The Dreaded Energy Bill & the Do-It-Yourself Energy Meter

dpslusser

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Join Date
Jan 2016
Location
PA
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Hey guys.

A little sticker shocked the last few months with how much my electric bill has been. Even though it is summer, we haven't been home much to be hammering on the A/C. Logging onto my account, my usage it about 1/3 more this year, than last year; and I;m not totally sure why.

So...recently, I installed a "SCADA" system in my house using a PLC and Raspberry PI. And since the PLC sits 4 foot from my breaker panel, I am contemplating a way to "peer" check the power company's recorded usage for each month. Or...find out, what in my house it utilizing the power.

First off. I have NEVER reviewed the energy bill at this detail, and it may be that I just got done working 12 hour days. But, can someone explain to me what the bill means when it states that I used 1,818 kWh?

Currently my average per kWh cost is 12.1 cents.


Secondly. I scoped out some Dwyer 4-20mA, CCT40 split-cores to slap on my phases. Any better suggestion or route?

How would one tackle the calculation for "peer" checking the power bill?
 
Here's one solution...

I use these for Load-Shedding across So. Cal., particularly from June to October when Tier Demand Charges can be 3 or 4 times what some users actual energy consumption was for the month. It has to do with Edison's Demand Interval periods. Anyways, these monitors are private labeled by several players (Eaton, Schneider etc.) and do all the calculations at an accuracy that allows them to be used as sub-meters in apartment complexes or wherever - legally. So they're pretty good. I communicated to them via MODBUS and then the PLC would "shed" certain pieces of equipment if the Demand Interval the customer wanted to stay below was being approached. Typically a demand interval is 900 seconds/15 minutes. Then when you enter the new Demand Interval period, you bring the equipment back online. Everything has to be prioritized and selected based on how critical the equipment is to the process or facility.
Anyways, you can find them on ebay sometimes pretty cheap too.
 
First your KWh is kilowatt hours. So If you use a are consuming 1000w of electricity for an hour that would be one kilowatt hour, or you were consuming 2000w of electricity for an hour that would be 2 kilowatt hours, or you could run a 100w lightbulb for ten hours and that would be 1KWh.

A few things thoughts:

Were you recently upgraded from an old electromechanical meter to a smart meter? A few people around here had issues when their meter was upgraded not because the new meters were inaccurate but because the old meters were running "slow" and not adding up all the usage properly.

I would look at the big power users Hot tubs, well pumps, electric water heaters, sump pumps, etc.

Just reading the current using one of those CT's won't be enough to calculate the power. Electrical power is a combination of voltage, current, and their phase relationship between each other. You can have current flowing and not actually be using power. You could use the CT though to monitor suspect circuits and see how much their drawing and how often they run. Revenue grade meters are usually pretty dang accurate. If you have a smart meter some of them will give you your real time demand reading and you can use that also to try and see where the problem might be.
 
in some locations, the local electric utility company is actually your best friend when it comes to figuring out where you're using/wasting energy ... personally I'd check with them first – you might be able to have them come out and do a free "energy audit" for you ...

one quick check that you can make yourself - is to make sure that there's no water constantly dripping from the drain line on your water heater's pressure relief valve ... that's a sneaky one that can cost a bundle because you're paying to heat the water that's just flowing down the drain ...
.

energy_checkup.jpg
 
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If the KWhr meter is a newer version with some electronics they
normally have an LED that pulses faster when more power is consumed

My KWhr meter does 600 pulses per 1 KWhr
So if you count those pulses into your PLC you can calculate your energy usage
 
Another big item that will run your electric utility bill through the roof is improper maintenance on your central A/C system.

Evaporator and Condenser coils need to be cleaned every year at a minimum.
If either or both of these coils are not perfectly clean then it makes heat transfer very inefficient, resulting in you A/C running much longer to cool your home.
(or more correctly stated "to remove the heat from you home") :)
 
To add to Berring C Sparky post make sure the outside units fan
is working and that vegetation does not impede that air flow

Is the unit short of refrigerant gas is another possible problem.
 
And unfortunately, I bet a very large percentage of units are charged incorrectly by the installer. Charging to "beer can cold" instead of weight, superheated, subcool, etc is pretty common. As is putting in systems with wet lines since most people will put on vacuum for a few minutes then dump gas.
 
Just FYI, a couple of common causes for a bill jumping like that from one year to the next is either an electric water heater that is malfunctioning and not turning off, or a well pump doing the same.

The quick check on that is to turn off all of your appliances etc,. then turn off all of your individual breakers (not the Main), then look at the meter. If it's not recording usage, turn each breaker on one at a time and observe what happens. If you see the meter start registering usage, but whatever it is feeding SHOULD be off, there's your culprit.

By the way, not as common, but not unheard of: your next door neighbor has a pot growing operation next door. He ran an extension cord over to your house under the bushes and plugged into some outdoor receptacle that you never use and don't look at.
 
Man I am glad I added the correct terminology in parentheses to the end of my first post, I figured some of you guys had some HVACR background.

I hold a HVACR Contractors License as well as my Electrical Contractors License.
When I owned my own business contracting, I would preach to all my customers that they must have there unit serviced at least 1 time per year and recommended 2 times per year was even better.
I have been out of the contracting business now for 10 years (today in fact) and last week my wife called me and said the A/C was not working, I am at sea so I had my father go over to look at it, and.........it was a dirty condenser coil, seems I have forgotten to clean it for, oh about 6 years now.......seems like whatever we do for a living is the most neglected thing at our own homes. :)

I should have known this by my ever increasing electric bill also.

BCS
 
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The power at any given time, in kW, is the instantaneous voltage multiplied by the instantaneous current. If you have a perfect sinewave for voltage and a perfect sinewave for current, then the average power is V_rms * I_rms * cos(ø), where ø is the difference between the peak of the voltage and the peak of the current, measured in degrees of the sinewave. If they are exactly 90degrees apart, the power is always zero, if they are 180 degrees apart, then you are supplying voltage to the grid. If they are 0 degrees apart, then you win! (Where the game is either power factor correction, or not having any inductive or capacitive loads). The term power factor is often used in place of cos(ø).

However, if you do not have perfect sinewaves, you need to calculate the power at every instant and then integrate.

You can use some circuitry to convert the voltage into a signal that can be read by the PLC.

It sounds like you have some circuitry for the current, but it gives you the amplitude of the RMS current, not the instantaneous current. This is fine if your power factor is very close to 1, as you can assume pf=1 and just pay extra for your conservative assumption. The above formula is then P_ave =V_rms * I_rms.
However, I'd your pf is not near 1, you will be inaccurate by exactly that much.

You could get a current transformer which rather than having an RMS output, has an instantaneous output, but as per Miss Google, (http://www.ccontrolsys.com/w/Measurement_Errors_Due_to_CT_Phase_Shift) you will still be inaccurate.

You could perhaps work out a mathematical model of your current transformer to account for these measurement errors and cancel them out.

Now if you are worried that you do not have a perfect sinewave and want to integrate manually, the sample time of your PLC will introduce errors. For example the compactlogix 1769if4xof2 has a sample time of about 5ms, which only gives you four points across your 50hz cycle (less if you live in 60hz land). Perhaps you could get better sample times with the raspberry pi, although from memory this doesn't have any analog I/O.

Or you could purchase and install a Watt Meter, preferably one that is certified for billing, and integrate this into your PLC.

Of interest, do you have 3phase? The V*I gets tricky in this case. Usually you can just multiply by sqrt(3).
 
In PA. you are allowed to pick the power generation supplier of your choice. I see your average KWH is 12.1 cents. Mine is a fixed rate for one year at 6.28 cents per KWH. Don't know if this would help you or not. www.papowerswitch.com
 
By the way, not as common, but not unheard of: your next door neighbor has a pot growing operation next door. He ran an extension cord over to your house under the bushes and plugged into some outdoor receptacle that you never use and don't look at.

jraef, Northern California = Humboldt County??
 
Slightly offtopic, but you can also get Kill A Watt meters to measure individual appliances. I've borrowed them for no charge from my local library.
 
Even more off topic, but What's AustralIan doing in the UK? What could have possessed you to move away from the World's Most Liveable City 6 years running? :confused:
 

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