Previous in Forum: 1ka howmany ampire Next in Forum: White IR Lamps vs. Red IR Lamps: What's the Difference?
Commentator

Join Date: Jul 2008
Location: INDIA - GOLDLAND
Posts: 89

# electricity consumption

09/12/2008 4:50 AM

If we run domestic fan at low rpm OR high rpm .is electricity consumption is same or different. This may be very basic question. But need answer.

Interested in this topic? By joining CR4 you can "subscribe" to

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Power-User

Join Date: Jan 2008
Posts: 141
#1

### Re: electricity consumption

09/12/2008 5:54 AM

Assuming that you are using one model of fan. You should use less power when the fan is at a lower RPM. The power used in the motor is dependent on how much work the motor is doing. When you run the fan at a higher speed you are pushing more air, therefore, you are doing more work. This would lead to greater use of power.

__________________
Perfection is achieved, not when there is nothing left to add, but when there is nothing else to take away
Commentator

Join Date: Jul 2008
Location: INDIA - GOLDLAND
Posts: 89
#2

### Re: electricity consumption

09/12/2008 6:38 AM

Thank you for your answer. But when we use regulator to select the speed, is there any impact of speed on losses [heat in resistance] made in regulator.

Also , can anyone have sample calculation to calculate the energy loss.

Sanjay

Anonymous Poster
#5

### Re: electricity consumption

09/12/2008 10:53 AM

For a given system, the theoretical fan laws state that the power is proportional to the cube of the RPM.

For calculations: http://www.airturbine.com/tools/fanlaws.html

Guru

Join Date: Jan 2007
Location: Centurion, South Africa
Posts: 3921
#3

### Re: electricity consumption

09/12/2008 6:53 AM

Is this a DC fan?

__________________
Never do today what you can put of until tomorrow - Student motto
Commentator

Join Date: Jul 2008
Location: INDIA - GOLDLAND
Posts: 89
#4

### Re: electricity consumption

09/12/2008 7:00 AM

it is household AC fan [230 V , Singal Phase]

Power-User

Join Date: Apr 2007
Posts: 319
#6

### Re: electricity consumption

09/13/2008 2:44 AM

I believe if you are referring to the pedestal fans they use fractional horse power motors and then power consumption is more or less proportional to the speed of the fan.

But when it comes to ceiling fan where you have a separate regulator my honest answer is I don't know!

__________________
sisira
2
Guru

Join Date: Jan 2007
Location: Sitting directly behind my keyboard in Albuquerque - USA
Posts: 592
#7

### Re: electricity consumption

09/13/2008 5:32 AM

Try looking at your kWh meter with all fans on high, then all fans on low. If you have a spinning wheel type meter, you may need a stop watch to see such a small change. Or a clamp on amp meter.

__________________
If it eats, it's going to be trouble!
2
Guru

Join Date: Sep 2006
Location: NSW Australia
Posts: 1085
#8

### Re: electricity consumption

09/13/2008 6:29 AM

There are some very neat small digital power meters for sale about \$35.00 which plug into the power point, these will give you min / max and live readings also consumption cost. They will prove higher speed consumes more power.

Garth

__________________
Dont get on to the roundabout if you dont know how to get off
Power-User

Join Date: Apr 2007
Posts: 319
#9

### Re: electricity consumption

09/13/2008 9:26 AM

can you please tell us some specific brands? If you feel uncomfortable giving names in an open forum like this my email is sisiraa@gmail.com. Thanks in advance

__________________
sisira
Guru

Join Date: Sep 2006
Location: NSW Australia
Posts: 1085
#10

### Re: electricity consumption

09/13/2008 10:53 PM

Sisira

CAT. NO. MS6115 you might need plug & socket adapters

Regards Garth

__________________
Dont get on to the roundabout if you dont know how to get off
Power-User

Join Date: Apr 2007
Posts: 319
#11

### Re: electricity consumption

09/14/2008 2:34 AM

Thanks Garth.

__________________
sisira
Anonymous Poster
#12

### Re: electricity consumption

09/15/2008 11:04 AM

When you turn the fan up you will move more air. More air moved equals more work done. More work done equals higher load. Higher load means higher current which means more power (electricity) consumed.

To verify, place an amp clamp on one leg of the power cord.

Travis

Guru

Join Date: Nov 2006
Posts: 721
#13

### Re: electricity consumption

09/18/2008 6:07 AM

The fan power consumption varies as the cube root of speed etc as mentioned are all correct.In industrial fans the speed is varied by Damper , V/f drive or by other means where the voltage is reduced ,thereby reducing the RPM resulting in reduction in power consumption.In the domestic fan the speed is reduced by inserting the resistance of the regulator.Let us say if W is the fan power rating, V the voltage , I the current and for convenience let us omit PF.VI=W .When the fan is running at full speed the resistance is totally cut out.However the fan speed is reduced by including the Resistance in the circuit.Lowest speed we have the max . resistance and at intermediate steps we have different values of resistance.At the lowest speed If resistance is Rmax then V remaining the same I^2 Rmax is the voltage drop and Voltage applied to fan motor is reduced with reduction in speed.No doubt fan may require less power but as voltage and hence current remains the same the power is wasted as Heat loss.That is why you can feel the regulators warm after running the fan in low rpm continuously.So in effect there is no saving as power that result as saving due to Fan requiring less power is wasted as heat in the regulator resistance.

__________________
To avoid crticism do nothing,say nothing,be nothing
Power-User

Join Date: Apr 2007
Posts: 319
#14

### Re: electricity consumption

09/18/2008 7:08 AM

I believe what you say is correct with ceiling fans and old fashion fan regulators. But I do not think it is same with modern day electronic fan regulators. With them you hardly feel any heat in the regulator.

When it comes to pedestal fans I believe what they use are fractional horse power motors and as the name implies when you reduce the speed power consumption also drops.

For industrial fans when you reduce fan speed by way of a VFD where motor speed is reduced by changing frequency power consumption drops proportionate to the speed. But if you put a damper to reduce the flow depending on the fan characteristics curve power may go up or down.

__________________
sisira
Guru

Join Date: Nov 2006
Posts: 721
#15

### Re: electricity consumption

09/18/2008 11:18 AM

Yes .I had in mind only the type regulators.The power consumption is the same at full speed in both type of regulators.At lower speeds while there is no saving in coventional old types there is a saving with the use of electronic regulator .This has been tested and proved.

__________________
To avoid crticism do nothing,say nothing,be nothing
Commentator

Join Date: Jul 2008
Location: INDIA - GOLDLAND
Posts: 89
#16

### Re: electricity consumption

09/19/2008 6:58 AM

yes, i am agree with your conclusion. In the same line i also thinking. Because regulator gets heated at low speed. So wasted power is converted into heat.

Also, at low speed workdone reqd. by fan is lower than at higher speed. So there may be some sort of saving at lower speed !

If it is assumed that fan is running at vaccum without any air resistance, then it will be interesting to calculate power consumption.

Interested in this topic? By joining CR4 you can "subscribe" to