You've got a lot of options available, but one comment about step mashing.
again... it's a technicality/semantics thing, but neither RIMS nor HERMS is capable of a 'true' step mash according to folks who are sticklers for rules. Step mashing means you have an extremely rapid rise from one temp to the next, taking place almost instantly.
What can be done with recirulating systems is a slower temp increase. More of a 'ramp' than a 'step' simply because it takes a couple minutes to change temps. But, I can testify to the fact that a HERMS can do it. I don't do multiple rests on my mash, but I have many times done a temp rise at the end of the process to get things up to 170*F. For a 5 gallon batch, I can make the change from 152*F to 170*F in about 5 minutes with my system (5500W element in my kettle with the HERMS coil).
Personally, I think a couple minutes to make a temp change is close enough to a 'step' mash, so I would say you are going to be able to do whatever you want.
anyway... back to options for your system....
1 or 2 vessel
1 pump
1 or 2 electric elements
1 or 2 tier
no-sparge is acceptable to you
a brutus 20 type system could be done.
- MLT on top tier circulating mash through a RIMS using one PID
- E-kettle on bottom tier heating strike water while mash is happening with second PID
- when mash is done, create the full loop: MLT flows into e-kettle while e-kettle is pumped up into MLT. circulate like that until the gravity at all places is the same and then shut off the pump and let the MLT drain into the e-kettle
2 PIDs, 2 probes, 2 elements, 2 vessels, 2 tiers, 1 pump... not sure how to classify that kind of sparging.
A no-sparge RIMS could be done
- MLT on top tier with half the water in it
- E-kettle on bottom tier with half the water in it
- let gravity drain MLT to kettle and use pump to return it to MLT
- circulate in that full loop using just the element in the kettle to maintain temps
I have no idea how well this would work, but it uses:
1 PID, 1 probe, 1 elements, 2 vessels, 2 tiers, 1 pump, no-sparge.
You would have longer 'ramp' times on your mash stages because you would have to heat all of the water up instead of a fraction of it like a system that uses sparging.
A no-sparge HERMS could be done
- MLT with all the water in it
- E-kettle with just enough water to cover the element and coil.
- pump MLT through coil and back into MLT
- when done with the mash, dump the water out of the e-kettle and pump MLT into it.
I have no idea how well this would work, but it uses:
1 PID, 1 probe, 1 elements, 2 vessels, 1 tier, 1 pump, no-sparge.
You would have longer 'ramp' times on your mash stages because you would have to heat all of the water up instead of a fraction of it like a system that uses sparging.
I have actually been thinking about trying this on my system at home, just to see how well it works.
A fly-sparge RIMS could be done
This is what eric was talking about.
- MLT with just the necessary water for mash in it
- E-kettle empty at the start of things.
- pump MLT through RIMS tube and back into MLT for mash.
- when done with the mash, slowly pump MLT into kettle at the same time as ground water from a hose is pushed through the RIMS tube to be heated to sparge temps on-the-fly
2 PIDs, 2 probes, 2 elements, 2 vessels, 1 tier, 1 pump, fly-sparge.
or, if you are OK with waiting until sparge is completely done before you start heating wort to a boil in the kettle, then it means that you don't need two elements running at the same time. You can switch which element is being controlled by the PID.
1 PID, 1 probe, 2 elements, 2 vessels, 1 tier, 1 pump, fly-sparge.
I am sure there are other options. This is just what I immediately thought of.
Keep in mind that to stay under 30A, you are going to have to be mindful of element sizes in any system that uses 2 elements and wants them to be capable of running at the same time.
I know you are wanting to stay away from a third vessel, but here's a comment: if you ferment in buckets, then you are going to have a third vessel with you. In my system, my third vessel holds only hot water, and only for a few minutes. I happen to use a keg (because I had it), but it could just as well be a plastic bucket, too.
My system is a batch-sparge HERMS
1 PID, 1 probe, 1 elements, 3 vessels, 1 tier, 1 pump, batch-sparge.