Wednesday, September 29, 2010

Power Company Came to the House

A really nice guy came to the house to check the meter.  His work order said that he was sent out on a call to check for a too high reading, nothing to do with demand.  He actually couldn't check demand because that takes special equipment that he didn't carry in the field.  Soooooo, he tried to check the meter accuracy under load, but couldn't get a pulse reading using a laser to reflect off the aluminum wheel (Arizona sun was too intense) and just pulled the meter and took it with him.

I now have a much smaller, smarter meter that he assures me is programmed for a hour's demand, and the old one will be checked to see how it's programmed and if it is recording accurately.  This meter has an infrared pulse output that can be used to measure power.  I'm pretty happy with the current measurement techniques so I may not mess with that.

So, it seems they don't understand demand across the company and they can't get a work order correct.  The drama will continue since I insisted that I be notified of the results of the tests on the meter.  I expect that to happen because the meter guy was really interested in what I was doing and how the meter was actually working.

Friday, September 24, 2010

Power Company Rescheduled

They were too busy to get to me this morning as planned.  They have rescheduled for 0900 next Wednesday, the 29th.  This is the second time they have rescheduled.

Wednesday, September 22, 2010

Mathematics of Demand Billing

Some interesting math on Demand.  Average is really the arithmetic mean.  This is illustrated by:

\bar{x} = \frac{1}{n}\sum_{i=1}^n x_i  =  \frac{1}{n} (x_1+\cdots+x_n)

Which would be expanded to:

1/60 ( X1+ X2 + X3 ....+ X60)

Since each X is the sum of the draw of all of the appliances in the household for a minute and there are 60 of them (60 minutes in an hour) what they're actually measuring is the usage separately for every hour during the peak period for a month and keeping the highest value to be used in billing calculations. This is a rolling average covering every 60 minute period during the peak for the month.

This would mean that a test where a 1000W appliance is run for 15 minutes and nothing else was run for an hour would result in (1000 * 15) / 60 = 250 Watts.  Exactly what they are predicting will happen.  However, if a base load of 500W runs continuously and we add the 1000W appliance we will get:

((1000 * 15) + (500 * 60) ) / 60 = 750 W

This is completely supported by the data in my previous post where I did the calcs for each minute during the example hour.  By the way, my Demand reading so far this month is 1.8kW.  Been keeping it pretty lean.

This is going to be an interesting test on Friday.  I may come out with egg on my face.

OK, so they forecast rain .....

The meeting with the power company has been postponed to Friday at 0900.  What?  they don't want to work on the meter in the rain?

Actually, neither do I.

Tuesday, September 21, 2010

Update from the Power Company

While I was composing the post below I got a call from the lady at the power company.  Thursday at 0900 a person is going to come out and shut down the power and measure it for an hour to get data on what is being recorded vs. what is actually being used.

This is going to be fun.  Oh, I got her name this time.

Call Back from the Power Company

Based on the note to the Corporate Commission, I got a call from APS yesterday.  A really nice lady that totally understood what I was talking about discussed what I had found.  She described the measurement as taking the kW reading every minute, averaging it over sixty minutes and then holding the value.  It would keep the highest number between meter readings.  That corresponds exactly to the definition that is both on the web and in their tariff.  When I told her that was NOT what I was seeing; I saw it keeping the highest reading as I previously described; she said that she would have to check more deeply and would get back to me.

She agreed that my measurements (as I described them) made sense, but that should not be what the meter recorded.  We discussed the recirculating fans in my house and how they only worked for a few minutes, far less than an hour and how an average should always be less than the peak.  I also told her that one of their engineers told me that it held the highest current usage and that a manager in metering told me it held 15 minute interval averages.  Seems people there don't have a clear understanding of how Demand is supposed to be measured much less how it actually is.

The unfortunate part is that I didn't get her name.  I was working on my pool at the time and took the call in the back yard where I didn't have anything to write on.....darn.

Just to keep it in the record, this is the detailed explanation of the meter's operation I received via email from a person working in the metering department at APS:

The explanation of “Demand” on the APS web site, although accurate is a simplified definition.  The residential meter is set up to record the average demand over a 60 minute period. Your example below of a 1000W light bulb is a good one to start with.  If the 1000 W bulb was on for 15 minutes during the 60 minute interval, it would record only ¼ of the 1000W because the meter needs the entire 60 minutes to “build up to” the 1000W load.  This example is assuming that there are no other loads on before or after the 15 minutes the light bulb was operating.

In most homes, there is some load on all the time (refrigerators, clocks, remote control devices etc) so the actual situation would look more like this:

4pm – 4:15 pm – 1000 watt light
4pm – 4:10 pm – 5000 watt A/C
4pm – 5pm – 500 watts misc ceiling fans, etc
4:20 pm – 4:30 pm - 5000 watt A/C
4:30pm – 5pm – 1000 watt television
4:40 pm – 4:50 pm - 5000 watt A/C

From 4pm to 4:10pm the meter sees (1000 x 1/6) + (5000 x 1/6) + (500 x 1/6) = 1083 watts (1.08kW)
From 4:10 pm – 4:15 pm the meter sees (1000 x ¼) + (500 x ¼) = 375 watts (0.37 kW)
From 4:15 – 4:20 the meter sees (500 x 1/3) = 167 watts (0.16 kW)
From 4:20 – 4:30 the meter sees (500 x ½) +( 5000 x 1/6) = 1083 watts (1.08 kW)
From 4:30 – 4:40 the meter sees (500 x 2/3) + (1000 x 1/6) = 500 watts (0.50 kW)
From 4:40 – 4:50 the meter sees (500 x 5/6) + (1000 x 1/3) + (5000 x 1/6) = 1583 watts (1.58 kW)
From 4:50 to 5pm the meter sees (500) + (1000 x ½)  = 1000 watts (1.00 kW)

The Demand for this 60 minute period is 1583 watts.  The meter will record 1.5kW.  If this reading is the highest for the month, the meter places this reading into memory and it stays there until a higher reading is recorded, or the monthly demand reset happens.  The monthly demand reset returns the reading to zero and we begin the cycle again.
However, if you remember your definition of average from high school, the explanation above doesn't cut it. The explanation is describing a measurement of the maximum current draw for a short period.  Since the meter would hold the highest measurement, for the entire month this could cost you a bunch.  People should remember that an average is a sum of several items divided by the number of items.

If one were to analyze this minute by minute there is a very different number:

1000W 5000 W 500 W 1000 W
         Bulb        A/C          Misc          TV          Usage     Demand
0 1000 5000 500 108.3 6500
1 1000 5000 500 108.3      6500
2 1000 5000 500 108.3      6500
3 1000 5000 500 108.3 6500
4 1000 5000 500 108.3 6500
5 1000 5000         500 108.3 6500
6 1000 5000 500 108.3 6500
7 1000 5000 500 108.3 6500
8 1000 5000 500 108.3 6500
9 1000 5000 500 108.3 6500
10 1000                       500 25 1500
11 1000                       500 25 1500
12 1000                       500 25 1500
13 1000                       500 25 1500
14 1000                       500 25         1500
15                                  500 8.3 500
16                                  500                       8.3 500
17                                  500 8.3 500
18                                  500 8.3 500
19                                  500 8.3 500
20                   5000 500 91.7 5500
21                   5000        500 91.7 5500
22 5000        500 91.7 5500
23 5000 500 91.7 5500
24 5000 500 91.7 5500
25 5000 500 91.7 5500
26 5000 500 91.7 5500
27 5000 500 91.7 5500
28 5000 500 91.7      5500
29 5000 500 91.7 5500
30 500 1000         25         1500
31 500 1000         25         1500
32 500 1000 25 1500
33 500 1000 25         1500
34 500 1000 25         1500
35 500 1000         25         1500
36 500 1000 25         1500
37 500 1000         25         1500
38 500 1000         25 1500
39 500 1000         25 1500
40 5000 500 1000 108.3 6500
41 5000 500 1000 108.3      6500
42 5000 500 1000 108.3 6500
43 5000 500 1000 108.3      6500
44 5000 500            1000 108.3      6500
45 5000 500 1000       108.3      6500
46 5000 500 1000 108.3 6500
47 5000 500 1000 108.3 6500
48 5000 500 1000 108.3 6500
49 5000 500 1000 108.3 6500
50 500 1000 25 1500
51 500 1000         25 1500
52 500            1000 25 1500
53 500 1000 25 1500
54 500 1000         25 1500
55 500 1000 25 1500
56 500 1000 25 1500
57 500 1000 25 1500
58 500 1000 25 1500
59 500 1000         25 1500

KW used in hour 3750
Max Demand 6500
Avg Demand 3750

Granted, my number is higher than the guy's from the power company, but it is still far less than the 6500 peak demand used for a few minutes in the example above.  Somebody somewhere is doing something wrong.  It may be me, but I don't think so.

I want people that read this to keep in mind that I have consistently been treated politely both by APS and the Corporation Committee.  Each person I talked to was considerate and actually tried to understand my concerns.  Usually when dealing with someone on a item like this people seem to get testy and often they put you on hold until your patience expires and you slam the phone down in disgust.  This kind of thing has not happened.

Tuesday, September 14, 2010

Got the State Corporation Commission Involved.

In an earlier post I described my MANY discussions with the power company about how they were calculating 'Demand' and my findings.  An engineer there agreed with me and was going to see about changing the definition.

So far, that hasn't happened.

Meanwhile, I got a copy of their Tariff and read it.  Based on my findings, they are not compliant with their tariff and that's against the law.  The tariff gave essentially the same definition for Demand as their web site and disagreed with my data.  So, after waiting to see any action on their web site or further contact I sent the following email to the Arizona Corporation Commission.  This body is similar to other state's Public Utilities Commission and handles this kind of thing

On 9/4/2010:

 The APS published description of  ‘Demand’ is :
 This component is part of the pricing for the Combined Advantage plans. "Demand" or kW is the average kW used during the 60-minute period of maximum use during the on-peak hours of the billing month. The kW used is determined from readings of your APS meter.
 As taken directly from their website at on 8/25/2010.
 Additionally, the rate tariff defines this same item as:
 For billing purposes, the kW used in this rate schedule shall be based on the average kW supplied during the 60-minute period of maximum use during the customer’s On-Peak hours, as determined from readings of the Company’s meter.
 Again, taken from the APS web site at  on 8/25/2010
 However, this is not what they do.
 A normal person reading the either of the descriptions above would, reasonably, think that APS measures the power usage for an hour and averages the hour’s usage then picks the highest of all the hours for a month and then bills the customer for that number.  Extensive research, testing and observation as well as direct conversations with APS personnel and residential power meter manufacturers have led me to believe they simple take the highest amount of usage for the month and bill for that.
 This may seem like a trivial difference at first glance, but suppose a person has an extremely short period of high use on a single occasion during the month.  They would be billed for that usage at a very high rate.  Simply switching on an additional air conditioner, and then noticing that it was after the beginning of the peak period and switching it off would result in 3 kW additional demand and the subsequent charges in the monthly bill.  During certain peak periods in the summer this could cost as much as $60. Multiply this by the customer base using this rate schedule and it becomes a very significant amount of money.
 To help one understand better a simple case study can be described.  One has a 1000 watt light bulb and turns it on for 15 minutes by mistake during the peak period.  This would result in an additional .250 KwH usage (1000 / 4 for the quarter of an hour), and an additional .250 KwH peak usage and an additional 1 KW peak demand.  The charges would be approximately 3 cents for the power usage and over 13 dollars for the demand component.  Whereas, with the above described ‘average’ method, the additional amount would be .250 KwH for the usage and .250 for peak demand, a very substantial difference.  Moreover, there are other charges derived from the demand number such as Demand Generation and Demand Delivery.  These are not trivial amounts.
 I took the following description directly from a power meter manual supplied to me by the APS Metering Division:
 For block interval, demand calculations are made at the end of each completed demand interval. This method is similar to the way mechanical demand meters operate. As load is applied to the demand register, an indicating pointer and maximum demand indicator are driven upscale. At the end of each interval, the indicating demand pointer is returned to the zero position, and the maximum demand pointer retains its highest or maximum position.
Please note that I’m not disputing charges or rates; I’m describing inaccurate and very misleading descriptions of how APS calculates power charges.  People trying to minimize the impact an electric bill has on their family during these troubled economic times need accurate information to make good decisions.  Conversely, this is a extremely rewarding mistake from APS’s perspective that could, and maybe has, resulted in huge windfall amounts.  I’m not sure of the legal impact of the difference between what APS is actually doing and the description in the tariff.  I’m assuming the tariff is a legal document and someone holds them accountable to it.
David Thompson
 I waited until 9/14/2010 and sent the same mail again along with a phone message to the head of the Utilities Division of the Commission.  Guess what?  I actually got a phone call from a nice lady named Trish.  She said she was forwarding my comments to the executives at APS (the power company) for their comments and that both they and Trish would contact me again after the response.

Can you believe it?  I've actually gotten responses instead of being stone-walled.  I haven't seen any actual action to speak of, but it's encouraging.

Saturday, September 4, 2010

Fighting With The Power Company

 I'm near Phoenix Arizona, USA and my power company is APS.  They have "Demand" billing which means they measure your usage of power and take your peak usage for a month and add a surcharge for delivering that much power.....regardless of how long you actually use it.  So for example: you have the dryer running and the A/C kicks on, that's 1400 Watts for the toaster and 2000 for the dryer you just hit 3.4 kW for a two minute run of the toaster.  During the summer at a demand charge of $13.404 per kW plus a "Generation Charge" $7.114 per kW plus a "Delivery Charge" of 2.089 per kW you just hit over $60 for less than 10 cents of electricity.

Yes, you're reading it right.  They charge separately for Usage (kWh), Generation (kW) and Delivery (kW), and the kW items above are billed based on the single largest use of power during peak periods anytime during the month.  So at any point during the peak periods someone can mistakenly turn something on and WHAM, you've got a monster power bill and you don't even suspect it.  All the compact fluorescent bulbs in the world can't make up for one mistake with a water heater, or heaven forbid, an A/C compressor or welder.

To add insult to injury, they have the following definition of "Demand" on their web site:
This component is part of the pricing for the Combined Advantage plans. "Demand" or kW is the average kW used during the 60-minute period of maximum use during the on-peak hours of the billing month. The kW used is determined from readings of your APS meter. 
This implies that they average the usage over an hour and you get billed for the highest hour of the month.

This is simply not true.  I discovered the definition was wrong when I finished the system to measure power usage in real time.  I never had an hour where I exceeded 2.4 kW and those periods were for a very short time, far less than an hour.  However, when I got the bill they listed 2.2 kW as the demand.  I called and asked why and they told me it was what the meter recorded.  The meter reading is God.

So, I talked to the customer support people several times, the metering people several times, the meter manufacturer a couple of times and finally got an extensive manual on the meter itself.  Armed with this I asked to talk to an engineer that understood their metering.  Guess what?  I actually got a call back!!

Even stranger, the engineer agreed with me.  The definition on their web site was clearly wrong and they don't do any averaging; they take the highest demand and hold it over a month.  I get billed for any mistake I make in power usage.  The engineer agreed to discuss this definition with others and get a correct definition in place.

This was back on 8/24/2010.  Still waiting, we'll see.