The 3-vessel brewhouse configuration allows for more flexibility in brewing styles and productivity.
The configuration is typically either 1) Mash Tun, Lauter Tun, Kettle/Whirlpool, or 2) Mash/Lauter Tun, Kettle, Whirlpool. Choosing between these two configurations depends on the intended benefit of the 3rd vessel.
If the brewery plans to brew a lot of recipes using step infusion and/or decoction mashes, the use of a dedicated Mash Tun would make sense. If the goal is to reduce the amount of time taken by each brew, the use of a dedicated Whirlpool would be a good choice.
An alternative configuration can be to use a Mash/Lauter Tun, and two Kettle/Whirlpool vessels. This configuration would allow for simultaneous boils and also offer the brewer a kettle to use for sour beer production while maintaining throughput of other brews in the second kettle. The image below depicts a Mash/Lauter Tun, Kettle and Whirlpool. Starting from $135,000.