Power Down with DMAIC

Energy & Sustainability Science
Power Down with DMAIC


If your electric company has tiered rates, you’ll pay a reasonable price for a little electricity, a higher price for more — and a vastly higher price if you use too much.

To reduce my bill, I’ve started carefully measuring my household electricity usage, and trying different things to reduce it. I’m using the approach that’s taught to engineers, called the DMAIC process:

Define — state the problem to be solved

Measure — quantify the problem

Analyze — find the root cause of the problem

Improve — fix the problem and measure the results

Control — make sure the improvements are sustained, and detect new problems that crop up

Here’s how I applied the process to my problem.


I don’t want to pay the highest rate for electricity.


I need a way to measure energy usage. I wanted to learn, for instance, whether an electric stove is more or less efficient than a microwave. A number of companies have started selling home energy and water usage systems with sophisticated analysis software (see page 48, “Home Energy Dashboards”), but I went the less expensive route and bought two different instruments to measure how much electricity my house’s appliances and systems were using:

» The Kill A Watt EZ (p3international.com) power meter monitors the energy usage of whatever appliance you plug into its standard outlet (Figure A). It measures power on a 110V line up to 1,875W. Using it, I learned that Mr. Coffee uses 850W even after the coffee finishes brewing. Turning it off right away will save me at least $50 a year. I also found some lamps that were still using wasteful incandescent bulbs.

» The Black and Decker Power Monitor (blackanddecker.com/energy) is good for measuring the big power hogs and whole-house usage. It isn’t as precise as the Kill A Watt, having only 100W resolution, and it only measures down to 300W. But it continuously reads the electric utility meter on the side of your house (Figure B), and wirelessly sends a power consumption measurement to a handheld monitor.

It helped me learn the rhythm of power usage in my house, especially heating, cooling, and refrigeration. To measure a single appliance with it, I turned the appliance on and off, and recorded the change in household power shown. (If other appliances such as the furnace or the refrigerator kick on during the measurement, you have to try again.)

I was disappointed to learn that neither microwaves nor conventional electrical stoves are efficient, and used equal amounts of power to boil 2 cups of water. I asked Kirsten Sanford, Ph.D. (aka Dr. Kiki, creator and host of the radio show and podcast This Week in Science and the TV show Food Science) about this. She let me measure her induction stove, which has an element that becomes cold to the touch right after you use it, and it turned out to be about 3 times as efficient as either the electrical stovetop or the microwave.


What do your measurements tell you about the problem?

» The appliances that use the most juice tend to be expensive, and you may not have the cash to replace them now.

» Some appliances, such as the hair dryer, use a lot of watts but aren’t on for long. Others, like my Mr. Coffee, waste power for as long as you’ll let them.

» The microwave wins for small jobs and the stove wins for big jobs, but only by a little bit.

» And of course, incandescent lights use way too much power.

I tried a compact fluorescent lamp (CFL) bulb in a ceiling fixture, but it burned out quickly. What was the problem there? A web search found all sorts of complaints about CFLs, but the one that made the most sense was that the electronics in the base tend to get too hot when the bulb operates upside down. That’s how the bulb is positioned in my ceiling fixture — inverted.

I measured the temperature of my CFL (see page 55) and found that it ran much hotter upside down — sharply reducing its working life.


The next step was to take action to lower my bill, based on my analysis. Here’s what I did.

1. Using the whole-house energy monitor, I turned energy saving into a game. I wanted to see the meter go down, so I went around turning things off, trying to see how low I could make the number go. I “won” when my house was using less than 300W, which is the lower limit for the meter. By leaving the meter on the kitchen table, it was convenient to “play again” any time.

I quickly became one of those people who go around turning off lights and carefully thinking about what I want before I open the refrigerator. Since I know the power consumption of all my appliances, I know which ones are most important to use wisely.

2. I modified the inverted CFL bulb by cutting the base in two and making a lamp harp to suspend the ballast circuit below the bulb. I ran wires from the base down through the bulb coil, and into the ballast through holes drilled in the side (Figure C, and highlighted box on next page). This solved the overheating problem, but the ballast created an ugly shadow. I’m sure you’re familiar with the look of a dead bug in a light fixture — this looked more like a dead rodent. I didn’t even bother showing it to my wife. Ideas for improvement are welcomed.

I gave up on the inverted design, for this fixture at least, and switched to an instant-on, high-power-factor CFL bulb made by U Lighting America. It has a 125°C-rated electrolytic capacitor and it’s dimmer-compatible, meaning it also works in lamps that use solid-state switching, such as motion sensors.

3. I changed my always-on Linux server from a desktop machine to a hacked Western Digital NAS drive running Linux on its embedded ARM processor, which uses less power than the desktop server.

4. I found that some appliances used appreciable standby power. I put those on a power strip so that I can turn all of them off. (My new internet radio was the worst offender.)

5. I got an Isolé IDP-3050 occupancy-sensing power strip for my garage, and plugged the main lights into it. I often get distracted and walk away without turning off the garage lights. The power strip senses that I have left and turns them off after an adjustable delay.

6. I also got a Smart Strip LCG3 power strip that automatically switches off outlets based on the draw from its one control outlet. This is ideal for a television, where you’d like to turn off several components at the same time as the TV. The power strip also has unswitched outlets, so that you don’t lose time on clocks, for example.

Since I live TV-free, I haven’t found a place to use this yet! I was hoping to use it with a computer, but the requirements for the power up and power down sequencing of the computer are too complex for this approach.


Control requires ongoing monitoring. The power company reminds me every month how I’m doing! So far, I’m happy to report that my electric bills are lower than they were last year. This is remarkable because I was using CFLs even before I made the changes.

The DMAIC process helped me find a few energy leaks, and cut my usage from 19.9 kilowatt-hours (kWh) per day last year to 16.4kWh/day this year. My baseline rate is 12.6kWh/day, so my reductions put me just under the really high rates, which begin at 130% of baseline.

I’m saving about $28 a month. I’ll continue to use DMAIC to see if I can reduce my bill even more.

Too Hot in the CFL

When I suspected that overheating killed my CFL bulb, I cracked it open to look at the electronics. I built a tool to open the base by drilling a 1″ hole in a block of wood. This holds the bulb by the base. Using a screwdriver as a lever, I pried apart the seam in the plastic base. To make it easier, I created a fulcrum from a scrap of aluminum angle. With practice I was able to separate the base without much effort. The CFL base easily snaps back together, and the light still works (FIgures D and E).

CAUTION: Wear gloves and safety glasses if you open CFL bulbs. Don’t touch the spiral glass tube; pushing the glass won’t persuade the plastic to move. Work in a well-ventilated area such as outdoors or in a garage.

The bulb contains mercury, and should be disposed of according to the directions at lamprecycle.org. Don’t fear the mercury — if the bulb breaks, the 5mg of mercury in it is unlikely to hurt you because it’s in metallic form and it’s a tiny amount. Just take care not to touch it or breathe it, air out the room for 15 minutes or more, and follow cleanup instructions at epa.gov/mercury/spills/index.htm#fluorescent.

The circuit in the base of the CFL is called a ballast (Figure F). It regulates the current drawn by the bulb; even as the AC voltage fluctuates, the current stays the same. It uses a 20µF 200V electrolytic capacitor with a temperature rating of 105°C (221°F). The capacitor is expected to last 10,000 hours — but for every 10°C (18°F) of heat above its rating, its lifetime drops by a factor of 2.

You can measure the temperature inside your CFL bulb with a thermocouple. Sears sells a voltmeter that comes with a thermocouple and measures temperature (Figure G). Take apart the plastic CFL base, drill a small hole in it, and put the thermocouple inside. (Because the thermocouple is made of wire, take care that it doesn’t short-circuit the electronics.)

After it warms up, you’ll find that the temperature in the base of the CFL varies when you change the orientation of the bulb. Measure it in a variety of positions, and try it in a totally enclosed light fixture.

I found that the enclosed fixture causes only a small rise in temperature, but there’s a large increase when the bulb operates upside down.

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Tom Anderson

Tom Anderson is the chief bottle washer at Quaketronics and shows up at his local Perl Mongers and Dorkbot meetings.

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