Momac
Well-Known Member
Provide one 110Ah leisure battery per fridge for every 24hrs that you wish to be stopped without charging batteries.
Fridge power consumption
- Thread starter pessimist
- Start date
PaulRainbow
Well-Known Member
You said "A fridge should be designed to not cycle frequently as cycling is a cause of considerable efficiency losses, so to run longer at lower pump speeds is the optimum situation. I would suggest a fridge running at 1/3 duty cycle is incorrectly set up and needs a lower pump speed. "
So if it's not meant to cycle frequently, why is a 1/3 cycle wrong ? Especially when the figures you quote for the domestic fridge suggest that's exactly what that one is doing.
Do you know what my pump speed is set to ? I don't need to improve things, my fridge is set to a low temp and is switched on 24/365 It's a very economical fridge and during Summer months my boat is entirely self sufficient in terms of electricity.
Yet you would rather use a DC compressor, which then converts power internally to AC to run the motor? You are going to waste power that way anyway.
There you go again, distorting figures. The domestic fridge you linked t is running a 1/3 cycle to get to the figures you quote. Yet you keep constantly using 2/3 or now 50% cycles for a boar fridge.
Oh right, so your cheap domestic fridge figures are spot on, but marine fridge manufacturers are quoting incorrect figures.
If it was such a great idea to fit domestic fridges, such as the £180 one you link to, why do you suppose all of the boat builders are fitting DC fridges costing several times that ?
William_H
Well-Known Member
For the OP re a timer. You can make a temporary timer from a clock with an electronic movement. They run on 1.5v battery. You can get 1.5 volts from a voltage divider of a 1000 ohm resistor and a 120 ohm resistor in series across the 12v supply. (as switched by the thermostat) wire the clock across the 120 ohm resistor on the negative side in place of the battery. Or drive the clock froma buck converter set for 1.5v output. Just set the clock to 12 hrs and note the time on the clock after a period 24hrs or whatever is convenient.
Re cooling of the system. yes we tend to think of the condensor coils as the part needing cooling but the compressor itself gets hot and should be cooled with a fan.
ol'will
Re cooling of the system. yes we tend to think of the condensor coils as the part needing cooling but the compressor itself gets hot and should be cooled with a fan.
ol'will
Zing
Well-Known Member
If you run a duty cycle of 1/3 you are cycling twice as often as with a 2/3 duty cycle. That’s my point and of course I don’t know or need to know your pumps speed. Just set it slower is my polite advice, especially if you have long pipe runs with a high refrigerant volume.
A DC compressor and an AC compressor are both AC. You just choose how to feed it by buying a DC input or an AC input unit. The compressor does the conversion if needed with a DC input, so your not wanting to use an inverter is not capable of being resolved.
No distortion, the comparison makes my point better. If my marine installation ran slower it would be even worse.
I just picked a random fridge, so as to not over argue with extreme examples. There are much better fridges and if you look at the 4* fridges, my point is made even better and they are still cheaper than marine fridges.
I’m away now. I won’t be able to respond for a while.
PaulRainbow
Well-Known Member
Far too much nonsense for me to waste any additional time replying to you.
Have a nice day.
vyv_cox
Well-Known Member
By 1/3 and 2/3 do you mean compressor on in the first figure and total time in the second? Running a fridge that is on for 2/3 of the time cannot possibly be more efficient than one that is on for 1/3 of the time. If by efficiency you mean the same as I do, i.e. achieving the desired result with the minimal input of power. My battery bank would not survive 2/3 for one night, whereas at 1/3 it runs the whole summer.
PaulRainbow
Well-Known Member
In post #15 i said "Your figures are distorted. if the fridge on your boat runs 2/3 of the time, it's a poor installation, mine runs for about 1/3 of the time. "
Zing now claims "If you run a duty cycle of 1/3 you are cycling twice as often as with a 2/3 duty cycle. "
Makes no sense to me.
Caladh
Well-Known Member
Tbh Zing, on this forum it’s a bit of a waste of time trying to argue with Paul as he is an extremely well respected boat expert on all things electric. As Paul says, if your figures are correct why don’t we all use inverters with 230v domestic fridges ? unless I missed it I’d be interested to know what your boat is and your power setup ie. no and size of batteries, solar, generator etc
Zing
Well-Known Member
It's not actually possible to run it longer unless you leave the door open. What I was saying is you have a choice of running the compressor slowly and running it more often in the cooling cycles. In the example I gave, every time the fridge cycles between set points of on and off it will run twice as often if the pump runs twice the time during the cool cycle - a cooling duty cycle of 1/3 of continuous cooling run time will result in twice as many stop start cycles compared to when you run slower to achieve 2/3.
Each time you turn on you have to pump a vacuum, which produces zero cooling. That is where energy is lost and why a longer pump run time, all other things being equal, is more efficient.
Plum
Well-Known Member
Agree with your quoted typical figure of a boat fridge. I have the Waeco CRX50 fridge and according to my measurements and timmings the annual energy consumption works out at 105kWh ! .
www.solocoastalsailing.co.uk
Plum
Well-Known Member
You are not comparing like for like. For the same heatpump efficiency and insulation efficiency, a smaller fridge will be less efficient as, for its smaller volume, it has a proportionately larger surface area, hence greater heat tranfer.
www.solocoastalsailing.co.uk
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Zing
Well-Known Member
There’s a test done here, which supports my contention that bog standard mains powered units are the most efficient. Note he didn’t even use an efficient one, so much better results are possible:
PaulRainbow
Well-Known Member
Seriously ?
At 49:00 did my ears deceive me, or did he say the gas absorption fridge was the one to have on your boat or caravan ?
Besides, who in their right mind would accept a presentation from Sterling, where (assuming you ignored his advice to use the gas fridge) the conclusion is you use a domestic fridge and one of his inverters.
Neeves
Well-Known Member
A good way to make your fridge more efficient - don't open the door, or not frequently and keep it full.
Jonathan
Jonathan
[70521]
Well-Known Member
I also fill empty spaces with styrofoam chips, you know the stuff you get in packaging. More insulation.
PaulRainbow
Well-Known Member
Neither did he use one of the more modern 12v fridges with a DC compressor.
Charlie also suggests that buying a domestic fridge is cheaper. Yes, a cheap and nasty, free standing fridge is maybe £150. The Combi he uses in the demo costs over £700, so you spend nearly £900 and have a cheap and nasty fridge. Personally, i wouldn't entertain a free standing fridge onboard. A reasonable quality built in domestic fridge is around £400, so now we're spending £1100 plus. We can go for a cheaper inverter, but then the idle overhead almost doubles and we're still going to have to pay about £400 for a decent inverter, so it's £550 for a small inverter and a cheap and nasty fridge (about the same as a decent 12v fridge) or about £800 if we buy a decent fridge.
As for efficiency, he's having a laugh. He, and you, also fail to take into account the inverter inefficiency and the fact that all of the time the fridge is not running, the inverter is wasting power, it has a standby overhead.
A 4 amp fridge, running for 1/3rd of the time, will use 32ah in a 24 hour period. Run a 4 amp fridge through an inverter and you can add 10% to the consumption for all of the hours it's running, as a minimum, so that's an additional 3.2ah. You can then add another 8ah if the Sterling figure of a 0.5a standby current can be believed, or almost 16ah if we're using the cheaper inverter, for when the fridge isn't running.
12v fridge, running 1/3rd of the time @ 4a = 32ah in 24 hrs
240v fridge, running 1/3rd of the time @ 4a = 51.2ah in 24 hrs using the Sterling Combi
240v fridge, running 1/3rd of the time @ 4a = 43.2ah in 24 hrs using the cheaper inverter
If it was such a great saving, don't you think the production boat builders would be fitting them ?
The suggestion of using the 3 way absorption fridge on a boat is utter nonsense.
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superheat6k
Well-Known Member
Absorption fridges are very inefficient, and will only offer a holding capability on 12v, and on LPG (butane or propane gas) are positively lethal on a boat because the risk of exhaust fumes re-entering the boat, and possibility of ignition of gas or flammable vapour accumulations from the bilges due to the continuous flame present when operating on LPG.
For any fridge best efficiency is achieved by keeping the discharge pressure down, which is why water cooled condensers in warmer climates are far more effective. Cooling the compressor is less of an issue becuase most of the cooling is provided by the cold suction gas entering.
A well ventilated condenser low down in the boat where the air will naturally be cooler in the Summer will help with an air cooled condenser.
For a cabinet style fridge then a small computer fan along with suitable vents to allow decent air circulation behind the fridge will make a tremendous difference to its efficiency. Installing a fridge into a sealed or poorly ventilated space is a recipe for poor performance and a short life.
As an aside to this thread a mention of HFC phase down, for fridges notably R134a, is something that will affect newer equipment coming to the market over the next couple of years.
With the phase down of R134a it is likely use of propane R290 or Iso butane R600a for boat fridges will increase, and the small volume of refrigerant should not create any undue additional fire hazard for cabinet fridges, but not so sure about split system fridges with locally plumbed systems. An engineer installing such systems must be Gas Safe registered (F Gas registration alone is not valid for pure hydrocarbon refrigerants) plus be suitably experienced with marine fridges. Not too many of those chaps available.
As an alternative to R134a then R1234YF would provide a low flammability solution, but any locally installed system may require a Fire Safety risk assessment (happy to check the specific rules for this as it might be volume related). R513A would provide a non flammable solution.
For those interested in refrigerant developments those with AC systems have a bigger problem. R407C has no replacement in the pipeline at all, as it was a technical replacement for R22, which has now been largely superseded in large systems by R134a equipment. The other common gas used in AC is R410A, which for small systems in being replaced with one of its base components R32, which itself also has a low flammability, and as a result a room size limit. But R410A provides a better heat volume per equipment volume than R134a, which is why R134a is noot much used for AC on boats - the compressors will typically be over twice the swept volume capacity for the same net cooling effect.
Availability of HFC based gases depends upon their Global Warming Potential and the governing factors behind the phase down and its affect upon market price and availability are very complex. This year will see a marked reduction in HFC availability and procurement of new equipment on an HFC refrigerants should be questioned.
For any fridge best efficiency is achieved by keeping the discharge pressure down, which is why water cooled condensers in warmer climates are far more effective. Cooling the compressor is less of an issue becuase most of the cooling is provided by the cold suction gas entering.
A well ventilated condenser low down in the boat where the air will naturally be cooler in the Summer will help with an air cooled condenser.
For a cabinet style fridge then a small computer fan along with suitable vents to allow decent air circulation behind the fridge will make a tremendous difference to its efficiency. Installing a fridge into a sealed or poorly ventilated space is a recipe for poor performance and a short life.
As an aside to this thread a mention of HFC phase down, for fridges notably R134a, is something that will affect newer equipment coming to the market over the next couple of years.
With the phase down of R134a it is likely use of propane R290 or Iso butane R600a for boat fridges will increase, and the small volume of refrigerant should not create any undue additional fire hazard for cabinet fridges, but not so sure about split system fridges with locally plumbed systems. An engineer installing such systems must be Gas Safe registered (F Gas registration alone is not valid for pure hydrocarbon refrigerants) plus be suitably experienced with marine fridges. Not too many of those chaps available.
As an alternative to R134a then R1234YF would provide a low flammability solution, but any locally installed system may require a Fire Safety risk assessment (happy to check the specific rules for this as it might be volume related). R513A would provide a non flammable solution.
For those interested in refrigerant developments those with AC systems have a bigger problem. R407C has no replacement in the pipeline at all, as it was a technical replacement for R22, which has now been largely superseded in large systems by R134a equipment. The other common gas used in AC is R410A, which for small systems in being replaced with one of its base components R32, which itself also has a low flammability, and as a result a room size limit. But R410A provides a better heat volume per equipment volume than R134a, which is why R134a is noot much used for AC on boats - the compressors will typically be over twice the swept volume capacity for the same net cooling effect.
Availability of HFC based gases depends upon their Global Warming Potential and the governing factors behind the phase down and its affect upon market price and availability are very complex. This year will see a marked reduction in HFC availability and procurement of new equipment on an HFC refrigerants should be questioned.
CAPTAIN FANTASTIC
Well-Known Member
I have been using a cheap (~£70) 230v small fridge/freezer purchased from Argos 12 years ago using a cheap Maplins modified sine inverter (~£60) . I leave it on 24/7 it uses very little power and keeps everything cold, also it makes ice for G+T. It looks good, rust free, and it is big enough. Why people don't use them, it's a puzzle.
geem
Well-Known Member
Interested to know how you work out that domestic fridges are more efficient?
This link would suggest the DC motor driven compressors we are using are up there in terms of efficiency. I dont see where you work out domestic fridges are inherently more energy efficient.
Direct current compressors
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Beneteau381
Well-Known Member
Really?
"Each time you turn on you have to pump a vacuum, which produces zero cooling" really? A fundemental lack of understanding of the refrigeration cycle!