Dialing in temperature on a commercial HX espresso machine

[RefreshmentCat]

I recently received my Scace device and have been using it on a few commercial HX machines. I'm experiencing a pattern - initial brew temp about seven to ten degrees higher than subsequent brew temps (which tend to stabilize). I didn't receive a scrap of instructions on how to use the device (not a big deal) or how to make adjustments on machines based on the data collected (a bigger deal). I know I can adjust the pressurestat to affect brew temps but what about adjusting the boiler level? I'm thinking that raising the boiler level will insure the entire heat exchanger is immersed in water, thereby giving greater thermal stability. It seems if part of the heat exchanger is out of the water it will create "hot spots". Is the logic valid? Anyone know? Greg?

[HB]

I recently received my Scace device and have been using it on a few commercial HX machines. I'm experiencing a pattern - initial brew temp about seven to ten degrees higher than subsequent brew temps (which tend to stabilize).

That sounds normal. The Elektra A3 is a commercial size group and boiler; it also performed best with a "warning flush" prior to the flush for the actual extraction (i.e., flush... wait a few minutes... flush... pull shot). This is well documented in the Buyer's Guide and in the supporting notes from The Bench.

I didn't receive a scrap of instructions on how to use the device (not a big deal) or how to make adjustments on machines based on the data collected (a bigger deal).

Google is your friend ("scace device instructions"): Scace Thermofilter Temperature Device - Instructions.

Keep in mind, however, that the Scace thermofilter instructions isn't a how-to on tuning your equipment. The thermofilter is a calibration device you can use to validate your espresso machines are performing similarly in your cafes; it is not intended to simulate the temperature profile of an extraction. The thermofilter is designed to accurately and precisely measure the output boiler temperature at the group in a way that's comparable across the same espresso machine model, but the readings are not necessarily meaningfully compared across different designs. In other words, you can use it to tune your espresso machine. To some extent, others can advise you based on what they've found on theirs, but the value of their suggestions depends on how well correlated their boiler / brew temperature characteristics are with your espresso machine. There is a good correlation between double boiler espresso machines (flat is flat). It's more complicated for HX espresso machines because the resultant profile depends on the intentional "HX hump" of the brew temperature and intentional (or not intentional) manipulations of the flush regime by the barista.

I know I can adjust the pressurestat to affect brew temps but what about adjusting the boiler level? I'm thinking that raising the boiler level will insure the entire heat exchanger is immersed in water, thereby giving greater thermal stability. It seems if part of the heat exchanger is out of the water it will create "hot spots". Is the logic valid? Anyone know?

Most heat exchangers are partially submerged; the La Spaziale commercial line of espresso machines have heat exchangers that are entirely bathed in steam. Changing the steam boiler's water level will have an impact on the heat exchanger efficiency and a requisite change in flush (e.g., higher water level = faster recovery, longer flush). That's where the Scace thermofilter really earns its keep: You can in a short afternoon map out all the scenarios and vary the espresso machine settings to your preference. Prior to my standardization using the thermofilter, I literally spent weeks mapping it out with thermocouples and the results were not necessarily reliably reproducible by others.

[gscace]

I recently received my Scace device and have been using it on a few commercial HX machines. I'm experiencing a pattern - initial brew temp about seven to ten degrees higher than subsequent brew temps (which tend to stabilize). I didn't receive a scrap of instructions on how to use the device (not a big deal) or how to make adjustments on machines based on the data collected (a bigger deal). I know I can adjust the pressurestat to affect brew temps but what about adjusting the boiler level? I'm thinking that raising the boiler level will insure the entire heat exchanger is immersed in water, thereby giving greater thermal stability. It seems if part of the heat exchanger is out of the water it will create "hot spots". Is the logic valid? Anyone know? Greg?

Everything inside the boiler is at nominally the same temperature give or take a couple of degrees. However, the heat exchange from boiler water to the brew water through the heat exchanger wall is lots faster through the parts immersed in liquid water. Depending on the layout of the hx, boiler water level will have an effect or not. For example, if the hx is horizontal and submerged all the time, well obviously level ain't gwine do nada. If the hx is vertical, or inclined as is practice in e-61-style machines, then the amount of heat transfer per unit time (power, actually) from the boiler water to the hx water will vary with varying boiler water level. Other things to consider are length of re-entrant tube within the hx, if so equipped, and the ratio of cold water mixed with hx water during brewing. E-61 style machines have some cold-water mixing due to the plumbing layout and size of the tubes and internal restrictions. Dunno about the machines you are working on.

Declining shot temperatures as brewing frequency increases is unfortunately typical of a lot of designs. It takes very clever engineering and implementation to make a hx machine produce the same temperature over all duty cycles. It's possible to do so, but you gotta really do your homework, or else be an amazing machine tech.

A good strategy for the machines that you are working on is to use your Scace to learn how much flushing is needed to trick the machine into thinking it is working at high brewing frequency. Once you learn this, you compensate for a lot of machine design deficiencies. You can use your Scace as a training tool as well as a machine setup tool.

Holler if youse got mo questions. Might be worth talking on the phone. I'll give you my phone numbers if you pm me.

-Greg

PS - There is an instruction set that I did a while ago, but we are working on a DVD that demonstrates use and discusses testing technique, barista training, machine fault diagnosis etc.

[gscace]

Dan:

There's a pretty decent body of work demonstrating that average temperature transfers pretty well from one machine to another, regardless of hx or double boiler config. Unfortunately the work is proprietary.

-

[RefreshmentCat]

I've used my Scace on a Cimbali M39, an Astoria Argenta and a Conti (can't remember the model) - all are two groups. If the M39 is like the other Cimbalis then I believe the heat exchangers angle down into the boiler at about a 45 degree angle and I believe the factory water level setting leaves the top 20% of the exchanger tube above water. I conjectured that the exposure to steam contributed to the really high initial shot temp (over 10 degrees hotter than subsequent shots) but maybe that is my History major logic.

I think the Astoria's exchangers are horizontal but I've never ripped into one deeply enough to know. After raising the boiler temp/pressure I was pleasantly surprised to see that after one purge cycle the brew temps seem to settle in nicely shot after shot. Since I adjusted the pressurestat and instructed the cafe staff to do at least one purge cycle before pulling a shot the espresso is hugely improved. They are using Illy and it's the best Illy shots I've had in years.

The Conti is...well, I'll hold my tongue. I don't know anything about the HX internals but I do know that it's a full sized car with a lawn mower engine. It comes out of the gate pretty hot then hits the target but keeps going down with each subsequent pull.

I work on Unic's a lot and I believe the HX is half submerged with the autofill probe all the way down. I know they run horizontally. I'm thinking about modifying them so the cold water inlet tube is extended and directed to the back of the heat exchanger for a "FIFO" system. The factory set up has the water inlet coming into the front of the HX (near the group head) but I could see the water in the back of the HX not getting displaced because the cold, fresh water coming in is closer to the group. Maybe that's why I need to crank the Unic's temp up quite a bit to get the brew temp right. Cimbalis have the fresh water tube extending to the back of the HX and, if the temp is set right, they brew beautiful shots.

I've just cut off the bottom of a Unic portafilter and if I shave down the inner diameter so it's 58mm I'm hoping my Scace will fit in so I can really test Unics.

[jesawdy]

Everything inside the boiler is at nominally the same temperature give or take a couple of degrees. However, the heat exchange from boiler water to the brew water through the heat exchanger wall is lots faster through the parts immersed in liquid water.

I'm still not convinced this is the case.

As Eric pointed out here in Boiler Fill Level Impacts Shot Temperature Stability in PID'd Espresso Machines (and which should be of interest to the original poster), the Heat Transfer Coefficient is several times higher for a Steam/Copper/Water interface versus a Water/Copper/Water interface.

What is, however, easier to see is the decrease in average shot temperature as the boiler water level is raised or the increase as the level is lowered. As DaveC points out, he brought this subject up in another post and was met by some skepticism, certainly by me and perhaps others. The skepticism was not well founded.

The overall Heat Transfer Coefficient (U) for a Steam-Copper-Water "system" is 205 Btu/ft2-hr-F or 1160 W/m2-K whereas the overall Heat Transfer Coefficient (U) for a Water-Copper-Water "system" is 60 to 80 Btu/ft2-hr-F or 340-455 W/m2-K

The above data was extracted from this reference: http://www.engineeringtoolbox.com...icients-d_284.html

I haven't found much in very simple looking to say any different (and I dragged out some texts when this was posted). That said however, an air layer, condensate layer, water layer (from wet steam) would all insulate the Steam/Copper interface. Enough so that it would be detrimental and the Water/Steam/Water interface would be better? I don't know but I should think not. The thermal resistances of these layers is explained a bit here:

http://www.spiraxsarco.com/resour.../heat-transfer.asp

Of course if anyone has played with more machines and a Scace thermofilter than you, I would be surprised. Have you played with steam/water interface levels yourself?