\n";
$link="";
$displayTime="";
$calcdCostPerYear="";
if ($image != "")
{
$link = "![](\"$image\")
";
}
echo " $link | \n";
echo " $description | \n";
echo " $measuredWatts | \n";
if ($measuredWatts != "")
{
$calcdKWhPerMonth = number_format($measuredWatts * 24 * 365.25 / 12 / 1000, 3);
}
#echo " $calcdKWhPerMonth | ";
if ($measurePeriodHours != "")
{
if ($measurePeriodMinutes == "")
{
$measurePeriodMinutes = 0;
}
$displayTime = "$measurePeriodHours:$measurePeriodMinutes";
}
echo " $displayTime | \n";
echo " $accruedKWh | \n";
if ($accruedKWh != "")
{
$calcdKWhPerMonth = number_format($accruedKWh * 24 * 365.25 / 12 /
($measurePeriodHours+$measurePeriodMinutes/60), 3);
}
echo " $calcdKWhPerMonth | \n";
if ($calcdKWhPerMonth != "")
{
$calcdCostPerMonth = '$' . number_format($calcdKWhPerMonth * $KWHbaseline, 2);
}
echo " $calcdCostPerMonth | \n";
if ($calcdCostPerMonth != "")
{
$calcdKWhPerYear = $calcdKWhPerMonth * 12;
}
echo " $calcdKWhPerYear | \n";
if ($calcdKWhPerYear != "")
{
$calcdCostPerYear = '$' . number_format($calcdKWhPerYear * $KWHbaseline, 2);
}
echo " $calcdCostPerYear | \n";
echo " \n";
}
?>
Household Electrical Power Use and Cost
Study of device electricity consumption and annual cost
Philip Shuman
Overview
In searching the internet, I found very little data on ACTUAL power consumption
statistics for various household items. In order to calculate ROI for investing
in power saving devices, one must know how much your current devices are using.
Many devices will have their MAX current
draw printed on the back, but how close does the printed number come to their
actual use? I purchased a
P3 Kill-A-Watt
power meter to measure how much electricity each device uses. As a
service to humanity, I documented my findings provided here.
Means of Measurement
The Kill-A-Watt is capable of giving many different readings, but two are
useful in calculating use as it applies to money out of my pocket:
- Watts: This will tell you how many Watts are being drawn at the
current instant. For devices with a constant power draw (light bulb), this is
enough for you to calculate Cost per year. For devices with varying power draw
(refrigerator) this doesn't really help much.
- KWh and Time: The KWh reading will tell you how many KiloWatt Hours
have been used and in conjunction with the length of time the meter has been
plugged in, you can calculate Cost per year based on the sample time. Obviously
if you measure your Air Conditioner for 24 hours when it is snowing outside,
do not use that data to figure the rest of the year.
Data:
US Dollars per KiloWatt Hour (KWh):
| Photo: |
Description: |
Measured Watts
(realtime) |
Measurement Period
(hours:minutes) |
Accrued KWh |
KWh per month |
Cost per month |
KWh per year |
Cost per year |
| Computers |
(on, charged, with display, idle)","22","","","");?>
(on, charged, display off, idle)","14","","","");?>
| Computer Monitors |
| Computer Accessories |
| Electronics |
| Household |
| Lighting |
Notes
- Watts are only measured in whole numbers. When reading 4 or 5 watts,
the annual cost could be off by a significant percentage, but relatively low
cost.
- Time is measured in hours and minutes until it hits 99:99, then switches to
hours only. Measurements over 100 hours may have actually more minutes, but
were truncated in the display. Again, the error factor is low.
- Most entries above assume the device is left on all year long, with the
exception of entries that say "(my usage)" in which case it is an actual
measurment of how much I used it during that period. Want to know what 40 hours
a week looks like instead of always on? Divide the Cost per year by 4 for a
good approximation.
Philip Shuman
http://www.shuman.org/
philip at shuman dot org
July 29th, 2011