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MintakaCat
06-20-2009, 09:36
Awhile back there was some debate as to the energy efficiency of the Nesco brand dehydrators here on WhiteBlaze.net. These dehydrators are very popular with the hikers on this web site, along with others such as the Excalibur brand that I currently have.

In order to settle the debate I purchased a Nesco FD-75PR dehydrator and ran some comparison tests between it and the Excalibur 2400. Here are the results:



http://farm4.static.flickr.com/3583/3643947990_ef0a7dd3f8_o.jpg
The Nesco FD-75PR average current was 2.67 AC Amps at the 135° setting. This was calculated with a peak current 5.7 amps at 51 seconds over a 2 minute time frame and a minimal current of 0.43 amps at 69 seconds.

2.67AC Amps x 120VAC = 320.4 Watts



http://farm4.static.flickr.com/3617/3643144401_567b451723_o.jpg
The Excalibur 2400 average current was 1.1 AC Amps at the 135° setting. This was calculated with a peak current 2.1 amps at 58 seconds over a 2 minute time frame and a minimal current of 0.17 amps at 62 seconds.

1.1AC amps x 120VAC = 132.0 Watts



The Nesco emitted an additional 188.4 watts power than the Excalibur. To get a better understanding of how much additional heat that is, put your hand over a 60 watt incandescent light bulb and feel the heat. Then imagine the heat of three of those light bulbs and that is the additional heat the Nesco FD-75PR is putting out above what the Excalibur 2400 would do.

As for the Nesco FD-75PR having 5 trays and the Excalibur 2400 only having 4 trays, the Nesco only has 8% more tray area than the Excalibur. The Excalibur has 12 inch by 12 inch trays giving a total square footage of tray area of 4 square feet.

The tray area of the Nesco was a bit more challenging to calculate because it uses round trays that are 12.75 inches in diameter with a 2 inch diameter hole in the middle. Using the formula of Area = π x r2 the area per tray came out to be 0.8644 square feet. The total area for five trays would be 4.322 square feet or 8% more tray area than the Excalibur.

Another selling point of the Nesco brand is that it dehydrates faster than other models, however in comparing the recommended drying time in both manuals the numbers are approximately the same. There were some foods listed in the Nesco manual that required less drying time than the Excalibur such as apples, peaches, figs, beets and pineapples. However, the Excalibur listed faster drying times for bananas, blueberries, asparagus, corn, mushrooms and peppers.

In terms of costs, the average price of the Nesco FD-75PR is around $66.00. The average cost of the Excalibur 2400 is around $113.00, making the Excalibur $47.00 more expensive than the Nesco. This is probably why the Nesco brand is so popular.

Just for fun, I calculated how long you would have to run the Excalibur in order to utilize the energy savings to cancel out the cost difference of the Nesco. If you use the Department of Energy figures, the average cost of residential electricity is 9.75¢/kWh (March 2009). With that cost figure you would have to run the Excalibur 2558 hours (106 days) in order for the energy savings to cancel out the additional $47 costs. This figure does not take into account the lower heat load placed on your home cooling system so in reality this time might actually be less.

Bottom Line: The Excalibur 2400 used 42% of the energy that the Nesco FD-75PR required to accomplish the same task with approximately the same amount of food. However, the Excalibur 2400 did cost $47 more than the Nesco FD-75PR.

If the whole issue of carbon footprints and green living is important to you then the Excalibur 2400 would be a better choice for you. If the initial costs are more important to you then the Nesco FD-75PR would be a better choice.

If you plan to use your dehydrator a great deal then the Excalibur 2400 would be better in the long run, if not then the Nesco FD-75PR would be the better choice.

Lyle
06-20-2009, 10:09
My concern would be the accuracy of the temperature being maintained. With such great energy fluctuations, does the Nesco actually hold a constant temperature, or is it possibly, actually, cooking the food at times?

That is one of the dangers I've seen being warned about in various dehydrating manuals.

MintakaCat
06-20-2009, 10:28
I think the reason the Nesco has such large energy fluctuations is primarily due to its design. With the heating element and fan both being top mounted this requires a greater CFM on the fan in order to force the hot air down (hot air tends to rise). I think because of this there is a larger turn over in air in the dehydrator and thus the need for more power.

The Excalibur uses a side mounted design that requires less air flow and thus less power.

Rocketman
06-20-2009, 10:30
An important factor, if you are going to be dehydrating a lot of food is the capacity of the unit.

The Excaliber appears larger and possibly holds more food making the total drying time and effort smaller.

Do you have figures on this capacity difference?

The correct way of calculating average power is to use the definition of instantaneous power.

P=(V)**2/R or P = V*I or P=(I)**2*R where **2 indicates squaring or raising to the second power. Resistance is usually taken as a constant in these types of calculations, but current and voltage are explicitly varying at 120 cycles per second, and the voltage varies from a maximum of +170 to a minimum of -170 with an RMS equivalent of 120.

[Many calculus classes assign this as a problem, and virtually all Electricity and Magnetism calculus based classes cover this explicity].

You need to take the average of the power as defined above. If you compute the power from the time average values of volts and/or amps, you don't get the same result as if you use the Average of the square of the values.

The average of the square is not the same as the square of the average.

The 120 AC voltage is a Root Mean Square (RMS) average of the instantaneous voltage. In calculus, you calculate the mean of the square of the instantaneous voltage for one or more cycles.

If the voltage and currents were Direct Current (DC) your calculation would be correct.

It seems evident, nevertheless, that the less expensive Nesco unit loses more heat while maintaining a given temperature (on the average). There could be several reasons for that. First, the fan in the Nelco could be just pushing much more air through the unit than is the fan of the Excaliber. The (postulated) higher rate of flow of heated air would drain more power because more heated air is exhausted into the room. This is known as forced convection heat flow. A multispeed fan could be used to cut down the airflow to just that which is needed for the number of trays used, and this would cut down on the power wasted from high heat exhaust.

Second, there could be an insulation effect. The inexpensive Nelco unit has a thin single wall to retain heat, and the structural details of the Excaliber may have a double wall or other means of cutting down on the conduction heat flow through the walls, top and/or bottom.

The inexpensive Nelco can be expanded from 4 to 12 trays, according to my old Nelco instructions. So the drying capacity can be trippled, and it is unknown by how much the power consumed will increase.

I have long ago decided that if I were to buy a dehydrator now, based on what I have learned, I would most likely buy the Excaliber unit, or one of their units, because of the increased capacity that seems to be basic to the unit. I am a little offput by the plastic trays, even though nothing bad has ever happened to them.

MintakaCat
06-20-2009, 10:52
I think you need to go back and read it closer. The graph is of AC current not ac voltage as indicated on the left side.

Also whenever you see 120VAC they are referencing the root mean squared (RMS) voltage and not peak to peak voltage.

Snowleopard
06-20-2009, 11:10
Very nice, MintakaCat!!
If I end up using my Nessco FD-75PR a lot, I guess I'll have to replace it with an Excalibur.
I'll probably dry my first load this week.

MintakaCat
06-20-2009, 11:58
Do you have figures on this capacity difference?


Yes, I covered the capacity in my post.:D



The correct way of calculating average power is to use the definition of instantaneous power.

P=(V)**2/R or P = V*I or P=(I)**2*R where **2 indicates squaring or raising to the second power.


I think if you look closer you will see Ohm’s law applied to the above post where the wattage is calculated.



Resistance is usually taken as a constant in these types of calculations, but current and voltage are explicitly varying at 120 cycles per second, and the voltage varies from a maximum of +170 to a minimum of -170 with an RMS equivalent of 120.



Household voltage is at 60 cycles per second. Are you thinking of 120 cycles per second when you rectify a AC voltage for a DC supply. I doubt there is a rectifier in these heating elements, but I could be wrong.:-? Maybe I could install a 5U4???




You need to take the average of the power as defined above. If you compute the power from the time average values of volts and/or amps, you don't get the same result as if you use the Average of the square of the values.



Honestly, I think you’re trying to split hairs here. Yes, I am aware of the changing curent levels involved in the time constant calculations with resistive loads and the effects of inductive and capacitive factors to those loads. But, I don’t think it would affect the outcome by that much. I think the purpose was to determine if the Nesco used the full 700 watt rating all the time and the tests shows it does not.



It seems evident, nevertheless, that the less expensive Nesco unit loses more heat while maintaining a given temperature (on the average). There could be several reasons for that. First, the fan in the Nelco could be just pushing much more air through the unit than is the fan of the Excaliber.


Yes, this was my point in my second post.



The inexpensive Nelco can be expanded from 4 to 12 trays, according to my old Nelco instructions. So the drying capacity can be trippled, and it is unknown by how much the power consumed will increase.



Yes, increasing the load on the unit would have an impact of power consumption. You can see this in the power ratings of all dehydrators with additional trays to get a feel for additional power required.

Look if you like your Nesco I understand. It seems to be a well built unit. I'm not trying to put them down, I'm just running some honest tests on these units.

But hey, I do enjoy a good technical discussion. We should go hiking sometime and talk electrical power:D

skinewmexico
06-20-2009, 12:41
Cool. Now go buy a L'equip and test it!!

mudhead
06-20-2009, 17:36
OK- Maybe you could translate the geek speak for me.

Which is easier and produces a better product?

For a non technical user.

MintakaCat
06-20-2009, 18:17
OK- Maybe you could translate the geek speak for me.

Which is easier and produces a better product?

For a non technical user.


LOL, no problem.

The Nesco cost less and is expandable.

The Excalibur uses less energy.

They both do the job in about the same amount of time and they both are good products that appear to be well made.

Pedaling Fool
06-21-2009, 09:19
...Another selling point of the Nesco brand is that it dehydrates faster than other models, however in comparing the recommended drying time in both manuals the numbers are approximately the same. There were some foods listed in the Nesco manual that required less drying time than the Excalibur such as apples, peaches, figs, beets and pineapples. However, the Excalibur listed faster drying times for bananas, blueberries, asparagus, corn, mushrooms and peppers...
I'd be interested in a side-by-side comparison to see if the drying times are about the same. The manual of my older dehydrator was way off on estimated drying times.

MintakaCat
06-21-2009, 09:28
I'd be interested in a side-by-side comparison to see if the drying times are about the same. The manual of my older dehydrator was way off on estimated drying times.

Yea, I was thinking of doing that but my schedule is such that I just didn't have the time. For the most part the Excalibur (which I've had for about 6 months now) matches the estimates in the manual. Nesco seems to be a pretty good product so I would bet it's estimates would be spot on.

Besides, I told Kanga she could have the Nesco and I didn't want to hold up that promise. :)

robyn11
07-20-2009, 20:23
If anyone wants to get a bit more exact on what it costs, electricity wise, to run a dehydrator, the below calculator uses residential costs by state. Your local utility may be different but this is a good estimate.

http://food-dehydrator.com/food-dehydrator/calculator/food-dehydrator-electricty-calculator.aspx

Snowleopard
07-20-2009, 20:34
Robyn11, it looks like that site requires knowledge of the average wattage. I suspect that whoever made that calculator didn't think about the fact that the dehydrators cycle on and off to keep the temperature you set. While they are in the on part of the cycle they draw the rated power, 750W for my Nessco 75pr. When it's in the off part of the cycle it draws 0 W.

robyn11
07-20-2009, 22:16
yes, agree, I did say a bit....the average will obviously depend on a number of factors including the dehydrator, temperature set, food load, etc. Thanks

skinewmexico
07-21-2009, 13:32
I just need one with a temperature setting. My Open Country is terrible on veggies.