I like the sounds of the second hop addition timings that you listed so I might just give it a try..
Which one the first or second suggestion?
I'm trying to setup the calculator and am struggling to achieve the IBU results that I should be getting. If I put the utilisation to 80% on whirlpool or hopback it sends the IBU through the roof and the same with 30%... I think there must be something I am not understanding...
Sorry, I should have been clearer.
I meant 80-90% (or 10-30%, respectively) of what a boil @210F (100C) of that duration would give you. So if boiling for 10' would yield 20 IBU, expect (or calculate) 80-90% of that (16-18 IBU) for a 10' hopstand at flameout (wort temps ~200F (93C)).
Similarly, if a boil for 30' would yield 40 IBUs expect only 10-30% of that at 150F (65C).
The lower the wort temps, the lower the isomerization (bittering, IBUs) and according to some reputable sources, none below 140F. Don't expect a linear relationship either, it's a curve.
Now at those lower temps more flavor and aroma are retained in the wort since less gets isomerized (less bittering), blown off with evaporation, and escape other ways. You do need longer steeping/whirlpool times the cooler its gets to extract all the goodness, say 20-60 minutes. I often do first whirlpool addition for 20' at ~160F followed by a 2nd whirlpool charge for 30' at 140-150F. The first whirlpool hops stay in the wort all that time as well as any other hops that were added earlier and during the boil. Then I quickly chill to pitching/ferm temps.
I'm not familiar with Brewer's Friend's recipe formulation software and not sure how it calculates or how correctly it estimates IBUs for whirlpool/hopstand hops IBU contributions at much lower temps (especially far below boiling). Does the [?] explain what kind of values to input in the [Util] boxes?