Recirculation Infusion Mash System
A RIMS system involves you constantly draining the wort from you mash, pumping it through a heating element, and returning to the top of the mash. You will be rewarded by this method with a clearer wort than manual recirculating, and more consistent mash temperatures, which will make you better beer.
Most RIMS systems are made up of a tube that has in and out connections and contains an electric heating element. The wort temperature is monitored by a sensor placed in the RIMS tube and the temperature controller tells the heating element to turn on and off as the temperature changes. The contorller needed for this mashing method is identical to a <a href="http://brewingsite.com/archives/149" title="HERMS 101">HERMS system</a>.
A variant of the RIMS method involves heating the mash tun directly with gas from the bottom. The wort is still recirculated from top to bottom, but not over a heating element. This method was made famous with the Brutus 10 design.
To build a RIMS system, you will still need the same 3 vessels in standard all grain brewing. You will need a way to heat your HLT, mash (RIMS tube or directly), and your boil kettle. You will also need a temperature sensor and temperature controller, a pump, and two hoses.