I have read about many recirculating mash systems. From RIMS to HERMS. Some heating electrically and some using propane or natural gas.
When i designed and built my sculpture i wanted to be able to do step infusion and be able to recirculate my mash.
I did things a little differently but--- from what i read, no body does everything the same way... And everyone make great beer!
TO HEAT the mash tun i use the burners to heat water up strike temperature for the first mash rest. After that i pump hot water from the hot liquor tank through 50 feet of copper coil wrapped around the inside of the mash tun, then the water goes back to the hot water tank in a continous cycle. The hot water tank is heated to 180-190 degrees and held there by the propane burner. The water recirculated in the mash tun through the copper coils is about 20 degrees less then that. The pump is regulated by a Ranco temperature control with the probe inside the mash tun. Once set mash temperature is reached the Ranco device shuts the pump off. If the mash temperature falls too low the Ranco device automatically turns the pump back on until the set temperature is reached again. An electric mash agitator is set inside the mash tun and ensures even heating. Once the final rest is complete the Ranco device is set for mash out temperature. Hot water is cycled until the mash out temperature is reached.
TO RECIRCULATE the wort for several minutes and create clear runnings after mash out i simply pump mash water from the bottom of the mash tun to the top of the mash tun.
*Hot wort never runs through copper coiling, when it is recirculated it goes directly from the bottom of the mash tun to the top of the mash tun. The copper coils are by-passed.
TO SPARGE i simply pump the hot liquor tank water over the mash with a sparge arm and simotaniously drain wort into the boil vessel at a SLOWER rate. The slower rate allows me to automate the sparging process by a float switch connected to the pump (water always comes into the mash faster then is leaves until all sparge water/water from hot liquor tank is emptied). The calculated amount of water is already in the hot liquor tank and when pump runs dry, sparging is done. When the runnings into the boil vessel is complete, boiling begins.
The heating, recirculating, and sparging run through the same hard copper plumbing with bypass valves and 1/2" inner diameter hot water tubing with quick disconnects on the ends of the hard copper plubing to control what pumps-what-where-when... (see diagram, involves turning valves)
To make the system even more versital (not shown in the diagram) i turned my boil vessel into a second mash tun and added a fourth vessel-- a 60 gallon copper riveted water tank converted into a boil vessel.
The two mash tuns allow me to brew one 30+ gallon batch of beer or two completely seperate 15+ gallon batches at nearly the same time (mash at the same time then boil one after the other).
All four vessels have 150,000 BTU burners under them.
Each mash tun has it's own seperate but identical pluming. Each uses its own pump-- although you could easily only use one pump and rotate it with disconnects. I use a two tier four vessel system. Two 15 gallon mash tuns, one 15 gallon sparge vessel, and a 60 gallon converted water heater (beautifully copper riveted). The system is automated to a degree with a Ranco temperature controller and float switch to automate sparging.
Honestly less complicated then most RIMS systems i have looked at on line. The benefit of this system is i avoid pumping hot mash water through copper coils or scortching electrical elements, have great control of temperature during step mashes, and utilize one pump per mash tun. The amount of plumbing is typical of other systems and probably easier to construct.
I have easy designs to follow for anyone, as it's the least i owe from all the knowledge gained from forums like this.