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Thread: Heat Exchanger machines and Boiler sizes....

  1. #1
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    Heat Exchanger machines and Boiler sizes....

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Hey all!

    Came across a machine today that I have never seen/heard of before. Brand is Amica and is sold through the Coffex chain. Looks very similar to a La Cimballi JNR and when they were sitting side-by-side, youd swear they shared the same DNA.........(Coffex distribute the La Cimballi range...)

    Anyway, was a great little?!? unit but one thing stopped me in my tracks....It has a 4lt Boiler :o

    Surely this is too big for domestic use??

    I told this story to my wife that I liked the machine, but heating up 4lts of water for 2 caps in the morning is uncouth! She replied - "How is that bad, why cant you just put 1lt of water in the tank for the mornings you make 2 coffees and fill it up when guests come around.?"

    I said I have no idea why I cant do that..... But I knew some people on this site would. ;)

    What stops me putting only a small amount of water into a large boiler on a daily basis??

    Yes, Im aware in advance there will be a really simple answer to my question, but if you dont ask...... :-[

    Regards,

    James


  2. #2
    Super Moderator Javaphile's Avatar
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    Re: Heat Exchanger machines and Boiler sizes....

    Howdy James,

    Ill take a shot at answering your questions.

    First off on most HX boiler type machines the boiler is only filled roughly half-way. So in a 4lt boiler youd only have 2lt of water in it. The rest of the space is needed for the steam. As too whats stopping you from only using 1lt, nothing, as long as 1lt fills the machine to the minimum water level. ;D How-ever, before you do that I think you may be under a misconception. The water used to brew the espresso does not come from the boiler in the commercial La Cimbalis. Room/line temp water is injected into the HX unit in a seperate system from the boiler water. The boiler water is there to heat up the HX, assembly which then heats up the brew water, to provide hot water via the hot water tap, and to provide steam for pressure in the boiler and to the wand(s). If the water level in the boiler falls below the minimum allowed bad things happen. :-/ Your heating elements are no longer covered by water and will overheat and burn out.

    The La Cimbalis (and virtually every other commercial or even near commercial machine Ive heard of) have an auto-fill boiler. While most of them can be tweaked for different fill levels personally I leave them alone as long as theyre working properely.

    As to the economics of heating up 1lt as oppossed to 2lt in the boiler I suspect it is not all that much cheaper, and in fact may actually cost more. The water in the boiler is heated up until it has produced enough steam to bring the boiler to a pressure of 1.2-1.4 atms. It takes 1 calorie of heat to raise 1 gram of water 1 degree C. So to bring that 1lt of water from room temp (say 20C) too 100C would take 80,000 calories. If I recall my chemistry and physics correctly it then takes 80 calories to turn 1 gram of 100C water into steam. Its been enough years I no longer remember how many grams of steam it takes to put a 1lt volumn under 1.2 atms but I suspect that the energy required is pretty close to what it takes to heat that volumn of water from room temp to boiling. All in all the electricity saved would be tiny, and the possible losses (a burned out heating element) so expensive as to not make the risk worth while IMHO. :)

    Hope this helps. :)


    Java "The only stupid question is the one thats never asked" phile

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    Mal Dimal's Avatar
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    Re: Heat Exchanger machines and Boiler sizes....

    Hi,

    If heating up that amount of water was a concern to you, you could always insulate the boiler (if it wasnt already insulated) and reduce the energy wastage that way. You could also fit a Temperature Controller (PID?) to the boiler to further stabilise the water temperature and reduce energy wastage... so there are always ways and means available to overcome problems.

    Cheers,
    Mal.

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    Re: Heat Exchanger machines and Boiler sizes....

    Not sure what this machine is as the only Amica Ive heard of is an Isomac and that has a 0.7l boiler. Are you sure 4l wasnt the reservoir size?

    A bigger boiler offers more temperature stability when pulling a lot of shots and steaming a lot of milk. If you are only drinking a couple of cups a day you are way short of leveraging the benefits of this machine and I imagine it will chew a lot more power than a machine with a smaller boiler.

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    Re: Heat Exchanger machines and Boiler sizes....

    Quote Originally Posted by Javaphile link=1110449844/0#1 date=1110464723
    As to the economics of heating up 1lt as oppossed to 2lt in the boiler I suspect it is not all that much cheaper, and in fact may actually cost more. *
    Er no. It may be that a bigger boiler will be shaped so less heat is lost from it so that less energy is needed to maintain the temperature once it has heated up but heating 1lt to 120deg Celcius will take twice as much energy as heating 2lt of water to the same temp. The amount of water needed to be vaporised to set the required pressure in the headspace is miniscule, even if the head space is doubled so the energy requirement for this side of things will not change greatly as headspace is varied.

    You are right about the maximum headspace/minimum water level, though. These HX machines can only be adjusted so far to reduce the water that is heated in the boiler as the hesting elements must be fully covered (water is a much better conductor of heat than steam).

    I could rant about the suitability of HX machines for domestic use but Ive done enough of that. :-X

    Greg

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    Re: Heat Exchanger machines and Boiler sizes....

    Hi All,

    Thanks to all for your input.

    The Amica title is the actual brand and not a model name, I have never seen this before and printed/research material is almost non existant........but the saleswoman did give me a wink when I hinted at how closely the machine resembles the La Cimballi..... :-/

    The boiler is definately published as a 4lt, the machine itself is slightly bigger than a Diadema or Giotto - weighs 34kg too!!

    So I guess the bottom line is that I dont have to fill the machine up every morning as there will always (hopefully!) be some water in the boiler that will replenish itself as required from the tank - Which has answered my question!!

    And yes Java, I did have a slightly different idea of how a HX works - thanks for clearing things up ;)

    Again, Thankyou to all.

    BTW - When my new machine finally makes it to my bench, I will be conducting an experiment that measures power usage over different conditions i.e. left on for 24/7, turned on for 1 hour before brewing and then turned off, left on overnight only etc. I have access to power clips and a data recorder, so the results will be reasonably accurate and an interesting to say the least. Will publish the results when obtained.

    Regards,

    James

  7. #7
    Super Moderator Javaphile's Avatar
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    Re: Heat Exchanger machines and Boiler sizes....

    Doing some further investigation to satisfy that itch in the back of my brain I find (at 1 atm) the 80cals of latent heat is for ice/water, while the latent heat for water/steam is 540cals.

    As best I can figure it takes about 4 grams of water to produce 1.2 atms of pressure in a 1lt volume.

    Running all these numbers through the old abacus shows that by not adding that 2nd liter of water to the boiler it would save less than a penny of electricity.

    Another consideration is the reduced thermal stability with the lower water level. Because that liter of water is not there as a heat reservoir the HX may not be able to heat the water up to the proper temp as the pull progresses.

    Java "Cant resist scratching that itch" phile

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    Re: Heat Exchanger machines and Boiler sizes....

    Hmmm. Lets check for ideal gases (which steam isnt).
    pV = nRT and for pressure in pascals, volume in metres cubed, n as moles of gas molecules, T in kelvin, then R = 8.314570 (J)(K-1)(mol-1)
    giving n = pV/8.314570T

    so if p = 1.2 bar = 121590 Pa, T = 110 degrees Celcius = 383.15 K, V = 1 litre = 0.001 metres cubed then
    n = 0.0382 moles and the molecular weight of water is about 18 so the mass of water needed to fill this volume at this pressure is 0.687g so 371 calories or 1552 joules of energy is required to vaporise enough water to reach this temp and pressure.

    Of course this neglects the air that is already on the boiler. Since the initial 1 litre of air already at 1 bar, if that doesnt heat up (a bad assumption but will do for worst casing) then the partial pressure for the water required will only be 0.2 bar so the amounts to pressure up the boiler drop to 0.137g, 74.2 cal/310J.

    Greg

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    Super Moderator Javaphile's Avatar
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    Re: Heat Exchanger machines and Boiler sizes....

    Quote Originally Posted by kaanage link=1110449844/0#7 date=1110948878
    Of course this neglects the air that is already on the boiler. Since the initial 1 litre of air already at 1 bar, if that doesnt heat up (a bad assumption but will do for worst casing) then the partial pressure for the water required will only be 0.2 bar so the amounts to pressure up the boiler drop to 0.137g, 74.2 cal/310J.

    Greg
    Hhhmmm....If you consider the air initially in the boiler before heat is applied to be at 1 atm then the final pressure of the boiler is at 2.2 atm. The final pressure in the boiler is 1.2 atms above ambient, not absolute. :)

    Another way to look at this is how much does it cost to heat up just that 2nd liter of water? It will take roughly (roughly because of varying starting temps dependent on the ambient temp at your location) 80,000 calories. 80,000 calories equals 0.09304 kilowatt-hours. I dont know what yall are paying for electricity down there but up here in Minnesnowta were paying 7 cents per kilowatt-hour. Hence heating up that liter of water would cost 0.65128 cents. Ergo your *maximum savings by not putting in that 2nd liter of water would be less than 2/3rds of a penny.

    Personally Id rather pay that 2/3rds of a cent then run the risk of burning out my heating element due to too low of a water level, not to mention that your system will have better thermel stability with that 2nd liter of water in it.

    If youre seriously wanting to save energy costs probably the best thing you could do is to insulate the boiler.

    The only place that you save energy by not adding that 2nd liter of water is on the initial heat-up. Once your system has reached full temp/pressure the cost of maintaining that temp/pressure (ideally) is the same no matter what the ratio of water to steam is in the boiler. In reality, unless your heating control is using fuzzy logic the cost of maintaining the temp/pressure will be greater in a system with less water.

    The rate of heat loss is an expoential, not linear, funtion of the difference in temperature. Water holds a *lot more heat than steam does at a given volume and pressure. When your thermostat detects that the boiler has reached its proper temp and turns off the power to the heating element heat is still being put into the boiler until the heating element has cooled down to ambient (in the boiler) temp. In a system with 2 liters of water that extra heat will not raise the temp of the boiler as much as one with only 1 liter of water, thus resulting in less heat loss in the system with 2lt than in the one with 1lt.

    Java "Isnt physics fun?" phile

  10. #10
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    Re: Heat Exchanger machines and Boiler sizes....

    Behmor Brazen - $249 - Free Freight
    Ah, ok. Boiler pressure is relative, not absolute so the 1st set of calculations is closer to reality.

    And insulating the boiler will speed warm up too.

    "All science is either physics or stamp collecting" - Rutherford :D

    Greg



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