Here is something I had been working on a while back but wanted to make sure its outcome matches what I'm seeing in my brewing:batch_sparge_simulator.xls
It's a spread sheet that allows you to simulate an up to 3 run-off batch sparge (which includes no-sparge) and party gyle brewing. While it may look complex here is what you enter:
* E5-E8 gets your unit preferences.
* E11-E15 gets info about the 1st mash. grain weight, extract potential and anticipated conversion efficiency.
* E18-E19 gets info about the apparent grain absorption. Use 0.12 gal/lb or 1.3 l/kg if you don't know it. The efficiency calculator i have can calculate it for you if you supply enough data
In E22 you find the possible volume and gravity you can drain from the mash. It assumes that you would collect this volume but you can change this in E25. The section on the right shows you what you could make from that if you boil it down. 10-15% is a realistic boil-off but you can push it higher if you need to.
If you do a 2nd run-off enter the amount of water you add into E29. If you add grain, you can specify this in E30. The spreadsheet assumes it has the extract potential of the initial grist.
Then it calculates for you how much more wort can be drained and what the expected gravity is. Again, you can specify how much you collect. Note that all these volumes are temperature corrected. If you use a measurement that you took on brew day you need to correct it for temperature.
Now there are a number of permutations on the combination of run-offs:
* 1st and 2nd (typical 2 run-off batch sparge)
* 1st, 2nd and 3rd (typical 3 run-off batch sparge)
* just 2nd
* just 3rd
* 2nd and 3rd
For all of these it lists the efficiency and what volume/strength you should expect from them.
I hope this helps. I still plan to do a party gyle at some point but have no idea when I will do that. It also worked well for calculating the efficiency of partially drained batch sparges. This means you don't let the grain run dry by collecting less than you could. It happened to me when I got my Weissbier lauter stuck halfway through the 1st run-off. I just added more water and made it a 3-runoff batch sparge.
Let me know if the results don't match your brewing observations. The theory behind this spreadsheet is the same I used for my efficiency troubleshooting work and the batch sparging analysis.