@TomGeorge hi and thanks for the warm welcome! I have not tried it yet, but yes that was the intention. Once I hit the target value the flow stops. My assumption would be that the some water might drip out at the end but it should stop fairly quickly.
The water steam mix scenario is a good one! I don't think that a "spitting" of water steam mix would be very good so I will need to find a way how to avoid that. Maybe moving the container all the way to the outlet would be good enough.
For the sake of this chat, lets change the temperature requirement to a max of 90degC. I consider the 100degC case as a nice to have and not a must (so could be implemented at a later stage)
Those funny taps that give instant boiling water have an insulated tank below hold the near boiling water .
I donāt think youāll get āinstant ā hot water any other way unless you are prepared to have some cold run off first , or something extremely complex .
Donāt forget a pressure relief valve
Time to tell us what the project actually is supposed to do ?
From your specsheet, (interesting looking device -- I was imagining a spa-like FTH with much larger scale plumbing) I see that the Flow Through Heater volume is 4ml. How does that compare to the distance/volume to the outlet temperature sensor and outlet pipe?
Iāve been interested in automating my pour-over coffee making ritual for some time and havenāt really progressed much because the water heaters I have seen are not very āprettyā. Meant to be imbedded inside a coffee machine they are quite utilitarian looking. The Ferro unit is much better looking and I look forward to hearing back from the manufacturer as well as following this discussion.
The detailed design has not been started yet. What I am working on now is the proof of concept, so no enclosure or anything, just bare pipes and buckets
Well, any distance between the heater and the sensor will make it harder to control, and any distance between the heater and the dispenser will make the delivered volume proportionally cooler. Even if you get the heater to temp perfectly and instantly, pushing 50ml of ambient temp outlet water in a 100ml cup before 100ml of perfect 100Ā°C water flows through the heater into the outlet pipe would be disappointing.
Yes that makes total sense. The second Thermocouple is actually integrated inside of the FTH's housing, right before the outlet. So from that perspective I think it can't get better. Then it is just a matter of how far away is the outlet and how much heat will be lost along the way to get there. The Thermocouple on the Inlet should obviously be as close as possible to the FTH.
Ultimately it also come back to how accurate can the system be and how much tolerance do I allow.
But very good points here in this chat! Very thankful for that!
Thatās one of the issues Iāve identified as well. Delivering a known quantity of water at a certain temperature using a flow through heater is not a trivial problem. The way I do it manually is to heat a larger quantity of water in a reservoir to temperature and then dispense from that.
The flow through heater has the possible advantage of heating a quantity of water faster than, for example, an immersion style heater but I donāt see how one could regulate the outlet temperature quickly enough to be useful for real time dispensing. Iām of the opinion that some sort of closed loop recirculating system is necessary.
If the sensor and the ultimate outlet were at the heater block, and you didn't have to worry about steam, you could bring the block all the way up to temperature, and then start and modulate the flow.
You'd then know the outlet temp, the heat capacity of the fluid, and the input temp, so with a bit of calibration of heater efficiency, you could calculate how many watts (and therefore the PWM) you'd need for any particular flowrate.
Another issue is finding a pump that can operate reliably at the temperature of the hot water. Most commercial machines pump room temperature water through the heating system rather than pump heated water. Iāve considered pressurizing a heated reservoir with an air pump after the water reaches temperature.
I am looking into Pumps at the moment. I don't think the temperature of the heated water plays such a big role (unless you use a closed loop) as the pump is located before the heater. A valve could avoid any backflow so that the pump never gets into contact with any water at a higher temperature than the water in the tank (which should be room temperature)
Agreed. I donāt think itās feasible to get reliable water temperature without using a closed loop system though.
If youāre only making espresso, the problem is not so difficult to solve due to the higher temperature used and the ability to dispense water directly into the portafilter but for pour over coffee, the technique uses a little lower water temperature and a slower dispensing process so I think that requires a different process.
Iāve found that water cools rapidly in certain containers so Iām considering using a flow through heater dispensing into a reservoir to get near boiling water that then is allowed to cool down to the required temperature.
I am still looking into the Solid State Relays, but struggle to decide on a SSR that I can proceed with. As the FTH will be operated on 230V and can draw Power between 1000 and 2300W the SSR needs to be able to transfer 10Amps max. On the Input / triggering side of the SSR we have the Ardunio, which if directly connected would trigger at 5V. All the SSR Modules that I find are rated for 2A, which would not be sufficient. Can anyone point into the right direction?
I worked a bit on the actual schematic of how to connect the whole system for the first trial run. As I am not an electrical engineer by training I would appreciate any feedback on how to make this system safer an more reliable. I have not added any additional electrical components yet. Please not that I have added a second thermocouple to show the outlet thermocouple even though the FTH has an integrated one. The SSR has not been selected yet.
