PID temperature drop during shots - Page 2

September 2nd, 2016, 10:15 pm

AssafL wrote:Not really. Electronics cannot make up for physical realities of thermodynamics. You can increase heater wattage (like a flash boiler) and you will probably shorten the duration of the drop - probably followed by an overshoot (over your target temp). Physics always plays the trump card.

Machines that keep a constant temperature all have two systems to cope with the thermal mass of cold water:
1. Large boilers (e.g. a GS/3 has a 1.9 liter coffee boiler).
2. Heat exchangers (e.g. the Mini Linea has a heat exchanger to warm up the water before it enters the small boiler).

The latter sacrifices the steam boiler steam availability for coffee temperature stability (or have humongous boilers with powerful heaters).

In theory - one can route a long copper tube near the steam boiler - but I am not sure what will happen if you actually coil it around the boiler. Water inside the pipe will try to boil. Systems that have heat exchangers keep the pressure in the coffee boiler at above the steam pressure (using check valves) - and the HX tube submerged. So inside the tube the water may be superheated but still liquid. I don't know whether the Profitec won't allow water to boil in the tube.

BTW - heating the water too much is also a physical trump card - as an example, the GS/3 has a hot and cold water mixer to reduce the temperature of the water to around 90-92C. The reality of this heat exchanger and mixer and the system of check valves around it is probably 50-60% of the problems the GS/3 has with leaks and other disasters. It is an unfortunate price GS/3 owners pay for the physical realities of thermodynamics.

Explain to me how a small hx line in the Linea Mini has any impact on steam availability? Its the same boiler as the gs3 and its set to 2bar. The mini isn't an hx machine it just uses a hx preheat like to a brew boiler.

#12: Post by **AssafL** » September 3rd, 2016, 3:09 am

Both the Linea and GS3 have very large steam boilers. Very large for home use....

It is affected but by a tiny amount. Not noticeable in fact. But thermodynamics says there is some impact.

#13: Post by **jonr** » September 3rd, 2016, 5:50 pm

At one point, I was ready to use pressurized air instead of water to force the water out of a small brew boiler and through the group. I suspect it would have worked quite well (very flat temp profile), but then I realized that a flat profile isn't optimal (or certainly not optimal for all coffees/roasts).

#14: Post by **JohnB.** » September 3rd, 2016, 6:55 pm

I believe that the Slayer 1 group uses copper tubing wrapped around the steam boiler as their preheat system. No idea how well it works. The Speedster uses a stainless HX inside the 3.5 litre boiler with an 1800W heating element. No check valves between the HX & brew boiler. There is one inside the expansion valve at the inlet to prevent hot water from flowing back into the inlet pipe.

The pipe between the HX & brew boiler winds around the right side long enough to cool the water close to brew boiler temp before entering the boiler. There is little change in the brew boiler temp showing on the PID during a shot.