If I may add one thing about batch sparging in particular. When I used to mash indoors and boil on a Blichmann burner outdoors and had a Monster Mill 2 with a tighter than average gap setting my efficiency was a consistent 86%. With my new setup in an apartment my efficiency lowered, now have a Monster Mill 2 Pro, same gap setting but my efficiency has gone to 77%-83% mainly due to having less sparge water to use as my boil off in the Robobrew v3 is one gallon per hour less than what I used to boil off. Anyhoo, the point I want to add is when doing my new setup I went with a half inch ball valve on my cooler whereas I used to have the 3/8" valve. Denny recommends opening the valve all the way for maximum flow to set the grain bed quickly. I never did that before but this time went by that advice and personally I don't agree with it at all. I'm finding, at least with my 1/2" valve, that the runoff is too fast and compacts the grain bed in a negative way. As a result I'm seeing some wort still sitting in puddles after I've runoff. That means that wort isn't getting through the grain bed. I'm brewing tomorrow and will go back to slowing the flow like I used to and report back if that stops this from happening.
Rev.
A lower boil off means lower pre-boil volume for the same post-boil volume. A lower pre-boil volume for the same grain weight results in a lower lauter efficiency. The metric the characterizes this is the grain weight to pre-boil volume ratio (note this is not the same as mash thickness, or its inverse.) The higher the ratio, the lower the lauter efficiency, all else being equal. The following chart shows this effect. A typical MLT has a grain absorption rate of about 0.12 gal/lb, so the solid lines apply.
Let's look at a couple of cases. Both are 11 lb of grain, and 5.5 gal post-boil volume. The first case we assume 2 gal/hr boil off, which implies a 7.5 gal pre-boil volume. In this case the weight to volume ratio is 11 / 7.5 = 1.47 with a single batch sparge lauter efficiency of about 88.5%. The second case we assume 1 gal less boil off than the first case, for a pre-boil volume of 6.5 gal. Here the weight to volume ratio is 11 / 6.5 = 1.69 with a single batch sparge lauter efficiency of about 86%. Mash efficiency equals conversion efficiency time lauter efficiency, so in the case of 100% conversion efficiency, mash efficiency = lauter efficiency. If conversion efficiency is less than 100% then mash efficiency is less than lauter efficiency.
I think Denny's advice on run off rate should be modified to "run off as fast as your equipment will let you, without excessive grain bed compaction." It may be with Denny's equipment, he could not hit a run off rate high enough to over compact the grain bed. I think a good way to determine max run off rate for your equipment, crush, etc. is to calculate the grain absorption ratio, which is given by:
Absorption Ratio = ((Strike Water Vol - MLT Undrainable Vol) - First Runnings Vol) / Grain Wt
The MLT undrainable volume is the volume of liquid left in the MLT after draining water from the MLT with no grain in the MLT. Ideally this volume is zero, as the larger this volume, the lower your lauter efficiency. A typical MLT grain absorption ratio is about 0.12 gal/lb. As long as your ratio doesn't increase from that, you are not draining too fast. If that ratio goes above 0.12 gal/lb, then your MLT is no longer draining freely and completely, so draining too fast.
Brew on