Supercooling in the Desert: May 22, 2018 a day that will live in infamy !

This is the day I got clobbered by APS (my power company)

Look just before 8PM (20:00); see that bunch of spikes? My peak billing period lasts until 8, and something was sucking power before the period ended ! Let me expand the little piece that shows the problem:

That little period from about 7:24 to 8:00PM was the clothes dryer.

Yes, just a little before the end of my peak period a guest started the dryer to do some clothes. It wasn't their fault, they didn't know that the fascist power company would be watching to see if such a thing happened.

The peaks run as high as 7.4 kW, and it was doing this for a little over a half hour. The APS chart shows it like this:

And it was almost impossible to find. I looked for quite a while before I noticed it. I put the arrow on there to show you the tiny little green area that resulted. It shows up a little better on a single day chart:

That minor little slope up in the green area is where the meter saw the dryer running. It's recorded as "usage 3.18" during the 7-8PM hour. In theory, this should be my high 'demand' number that is calculated into my bill for the month.

I guess I should do a little calculating to see how this works to help me understand and avoid it even more stringently in the future. Let's look at the detail portion of my bill first:

So, the demand number wound up being 3.17 and is used as a multiplier in several items in billing. Here's the rate sheet for the plan I'm on:

So, my 'On-Peak Demand Charge' is 17.438 * 3.17 for $55.28. But, there's nothing on my bill that says that. Guess what? To make it more complicated and harder to understand, they actually split the $17 charge into two components and calculate them separately. From their tarif sheet again:

Notice how the two numbers, $4.000 and $13.438 add up to the $17.438 they call the 'On-Peak Demand Charge'. OK, fine, I have a calculator and can punch in numbers like anyone else. 4.000 * 3.17 = 12.68 and 13.438 * 3.17 = 42.60, and they add up to the 55.28 I got above. So I should see:

Delivery On-Peak Charge 12.68
Generation On-Peak Charge 42.60

Or something similar on the bill, and indeed I do. Sort of:

Demand charge on-peak - delivery $12.40
Demand charge on-peak - generation $41.66

If you look at the bill, you'll see them on there. The sum of the two charges is $54.06 which is darn close to my initial $55.28. The reason for the difference is that APS made a mistake in the original rate change request and has to use the demand number to one significant digit and they can't round, so the actual demand number they get to use in this case is 3.1kW. That's on the bill also, so I don't even have to do the truncation itself:

Your billed on-peak demand in kW 3.1

That's a good thing because rounding would have put me up to 3.2 and would be paying even more.

Now, I got the cost all figured out, the dryer running cost me some amount, but how much extra based on past performance. To get that, I'm going to look at last month to see; taken from last month's bill:

Your billed on-peak demand in kW 1.5
Demand charge on-peak - delivery $6.00
Demand charge on-peak - generation $20.16

That stuff totals up to $26.16, so my dryer cost me $27.90 last month because I didn't keep it under control. It's actually a little bit higher because the rate per kW during peak is higher ($0.08683 vs $0.05230), but that's only 3 cents per kw, and the dryer only uses 7.5 kW at around a 50% duty cycle for 3.75 kW or $0.32 extra. I'm willing to ignore that.

Now is the appropriate time to talk about how APS gets that demand number. As I mentioned in another post, they average each hour and compare it to the maximum hour during the billing cycle. That gives me 5 vulnerable periods each day: 3-4, 4-5, 5-6, 6-7, 7-8. So, the dryer kicked on and sucked power in bursts like all electrical heating appliances and those bursts pulled 7.5 kW for a short period. The bursts were roughly half the time, so it worked out, on average, to the 3.17 kW number that APS measured. It would be too much to read if I did all the calculations, but you see what I mean. That 3.17 was the highest reading so far that month, so it kept it and continued to look for a higher hour; fortunately, it didn't find one, and that's how the month's bill came to be. Next post I'm going into how to read our smart meter so folk can actually see what is coming. Unless one goes to the trouble of doing what I've done, you can't catch it real time and stop it; you can only see the what's already happened.

This is not going to break me, but it does lose me some bragging rights. Because I didn't keep control, I'm out about 28 bucks. Be warned though, if the hot water heater had kicked on, and the stove was running, this would have been a monetary disaster. Thank goodness it was only the clothes dryer and that close to the end of peak !

There you are, an example of how power can get out of control no matter what you do and how much attention you pay to it. Something will slip in and get you from time to time. Overall though, keeping tabs on my power has saved me thousands over the years. This post is also good for folk that don't completely understand how that 'Demand Billing' stuff actually works, and how to tell if you're messing up.

The parts to prevent this from happening to me again are already on order.

Previous post in this series is <link> then next is <nothing yet>

Supercooling a House in the Desert: part 3

I'm going to talk about the APS (Arizona Public Service) phone software for monitoring your power. For folk that don't live here (Arizona, USA), much of this will be of little value. It might give you a clue as to how your own power company works, but this is directed at my neighbors.

I'm not going to describe how to look at your bill, or make a payment, etc. I want to talk about the usage numbers and graphs they provide so you can monitor how good or bad you're doing at saving money by juggling power usage.

First though, I want to explain a bit for people in other countries with different rules around providing power. The name, Arizona Public Service is historic and not actually reflective of what it is. APS is a private company that supplies power to a big part of Arizona. They are publicly held (as in stockholders) and regulated under Arizona's version of a public utilities commission, the Arizona Corporate Commission (AZCC). The AZCC is also in charge of licensing corporations in this state. So, if APS wants to increase its rates to customers, it has to get approval from the AZCC. Confused yet?

One of the things that is part of every submission for a rate increase is the statement, "fair and reasonable return on investment." Which means that if APS runs their business sloppily and doesn't make enough profit, they ask for a rate increase to increase the profit. Nice business to be in. If you screw up a business decision, there's someone out there that will guarantee you a profit.

No, I'm not being completely fair, there are various government requirements that APS is forced to meet, and those do increase their costs. But, every time one of those comes along, a new 'fee' is added to our bill. AZCC approval of these items is almost automatic.

Enough background, on to the actual application.

The app is called 'APS' and is on the google play store for download. Once you get it installed, you can log in to your web account with APS and look at billing and usage. There's also hints on ways to save, but that's just the usual things that we see every day about conservation. The last choice is 'apsFYI' that is the same things that they send with the bills. I'm not going to discuss the billing areas; it's hard to remove my account information from every single illustration. I may get to that at a later point though.

Lets go to 'MY USAGE' and see what it shows for me when I do it, that's where the fun stuff is:

You get a nice display that shows your percentage of use on peak. That means of the amount of energy you used so far this billing period, some percentage was during the peak demand period. Mine was 7%, which must mean that the rest, 93% was off peak usage:

And they have a display for that as well. The real data that can actually help is found by touching the 'Detailed Energy Usage' link at the bottom.

This is actually a nice chart that shows my energy usage for the last 6 days. It's only been six days so far this period. The bars are divided into peak usage, green and off peak usage, blue. The height of the entire bar is my total usage for that particular day. So, I used a lot off peak and only a little bit on peak; the actual values for these can be displayed by touching one of the bars.

So, what does this mean? It shows you when you are using the most power, on peak or off peak, and that's important because the billing rates are considerably different. I want to use as little as possible on peak and concentrate my usage to the off peak periods. That way I can use the larger appliances and pay the least possible for it.

If you touch 'LAST CYCLE' you'll be shown the entire period and you can inspect each day to see if you ran something big during the peak period.

This display can be scrolled left and right to get to a particular day. You can then see the days where you used the most power and work out a plan to deal with it in some fashion. Notice that I used almost 80Kwh on the 28th; it was Saturday and off peak, so I just let the AC run. Rates are much cheaper off peak and I can afford to do this. You certainly wouldn't want the green area to get large because that would result in probably an excess of $100 addition to the bill.

Up at the top of the display is a drop down menu currently labeled 'Daily Energy Use', This menu will let you look at a more detailed display that will actually show you your usage times. Here's mine:

For the last week this displays my usage on a time line so I can get an idea when my major usage occurs. My chart above shows that I cut the usage way back during the peak period (green) and then let it run wild the rest of the time. The big peaks just after the demand period is the AC kicking on full bore to cool the house back down to where I normally keep it. Also in there is the stove, dryer, pool pump, all the things that use a lot of power. See how I control my usage to only the cheaper times?

The reason they call this 'Demand' is because you can scan the green area to see when something turned on a drove the demand number up. They save the highest of the green parts as your demand number and use it as a multiplier on your bill.

If you choose 'Day' up near the top, you can get one days usage and a good indication of the time of day that you used a lot of power.

My big power usage spike came after the peak period (green), so I paid the lowest price for it. Notice how I keep the green area (peak usage) as low as possible? That keeps my demand number down to save money. You can get to a specific day by using the little calendar symbol on the upper right.

Doing this will allow you to zero in on some usage period that may be giving you trouble. Fridays after work when you're hot and kick the AC on too early, or the day the kids were home and fooling with the thermostat come to mind. Little things like that can mess up the demand number and cause an unexpected large bill.

That's pretty much the guided tour of the APS app. It can tell you how well you did at controlling usage and help isolate troublesome events. What it doesn't tell you is how you are doing right now. You can't get the current day, or a close to real-time display to tell you something is on that shouldn't be. You can only look back.

My contention is that this nice display was designed to help the APS representative prove it was your fault you get a large unexpected bill. However, given enough time, you can use it to learn what hurts and what you can get away with; you just have to pay for the mistakes when they happen.

Previous post on this subject <link>  Next post on this subject <link>

Supercooling a House in the Desert: part 2

Last post I examined how much my house's internal temperature rose over an eight hour period of temperatures that exceeded 100F with no AC at all during the period. That gives me a feel for how much I'll need to cool the house down during the peak period, but to really understand how to control things a closer examination of some other things needs to be done. First, lets look at recirculating the air inside the house between rooms.

Recirculation can be done easily by simply leaving the AC fan on and set the mode of the compressor to 'OFF'. This will move the air around the house and even out the temperature of the various rooms. Essentially you're taking cool air and displacing some warmer air in areas that might be hot spots. I tried this and found it to really works well for evening out the house.

However, I'm really frugal (aka cheap) and having both of my AC motors running all the time was too much for my personal sensibilities. I stagger them so only one is ever running, and I don't run them all the time. Here's a chart to show you what is happening.

Those little steps in there are each fan running as measured by my whole house device. It actually monitors the house's incoming power real time <link>. There's other stuff going on in the house, so the graph isn't a perfect set of steps. If you look closely, you'll notice that one of the fans pulls more power than the other; that's because one AC is a 5 ton and the other a 3, so they use different sizes of motors in the air handler.

There are thermostats that can handle recirculation for you, but they are rare. I had a couple for a while before I built my own and they worked fine. A bit hard to set up though; the manual was many pages long. My plan over time is to get rid of the thermostats entirely in favor of a computer that monitors the temperature in each room and adjusts the fans and compressor for the most comfortable environment. I'm probably a year away from that goal. Folk that don't want to bother with that can look around, there are lots of good thermostats out there.

Note that I DO NOT recirculate during the peak period. I'm just too cheap for that. Instead I use ceiling fans to move the air around in a single room and keep it feeling fresh. No, this doesn't even the entire house out, but it does well in the most used rooms. This is another of the list of personal preference items you need to consider.

Now, let's talk about the high surge current that an AC compressor uses when starting up. It's an absolute fact that most electric motors pull very high current when they first start up. When I looked at my AC compressors, they pull around 4kW when running, but the peak surge getting them started was way up around 14kW. Yes, that's nothing to laugh at; it's a lot of power.

But, it's only for a second or two. Here's a chart that shows the spikes created by starting an electric motor. In this case, it's my refrigerator, freezer and the freezer out in the garage.

I especially like this graph because I caught the garage freezer for the entire starting spike. A limitation of measuring power is that you have to capture discreet instances of power, you can't get everything. I capture it in about 1 minute intervals and often miss most of the rising spike. It's just impossible to grab everything all the time; there isn't enough storage to keep it. The reason I used the appliances is that I don't filter the readings as much. If you don't filter the reading, they're all over the place and you can't get any accuracy at all because of the inherent noise. The whole house power would be a real mess to try and read with the start up spikes from everything in the house showing up.

But back to the spike, notice how much higher it is than the run current just next to it? Here's a cutout of that particular piece all by itself.

While the normal run current is only around 100W, the starting surge is almost 900W, but also notice that it is only for less than a minute. Since the peak demand number is for an entire hour, that's not enough to impact it. The surge peaks of  electric motors is so small in actual power used that it just doesn't matter on your power bill.

There is another reason to avoid the incessant cycling of larger motors though, wear. On something like a freezer it doesn't matter much because they are fractional horsepower motors, but on an AC unit, starting and stopping a compressor is tough on the mechanics. Bearing, armatures, pulleys, etc wear out often enough, we don't want to increase the wear by 'short-cycles' on the motors. When you start it, let it run a bit if possible.

But ignore the uninformed when they speak about the huge power usage of the AC starting; it just isn't a problem. Unfortunately, many of the uninformed are AC 'experts' that we all have to listen to from time to time.

Now, since I mentioned the appliances, let me expand a bit on them. I have separate appliances for the refrigerator and freezer as well as a chest freezer in the garage. These have to run all the time to keep my food safe. I don't want to spend the money on spoiled food instead of power. I've already charted the usage of all of them above, let's look at a stacked chart of their power usage during a typical peak period. Stacking means that I add each chart line to the others so you can see the total usage of all the appliances at a glance.

I also filled the items so they would be easier to see. The fridge and garage freezer use around 100 W each and the house freezer uses about 130 W. Since they don't always run, there are actual periods where no power is used by the appliances, but not very often. The fridge runs about half the time in long periods, while the garage freezer runs in predictable periods, but still about half the time. The house freezer runs the most, partly because it has two defrost cycles a day that it has to recover from opening the door to get ice which lets the cold out. You can actually feel the cold air hit your feet when you open the door on this stand up freezer. Very convenient though.

The appliances create an almost constant draw on power that is roughly 350 watts. Combine this with ceiling fans (a necessity in the desert to keep the air moving) and the usual passive devices and my particular baseline power usage is close to 500 watts ... constantly. Everything else I run just adds to it. I don't think I can get it below that without some risk to my food supply.

It's important to note that the fridge and freezer in the house vent right into the kitchen. That takes the heat that may be inside the appliance and dumps it into the house making it necessary to remove that heat with the AC. This is good in the winter since it will keep the house warm, but not so good in the summer where you have to get rid of that heat. I may someday have to look at that as a factor, but it's a really hard thing to measure.

So, factoring all this with the appliances, the very best demand number I can possibly get is .5kW. That would actually be great, there's always something. microwave popcorn, lunch, TV, whatever makes life more fun and comfortable will creep into my power bill.

Remember, your mileage WILL vary. Your lifestyle, house, habits and the way you hold your tongue will conspire to create your own personal profile. Use this as data for decisions, not as an absolute.

Previous post on this subject <link>  Next post on this subject <link>

Supercooling a House in the Desert

A while back I ranted a while about power politics in the desert <link>, and after some thought and because I've been doing this for years now, I decided to post a few articles on 'supercooling' a house to lower power bills. Another impetus is that the latest rate increase has caused many people in my area to feel the 'heat' of the new power company rate increase.

First, what the heck is 'supercooling'?

This term came about over time because people (me!) were clobbered by power bills based on the 'demand' billing method. I first posted about this quite a while ago and even dedicated a page to it back then <link>. As I pondered and tested, I created thermostats and temperature gauges, and a lot of other stuff. This blog was actually the result of experiments and actual devices that have been copied by people all over the world to mimic some portion of my efforts.

One of the methods I tried was to cool the house way down during the off peak hours and then turn the AC off entirely during the peak period, and let the house coast through the peak period. That made my power bill the envy of all the neighbors. They weren't willing to do the same thing, but they commented on my work many times.

So, supercooling is cooling the house down a bunch before the peak period begins, turning the AC completely off during the peak and then turn it back on after the peak period ends. This is all the result of demand billing explained on the link above <convenience link>. For folk that live in the cold country, this will work the opposite way as well. You can heat it way up and then let it coast. However, I don't have any direct experience with that living here.

My early efforts resulted in great savings under what I would have been paying. So much so that solar power companies can't match me. I had inadvertently beaten the ability of solar power to save money. Here is a chart of my power usage back then:

I know, ancient charting software. But forgive me, this was in 2009 and I was new to this blogging thing.

It was very important to me that I kept the power usage to the absolute minimum during the peak period, and in those days it was from noon to 7 PM. I actually used more power this way, but paid a much smaller bill. The huge spike in power just before the peak period is me supercooling the house before I shut off the AC units entirely from noon to seven.

Basically it worked ! I was a happy puppy and decided to automate the house and take control of my power usage so I couldn't get screwed by an accident again. Thus, the adventure of the the last years began.

So, that's supercooling and my adventure into it.

Now it's time to study it some more because people want to know what to do to accomplish some of my results. Not everyone wants to tear out walls, climb up on the roof or bury wire to the septic tank. They just want to understand how to save some money.

That's quite enough background for now. Let's get to the first experiment I did.

Before the new rate increases came into effect I modified my thermostat code <link> so that the peak period was from noon until 8PM; this is a union of the new peak period 3PM to 8PM and the old, 12 noon to 7PM.  I did this so that whenever they actually implemented the rate change I wouldn't be caught by surprise and get an outrageous bill. It worked, the transition was smooth and I didn't get any bad surprises. Since it was for a very long period, it was perfect to test the heat rise inside the house; I just had to wait for a hot day.

Naturally it came with a vengence, and I was already gathering data, so first I did one set of rooms that are wide open to each other no restrictions on the air flow and are air conditioned (duh). For the test I let them cut off automatically at NOON, because I wanted enough time for good measurements. I kicked them back on at 8PM .

Here's a graph showing the set of rooms and the outside temperature. You can tell which is which. At noon, the room temperature was 76F and at 8PM the room temperature had risen to 81F for an increase of 5 degrees.  I haven't done it for only the period of 3PM to 8PM yet, because I wanted to understand the rise in temperature so I would know the settings to try first. Here's the graph:

I was surprised how little the temperature changed without AC when the outside temperature varied up to 105F. Of course your mileage will vary due to every factor known to man, things like: did you open the doors, curtains open, insulation level, ceiling fans, etc. Most everything inside and outside your house will have an impact. However, for me it means I can lower the temperature by five degrees and survive until 8PM from 3PM when the temperature is in the low hundreds. I'm sure that I'll have to drop another degree or two when it gets in the teens, but I have a place to start.

I did notice that the concrete floor was absorbing heat. It seems the sun shining on the foundation outside was travelling UNDER the insulated walls and radiating into the house. The walls in that area were cool to the touch, but that's subjective. I'll have to go around the house and check the temperature on the exposed areas to see what the floor temperature is; it may just be over-sensitive bare feet. Good excuse to buy an infra-red thermometer.

What? you want to see the power usage during the same period to see how things are going power-wise?

Notice that from noon until 8PM I use almost no power. The little rise towards the end of the period is my TV and the hump around 3:50 is me warming up some stuff in the microwave. I didn't supercool the house for this test, but I did let everything kick on normally at 8PM. That's the huge spike you see on the right.

Yes, I watch the power that closely, at least during peak periods.

One of the fallacies I see mentioned a lot is staggering appliances. This will help during the peak period by keeping the dryer from adding to the AC or something similar. That keeps the demand number lower during ONLY this period. The rest of the time (off peak) it doesn't matter at all. During those periods power is power, so go ahead, run the dryer. During peak, keep that darn thing turned off. You don't need that shirt right now, wear the least dirty one from the laundry instead.

I'll be doing more observations and experiments over the next weeks, months, whatever, and I'll try to keep links between the posts so you can follow along (if you actually care about this kind of stuff) without hearing about hydraulics, septic sensors, old tractors, wifi controls, etc.

This could get interesting and a good place for me to look when I forget why I started this mess.

Oh, this page will attract spam like crazy. Every solar service in the world will be posting something with a hidden link in their name or some word inside. There will be arguments aplenty about the costs of solar vs nothing. Off grid suggestions will probably abound. I know how to deal with this ... I delete it. So, solar sales people, don't bother, you'll just get deleted. Same for people that want to compare their solar savings, gone. Also, at some point, I'll actually have to turn off comments because I get tired of messing with the constant spam. And, I love suggestions for things to look at (if they don't cost me much).

But for now, comment away.

Previous post in this series <link> Next post <link>