Heater Bank Control with Binary Sequencing saves controller outputs!

Heater banks are used all over buildings and in industry to heat up all kinds of things - water, air, oil, chemicals.

The most common form of temperature control, is single step on/off control. Geysers, ovens and split type air conditioners typically work this way.

For small applications, this is an acceptable form of control, but on large applications it becomes rather harsh on an electrical supply system if the entire load is switched in and out all the time.

By splitting the elements of a bank in two, one can do 0/50/100%.

Split it in 3 and you get 0/33/67/100%.

However, by now you need 3 digital outputs on your controller and for those who have worked with these devices, anything more than this allocated to a single function, makes you think hard if it can be afforded.

If you run out of outputs, you may need to buy another controller that will be under utilised - apart from the software challenges that can be introduced using more than one controller.

This is where binary sequencing comes in - and it is a very cool way of practically feeling the effect of 1's and 0's.

Converting from Binary to Decimal, it goes like this:

0 = 0

1 = 1

10 = 2

11 = 3

100 = 4

101 = 5

110 = 6

111 = 7

See the pattern? Because we work on the base 2 system, each time we add a 1 in front, the value of that number is twice the value of the 1 before it, so you get 1, 2, 4, 8, 16 etc. All we do now is add them all up.

How would we apply this to a heater bank?

If the bank becomes large enough in terms of number of elements - as little at 3 elements mind you - you can allocate the capacity of the elements in the binary ratio. It is very easy to do.

Lets say you have a heater bank with a total capacity of 27 kW by using 3x 9kW elements.

Option 1 is to do 3 step control 0/33/67/100% with 3 outputs. Bang Bang Bang.

Option 2 is to do Binary Sequencing and this will use only 2 outputs. By allocating 1 element or 9 kW to one output, and 2 elements or 18 kW to the other, you can also get 0/33/67/100%.

Instead of Bang Bang Bang, it now goes Bang, BANG, BangBANG. First only step 1, then only step 2, and then both together.

Wollah! You saved an output, and got your capacity control with no physical changes to your heater bank!

By using 3 outputs, you will have 7 steps of control! That could be good for a much larger bank where we would perhaps then have 9, 18 and 36kW as steps for a total of 63 kW.

However, this will cause a significant increase in switching cycles of contactors and relays which all have a finite number of cycles it can do. This cannot be ignored as replacing switch gear is expensive. In this case, it might be worth the while to opt for solid state contactors.

Many controllers these days supports binary sequencing and it can be a life saver if you need to reconfigure a large heater bank for softer steps. This can become important for maximum demand control of your ESKOM supply.

Delta Solar CC developed a great CPD course called "The Nuts and Bolts of Industrial and Commercial Controllers" where concepts like this and many other things are taught.

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