Refrigerator

[catalinajack]

You're wrong about the Energy Guide. It's not a calculation based on assumptions. Its an actual test under set standards. Here's a link to the government regulation on the test:



https://www.google.com/url?sa=t&sou...AQFnoECB4QAQ&usg=AOvVaw2KStj5uBxrl4_sfrPZguD2



So you're saying a 120 VAC appliance run off a pure sine wave inverter consumes 300% of the electricity of when its plugged into shore power? The refrigerator consumes no more electricity on a pure sine wave inverter. There's no difference as far as what the refrigerator is consuming. The inverter consumes a little more electricity to do the conversion. The average conversion cost is under 10%.



Please show me your math or link an explanation of what your claiming.



Ted

No, Ted, that is not what I said, not even close. Of course, when on AC the fridge consumes exactly the same number of watts when on shore power or an inverter except for one Itty bitty thing, the 13-15% inversion loss factor. And, to my way of thinking, what matters is not the yellow sticker or its methodology, it is the MANUFACTURER'S specs on the power consumption of its compressor motor. And, by the way, please explain how any estimate, the yellow sticker, can be made without an assumption, you know, like how many hours a day will the average fridge run.

You want numbers? Here are some. These are based on a brand new (efficient?) Summit 4.2 c.f. 120VAC fridge as compared to a Vitrifrigo 4.2 model combo AC/DC assuming a duty cycle of 12 hours per day. Adjust as you will for a higher or lesser duty cycle, the assumption part of the equation. The comparison must be done in watts according to Ohm's Law, the only measure that means anything, not the yellow sticker, not somebody's plug-in meter.

The Summit compressor draws 1.0 amp AC.
The Vitrifrigo draws .57 amp AC.
The Vitrifrigo draws 3.75 amp DC.

Summit - 1.0 amp x 120V = 120 watts
Vitrifrigo AC - .57 amp x 120V = 68.4 watts
Vitrifrigo DC - 3.78 amp x 12V = 45 watts

So, assuming a 12-hour per day duty cycle, the Summit uses 1,440 watts while the Vitrifrigo on DC uses 540 watts. On inverter, the Summit will use 1,627 watts factoring in the inversion inefficiency.

As you can see, the marine fridge is far more efficient than the domestic Summit fridge and, yes, when compared to straight DC operation, the number is indeed almost exactly 300%. As requested, I have included a link, a link to the Fluke website which explains Ohm's Law in detail. Ted, there is no escaping the principles of Ohm's Law.

https://www.fluke.com/en-us/learn/blog/electrical/what-is-ohms-law

Now, if you have a large battery bank and you don't care about these numbers, AKA facts, that's fine. If your user profile is such that you marina hop or anchor infrequently, these facts do not matter much. For for some boaters, it is important. None of this considers initial capital cost and is irrelevant to the technical aspects of this discussion. However, I fully recognize that capital cost is relevant in all boating choices. None of this is to say that I would never consider using a domestic fridge on a boat. It all depends.

To bring my calculations to the yellow sticker format ($/year) assuming a cost of $.15/kwh:

Summit - (1,440/day x 365 days x .15) / 1000 = $78.84. Add 13% when on inverter.
Vitrifrigo DC - (540/day x 365 days x .15) / 1000 = $29.57

Obviously, the cost difference may be insignificant but, for some, the amp-hour consumption difference is meaningful. And that, folks, was the one and only point I was trying to make, perhaps ill-explained, but, still, the only point.

Summit - 120 amphours/day
Vitrifrigo - 45 amphours/day

Scale up for larger fridges. One last comment on the yellow sticker. That test would have been conducted in an assumed home environment, that is, in a room that would be at around a constant 70 degrees. Our fridges generally live in a much more demanding environment which requires longer daily duty cycles. Who can argue that any electrical appliance uses twice as much juice when run twice as long. Do your own calculations based on your own environment. The sticker is merely an estimate based on a set of assumptions. It can be no less.

 

[rslifkin]

You're assuming that the duty cycle for both fridges is the same in that comparison. Depending on insulation and how powerful the compressors are, that may not be the case. It's very possible that one may run 60% of the time and the other one only 40%.

Also, for a good size (7+ cubic foot) Danfoss compressor fridge, I'd expect to see draw in the 4 - 5 amp range depending on compressor RPM and fridge condenser and evaporator sizing, airflow, etc. So the 3.78 amp / 45 watt estimate strikes me as a little optimistic.

 

[O C Diver]

So, assuming a 12-hour per day duty cycle, the Summit uses 1,440 watts while the Vitrifrigo on DC uses 540 watts. On inverter, the Summit will use 1,627 watts factoring in the inversion inefficiency.

How totally absurd!

How can you not see that the insulation of the unit determines the cycle rate when the door hasn't been opened.

As a point of reference my Summit refrigerator is more than twice the size of your Vitrifrigo drawers. In a 24 hour day at anchor THE WHOLE BOAT doesn't consume 200 amp hours with an inside temperature in the 70s.

Here is the post from my refrigerator install thread regarding power consumption:

https://www.trawlerforum.com/forums/showpost.php?p=767840&postcount=97

From my test the consumption was 74 amp hours including the inverter. While I don't consider my test super accurate yours are absurd.

Adjusting your estimate of 120 Amp Hours for the size of my 10 cuft. refrigerator, you would estimate my power consumption at 285 Amp Hours. Your estimate looks to be 400% of my test.

Ted

 

[catalinajack]

How totally absurd!



How can you not see that the insulation of the unit determines the cycle rate when the door hasn't been opened.



As a point of reference my Summit refrigerator is more than twice the size of your Vitrifrigo drawers. In a 24 hour day at anchor THE WHOLE BOAT doesn't consume 200 amp hours with an inside temperature in the 70s.



Here is the post from my refrigerator install thread regarding power consumption:



https://www.trawlerforum.com/forums/showpost.php?p=767840&postcount=97



From my test the consumption was 74 amp hours including the inverter. While I don't consider my test super accurate yours are absurd.



Adjusting your estimate of 120 Amp Hours for the size of my 10 cuft. refrigerator, you would estimate my power consumption at 285 Amp Hours. Your estimate looks to be 400% of my test.



Ted

Absurd Ted? Ohm's Law is absurd? Wow! What is absurd is your attempting to compare different sized units and adding insulation into the mix. All I was showing was an apples to apples comparison. Your test is meaningless. I never said at anytime that your fridge was inefficient or inexpensive to operate or that your use calculations are inaccurate. All I said was a fridge of like size and like insulation and in the same enclosure with the same ventilation used for the same number of hours per day, a Danfoss 12VDC compressor will use 1/3 the energy of that which a 120VAC compressor will. That is an immutable fact.

You asked for numbers, I gave them to you. You asked for a reference, I gave it to you. Now you deny Ohm's Law just so that you can make yourself feel good about maybe having made a lesser choice. It's called self-delusion.

And I made no estimate of the power consumption of your fridge and I really don't care. The bottom line is that, when running, your fridge consumes triple the amount of juice that the same fridge used in your environment equipped with a 12VDC compressor would, whatever that amount is. Why is this so difficult for you to understand? Ted, obviously, you do not understand the underlying science and are trying to apply simplistic, meaningless observations to arrive at a completely ill-founded conclusion. Stop digging.

 

[FF]

The key difference between AC and DC refrigeration is the DC compressor on the DC units can be computer controlled to operate at a slower speed as needed..

If only enough power is used to match the heat intake of the box , it is the most efficient system.

So in theory the compressor should work 24/7 , but very slowly and efficiently.

Some mfg. tried this but got complaints "my reefer never shuts off" so now the best units will run 50 min an hour.

 

[rslifkin]

The key difference between AC and DC refrigeration is the DC compressor on the DC units can be computer controlled to operate at a slower speed as needed..

If only enough power is used to match the heat intake of the box , it is the most efficient system.

So in theory the compressor should work 24/7 , but very slowly and efficiently.

Some mfg. tried this but got complaints "my reefer never shuts off" so now the best units will run 50 min an hour.

Some of the new AC units have inverter driven variable speed compressors and do that as well.

 

[O C Diver]

Absurd Ted? Ohm's Law is absurd? Wow! What is absurd is your attempting to compare different sized units and adding insulation into the mix. All I was showing was an apples to apples comparison. Your test is meaningless. I never said at anytime that your fridge was inefficient or inexpensive to operate or that your use calculations are inaccurate. All I said was a fridge of like size and like insulation and in the same enclosure with the same ventilation used for the same number of hours per day, a Danfoss 12VDC compressor will use 1/3 the energy of that which a 120VAC compressor will. That is an immutable fact.

You asked for numbers, I gave them to you. You asked for a reference, I gave it to you. Now you deny Ohm's Law just so that you can make yourself feel good about maybe having made a lesser choice. It's called self-delusion.

And I made no estimate of the power consumption of your fridge and I really don't care. The bottom line is that, when running, your fridge consumes triple the amount of juice that the same fridge used in your environment equipped with a 12VDC compressor would, whatever that amount is. Why is this so difficult for you to understand? Ted, obviously, you do not understand the underlying science and are trying to apply simplistic, meaningless observations to arrive at a completely ill-founded conclusion. Stop digging.

Ok, let's look at this in the absolutely most simplistic way. What is the btu rating of the compressors in these refrigerators? Until you compare BTU output relative to power consumption, your numbers are meaningless.

Can you accept that if the Summit refrigerator compressor has 3 times the capacity (BTUs) of the Vitrifrigo compressor, it will consume 3 times the electricity?

This is no different than understand the compressor in a 15,000 BTU air conditioner will probably consume 3 times the electricity of a compressor in a 5,000 BTU air conditioner. Install these 2 air conditioners in the same room and you will find the 15,000 BTU unit runs about 1/3 as much as the 5,000 BTU unit and consume roughly the same kilowatts.

Why don't you just put the Summit refrigerator on your boat, put a killowatt consumption meter on both and run them for a week to compare actual power consumption.

How about posting the Summit refrigerator model number here, so we can see which one you're referring to.

Ted

 

[GoneDiving]

Some of the new AC units have inverter driven variable speed compressors and do that as well.

Here in Australia, you will struggle to buy a name brand AC fridge that isn't inverter controlled. It's only the cheapest, no frills, bar fridges that aren't.

With the level of legislation, reporting and star ratings (not to mention sheer economies of scale) it would be hard to find more volume per $ or volume per kWh than a residential unit. The one area they may loose out on is insulation thickness but that's about it.

 

[catalinajack]

Ok, let's look at this in the absolutely most simplistic way. What is the btu rating of the compressors in these refrigerators? Until you compare BTU output relative to power consumption, your numbers are meaningless.



Can you accept that if the Summit refrigerator compressor has 3 times the capacity (BTUs) of the Vitrifrigo compressor, it will consume 3 times the electricity?



This is no different than understand the compressor in a 15,000 BTU air conditioner will probably consume 3 times the electricity of a compressor in a 5,000 BTU air conditioner. Install these 2 air conditioners in the same room and you will find the 15,000 BTU unit runs about 1/3 as much as the 5,000 BTU unit and consume roughly the same kilowatts.



Why don't you just put the Summit refrigerator on your boat, put a killowatt consumption meter on both and run them for a week to compare actual power consumption.



How about posting the Summit refrigerator model number here, so we can see which one you're referring to.



Ted

Sure, I can accept that but that is not the point. Of course, a unit that produces three times the number of BTU will consume three times the energy. How many times do I have to say the same thing? Any comparison must be done like-for-like, used in the same environment. The Summit model is #AL55.

 

[sbman]

Sure, I can accept that but that is not the point. Of course, a unit that produces three times the number of BTU will consume three times the energy. How many times do I have to say the same thing? Any comparison must be done like-for-like, used in the same environment. The Summit model is #AL55.

I have found that at least in San Diego, my household fridge draws within 20% of the energy star label each day, the conditions here must be pretty similar to the testing.

Have you measured how many watts your fridges use per day? I'd be interested to know that number, their cubic storage size and the approximate condition (temperature) the measurement was taken in.

 

[kthoennes]

I just want the beer to stay cold without killing my batteries.

 

[O C Diver]

Sure, I can accept that but that is not the point. Of course, a unit that produces three times the number of BTU will consume three times the energy. How many times do I have to say the same thing? Any comparison must be done like-for-like, used in the same environment. The Summit model is #AL55.

Ok, so here is the Energy Guide for the AL55:



Doing the math, we find it consumes .68 killowatts (680 watts) per day if you don't open the fridge. After factoring in the inverter inefficiency (15%), projected power consumption is 782 watts. Catalinajack's estimate was 1,627 watts.

While there are no published consumption numbers for the Vitrifrigo units Catalinajack's numbers are 540 watts per day on AC. So the difference between the 2 unit on AC is 140 watts per day.

Worth noting is that the AL55 isn't an Energy Star appliance. There are appartment units that are significantly more efficient than this one.

Ted

 

[sbman]

Ok, so here is the Energy Guide for the AL55:

View attachment 123121

Doing the math, we find it consumes .68 killowatts (680 watts) per day if you don't open the fridge. After factoring in the inverter inefficiency (15%), projected power consumption is 782 watts. Catalinajack's estimate was 1,627 watts.

While there are no published consumption numbers for the Vitrifrigo units Catalinajack's numbers are 540 watts per day on AC. So the difference between the 2 unit on AC is 140 watts per day.

Worth noting is that the AL55 isn't an Energy Star appliance. There are appartment units that are significantly more efficient than this one.

Ted

https://www.vitrifrigo.com/ww/en/drw70a-all-in-one-single-compartment

I looked them up and a Vitifrigo DRW70A states 250 watts per 24 hours with fridge at -4C and 25C air temp. It's a 2.8 cubic foot drawer fridge that I looked up that runs on 12 or 24 volts DC.

That's 88 watts per cubic foot per day for the Vitifrigo.

My Magic Chef 9.9 cu. ft household fridge uses 1000W including inverter losses and 24x7 inverter idle power on a 77-82 degree day with no openings (less on a cooler day of course). 101Watts per hour per cubic foot. That's with both a freezer and a fridge in one unit, so it's not a direct comparison. I power it with 1200W of hard panel solar, so I've got the power budget to keep it running.

The household fridge is clearly not 3X more power usage though. 15-20% more power consumption for the Magic Chef over a Vitifrigo in real life usage is more like it. Comparing like-like requires comparing the overall system in a similar real world setting.

A Vitifrigo is ~ $750/cubic foot. My household fridge is ~ $100/cu ft including a dedicated inverter to run it. The Vitifrigo is clearly a higher end product that has many attributes that make it a desirable solution, power consumption is just one point. Fitment, quality, warranty, etc...

 

[O C Diver]

https://www.vitrifrigo.com/ww/en/drw70a-all-in-one-single-compartment

I looked them up and a Vitifrigo DRW70A states 250 watts per 24 hours with fridge at -4C and 25C air temp. It's a 2.8 cubic foot drawer fridge that I looked up that runs on 12 or 24 volts DC.

That's 88 watts per cubic foot per day for the Vitifrigo.

My Magic Chef 9.9 cu. ft household fridge uses 1000W including inverter losses and 24x7 inverter idle power on a 77-82 degree day with no openings (less on a cooler day of course). 101Watts per hour per cubic foot. That's with both a freezer and a fridge in one unit, so it's not a direct comparison. I power it with 1200W of hard panel solar, so I've got the power budget to keep it running.

The household fridge is clearly not 3X more power usage though. 15-20% more power consumption for the Magic Chef over a Vitifrigo in real life usage is more like it. Comparing like-like requires comparing the overall system in a similar real world setting.

A Vitifrigo is ~ $750/cubic foot. My household fridge is ~ $100/cu ft including a dedicated inverter to run it. The Vitifrigo is clearly a higher end product that has many attributes that make it a desirable solution, power consumption is just one point. Fitment, quality, warranty, etc...

Thanks!
Interestingly waypoint on their power consumption. A shame the 4.2 cuft drawer isn't listed on the site.

Ted

 

[catalinajack]

https://www.vitrifrigo.com/ww/en/drw70a-all-in-one-single-compartment

I looked them up and a Vitifrigo DRW70A states 250 watts per 24 hours with fridge at -4C and 25C air temp. It's a 2.8 cubic foot drawer fridge that I looked up that runs on 12 or 24 volts DC.

That's 88 watts per cubic foot per day for the Vitifrigo.

My Magic Chef 9.9 cu. ft household fridge uses 1000W including inverter losses and 24x7 inverter idle power on a 77-82 degree day with no openings (less on a cooler day of course). 101Watts per hour per cubic foot. That's with both a freezer and a fridge in one unit, so it's not a direct comparison. I power it with 1200W of hard panel solar, so I've got the power budget to keep it running.

The household fridge is clearly not 3X more power usage though. 15-20% more power consumption for the Magic Chef over a Vitifrigo in real life usage is more like it. Comparing like-like requires comparing the overall system in a similar real world setting.

A Vitifrigo is ~ $750/cubic foot. My household fridge is ~ $100/cu ft including a dedicated inverter to run it. The Vitifrigo is clearly a higher end product that has many attributes that make it a desirable solution, power consumption is just one point. Fitment, quality, warranty, etc...

I give up. You guys are comparing different units and trying to extrapolate. And using the energy stickers, AGAIN, means nothing. The only comparison that means anything is the actual consumption when the compressor is running. How long it runs dictates how much energy it uses and to make any sort of comparison that means anything it must be done with units of the same size in the same environment. I really don't understand why this is so difficult to comprehend. Ohm's Law is incontrovertible. In an earlier post I laid out all the numbers. I suggest you all go back and try to understand it. It is what it is. Trying to reckon this with some sort of layman's logic just doesn't work. Truth be told, it took me a long time and lots of reading before I came to understand the science but it is science and the laws of science are, yes, laws, not theories, not postulates.

 

[O C Diver]

I give up. You guys are comparing different units and trying to extrapolate. And using the energy stickers, AGAIN, means nothing. The only comparison that means anything is the actual consumption when the compressor is running. How long it runs dictates how much energy it uses and to make any sort of comparison that means anything it must be done with units of the same size in the same environment. I really don't understand why this is so difficult to comprehend. Ohm's Law is incontrovertible. In an earlier post I laid out all the numbers. I suggest you all go back and try to understand it. It is what it is. Trying to reckon this with some sort of layman's logic just doesn't work. Truth be told, it took me a long time and lots of reading before I came to understand the science but it is science and the laws of science are, yes, laws, not theories, not postulates.

Nobodys questioning Ohm's Law, it's your assumption of a 50% duty cycle that has no basis in fact. If you can't prove your assumption (your term) of a 50% duty cycle, your killowatt consumption numbers are meaningless.

Ted

 

[hollywood8118]

It is simply how many amp hours of DC you use in a given length of time for either a DC unit or a AC with inverter, nothing more. All refrigerators made for either residential or marine use could do better, just look at the efficiency of the Dc units used in off grid homes for real energy savings.

HOLLYWOOD

 

[sbman]

I give up. You guys are comparing different units and trying to extrapolate. And using the energy stickers, AGAIN, means nothing. The only comparison that means anything is the actual consumption when the compressor is running. How long it runs dictates how much energy it uses and to make any sort of comparison that means anything it must be done with units of the same size in the same environment. I really don't understand why this is so difficult to comprehend. Ohm's Law is incontrovertible. In an earlier post I laid out all the numbers. I suggest you all go back and try to understand it. It is what it is. Trying to reckon this with some sort of layman's logic just doesn't work. Truth be told, it took me a long time and lots of reading before I came to understand the science but it is science and the laws of science are, yes, laws, not theories, not postulates.

No it doesn't matter one bit what the instantaneous current draw of the compressor is. There's more to electrical theory than ohms law, the power equation is pretty important too and Watt Hours are a much better unit to use for comparison.

Its a very simple comparison from unit to unit. For the vitifrigo I looked at, the manufacturer states how much power is used in total in 24 hours, at a given room temperature and fridge temperature. Where is the extrapolation?? Are they lying? At the price they charge for their units, I'd hope they ran an actual test and used their results to make that statement!

Total energy used is inherent in the design and is the total energy load required for that particular unit to maintain the temperature they state in the environment they state. What difference does it make if the device uses 2.5 amps running or 120V or 12V or 40 amps running or if it runs 50% of the time or 10% of the time? It's the overall system performance that matters. This can be divided over the amount of cubic storage it contains to get a rating of how much power is needed to cool that much storage space for that particular unit. Watt hours per cubic foot. It's very simple.

My fridge in 75-85 degree room temperature (boat warms up during the day) draws about 1000W with ALL variables accounted for, my monitoring system measures the energy consumption, it tracks room temp and current/voltage on both the AC and DC sides of the system so I know exactly how much energy it uses and the conversion losses. I know what size it is too. I can post charts and graphs. So far today it's used 900W and there's three more hours to go today so I think it's going to come in at about 1000W yet again for the day. Funny thing is, it's almost exactly what the yellow sticker said it would be.

There's no guessing or labels, just cold hard facts. I can also see the duty cycle and the instantaneous current. It draws 84-120 watts when running. What does that matter? The total energy consumed to do the work over a period of time is what matters and that's 1000W, 78.125 amps out of my 12.5V battery bank in 24 hours in a 75 degree environment.

Actually the 'energy star' labels are very good and are in no way meaningless. It happens that I've measured several fridges in houses at average room temperatures (75 degrees) and over time they actually draw what the energy sticker says they will. You can take the energy star KWhr number, divide by 365 and have a really good idea of how much power it will draw per day in typical room temperatures.

My fridge is 'energy star' rated at 329KWhr/yr. Divide by 365 days and you get 900 Watts per day. With my inverter losses added in, it's pretty dang close to that as I've measured it, repeatedly. How could that yellow label have known that after putting in all that time and effort on equipment to measure and monitor that I'd come up with basically the same number? It's almost like someone tested it and used the results to make the sticker.

 

[catalinajack]

No it doesn't matter one bit what the instantaneous current draw of the compressor is. There's more to electrical theory than ohms law, the power equation is pretty important too and Watt Hours are a much better unit to use for comparison.



Its a very simple comparison from unit to unit. For the vitifrigo I looked at, the manufacturer states how much power is used in total in 24 hours, at a given room temperature and fridge temperature. Where is the extrapolation?? Are they lying? At the price they charge for their units, I'd hope they ran an actual test and used their results to make that statement!



Total energy used is inherent in the design and is the total energy load required for that particular unit to maintain the temperature they state in the environment they state. What difference does it make if the device uses 2.5 amps running or 120V or 12V or 40 amps running or if it runs 50% of the time or 10% of the time? It's the overall system performance that matters. This can be divided over the amount of cubic storage it contains to get a rating of how much power is needed to cool that much storage space for that particular unit. Watt hours per cubic foot. It's very simple.



My fridge in 75-85 degree room temperature (boat warms up during the day) draws about 1000W with ALL variables accounted for, my monitoring system measures the energy consumption, it tracks room temp and current/voltage on both the AC and DC sides of the system so I know exactly how much energy it uses and the conversion losses. I know what size it is too. I can post charts and graphs. So far today it's used 900W and there's three more hours to go today so I think it's going to come in at about 1000W yet again for the day. Funny thing is, it's almost exactly what the yellow sticker said it would be.

There's no guessing or labels, just cold hard facts. I can also see the duty cycle and the instantaneous current. It draws 84-120 watts when running. What does that matter? The total energy consumed to do the work over a period of time is what matters and that's 1000W, 78.125 amps out of my 12.5V battery bank in 24 hours in a 75 degree environment.



Actually the 'energy star' labels are very good and are in no way meaningless. It happens that I've measured several fridges in houses at average room temperatures (75 degrees) and over time they actually draw what the energy sticker says they will. You can take the energy star KWhr number, divide by 365 and have a really good idea of how much power it will draw per day in typical room temperatures.



My fridge is 'energy star' rated at 329KWhr/yr. Divide by 365 days and you get 900 Watts per day. With my inverter losses added in, it's pretty dang close to that as I've measured it, repeatedly. How could that yellow label have known that after putting in all that time and effort on equipment to measure and monitor that I'd come up with basically the same number? It's almost like someone tested it and used the results to make the sticker.

Okay. Here is what I will do. Tonight, I am going to turn off shore power and turn off all loads other than my two 4.2 c.f. Vitrifrigos. In the morning after X number of hours, at least eight, I will observe the number of amp-hours drawn from the batteries and extrapolate to 24 hours. Perhaps I will have to eat crow and I will stand up and do so if that is the case. I will leave it to you to judge.

As for Vitrifrigo lying about their product's consumption I suppose so but I would be interested to know what numbers they report. I get the impression that the numbers are pretty good else why would you be so skeptical. How could they arrive at their number without running a controlled test pretty much what you are reporting? The 78.125 amp-hours you state, does that number come from your battery monitor?

Why does it matter that your fridge is consuming 84 - 120 watts when running. Oh, I don't know, perhaps it is analogous to how much fuel is being consumed when my diesel engine is running.

 

[kthoennes]

I know electric guys love to debate each other, but even with my relative limited knowledge, it seems to me this debate is getting kind of silly. I think we get it - I drive a Nissan Squirt (or whatever) that gets 100 miles to the gallon, and I burn 6 gallons driving to Chicago. Or I drive a Caterpillar earth mover that gets 1 mile to the gallon, and I burn 600 gallons driving to Chicago. On one hand we're talking about instantaneous or at least per unit efficiency. On the other hand we're talking about cumulative fuel burn. If my objective is only to move my body from point A to point B - or in this case keep the beer cold as efficiently as possible - the Nissan Squirt is better.

And if you toss me the keys to both and tell me to get to Chicago, same route, with as little fuel consumption as possible, quote me the mpg or the cumulative fuel burn, ultimately doesn't matter, I'll still take the Nissan.

 

[Datenight]

I know electric guys love to debate each other, but even with my relative limited knowledge, it seems to me this debate is getting kind of silly. I think we get it - I drive a Nissan Squirt (or whatever) that gets 100 miles to the gallon, and I burn 6 gallons driving to Chicago. Or I drive a Caterpillar earth mover that gets 1 mile to the gallon, and I burn 600 gallons driving to Chicago. On one hand we're talking about instantaneous or at least per unit efficiency. On the other hand we're talking about cumulative fuel burn. If my objective is only to move my body from point A to point B - or in this case keep the beer cold as efficiently as possible - the Nissan Squirt is better.

And if you toss me the keys to both and tell me to get to Chicago, same route, with as little fuel consumption as possible, quote me the mpg or the cumulative fuel burn, ultimately doesn't matter, I'll still take the Nissan.

:lol:

Rob

 

[FF]

"Some of the new AC units have inverter driven variable speed compressors and do that as well".

Great , its about time ! I know the air cond with mini splits do this , so reefers are finally catching up.

Its sad that the large noisemaker folks haven't caught on and most still run at a specific RPM , even with tiny loads.

The small camping gen sets have had inverter output and variable speed for decades.


************

"I just want the beer to stay cold without killing my batteries."

Me too, that's why we prefer use propane ,

 

[O C Diver]

No it doesn't matter one bit what the instantaneous current draw of the compressor is. There's more to electrical theory than ohms law, the power equation is pretty important too and Watt Hours are a much better unit to use for comparison.

Its a very simple comparison from unit to unit. For the vitifrigo I looked at, the manufacturer states how much power is used in total in 24 hours, at a given room temperature and fridge temperature. Where is the extrapolation?? Are they lying? At the price they charge for their units, I'd hope they ran an actual test and used their results to make that statement!

Total energy used is inherent in the design and is the total energy load required for that particular unit to maintain the temperature they state in the environment they state. What difference does it make if the device uses 2.5 amps running or 120V or 12V or 40 amps running or if it runs 50% of the time or 10% of the time? It's the overall system performance that matters. This can be divided over the amount of cubic storage it contains to get a rating of how much power is needed to cool that much storage space for that particular unit. Watt hours per cubic foot. It's very simple.

My fridge in 75-85 degree room temperature (boat warms up during the day) draws about 1000W with ALL variables accounted for, my monitoring system measures the energy consumption, it tracks room temp and current/voltage on both the AC and DC sides of the system so I know exactly how much energy it uses and the conversion losses. I know what size it is too. I can post charts and graphs. So far today it's used 900W and there's three more hours to go today so I think it's going to come in at about 1000W yet again for the day. Funny thing is, it's almost exactly what the yellow sticker said it would be.

There's no guessing or labels, just cold hard facts. I can also see the duty cycle and the instantaneous current. It draws 84-120 watts when running. What does that matter? The total energy consumed to do the work over a period of time is what matters and that's 1000W, 78.125 amps out of my 12.5V battery bank in 24 hours in a 75 degree environment.

Actually the 'energy star' labels are very good and are in no way meaningless. It happens that I've measured several fridges in houses at average room temperatures (75 degrees) and over time they actually draw what the energy sticker says they will. You can take the energy star KWhr number, divide by 365 and have a really good idea of how much power it will draw per day in typical room temperatures.

My fridge is 'energy star' rated at 329KWhr/yr. Divide by 365 days and you get 900 Watts per day. With my inverter losses added in, it's pretty dang close to that as I've measured it, repeatedly. How could that yellow label have known that after putting in all that time and effort on equipment to measure and monitor that I'd come up with basically the same number? It's almost like someone tested it and used the results to make the sticker.

Thank you!

Clearly you explained it better than I did.

Ted

 

[rslifkin]

Its sad that the large noisemaker folks haven't caught on and most still run at a specific RPM , even with tiny loads.

The small camping gen sets have had inverter output and variable speed for decades.

With gensets, it's a tradeoff. Most bigger units run at low enough RPM that the noise advantage of variable speed isn't as big. And it's a mixed bag on fuel economy. The inverter units are more efficient under light load, but less efficient than a standard unit when closer to full load. And unless you oversize the inverter significantly (at great extra cost), they don't generally have the same motor starting grunt as an equivalent rating standard genset (assuming both gensets have adequately sized engines for their rated output).

 

[O C Diver]

"Some of the new AC units have inverter driven variable speed compressors and do that as well".

Great , its about time ! I know the air cond with mini splits do this , so reefers are finally catching up.

Its sad that the large noisemaker folks haven't caught on and most still run at a specific RPM , even with tiny loads.

The small camping gen sets have had inverter output and variable speed for decades.

The unfortunate down side to this technology is it's sensitivity to surges and distant lightning. A power surge took out the control board and blower motor on my home central air unit. The blower motor being variable speed with the control module on top and a dozen wires going to it, would have been $800 (not counting labor) if not covered under warranty. Asked the technician what a normal motor would cost. His comment was that they don't fail from momentary power surges.

Better have a good warranty with some of this new technology.

Ted

 

[sbman]

I know electric guys love to debate each other, but even with my relative limited knowledge, it seems to me this debate is getting kind of silly. I think we get it - I drive a Nissan Squirt (or whatever) that gets 100 miles to the gallon, and I burn 6 gallons driving to Chicago. Or I drive a Caterpillar earth mover that gets 1 mile to the gallon, and I burn 600 gallons driving to Chicago. On one hand we're talking about instantaneous or at least per unit efficiency. On the other hand we're talking about cumulative fuel burn. If my objective is only to move my body from point A to point B - or in this case keep the beer cold as efficiently as possible - the Nissan Squirt is better.

And if you toss me the keys to both and tell me to get to Chicago, same route, with as little fuel consumption as possible, quote me the mpg or the cumulative fuel burn, ultimately doesn't matter, I'll still take the Nissan.

Well, the claim is that a particular brand of drawer fridge is 3X more efficient than a household fridge. This would be fantastic news, amazing in fact. Like saying you can drive a Volvo earth mover to Chicago on 200 gallons instead of 600 that the CAT uses.

At some point you run out of either energy input (in my case solar) or storage capacity (batteries) and a fridge using so much less power would be worth the money in that case even to someone cheap like me. Energy saved is energy you don't have to produce and store.

 

[sbman]

Okay. Here is what I will do. Tonight, I am going to turn off shore power and turn off all loads other than my two 4.2 c.f. Vitrifrigos. In the morning after X number of hours, at least eight, I will observe the number of amp-hours drawn from the batteries and extrapolate to 24 hours. Perhaps I will have to eat crow and I will stand up and do so if that is the case. I will leave it to you to judge.

As for Vitrifrigo lying about their product's consumption I suppose so but I would be interested to know what numbers they report. I get the impression that the numbers are pretty good else why would you be so skeptical. How could they arrive at their number without running a controlled test pretty much what you are reporting? The 78.125 amp-hours you state, does that number come from your battery monitor?

Why does it matter that your fridge is consuming 84 - 120 watts when running. Oh, I don't know, perhaps it is analogous to how much fuel is being consumed when my diesel engine is running.

https://www.vitrifrigo.com/us/us/drw180a-all-in-one-single-compartment_2

The numbers Vitifrigo post are well within reason for their little drawer fridge. It's a bit more efficient overall than my household fridge. The numbers they post for it in freezer mode are terrible. They state 1.1 kWh/24h (12/24Vdc) for a small 2.8 cu/ft freezer. That's more power than my entire 9.9 fridge uses with a freezer about the same size attached.

Your test/measurement would be very interesting. 24 hours would be better, but 8 will tell some of the story. I am not skeptical of the numbers Vitifrigo posts, they sound correct. I'm not skeptical of energy star numbers either, I've measured enough fridges to know their testing is pretty accurate. I'm skeptical that any fridge is 3X more efficient than any other.

The Ah consumption is from my battery monitor, yes. Remember that Ah is a unit of Amps/Hour, but that is not power/hour because voltage is not included. Power is volts * amps = watts. Energy consumption is measured in Watts/hr = Wh. Your battery monitor integrates the data with samples taken multiple times per second which is helpful because neither voltage or current is stable, they vary. Integrating Volts*amps gives you the real picture.

If we were measuring your diesel engine and trying to compare our boats MPG, we would not take your idling fuel consumption, multiply it by the hours required to go a distance and then claim that's the boats MPG. Nor would we put it in gear against the anchor and, note it's fuel consumption and multiply that by a few hours to find the MPG. We'd motor up and down a measured course in both directions (to cancel out wind and current variations) a few times and make notes of the consumption to do so, divide by our fixed course distances, then we could compare notes on our MPGs. That would account for the entire system, hull design, propeller losses, engine design, weight, transmission losses, etc...

 

[sbman]

I know electric guys love to debate each other, but even with my relative limited knowledge, it seems to me this debate is getting kind of silly. I think we get it - I drive a Nissan Squirt (or whatever) that gets 100 miles to the gallon, and I burn 6 gallons driving to Chicago. Or I drive a Caterpillar earth mover that gets 1 mile to the gallon, and I burn 600 gallons driving to Chicago. On one hand we're talking about instantaneous or at least per unit efficiency. On the other hand we're talking about cumulative fuel burn. If my objective is only to move my body from point A to point B - or in this case keep the beer cold as efficiently as possible - the Nissan Squirt is better.

And if you toss me the keys to both and tell me to get to Chicago, same route, with as little fuel consumption as possible, quote me the mpg or the cumulative fuel burn, ultimately doesn't matter, I'll still take the Nissan.

Also. Toss me the keys to both and I'd take the CAT to Chicago always. Given that opportunity I don't care about fuel consumption.

 

[Mako]

LOL. Or you could drive this and get 35 feet per gallon at 1 mph

 

[Alaskaflyer]

Why does it matter that your fridge is consuming 84 - 120 watts when running. Oh, I don't know, perhaps it is analogous to how much fuel is being consumed when my diesel engine is running.

Edit:never mind, someone else hit it.

I for one am following with interest.