Essentially this looks to be a buck converter, basically a switched mode AC to AC converter that regulates the household supply to 220V.

The theory is that, by lowering the supply voltage the power consumption of any purely resistive load will be reduced in direct proportion to the voltage drop. However, this ignores the fact that many household appliances will not be pure resistive loads, in fact many will have their own switched mode down converters and so will draw exactly the same amount of power on 220V as they would on 240V

Add in that the VPhase unit itself will not be 100% efficient, at best it might use 2 to 5% of the supplied power, and I seriously doubt that the stated 10% saving will be achieved by all, or even most users. They quote 1% for losses, but this implies a 99% efficient converter, which is way better than any I've heard of.

If you have a home where most electrical power is drawn by resistive loads (incandescent lamps, electric heaters, kettles etc) then the saving may be achieved. If you have a home where most electrical power is consumed by devices with regulated supplies (electronic appliances, pretty much anything motor driven, CCL and LED lighting etc) then the chances are that the savings may not materialise.

Some discussion here: http://www.greenbuildingforum.co.uk/forum114/comments.php?DiscussionID=3804 starts about VPhase about half way down the page.
The savings would be dependant on the equipment you had. Kettles won't save anything, they will just take longer to boil on the reduced voltage, incandescent lamps will be dimmer and use less electricity unless you added more because it was darker. I can't see anything with a switch-mode power supply saving anything e.g. PC, TV, low energy lamps, but they claim otherwise and I haven't measured any of these. Things with motors should save energy, so fridges, washing machines, vacuum cleaners etc. Regarding efficiency, 1% is probably about right because they only have to make about 20V and put it in anti phase to the mains to reduce the voltage.
HTH, Brian

<blockquote><cite>Posted By: brig001</cite> Regarding efficiency, 1% is probably about right because they only have to make about 20V and put it in anti phase to the mains to reduce the voltage.
HTH, Brian</blockquote>

Good point, I'd not thought of that approach, it would be more efficient than a straight buck converter.

Work I've done on switched mode supplies (which are pretty much the norm now in virtually all electronic appliances, from TVs to PCs) shows they have a fairly constant efficiency with input voltage, so should draw the same power over a wide range of input voltages, giving no saving at all on a lower supply voltage.

Similarly things like modern washing machines often use motors that are electronically driven to speeds set by the controller, so lowering the voltage will just cause them to draw more current, keeping the power the same.

The refrigerator motor is an interesting case, as it will, in all probability, be an induction motor, with it's operating speed set largely by the mains frequency. It will undoubtedly deliver less power on a lower voltage and may work with a greater slip loss, but will this result in less power being consumed? I doubt it, as we will still want the fridge to run at the same temperature and it will take a given amount of power to do that, so my guess is that the power consumed would be near enough the same on either 220 or 240V, it will, in all probability, just run for a bit longer on 220V than it would on 240V.

<blockquote><cite>Posted By: CWatters</cite>I suppose it might make some equipment such as computers and TV HD recorders more prone to drop out due to noise spikes?</blockquote>

Probably not, as most of these things already use wide range switched mode supplies (it's common now to find that these things can run on any voltage from 115V to 240V without needing to flick any voltage range switches). I have used a 240V AC nominal laptop supply on an 80V DC battery and found it worked just fine, so I doubt that running it on 220V would have any impact on performance.

The other issue is that people probably fit them when they are on an economy drive...so they may also have started to do other things like use the tumble dryer less at the same time.

I too think you're probably right. Once people start to become aware of energy use they (may be subconsciously) start switching things off.

Here's a good example. For around 20 years now I've been using a plug-in power monitor to check the consumption of household stuff and have devised strategies for minimising power use (time switches, changing lighting, not leaving stuff on standby etc). I've repeatedly remarked to SWMBO about the things in the house that use a lot of power and the things that don't use as much, with the aim of getting the basics across about reducing energy use.

Recently we acquired one of those remote power meters that monitors the incoming supply current and gives a live display of household power use. In the space of a couple of weeks this thing has had more effect on SWMBO power usage than anything I've said for the past 20 years. She even pointed out how wasteful using excess lights is, something I've been quietly fuming about for years (she was in the habit of partially pulling the curtain for shade and then turning a light on to read..............).

It seems that the impact of seeing big numbers on the power screen is significantly greater than any amount of "education". I'll be very interested to see how our long term energy use changes - early indications are that we're already about 10% down, which bodes well.

<blockquote><cite>Posted By: Shevek</cite>What do people make of this? Anyone used one?
<a rel="nofollow" href="http://www.vphase.co.uk/">http://www.vphase.co.uk/</a>

<a rel="nofollow" href="http://www.vphase.co.uk/how-it-works">http://www.vphase.co.uk/how-it-works</a>
"The UK electricity distribution network operates at a nominal 230V, although in practice average voltages are more likely to range between 240V and 245V. The VPhase unit manages voltage to a stable level, normally 220V in the UK, regardless of the incoming supply voltage"</blockquote>

Well not wanting to prejudge everyone... I installed one in a new house recently, selecting all non-heating circuits ( which exceeded the number of all heating circuits 15- 12) and then had to guess how much 'savings' might be made.
So any ideas how to calculate this?
NB. No pre-existing data, no before and after vPhase readings, no historical data yet.

If I had designed the thing I would have included a built in meter to tell you. After all what could be a better advert than your neighbour telling you how much he'd saved?