Reverse HERMS

[Beerisyummy]

It looks like you're just pumping water, how did you manage to get it up to 110°C?

I was in a small town where Propylene Glycol was unavailable. $0.65 worth of table salt ended up being the easiest solution at the time.

BdE, there seems to be a human head protruding from your mash tun!

 

[Adr_0]

Righto. Make sure you differentiate between flow and velocity - for a fixed flow, larger diameter means lower velocity so this changes the situation. You can't just talk about velocities in this scenario because it's driven by a pump.
If you care, I have the formula out of a heat transfer text book which shows the relationship between diameter and temperatures to determine your heat transfer convection coefficient. Can't do it now due to phone.
Make sure you pour a glass of your best home brew prior to reading though - it's riveting stuff.

I probably have the same textbook...

To translate:
- The governing equation is q (heat transferred per second) = h (heat transfer coeff) x Area x diff T
- 3/8" tube has 27% LESS heat transfer capacity than 1/2" based on Area only - makes sense and most people understand this
- 3/8" tube however has 76% HIGHER heat transfer coefficient due mostly to the increased velocity and turbulence
- 3/8" tube OVERALL (when these factors combine) can transmit 28% more heat power per metre for a given flowrate than 1/2" tube

3/8" tube is also cheaper, but unfortunately fittings are a bit annoying to find - you can braze 1/2" fittings on without a drama though.

As I said in a previous post, this is well understood in the industry (gas processing, refining, chemical processing, LNG) but always has to be weighed up against pressure loss in the pipe. This is particularly relevant to centrif pumps and you need the pump curve from the manufacturer (or do a bench test) and then you can use your hydraulic calcs to see where the system will operate on the pump curve.

Anyway, let's get this back to reverse HERMS....

 

[Adr_0]

And I guess the application to reverse HERMS is not to underestimate how important flow is IN and AROUND the tubes.

So hammer it through the tube - as long as your heat can keep up - buy also make sure you get good flow through the grain bed. This with a decent temp difference will help your ramp time.

When you first said 'reverse' I thought you might have drawn from the top of the bed and pumped in to the bottom. Probably great for mash/lauter efficiency and heat transfer buy probably not the best for grain bits in your pump. You would also need a pump with a fair bit of suction lift.

If anyone has a system like that, I would love to see it...

 

[Parks]

When you first said 'reverse' I thought you might have drawn from the top of the bed and pumped in to the bottom. Probably great for mash/lauter efficiency and heat transfer buy probably not the best for grain bits in your pump. You would also need a pump with a fair bit of suction lift.

If anyone has a system like that, I would love to see it...

This is something like what I am planning. My plan is to have flow reversible so I can prime the system normally then reverse the flow for herms. Then when it gets to mash out temp go back to normal for clarification.

 

[Beerisyummy]

This is something like what I am planning. My plan is to have flow reversible so I can prime the system normally then reverse the flow for herms. Then when it gets to mash out temp go back to normal for clarification.

That's pretty much what I do. The efficiency and clarity is great using this method. No stirring needed.

 

[Adr_0]

This is something like what I am planning. My plan is to have flow reversible so I can prime the system normally then reverse the flow for herms. Then when it gets to mash out temp go back to normal for clarification.

Awesome...

 

[S.E]

Something I've been thinking about for a while and another thread has prompted me to put this up. I'll call it a reverse HERMS. It's reverse as the coil goes into the mash and fresh hot water is recirculated through it. The same reverse HERMS / heat box then can double for both the mash and the HLT heating requirements.

Benifits
Only one set of heating elements is required for both HLT and HERMS
Reverse HERMS / heat box could just be a kettle with inlet and outlets plumbed into it.
No wort contact for the heating element (removed possibility of scorching / burning elements etc)
Only fresh water is pumped through the HERMS coil. Easier to keep clean.
Mash coil doubles as an immersion chiller.
Mash coil helps heat more uniformly.
Instant cutoff of heating, no temperature overshoot due to thermal mass in HERMS unit. In this case water just stops flowing.
No need to holes for heating elements in the main vessels.
Option to push a second coil in the HLT meaning no water from inside the coils touches brew water/wort.

Drawbacks
Second pump is needed to recirculate mash. Pumps are not that expensive.
You would not want the solenoids switching at SSR speeds. But I do not think you would not need to.
You would need a couple of liters of water at all times in the HLT. In my case I keep some water there for clean ups anyway.
Option to remove the solenoid and have a second pump keeping the HLT and mash flow separate. Not sure if this is worth while.

Other thoughs
Solenoid block may allow either flow to happen. When the mash needs heating it flows through there. Otherwise the HLT can get the hot water. If there is enough heat potential in the reverse HERMS both outlets may be able to flow simultaneously.
Possibly leave the pump and HLT open always, and only switch the flow through the mash as needed.


A second option....
Don't have a reverse HERMS box and flow water from the HLT through the coil in the mash tun.

The downside to this is the thermal mass of the HLT may make ramping slow as the HLT cannot exceed the set temperature for it, whereas the separate HERMS can jump up above the desired temperature range to push ramp rates faster. ie. When a ramp to mashout is required, the HLT is set to 77-78c. So the water going to the mashtun coil will not exceed this temperature. With the first idea, the heat box may get up to 90c making the change in temperature faster. Also the heating is heating both the HLT and mash at one time making it slow.

Your first drawing is the same as a domestic hot water and central heating system as used in colder climates only the reverse HERMS in your drawing would just be a boiler (no coil inside) and the flow pumped from the top outlet and return to the bottom. Your mash tun would be the hot water cylinder and the HLT would be a radiator (or radiators in each room).

I have built lots of central heating and hot water systems for myself, friends and family back in the days when everyone installed their own solid fuel or gas boilers and re wired their own houses.

I had thought but never got around to doing something similar with my brewery so will be interested to hear how you get on with this. My plan had been to use my brew kettle to heat all the mash and sparge water first then pump some to the mash tun and re circulate the sparge water through a copper pipe snaking back and forward flat on the bottom of the MT just above the manifold or FB to maintain mash temperature while using a second pump to re circulate the mash. Then when the mash was finished pump the sparge water from the kettle to the HLT.

Cheers Sean

 

[TheWiggman]

Adro, it's valid indeed for HERMS or reverse as selection of pipe is one of those thumbsuck things where you're safer going more than less. The result could be twice as much real estate taken up by the HERMS tube.
The maths was right in your example but there is an issue with the application of the Dittus-Boelter equation for the Nusselt number. Assuming a different equation was used, this would change the result completely.

I might rasie a new thread about this for the eggheads and maybe knock up a spreadsheet to do the calcs for critical review.

What's super-critical though is like you said is flow over the reverse-HERMS coil. This will have a massive impact on the efficiency of the HERMS. If put straight on the grain bed without flow (which is not how beerisyummy's system operates, fortunately for him) there will be slower ramp times, hot pockets and the measuring point for the temp control will have a huge bearing on the system design.
The only other way I think this could be addressed is through a recirc system. Or maybe a running mash paddle?

 

[Adr_0]

Adro, it's valid indeed for HERMS or reverse as selection of pipe is one of those thumbsuck things where you're safer going more than less. The result could be twice as much real estate taken up by the HERMS tube.
I can't tell you how many times in my career as a process and project engineer we have replaced pumps, control valves, flowmeters and water pipelines because somebody has thought 'bigger is better'. The key is that you have you evaluate the system in place. If you want to apply safety factors, understand the impact they may have on the system.

The maths was right in your example but there is an issue with the application of the Dittus-Boelter equation for the Nusselt number. Assuming a different equation was used, this would change the result completely. You are welcome to try as many correlations as you like - make sure you post your results for everyone to see. Don't forget the pump curves.
And if you're talking laminar flow, remember this is like trying to get a faster boil by turning the heat down on your burner.