Scale up recipes and Fly Sparge?

[OldStoveBeer]

Hi all,
Thanks to all of the awesome info on this site, we now have a HERMs system that is almost complete! It consists of 20 gallon HTL and BK, and a slightly larger MLT.
I was hoping someone can help us out with what I assume is a pretty simple question though. When using a recipe for a 5 or 10 gallon batch, how do we properly scale up to 20 gallons? On a high level, one could just assume multiply everything (grain bill, hops, H2O) evenly to get to 20 gallons, but I’m not sure that would fly (rather ask first than risk wasting an entire batch under that assumption).
Also, most people seem to fly sparge for “45 minutes”. Do you guys generally try to set the flow of the sparge to fill the kettle to the top in ~45 minutes, or is more of a matter of just rinsing the grains for 45 minutes regardless of the final BK level? Obviously it would take longer to fill our 20 gallon kettle at the same sparge-flow rate as a 5 or 10 gallon batch, so if it was a matter of 45 minutes, we would have to have a quicker flow…which intuitively doesn’t seem right.
Once the first runoffs get to the BK, I assume just sparge until the kettle is at the level of what the recipe calls for (i.e. 20 gallons), right?
Any help is much appreciated. Pics coming soon!
Thanks,
OS1

 

[CKing]

I'll empty 5 gallons of sparge water into the mash tun in approximately 40-45 minutes.
After the hot liquor tank is empty I'll typically open up the valve on the mash tun to collect the remaining volume.
Efficiency has been very good using this method.

 

[OldStoveBeer]

Thanks, but what is your final desired volume in the BK? I'm trying to figure out the amount/rate for 20 gallon batches

 

[CKing]

7 gallons +/- depending on total boil time....I like to have around 5.75 gallons once the boil is done so I'm assured to have at least 5 gallons once it's time to bottle.

 

[ajf]

I brew 5g batches, and I used to use a 5g MLT which had a diameter of 9". For a typical brew with an OG of 1.055, it used to take me about 50 - 60 minutes to sparge (fly sparging). For a 1.075 OG brew, it would take me about 90 minutes to sparge, and get the same efficiency.
Then I switched to a 10g MLT with a diameter of 12 inches. For the same brews, and the same efficiency I can sparge in ~30 minutes (1.055 OG), or ~50 minutes (1.075 OG). When I thought about it, I realized that the times are inversely proportional to the cross sectional area of the MLT, which means that the rate of flow of the sparge water through the grain bed is approximately the same with the long sparge in the narrow cooler, or the short sparge in the wide cooler.
This has always worked for me, but I cannot guarantee that it will for you.

-a.

 

[RoadKing]

You want to have your final volume in your Boil kettle at the end of your sparge.(plus your boil off).
With bigger batches I would sparge for at least an hour.