HomeRoast Digest


Topic: Roaster efficiency (20 msgs / 391 lines)
1) From: Alchemist John
I couldn't help myself and decided to pull out a couple reference 
books an do some calculations.  From the best I could determine, 
taking into the heat capacities of coffee (wet and dry) and water's 
various forms (heat capacity (water and steam), heat of vap, etc), it 
does indeed look like 1 kg/kw is more than feasible.   The number 
that fell out for me was 9.6 minutes to have sufficient power to take 
to 1 kg of green coffee and profile it to 455 F with 1 kw (of heater power).
I agree - quit wasting it.  As Tom has pointed out, it is a balancing 
act.  But sub 20% efficiency (8 oz in 16 minutes at 1.3 kw) isn't 
real balancing IMO (that example is closer to 10%) - it is poor 
design (or maybe ignorant design).  I think most designs are way 
overboard with air circulation with no forethought about 
design.  Sure, some is needed, but 1-2 cfm should be way more than 
enough.  Sure, move 50 to 100 to 200 cfm and watch your heat go 
away.  I mean, come on.  Most roasters are not 1/2 cf.  1-2 air 
turnovers per minute is more than enough if not overkill.  I think I 
will go and calculate the heat capacity of the air (moist) in the 
roaster and how many cfm's you need to maintain a target of 50% 
efficiency (1 lb at 1 kw in 11 minutes is 40%).  My current roaster 
setup is 30% efficient and had almost no fine tuning of heat 
conservation, although what I can say is insulation (big surprise) 
took it from 22% to 30%, and I have WAY more insulation I can do.
BTW, to get comparable numbers in the above efficiency comparisons, I 
am using (bean mass)/(roast time)/(kilowatts).
I can feel a design taking shape....
At 04:23 7/26/2007, you wrote:
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John Nanci
AlChemist at large
Zen Roasting , Blending & Espresso pulling by Gestalthttp://www.chocolatealchemy.com/

2) From: Scott Marquardt
When I was fussing around with this:http://scott.marquardt.googlepages.com/roastcoffeeinamugI concluded that apart from method (drum, fluid bed, IR), it would be easily
possible to roast a gram of beans with a watt of power.
I came darned close, as it turns out. And given how inefficient what I was
doing was (what a phrase -- so efficiently connoting what it's expressing),
it's interesting that you calculate darned close to what I figured might be
the limit case.
Something like that.
- S
On 7/26/07, Alchemist John  wrote:
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3) From: Scott Marquardt
Argh, not the best link:http://scott.marquardt.googlepages.com/radiantcoffeeroasting 0:00 / 70
 5:00 / 227
 10:00 / 323
 13:36 / 390 (first crack begins)
 16:00 / 443
227 grams with 250 watts in 16 minutes
On 7/26/07, Scott Marquardt  wrote:
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4) From: Lynne Biziewski
Scott, I think you have way too much time on your hands.
; > )
Actually, I loved the site & the project. I was going to ask you if you
used Legos for this, but then I noticed that you mentioned & linked to
Fischertechnik. Very cool. Have to show my son - he's always been a
builder/creator/engineer type - did all I could to encourage this when he
was a kid, despite my own deficiency in those genes.
Lynne
On 7/26/07, Scott Marquardt  wrote:
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5) From: David Rolenc
Very cool!
Scott Marquardt wrote:
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6) From: Scott Marquardt
Hmm. Thought I already had. This has been a while, now. I'd really like to
return to it using some longwave IR emitters, which should solve the proble=
m
of absorpton variation that exaggerates inconsistency with heterogenous pre=
p
beans. Halogen showed the energy levels work, and also showed that shortwav=
e
IR doesn't cut it for all beans.
Others have tinkered with IR and halogens before; I like to think that if I
contributed anything original, it's the notion of roasting in a
vacuum-insulated container. The ability to just grab the thing with one's
bare hands when the interior is 450 degrees, is just too fun.
- S
On 7/26/07, Robert Yoder  wrote:
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7) From: Scott Marquardt
Oh -- and I'd also like to just aim a hot air gun into the thing. I think
that could work really, really well!
- Scott
On 7/26/07, Scott Marquardt  wrote:
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8) From: Leo Zick
1 kg/kw sounds like it would work under ideal conditions.. but what about
the ability to control heat through the cycle?
1 kw wont be enough power to produce fast ramp cycles mid roast.
On 7/26/07, Scott Marquardt  wrote:
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9) From: Scott Marquardt
Agreed. Spot capacity has to exceed average power use, to be sure.
It's like how a kitchen table should always be a bit bigger to accommodate
unanticipated guests -- even if the average amount your own kids shovel in
never quite empties the fridge.
;-)
- Scott "will foist oddball analogies for coffee" Marquardt
On 7/26/07, Leo Zick  wrote:
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10) From: Alchemist John
Indeed very cool.  That puts you right in the 60% category.  1 kg 
with 1 kw in about 9 minutes is what I worked out for 100% 
efficiency.  I would not ever expect to see that as that does not 
take into account any container.
At 10:03 7/26/2007, you wrote:
<Snip>
John Nanci
AlChemist at large
Zen Roasting , Blending & Espresso pulling by Gestalthttp://www.chocolatealchemy.com/

11) From: Alchemist John
At 14:37 7/26/2007, you wrote:
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Actually it will.  There is more than enough raw 
power to get the beans to temperature for a 
proper profile.  As it was said earlier, a huge 
portion is about heat conservation and IMO efficient heat transfer.
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 homeroast
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marquardt.googlepages.com/radiantcoffeeroasting 
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uardt.googlepages.com/roastcoffeeinamug 
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marias.com/mailman/listinfo/homeroast 
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as.com/maillistinfo.html#personalsettings 
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John Nanci
AlChemist at large
Zen Roasting , Blending & Espresso pulling by Gestalthttp://www.chocolatealchemy.com/

12) From: Scott Marquardt
The thermal carafe insulates so well, that dealing with heat loss through
the opening becomes the main concern.
Since thermal carafes are a dime a dozen in thrift stores, this is an
experiment anyone can try. Admitedly an apparatus to rotate the thing is not
as straightforward to implement, but I'd expect to see some ingenious
designs if a lot of people applied themselves to this approach.
On 7/26/07, Alchemist John  wrote:
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13) From: Dan Bollinger
This is a multi-part message in MIME format.
Probably true. Commercial roasters require much less than 1kW/kg, =
something in the range of 4-600W. Of course, they have the advantage of =
economy of scale. I tried to find the exact number, but couldn't find it =
in my notes.  Dan
  Actually it will.  There is more than enough raw power to get the =
beans to temperature for a proper profile.  As it was said earlier, a =
huge portion is about heat conservation and IMO efficient heat transfer.

14) From: John Moody
They run much higher power in the afterburner.
John

15) From: Leo Zick
4-600w?  id have to see it to believe it.
my guess is that you need 4-600watts just to overcome losses while trying to
create a fast ramp, in addition to whatever the ideal wattage is for a roast
size..
On 7/27/07, Dan Bollinger  wrote:
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16) From: Leo Zick
but dont you need additional power to better control ramp speeds?
also i understand what youre saying about thermal efficiency, and i agree,
airflow is the biggest antagonist.  what i dont get is why keeping the air
trapped is a good thing.  i suppose like i read, you could make a heat
exchanger, recycle some air,use some fresh air, and seal the crap out of th=
e
roaster..but whats the roi on such a device?  think it would even pay for
itself with the minute amount of electricity saved over x years?
while a kw may be efficient, it really isnt all that much. im sure your wif=
e
spends more $ using her hair dryer..
On 7/26/07, Alchemist John  wrote:
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17) From: raymanowen
"They run much higher power in the afterburner."
Therefore, I'll just design an efficient gas flame afterburner, and heat
won't be lost in the AB, but used to make certain orbs hot.
Good place to start the design.
Cheers -RayO, aka Opa!
On 7/27/07, John Moody  wrote:
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-- 
"When the theme hits the bass, I dance the Jig!" - -Virgil Fox at the Mighty
Wichita (ex- NYC Paramount) WurliTzer- 1976

18) From: Leo Zick
just install a cogen plant in your house, and use the byproduct heat to
roast coffee
On 7/27/07, raymanowen  wrote:
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19) From: Dan Bollinger
This is a multi-part message in MIME format.
Its quite simple, really. As the size of the roaster increases the ratio =
between the volume to exterior surface heat increases dramatically. This =
means less heat is lost to the environment per pound of beans roasted. =
That's one reason why commercial roasters use one big roaster instead of =
lots of little ones. 
  4-600w?  id have to see it to believe it.
  my guess is that you need 4-600watts just to overcome losses while =
trying to create a fast ramp, in addition to whatever the ideal wattage =
is for a roast size..
  On 7/27/07, Dan Bollinger  wrote:
    Probably true. Commercial roasters require much less than 1kW/kg, =
something in the range of 4-600W. Of course, they have the advantage of =
economy of scale. I tried to find the exact number, but couldn't find it =
in my notes.  Dan
      Actually it will.  There is more than enough raw power to get the =
beans to temperature for a proper profile.  As it was said earlier, a =
huge portion is about heat conservation and IMO efficient heat transfer.

20) From: Scott Marquardt
There's a mathematician joke about re-defining the outside as the inside in
there, somewhere . . .
- Scott
On 7/28/07, Dan Bollinger  wrote:
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