Monitoring Water Heater Power

Well, I can now monitor my hot water heater power usage. The step-down transformer I got <link> worked just fine and I managed to put together all the pieces and now have it out there running just fine. I mounted the transformer on the lower right of the picture below. I used exactly the same technique that was used in the power converter it came out of, high adhesion two sided tape.

What I did was to spread some silicon grease on the bottom of the transformer then put the tape on one side. I pressed the grease down on the enclosure and slid the transformer back until the tape adhered to the back of the enclosure. This way I used the entire steel enclosure as a heat sink for the transformer. I used the same idea for the three phase solid state relay (SSR) that actually controls the power to the water heater.

In case some of you haven't worked with power transformers, they get hot. It seems like no matter how high the rating, they generate more heat than expected, and can cause problems over time. That's why I was careful about giving the heat generated somewhere to go.

Just to the left of the transformer is an Arduino with an XBee shield on top, and just left of that is a AC to 5VDC switching power supply.

This little power supply is really nice:

I got it from itead.com a while back because I knew I would need a small power supply in the future and wanted to try one out. Unfortunately, they retired this model and I only have one left. I guess I'll have to hunt down another one sometime in the future.

I took the easy way out in mounting both the Arduino and the power supply, hot glue. It just wasn't worth the effort to build something special to hold them in place, so I grabbed a piece of plywood and mounted them to it. Worked fine, and they'll still be easy to get to if I want to change something or fix it in the future.

The enclosure is from Home Depot and I've had it for a while now. It's been the enclosure for the big SSR in the middle of the box for years, I'm just now adding more circuitry to it.

I'm interested in monitoring the power right now, so I haven't moved the code to control the SSR over to this Arduino yet, but that will come in a few days. That control is still part of my garage controller that also controls the garage doors. As a matter of fact I had power applied to the water heater when I took this picture; you can tell because the LED on the SSR is on. The control for that comes through the small wire on the top and connects to the left side of the SSR.

I was a bit worried about how far the little XBee would reach since it would be inside a grounded metal box once I put the lid on, but it worked well enough that it got to another XBee and the network took care of the store forward part I needed to get away with this.

It looks pretty good up there on the wall above the water heater:

Now I can glance up at the display and tell immediately if the solar pump is working, the mains power is being used or nothing is going on. To measure the power used by the solar pump and temperature controller I used the transformer mentioned above to reduce the power from 240 to 120 and put a plug on the front of the enclosure.

Notice that the solar pump is running when I took the picture. It uses about 80 watts to circulate the fluid from the collector on the roof through the heat exchanger inside the water heater. It has to run a long time to heat the water up inside, but at 80 watts, I don't even notice the power usage.

Now that I can see all the power data for the water heater, I can pretty much write it off as a large factor in my power bill.

Above is a chart of the last 24 hours of all the power usage by my solar water heater. Notice that there is one peak of main usage around 10AM and some light usage at other times. The large peak is too short in duration to cause a problem with the 'demand' billing and the light usage is around 80 watts from the solar pump.

Here's a chart of just the solar pump running:

The gap just to the left of middle is me installing stuff. Yes, I turned off the breaker; I have a healthy respect for 240VAC directly from the mains panel. All the jagged readings on the lines are the circuitry doing measurements and sending them off through the XBee. I have blinking lights on the Arduino and displays of the PZEM-0400 that are constantly changing. Makes for an interesting display.

Now before the more astute readers out there start picking on me for parasitic power usage, here's a chart of the power usage when nothing is heating at all:

The usage when nothing is heating varies between 3 and 10 watts, that will take a long time to add up to a full kilowatt and even show up on my bill. If you look up above at the first chart, you'll see that this is the condition that the water heater is in most of the time.

Actually, when I looked at parasitic power a few years ago, it just wasn't a problem. I have a baseline of roughly 500 watts that is used all the time. Things like ceiling fans, necessary appliances, phone chargers and such do add up, but what are you going to do about it? You have to keep the food cold and a 10 watt device running just isn't worth bothering with. All the hype about this just doesn't add up.

So, I did all this just to find out that my water heater is doing a really good job of saving me money. To heat the 80 gallons of water in my heater using the rule of thumb number of 0.166 kWh per gallon (60 degree F increase) for 80 gallons is 13kWh of power. I get it for a few hours of 80 watts in full sun. And, sunny days are not something in short supply around here.

I'll use the charts and power control to find a happy medium between using sunshine and mains power for keeping the power bill under control. I'm sure I can fine tune this over time. Plus, for the rare cloudy day, I can always crank on the power during off-peak periods to handle my hot water needs. I have special web code to do that from anywhere <link>.

I'm not quite done with the water heater yet though. I want to put a couple of thermometers up against the tank one at the top and one at the bottom to measure the actual temperature of the water. I also want to move the code that controls the SSR over to the new device so I have all the water heater code in one place.

But this little exercise has opened the doors to another possibility. All of my 240 volt appliances should have monitoring like this. I can get several of the power monitors and install them for the AC compressors, AC air handlers, dryer, and maybe even the microwave. Heck, I could monitor the kitchen oven as well. Hmmm, I could use another SSR and keep the darn clothes dryer from messing with my power bill, that has happened twice now. Someone needs clothes dried and they turn on the dryer during the peak period. I can actually put a stop to that by doing what I've done with the water heater.

How come every project leads to another?

Ordering Chinese Devices Through Amazon

This isn't a complaint session about Amazon, they've done well by me <link> several times, nor am I going to complain about Chinese products; a lot of the posts on this blog are about those items. This is just the story about a single product that I thought my readers would enjoy.

I needed a 240VAC to 110VAC transformer to provide power for my latest project, increased monitoring of my solar water heater. The 45 watt pump that moves fluid from the rooftop collector actually measured 68 watts when I plugged it into a Kill-a-watt to measure it. I know how this stuff goes, so I figured I'd probably need a 200 watt transformer because they always over rate these things in the specs, and I should probably stay below 50% of rating to get good service.

Have you checked out the prices on those things? A simple 2 to 1 transformer can cost as much as one can pay. The prices I found started around $37 and went up indefinitely from there. I know these things exist and shouldn't cost as much as some televisions, so I looked for another solution. I thought I found it and ordered one of these:

It's a 220 to 110 transformer rated at 200 watts for converting power for US travelers abroad. The images on Amazon showed the interior and it is a simple transformer with no other supporting circuitry to worry about. This should be perfect and only costs $16. That's less than half the price I found for the transformer inside.

It came in today and I rushed to unwrap it --- it rattled. There was something broken inside that sounded like a piece of plastic. But first, here's a picture of what I received:

First, notice the plug. It's a normal non-polarized US plug, not the European round pin plug shown on the Amazon page. Why would they put a US plug on something that was designed to be used outside the US?

Since I was going to dismantle it anyway, I took it apart.

There was the transformer I needed, but what had happened was that the transformer had come loose from the case, banged into the molded socket and broken one of the plastic pieces. The transformer was supposed to be mounted with some of that high strength two sided tape. I've used this tape several times and it really works great; why did it fail? Well, here's a shot of the tape:

Don't see it? They didn't remove the paper from one side of the tape. Like all two sided tape rolls, there is a piece of paper on one side of the tape. You cut off a piece, stick it to whatever you're attaching, then peel the piece of paper off and adhere the tape where you want it. This simple technique holds lots of things in our everyday life in place. The decorative molding on your car is probably held on this way, and you drive it at speed down the road every day. This stuff is good, if you actually remember to take the paper off.

What happened is that Amazon took the converter off the shelf in its box, shoved it into a padded envelope and shipped it to me. One of the conveyor belts somewhere dropped the envelope a little ways, the  loose transformer banged against the molded socket and broke it. That was how my rattle came to be.

If I wasn't going to only use the transformer, I would have returned it for another one. But the part I needed came through the ordeal unscathed. Unfortunately, there are no numbers on the transformer at all. No manufacturer, no nothing that can help me trace it to buy another. Maybe someone reading this will have some idea where I can source another when I need it.

So, even though the plug is dumb, it arrived broken and would have been intrinsically unsafe in use, it fits my needs perfectly. I saved at least $15 buying this instead of a transformer from a regular supplier.

Go figure.

PZEM-004: Now to actually use it for something

Literally hundreds of these energy monitors have been sold, but judging from the various articles I've run across, not too many of them have actually been used to meaningfully monitor power around the house. I'm going to install one of them on a troublesome device and actually use it to help understand my power usage. My current victim is my hot water heater.

I've described it before <link>, it's a solar hot water heater with a helper element in it for times when the sun isn't shining. Basically every day here in the desert I'm supplied with unlimited heating for water, but how often do I need the heater element? The element is designed to turn on any time the temperature drops below a certain temperature, but I have no idea what temperature that is. I have the solar heating set for 138F, and since it is an 80 gallon heater, this supplies my needs quite well. Nevertheless, I still want to understand the device and how it uses power.

The first thing I need to do is both read the serial output from the power monitor and be able to transmit it to my house controller so I can save the readings over time. This turned out to be a problem because an arduino only has one hardware serial port. It is possible using software to get another one, but having two software ports is a problem.

The SoftwareSerial library allows for two serial ports, but you can only work with one at a time. Each time you switch ports, the input buffer for the other one is cleared. When I tried it, that meant that the buffers were wiped such that I couldn't actually get enough data from either the XBee or the power monitor to construct a usable packet. I want the serial port for debugging and commands, so I had to work out another method.

What I did was set up a timer that fires off every 15 seconds to interrogate the power monitor, saving the data in global variables. Every 30 seconds another timer fires and sends a report of whatever the variables happen to hold at that time over the XBee network. This way I have reasonably fresh data to send every thirty seconds and only use the two software ports one at a time.

The exception is that in the main loop of the code I check for incoming data from the XBee network at every iteration. Basically in the idle periods between gathering and reporting, I check the network. To prevent the arduino startup from sending bad data from the variables that aren't filled in yet, I read the power monitor before I do anything else. Then I wait for a time message from my house clock, set the two timers and let it run.

It seemed to work pretty well.

Now, how the heck am I going to attach this mess to the water heater? I'm dealing with mains voltages here, I can't just stuff it in a cardboard box and hang it by its USB cord on a nail. This will take some consideration. Additionally, since there is no neutral line to the water heater, everything needs to work from a 220VAC source. Yes, I know, most of the world already has this to deal with; for me, it's a new experience.

Being impatient, I took a big rag and insulated (if you can call it that) the top of the water heater and hooked the power monitor to the high power solid state relay that I use to control the power to the water heater. Then I draped the USB cord over to a wall plug for 5VDC power to the arduino and XBee combination. This way I could actually watch the water heater power usage real time and work on the software to add the data to my Graphana display.

I had some foresight though, I put in plugs for the connections to the CT, 240VAC voltage monitor and serial input so I wouldn't have to flip the breaker when I did something, and it worked like a charm after some programming to save the data I had gathered and a little work in the charting software:

Granted, it's not much to look at. The heater only turned on three times, and even then, it was only for a minute. Slow day around here, but notice that the spikes are 4500 watts. This thing can really pull the power; remember, the solar is running also.

What is happening is that using hot water causes the temperature in the tank to drop and both the solar and the helper element kick on. This heated the water back up in a hurry. Or, maybe I have a bug I haven't discovered yet. Over the next few days I intend to look at how hot water is used for showers and general use around the house. I won't get good data on how this thing is working until I can also monitor the small solar pump as well, but that will take some thought, and probably, some more parts and pieces. Keep in mind that the small pump is 120VAC and I'm working with 240 at this point. A transformer maybe??

My data gathering will be impacted by the fact that the water here doesn't get cold enough to need much of it. This time of year, the rest of summer and early fall, one can take a shower with nothing but the cold water turned on. The best we get for cold water is tepid, and maybe use a tiny bit of water from the hot side. Not that way in the winter though, then hot water usage is much higher.

I'm starting to like the PZEM-004; when this project is running, I want to look around at other similar devices. It's hard to beat less than $15 for a device like this. I certainly can't build an equivalent for less.

I'll put the code for this on github when it is a little farther along. There may be too many bugs right now.

Previous post on PZEM-004 <link>

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>

More on House Power Monitoring: Prebuilt Device

There's been a lot of new devices appearing on the market for monitoring power. I decided to get one and see what was actually going on. I prowled around Alibaba for a while and settled on this one, the PZEM-004:

The reason I picked this one is that it has a TTL serial output that I can play with as well as a display, and for a long time now I've wanted a display to put on the water heater to show me when it is actually using power. This might just fit the bill as well as giving me an output that I can use to record the actual power usage. Since the water heater is 240VAC, this should do the job. If it works.

Naturally, when it came in, I took it apart to see what was inside:

The power and CT inputs are on the right and a ttl serial port is on the left. The two big chips that do the work are: Atmel 24C02N a 2 wire serial eeprom <link> and SDIC RWTS SD3004 energy monitoring chip <link>. 

These 'energy monitoring chips' are a relatively recent thing. Manufacturers took the interest in smart meters and energy monitoring seriously and produced a whole lot of special purpose chips to sell. They're pretty nice, and for an industrial application, do a good job. Every smart meter out there has something similar inside it. The problem I see with them is that for a person like me, they're too darn complicated. They take a bunch of support circuitry and need special commands to do what you want. For the time being, my own devices will use the older methods I already understand, unless this device changes my mind.

The rest of the circuitry is power supply, serial interface, support for the displays and such. I can't recommend that people get one of these because there is no clear separation between the parts that can kill you and the rest of the board. They appear to be relatively safe, but missing are the board cuts and clear indications of where the high voltages run. For a beginner that wants to start monitoring devices, this could get them in trouble.

But, trouble seems to be my middle name.

My water heater is solar. I have a panel on the roof of the garage that heats water, and when the temperature in the heater is less than the temperature of the solar heater, it pumps water from the panel to a heat exchanger inside the water heater. The heat exchanger is necessary because the fluid used in the panel is partly ethelyene glycol to avoid the possibility of freezing up there on the roof. The heater tank is 80 gallons to hold enough hot water for a long time. There is a little 45W motor that moves the water around to do the heat exchange.

Additionally, there is a helper element inside the hot water tank. The helper element is activated whenever the water needs heating, including when the sun is out and the solar is working. They recommend that people put a timer on the helper element, instead I hooked it into the house controls <link>. So this device gives me the ability to use the serial output from the power monitor to record the energy used by the heating element of the water heater.

But, why is that important to me since I have a solar water heater. Firstly, because I can. Secondly, it would be good information to know what a water heater actually uses in energy for my purposes. Heating a bunch of water is an efficient task since the element is actually submerged in there, but it still uses a heck of a lot of power. I want to understand this.

The very first thing I encountered was hooking the darn thing up in some kind of test bed. I really didn't want a bunch of jumpers carrying 220 hanging off my water heater, so I cut up an old extension cord and built a test bed for a 110VAC light that had two bulbs. That way I could change the bulbs and see different values as a kind of calibration test. I made darn sure the wires weren't exposed so I wouldn't rest my arm on them. The meter worked fine and actually gave a reasonable reading first try.

Next I went looking for how to hook up the serial port to my laptop. The USB to ttl serial cable that came with it had a fake chip in it and wouldn't work. I chased down the correct drivers for the chip and got the serial working, but couldn't find the proper baud rate anywhere in the (slim) documentation that came with it. That got me to searching the web for information.

Really fortuitous problem. There are a lot of sites out there that have messed with this device and put up examples. I even ran across a library to support it in github <link> so I wouldn't have to do everything from scratch. By the way, the baud rate is 9600!

So, I added a little arduino to my test setup and started to peck away.

Yes, I know it's not the safest setup in the world, but as long as I remember to pull the plug before grabbing that metal screwdriver, I should be OK.

As you can see, the monitor worked first try and all the displays worked. The picture missing some things is an artifact of the pulsed display. I didn't have as much luck with the software I found though. It took me a bit to figure out what 'yield();' was that was keeping me from compiling, but it turns out that that is simply a delay(0) for the esp8266. I added a stub for that.

Everything worked from then on Here's the serial results as it came out of the box:

The power, voltage and stuff was right on the money when I compared it to other devices I have around the house. The current transformer they supply is one of those that you have to remove the wires to use. You can see it in the picture above. In some places you can't get the wire loose for various reasons, so I tried a SCT-013 that can be found all over the place and I happened to have. The results were not as pleasant:

If I need to use one of those, I'll have to hunt down and change the burden resistor since I can't get to the calibration. The displays shows one bulb at first and two about half way down; roughly half what it should be. There are no markings on the supplied CT, but I bet it has half the windings of the SCT-013.

(Edit: I looked up the various datasheets, the SCT-013 has a ratio of 1:1800 and the split core version of the included CT is 1:1000. Not quite half, but close. There is a split core CT that will work with this, the PZCT-02, that costs about five bucks and has a 30 day delivery. I'd still like to be able to use the SCT one though)

So, now I'm at a decision point. Do I add this to the water heater setup or not? If I do, do I use a separate system from the garage device. The garage is currently handled by an Arduino that controls the water heater and the garage doors. This device could be for the water heater like I have one for the freezer and such.

Decisions, decisions.

Continuing with this device <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.

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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.

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Another Garage Sale Find

I found something else at a garage sale that I'm going to write about. I promise I'll get back to technical projects for a while after this.

I was looking through a bunch of really old TV repair equipment. There was even an old B & K sweep marker generator there.

The guy had lots of old equipment. Looks like he had bought out a storage locker that was abandoned by an old TV repair shop.

This was in the days when tubes (young folk, look it up) were used. Back when we actually had tube testers to tell us if it was bad. We'd slap the side of a tube gently with a screwdriver to see if sparked. Ah, those were NOT the good old days. I didn't buy any of the electronics, they were just too old and that stuff, while magnificent in its day, just wouldn't do the job today. I don't really want to start a museum.

After spending some time prowling and remembering, I stumbled on a wine rack. It wasn't special, but he wanted $12 for it and the metal rings it had in it were more than that at the steel supply, so I bought it.

I took it home and stuck it on the counter top where I wanted it and it didn't look too good.

It was too dark for the room, and too wide for the spot. Crap, I should take a tape measure with me for things like this. Actually, that wouldn't have worked because garage sales are all impulse items or rare finds that you can't turn down. You never find the exact right thing when you're looking for it.

I guess I could sell it at my own garage sale, but I did buy it for the rings that hold the bottles. Maybe I should pursue that.

If you notice, I have unlimited space up top and a cabinet that is three rings wide would fit in the space, so I got inventive. I took the 4 x 6 arrangement

Got out my hand grinder and welder and turned it into a 3 x 8 arrangement of the rings.

I took the rings inside and sure enough, it would fit. So, then I needed a new box to hold it. I just happened to have some hickory plywood left over from my cabinets; the guy that designed them over ordered. Naturally I kept the excess because that stuff is expensive. Now was a chance to actually use some of it instead of moving it around the garage from time to time.

I built a basic box with no back:

then test fitted it into the same spot as before:

Yep, it was going to fit. I used crown molding for the base so it would be a little more stable and to cover up some saw marks. I had this left over also. Now, to finish it off , it was just install the metal rings. 

Add a little finish to make it shine a bit, and move it back into the house.

Now it fits the space and matches the existing cabinets. I have more room for wine bottles than I have interest in buying wine. Perfect.

Yeah, I know, I could have bought the rings off ebay and done exactly the same thing, but I never thought of that. Also, each time I visit a garage sale, I come away with more work to do.

I hope  I don't find a '32 Ford at a garage sale.