Tuesday, June 3, 2014

My Freezer and the Iris Smart Switch, Measuring Power

I went to Lowe's Home Improvement the other day to get supplies for jobs around the house that need to be done, you know caulk needing replacement, some spray foam, wire brush, the things we all have to get from time to time, but somehow, I wound up in front of the Iris display.  Shame on me.

When I got home with the stuff I needed, and my new Iris smart (which was NOT on the list) I decided to hook it to my freezer so I can monitor both big appliances in the kitchen.  Since I was lazy the last time I played with these devices, I had to modify the code to support more than one switch.  That wasn't too hard.  The switch connected first try and started reporting.  I was a bit surprised at what I got out:

I labeled a couple of interesting things; remember I have separate refrigerator and freezer, this is the freezer only.

The spike and drop at point A is the automatic defrost running.  The way these things work is there is an actual heating element on the evaporator in the freezer, and a timer runs it a couple or more times a day.  The timer kicks on and the heater brings the evaporator up to 40°F when a thermostat on the evaporator coil opens and turns off the heater.  The rest of the defrost cycle runs and control goes back to the temperature control system.  Which usually means the compressor kicks on.  This period of time allows the water to drain away into a pan where a fan evaporates it.  My defrost cycle falls in the 'Peak' period of billing, so that's not good.  The timer also runs on a little less than a 24 hour cycle, so it doesn't kick in at the same time each day.

This all means that I have a heater kicking on during the peak period that could be run some other time.  Fortunately, there's a little slot on the defrost timer that allows it to be advanced such that the defrost time can be moved, but since it will eventually move back into the peak period, I'll have to readjust it from time to time.  Notice it runs twice a day, that'll just complicate matters a bit.  This little timer may be a good place to put an Arduino synced up to my house time for absolute control of the defrost cycle.  No, I'm not getting too anal about this ...

Point B is the lights inside the darn thing.  This freezer has 8 stinking lights in it; four on the top, and four on the bottom.  Time to see if I can get a deal on led lights to replace these incandescents along with the ones in the fridge.  I mean the lights actually use more power while they're on than the compressor does.  Granted, they aren't on very often or for very long, but crap, close to 300 watts to light up the freezer?

Point C is the automatic ice maker.  When ice is low, this thing kicks on periodically to roll the new cubes into the tray and opens a valve to let water in for more.  This seemingly simple operation uses over 150 watts.  This is also short lived, so it can be tolerated.

What surprised me was how long the compressor runs.  I was worried that there may be something wrong since low coolant pressure or an air leak can cause the compressor to run too much.  I went to the GE site and looked up their explanation of the compressor cycle and what I'm seeing is perfectly normal.  The compressor on a freezer can run from 75 to 90 percent of the time under normal operation.  This seems excessive, but the motor is designed to take this much use.  It only uses 130 watts, so that's not too bad, and it does cycle somewhat, especially in the late evening early morning period.

What's becoming more apparent over time is the insignificance of parasitic power devices.  Little things like cell phone chargers that are left plugged in, televisions that look for remote control signals, wireless phones, etc.  I'll start checking on these devices, but it appears that all of them are roughly equivalent to a 60 watt light bulb.  You'll get a lot of bang on the power bill by paying attention to the lights and ignoring the small devices around the house.

Now, I have to get the caulk gun and get back to what I'm supposed to be doing.


  1. That was a good read... surprises abound, so do distractions. I went through my house a month or so ago, powered-off all the circuit breakers, then switched them back on one-at-a-time, while reading my "power meter" (a battery powered Rainforest gizmo that uses Zigbee to read the utility company's smart power meter) and was fascinated that my two thermostats and their accompanied transformer uses 15 watts (about $3/month)... a trivial amount, but a lot more than I expected. My network routers use 15 watts each, my LCD TVs use 15 watts each (in "off" mode), cable set-top boxes take 15 watts (in "off" mode), the house alarm uses 15-20 watts in non-alarmed mode... seems lots of things use about 10-15 watts in "standby". I too use the Iris switch for power measurements, but it's been behind the refrigerator for quite a while and I've been too lazy to move it.

    1. Wow, I may have to reconsider the parasitic devices. But, thinking about it, 15W is around a tenth of an amp at 120 volts. I wonder if the measuring devices are messing up at that low a level. I'll drag out the kill-a-watt and try a couple of my parasites to see what I get.

      However, the AC thermostats truly are power hogs. The thermostats themselves usually are fine, they are in the low micro or milliamp range and most of them are battery powered. The problem comes from the circuitry in the furnaces and refrigeration systems. When an engineer is designing something that pulls 4-5 kilowatts, they don't think about a tenth of an amp parasitic draw.

      Good, another distraction.

  2. hey dave, Have you posted the updated code anywhere? (I'm the guy that was showing up as Unknown (no idea why) on the other page talking about the Almond+, etc..

    1. Not yet, but I will. I wanted to wait for my next switch so I could change the code again to recognize a new switch being added. For this one, I just disconnected the first one, joined the new one, then changed the code to support two switches after they were joined. This isn't the best way to do it.

      I also want to open one of them up and figure out how to jump the relay so it will never turn off. I'm not comfortable with a switch in the line to my freezer long term. Too easy to mess up and ruin a bunch of food.

    2. Gotcha. there's nice internal pics too on the FCC ID search of the insides.