PowerSwitch

I haven't bought one of the energy monitors that have been coming onto the market over the last year or some. Does any PowerSwitcher have any experience using them?

This site has a review of some of them.

http://www.smartplanet.com/reviews/tech ... nitors.htm

AFAIK all these energy monitors only measure current and not voltage, and are therefore inherently inaccurate.
The absence of voltage measurement also means that they can not measure power factor, and therefore give an unduly pessimistic reading on loads with low power factor.

On a simple resistance load such as a heater, there is a lot of difference between 10 amps at 250 volts and 10 amps at 220 volts.

On a load with poor power factor such as some flourescent lights, the result could lead to consumers grossly over estimating the consumption of flourescent lamps, and perhapd deciding wrongly that they may as well use incandescent bulbs.

The plug in power and ernergy monitor sold by Maplins is better in this respect since it DOES measure voltage and power factor, though only of a single appliance, not the whole house.

I've been using one of the Efergy monitors which we bought from Maplins for £30 in a sale.

Seems consistent but reading Adam2's post it looks like the accuracy is questionable! However, the main benefit for me has been that it is constantly drawing our attention to saving energy which is how we've cut our usage by 58% over the last few months.

I also use the Plug-In monitor to measure individual appliances.

Presumably, the monitors assume a grid voltage of around 240V.

As domestic users pay per watt rather than per volt-amp, I guess power factor doesn't matter for ££ saved, although it will distort the overall energy and carbon figures.

As you say rs, there is value in using both the individual power meter (which I have been doing) to get more accurate quantified information and the household monitor to get a more general view of when you are using a lot or a little. The household monitor would help in habit changing rather than in capturing accurate data.

Adam1 wrote:Presumably, the monitors assume a grid voltage of around 240V.

As domestic users pay per watt rather than per volt-amp, I guess power factor doesn't matter for ££ saved, although it will distort the overall energy and carbon figures.

Yes I believe that they assume a 240 volt supply, and will therefore be inaccurate at other voltages.

Domestic consumers are indeed charged per KW/hour, not per KVA/hour,however these energy monitors appear to measure KVA/hours, and would therefore over read substantialy on floursecent lights and some types of motor.

Large power consumers are penalised for poor power factor and have a clear financial incentive to improve it.
Domesticly, poor factor makes no difference, 1KW at unity power factor will cost exactly the same as 1KW at 0.5 power factor.

I emailed Adam2's comments to Efergy, here is their response:

The information written by the person is correct - the voltage is not measured, and so can not measure power factors. So his theory is correct. Electric meters also do not measure power factors of an appliance, and only measure delivered power.

Supply voltage tends to vary slightly from 240V - so you'll very rarely have anything under 238 or above 242

We complete in house laboratory test and with readings falling between 0-13 kW we achieve a + / - 7% accuracy. Unlike an electric meter the purpose of the device is mainly for behavioural change and making the user more aware of electricity use - and not as a measuring device.

Adam1 wrote:...The household monitor would help in habit changing rather than in capturing accurate data.

Yes, our monitor records usage over hours, days and weeks etc but I do not use those features.

It's more of an instant thing, I walk past see 1.2kw in the display and I immediately wonder what is switched on. Probably quite sad I know, but I then usually hunt around the house for the offending item

Yesterday I couldn't figure out what was using 1.5kw until I finally realised it was the toaster!

I find the monitor also very useful last thing at night. If it's hovering around 0.1kw then I know everything is off.

Can your Efergy unit run on mains too? Is it better than the others on the market or did you just go for it because it was on sale at Maplins - as good a reason as any!

Didn't realise these were so cheap now! I'll get getting one of the cheaper ones.

More reviews here:
http://www.reuk.co.uk/Eco-Eye-Review.htm

Adam1 wrote:Can your Efergy unit run on mains too? Is it better than the others on the market or did you just go for it because it was on sale at Maplins - as good a reason as any!

It runs on batteries, both in the main unit and wireless transmitter.

I think the Efergy and Owl are almost identical. The Wattson is very expensive in comparison.

We have the efergy meter, its good although a funtion to link it up to a computer to compare month to month etc would be good. I think one of the others has this function.

rs wrote:The Wattson is very expensive in comparison.

Does have USB port, which gives very detailed data
Analysis software was written by a dork in a bedroom... very poor

I like the Wattson and have tried to pursuade them to open source the software(publish interface) , instead of the moronic macromedia app....

It also records micro gen as well

Next release of the software was due in Feb, then April, now Sept...

Wait for the software update.... then decide, don't buy until the software improves

Adam1, I have an electrisave that I was given by the council still in the box with instructions etc so could let you have that if you haven't already got one.

tomhitchman wrote:Adam1, I have an electrisave that I was given by the council still in the box with instructions etc so could let you have that if you haven't already got one.

Oh yes please. That's very kind of you. Thanks. I'll PM you.

We have the marvellous Maplins monitor (L61AQ), Christmas present from my brother (you see Christmas has its uses!) and yes it does power factor etc...but as you say only one plug-socket at a time, so not the house's whole energy consumption (but we have a flashing electricity-meter for that purpose: one flash per 3.6 sec means someone somewhere is using 1kW).