Event triggers based on power consumption

[Steve Q]

I have been exploring how to use power consumption to trigger Homeseer events. I am using the CR3110/DS2438 power monitor I designed on one of circuits in my office ( http://board.homeseer.com/showpost.p...1&postcount=20 ). The graph below shows the power consumed over a 5 day period. The flat line portion (about 52 watts) is my Homeseer Computer. The higher values are periods when I was using my other computers. Based on this information I have created 3 Homeseer events:

1. A power failure event (a log entry and an email) when the power consumption drops below 50.
2. A power restored event (a log entry and email) when the power returns above 50.
3. A reminder announcement to turn off my office computer at 11:45 PM if the power is above 75 watts.

It will be interesting to see how many events might arise based on power consumption.

Steve Q

[Michael McSharry]

If your HS computer is the one managing the events then how will it know that power has gone below 50? Likewise how will it see an event where it goes from below to above?

[Steve Q]

If your HS computer is the one managing the events then how will it know that power has gone below 50? Likewise how will it see an event where it goes from below to above?

Michael,

Homeseer, my cable modem, and 1-wire are all plugged into my UPS. So they are running off the battery; no power being used upstream of the UPS. I have about 30 minutes after the power goes out. When the power comes back up everything restarts. I'm thinking about whether or not to implement a graceful shutdown of homeseer after 20 minutes; or perhaps I should just let it die. Not sure. Since I'm tracking ON/OFF of all my HVAC stuff, Homeseer is frequently writing data to the hard drive. I don't know what would happen if the power would fail during a write.

Steve Q

[HomeTech]

Slightly related queston. Could this be used to monitor a whole house electric usage in K watt hours?

If so how would you set up two (2) CR3110 to meter 2 phase here in the US.

The DS2438 would need to add both metered phases together some how?

[Steve Q]

Yes, You could put a CR3110 on each leg of the 220V feed. However, I don't think this would be very accurate because I believe it would be double counting anything that uses 220V. My idea is to monitor individual circuits. There are some specific products that have been designed to measure whole house power usage. I think you would be better served with something like TED the energy detective.

I am not really very interested in measuring the whole house power consumption. I can get that data from my power company. They can tell me how many KWhrs I'm using by hour for each day. I have looked at this data and I don't find it very useful. What I have found helpful is to measure the loads on each circuit (I used a clamp-on amp meter). The first thing I discovered was that my Home Theater uses 80Watts when everything is turned OFF (ie standby).

My goal is to add a power monitor to those circuits that have several items that use a significant amount of power. For example, my outside flood lights (6 units x 2-100W halogen bulbs in each unit) are motion controlled, but I don't have a clue how often they turn on at night. With a power monitor on that circuit, I would know how much power they are using and I could even have Homeseer switch some of them off.

Steve Q

[Steve Q]

Slightly related queston. Could this be used to monitor a whole house electric usage in K watt hours?

If so how would you set up two (2) CR3110 to meter 2 phase here in the US.

The DS2438 would need to add both metered phases together some how?

I have added a DS2438 to one of the main legs of incoming power cable. Since the current level can be very high, I add a 500 Ohm burden resistor across the CR3110 current transformer.

Attached a a graph of a couple of days of "power" usage. As you can see it is pretty difficult to determine what each spike represents. I know that some are due to the water heater, oven, and electric baseboard heaters. I'm not sure how this data can be used. Suggestions would be appreciated.

Steve Q

[HomeTech]

Looks like its gathering data. I guess the next thing would be to gather one month of data and plot that on a daily basis for 30 days. Then start the next month from that point.

Maybe Michael can provide some guidance as to how to set up the plotting and graphing.

At some point I would check the electric meter on the house and see how acurate to the kwh its gathering data.

[BrettS]

I have added a DS2438 to one of the main legs of incoming power cable. Since the current level can be very high, I add a 500 Ohm burden resistor across the CR3110 current transformer.

Attached a a graph of a couple of days of "power" usage. As you can see it is pretty difficult to determine what each spike represents. I know that some are due to the water heater, oven, and electric baseboard heaters. I'm not sure how this data can be used. Suggestions would be appreciated.

Steve Q

I use a TED to collect my power data and that has an interesting feature called "Load Profiling". The theory is that most of the devices that cause those high spikes use the same amount of power whenever they are on. You can use the TED software to 'learn' how much power your large appliances use and then, theoretically, know when they come on. For example, my electric water heater draws about 5kW, so if the TED software sees a sudden 5kW spike then it knows that the water heater came on. When it sees a sudden 5kW drop, then it knows that the water heater shut off.

It's a very interesting concept, but unfortunately I really haven't been able to get it to work terribly reliably. It worked reasonably well with my water heater, but I discovered that both of my heat pumps, my microwave, and my oven all use very close to the same amount of power, so the software can't tell which appliance was actually turned on. Additionally, each of those devices uses about 2.5kW, so if two happen to start or stop at close to the same time then the TED software sees a 5kW spike or drop and thinks it was the water heater.

Depending on the appliances you use and how much power they draw you might be able to do something similar to this.

I've also discovered that watching the current power draw is kind of intersting, but not terribly useful because it's difficult to tell what is drawing so much power. I can easily get a spike of 12kW or higher if my water heater and several other appliances come on at the same time.

I've debated trying to use some other method to determine when my large appliances are on and then, based on the amount of power they draw, have HS subtract their power usage from the total number. Maybe even subtract my 'baseline low' number as well. That way if the lights, TV's, ceiling fans, etc are all off then it should read 0. Theoretically, then, I could see how much power the lights and TV's and everything else that people in the house can control are actually using. That might be a better number for people to use to try to conserve electricity. Right now, if I look at the total and see 5.something kW I know that the water heater is on, but I don't really know if someone left the downstairs TV on, becuase the 40 or 50 watts that uses would be buried in the total.

In practice, though, I really don't know how well that would work.

Incidentally, it looks like the label on the last graph you posted is wrong... It reads Volts, but I believe it should read kW.

Brett

[Steve Q]

Brett,

Thanks for your reply. Your comments about the TED are most interesting. You are confirming one of the concerns I have about whole house power monitoring, namely that it is still hard to know what is using the power. My approach to power measurement is to monitor each of my major appliances to know when they come ON and turn OFF. I have a current sensor on each major appliance (16 appliances) and I track the total ON time for each of them. I have a big spread sheet with all this data on a daily basis, and I compare it to my electric meter reading. So I have a good handle on how often my appliances are running and I have implemented many Homeseer controlled events to turn them off whenever they are not needed.

However, the smaller stuff like lights, transformers (wall warts), clocks, etc. don't draw enough current to trigger a current transformer, so I have added a current monitor to several circuits to try to find other power wasting devices. This led me to add a power monitor to the main leg as an experiment just to see what the graph would look like. And it looks exactly as I expected; lots of spikes... but also a nice flat line at zero during the night (except when the water heater turns on). And I know what most of the spikes are because I can compare the time of the spike to my log of the ON/OFF times of my appliances.

I think the combination of tracking individual appliances and monitoring the main feed and some individual circuits provides a wealth of information.

BTW the graph is correctly labelled. The output of the DS2438 is 0 to 10 volts.

Steve Q

[vc1234]

However, the smaller stuff like lights, transformers (wall warts), clocks, etc. don't draw enough current to trigger a current transformer,

Steve,

If you want to measure low power device energy consumption, you may consider using the ADE7753 chip (that's what I am doing). The chip measures active and apparent power, RMS voltage and current, mains frequency. It communicates over a simple SPI interface and does not require too many external components ( http://www.analog.com/static/importe...ts/ADE7753.pdf). The chip costs about $5 at DigiKey. You will also need a couple of resistors and capacitors as well as a 3.58MHz crystal (optional).

With a CR3100 and a 100 Ohm burden, I've accurately measured loads as low as 10Watt using +/0.5V full range input of the ADE7753 current channel. For greater precision you can go as low as +/-75mV full range on the current ADC channel.

Also, with fluorescent lights, computers, and other low power electronic gadgets, measuring just the current leads to a substantial error due to the power factor and non-sine current waveform. The large resistive loads like water heaters and baseboards can be measured quite accurately by just measuring amperage and multiplying by 120V or whatever voltage you might use.