Chris' Coffee was kind enough to lend a new Alex Duetto, and over the past week I finished a short series of temperature tests. My test machine is a 115V version as sold in the US. It has a Gicar PID with 1F temperature resolution.

I instrumented the machine with a couple of additional sensors: 1) a K thermocouple fastened to the top of the brew boiler (see photo below); and 2) a K thermocouple inserted into the grouphead using one of Eric's E-61 adapters.

The stock machine uses a NTC thermistor, inserted into a thermowell in the brew boiler, for PID control of brew boiler temperatures. The steam boiler is controlled using a traditional pressurestat.

Fresh water is fed into the brew boiler through a heat exchanger that passes through the steam boiler. The fresh water supply to the brew boiler enters through the top. When the steam boiler is on, the supply water to the brew boiler is preheated by the HX. But the steam boiler can be switched on, or off, independently of the main machine switch, allowing operation either with, or without, preheat of the brew boiler supply water.

The objectives of this study were:

• Determine optimum (or nearly optimum) tuning parameters for the Gicar PID
• Examine intrashot temperature behavior
• Examine recovery and intershot stability with a series of closely spaced shots
• Compare behavior with steam boiler on (preheat) vs steam boiler off (no preheat)

Data were collected on three calibrated thermometers:

• Omega HH506RA connected via RS-232 to laptop (for realtime plotting during PID tuning)
• A pair of Fluke 54 II thermometers (data uploaded using Flukeview Forms)

The brew boiler thermocouple sensor consists of a 24 AWG type K bead probe soldered on to a thin brass plate. The plate was punched to allow the M4 stud from the safety thermostat to pass through. The safety thermostat was removed, thermal paste spread thinly on the mating surfaces, the new plate was placed against the boiler surface, and the safety thermostat was threaded back into the boiler, clamping the sensor tightly to the boiler. (I have had poor success using small bare bead probes in similar situations on other projects, and this plate assembly worked much better).

Test Protocol

I allowed the machine to warm up for several hours, with PF locked in, before logging any data. Each series of tests consisted of the following steps:

Time     Activity
0:00     remove PF, flush 3 oz water through grouphead
0:45     lock PF in place, begin data logging
1:00     start Shot 1
1:25     stop shot, remove PF
2:45     lock PF in place
3:00     start Shot 2
3:25     stop shot, remove PF
4:45     lock PF in place
5:00     start Shot 3
5:25     stop shot, remove PF
6:45     lock PF in place
7:00     start Shot 4
7:25     stop shot, remove PF


Brew water temperature estimates were recorded using a Scace thermofilter with type T thermocouple and a Fluke 54 II thermometer. Grouphead temperatures and boiler temperatures were recorded using type K thermocouples (previously described) and a second Fluke 54 II. Data were recorded at 1 second intervals.

For each series of shots, three plots were created:

• combined plot of boiler temperature and grouphead temperature vs time
• continuous plot of temperatures recorded on the Scace device vs time
• overlaid plots of 4 individual 25-second duration shots

Next: temperatures logged with steam boiler OFF (no preheat)

Temperature Tests with Steam Boiler OFF (no preheat)

The Gicar PID was set to 220F. The steady average temperature reported by the thermocouple sensor added to the top of the boiler was approximately 217.6F. This difference may be due to any number of factors. But since this offset (~2.4F) remained relatively constant throughout testing with the steam boiler off, the readings from the thermocouple give a good indication of when the boiler temperature has stabilized.

In fact, the PID display generally showed a return to steady temperatures more than 30 seconds prior to the sensor on the top of the boiler stabilizing.



Plot showing boiler temperature recovery between shots (above)



Plot showing continuous record of Scace device temperatures during test session (above)



Plot of instrashot profiles for 4 shots closely spaced (above) [Note: typo noted in legend for Shot 1. Correct average shot temp is 200.24]

The instrashot profiles had a very slight hump at the start, and then remained almost dead flat. The average shot temperatures (calculated by averaging 16 readings, from 10 seconds to 25 seconds) were as follows:

• Shot 1 = 200.2F [EDIT: typo corrected 9/28/08]
• Shot 2 = 200.1F
• Shot 3 = 200.0F
• Shot 4 = 199.7F

Next: temperature measurements with steam boiler ON (with preheat)

Temperature Tests with Steam Boiler ON (with preheat)

Following the conclusion of the "no-preheat" tests, I switched on the steam boiler and waited over an hour to let everything stabilize. An identical series of shots was pulled with the steam boiler ON.

Comparing the plot below to the corresponding plot for the no-preheat sequence immediately shows the effects of preheat provided by the steam boiler. The drop in brew boiler temperature during a shot is greatly reduced, and recovery to stable brew boiler temperature is considerably faster.



Plot showing boiler temperature recovery between shots (above)



Plot showing continuous record of Scace device temperatures during test session (above)



Plot of instrashot profiles for 4 shots closely spaced (above)

Again, the instrashot profiles had a very slight hump at the start, and then remained almost dead flat. The average shot temperatures (calculated by averaging 16 readings, from 10 seconds to 25 seconds) were as follows:

* Shot 1 = 201.7F
* Shot 2 = 202.0F
* Shot 3 = 202.0F
* Shot 4 = 202.1F

For the same PID SV = 220F, shots made with preheat averaged approx. 2F hotter than shots made without preheat. A portion of this rise can be explained by a corresponding slight rise in the boiler temperature recorded by the brew boiler thermocouple and by the rise recorded in group temperature (from ~197F to ~199F). Possibly the remainder of the 2F rise is explained by the warmer supply water entering the brew boiler during the shot.

Comments and questions about the information posted here are welcome. Thanks for reading.

Jim

It is interesting* to see there's quite no difference in temp profiles from steam boiler on to steam boiler off.


EDIT
* changed into 'interesting' from 'really nice'... I made this comment without reading the discussion in Duetto thread sorry everyone

jggall01 wrote:Test Protocol

I allowed the machine to warm up for several hours, with PF locked in, before logging any data. Each series of tests consisted of the following steps:

Time     Activity
0:00     remove PF, flush 3 oz water through grouphead
0:45     lock PF in place, begin data logging
1:00     start Shot 1
1:25     stop shot, remove PF
2:45     lock PF in place
3:00     start Shot 2
3:25     stop shot, remove PF
4:45     lock PF in place
5:00     start Shot 3
5:25     stop shot, remove PF
6:45     lock PF in place
7:00     start Shot 4
7:25     stop shot, remove PF


On another thread we have been speculating on the effects of ambient temperature changes on brew temperature. I also think most people turn their machines off at night and do not have the luxury of a several-hours warmup in the morning. Would it be possible to run tests that reflect some common usage patterns such as:

1. A first-shot-in the-morning in a cold kitchen after a 15 min. warmup.
2. Same after a 30 minute warmup (for those with a timer).
3. A warm mid-day kitchen after a 30-min warmup.
4. A cool evening kitchen after a 30-min warmup.

I'm asking this, because I think temperature offset stability is also important, and that the ability to pump out several identical shots in a row for guests may be less critical than coping with variations in room temperature and less-than-ideal warmup times. In other words, will my mid-afternoon espresso taste the same as my wake-up espresso? (This may be less of an issue for us in Southern California than for people who run the house thermostat low in frostier climes.)

Marshall -

I don't have enough data to answer precisely. Instead, I can provide information regarding the likely temperature of the grouphead after varying amounts of warmup time (see plot below).

After 15 minutes warmup, the grouphead temperature is still 16F low. Very roughly, you might expect this to result in a shot that is ~8F low. So I would say the machine is not ready to go after 15 minutes.

After 30 minutes warmup, the grouphead is a little less than 3F low. Again very roughly, this might produce a shot 2F low, or maybe even better. So I would say that shots pulled after 30 min warmup would still be very drinkable, but not optimum.

On the Duetto, it took 35 minutes for the grouphead to be 99% warmed up, and 46 minutes to be 99.5% warmed up. I guess we could then consider 35 minutes to be a "good" warmup, and 46 minutes to be a "best" warmup.

I know this is not a full answer to your question. If time allows, I will measure some shot temperatures after 15 minutes and after 30 minutes and see how close my rough guesses were.

Jim



Duetto warmup with steam boiler OFF, room ambient temp ~77F

Why 15s between lock in and pull?

I'd like to see a series with 4, 8 and 16 minute intervals, a 1oz. cleaning flush after the 'shot' and the PF left in the group until 30s before the shot.

cafeIKE wrote:Why 15s between lock in and pull?

Primarily for the benefit of the tester (so he wouldn't mess up the intervals). I think you are implying that 15s is a long time. In hindsight, I probably could have shortened this from 15s to 5s or less and still stayed on track.

But examination of the data suggests this might not have had an important effect on the results:

• Sequence no.; Scace temp at start of shot; average shot temp
• 1; 157.2; 200.2
• 2; 163.8; 200.1
• 3; 168.9; 200.0
• 4; 166.8; 199.7

I suggest that there would be better correlation between the start temp and the average temp if the lock-in timing were important. Instead, the difference in average shot temp is only 0.2F at the two extremes of the beginning Scace temperature (157.2F, 168.9F).

cafeIKE wrote:I'd like to see a series with 4, 8 and 16 minute intervals, a 1oz. cleaning flush after the 'shot' and the PF left in the group until 30s before the shot.

Good point. Those intervals would tell us more about the thermosyphon loop and its ability to maintain the grouphead temperature. My testing was slanted towards getting the PID tuned. If time allows, I'll pick one of those intervals (probably 8 minutes) and test as you suggested.

Jim

Thanks Jim! This information is fascinating!

Actually, without wanting to push it, I'd be interested in two or three additional things as well...

1. Do a similar test to the HB review of the Alexia with PID, that is, 2 minutes recovery between shots, rather than 2 minutes from start of shot to start of shot. I would hope that the preheat off recovery would be improved significantly by the additional 25s recovery time and preheat on would be even more stable shot to shot.

2. A walk-up shot with no flush (both preheat off and on). That is, do we need to flush at all?

3. A vastly reduced initial flush: 3 oz seems way too much for a dual boiler, particularly with preheat off, and then to only give the boiler and thermosyphon less than 1 minute to recover before the first shot seems harsh. Where did 3oz come from?

4. A 1oz (3 second) flush sometime between shots (time to be determined!), to simulate "cleaning the group of grounds and coffee residue."

Marshall wrote:On another thread we have been speculating on the effects of ambient temperature changes on brew temperature.

Marshall, I agree entirely and would like to see some data on this. Given that you owned a PID'd Zaffiro for many months, have you any data to share on this? Did you find the need to keep tinkering with brew temps throughout a variable day? What was the warmup time like for you? I cannot imagine these issues would be vastly different.

Thinking about offset variability due to ambient changes: With a 20F offset from boiler to shot temp, in 70F ambient, at boiler temp of 220F, we have 20F offset for 150F temp delta from ambient to boiler. Would we therefore not expect no more than 1F delta in shot temp for each 7.5F delta in ambient temp? It would be interesting to test this. However, if this is the case, small tweaks can be predicted (if you know the ambient temp). I've yet to see whether such predictions come true, since the ambient in our house has been pretty consistent (18 to 20C) for the last few weeks. Perhaps in the coming winter months I will find out more?

Or, of course, use the PID control as a way to (resonably accurately) adjust by taste!

All the best,

Martin

Mole wrote:Marshall, I agree entirely and would like to see some data on this. Given that you owned a PID'd Zaffiro for many months, have you any data to share on this? Did you find the need to keep tinkering with brew temps throughout a variable day? What was the warmup time like for you? I cannot imagine these issues would be vastly different.

I'm sure they wouldn't be very different, but I don't have any measurement equipment. I never thought a Thermofilter and Fluke were a good investment to check my machine once a year, and I had no other use for either. A friend was kind enough to ship me a Thermofilter and Fluke last winter on loan to check my offset, which turned out to be about 22F one early evening. It didn't occur to me at the time to try it at different times of the day.

It does seem to me that, for home users, the effects, if any, of ambient temperature changes are much more important than recovery times, because we have to deal with them every day. Parties are just once in a while.

Mole wrote:3. A vastly reduced initial flush: 3 oz seems way too much for a dual boiler, particularly with preheat off, and then to only give the boiler and thermosyphon less than 1 minute to recover before the first shot seems harsh. Where did 3oz come from?
Martin

I'm curious why 1 minute recovery post flush seems harsh. To me seems quite lenient. I'd expect to be able to pull back to back shots in well under a minute following post shot flush and next shot. I'd expect with steam boiler on for brew boiler HX pre-heat to be able to pull continuous back to back shots as fast as barista PF build skills allow. My lowly HX Bricoletta only needs ~35sec recovery post shot flush to flush down to temp for next shot's flush and go. Though would agree 3oz stabilizing flush for DB might be more than necessary, temp tests will bear that out.

jggall01 wrote:Marshall -

I don't have enough data to answer precisely. Instead, I can provide information regarding the likely temperature of the grouphead after varying amounts of warmup time (see plot below).

After 15 minutes warmup, the grouphead temperature is still 16F low. Very roughly, you might expect this to result in a shot that is ~8F low. So I would say the machine is not ready to go after 15 minutes.

After 30 minutes warmup, the grouphead is a little less than 3F low. Again very roughly, this might produce a shot 2F low, or maybe even better. So I would say that shots pulled after 30 min warmup would still be very drinkable, but not optimum.

On the Duetto, it took 35 minutes for the grouphead to be 99% warmed up, and 46 minutes to be 99.5% warmed up. I guess we could then consider 35 minutes to be a "good" warmup, and 46 minutes to be a "best" warmup.

I know this is not a full answer to your question. If time allows, I will measure some shot temperatures after 15 minutes and after 30 minutes and see how close my rough guesses were.

Jim

<image>

Duetto warmup with steam boiler OFF, room ambient temp ~77F

For typical home use how fast the group comes up to temp idling is good to know. But what might also be useful for a home user that chooses not to use a timer (or gets up way earilier than anticipated before their alarm goes off) is how fast the group can be brought up to temp once the brew boiler is up to temp via flush pause flush pause flush routine. I've needed to use that technique occasionally with my HX Bric'. (Eric's thermometer installed.)

I wish I could be answering Alex Duetto questions myself and almost pulled the trigger. But instead decided to wait and bought another Linea (4grp being field stripped and rebuilt with dual PIDs) anticipating opening 2nd cafe early Spring...

Marshall wrote:I'm sure they wouldn't be very different, but I don't have any measurement equipment. I never thought a Thermofilter and Fluke were a good investment to check my machine once a year, and I had no other use for either. A friend was kind enough to ship me a Thermofilter and Fluke last winter on loan to check my offset, which turned out to be about 22F one early evening. It didn't occur to me at the time to try it at different times of the day.

It does seem to me that, for home users, the effects, if any, of ambient temperature changes are much more important than recovery times, because we have to deal with them every day. Parties are just once in a while.

I also lack any decent measuring equipment, which is why I'm trying to jump on the chance to ask someone who has! (As you say, a Scace and Fluke are just too much to calibrate a single machine, then put in the cupboard for only very rare use.)

I agree that first shot stability would be paramount for home users, but I regularly make 3 to 4 shots in a row for me and my parents, so I am also interested in the best shot to shot interval to use. I work slowly and enjoy the process, but about 1 shot every 2 minutes is my (unstressed) routine. I could work much faster, but I wouldn't want to be much slower!

I personally think that indoor temps, particularly for us where the kitchen is in the middle of the house, do not vary drastically throughout a day, except perhaps in the heart of winter. I have a digital thermometer unit that tells me the inside and outside temp (useful for roasting) and even when I think it is cold, or hot, the difference is not as drastic as I would have thought.

I also think that there are limitations with any machine at this price point: if I could find out what effect ambient temp had on shot temps, I would happily add small adjustments into my routine, using my notes as a starting point to be adjusted by taste.

All the best,

Martin

miKe mcKoffee wrote:I'm curious why 1 minute recovery post flush seems harsh. To me seems quite lenient. I'd expect to be able to pull back to back shots in well under a minute following post shot flush and next shot. I'd expect with steam boiler on for brew boiler HX pre-heat to be able to pull continuous back to back shots as fast as barista PF build skills allow. My lowly HX Bricoletta only needs ~35sec recovery post shot flush to flush down to temp for next shot's flush and go. Though would agree 3oz stabilizing flush for DB might be more than necessary, temp tests will bear that out.

Three reasons really. Firstly, I am going on the routine used to test the Alexia with PID here on HB, that is:

* Warmed machine with portafilter and Scace thermofilter installed for 60 minutes minimum,
* Portafilter removed and pulled a warming flush of ~3 ounces,
* 2 minute recovery and then pulled a "garbage" simulated shot (data captured this as Shot A)
* Pulled 5 shots with 2 minute recovery between shots, start dump of thermofilter for each shot (Shots B-F),

Secondly, as you say, it is NOT an HX machine and therefore does not run hot. It does not need to be cooled down, and my experience would suggest it also does not need to be warmed up: if it does, a 1oz flush seems perfectly adequate. It is much harder for a thermosyphon to recover lost temp when it is running at optimum brew temp (i.e. small offset). I would have thought that an HX machine would recover from a small over-flush quicker since the thermosyphon will circulate much hotter water through the group.

Thirdly, and you mention this, with preheat on I think you could work much faster (although may notice a slight rise in progressive shot temps, you could perhaps flush to reduce this). The boiler seems to need no time to recover (it does not drop any temp during a shot, except for perhaps the 1 degree temp drop associated with normal cycling operation). It then seems to be perfectly stable, as if the group has no need to recover (in fact, I guess it could need to cool a little, I have no idea).

With preheat off, the temp in the boiler can fall a few degrees during a shot (just like the Alexia) and needs more time to recover. We see in the graphs above, and with the Alexia review, that progressive shots cool a little without preheat. My thinking is that the inrush of cold water cools the boiler. Not a problem, the PID can recover in well under a minute, but it is my belief that in this time the thermosyphon is not maintaining heat in the group as effectively, or possibly even removing heat from the group. I see this backed up by the fact that the boiler temp recovers, then seems to drop a degree and sit there for a while until the group stabilises (I use very conservative PID settings to prevent overshoots, which work well for my routine). When it ticks back up to set temp, I feel the group is now ready. With more aggressive PID settings I may not see this behaviour visually, but I believe it is happening.

This is also why I feel 3oz is just too much. It is much faster flowing (perhaps 10 seconds) than a proper double shot (25-30 seconds) and so would cold shock the boiler more than a normal double shot. The first shot on the Alexia review is taken to be a "garbage shot" since it is cooler, and the Alexia was given 2 minutes to recover after the initial 3oz flush.

With preheat off, about 105 seconds between (single) shots (end of last to start of next), which includes a 1oz cleaning flush at about the 45 second point, seems to work just fine, with my conservative PID settings. With preheat on, far less time seems to be needed, even with the 1oz cleaning flush.

Of course, this is all just my humble opinion.

All the best,

Martin

Mole wrote:I personally think that indoor temps, particularly for us where the kitchen is in the middle of the house, do not vary drastically throughout a day, except perhaps in the heart of winter.

And mine is in a bar in the center of my home. But I was also thinking of the majority (I assume) of owners who keep their espresso machines in the kitchen, which typically features lots of glass and is prone to be chilly in the morning and may get hot when using the oven. The OP's tests were done at 77F, and I would not be surprised to find a range of 60 to 85F in many kitchens.

[Edit] I hope we are not focusing on minutia, while missing the elephant in the room.

Marshall wrote:On another thread we have been speculating on the effects of ambient temperature changes on brew temperature. I also think most people turn their machines off at night and do not have the luxury of a several-hours warmup in the morning. Would it be possible to run tests that reflect some common usage patterns such as:

1. A first-shot-in the-morning in a cold kitchen after a 15 min. warmup.
2. Same after a 30 minute warmup (for those with a timer).
3. A warm mid-day kitchen after a 30-min warmup.
4. A cool evening kitchen after a 30-min warmup.

I'm asking this, because I think temperature offset stability is also important, and that the ability to pump out several identical shots in a row for guests may be less critical than coping with variations in room temperature and less-than-ideal warmup times. In other words, will my mid-afternoon espresso taste the same as my wake-up espresso? (This may be less of an issue for us in Southern California than for people who run the house thermostat low in frostier climes.)

Some additional test data to at least begin to address these issues:

Room ambient = 76.5F
Brew boiler SV = 222F
Steam boiler = OFF
Expected brew temp (when fully warmed up) = 202F

15 minute warmup:
@13:00 Group temperature = 177.4F before 3 oz warming flush
@15:00 Group temperature = 185.3F at beginning of shot
Avg. shot temperature = 188.9F

30 minute warmup:
@28:00 Group temperature = 197.6F before 3 oz warming flush
@30:00 Group temperature = 198.8F at beginning of shot
Avg. shot temperature = 200.1F

45 minute warmup (fully warmed up):
@43:00 Group temperature = 200.1F before 3 oz warming flush
@45:00 Group temperature = 200.4F at beginning of shot
Avg. shot temperature = 201.8F

Comments and conclusions:

• An increase in brew boiler SV of 2F resulted in an increase in shot temperature of ~1.6F (comparision to first shot in sequence in previous tests).
• The group temperature is a very good indicator of the readiness of the machine.
• The shot at 15 minutes was ~13F cooler than when fully warmed up.
• The group temperature at 15 minutes was ~15F cooler than when fully warmed up.
• As the group temperature gets closer to the final value, the correlation becomes better.
• A plot of group temperature vs warmup time is "plenty good" for estimating the resulting shot temperature of a partially warmed up Duetto.

Simulated shots using Scace thermofilter at varying amounts of warmup time (above).



Group sensor readings.

Jim

Marshall wrote:'snip'

[Edit] I hope we are not focusing on minutia, while missing the elephant in the room.

I know that this is off topic but - where do you talk about drinking coffee?

jggall01 wrote:15 minute warmup:
@13:00 Group temperature = 177.4F before 3 oz warming flush
@15:00 Group temperature = 185.3F at beginning of shot
Avg. shot temperature = 188.9F

30 minute warmup:
@28:00 Group temperature = 197.6F before 3 oz warming flush
@30:00 Group temperature = 198.8F at beginning of shot
Avg. shot temperature = 200.1F

45 minute warmup (fully warmed up):
@43:00 Group temperature = 200.1F before 3 oz warming flush
@45:00 Group temperature = 200.4F at beginning of shot
Avg. shot temperature = 201.8F

Think I'll invest in some timer company stock before the rush starts.

jggall01 wrote:Some additional test data to at least begin to address these issues: ...45 minute warmup (fully warmed up)...

The e61 { on a Vibiemme } takes 52 minutes to flat line.
Placing a tea towel over the group cuts this time in half.