Why Either 77kw Or 28kw Power Can Boil Similar Volume Kettle

Why would either 77 kW or 28 kW boil a kettle of similar size?

I recently had a discussion with a customer about the heating power of his 1500L brew kettle. They currently only use 28kw of heating power to boil 1200L batches of wort and it works well. However, our standard heating element for a 1500L capacity is about 77kw.

So we exchanged calculations and operational details together and found out some interesting things.

How we calculate the electric heating power of a 1500L kettle.

We calculate the power mainly based on the heat exchange principle.
Our calculation is to heat the wort/wort at a rate of 1-1.5°C per minute.

The estimated energy required to heat 1500L of wort from 78°C to 100°C is approximately: 1500Lx4200J/kg.°Cx22°C=1.386×10^8 J=38.5KW.h

If we assume that the wort is heated from 78°C to boiling temperature in about 0.5 hours (0.7°C per minute, which is slower than 1-1.5°C because we want to minimize the heating power), then the power of the heating element ends up being approx.
38.5KW.h/ 0.5hr = 77KW

The elements inside our standard 1500L kettle are installed like this.
9kwx6pcs+8.3kwx4pcs=87.2kw, of which 4pcs 8.3kw are spare.

Based on the customer’s current experience, what is the heating rate for a 28KW heating element power?

So what I currently do with the elements is once the liquid is over the top of them, I turn them on and fiddle with it until I reach the total capacity of the KTL. Once the KTL is full, it usually takes about half an hour to reach boiling level, if you do that.

The elements I currently have are four 7KW 3 phase elements. This is in both the KTL and HLT.

It takes at least an hour, probably more like 1.5 hours, so the slow heating time shouldn’t be an issue since that’s what I’ve done so far.

I haven’t had any problems with scorching and the way your elements are set up is much better than what I have now, which is 4 straight 1200mm elements in one place.

So what we found out is that the difference is that we are calculating the power based on the 1500 liters of wort that starts heating up after it’s all transferred.
And the customer’s experience is that the wort starts to heat up once the wort is over the top of the heating element. Therefore, it is still possible to use only 28 kW of heating power, because they actually heat up in 1.5-2 hours (they heat up from the boiling process).

After combining the customer’s experience, and taking into account the need to ensure adequate heating capacity once required, we finally agreed on a solution.

We will make three breakers for 77kw of power, dividing the elements into three groups.
For example: 27kw + 24kw + 26kw
The customer can start any one of these groups to heat the wort, as they do now for their existing brewhouse.
They can also start both groups of elements, or start them completely if necessary.
This also reduces the risk of scorching, as they have the freedom to choose to turn on only one or both sets of elements in the event of a scorching problem.

What is your experience or advice?

We are a manufacturer of beer brewing equipment. We would like to exchange ideas with you. It’s fun and allows us to continuously improve the design of our equipment based on your feedback or suggestions.