash temperature have a temperature probe and a thermostat to make small adjustments on the fly.

 

[Ian9365]

Crumbs I seem to have opened a can of worms don't I. I appreciate all the answers especially IanM.

Some of us are scientists! My answer to the question is... don't bother. .

On the face of it, it sounds like good advice. However I am guilty yet again of not properly phrasing my question, so possibly not.

To get it even you will need to recirculate like an all-in-one system

That is my intention

You'll never balance the heat going and coming out with an equation which is why all commercial and home-brew electronic setups that keep a constant mash temperature have a temperature probe and a thermostat to make small adjustments on the fly.

I fully take your point and I wasn't hoping to anyway. I have a never used split rims tube assembly from Brew Builder complete with their LWD 3Kw straight element and a quality PID and SSR, all purchased a couple of years ago for a project that never got of the ground. I now have much more time on my hands and so its time to put it to some use. I should have explained all this at the start, it would have saved all your time. Im not any sort of PID expert and maybe they are all the same but I can set on this one a maximum wattage that it will allow the element to use. What I was really looking for was a maximum figure so I could set this value. Unfortunately my main heat source is a Buffalo 3Kw induction hob which cannot be controlled with a PID

 

[Chippy_Tea]

Some of us are scientists!

 

[IainM]

Crumbs I seem to have opened a can of worms don't I. I appreciate all the answers especially IanM.



On the face of it, it sounds like good advice. However I am guilty yet again of not properly phrasing my question, so possibly not.



That is my intention



I fully take your point and I wasn't hoping to anyway. I have a never used split rims tube assembly from Brew Builder complete with their LWD 3Kw straight element and a quality PID and SSR, all purchased a couple of years ago for a project that never got of the ground. I now have much more time on my hands and so its time to put it to some use. I should have explained all this at the start, it would have saved all your time. Im not any sort of PID expert and maybe they are all the same but I can set on this one a maximum wattage that it will allow the element to use. What I was really looking for was a maximum figure so I could set this value. Unfortunately my main heat source is a Buffalo 3Kw induction hob which cannot be controlled with a PID

Oh. 700W and an inkbird should do the trick nicely.

 

[LED_ZEP]

@Chppy_Tea Your comments makes me chuckle whenever the subject gets around to science. I've expressed it as a formula for you... Science²=CTsquirm