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): 0.1143

Photo:	Description:	Measured Watts (realtime)	Measurement Period (hours:minutes)	Accrued KWh	KWh per month	Cost per month	KWh per year	Cost per year
Computers
	Pentium 133MHz Firewall, single IDE drive	36			26.289	$3.00	315.468	$36.06
	IBM Thinkpad T43 Pentium Mobile 2.00GHz (on, charged, with display, idle)	22			16.065	$1.84	192.78	$22.03
	IBM Thinkpad T43 Pentium Mobile 2.00GHz (on, charged, display off, idle)	14			10.223	$1.17	122.676	$14.02
	Linksys WAP11 (on 24/7)	4			2.921	$0.33	35.052	$4.01
Computer Monitors
	CTX 17 inch CRT Monitor (idle)	3			2.191	$0.25	26.292	$3.01
	CTX 17 inch CRT Monitor (on 24/7)	98			71.564	$8.18	858.768	$98.16
	CTX 17 inch CRT Monitor (my usage)		370:00	10.3	20.336	$2.32	244.032	$27.89
	Dell 19 inch P992 CRT Monitor (idle)	1			0.730	$0.08	8.76	$1.00
	Dell 19 inch P992 CRT Monitor (on 24/7)	121.5			88.724	$10.14	1064.688	$121.69
	Dell 19 inch P992 CRT Monitor (my usage)		189:00	3.17	12.252	$1.40	147.024	$16.80
	Dell 1907FP 19" LCD Monitor (1280x1024 60Hz DVI)	24			17.526	$2.00	210.312	$24.04
Household
	Refrigerator: 1990s vintage		99:38	10.72	78.598	$8.98	943.176	$107.81
	8 inch Household fan 110vac (on 24/7)		423:00	8.01	13.833	$1.58	165.996	$18.97
	Two 4 inch PC fans with 110vac power supply (on 24/7)		97:00	0.37	2.786	$0.32	33.432	$3.82
	Plug in style air freshener 110vac (on 24/7)		291:00	0.42	1.054	$0.12	12.648	$1.45
	Fountain pump (750liter/hour) (on 24/7)	8			5.842	$0.67	70.104	$8.01
	Brother intelliFAX 600 (idle)	6			4.381	$0.50	52.572	$6.01
	Brother intelliFAX 600 (idle)		231:00	1.54	4.870	$0.56	58.44	$6.68
	AudioVox CNR 4 cell phone charger (idle)		69:07	0.00	0.000	$0.00	0
	iRobot Roomba 550 fully charged (idle)	4			2.921	$0.33	35.052	$4.01
	Sceptre 32inch LCD HDTV X32GV-Komodo (idle)	0			0.000	$0.00	0
	Sceptre 32inch LCD HDTV X32GV-Komodo, on 24/7 with backlight at 0	100			73.024	$8.35	876.288	$100.16
	Sceptre 32inch LCD HDTV X32GV-Komodo, on 24/7 with backlight at 4	119			86.899	$9.93	1042.788	$119.19
	Sceptre 32inch LCD HDTV X32GV-Komodo, on 24/7 with backlight at 9	144			105.155	$12.02	1261.86	$144.23
	Sceptre 32inch LCD HDTV X32GV-Komodo, on 24/7 with backlight at 10	149			108.806	$12.44	1305.672	$149.24
Lighting
	50W Desk Halogen Lamp (high)	53			38.703	$4.42	464.436	$53.09
	50W Desk Halogen Lamp (low)	37			27.019	$3.09	324.228	$37.06
	100 mini Christmas lights (incandescent)	39			28.479	$3.26	341.748	$39.06

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
November 7th, 2009