I was interested in how Decent espresso ensures consistent brew temperatures, but I only found scattered (and old) information regarding it. This thread A morning with the Decent Espresso machines and this video http://www.youtube.com/watch?v=HtWTT2BSZMI gave some decent information which I've summarised below:

-Cold water tank
-Warm water tank heated to 50C (heating with it's own heating element, not sure which type)
-Warm water pumped through coiled pipe heater to 5C above brew temperature (not sure what element type again)
-Hot and cold water mixed for desired temperature towards brew group head
-Brew heat is heated with a cartridge heater slotted into brass, which is isolated from the rest of the machine.
-PID or predictive control to control the cartridge heater and hot coiled pipe heater

So essentially there are 3 water tanks/parts, cold, warm, and hot. Is my understanding correct? I'm wondering if this is the most efficient method for good temperature control for low volumes.

Whether it's the best is a question for a scientist or engineer. If all you want is stable, maybe a saturated group like an LM is better, but if you want to pull consecutive shots at different temperatures or want to have the first few grams of water at a higher temperature to make up for the cold coffee and then drop the water temperature for the remainder, it's a really good way to solve the problem. The Decent was meant to allow doing almost almost anything in a profile and it currently pulls that off better than any other commercially available machine. Is it perfect, not even close, but if you want it's capabilities, there is currently no other choice.

It's actually the BEST method for low volumes. By having the sensors monitor the temperatures just before the portafilter, the Decent can make adjustments on the fly. I can't think of any other way to accurately not only control fluctuations, but also make repeatable adjustments according to a formula.

ira wrote:Whether it's the best is a question for a scientist or engineer. If all you want is stable, maybe a saturated group like an LM is better, but if you want to pull consecutive shots at different temperatures or want to have the first few grams of water at a higher temperature to make up for the cold coffee and then drop the water temperature for the remainder, it's a really good way to solve the problem. The Decent was meant to allow doing almost almost anything in a profile and it currently pulls that off better than any other commercially available machine. Is it perfect, not even close, but if you want it's capabilities, there is currently no other choice.

I agree it's an amazing system, but was just wondering what the actual system layout and general components are. I found the below diagram, but the detail was lacking and it's not the latest version (the flow sensor is still there but they removed that).

The diagram shows the hot and cold water pump, but this comes directly from the water tank, which is at 50 C (yet there is no water heater going into the water tank in the diagram). I'm assuming there's a separate cold and hot water tank?

Also what type of heater is used for the water heating? It looks like a thermocoil design, anyone know more about this? Is it enclosed in brass or copper?

The 50°C water tank is a feature which is not often used as far as I can say.
Additionally, as far as I know, there is no heater in the tank. Instead, the "hot water return path" in your diagram is used to heat the tank. At least that is what I would do.
But I have to admit I never saw a Decent Espresso machine.

Edit: There is also only one tank. The water is mixed by bypassing the thermoblock. As far as I can tell the diagram you posted is valid and everything is depicted.

Edit2: Heater is a thermocoil. It is a stainless steel tube embedded in aluminum with the heating coil for good heat distribution. You can see them as spare parts on the Decent site.

The water in the tank can be heated by recirculating water through the thermoblock. There is no need for that unless you want to use water faster than the thermoblock can heat it up, i.e., almost never. As I understand it, the thermoblocks are comprised of a stainless tube embedded in a heater, 1000 or 1200W as I recall.

Sham wrote:I was interested in how Decent espresso ensures consistent brew temperatures, but I only found scattered (and old) information regarding it. This thread video gave some decent information which I've summarised below:
.......
-Warm water tank heated to 50C (heating with it's own heating element, not sure which type)
......

IIRC, the water reservoir is no longer heated to 50C as mentioned in that 2016 thread. There's a thread somewhere where it was mentioned that the pourover profile could preheat the reservoir in order to get the proper water temp at the reqd flow rates. As mentioned by someone else upthread, the reservoir water can be preheated but the reservoir does not have its own heating element.

From that diagram one can see where the temp sensors are (appears to be 5 total pre manifold, 2 post manifold) and I''ll speculate that those are used to control the heaters as well as the cold or hot water pumps to get the temperature at the grouphead and prior to the puck. How fast or what the time constant is for the control loop I'm going to assume is part of the "secret sauce".

Decent lets you program a profile to preheat the tank before a shot. This is done as mentioned by recirculating water. It's mostly used in pour over profiles where the volume and rate of water to be delivered is enough that the heater can't keep up without the incoming water being preheated. That's my understanding anyway from using the DE1 for pour overs. Of course it prolongs the 'shot' time because the tank must reach the target preheat temp before the 'shot' starts.

This video goes fairly deep into the water flow, heaters, and internals: