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  • home made heat exchanger for small boiler machines

    saw on another site a thread outlining the advantages of preheating the water prior to entry into the boiler by running it through a small heat exchanger that is mounted touching the boiler..apparently gives really good temp stability during the shot...anyone done this? am thinking it might be fun to do to the Gaggia Classic now I have done the PID install...nice and basic..some copper tubing wrapped around the boiler and runs in between the pump and the boiler..have not done the calculations to work out what volume would be preheating at any one time whilst the machine was idle....but I am guessing it could be up to 100 mls which would be pretty good

    any thoughts?

  • #2
    Re: home made heat exchanger for small boiler machines

    Gday mate...

    Fellow CoffeeSnob (and Uni Physicist) "Sparky", has completed a lot of experimentation in this area so perhaps you could chase down some of his early posts using the Search tool or maybe drop him a PM. Will save you having to "re-invent the wheel"....

    Mal.

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    • #3
      Re: home made heat exchanger for small boiler machines

      cheers Mal...that is a little extreme compared to my ambitions! might go with something like the copper tubing idea as an experiment to see how stable the temp is through pulling a shot methinks...no need to add additional PIDs and heat tracing etc...! bloody hell that is dedicated...

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      • #4
        Re: home made heat exchanger for small boiler machines

        It works really well. Sparky & I had a fair bit of correspondence on this when I did it with an old Gaggia Coffee and a thermoblock from a broken Saeco. With the PID on the Gaggia, you will get almost flat temp profiles. Jamming it all into the case is a bit of a task but it can be done.

        Copper tubing as a preheat will work OK on a Gaggia since the elements are external (waste of time on machines with internal heating elements). Just how well it will reduce the temp drop during extraction will have to wait for your report  . I would expect thin tubing to work best since the pressure loss may help reduce the pressure enough so that the OPV doesnt need to operate.

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        • #5
          Re: home made heat exchanger for small boiler machines

          Bidtfaun

          Id be interested in something similar for a Silvia, Ive seen it done somewhere [HB??] and the results were good.
          Silvia has a larger boiler, but the volume in tho coil was in order of 30-40ml...IIRC.
          I reckon this would give you back to back double shots.

          Please keep posting if you persue this, I be keen to know where/who can "wind" the tube.

          Cheers Reuben

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          • #6
            Re: home made heat exchanger for small boiler machines

            Originally posted by 5146564150574651230 link=1239595260/4#4 date=1239847996
            I be keen to know where/who can "wind" the tube.

            Cheers Reuben

            I plan on removing the boiler and winding around it...copper tubing is pretty damn soft really...just keeping it neat and as snug as possible and I reckon itll work a treat...I plan on putting some barb connectors on each end either using braising (solder), or compression fittings..both would work-you just want to ensure its watertight!

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            • #7
              Re: home made heat exchanger for small boiler machines

              The coil on the Sylvia basically makes the boiler act larger in size but overall has much less effect than on a Gaggis since the Sylvia water inlet does not directly affect the shot temp while the Gaggias inlet in the group will cause an unavoidable temp drop during a shot. The inlet coil will flatten the Gaggias shot temp profile while the Sylvia will have a little better intra shot temp stability but thats all.

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              • #8
                Re: home made heat exchanger for small boiler machines

                Originally posted by 3F35353A353331540 link=1239595260/6#6 date=1239856403
                The inlet coil will flatten the Gaggias shot temp profile
                This is exactly what I am aiming for.....I am getting around a 3 deg drop through the shot with the PID..was a lot more before the PID install..like 10+ deg..and then the thermostat would close again and the temp would shoot up to 120 deg...bloody ridiculous really...

                might do it this weekend

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                • #9
                  Re: home made heat exchanger for small boiler machines

                  Originally posted by 0C272A3A282F3B204E0 link=1239595260/7#7 date=1239875305
                  Originally posted by 3F35353A353331540 link=1239595260/6#6 date=1239856403
                  The inlet coil will flatten the Gaggias shot temp profile
                  This is exactly what I am aiming for.....I am getting around a 3 deg drop through the shot with the PID..was a lot more before the PID install..like 10+ deg..and then the thermostat would close again and the temp would shoot up to 120 deg...bloody ridiculous really...

                  might do it this weekend  
                  BIDTFAUN

                  Depending on your PID there may be an alternative approach.

                  I have one of those non-site sponsor chinese PIDs and mine is actually optimised/programmed for Gaggias.
                  There is a dead band setting [in my case it has been factory preset & removed from view] available in some PIDs.

                  My deadband setting appears to be set to 10C, what it does is bypass the PID operation once the temp has dropped 10C below the setpoint.
                  In effect the heater is switched hard on at this point.

                  If you have this parameter available, enable it and set it to 10C.
                  As you are pulling your shot [in the Gaggia], the deadband will kickin around the 18-20 sec mark and give you heating for the remainder of the shot.
                  This is basically an automated workaround of the standard Gaggia practise of hitting the steam switch towards the end of the shot.

                  Could be worth a try.

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                  • #10
                    Re: home made heat exchanger for small boiler machines

                    Originally posted by 2334243322253423510 link=1239595260/8#8 date=1240095061
                    My deadband setting appears to be set to 10C, what it does is bypass the PID operation once the temp has dropped 10C below the setpoint.
                    In effect the heater is switched hard on at this point.
                    A high proportional gain (i.e. low value for P) and/or a high derivative gain (i.e. high value for D) will normally result in 100% power being applied well before a 10C drop has been realised.

                    So if your PID does not have a band override parameter like reubsters, you can probably make it behave the way you want using conventional tuning methods.

                    Looking at the small dataset from my single Gaggia PID project, Im convinced that having the heater kick on during a shot is a good thing on Gaggias.  It helps reduce the large drop in brew temperature that otherwise would result from having a relatively small boiler.  

                    Conversely, on machines with larger or more massive boilers, including Silvias, I believe that a flatter intrashot profile can be achieved by keeping the heater turned off for as long as possible.

                    Jim

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                    • #11
                      Re: home made heat exchanger for small boiler machines

                      Originally posted by 2037273021263720520 link=1239595260/8#8 date=1240095061
                      There is a dead band setting [in my case it has been factory preset & removed from view] available in some PIDs.
                      cheers for the advice..

                      what was the parameter called in the PID? what code was allocated to it....and how did you find it?

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                      • #12
                        Re: home made heat exchanger for small boiler machines

                        Bidtfaun,

                        You got a manual of the seller?
                        If you didnt, try this:
                        http://www.e3b6a5y.com/365/WiringDiagrams/new2006power.pdf

                        It appears to be very similar to my PID. I dont think that there is a band over ride.

                        You could use the alarm system (see page 6, fig 2 of the link) to drive another relay parallel to the SSR. There wouldnt be much room left in you Gaggia!

                        Probably best to try Jims suggestion first.

                        Maybe a little of topic but got this good description of PID from a RS publication:

                        In simple terms, PID control can be thought of as:
                        Proportional - How hard you drive the output
                        Integral - How often you drive the output
                        Derivative - Drives the output with respect to the current rate of temperature change.

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                        • #13
                          Re: home made heat exchanger for small boiler machines

                          yes I got a manual (identical to the link you posted) but as was mentioned by reubster it could be a function that is disabled/hidden..ie not disclosed in the manual....

                          i have found the 3 degree drop to be pretty acceptable and this was achieved with the autotune function...my knowledge of PID is very limited....what are the values you have set and what are the results?

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                          • #14
                            Re: home made heat exchanger for small boiler machines

                            I just ran with the auto tune. Found that was good enough.
                            I have a Silvia so the tune would be different.

                            Found also that there is a fare amount of lag in my system. I use the same in my Corretto roaster. Seems to be about a thirty sec thing. Could be the thermocouple or the PID.

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                            • #15
                              Re: home made heat exchanger for small boiler machines

                              Heres a good (laymans) explanation of what PID is and what it does... http://www.eurotherm.com.au/email/email_9_2.htm Might be helpful to gain an understanding of these controllers do...

                              Mal.

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