1 - LM has a saturated group. Depending on your specific Linea (different generations have had slightly different designs in terms of grouphead) the offset is slightly different but the saturated design means the offset is always reasonably small. You will, of course, need to ID what the offset is. In general, you'll find that (once in steady use post idle) an est 2s flush tends to be sufficient to manage.

2 - intake water preheat like you describe has been part of the Kees machines for a while - and Schomer modified his machines in the same manner. I believe both used copper for this purpose. The challenge, of course, is that when not in active use - water will still be within the copper tubing and will as a result now be hotter than brew temp. I've talked to both Terry Z and Kees in the past about calculating the optimal volume and thus the amount of "copper coil" you should use - but honestly don't remember much about how it's done. The alternative, of course, is to use a heat exchanger set-up in the steam boiler for preheat. Now... the reality is that intake water preheating is unlikely to be really important for home use. It's intended to address issues with very busy cafe use where frequent autofilling results in boiler and brew temp dropping outside of range. While understanding offset between boiler temp and brew temp is, IMHO, vital for home (as well as cafe) use -- I think intake preheating is (at best) a tiny optimization for home use.

malachi wrote:The alternative, of course, is to use a heat exchanger set-up in the steam boiler for preheat.

That's how the GS/3 does it -- the intake water runs through a tube in the steam boiler before it gets to the brew boiler.

mitch236 wrote:I can see where a busy cafe would have much more severe issues but since installing the PID, I notice a significant drop in temps just after one 1.5oz shot. Maybe about 5-7f. It seems temp consistency is of upmost importance, it would seem a 5f variance is alot. Perhaps I'm wrong. But I can't imagine wrapping the steam boiler would account for much more than a 3-4 second purge before pulling a shot but maybe I'm wrong there too. So much to learn!!!

Don't know whether you have an older EE or AV Linea but both have the issue of low temp from idle, AV much more severe than EE. It's not actually the group that's under temp but the external plumbing the water flows through leaving then re-entering the group during a shot. (Hence the newer Piero groups which eliminate this issue) The AV will yield more under temp from idle shot because of the volumetric flowmeter mass which must be brought up to temp. I can only imagine the brew boiler temperature dive on a 1 group flushing must cause. On a 3 group Linea with it's large 5L brew boiler doesn't phase it (hardly) at all. But on a 4 group with it's two 3.4L brew boilers (one for each pair of two groups) it's a real issue. (have 1 3g, 2 4g's) So yeah can easily see a 1g's 1.8L brew boiler temp would majorly dive. In production pulling shots on the 4g's you have to alternate group boilers or wait for temp to come back up after pulling the shot and post shot group flush. Which is a PIA when often want the two brew boilers at different temps! I too have thought about pre-heating the incoming water via tube wrapping the steam boiler on my 4g's but haven't found/made the time yet. Modding with Piero groups would be more elegant, but at about $600 per group (including labor to further mod since mine are older style bolt on groups and Piero mod designed for bolt ons) for my 2 4AVs that's close to $5k I just don't have.

From idle flushing with pin holed back flush blank to minimize brew boiler temp dive does work better than full flow flushing.

mitch236 wrote:So I came up with a solution. I am going to find a flexible heat tolerant tubing and wrap my steam boiler and put it in line with my water feed so that the water entering my machine is preheated. I have no idea how much heat I can transfer but that steam boiler is mighty hot!!

I'm sure this has been thought of before so I'm curious about how it turned out for others who have tried.

That is also what the expobar Brewtus (aka expobar minore) uses circa 2004

http://www.home-barista.com/expobar-brewtus-review.html

"The Expobar Brewtus takes the current prosumer dual boiler machine design one step further by introducing an important element: It pre-heats the water via the steam boiler's heat exchanger before it enters the brew boiler, as shown in the diagram to the right. This feature is essential to Brewtus' jump in temperature stability and control.

The pre-heated water has another side benefit: It is practically impossible to outrun the machine. A typical prosumer HX will give up the ghost after 8-9 shots in a row if done in rapid succession. Most machines need time to recover. Incoming cold water from the water tank reduces the water temperature in the boiler, which affects the boiler's ability to quickly recover. Pre-heating the water before it enters the brew boiler tackles that problem. The Brewtus is capable of delivering 30 shots in 30 minutes without blinking, thanks to the routing of the incoming water from the pump to a heat exchanger passing through the steam boiler. The near brew temperature water then continues to the brew boiler.

Brewtus' innovation isn't really new since a similar feature is available in top commercial dual boiler machines like the Synesso Cyncra and the La Marzocco GB5, and has been a common commercial modification for more than a decade. Expobar's innovation was the application of an existing proven technology and implementing it cleverly to fit a specific need."



Cheers

Friends!
In drawing water circulates counter-clockwise (during brew). Why not on the contrary?
Why water arrives in group from a thermosiphon, instead of on the other hand?

The drawing is idle state.
When brewing, water flows from the top and bottom of the boiler. That's why there is an offset from the boiler set point to brew temperature. The water in the bottom of the boiler is much cooler than the set point, which is normally read at near the brew boiler top.