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Killawatt Myths

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Posted by bealiba on August 4, 2007, 11:30 am
 
The Killawatt Myths

First of all, the Killawatt (and its brothers) is a handy tool. Like
all tools it must be used correctly.

For many people though it is a party trick used to impress others.
This is not a correct use.

Myth 1

You need to use a watt metre to do an energy audit.

This is false.

In most instances the loads (appliances) are not available to be
measured. You are perfectly safe to use the appliances rated energy
use as provided on the compliance plate of the appliance you are
considering using.

Myth 2

All loads in the energy audit should be measured at the setting you
think you will use.

This is false.

Sizing a system to the energy use less than an appliances full rating
leaves no leeway for changes in use patterns. Such a system may suit
your needs today but fail in the near future. A baby, a sudden illness
or a new appliance can bankrupt a system. You can not add a load to a
system that is only just meeting the demand.


Posted by wmbjkREMOVE on August 4, 2007, 3:02 pm
 
On Sat, 04 Aug 2007 11:30:06 -0000, bealiba@gmail.com wrote:


Apparently you're easily impressed. How many parties have you been to
where people were showing off $0 devices?


One cannot do an *audit* of any variable-load appliance without some
sort of Watt-hour device. If one cannot make an audit, then an
estimate will have to do. These articles cover the subject nicely.
http://www.homepower.com/files/promised/loadcalc.pdf


No, in most instances the load *is* available. When it's not, it's
still better to *measure* the energy consumption of a similar
variable-power load (or use another's measurements) than to estimate.
Multiplying a max-power rating that doesn't reflect normal use, by a
time that may or may not be accurate, is a recipe for a faulty
estimate. Adding up multiple faulty estimates compounds the problem.


No, those ratings on are irrelevant when auditing, and often next to
useless for making an accurate estimate. For example, computer power
supplies are rated at max capacity, but oft times a machine with a
350W power supply, uses a max of <100W in real life. Additionally,
hours of use is one of the most frequently underestimated numbers in
home power system planning. It's far better to *measure* those hours
than estimate them.  


No, an *audit* will measure the load in conditions as close as
possible to the expected use. One might adjust for different
conditions if need be. For example - if you measure a dishwasher set
to energy-saver mode, then you might want to allow something extra for
the occasional time it might be used in full-power mode. Or if you
measure a fridge's consumption during warm weather, you might want to
subtract something to account for the rest of the year's cooler
temperatures. You'd make the same adjustments to an *estimate* based
on appliance energy rating labels.... after you figure out the
conditions the manufacture used to establish the rating, and how much
different your own application might be. Obviously trying to work
backwards through those numbers is pretty silly if the load can
instead be measured accurately with a $0 device.


Thank goodness we have you to tell us that loads that weren't
accounted for, aren't accounted for. <snorf>

Anyway, I note that in another thread you imply that if one doesn't
live off-grid, then he's not qualified to give advice here. Which begs
the question - how many KillaWatts have you used? How many electric
fridges, dishwashers, and clothes washers etc. have you measured?
Since you obviously don't have *any* experience measuring
variable-power loads, then by your own reasoning you shouldn't be
giving advice on the subject, much less lecturing on what you imagine
others are doing wrong. Why not get a Watt-hour meter, measure some
variable-power loads with it, and *then* report on your experience?

Wayne

Posted by bealiba on August 4, 2007, 11:23 pm
 On Aug 5, 1:02 am, wmbjkREM...@citlink.net wrote:

nicely.http://www.homepower.com/files/promised/loadcalc.pdf

Drivel. You have no idea what your loads or input is. Why don't you
take your party trick and tell us what all your loads are?


Posted by Vaughn Simon on August 4, 2007, 3:11 pm
 

    Yes, I agree that would be a perfectly safe thing to do...if you want to
drastically oversize the system.  The wattage ratings marked on appliances
seldom reflect reality, and they can never reflect usage patterns.  I have seen
appliance markings that obviously reflect the rating of the appliance's power
cord!  I am a licensed electrician, and I can tell you that houses are not wired
that way, and it would be a total waste to design the power source that way.

     Any domestic power system "design" that does not take usage patterns into
account is not a design at all.

     And you are trying to preach to us about design?    Give it up!

Vaughn



Posted by bealiba on August 4, 2007, 11:20 pm
 wrote:

wired

More Drivel. Prove you assertion that it would drastically over size
the system.


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