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Anova Sous Vide Circulator (Part 2)

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#421 pbear

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Posted 19 June 2014 - 10:48 PM

I was a bit surprised when doing a long cook in a cooler at 60°C that the outsides of the cooler were pretty warm..

 

Can't speak to the rest, but this isn't surprising.  Insulation isn't magic and it's never 100% efficient.  Eventually, heat from the water bath will saturate the insulation (figuratively, not literally) and warm the outside surface, where it then dissipates into the air.  But the rate of transmission through an insulated container will be much less than that of an uninsulated one, which is what you're after.  The easiest way to measure this would be to put a watt meter (available from any hardware store) on the input, i.e., the circulator.



#422 Chimo

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Posted 20 June 2014 - 06:08 AM

Has anyone plugged their circulator into a power meter over the course of a long cook? It would be interesting to see how efficient they are, and to compare different water containers.


I have a "Kill-a-Watt" meter that I plugged the Anova into on one of my first cooks. I recall calculating the energy cost of the cook, but I don't recall the numbers. I will try to remember to give it another go this weekend. I do recall being a bit surprised by the steady state power that the circulation motor drew.

To comment on the UPS discussion, most consumer models are of the off-line type, meaning the mains provide the power until it is lost and then battery inverter circuit kicks in after a percentage of a cycle. As far as the output waveform, some use a modified square wave, some use pulse width output fed through a smoothing filter to replicate a sine wave. Very few consumer models actually output a pure sine wave.

#423 dcarch

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Posted 20 June 2014 - 06:46 AM

I have a "Kill-a-Watt" meter that I plugged the Anova into on one of my first cooks. I recall calculating the energy cost of the cook, but I don't recall the numbers. I will try to remember to give it another go this weekend. I do recall being a bit surprised by the steady state power that the circulation motor drew.

To comment on the UPS discussion, most consumer models are of the off-line type, meaning the mains provide the power until it is lost and then battery inverter circuit kicks in after a percentage of a cycle. As far as the output waveform, some use a modified square wave, some use pulse width output fed through a smoothing filter to replicate a sine wave. Very few consumer models actually output a pure sine wave.

 

Most circulators use simple shaded pole motors, which are somewhat efficient. To circulate water, you need very little power. However, they just don't make special shaded pole motors small enough just for sous vide use.

 

Inverters invert by switching (pulsing, chopping) DC to transform to higher voltage, switching means on and off. on and off means square wave. Pure square wave can do damage to some electrical devices. So they have to reshape square waves to more like sine waves.

 

dcarch



#424 paulraphael

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Posted 20 June 2014 - 07:17 AM

Can't speak to the rest, but this isn't surprising.  Insulation isn't magic and it's never 100% efficient.  Eventually, heat from the water bath will saturate the insulation (figuratively, not literally) and warm the outside surface, where it then dissipates into the air

Yes, but the question is how much. You can calculate the R-value of insulation by measuring the surface temperature of the vessel relative to the ambient air temperature, and comparing to the temperature differential between inside and outside the vessel.

 

The higher the R-value, and the lower the temp. variation between in and out, the less warm you'd find the outside of the vessel. If the cooler were filled with 1/2" closed cell foam, which has very high r-value, I'd expect the warmth of the cooler on the outside to barely perceptibly warm to the touch. At least with a 140F cook, which is only about 70F warmer than the air in the room.

 

I haven't done the math, so I could be wrong about it. Maybe it's well insulated and I should expect it to get as warm as it does. If that's the case, though, a 30 quart cooler with that much warm surface area makes for a pretty big radiator. It's definitely burning up some watts. Imagine the light bulb it would take to warm up a big cooler that much.



#425 KennethT

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Posted 20 June 2014 - 08:30 AM

At the time, my vessel was just a large stockpot (All-Clad anodized aluminum (a wedding gift)), uninsulated. Like I said before, my PID controller has a function that displays percent output. So, while the bath is heating and the heating element is on full power, the controller shows 100% - which is 1000W since I was using a 1000W element. As the bath reaches temperature, the controller begins cycling the power to the element. I was most interested in power used once the bath reaches steady state, comparing the covered vs. non-covered values at various temperatures.

So, obviously, the covered pot was much more efficient, since it didn't constantly lose temperature due to evaporative cooling - which is much more substantial (depending on bath temperature) than the loss due to radiation/convection with the air around the pot - especially if there is no breeze.

Also, keep in mind that in my system, the heater is not submerged in the water, but instead, heats the pot like an electric burner. This type of heating will be less efficient than the submerged type.

Anyway, at a bath temp of 185F, the covered pot required an on-cycle of about 20% (200W). An uncovered pot used more than double that amount at that temperature. At 140F, the covered pot required an on-cycle of about 10% (100W), while the uncovered version used about 50% more (150W). At my preferred salmon cooking temp. of 115F (I gradient cook my salmon using SV dash), the covered and uncovered values are practically identical, at about 4-5% (40-50W).

I never tested an insulated bath because, at the time, I was designing the circulator with an eye towards production for the mainstream. So, it was designed to look less like lab equipment, and more like a kitchen appliance. How many mainstream people can you imagine wrapping their pot with insulation? And, once I saw the steady state values and compared them to traditional cooking methods, I figured that an extra few percent (meaning maybe 100W max.) would be inconsequential to the eventual marketing. SV, by its nature, is already orders of magnitude more efficient than using your oven.

Like pbear said, given enough time, even the best insulation will eventually equilibrate to the bath temperature. But, even though the outside may be warm to the touch, I'd guess that the power outputs would be less than an uninsulated bath. If you think of an analogy to a wetsuit when diving, the outside of the wetsuit will still feel warm, however, the wearer is still significantly warmer wearing it than not. The wetsuit traps water between it and the wearer, and the dead water, once warmed to body temp, doesn't require much more heat to stay at equilibrium. So, let's say you were diving in 50F water - with the suit, you might get uncomfortably cold after about an hour or two (I found this out by experience years ago), but without the suit, you wouldn't last 5 minutes!

Paul - in your situation, I wonder if the Reflectix is doing very much, other than limiting evaporative cooling. It might be just as well to use the tight fitting lid without it. Once the air space between the water and lid becomes saturated at 100% humidity, evaporation will stop, assuming there are no leaks where humidity can escape. At a certain point, increasing side insulation is "gilding the lily" so to speak - a lot more effort for not much gain.

ETA: Paul - Maybe a way to save a bit more energy would be to wrap the cooler with a reflective surface - like aluminum foil or something to reduce the radiation losses. Having a surface with lower emissivity should help. So then, the primary heat loss would be through convection, which, unless there's a breeze, should be minimal.

Edited by KennethT, 20 June 2014 - 08:35 AM.

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#426 DiggingDogFarm

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Posted 20 June 2014 - 10:09 AM

FWIW, PedroG's post (No. 17) in the following thread shows what kind of difference an insulated cover, etc., can make in terms energy consumption when sous-viding....

 

http://forums.egulle...oing-sous-vide/


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~Martin
 
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#427 Chimo

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Posted 20 June 2014 - 02:29 PM

FWIW, PedroG's post (No. 17) in the following thread shows what kind of difference an insulated cover, etc., can make in terms energy consumption when sous-viding....

http://forums.egulle...oing-sous-vide/


Thanks for the link. There was also some interesting tidbits on the kill-a-watt meter in there. It may not be fully up to the task with respect to getting the steady state power requirements of the SV due to its relatively slow data sampling frequency. During warm up I would expect the SV's heating element to be on at 100% duty cycle.

Two key factors in designing a battery-based backup would be the maximum demand (known) as well as the energy required for the desired hold time. As discussed here, that energy requirement will be a function of many variables. Sounds like a fun problem to ball-park!

#428 Chimo

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Posted 20 June 2014 - 02:58 PM

...

Inverters invert by switching (pulsing, chopping) DC to transform to higher voltage, switching means on and off. on and off means square wave. Pure square wave can do damage to some electrical devices. So they have to reshape square waves to more like sine waves.

 

dcarch

That's correct.  I have also seen and built other inverter circuits that have varying output waveforms.  Devices with motors are particularly sensitive to UPS output waveform.  A corded drill is a handy, if simple, check of how well the output has been smoothed to a sine wave's energy.

 

I noticed that there are a lot of other engineers/techs in this forum.  Good to see!



#429 Chimo

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Posted 20 June 2014 - 08:52 PM

I did a batch of 63.5C eggs and then some 78.4C asparagus tonight and had the Kill-A-Watt (k-a-w) plugged in. The container was a small Coleman cooler with a top opening approx 10"x12".  As predicted the start-up draw was about 1050W.  Once temperature was reached, the k-a-w readings fluctuated from ~30W to 500W with greatly varying KVA readings as well as the power factor varied as well and dipped to as low as 0.48. The power factor still read low when the k-a-w was drawing a few hundred watts.  I would not trust this device to provide an accurate tally of kWH for a cook.

 

As a side note, once the bath reached a steady state temperature, I removed the reflectex lid I had covering the cooler. The k-a-w indicated that the power demand went from ~30W to over 200W to cope with the evaporative losses.  Once I replaced the cover, the k-a-w soon settled back down to the lower power demand numbers.



#430 pbear

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Posted 21 June 2014 - 12:27 AM

Yes, but the question is how much. You can calculate the R-value of insulation by measuring the surface temperature of the vessel relative to the ambient air temperature, and comparing to the temperature differential between inside and outside the vessel.

 

The higher the R-value, and the lower the temp. variation between in and out, the less warm you'd find the outside of the vessel. If the cooler were filled with 1/2" closed cell foam, which has very high r-value, I'd expect the warmth of the cooler on the outside to barely perceptibly warm to the touch. At least with a 140F cook, which is only about 70F warmer than the air in the room.

 

I haven't done the math, so I could be wrong about it. Maybe it's well insulated and I should expect it to get as warm as it does. If that's the case, though, a 30 quart cooler with that much warm surface area makes for a pretty big radiator. It's definitely burning up some watts. Imagine the light bulb it would take to warm up a big cooler that much.

 

I'm pretty sure we're using the same assumptions regarding the science.  Where we differ, I think, is over expectation.  So, yes, R-value will tell us how effective the insulation.  It's a gradient.  Say the inside temp of whatever is being insulated - whether a sous vide bath or a house - is X and the ambient temp is Y.  How fast Y will "wick" heat from the box is a function of the heat coefficient of air.  How fast X will pump heat into the insulation is a function of the heat coefficient of the medium inside the box.  The important difference between a sous vide bath and a house is that water is much more efficient at transferring heat than air.  That's why we're using it.  Sauce for the goose is sauce for the gander.  Just as a sous vide bath efficiently heats the pouches, so too does it efficiently heat the insulation.  Which is why I say I'm not surprised the insulated box gets warm on the outside.

 

Relating back to the OP, what I think this means is that it's not realistic to expect a UPS to maintain a sous vide bath for long.  For a flicker, sure.  Even for several minutes.  More than this, though, not so much.
 



#431 dcarch

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Posted 21 June 2014 - 04:17 AM

I don't know if many "beer coolers" are insulated.

 

Mostly they are "Isolated" by using double layer construction. No insulation, just air space, between the layers.

 

An "isolated" vessel, if with vacuum in the space is extremely effective in not loosing heat, such as in a thermos bottle.

 

dcarch



#432 paulraphael

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Posted 21 June 2014 - 08:49 AM

I don't know if many "beer coolers" are insulated.

 

Mostly they are "Isolated" by using double layer construction. No insulation, just air space, between the layers.

I was wondering about this. I looked up my cooler on the Coleman site. All it says is "insulated case for longer ice retention." It does not say "insulated lid," and indeed the lid had nothing in it. 

 

Some of their other coolers are fancier, and the site goes into more detail about what's in there. I don't feel quite curious enough to drill a hole and take a look.



#433 DiggingDogFarm

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Posted 21 June 2014 - 09:33 AM

Most (if not all) poly cooler lids are not insulated.


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#434 rotuts

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Posted 21 June 2014 - 10:19 AM

correct.  they are after all 'coolers'  and do not need an insulated top

 

if they were meat to keep food warm also, then the tops would be insulated.

 

the coleman's I have do indeed have foam insulation in the 'body'  nada in the top.



#435 DiggingDogFarm

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Posted 21 June 2014 - 12:06 PM

Good coolers, back in the day, had insulated tops and they worked much better.

Coolers are often used out in the sun where an insulated top is a good idea. :smile:


Edited by DiggingDogFarm, 21 June 2014 - 12:06 PM.

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#436 dcarch

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Posted 21 June 2014 - 01:08 PM

correct.  they are after all 'coolers'  and do not need an insulated top

 

if they were meat to keep food warm also, then the tops would be insulated.

 

the coleman's I have do indeed have foam insulation in the 'body'  nada in the top.

 

Cut a 1/2 hole, fill it with Styrofoam beads, or Perlite. Duct tape the hole.

Will work much better.

 

I have not had a chance to try this out: A few drops of oil on the water will prevent evaporation.

 

dcarch



#437 paulraphael

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Posted 22 June 2014 - 11:56 AM

These Coleman "xtreme" coolers have insulated lids. I'd have gotten one if I'd known about them. A lot cheaper and easier than my questionable project of insulating the lid with foam.  Some people have questioned the value of the lid insulation, but I'm betting it's worth at least a little. I also use reflectix.


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