I brew in a single tier, two pump, three vessel system using a single HERMs coil for maintaining the mash temp and cooling the wort post boil. All very good information in this thread ... here are some of the specifics of how I handle these problems on my system.
1) For my system, I maintain the HLT to 6 degrees above my desired mash temp and have the pumps at full flow during the recirculation/mash period. In the last 15 minutes of the mash, I turn the pumps off and rerun the hoses to push sparge/HLT water through the HERMS coil for when I start the fly sparging. The other set of hoses are set to continue recirculating the mash through the pump at slow sparge rates to ensure clean/husk free wort gets collected. The HLT is heating up to 170 during these 15 minutes.
2) I tried a step mash on this system once and i won't do it again using the HERMS system. Ramp up times just took too long and resultant beer had zero body.
3) Because of the above issue, I do not do a traditional mash-out. The HLT water at 170 will keep the mash temp steady and/or raise a bit over time ... either is fine as long as temps don't drop in the mash tun (temps drop without denaturing the enzymes and you will lose your intended body). Alternately, I wait until I have a couple of gallons (11 gallon batch) collected and turn my boil kettle burner on low to slowly heat the collected wort. Basically I am denaturing the enzymes in the boil kettle instead of the mash tun. Same result and it saves time since the wort is already at 180 degrees by the time I am done sparging and ready to start the boil.
Hope this helps.
