HERMS vs. "Counterflow" HERMS

OK, I got the mash done. It's better now that I limited the pump reruns, but I think I need to limit the pump on time as well when I get near the set point.

4C(7.2F)/minute mash temp change, but the probe was quite near the top of the grains.... Easiest way to get fast ramp times is to place the sensor "right"
Overshoots are about 0,8C at the peak.

Are these just throw-away test mashes to test out your equipment and processes because those mashes are RIDICULIOUSLY long?? (1 hour and 45 minutes longer than necessary for 95+% of grists...)


Adam

It's mainly because I don't have any idea what I'm doing. I've just been reading about mashing and I guess this one will be a quite dry beer

Here's how my plumbing is done (about):

I use the HERMS CFC pump to make a whirlpool as well and that makes things a little bit more complicated.

bendiy said:

You're confused on the counter-flow HERMS process. I don't control the HTL temp, I just want it to be pretty hot so it has more thermal energy to transfer to the Mash. 180F to 200F is fine and you can do that manually. You do want to avoid boiling so you don't get bubbles in the line. I've found that the recirculation will pull enough heat out to avoid a boil.

Click to expand...

Ah, yes I see that the flow rate of the controlled liquid through the CF Heat Exchanger is the primary modulator. I overlooked that but it doesn't come into play in my final analysis anyway.

One needs to ask a few questions about this process.

The problem: Temperature stratification in the HLT of a HERMS during the mash. If the temperature of the liquid in the HLT is not uniform, there will be inaccuracies either in regulating the MASH temp or regulating the Sparge temp, depending on where you put the probe.

The stratification problem usually manifests itself as hotter water near the top of the tank and cooler water near the bottom. During a sparge, if one is regulating the sparge temperature from the water drawn from the bottom of the HLT, it will become a problem as the temperature will sneak up during the sparge, and there is not a very good means of cooling water by a few degrees very quickly in-line with a pump. SO...

Question 1: How do I solve the temperature stratification problem?
Answer: There are several ways.

a.) use a pump to recirculate the HLT water.

b.) use a dedicated stirrer in the HLT.

c.) use your CFC to recirculate the HLT and MLT simultaneously.

Question 2: Which way is best?

Answer:

You decide. I'm going with a.).

mightynintendo said:

The problem: Temperature stratification in the HLT of a HERMS during the mash. If the temperature of the liquid in the HLT is not uniform, there will be inaccuracies either in regulating the MASH temp or regulating the Sparge temp, depending on where you put the probe.

Click to expand...

If this is the only problem that you're focusing on, then I agree that just stirring / recirculating the HLT are probably the way to go. BUT many of us are trying to solve more brewing problems that just that.

If you have an uninsulated, nondirect-fired mashtun you need a method to add heat to the mash; HERMS is certainly a solution to this second problem.

If you want the ability to step mash and direct-fire isn't an option, HERMS / RIMS are your possible solutions. The rate of temp rises has been one of the biggest "cons" against HERMs, as obviously is temp stratification in the HLT. Using a counter flow chiller in this manner solves the temp stratification issue (both in the HLT AND in the mash where it's even more important) and the rate-of-rise issue, as a recirculated mash it also results in incredibly clear wort.

Electric brewing is also gaining in popularity very quickly; one of the primary benefits is being able to brew indoors all year long because of a lack of carbon monoxide and a lack of an open flame -again a system where you're generally not going to be applying direct heat to the mash and need external heat.

Summary: This solution makes HERMS better and addresses 2 of the major HERMS concerns; it's a big step forward. If you're not interested in HERMS then why would you bother to comment on a thread that's about traditional HERMS vs. Counterflow HERMS? (this is called "trolling" in most parts of the interwebs)


Adam

biertourist said:

If this is the only problem that you're focusing on, then I agree that just stirring / recirculating the HLT are probably the way to go. BUT many of us are trying to solve more brewing problems that just that.

If you have an uninsulated, nondirect-fired mashtun you need a method to add heat to the mash; HERMS is certainly a solution to this second problem.

If you want the ability to step mash and direct-fire isn't an option, HERMS / RIMS are your possible solutions. The rate of temp rises has been one of the biggest "cons" against HERMs, as obviously is temp stratification in the HLT. Using a counter flow chiller in this manner solve the temp stratification issue and the rate-of-rise issue.

Electric brewing is also gaining in popularity very quickly; one of the primary benefits is being able to brew indoors all year long because of a lack of carbon monoxide -again a system where you're generally not going to be applying direct heat to the mash and need external heat.

In a statement this solution makes HERMS better and addresses 2 of the major concerns; it's a big step forward. If you're not interested in HERMS then why would you bother to comment on a thread that's about traditional HERMS vs. Counterflow HERMS? (this is called "trolling")


Adam

Click to expand...

Well thanks for the lovely accusation of trolling.

Obviously you haven't been paying very close attention to this thread. If you were, you would know that I AM interested in building a HERMS and have said so many times already. This thread is about the benefits and detriments of using a CFC as a heat exchanger during the mash of a HERMS system.

Furthermore, I STARTED this thread. How is it even technically possible to troll my own thread, unless this thread's sole purpose was to troll?

But anyway, there's no trolling here. I think that using a CFC as a mash heat exchanger looks very promising. From the plots it appears that all the mash final temps finished too cold, but that wouldn't be a problem if one was targeting 170F instead of 165F. The rise times look to be around 10 minutes which is really quite good for 10 gallon batches. I have nothing against the use and I think using the CFC is an interesting take on the HERMS systems. I'm just going with a standard HERMS and recirculating the HLT water during the mash because it's easier to automate with an electric system. If I fine tune my system and see that I can't get good temperature rise times, I may very well consider moving towards a CFC HERMS in the future.

Lay off me. And don't go around calling people trolls when you have no idea what you're talking about.

mightynintendo said:

Furthermore, I STARTED this thread. How is it even technically possible to troll my own thread, unless this thread's sole purpose was to troll?

Click to expand...

:smack:
Well that's embarrassing...

My bad, fully apologize on the trolling comment, my brain was apparently taking a vacation today without me.

I hadn't read the thread in a quite a while and just jumped in at the newest posts and took one post out of the context of the rest of the thread.

I see that you're fully evaluating all the pros and cons and are looking at it from different angles one at a time. (I do the same.)

Ah don't worry about it. Everyone has moments like that.

If you want to see trolling, go check out the debate forum. Lots of fun stuff there and while trolling is explicitly prohibited, we find a way around it

biertourist said:

:smack:
Well that's embarrassing...

My bad, fully apologize on the trolling comment, my brain was apparently taking a vacation today without me.

I hadn't read the thread in a quite a while and just jumped in at the newest posts and took one post out of the context of the rest of the thread.

I see that you're fully evaluating all the pros and cons and are looking at it from different angles one at a time. (I do the same.)

Click to expand...

Hmmmm.


1. Open Mouth
2. Insert Foot
3. Chew Slowly

The comments earlier about Herms and stratification. You would have the problem of that regardless of a HERMS coil. If the HLT water is not being mixed, it will be hotter at the top, but not by much. The real problem with a coil is that is creates at barrier around the coil that cause the strification. If you look at threads about IC coolers and Jamill tube, they discuss this regarding a "heat blanket" around the IC Coil. I do remember that when we added the tube, our cooling time improved quite a bit. That is the reason I cycle around my HERMS. If you have a COUNTER FLOW CHILLER as a HERMS, you need two pumps but you will not have any problems with that. You can also ramp the temp quicker with a counter flow vs a regular HERMS.

BTW, I am thinking about switching back to my Counter Flow HERMS

.... to make thing as complicated as possible.

No matter which (HERMS)-system you choose, you will always have problems with the mash temperature control, if only one probe is used.

- if the probe is in HLT only, there's no way of telling what the mash temp really is and the stratification comes a real problem. Any steps in mash temp are slow to do and overshoots are really difficult to control. If you overshoot the HLT temp it takes for ages it to cool down. It works best when the HLT has a really small amount of water in it + a powerful stirring.

- probe in the wort output only. This limits ramp times as you can't heat wort over the set mash temp without complicated control system. I also noticed that the mash temp starts to creep up over time. I think this is the best solution, if only one probe is used. With a separate small HERMS-kettle this is a good way to control the mash.

- probe in the mash only, with a careful control (PID?) of the HLT temp (or a tiny HERMS-kettle) it might be doable. Any steps in mash temps are really difficult to do without overshooting and the lag time in probe feedback makes things pretty much impossible?

My solution is to use 2 probes for the control. One in the mash and one in the wort output (I used to have 3th one in the HERMS-kettle before moving into CFC-HLT-HERMS). The control sketch in the Arduino is made so that if mash temp is way off what the set mash temp is wort can be hotter than the set mash temperature. I reduce the amount of wort "overshoot" as the set mash temp is closing in and I finally set the wort temperature same as mash. This enables fast steps (with the CFC-herms) and there's no problems with the overshoot once the settings are right.

2 point temperature control can be done also with 2 "normal controllers". I used 2 Sestos's in series before the Arduino stepped into my life. 1 was 12V output and the other one with a relay output....

One thing that comes to mind ... it's really important to check what's your free flow out from the mash tun is. It can be quite slow and if too powerful pump is used it can create suction in the mash tun and stuck mash is more that likely outcome of that (been there) especially if false bottom is in use, braided SS seems to work better. If the hoses on the input side of the pump start to jiggle, the pump sucks
I've about 3L/min flow out from mashtun with the grains in (if I remember it right). The flow also limits the temperature step times.

I just made a new version of the control sketch. I added pump on time limiter when the mash is <0.5C from the set point. The pump can run only 3000ms and can be turned on again after 10000ms break. This seems to be taking care of the overshoots when HLT temperature is much higher than the mash. I got +-0.15C accuracy with 20L water in the mash tun.

One more thing that is great with the CFC-HERMS. There's no need for powerful heating element to get the mash step time short. Just a big kettle full of thermal mass.

Edit: A short plot of the test with the new settings. It's easy with the water only to keep temperatures in check, but this looks promising:

Mash drops 0.4C from the set point and wort goes down 0.7C max (because of heat losses in HERMS line).

Temp stratification isn't an issue in the HLT because its a black box system. The controller sees it needs to apply heat, it applies heat, and after given period of time, the outlet wort temp rises. The controller doesn't need to know what's going on inside the black box (i.e. the actual HLT temp.)

The tuning for a PID will vary greatly depending if the HLT is stirred or not, but that's the beauty of a PID, it can be tuned. But the moral of the story is, a properly tuned PID will account for the temp stratification. That's why it's not an issue. If you tune the PID correctly, it'll hold the out,et wort temp at the exact degree you wish.

My HERMS holds my mash temp at .0-.3* of my target mash temp (verified with a +/- .1 thermometer.)

What further level of perfection are you looking for? We're making beer, not a space ship.

I agree, I'm building "a space ship" here. If that bothers you, be happy with your build, never mind my stories, just make more beer

To me the main thing is, within this thread, how powerful the "black box" is. And what I've learned from my builds is that the counterflow HERMS is the best for me. That's all.

I didn't have a plotting system when I used "herms coil in the HLT with the stirrer"-system. It would be interesting to see, if anyone has any plots of how fast their systems heat the mash?

scottland said:

What further level of perfection are you looking for? We're making beer, not a space ship.

Click to expand...

Maybe you're not building a space ship but I'm an engineer and that's exactly what I intend to do. Yes, I'm going to fly my brew rig to Mars. :0)

Great thread! As I've been researching RIMS and HERMS and all the variations I'm still not clear on how fast of a temp change is considered a step vs a ramp. This CFC solution seems to be the fastest - am I wrong in that?

Carlscan26 said:

Great thread! As I've been researching RIMS and HERMS and all the variations I'm still not clear on how fast of a temp change is considered a step vs a ramp. This CFC solution seems to be the fastest - am I wrong in that?

Click to expand...

The temp change is fast but sparge temp creep seems to be the biggest demonstrated problem. Unless you keep the hlt water at the appropriate temp instead of just an arbitrary temp hot enough to get a good exchange at a fast flow.

mightynintendo said:

The temp change is fast but sparge temp creep seems to be the biggest demonstrated problem. Unless you keep the hlt water at the appropriate temp instead of just an arbitrary temp hot enough to get a good exchange at a fast flow.

Click to expand...

If you are referring my plots, I'm trying to get the HLT water down when I'm heating the mash to mash off. Otherwise my sparge water would be too hot and I would get all the tannins etc. in my beer. There's absolutely no problem to maintain the HLT temp as high as you want, just dial the HLT to over 90C (200F). Other thing that can be done is to add more water into the HLT. My goal is to use as little as water as possible, I'm trying to make it so that I can use all of it to sparge. This way I'll use less water/power.

In some stage you also said that the mash temp is a couple of degrees lower than set. This is not true, maybe you were watching the wort temperature? With the CF-Herms the wort temperature will drop under the set temp when the pump is not running. Same thing happens with all Herms systems, but it's biggest with CF-Herms as the HX-coil is in air, not in water and it cools faster. Same issue can be seen too with HERMS with a very low volume (small thermal mass) heating kettle (I used as little as 1 cup in on stage). This is what makes the need of having two sensors, it's almost impossible to calculate the mash temp from wort, if it's cooling the mash some of the time. The mash temp starts to creep up, if you only measure the wort temperature.

I'm adding a "keep warm"-sketch in my Arduino software for the CF-H. The idea is to make the wort temperature more stable i.e. compensate the heat losses in hoses to pump and back to the mash tun by running the heating pump in "right" intervals. Just to keep the HX-warm, not to heat the wort. I had similar sketch on my "induction small volume HERMS" and that worked to the perfection. My mash staid under the tolerance of my sensor at it's best.

Vesku, your input in this thread has been amazing. Thanks! Would you be willing to share your arduino code with us?

bikesnbeers said:

Vesku, your input in this thread has been amazing. Thanks! Would you be willing to share your arduino code with us?

Click to expand...

If I get it "ready enough" to be shared, I might. I shared it on one other forum, but it was so bad I later deleted It's not a much of a help for anyone at it's current state. My 1st code ever, 33kb of very confusing coding that needs an Excel sheet for a map...

And yet another thing I remembered I need to share (it probably has been addressed here before, but still). The problem of measuring wort temperature. I've had a massive (almost 2F, if I remember wrong) temperature difference just by alternating the sensor position and the "thermo well" material. I found it impossible to get reliable reading inside the hose, no matter what sort of adapter/sensor I've tried. I guess it's all about the laminar flow (Bill Bryson told me to use this term to impress everyone, just reading "A Short History of Nearly Everything") and turbulence that the sensor creates when inside the hose. I got the best results with all plastic T-sensor attachments (DIY of course). The sensor in the middle of the flow, the reading was still under what the real value was though. With a copper/ss the T acted like a heat sink and lowered the reading even more. If there's any thermal mass on the measuring device -> problems... And the best way to get rid of the problem is not to think about it (thanks again Bill).

Now my sensor is way inside the wort hose inserted from it's end. Straight against the flow of the wort. It's now showing reliable readings as long as there's a continuous flow ... any air trapped on the turbulence of the sensor and off we go. This was one more thing that made me use 2 sensors for the control. At least the one in the mash is not affected with a flow ... but the mash temperature varies depending where you measure it ... it's hard out there

OK, so the mashing temperatures can't be measured accurately no matter what. No worries, as long as there's means to repeat the mash schedule time after time with same results all should be happy. After that it's possible to really test what the different mash schedules do for the taste of the beer and not just guesstimate. The ability to plot the mash temperature really makes a big difference, if one wants to be sure what has happened during the mash.

Nice info.I use (2) STC-1000 controllers for my mash, the probes are small and waterproof. One probe is attached inside the RIMs output (return) which is Loc-Line in the MLT, the other probe is under the false bottom. The sensor in the Loc-Line controlls the RIMs element. There is also an analog thermometer "T"d into the MLT output after the ball valve. Between the 3 I get a good sense of the mash temp since there is always a small discrepancy between them.

Your control strategy sounds great.

The STC-1000 has a nice small probe with small thermal mass, I guess it has a NTC-resistor inside there at least I managed to fool the controller by replacing the sensor with a resistor. I use STC in a sauna that I build to control the heater. Also have one of them in my fermentation fridge. Only problem with this sensor is that it's not very linear over a large temperature range (can be a problem with step mashes or dual sensor setups).

Vesku said:

If you are referring my plots, I'm trying to get the HLT water down when I'm heating the mash to mash off. Otherwise my sparge water would be too hot and I would get all the tannins etc. in my beer. There's absolutely no problem to maintain the HLT temp as high as you want, just dial the HLT to over 90C (200F). Other thing that can be done is to add more water into the HLT. My goal is to use as little as water as possible, I'm trying to make it so that I can use all of it to sparge. This way I'll use less water/power.

Click to expand...

Is there a good controls mechanism for bringing the HLT water down to sparge temps during mashout, or is this done by hand?

I am still considering using this method...

I'm trying to control the burner on my HLT. The plan is to keep it at a constant 170F throughout the whole mash. Then when the mash is done and it's time to sparge, the HLT is at the perfect temp. I need to play with this some more and see if 170F is hot enough to get decent step ramps in the mash. When making the final step to mash out from 158F to 170F, if the HLT is only 170F, that ramp will not be very fast.

It may be easier to keep the HLT at 190F and cut the heat to it in the middle of the finial mash out step. Then the mash would pull the remaining heat out of the HLT and hopefully end up around 170F in both Mash Tun and HLT.

In the end, I may just keep it at 190 and throw some tap water in at the last minute before sparging to get 170F. 2 gal of 68F tap water will drop 190F 10 gal in the HLT to 170F.

For a normal HERMS setup to try to achieve a better step mash has anyone tried Shutting off the pump, raising the temp of the HLT say 10-15 degrees higher then there desired next step temp then kicking the pump on to see if they can get to the temp faster ?
Obviously checking the temp on the output of the MT when it hits desired temp kick the pump off again.
Or would this cause issues with stratification ?
I am interested in building a eHERMS setup and would like the ability to do a step mash if desired.

That doesn't help you at all. With the "traditional" herms-setup it's still down to the amount of the water you need to heat (HLT or dedicated herms-kettle) and the heating power that you have available. Those 2 things determinate how fast you can do the step mashes. If you have a very long hoses, big heat loses, then you might get a little better results.

I had a 3 quart herms kettle with 1 cup of water in my "traditional" herms-setup. That was the fastest way that I managed to do step mashes before moving to the counterflow. Here's the HX-coil I had on it:



I made another coil with a double length, but the mash heating power was the same as with the one above. I was using 2kW induction stove. One great advance with the small volume is that there's no stratification problems and the water cools / heats fast, no over- or undershoots either.

I will be using a 4500 watt heating element in both the HLT and the BK.
I would like to be able to use a step mash if I wish.
The HLT is a 7.5 Gal Kettle but I suppose could always calibrate it with less water in it.... but I plan on using the HLT to fly sparge with as well.
If i were to put the prob on the out side of the HEX would it matter how much water was in there when I decided to sparge ?
I would run the HLT throught the pump back through the HEX and into the MT for sparging.

If you can afford another pump and a CF-HX, I would do that. The beauty of the CF-HERMS is that you can use the water on the HLT to sparge straight after you have finished your mash schedule.

If you have the HX-coil in the HLT and reduce the water to get faster heating, you will have to play around with the sparge water. One option would be to use the BK to heat the sparge water and when your mash schedule is done (mash out) just transfer the needed amount of water into the HLT. I hope that made any sense....

I'm now using (or I were, I'm selling my brewing stuff) 80C water on the HLT and that works perfectly for the fly sparge too. There's quite a lot of heat loss when pumping this high heated water, so the 80C water is about 77C when it hits the grains. Here's the plot from the 2nd last mash I did, pretty spot on:


On the last mash, I didn't wet the grains before I milled and the grist was awful. I had pretty much a stuck mash, maybe only 0.5L/min flow from the mast tun (normally ~2.5L/min). I can see from the wort temperature, that it took way too long to heat the whole mash to the desired temperature. But at least the heating algorithm worked with the slow flow too. And I finally fixed the one sensor that was dropping out all the time. Here's the plot:


The plots have a switched colors to make it harder to read

My mash sensor is quite near to the top of the grain bed. I've noticed that it's way better to have a little too cold mash than to over heat the upper parts of the mash and release all the nice tannin flavors to your beer.

Too bad you are quitting because your posts shed more light on what goes on in HERMS than anything I have previously read.

I have been planning an eHERMS using a small electric kettle as the HX and controlling the wort exit temperature. But I like the idea of step mashes (I often brew with adjuncts) and my pump is pretty small. Based on your experiences I might try making a CF HX modeled on a copper Liebig.

I am clearly going to have to rethink my temperature measurement too. I was thinking of using metal thermowells inside stainless tees in the drain holes of my MLT/HLT. I had not considered the thermal mass of the probe housing.

As for placement, I am wondering how to measure the temperature at the top of the mash, allowing for different mash volumes. Perhaps a short metal tube containing the probe dangled down inside a bit of silicone air tube.

Thanks, I'm glad someone is getting something out of my yarns

I'm moving and can't take the gear with me, at least not the whole brewery. I might get back on to it with a bigger set-up once I know where I live next. I'm hoping I can get my hands on **** next, into bio-gas methane that is Maybe to make a bio-gas powered brewery. I would like to drive my next car with bio-gas too.

I use these for measurements: http://www.ebay.com.au/itm/5PCS-Waterproof-Digital-Thermal-Probe-Sensor-DS18B20-/140759967888?pt=LH_DefaultDomain_0&hash=item20c5f2a890 Sorry about the long URL, but it may help in future when the listing expires.

I've the mash sensor about 100mm in the grains. Just tucked in there. I was thinking to use more than one sensor and do some averaging, but I think it's best to not overheat any part of the mash. Just the sensor with a low thermal mass and near the hottest part of the mash. The wort temperature is telling it's story about the temperatures in lower parts of the mash anyway.

My wort sensor is inside the wort hose, inserted from the end of the hose. I've had the best results this way, no lag and no air bubbles trapped in turbulence. And again a low thermal mass.

I have recently moved to another style of RIMs. I heat the HLT with propane; that flows into pump1 which pumps into a 1650W 120V RIMs tube (1.5" SS pipe). The output of the RIMs tube flows into a 50' copper coil in my Igloo MLT which then returns to the HLT. I have sensors in my RIMs tube at the output and in my MLT. The controlling sensor is my MLT sensor which through BrewTroller, cycles pump1 and the RIMs element. I could do this without the RIMs and just pump HLT water through the copper coil but having the RIMs seems to help ramp up step mashes quicker.

The other thing I like about this is that I can use pump2 to recirc the MLT whenever I want or not at all. I try to pump the wort as little as possible and just recirc during mash out.

"One option would be to use the BK to heat the sparge water and when your mash schedule is done (mash out) just transfer the needed amount of water into the HLT. I hope that made any sense...."

The problem with this solution is that I can only run 1 element at a time.... using a 30amp GFCI circuit.....
I appreciate all your info thus far you are cracking into the HERMS system and exposing all the variables. I just have to decide if they are worth living with.
I already have a CF HEX I made but its out of high temp hose and a copper coil stuffed inside it, I wouldnt drink out of the water side so I probably wouldnt use the water for brewing.....

helibrewer said:

.... The other thing I like about this is that I can use pump2 to recirc the MLT whenever I want or not at all. I try to pump the wort as little as possible and just recirc during mash out.....

Click to expand...

That sounds good, how fast heating do you get?

Have you noticed some off flavors, if the recirculation is on all the time or why do you want to limit that? But you're right anyway, why recirculate more than is needed?

DC-pumps would be very handy, I think that I'll use those, if I ever build another setup. Just use PWM and slow everything down when temps are OK. The biggest cause of the need of heating the mash in my setup is the heat loses of the recirculation anyway.

Merzeone said:

The problem with this solution is that I can only run 1 element at a time.... using a 30amp GFCI circuit.....

Click to expand...

You could use a cheap power regulator to cut down the BK-power. I don't know how big patches you do, but you wouldn't need too much of a power to heat the sparge water during the mash. I've one cheap regulator that I use on my brew kettle.... http://www.ebay.com.au/itm/110951353705?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649 A little underrated for you, but if you only use it for regulating the power and bypass it with a switch when doing the boil it might do the trick. Or there may be similar products with a higher power rating.

I've been using my brewing setups for about one brew at the most, so I'm the last person to consult when it comes to the making the decision what type of system you can live with

Blimey, that power regulator costs less than a SSR + heatsink.

alien said:

Blimey, that power regulator costs less than a SSR + heatsink.

Click to expand...

Yes, and the only way to control the boil intensity is to control the amount of power that goes in.

There's a big triac inside, a really basic circuit, looks like a zero crossing.

Vesku,

Are you recirculating the mash the entire time and then periodically pumping 80C hot water through the heat exchanger?

It looks like you are repeatedly heating the wort running through the heat exchanger to over 70C. Do you not notice an effect on the enzymatic activity of the mash as beta-amylase is rapidly denatured at those temperatures?

Yep, I was recirculating the wort all the time and running the pump that heats the HX as necessary (sold almost all my gear, I'm in the process of building a new setup http://tinyurl.com/chgken9).

The mash it self was not heated over the set temperature, just the wort. I had quite a lot of water in the mash so that I had a big buffer of wort on top of the grains to prevent the "over heated" wort hitting the grain bed before it had a change to cool down a bit.

The efficiency was really good and the beer tasted and looked great, so I didn't worry about heating the wort over the enzymatic thresholds. I don't know if there's any science done on the subject i.e. what happens to the wort in this up and down process? I guess that all the commercial mash tanks with an external heating chamber have to "over heat" the wort too or it would take for ages to heat up the mash.

My new setup will use DC-pump for recirculating the wort and I'm going to put a PWM-speed control on it. The idea is that the pump goes fast when the mash temp is well below the set-point and slows down when near it. This should cut down the heat losses that occur when the pump is running full power all the time.

If I understand your distinction of mash and wort correctly, the enzymes are soluble so they are mainly in the wort. The ideal method would be to maintain the wort temperature at set point and wait for the grain bed to equalize, but it may be that the short time at elevated temperature has no significant effect as long as you get repeatable results.

I like your birch-bark stir plate.