Electricity calculations?
 

Just need to know if this looks about right, or am I having a blonde day...

I work 24 hour shift in a modern glass design building. The problem is that the company seem to ignore the fact that they leave all the lights on 24*7 on our floor. Now, not a problem when you have 150 people during the day, but out of hours there is only between 7 and 5. So why leave all the lights on? We have asked the building services team, but they seem uninterested and unconcernced by our requests. Saying its all controlled by computers and they cannot do anything because the zones are so big.

Any way did a quick count and was trying to calculate the cost of the lights running. Just want someone to confirm my costs before I put forward my idea......

Each ceiling fitting has 2, 40w bulbs. 250 fittings on for 12 hours.(ooh only from 19:00 to 07:00)


Therefore.
2*40*250*12 = 240,000 kWh

240,000 kWh * 9pence(cost per kilowatthour) = £21,600


So is that the running cost per year?

Any ideas?

The bulbs are 40W not KW, so it's 240,000W or 240Kw
So about £21.60 per day (12 hour period)
or £7884 for the year if a full 365 days

Could you show me your workings out Ollyk?

500 40w bulbs = 20000w per hour or 20kw

1 kw costs 9p

so 1 hour costs £1.80

12 hours cost £1.80*12 =£21.60

1 year costs 365*£21.60 =£7884.00

2*40*250*12 = 240,000 W used in 12 hour period < This is where you went wrong, you are working in W not KW at this point!
1000W = 1Kw so
240,000 / 1000 = 240Kw were used in the 12 hours
If it's 9p per Kw: 240 x 0.09 = £21.60 for the above 12 hour period.

There will be 365 12 hour periods in a year (assuming the lights are on all year round), so 365 x £21.60 = £7884.00

johnny ball would be proud of you!

I think you made 2 errors. Watts and not KW but you also forgot to multiply by 365 days which would have given you an annual cost of just under £8m :)

I feel I ought to point out the sloppy way people are treating a Watt and a Watt Hour interchangeably... ;)

a Watt is a unit of power, a Watt Hour is a unit of energy used.

As we know, the SI unit of energy is the Joule. One Watt is one Joule per second, therefore a Watt Hour is the equivalent of 3600 Joules of energy used.

Hope that helps :) ;)

And how much difference has all that made to the actual cost per year? :D

None at all... but it would have lost you marks! ;)

Still a hell of a waste of money and energy. Doesn't do much for global warming either.

Les

Maybe back in the days of O Levels, but these days it wouldn't matter, the orignal result would still have been given 75% of the marks because he showed workings and provided and answer, getting the units a little wrong would just be put down to dyslexia now and no marks would be deducted. :rolleyes: :D

"By The power of Scoobynet" I am saved. Many thanks for the help. Knew I should have listened to my college tutor! Never did understand Flemings Right Hand Rule also, but we won't go there.

Cheers to All.

Weird I was just thinking about that last night (no idea why)

First finger FORCE, seCond finger CURRENT, thuMb motion

And will the last one to leave this thread turn the lights out :D

Best not - I believe you'd get arrested for quoting it these days .... ooops! TopBanana's had it ...... :D

Interesting the amount of money being effectively wasted. There was an article on some web site the other day about how more efficient lighting would make a huge dent in the power consumption (of a country). Of the oder of about 20% of the total if I remember correctly. But the Gov. would rather tax the hell out of us rather than do anything that would really make a difference ....

Dave

Email just sent...... And that was a task. Scanned the whole Global Intranet site for an address and the only energy saving personal with a publised email are in Belguim, Holland and Lux.
Nothing at all for the UK! :(
Had to send it to a "cost-efficient" group email.

Lets see what reason they come up with NOT to do it.

You can go to the other extreme - At an office I used to work in they replaced the entire lighting system with IR activated lights on a timer giving you about 3 seconds after it stopped detecting you . You don't really need too much light in an office with loads of computers, but if you ever had the misfortune to need a dump, you would either do it in complete darkness or do it waving your arms around

Is supect the H&S card will be played

our office has motion sensistive lights. Very unnerving if you work late as the lights around you slowly turn off until you have your own little puddle of light left.

Is the life span of a fluorescent lamp also reduced by repetitive switching?

First Finger = Field, not Force. (Motion will be pushed in the same direction as Force, applying Newton's second law of motion)

Also, that's probably the left hand rule - i.e. as applied to motors etc. The right hand rule applies to generators, where the second finger is often described as induced EMF rather than current (although current is applicable)

Apart from that, you've got it about right. 5/10 - must try harder ;) :p

just slightly off the subject but about saving energy.
My bugbear is why the large department stores in winter appear to have the heating on high.
You go out shopping dressed for the cold weather & step into the shop & it's 75+F !!!
The shop assistants are swaning around in short sleved shirts 'cause it's hot in there.
If light bulbs cost 7k to run ,how much to heat a huge store?

It was a long time ago!

Definately the right hand rule I was thinking about... do I get an extra point?