Fridge consumption

pessimist

pessimist

Well-Known Member
Joined
7 May 2003
Messages
3,210
Location
Exmoor. Boat in Dartmuff.
Visit site
We thought we'd carry out an electricity usage audit on the boat starting with the fridge as it's generally acknowledged to be the greatest power hog. We bought an instrument similar to this to enable us to measure the consumption of individual items. We have a cabinet style fridge with no added insulation. I assume it is old but it is compressor driven. The device gives a total consumption of 34ah over a 24hour period. Shurely shome mishtake? I was expecting a rather higher figure. Is it possible or is my shiny new measuring toy wildly inaccurate?
Your thoughts welcome.
 
pessimist said:
We thought we'd carry out an electricity usage audit on the boat starting with the fridge as it's generally acknowledged to be the greatest power hog. We bought an instrument similar to this to enable us to measure the consumption of individual items. We have a cabinet style fridge with no added insulation. I assume it is old but it is compressor driven. The device gives a total consumption of 34ah over a 24hour period. Shurely shome mishtake? I was expecting a rather higher figure. Is it possible or is my shiny new measuring toy wildly inaccurate?
Your thoughts welcome.
Click to expand...

It depends on the duty cycle of the Fridge, ie how often it's actually working.

Mine draws 4 amps, however with a 50% cycle that's 48 AH, a 40% cycle would be 38.4 AH.

The duty cycle will be affected by the temperature the fridge is set at, the outside temperature etc.

Therefore having it set at 4 degrees C in a summer temp of 25 degrees C ambient will require more power than 4 degrees C in an ambient temp of 10 degrees C in the winter.

Also, it will not work as hard in the night as the ambient temp cools down.
 
Not sure about the duty cycle, particularly overnight, and haven't found a thermostat. The reading was taken over 24 hours last week when the temperature was in the high twenties. Very suspicius.
 
pessimist said:
No manual I'm afraid and I can't find one online.
Click to expand...

Ahhh,, that old problem.

Some of the meters will show the total time that power is being used, which would allow you to work out the duty cycle. Or alternatively sit close to it with a stopwatch for an hour :eek:

It's hard to confirm the reading without something to compare it to, but I wouldn't be surprised if 34 AH over 24 hours is pretty close.
 
I don't see why it is suspicious at all. Dolabriform has provided some quite representative figures, if anything I'd think his 40% cycle rather high for a reasonably insulated fridge. Your machine's reading is perfectly credible. If you don't trust it try running a known load on it with an ammeter in curcuit as referee - it only need be a halogen cabin light for instance (or even the fridge itself). As long as it measures the operating consumption correctly and shows close to zero when it isn't working - and that agrees with the ammeter you will prove its accuracy in a matter of minutes.
 
We have what must be about 100l top opening fridge and it draws on average about 2.1-2.2amps when the compressor is on. I recon it is on for maybe 1/4 to 1/3 of the time on average. It will work more depending on how often you open the door as well. So we are around 20ah in a day. And that was last week in the high 20s.

I've never used an amp meter, just the shore power charger current reading when the fridge goes on or off.
 
One other thing to add, it also depends on how full the fridge is and with what.
Different substances have different thermodynamic properties, air probably being the worst. So if you have a 1/4 full front loading fridge, every time you open the door a large amount of the cold will escape!
 
All high density stuff which gives good thermodynamic properties in the fridge, it is only used for gin, tonic, beer and ice cubes. ?
 
A reasonably accurate clamp meter confirms my modern portable engle topl8ader to draw 2 amps when running, A pals old front opening fixed cabinet style engle surprised me with only a 3 amp draw ,however poor insulation mean more frequent demand.
Was surprised by a huge 6 amp plotter draw ( full brightness on screen) obviously only concern when sailing. A big draw on the domestic water pump circa 7 amps..Good job he didn't install the victorian style bath in the forpeak
 
From practical experience I work on 24 hrs stopped per 100Ah battery per fridge.
This is given the usable capacity of one battery is 50Ah and it might not be fully charged when you stop.
Hot weather can eat into that .
I am pleased we only have the one fridge. I guess a new replacement fridge might consume less energy.
 
dolabriform said:
Different substances have different thermodynamic properties, air probably being the worst. So if you have a 1/4 full front loading fridge, every time you open the door a large amount of the cold will escape!
Click to expand...
Air maybe worst in the sense that it does not store much energy, compared to e.g. water, but this actually means the opposite of what was suggested above.
Heating or cooling air requires very little energy, the volumetric heat capacity of air is 3000+ times less than that of water,

A 0.33l can of beer you put in the fridge will take the same amount of energy to cool down as it takes to cool down 1000 litres of air -- that is completely replacing all of the air in a 100l fridge with room temperature air 10 times. Of course not all air gets replaced when you open the door, so the amount of cold that escapes is really quite small.
 
But your cans of beer don’t fall out each time you open the door and get replaced with new warm cans
 
I have just done exactly the same and after a number of days my energy consumption averages 1a per hour.
I run the 130l fridge continuously at its lowest setting which is sufficient to keep the beers cold and make ice cubes for the g&t.
I'd agree that this was less than expected but I have no reason to think the data suspect.
I'm currently in Portugal so not encountered the 30+ days if the med yet which may require a higher setting.

I'm going to switch to analysing the auto pilot next. Any thoughts on if this will consume more power than the fridge on a passage?
 
You must log in or register to reply here.

Share this page

Top