Another HERMS question

[Bionicmunky]

Hi all,

I've got all the bits on their way, but one thing is confusing me (Not difficult ).

With regards to mash, do I dough in as per usual leave a while then kick in the PID and pump. I'm reading that the PID will take some time to autotune, and it does this by increasing and decreasing the temp for up to 30mins of so. Do I start my mash timer once the PID has tuned? e.g. 90mins at 66c

Thanks in advance

J

[Graham]

You should autotune your PID before you use your aircraft-carrier in anger, using just water.

Depending upon how the PID autotunes, the temperature could ramp up and down like a yo-yo and overshoot considerably. It is not what you want for a real mash. Once tuned, the PID should save its constants in readiness for when you want to do the real thing.

[Bionicmunky]

You should autotune your PID before you use your aircraft-carrier in anger, using just water.

Depending upon how the PID autotunes, the temperature could ramp up and down like a yo-yo and overshoot considerably. It is not what you want for a real mash. Once tuned, the PID should save its constants in readiness for when you want to do the real thing.

You can come round and play once it's done if you wish Graham. Reminds me I need to get SWMBO's form filled in so we can go for that pint.

J

[Graham]

You can come round and play once it's done if you wish Graham. Reminds me I need to get SWMBO's form filled in so we can go for that pint.

I was wondering if you'd forgotten about that.

I should point out that you do not need to autotune every time you mash or use the PID, it is something that is just done once during a dummy run after installation (unless you change anything important).

[Aleman]

Another alternative would be to auto tune with a spent mash, that way you can be sure that it is as close to your actual mash environment as possible. I discovered significant differences between tuning it with water, and using it for real . . . . . possibly something I was doing, but auto tuning with a spent mash has sorted it for me.

[Bionicmunky]

Another alternative would be to auto tune with a spent mash, that way you can be sure that it is as close to your actual mash environment as possible. I discovered significant differences between tuning it with water, and using it for real . . . . . possibly something I was doing, but auto tuning with a spent mash has sorted it for me.

Cracking idea

[Oggy' Bar]

Another alternative would be to auto tune with a spent mash, that way you can be sure that it is as close to your actual mash environment as possible. I discovered significant differences between tuning it with water, and using it for real . . . . . possibly something I was doing, but auto tuning with a spent mash has sorted it for me.

I followed Aleman's advice and it worked for me....after I threw away my K-type thermocouple and installed a PT100 at the H/e outlet. My HERMS works a treat and always controls + or - 0.5C

Have fun

[Bionicmunky]

Thanks all,

Now do I make a heat exchanger out of an old 5 litre pan or do I use my HLT? I'm thinking a wide diameter 10mm coil in the lower part of the HLT. I'll then run the cooling water back to the HLT at the end of the brewday to use for cleaning. (previously didn't have a dedicate HLT).

[Oggy' Bar]

Thanks all,

Now do I make a heat exchanger out of an old 5 litre pan or do I use my HLT? I'm thinking a wide diameter 10mm coil in the lower part of the HLT. I'll then run the cooling water back to the HLT at the end of the brewday to use for cleaning. (previously didn't have a dedicate HLT).

Bear in mind that the H/E may need to respond quickly and this is much easier to achieve with a smaller volume H/E as it is quicker and cheaper to heat (or cool) 6L rather than 50L Also you may wish to heat up your HLT to 70+C for sparging while you are still mashing at 66C and this would not be possible if you are using your HLT as your H/E

I went for a seperate 6L insulated Nordic H/E with a copper coil inside and I find it very flexible.

[Aleman]

I happened on a Stainless Steel storage container in Woollies a couple of weeks back that is nearly 5 Litres, which is going to make an excellent HE . . . . should have been 12 quid got it for 5!





of course that is of no help to anyone now




However I would go for a separate HE for the same reasons outlined by OB.

[Andy]

My experience of using my PID is somewhat different to Grahams in that I autotune mine at the start of every mash recirc. Reason being is that variables have changed from the last time it was autotuned. For example, the valve throttling back the recirc pump output is in a different position so the wort flow through the HE is different. Each time you make such an adjustment then I autotune the PID. Only takes a few mins and it errr, does it automatically as it says on the tin And yes the wort temp does jump around a bit bit only +/- 2 degC ish and then only for a short period (less than a minute at each extremity typically). My PID takes nowhere near 30 mins to autotune, perhaps 2-3 mins.

[Graham]

It is not exactly my experience cos, urm, I haven't got one. It is just my general professional experience of PID.

If it can auto-tune continuously, that is auto-tune using its previous parameters as the starting point, rather than starting from scratch, so that it is only making minor adjustments, it would not produce such wide temperature swings while doing it and it would be much faster.

Auto-tuning usually produces a critically-damped system (unless you can enter a different damping factor), which means that a certain amount of overshoot and undershoot is programmed in, because that has the quickest response to a step-change in temperature. However, critical damping is not ideal in this situation because although the system can respond quickly to a drop in wort temperature, by turning the heater on, it cannot do anything active about a rise in wort temperature except sit and wait for it to cool down. Thus, ideally, it needs an over-damped system, so that it never deliberately overshoots. This might mean manually setting the PID parameters - not an easy matter. Of course if the flow-rate change, with a HERMS, it is stuffed because of the thermal mass of the water in the heat exchanger, but I cannot why it would struggle with a RIMS set up because it doesn't need to cope with that. There is almost certainly a set of PID parameters that would enable it to cope better with flow rate changes in a RIMS.

In fact, a HERMS is a complicated process control problem because of the thermal lags in the mash tun and heat exchanger and time delays in the pipework.

But in the end a degree or two here and there doesn't really matter.

[Andy]

Phil (seveneer) has a HERMS system using a small heat exchanger (1-2 litres I think) so his (significant) thermal lag is in the mash tun only

[Oggy' Bar]

Graham, Andy,

You are both correct about the thermal lag, but it is nowhere near as significant as you suggest.

My HE is 6L heated by a 2.2kW element. I don't retune my PID and I can change my pump flowrate at any time during the mash. The PID simply switches the element on less frequently if I reduce the flow, and switches it on for longer if I increase the flow. Either way output from the HE settles to its set value within less than a minute or so. (The thermocouple is in the HE outlet)

As Andy points out though...although HE outlet temp may be set to and vary very little from 66C, even if pump flowrates are changed...mash temp may take a few minutes to adjust to a change in pump flowrate. In practice though I tend to use a constant flowrate (very low) unless I am attempting to recover a badly calculated strike temperature where a higher flowrate achieves the mash temp more quickly.

As to the question which somebody out there must be thinking.

Can't a stable mash temperature within +-0.5C be achieved easily without the complication of a HERMS or RIMS.?

.....The answer is YES

[Oggy' Bar]

Oh and if you did want to reduce the mash temp by a large margin quickly....you could always fill the HE with ice cubes and water.