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sally_in_wales

Sava Plugs

Those plugs that are supposed to cut your energy use on the freezer, do they actually work? If so anyone recommend a make?
dougal

Sally, they are "somewhat controversial"...

See what nathanbriggs said here
http://forum.downsizer.net/viewtopic.php?p=319244#319244
and remember that he is the electrical engineer.

(Though one might however wish to quibble with the general truth of his final (and surely tongue in cheek) comment... Very Happy )

IMHO there are an almost infinite number of better things to do with money than buying those particular gadgets.
Marionb

I think Sally means the plugs that are specifically for the freezer - the thread link relates more to a device thats supposed to save electricity throughout the whole house...

I'm sure someone will correct me if I'm wrong... Confused
RichardW

I have 3. They do work. I test each freezer or fridge for consumption before fitting one. Not just for a short while but for weeks / months. Then after I again test consumption (using a plug in meter). My findings are they they save power on all fridges & freezers I have tried them on but the newer ones are quite good already so you wont save as much. This is because the newer ones dont use as much power so a 10% saving (aprox) is less on the lesser consumption. I have posted elsewhere (actualy in the link above) on here the savings made. The worse you item the more you will save.

Justme
dougal

nathanbriggs wrote:
The unit is basically a low impedance capacitor, which should in theory power factor correct your inductive loads like motors in refrigerators and such (if it is positioned close enough)

However the net effect will be close to zero saving, domestic electricity meters in the UK pay no attention to power factor as they are moving coil devices.


"Power factor" risks sounding horribly techie.
Its even worse.
Before I even indicate HOW techie it is, the point to recognise is that Power Factor Correction is what the device is about, and that is irrelevant to UK domestic electricity metering.
Commercial tarrifs can take account of power factor and peak load as well as the quantity of power used.
Right? What it does is irrelevant to UK domestic electricity metering.

Now then Power Factor.
AC.
Sine wave for voltage.
Sine wave for current, out of phase (by 90) with the voltage waveform in a purely inductive (reactive) load, but its in phase in a purely resistive load.
Real loads are combinations of inductance and resistance, so the phase difference is somewhere between 0 and 90. (And because of that the ratio of true to apparent power is less than 1.)
By adding capacitance, we add a reactive load that is trying to phase shift in the opposite direction.
Tune or guess the size of the capacitor right (so it matches and cancels out the inductive load) and we can make our load appear to be pure resistance, so the phase difference between voltage and current is back at 0, and the true and apparent power drawn are the same (so the power factor is 1). That's what the 'device' (a simple capacitor) is trying to achieve.
But remember, it doesn't matter to UK domestic electricity customers.

Long version (with equations and graphs!)
http://www.ibiblio.org/obp/electricCircuits/AC/AC_11.html
sally_in_wales

hmm, we were planning on getting a small A rated chest freezer, but maybe if its now and as energy efficient alreasy as we can get our hands on the plugs won't make a huge impact?
Anders

What brand are you going for Sally? We have been looking at bosch, iceking, miele. A+ (bosch) or A++ (Miele, Iceking), - but they are all expensive, especially Iceking and Miele.

Iceking:
http://www.greenandeasy.co.uk/product_single.php?product_id_sent=245&cat_id_sent=
Miele:
http://www.greenandeasy.co.uk/product_single.php?product_id_sent=78&cat_id_sent=
Bosch: http://www.bootskitchenappliances.com/productinformation.aspx?ID=6151&utm_source=AffiliateWindow&utm_medium=ProductFeeds&ExtCampaign=AffiliateWindow

Anders
RichardW

C rated large freezer will only use about 40-60 per year. To go from a C rated large freezer to an A rated one more than triples the price.

Justme

PS Is the above stuff about the whole house saver or the savaplug? If the sava plug how do you explain the reduced meterage that I am seeing? The meter mearsures the watts used the time & the Kwh. Also you can watch the watts reading live & without it pluged in the motor on start will draw say 400w & with it only 320w over the same amount of time. Is our cheap plug in meter reading a different type of load to what the house meter reads?
sally_in_wales

Anders wrote:
What brand are you going for Sally? We have been looking at bosch, iceking, miele. A+ (bosch) or A++ (Miele, Iceking), - but they are all expensive, especially Iceking and Miele.


Dunno yet, its one of the smaller square ones we want, so we've just started looking around
dougal

Justme wrote:
Also you can watch the watts reading live & without it pluged in the motor on start will draw say 400w & with it only 320w over the same amount of time. Is our cheap plug in meter reading a different type of load to what the house meter reads?

If its a digital meter, then AFAIK it almost certainly IS different.

The sheer inertia of mechanical meters 'averages things out' (and so doesn't take account of phase angle and hence power factor).
Digital meters need extra sophistication to average things out.

Here's an article about making your own power meter.
Importantly it uses an *analogue* "moving coil" meter.
Read through the attached comments and pay special attention to the explanation by "Mark Gray May 05, 2005" of WHY that circuit measures what your (analogue) domestic electricity meter does.
Note there is a 20 sec non-subscriber delay for website admission - its worth the wait!
http://www.elecdesign.com/Articles/Index.cfm?AD=1&ArticleID=3378

Phase angle correction, by a "sava plug" capacitor, *will* change what a simple digital power meter would show for an inductive load (like a fridge/freezer motor) but it *doesn't* change what the *analogue* house (payment) meter records.
Or at least that is my understanding of it! Nathan is the pro, so ask him directly if you need more than my faded and antique A level physics understanding of this topic. Very Happy
Helen_A

We bought ourselves a AA rated bosch freezer a few years ago now. It has *definately* been worth the extra cash (least of all the time that 9m old son turned it off at the wall in the height of summer and we came back from a week away to find that it had been off all that time. - it is so well insulated that most of the contents were still frozen and below zero in the middle of the expensive joint that DP had bought himself the day we went away...)

In terms of power use we think that it costs us around 25-30 a year to run. The current model of the same fridge is even more energy efficient, my friend with one reckons that it is costing her about 15-20 a year at most.

On the flip side we have a fridge that is older than I am (used to be my grandmothers) and that seems to use lots less electricity than a modern equivalent ( the equivalent current model would be D-E rated) would as well.

Helen_A
RichardW

Does it matter that out house meter is a digital read out one with no revolving disc?

Justme
dougal

Frankly, I dunno.
Ask Nathan! PM him.

My suspicion is that your billing meter is likely to have the extra electronics to make sure that you get charged on the same basis as the rest of us.
That sounds fair to me, but I've no idea whether its actually true! Very Happy
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