# DB vs HX design principals: clarification required



## grumpydaddy (Oct 20, 2014)

My understanding of HX machines is that a pipe runs through a steam generating boiler running hotter than is wanted for coffee and in so doing heat is added to the water in the pipe. The length of that pipe will determine the heat transfer as will the flow rate through the pipe.

I am less clear about how the group is kept warm.... is there generally a separate syphonic loop of some sort?

I understand that the above design must be based on cold water entering the pipe before the heat exchange and that the so called temperature surfing must be the practice of removing water that is too hot, having sat in the pipe in the boiler for a while, to allow for the designed pipe length and flow to provide water for the shot to be at the correct temperature.

Given that the temperature of the incoming cold water varies across the seasons, how is this compensated for?

Sure this is a somewhat simplistic description but do I have this right?

On then to the non steam boiler of the DB machine

Keeping the temperature of the water within close limits seems a simple exercise but again would one of you care to clarify the generally used method for keeping the group up to temperature. Is this generally done from this boiler or the steam boiler?

Happy with links clarifying if you know any.


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## h1udd (Sep 1, 2015)

I have an hx with a tank ... The tank pretty much ensures the water is the same all year round ... But there is variance there always will be ... But not enough for me to notice in taste ... The pre heating cup variance I notice more


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## Glenn (Jun 14, 2008)

Does this image help?

http://www.1st-line.com/store/pc/Heat-Exchanger-vs-Double-Boiler-d52.htm


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## marcuswar (Aug 19, 2013)

I think this diagram nicely explains how the thermosyphon works. The HX circuit forms a closed loop that the water flows around heating through the brew head. When a shot is pulled cold water is injected into the bottom of HX pipe and the top valve in the brew head opens up to allow the water to pass through the coffee.

AFAIK any compensation for temperature is simply down to the mass of the E61 brew head.


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## grumpydaddy (Oct 20, 2014)

Thanks Glenn

I cannot see that image Marcus


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## emin-j (Dec 10, 2011)

h1udd said:


> I have an hx with a tank ... The tank pretty much ensures the water is the same all year round ... But there is variance there always will be ... But not enough for me to notice in taste ... The pre heating cup variance I notice more


Can you elaborate on this post please, do you mean the water tank or boiler ? And what ensures the water "is the same" all year round.

Atb.


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## h1udd (Sep 1, 2015)

Sure. My hx is not plumbed in, so you fill a tank. That tank sits slap bang next to the boiler. I fill the tank with either room temperature bottled or filtered water. And the machine is on a good hour before first use and left on all day. The water in the tank varies a couple of degrees depending on if I have just topped it up, or it's been sat for a couple of hours .... However this variation seems to be negated by the time it enters the cup and it's only tenths of degrees out to 1 degree depending on heating cycle

my measurements are done with a thermocouple probe stuck into the tank and into the cup, so probably not the most accurate.


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## marcuswar (Aug 19, 2013)

No sure what happened with the image?

...any way the url is ; http://www.home-barista.com/forums/userpix/2_ecm_technika_group.png



grumpydaddy said:


> Thanks Glenn
> 
> I cannot see that image Marcus


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## Glenn (Jun 14, 2008)

You may need to be signed into HB to see the image


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## marcuswar (Aug 19, 2013)

I think you are correct (even though I never logged into HB as don't have an account) as I just checked the previous link and that one is now asking now asking me to login via Google account ?

Anyway in an attempt to avoid any further confusion here's a very similar image (lets hope this one works and stays around!);


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