how to save on kitchen/garage lighting

cypher007

i recently decided to replace my kitchen strip light, as id lost one diffusor end cap so left the diffusor off for many years, which looked a bit crap. anyway i also recently got an owl energy monitor, which i discovered told my my kitchen light was using about 64w instead of 36w, as printed on the tube. so i looked at some replacement strip lights in B&Q, and they do one which has an electronic ballast, instead of the old style transformer ballast. after fitting it the power draw has dropped down to 32w , and the light turns on instantly. i would recomend these style of strip light if you are replacing any or installing new, as the energy saved is substantial. heres a link to them:

http://www.diy.com/diy/jsp/bq/nav/nav.jsp?action=detail&fh_secondid=9279814&fh_view_size=6&fh_start_index=12&fh_location=%2f%2fcatal!!!1%2fen_GB&fh_search=strip+light&fh_eds=%c3%9f&fh_refview=search&ts=1230831516663&isSearch=true

you can also get electronic ballasts to fit in existing strip lights, but youd have to know what your doing to wire it correctly.

Jonesya

Does the owl energy monitor compensate for power factor? - a significant part of the difference between the two ballasts could have been the poor power factor of the magnetic ballast.

cypher007

im not sure if it does. i did hear though that the UK power grid doesnt take power factor into consideration for domestic homes, so any improvement wouldnt save you money anyway. also the standard strip lights have a B rating, these are A rated, so i guess they must be cheaper to run.

as a side note the ballast in a standard fitting gets hot, which is probably where the extra 30+W is going.

Cardew

Jonesya wrote: »

Does the owl energy monitor compensate for power factor? -

The Power Factor of your load doesn't matter in domestic applications - you are only billed for kWh not kVA.

Jonesya

Cardew wrote: »

The Power Factor of your load doesn't matter in domestic applications - you are only billed for kWh not kVA.

Exactly! Many of the household electricity usage monitors use a basic clip-on CT and do not have a voltage reference so cannot calculate power factor, hence they measure VA rather than W.

The original fitting was probably using 64VA / 36W, the new fitting with the electronic ballast is using 32VA / 32W. As you point out domestic users aren't charged for reactive power so the cost saving is minimal, just the few watts in reduced losses.

Cardew

Jonesya wrote: »

Exactly! Many of the household electricity usage monitors use a basic clip-on CT and do not have a voltage reference so cannot calculate power factor, hence they measure VA rather than W.

The original fitting was probably using 64VA / 36W, the new fitting with the electronic ballast is using 32VA / 32W. As you point out domestic users aren't charged for reactive power so the cost saving is minimal, just the few watts in reduced losses.

The Owl only measures kWh. Bear in mind that the display used is cost per hour, and you have to manually enter the cost per kWh. See

http://www.theowl.com/owl-resource-downloads.htm?phpMyAdmin=JyGlY89ytJF5kTNKZTVhMSGOlx6

I am not aware of any Owl type meter that measures VA, as far as I have seen they all measure watts. It would be pretty pointless to display to a customer that they are using, say, 3kVA when they are paying for 2kWh!!

Most of the 'plug in' type monitors used for measuring the power of individual appliances can toggle between VA and watts, but obviously use the latter value when displaying costs. The fan on my fan heater shows 25w and 38va.

Jonesya

How does the Owl measure real power then?

The Owl measures electricity usage using a clip on CT, it does not have a voltage reference and simply assumes V=230v when calculating consumption, the manual states that it assumes P=VI. I cannot see how it could measure active power as it cannot measure phase difference between V and I waveforms. It may state it measures active power but as far as I can see it can only measure apparent power.

Plug top monitors measure both because they can measure both current and voltage and hence detect phase shift to calculate active, reactive and apparent power.