4 replies to this topic

[kbcnetau]

Hi

Planning a new house, I'm trying to get as energy-efficient as possible; hot water service is going to be solar, lighting is all going to be compact fluorescent. Going through the list of "always on" equipment, I have come up with two fridges and a freezer; being relatively small, single phase units, I guess that the manufacturer would never have considered trying to get a decent power factor on the compressor motors - would these be a candidate for static PFC? Would there be a rule of thumb for sizing the capacitors for appliances like this?

Cheers

Matthew

[marke]

Power factor correction will not necessarliy improve the energy efficiency. It certainly will not improve the energy efficiency of the motor or appliance. What it will do, is reduce the current drawn from the supply and thereby reduce the losses in the supply if they are significant. Depending on where your supply is coming from, and what it is costing you, you may or may not want to consider power factor correction.
If you are taking your supply from the national grid, i.e. not generating your own, then you will get no reduction in your bill for having power factor correction. Domestic charges are based on KW Hours or units used. Industrial users are often charged for KWHrs used and in addition, have a KVA maximum demand surcharge added on to cover the poor power factor.
If you are generating your own power, then you may see some advantage from power factor correction if you have significant line losses. Be careful however, power factor correction can introduce other problems such as supply resonance which can create havoc with electronic appliances if your supply is weak.
If you have more data, we may be able to be more specific.
Best Regards

[Daniel]

Refer to the topic of "green home", if the pf correction doesn't do anything for the energy saving in domestic, it just draw less current when it connected to appliance. I don't understand that shouldn't be the electric meter run slower if less current being used? if the meter run slower, it means we pay less with the electric bill. Am I right?

[marke]

Hello Daniel

No, that is not correct.
The electrictricity bill is based on KW used, not amps used. It is possible to have a poor power factor and high amps, and yet pay low KW. Industrial and large users usually pay for a poor power factor so that they are effectively penalised for a poor power factor, but not domestic users.
a domestic consumer would pay the same for 20 amps at a pf of 0.5 as for 10 amps at a pf of 1.0.
Best regards,

[pblakeney]

There are two types of power; real power and imaginary power. Real power is measured in KW while imaginary (or reactive) power is measured in KVars (Kilo Volt Amp reactive). Real power or 'active' power contibutes to actual work being done on a system. Reactive power is power that is in the form of a magnetic or electric field. The meter does not measure reactive power because it averages out to zero. The power is returned to the source every half cycle. Whereas real power, the average is not zero and is some positve real number (unless your are supplying power to the grid). Generators still have to produce this extra power (for reactive power) and transformers and wire cables have to be sized big enough to supply the extra power. Industries are charged a penalty fee for power factor because of the significance it makes for power generation and line losses (I2R), and for having to provide bigger wires and transformers etc. The vector sum of the active power and reactive power is what is known as apparent power. Here is a good site to help with understanding PF better: http://www.nepsi.com/powerfactor.htm