Ask A Scientist© Physics Archive

name         Steven
status       student
age          30s

Question -   I am working on a project for a Marketing 230 at Elmhurst College.
I need to know how a kilowatt is consumed. I also need to know how a
kilowatt is metered and billed. How would a grocery store go about
lowering their electricity usage cost?
--------------------------------------------------------------------------
Connoisseurs will insist that a kilowatt be gently decanted and
allowed to ``breathe'' for up to 30 minutes at room temperature before
being consumed, but regular folks would tend to chug it straight from
the fridge, without even bothering to pour it into a clean glass, and
will assert that the flavor is in no way compromised thereby.
   Oops.  Sorry about that.
   Wouldn't it make sense to drop in on a neighborhood store and ask
the manager these questions?  They might be delighted with your
interest, especially if you offered to make some detailed analysis for
free and give them the results to use as they see fit. Just a thought.
   Electricity is metered by measuring the current through a motor
installed outside the store in a little glass case.  As more current
flows, the motor runs faster and it makes the little numbers the meter
reader records advance faster.  It is billed by the kilowatt-hour,
with one kilowatt-hour being the amount of electricity used by a 100
watt bulb in 10 hours.
   Personally, I'd guess a grocery store consumes most of its power in
refrigeration, which is an inefficient process, especially if you
leave off the doors of the refrigerators and/or pesky consumers keep
opening and closing the doors for no better reason than buying the
merchandise.  You could reduce the power consumed by installing doors
or flexible plastic flaps over the refrigerators to keep in the cold
air, or by facing the doors straight up (cold air is heavier than warm
air).  In frigid parts of the world you could perhaps chill by using
ambient air, sometimes.  That would involve a lot of capital expense
that seems unlikely to be recovered fast.  You could also perhaps buy
electric power at off-peak rate times and use it to chill water.  Then
you could refrigerate during peak rate times with your cold water.
Grayce
===================================

Eric Tolman
Computer Scientist

First of all, the measurement used by electric companinies is generally the
kilowatt hour, which means that you used 1000 watts of energy for an hour.

This electrical energy is used for any electrical device that is used by the
store.    This includes lights, heaters, air conditioners, registers,
scanners, etc.

Each device consumes energy at a different rate, and adds to the total
amount of energy used.

Lights are generally given a wattage that tells you how much energy they
use.  For example, if you have 10, 100 Wat light bulbs on for an hour, that
will use 1 kilo-watt hour of energy.

Some devices measure the power they use in Amps.  That can be converted to
Watts by multiplying the voltage and the amp rating.  For example, if you
have a 5 Amp motor which operates a saw and runs on 110 Volts, it uses 550
Watts of energy, and would use a kilowatt hour up in an 1 hour, 50 minutes.

Other devices may measure their energy consumption in horse power, and you
may have to convert that to watts--1 hp is equal to 746 watts.

So, to determine how much energy something in the store uses up, find out
how many watts of energy the device uses, and multiply that by the number
hours it is on during the month, and then divide by 1000 to get kilo watt
hours.

Obviously doing that for every device in the store would be a time consuming
process.  But, generally, heaters, lights, motors, scanners, printers,
copiers, microwaves, stoves are high-energy consuming devices.

The light company attaches a meter to the incoming power meter to the store.
This meter measures how much electricity passes through it and turns faster
when more energy is flowing, which sets some dials.  This works very much
like your car odometer.  Each month the power company records the number on
the meter, and subtracts the current number from last months to figure out
how many kilowatt hours were used.

Then, based on how many kilowatt hours used, they will bill you.  Usually
the cost is about 6 cents per kilowatt hour.

Hope this helps.

--Eric Tolman
==================================