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September 08, 2008

Metering Your Power Consumption

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Power_meter_small In this world of ever increasing energy costs, almost everyone is trying to save where they can.  I’m one of those people that try to watch our electric bills and understand where all the power is going...  only one problem - there is only one meter on the house.  This lonely meter tells me - via my bill each month - how many kilowatt-hours were consumed by our household.  Not really informative enough for me.  This is the equivalent of getting a bank statement with only the total spent for the month... you’d like to know where all that money went, right?

A good start would be to know how much energy is being used during the day in real time as you use it. I’ve heard about these little gadgets that monitor the power going into your house and wirelessly report your consumption in real time.  An example of these devices is the Power Cost Monitor which actually reads out in dollars per hour and total for the month.  This provides you immediate feed-back on the power usage of your home so you can make decisions on how to reduce your consumption.  What a great idea and it can be installed onto your existing meter without the need for an electrician.

So, my first call went to Florida Power & Light to find out what they can do to help me. After getting though the phone gauntlet and arriving at a human being I asked the question "Is there a way for me to read your meters remotely so I can watch our power consumption".  The answer was, "no, and attaching anything to the meter to read it is considered meter tampering - which is a very bad thing".  This first call did not go well and I didn’t really want to have them elaborate on the "which is a very bad thing" part of that answer. I couldn’t believe the utility company didn’t want me to try and save energy by closely monitoring my consumption.

Subsequent calls to FP&L also failed to find any advocates for such a device.  So I called the company that distributes the monitors and asked if they had ever heard of such problems.  They did agree that certain states and power utilities will not allow a homeowner to place anything in contact with the physical meter.  The utilities are afraid of people attempting to defraud them and steal power - understandable, but pretty hard core considering our energy crisis.  I would think they would embrace this technology and even sell it to you.  The whole ordeal made me want to run out and buy a complete solar installation and disconnect our house from the grid!  Maybe next year...

So my next option would require monitoring equipment to be installed in my main panel - and that has no effect on the utility since it’s on my side of the meter.  There are devices such as "The Energy Detective" available from the Power Meter Store that installs in your main distribution panel immediately following the meter.  This also has a remote unit that provides several real-time and accumulated power consumption numbers.  There is even a version that provides a computer interface and software to monitor and record your usage... a great feature.

Now that I solved the problem with monitoring the total power used by our home, what about the smaller appliances and systems?  There are devices called "Plug Power Meters" which connect in-line with smaller appliances or electronics.  These are watt meters with plugs and are very handy for looking for phantom or vampire loads - power drains caused by electronics that never completely turn off.  But why do electronics draw power even when off?  Let’s take a look.

Many modern electronic systems have microcontrollers (tiny computers) running inside of them to monitor various functions like remote controls, and front panel switches and buttons.  There may also be a clock or other display which are always on (e.g. your microwave oven digital clock). When you turn off the unit by pressing the power button, the microcontroller turns off various sections of the system, but remains on to monitor other buttons or a remote control.  That part of the system never turns off and continues to use energy.

Also, communications equipment such as a cable box remains in constant contact with the central office to monitor network status, receive commands, and to enable and disable services - even when turned off.  You may find only a slight reduction in power for these types of devices when powered down since they continue to communicate with the cable system.  That’s how my DVR records my shows even when I’ve turned it off (see my previous post "The Case Of The Missing 42 Minutes" ).

Sometimes, it’s simply bad design. Take your phone charger and look at the power consumption when the phone is disconnected. You may find it continues to draw power - maybe even one or more watts.  This is due to a lack of electronics to monitor the load.  When the load (your cell phone) is disconnected, the charger may continue to "try" and charge the phone unaware that it has been unplugged.  Low cost chargers are missing this type of circuitry. A better solution is to actively monitor the load and "disconnect" the system when the load (i.e. the phone) is absent.  A simple push-button can reactivate the charger or very low power stand-by electronics could automatically turn it back on when the phone is reconnected. A simple loop in the cable through the cell phone would work.  When removing the phone from the charger, the circuit would be broken signaling the system to power off.  All of these ideas solve the problem, but with additional cost.

For all of you wondering where those 3000 kilowatts of power went last month, it may be worthwhile to purchase a power monitor and find those offending units.  My breakdown was fairly simple... I live in Florida.  The months of July through September are the hottest often exceeding 95 degrees Fahrenheit during the day.  Air conditioning constantly fights to keep the inside of the house cool and constitutes about 40% - 50% of our usage.  Refrigeration is the next biggest followed by other large appliances (i.e. stove, washer, dryer, etc.).  Interestingly, lighting accounts for only about 20% of the total power usage in our home... however, it’s required every day all year long - unlike the air conditioning.  I need to investigate this more over a year’s period.

An interesting note... I installed automated thermostats on all of our air conditioning units (we have three large systems) and saw a dramatic savings in our power bills.  We paid for all the thermostats in the first 2 months and have been reaping the savings ever since.  It turned out that human error (or lack of memory) was wasting most of our power.  Leaving the temperature set incorrectly while at work or away was the biggest offender.  The new thermostats automatically adjust the temperature when we’re gone to save energy and then readjust the temperature to a comfortable level before we return home.

Hope this gives you something to think about.  Till next time...

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I'm in total agreement. I made sure to turn up my thermostat while I know everyone is away from the home to keep A/C costs lower. I also made sure that to keep costs down in the winter, I had a good radiant heating system that kept the family. Overall, it's a good system not only to conserve electricity, but unwarranted costs for times that you're not even there.

Amana PTAC

very nice blog. i need to start monitoring my power so i can save some money.

David Lincer

What about this boo boo.

The heat from inside the refrigerator, plus the power to move that heat from inside the box to outside gets dumped into the kitchen!

Then the AC of the house has to pull that heat energy from the kitchen out of the house.

A better answer would be to separate the condenser and fan (like the AC has) and put them outside.

If designed that way, could be more efficient.

My 25 cents on the topic.

(EZ Note: Right on!)

Energy Zarr

Regarding Chris' point on the A/C units working overtime... it depends on the thermal impedance of your house (yet another topic of discussion). The home thermal impedance is a measure of how easily heat will flow from one side of the walls (and ceiling) to the other. The best case implies infinite impedance where no heat flows. Thus, when you cool or heat the house it stays at the temperature you desire. Unfortunately, these impedances are always lower than optimal. In fact, my house has trouble maintaining a 20 degree (F) differential. This is why my electric bills were so high without the computerization of the thermostats. At the peak of the day (around 3:00 PM) during the summer time the outside temperature can easily reach 98 degrees (F). If you can only maintain a 20 degree differential, then the lowest temperature you can reach during that time is 78 degrees F. We often would leave for work with the controls set at 75 degrees F which would force the A/C units to run without stopping – a huge power drain and very expensive at the end of the month.

I may devote an entry to calculating your thermal impedance… EZ.

Chris Gammell

I think your point about the A/C taking most of the power is interesting, a point of low hanging fruit. I often worry about the power left on from my DVD player being paused, but completely forget about the A/C unit working it's heart out to get down that one last degree that I won't notice. I'd be interested in seeing the costs per degree on A/C and refrigeration units, as I'm sure they get exponentially higher as the temperature lowers (72 degrees as opposed to 74).

Robert

The blog posts are great! Just wanted to share that there's a company which sells a little device called the Kilovolt Amp Reduction (KVAR) Unit or KVAR Energy Controller (not sure how close this is to you but they're in Port Orange, FL and you can check them out http://www.kvarenergysavings.com/index.htm). Now this device won't tell you how much power you're consuming, but it can actually reduce the amount of wasted energy due to the reactive component of the total power your home utilizes.

You effectively get power factor correction (PFC) optimization because your reactive power is now supplied locally, which reduces the total power draw of your home (or industrial office space, etc.) from your power company and significantly lowers any subsequent monthly KVA demand charges (especially if FP&L does any type of KVA demand billing which could very well be the case).

I bought one for my home, had it installed in July and noticed a pretty significant savings rather quickly. The amount of power consumed at my home the month after I installed it was slightly more than the previous month, yet my energy bill was more than $100 less. It will pay for itself many times over...and if we decide to move, we can disconnect it and re-install it at our new home. I haven't received the Spetember energy bill yet, so I'm anxious to see if KVAR is the real deal. I'll let you know...

Andy Turudic

I cycled my A/C when I lived in North Carolina, trying, like you are, to save energy by turning off the A/C while at work. After about a year and a half, my stereo receiver refused to turn on...I took it apart and found a cracked solder joint. It seems the 20 to 30 degree temp cycle work hardened the solder joint to failure, since the big copper leads of the through-hole bridge rectifier in the power supply moved a LOT more than the phenolic PC board during temp cycle. Seems like nothing is ever free, is it?

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