how to run fridge and freezer at max efficiency?

Jolaaled

rogerblack wrote: »

The momentary energy usage is not important.
What's important is the time it's on, times the energy usage.
A plug-in monitor that you plug the appliance into like I linked earlier in the thread will do this.
Or, you can do it yourself.
If, for example, the freezer uses 200W, and turns on every 50 minutes for 10 minutes, then its average power use is 200 * (10/50) = 40W.
40W*24h = 1kWh.
The switch on 'spike' - if any is unimportant - look at what the use is a few seconds later.

Defrosting reduces the consumption of fridges noticably.
Freezers, not-so-much, unless they have very very thick frost, more than a centimeter.

Gosh..I'm learning so much from you guys..thank you all sooo much.
I had no idea that electrical appliances had a 'switch on spike' in consumption...that explains why my monitor gives a high reading when the fridge initially turns on, but then drops the reading about 30s later.

I'm going to do some recalcs to make some more accurate decisions.
My freezer does have some frost build up, but nowhere near 1cm, so I won't rush to defrost..thanks for the tips.

pappaking

There is some good info here; I have moved my freezer to the garage from the kitchen, I think it uses less energy there; I have it set at -18 deg. The fridge in the house is set at 5 deg. Do you think that these temperatures are a good balance for keeping the food in the correct condition, whist still being not wasting power? We have a boat that has only a 12volt. fridge in it. Overnight we always put a blanket on top of it. This defiantly reduces power consumption. In the summer we do the same to the chest freezer in the garage.

rogerblack

pappaking wrote: »

There is some good info here; I have moved my freezer to the garage from the kitchen, I think it uses less energy there

In some cases it may.
However, many domestic freezers are not rated to low temps.
http://www.whitegoodshelp.co.uk/wordpress/climate-classes-for-fridges-freezers-and-fridge-freezers/

Only class SN is rated to 10C, N only to 16C!

What happens when the temperature gets too low varies.
It may be that you just get condensation on the outside, leading to rust, and failure in a few years, or it may be the compressor fails.

My new (last year) hotpoint freezer is rated down to 10C, but it's worked flawlessly at down to 3C last year. (alas, this was the temperature in most of my house).
There were no indications of increased energy use, or in the initial spike of power usage rising over its summer figure, which might indicate problems turning on, and no condensation.

macman

Fit Savaplugs. I have these on both fridge and freezer.
http://www.energysavingadvice.com/energy-saving-products/savaplug.html

pappaking

rogerblack wrote: »

In some cases it may.
However, many domestic freezers are not rated to low temps.
http://www.whitegoodshelp.co.uk/wordpress/climate-classes-for-fridges-freezers-and-fridge-freezers/

Only class SN is rated to 10C, N only to 16C!

What happens when the temperature gets too low varies.
It may be that you just get condensation on the outside, leading to rust, and failure in a few years, or it may be the compressor fails.

My new (last year) hotpoint freezer is rated down to 10C, but it's worked flawlessly at down to 3C last year. (alas, this was the temperature in most of my house).
There were no indications of increased energy use, or in the initial spike of power usage rising over its summer figure, which might indicate problems turning on, and no condensation.

Thank you i will check the spec. The freezer is s/steel so i am
ok with the condensation. My old one did rust in the garage.

timbim_2

macman wrote: »

Fit Savaplugs. I have these on both fridge and freezer.
http://www.energysavingadvice.com/energy-saving-products/savaplug.html

Any proof they do anything? Looking at the blurb, something immediately caught my eye:

Full power is needed to start the motor but many appliances continue to maintain maximum power when it is no longer needed. The SavaPlug control's the supply of electricity to match the fridge's actual power needs thereby saving you electricity and money.

So where does the extra power that the motor doesn't need but still somehow draws go? And how does it control the power usage? How does it know how much cooling the fridge actually needs to do? Complete baloney!

rogerblack

timbim wrote: »

So where does the extra power that the motor doesn't need but still somehow draws go? And how does it control the power usage? How does it know how much cooling the fridge actually needs to do? Complete baloney!

It is possible, though complex, to measure the amount of cooling the fridge is trying to do by monitoring the current it draws.

Simplifying a bit.
The speed of the compressor in your fridge is constant - it's an induction motor.
The current it draws is proportional to the pressure drop across it, which is related to the difference between the inside and the outside temperature.

However, it also draws additional current, because of the excess voltage it's fed, in order to assure it starts up reliably every time, and that it works when it's +30C out and -20C inside.

As you reduce the voltage going to the motor - once it's running - initially, the speed is almost totally unaffected (it's an induction motor, and runs mostly at the same speed independant of load or voltage).
The voltage drops, and the current doesn't rise much - the power used is less.
As long as you don't drop the voltage too far - which will cause the motor to struggle, get hot, and draw more current.

This can - if you also vary the frequency of the AC line - be done even more efficiently.
This is part of the reason why 'inverter' air conditioners are considerably more efficient, especially at part-load, compared to normal ones.

Currently designing a 'variable frequency drive' - for a fridge, as a test for a much, much larger system.

I have no knowledge of the energy saving device mentioned.
It may be a valuable and useful tool.
It may burn out your fridge motor.