Voltage harmoniser ????

Hammyman

Fifer wrote: »

But if that was the case, it would assume that all appliances are optimised at the same voltage, which seems unlikely.

And it would completely ignore the fact that everything other than heating elements and incandescent lighting uses step down transformers coupled to voltage regulating power supplies which draw the same amount of wattage regardless at what the mains supply is. Or is the poster seriously telling us everything inside his TV runs at mains?

espresso

Hammyman wrote: »

Very. Lets put this to you.

Heating:
We're going to heat a room with an electric fire which is basically a resistor. It takes a certain amount of energy to heat a room by 1°C, lets say 100BTU. You have an electric fire which produces 50BTU/hr @ 240V so it'll take 2hrs to raise the temperature the 1C. Now lets change the voltage to 200V. Remember the formula for resistor in AC circuit is P=I x Vrms. If you lower the voltage to the fire, it lowers the heat and energy generated so in this case, the fire will now only be producing 41.6 BTU/hr. So in order to provide the same rise in temperature you'll still need 100BTU but you need to run the fire for longer ( 2hrs 20 minutes in this example) hence there is no saving when raising the temperature of the room by 1C - it'll just take longer - 20 minutes longer in this case. So overall, you'll still use the same amount of energy to achieve the required end result.

If you had actually read the thread or done some basic research for yourself, you would know that no energy saving will be made using voltage optimisation on heating appliances and these are not even connected to the unit, as there is simply no point.

OK, so lets move on from heaters. Lets take a device which needs to draw 1000 watts to provide enough power run the circuit at the required voltage for the load on the secondary side of the transformer, lets say something like a very power hungry telly.

P=I x V. Looking at the formula we can instantly deduce that in order for P to remain the same then if V lowers, I would need to increase. So going on 240Vrms supply, 1000 W would draw 4.16 amps. Going on a 200Vrms supply, 1000 W would draw 5 amps. Even though we've dropped the voltage by 1/6th, it would still use 1000W but would just draw more current if the voltage was lowered but at the end of the day as consumption is measured in kW and not voltage, it would still cost you exactly the same amount of money to run it for an hour.

Your example calculation is incorrect.

Yes Power = current x voltage but you are making the assumption that your 1000W load is a constant and if the voltage is lowered then the current must rise to compensate.

The power consumed is simply the product of amps x volts If you don't believe me go here and enter

Voltage = 240 V
Power = 1000 W

then click Calculate

Current = 4.1667 A
Resistance = 57.6 ohms

Now reduce the Voltage to 220 V

then click calculate

The Current now = 3.81994 A
The Power now = 840.2777 W

This assumes that the resistance is constant but the appliance has not changed, only the voltage has been reduced to the optimum level that the device was designed to operate at most efficiently. When the applied voltage is reduced the power is also reduced as the square of the voltage - transpose the formula yourself. Obviously not all devices can be considered as simply resistive but this is the basic proven principle of voltage optimisation energy saving that you do not understand. Typical single phase domestic measured savings have previously been given in this thread here.

And thats why on single phase they are snake oil for the most part. Sure they'll cut the cost in lighting but only if you don't change the bulb for a higher rated one because the level of illumination has dropped.

However in the example of the telly, you now have an additional problem. 5 amps is a standard fuse rating. As you know, to be safe you should use the lowest rated fuse possible so for a TV drawing roughly 4 amps, a 5 amp fuse could be used. Only problem is now that you've dropped the voltage, the current has increased to 5 amps so therefore its likely the fuse will blow. So going on the fact that most people don't know jack about electrics, they're likely to think its gone bang and will either call out a repair man or needlessly go buy another. I know its a bit pie in the sky but it does illustrate some of the shortfalls.

What was that you were saying about understanding ohms law? The only thing that comment is valid for is incandescent light bulbs. It isn't remotely valid for either of the examples I've posted above because Watts law is.

Your input adds nothing useful to this discussion!

...........

Avoriaz

fwor wrote: »

Well of course, it is complex. You haven't yet accounted for the fact that the speed with which the kettle's cutout operates will typically depend on how quickly it has been heated up, so you will get slightly different power consumption as a result of that as well....

The kettle's cutout operates when the water reaches boiling point and is irrelevant to power used.

fwor

Avoriaz wrote: »

The kettle's cutout operates when the water reaches boiling point and is irrelevant to power used.

It most cases, it's not that simple. The cutout cannot (for safety reasons) be in contact with the water. Most modern kettles typically work by having the cutout higher up than the water - often in the handle - where steam is conveyed up via a channel, passing heat up to the cutout - and that process takes time. In this situation, the rate at which the water heats up ~will~ affect the rate at which the cutout heats up, and therefore ~will~ affect how quickly it operates once the water is boiling - though the effect will only be small.

Fifer

espresso wrote: »

This assumes that the resistance is constant but the appliance has not changed, only the voltage has been reduced to the optimum level that the device was designed to operate at most efficiently. When the applied voltage is reduced the power is also reduced as the square of the voltage - transpose the formula yourself. Obviously not all devices can be considered as simply resistive but this is the basic proven principle of voltage optimisation energy saving that you do not understand. Typical single phase domestic measured savings have previously been given in this thread here.

And they are nonsense. You've still to explain how voltage optimisation can provide a 15% energy saving with incandescent lighting for the same light output.

And a 99.9% efficient transformer? I'd like to see that verified independently, rather than in a piece of advertising puff.

Hammyman

espresso wrote: »

...........

<walks off shaking head in disbelief>

I'll just say I have a BTEC HNC so have half a clue...

espresso wrote:

This assumes that the resistance is constant but the appliance has not changed, only the voltage has been reduced to the optimum level that the device was designed to operate at most efficiently.

Connected to this laptop is a charger. It is rated from 110V-240V input. What is its optimum voltage? And why is it able to work over such a large voltage range with no internal or external voltage selection? Or aren't you going to answer that because you know the answer will prove to the rest of the board that you were actually wrong when you slated me?

System

What voltage should this equipment optimised for?

If it is UK only kit then theoretically it should be optimised either for the stated UK voltage of 230V or possibly 240V (Even though the standard is 230V output is still around the 240V mark).

Even then the optimisation should cover the majority of the allowable voltage range I.E. 216V - 252V. The mid way point, and what should be the most efficient voltage if built correctly, is 238V so I would expect any equipment to work most efficiently at our current mains voltage of 240V

System

I've had a look at a few of the case studies from these companies that claim 13-20% savings.

In all cases, once things like heating and cooking are taken out of the equation as there can be no savings there as they are directly related to power input, The main thing left (about 95%) of the power use is light. The case studies concentrate on companies that have a very high light usage - hotels, large shops, factory type companies.

If you reduce the light then most people do not notice the difference especially when they are only visitors present for a short time such as in hotels and shops. Most offices can also get away with it as well as they tend to be overlit in the first place.

Fifer

!!!!!! wrote: »

If you reduce the light then most people do not notice the difference especially when they are only visitors present for a short time such as in hotels and shops. Most offices can also get away with it as well as they tend to be overlit in the first place.

If so, that's the snake oil. There are no efficiency savings. You are installing expensive kit to achieve what you could have anyway (and probably more effectively and efficiently) by using lower wattage lamps.

kwikbreaks

If there really were savings in energy consumption to be made every government struggling to meet their carbon output promises (ie all that have signed up to any) would be insisting their national grid voltages be reduced. I haven't seen any announcements along these lines.