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How to Estimate Residential Kilowatt-Hours (kWh)

12/07/2009 12:09 AM

Increasing cost of electric power has me very interested in measuring just how much power the various appliances in my house use. All I can do now is read kilowatt hour totals off my electric meter. Sometime next year I expect to get a smart meter that tells when the power is used and see my bills go even higher.

The only other thing I can do now is buy the little $25 Kill-A-Watt gadgets which work only on 120 volts and up to 15 amps. I can buy these and put them on the TV, computers, washing machine, fridge, freezer, microwave and anything else with an ordinary plug. But I have to go around periodically and read each one individually. My heavy hitters like the air conditioner, well pump, clothes dryer, electric range and hot water heater all run on 240 volts and would require expensive professional meters to record the same data.

So there is a product I'm ready to buy if someone will develop it for the consumer market. I suppose I could try building it myself; but I'm not a sparky and wireless computer connections are way beyond me.

Here's what I want:

1. Low cost transducers that read current flow via and receive nominal small amounts of energy by inductive coupling and then transmit amps and time of day wirelessly like by Bluetooth to a main box next to my computer. The transducers would work and look like the clamp-on ammeter attachments for DVM's. A small rechargeable battery might be needed to continuously measure small currents while the appliance is in a standby mode. I visualize a $20-$25 retail cost each in consumer market volumes.

2. The main box would be on continuously fed by a wall wart and connected to my computer USB. Turn on the computer and the box downloads all the data since the last download. Software in my computer lets me assign identification data, voltages and other stuff like power factor for each channel and then display or transmit data in a format I could customize. I look for a $100 retail cost for the main box and comparable package deals for entire systems with a set of transducers.

3. Also available would be a weatherproof version for use outside on ordinary extension cords (like for holiday decorations) and a special mounting/grounding kit for transducers that could be placed on the neutral main wire to measure total KWH used in the event of delays in the utility setting up a program for reporting customer power usage on a real time basis via the internet. Expected retail cost $35 and $50 for the grounded unit.

4 Further down the line might be a transducer that also measures power factor.

My question is when can we expect these systems to show up in my local big box store?

Ed Weldon --- in the land of the 42 cent kilowatt hour

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#1

Re: Counting the kilowatt-hours at home

12/07/2009 12:45 AM

Most of the household appliances I can think of use a pretty uniform current when they are on, so it might be sufficient to monitor on/off status rather than current. Plus monitor the main incoming current.

A stove has a variety of possible load combinations (burners cycling on/off), so maybe it deserves a single current monitor rather than as many sensors as heating elements.

I'm just thinking out loud here, but it would make sense to use the simplest instrumentation possible that does the job closely enough.

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#2
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Re: Counting the kilowatt-hours at home

12/07/2009 1:25 AM

Tornado -- I like the idea of an on-off sensor if it turns out to be a few bucks cheaper. Hot water heaters are pretty constant. Stoves vary a lot and the only real easy place to put a clamp-on is on the main 50 amp circuit going in. One point is that a variation in current draw can give an indication of problems with the appliance and suggests an additional preventive maintenance and troubleshooting function for the KWH counter system. In use a current measuting transducer could be put on an appliance to gain actual current data and then replaced by a cheap on/off two state transducer for ongoing use. Maybe the current measurer would be the only one with an internal battery for measuring low currents.

The consumer application really doesn't need great accuracy of measurement. the average user will focus more on relative readings than absolute amounts, detailed calculations and analysis. A product of this type designed to make engineers happy will end up costing a thousand dollars. To get real cost saving sales/production volume it needs to cost no more than a couple of hundred dollars for the system and peferrably down around $100. I think the payback for the average customer should be no more than 6 months or the interest won't be there.

BTW, a company could get a product like this off the ground by selling early production models to plant engineers who would likely be willing to pay a higher price to produce necessary margin to support low volume production.

Ed Weldon

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#3

Re: Counting the kilowatt-hours at home

12/07/2009 1:30 AM

Check around at marinas for used meters. I used to work at one, each boat is metered. The device is about the size of a dozen egg box, has two donut type things that have to have the individual lines for the appliance fed thru them, not that big a deal most of the time, just not quick to move from one thing to another.

I have one on my solar hot water heater, it lets me know if something changes.

When a marina upgrades its dock pedestals, which don't last too long around salt water, they may pile the old ones somewhere for parts. Make friends. These things retail not cheap, mine is made by Integrated Metering Systems, Fla., it's digital, will monitor two things at a time, separate meters.

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#6
In reply to #3

Re: Counting the kilowatt-hours at home

12/07/2009 11:27 AM

Mike -- Here's one of the IMS products. (thanks for the lead; IMS came right up on a Google Search)

http://esubmeter.com/store/product_info.php?cPath=34_50&products_id=128&osCsid=ba5ae8521fa58324dabfa145f706dcec

Not cheap at $277; but then you're paying for accuracy (they call it "revenue grade").

It's sort of like hand hald DVM's You can pay $300 for a top of the line Fluke. You can also pay $3.99 for one at Harbor Freight. Maybe these are the guys to make this happen for KWH meters though I doubt if the price will be as low as the DVM's.

Ed Weldon

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#4

Re: Counting the kilowatt-hours at home

12/07/2009 2:02 AM

How about a USB enabled device that could be installed within the circuit breaker panel, with as many clothes-pin-sized (larger for stove and water heater) CTs as circuits? Send the data to a PC with a spreadsheet program that can produce whatever logs or graphs one might need. Mass production could get the cost within popular range. The clamp-on idea would enable easy DIY retrofit, without disconnecting wires and sliding donuts over; although new installations could go with donuts. Just some ideas.

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#5
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Re: Counting the kilowatt-hours at home

12/07/2009 11:06 AM

GA!! I think the idea of simple little "clothes-pin" that reads out KWH to one or two decimal places on a visual indicator would be a super product in itself. Like some of the Apple products I suspect it will be no small feat of electronic engineering. Way beyond my level to do anything other than wish for.

I wonder about getting a thing like that to work at all in an electrically noisy environment like a circuit breaker panel. I suspect it would come with a yellow tag bigger than the product itself warning users not to place it on bare wires or inside circuit breaker boxes.

Maybe the only viable business model would be to sell them directly over the internet and ship them from a foreign place like Hong Kong where they are isolated from US courts. I recently bought some diodes from an outfit over there paying by Paypal. The shipping time and cost was very nominal.

Ed Weldon

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#7

Re: How to Estimate Residential Kilowatt-Hours (kWh)

12/07/2009 11:29 AM
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#8
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Re: How to Estimate Residential Kilowatt-Hours (kWh)

12/07/2009 11:48 AM

Wareagle -- Useful info in the link. Thanks.

But as I suggested in the opening question the Kill-A-Watt has limitations and for the big energy using 240 volt appliances more expensive meters need to be installed by an electrician and need to be individually read for data collection. This is still not very practical for the average homeowner hoping to knock $25-$50 bucks a month off his electric bill.

Ed Weldon

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#9

Re: How to Estimate Residential Kilowatt-Hours (kWh)

12/07/2009 12:07 PM

I think this is what you are looking for.

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#10
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Re: How to Estimate Residential Kilowatt-Hours (kWh)

12/07/2009 12:32 PM

JRaef -- GA!! Many thanks!! The TED folks are already there (well given the 3 months they need to fill back orders which probably puts delivery of product to order out into the early spring of next year) and their products look pretty interesting to me. Prices are a notch or two above what I figured; but that is understandable for a product line that has not grown to the market size that will offer economy of scale associated with most consumer electronics.

Gotta go see what this Google Power Meter is all about.

Thank you again, Ed Weldon

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#11

Re: How to Estimate Residential Kilowatt-Hours (kWh)

12/07/2009 11:20 PM

I think I think you'll find your meter here

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#12

Re: How to Estimate Residential Kilowatt-Hours (kWh)

12/08/2009 4:30 AM

Aren't all these monitoring devices (and the reason for their existence) a sledgehammer to crack a nut? Every appliance has a rating plate and, if this can't be read, the consumption can be estimated to "near-enough" accuracy. This will tell you which are the power-hungry devices.

So you switch off everything that's not required, and only use things when required. How can you save on that, no matter how much you monitor the consumption?

A few Golden Rules - anything that generates heat (heating, cooking, etc.) uses BIG KW - don't leave anything on standby - don't leave the freezer/fridge door open - switch off lights when you leave the room. Simple!! Don't need to buy a gadget to tell me this.

Or am I missing something here?

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#16
In reply to #12

Re: How to Estimate Residential Kilowatt-Hours (kWh)

12/08/2009 11:30 AM

M Daniels -- You are missing something here. Most of the heaviest power users have a duty cycle that is subject to internal control functions, external adjustment by a human user and performance deterioration due to wearout or external influences. They are not simple "on-off" devices like a light bulb. Stoves, air conditioners, hot water heaters, well pumps, refrigerators, freezers, clothes washers and dryers, electric room heaters and shop tools all have these characteristics.

Once you've taken all your Golden Rules to heart and made them a part of your everyday life where do you put your next efforts and limited resources to work? Which equipment improvement is most deserving of your attention? For me the "nut" is a big one. I'm looking at 62 cents a kilowatt-hour next year to air condition during the 105-110 degree summer heat periods.

For those of us with technical experience in some area of commerce analysis by numerical means has become the way we approach much of our problem solving. Having good measuring devices in one's kit is fundamental to doing the job right. When one is looking to save money a principal rule should be "Don't spend a lot to save a little". This is where careful analysis pays off.

For the rest? Go to that solar seminar, believe the talk about running you electric meter backwards and write that check for $15K or more. Or buy the 2 for $19.99 gadgets you clamp on your power cords to make the electricity more "efficient".

Ed Weldon

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#19
In reply to #16

Re: How to Estimate Residential Kilowatt-Hours (kWh)

12/08/2009 12:06 PM

Ed,

Fair comment, but I still mintain that all the appliances that you mention are capable of being used efficiently using the simple rule of "if it ain't necessary, don't switch/leave it on".

I'm not having a go at you, just trying to expand my knowledge as my background is more electronics than electrical - and you've hit the nail on the head by saying that "a principal rule should be "Don't spend a lot to save a little"". I couldn't agree more. I've known people buy an energy-efficient appliance to save money, and the payback time works out at longer than the expected life of the appliance (and the owner)! Some saving!

Here in the UK we are expecting news updates on the intent to furnish all domestic consumers with an intelligent meter to save meter-reading for the utility provider and also advise the customer of the information of the sort that you wish to gather.

Another rule to add to my Golden ones - use off-peak electricity whenever possible e.g. washing machines, spin driers, storage heating. Timers are cheap and can repay their cost very quickly.

By the way, at 62cents/KW hour any savings are worthwhile. WOW! I thought my electricity at about a third of that price (peak) was ridiculously expensive!

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#13

Re: How to Estimate Residential Kilowatt-Hours (kWh)

12/08/2009 4:54 AM

Sorry guys, the last "guest" post (No. 12) was me, my PC didn't log me in for some reason - sorted now, I think.

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#14

Re: How to Estimate Residential Kilowatt-Hours (kWh)

12/08/2009 11:01 AM

Ed,

Your utility, PG&E, has tools available on their website to help you analyze your usage. They also have information on appliance usage.

Some newer appliances have the ability to talk to a home area network (HAN). Several companies, including Google, are rolling out meters which can also talk to your HAN and provide real-time metering data. Also, most utilities are working hard on improved metering to better manage their business, and nearly all of us will be making some or all of that data available to the consumer.

I would strongly suggest asking the utility if they already offer something that would work for you. At the very least, they have extensive knowledge of what's available which could do what you want.

Tony --- in the land of the 10 cent kilowatt hour

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#18
In reply to #14

Re: How to Estimate Residential Kilowatt-Hours (kWh)

12/08/2009 12:00 PM

Thanks, Tony. I think your advice on getting help from the utility is good for most people. PG&E hasn't been a lot of help for me. They have all they can do just to keep the electricity on in the rural area where I live.

I'm looking at a major investment just to keep my energy bills in line and I have to be ready to do a lot of the engineering myself. I can't rely on the utility's "cookie cutter" approach designed for all the little boxes that people live in down town.

Ed Weldon

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#20
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Re: How to Estimate Residential Kilowatt-Hours (kWh)

12/08/2009 2:22 PM

Wow Ed

I'm feeling lucky to be in the 11-26cents per KWH range, up here.

Direct feed back is good. if you looked at the read out for the stove & you could see that it cost $2 to cook your breakfast eggs & coffee, you would pay more attention. My oven is propane, but has a glow plug to keep it lit, that draws 2 amps & an interlock that keeps the gas from coming on unless the GP is drawing current.

I recently had an experience with my neighbors. We have a shared well, the pump is hooked up to their meter. they were try to tell me it cost more than $50/month to run.

I did a bit of checking & came back with a figure of closer to $7/month, if both households were using 1000+ gallons per day

I love to put a meter in just for the pump, but the the payback just isn't there on a $250 meter.

Here's a fun little calculator widget

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#22
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Re: How to Estimate Residential Kilowatt-Hours (kWh)

12/08/2009 4:28 PM

Garth -- Thanks for the tip on "widget". Suggests to me that it would not be all that hard to put together a spreadsheet and go build a database on the stuff in my own house. Maybe I'll go hunt for some freeware first. (and buy a clamp-on ammeter attachment for my DVM)

Ed

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#23
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Re: How to Estimate Residential Kilowatt-Hours (kWh)

12/08/2009 5:48 PM

The ammeter attachment costs about as much as a whole unit [clamp on]

maybe Jraef would have some insight into the output from pickups, like you would find in a standard service panel... A cheap totalizer setup would get me where I'm trying to go [yeah I know, hijacking your thread].

having to convert a outputed number to kwh & applying what ever rate is no problem. I'd just make a chart with a spread..

The energy hog TV is probably a plasma, not a LCD.

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#21
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Re: How to Estimate Residential Kilowatt-Hours (kWh)

12/08/2009 4:25 PM

Ed,

I'm in the Bay Area myself, but where are you paying $0.42 per kWh? I only pay about $0.15 (not that this is cheap by any stretch either).

I thought of the TED when I was looking, but the C.O.B (Cheap Old Bastard) in me told me that I was just being lazy, wanting to read the meter in the comfort of my easy chair rather than go around measuring everything significant one at a time. So that's what I did; I bought a Kill-a-Watt and logged power consumption on major contributors over a typical week of use. Now I know, for instance, that my AC unit costs me, on average, about $0.97 per hour to run it on a hot summer day (it frequently gets over 100 in my area). My hot tub, left at 80 degrees when not in use, costs me about $0.72 per day to sit idle, but if turned up to 99 degrees when the wife and I want to take a soak, will cost me about $2.25 extra that day. It was an interesting exercise to be sure, it makes you think about all the little things you do. Boil a kettle of water for tea? 3.6 cents; blow dry your hair, about 3 cents; watch by old 32" CRT TV set, about 4 cents per hour, but watch my son's 28" LCD HD TV, about 14 cents per hour!

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#15

Re: How to Estimate Residential Kilowatt-Hours (kWh)

12/08/2009 11:25 AM

Hi,

Post #14 pwr2thepeople has the good idea.

Call the power company and request a home energy audit, most providers offer this survey for free. A home energy audit is very comprehensive of power usage levels, heating/cooling envelope etc..

Here is some help too http://hes.lbl.gov/

http://www.pge.com/myhome/saveenergymoney/analyzer/en/

http://www.pge.com/mybusiness/edusafety/training/pec/library/energyaudit/index.shtml

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#17

Re: How to Estimate Residential Kilowatt-Hours (kWh)

12/08/2009 11:41 AM

This would be a natural for the X10 system or Insteon system. It is surprising that a simple hall effect current sensor for X10 is not apparently available, (although I haven't really searched -- it just seems like a natural for this page, for instance). In quantity, these sensors could be made for a couple dollars each, ready to transmit via the X10 protocol. Production quantities might be hard to achieve, because most people do not worry about this stuff, to this level of detail.

At $.42 per kWh, I can understand your interest! Is that typical in the Bay Area??!!! That is 10 times what some people pay for off prime time (an unfair comparison, but...). That price would make solar cells really attractive.

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#24

Re: How to Estimate Residential Kilowatt-Hours (kWh)

12/09/2009 2:15 PM

U are all great.

I think the major thing this friend wants to know is how to measure the power consumption of his home appliances.If u cant find appropriate rated KWH meter installed,just simply get a clamp on Ammeter,clamp the life part of one appliance when switched ON and read off the current of that appliance,knowing the voltage,calculate the power and record it seperately.Do same to all other appliances in yr home and total all the power recorded individually,what u get is the total power consumed by yr appliances in the home.If the name plates are clear,check and total all the powers.

Secondly if u want to cut down on yr consumption,just as i do in my home,put ON only those appliances u needed most at a particular time,and put OFF all others not needed at that time.When u are out of the house,put OFF unneccessary loads or appliances.At night(Bed time),put OFF unnecessary loads as well.This way,u will cut down so much on yr consumption every month and will pay less.

If u have a KWH meter already,ensure that the setting is correct or get the authorised energy meter specialists to check and reset it,else it would be running too fast and recording higher bills at the end of the month.

Patrick Whowha

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Anonymous Poster (1); Blink (1); bwire (2); Ed Weldon (8); Garthh (2); JRaef (2); M Daniels (2); mike k (1); Patrick Whowha (1); pwr2thepeople (1); Tornado (2); wareagle (1)

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