Attic fan tests: 1 week of data

A quick update to the attic fan cooling experiment (check the previous post to read about the setup). I ran the fan for a few days in a row, from around noon to 5PM, at which point the HVAC kicked in until late into the evening. There were some HOT days and some WARM days, with a hot day with PM showers which produced some interesting data. from the WeatherShield sensor motes in the attic and the master bedroom below it. Here’s conceptually how an attic fan is supposed to work, in theory:Benefits of an attic fan

My cheap fan I installed in the attic hatch draws 85W on the high speed and uses ~0.45kWh for a 5h run time), not bad. Here’s the temperature graph after several days with different weather conditions, read on for explanations.Notice the huge temp swings of the attic, and the relatively small changes in the master below it.  July 29th was the HOT day with PM showers and moderate wind which cooled down the attic. I also had the fan going but the rain/wind cooled the attic quickly through the built in soffits and vents. On the rest of the days the fan did a good job of chopping the “hotbergs” tips off, they look like mouse bites :). To be more effective it has to be started soon after the sun starts to blast the roof around 10am. The master temps were zoomed in for more detail. Here are the humidity measurements: Continue reading

Cooling on the cheap: attic fan tests

For some time I wondered if there’s a way to move the cool air in the basement upstairs and make that living space a bit more bearable without running the AC all day long when everyone is gone. As soon as the sun rises and starts hitting the roof in the morning, the attic temps start to blast up towards 150° at the peak around 6pm. The side walls and windows also heat up, act as heat radiators and contribute to warming the interior spaces. Once that attic space and side walls are super heated after a day-long sun blast it’s very hard to cool the interior back down, while heat radiates quickly inside and fights the HVAC’s cooling efforts. The attic 20″ blown insulation does a great job keeping the 2nd level way cooler than the attic, around 87°F, but still feels very toasty, and the decade old HVAC runs almost non stop from 4pm into 11pm to make it bearable enough to go to sleep. All this while the basement temps range from 65-75°F during the day, nice and cool.

Googling around I found some solutions that involve using the HVAC fan to push air from the basement or lowest point in the house all the way upstairs and into the attic (opening the attic hatch). Attics have vents that allow air to flow through and out. So this air movement pushes cool air through the house and into the attic and then outside through those attic vents, thus keeping the attic air from super heating. The outcome is that the HVAC AC will have an easier time to cool down the home in the afternoons, running for less time while the temps bounce less throughout the cooling cycles. Unfortunately running the HVAC fan also requires a vent to be cut into the basement HVAC pipe system so the cooler air can be pulled by the fan and moved up, rather than the air from the return pipes (which brings it from upstairs). I don’t really want to do that, since the HVAC fan is a big heavy 220V inefficient motor.

So I’ve just started playing around with some WeatherShields and a cheap Lasko box fan ($17 from HD) that I’ve installed on a thick cardboard cutout which replaces the attic hatch. The fan is good enough for proof of concept and allows easy hacking of the speed knob displacement into the cardboard so I could change speeds from inside the home without climbing on a ladder all the time. For now the power is provided through an extension cable until tests are done, then I plan on making a SwitchMote controlled power outlet in the attic where the fan can plug in, so this could be turned ON/OFF automatically by the Gateway.

Here are a few photos of the fan mod and install. This is just a temporary fitting for some basic tests. A final install would have the fan attached more securely with no air gaps etc.:

I put together 2 WeatherShields for this test, and added a dedicated Weather node to the gateway. This was a good way to test WeatherShield readings side by side. Results are impressive, I could not see the temp and humidity readings be more than 1% off from each other. BTW I’ve added the new Weather node icon and node definition on the Gateway github repo, and I’ve posted the low power sketch I used on these weather nodes.

Basic fan test data & conclusions

Each level is ~1500sqft, with the attic having a steep slope, so a large air volume. I’ve put one weather sensor node on the second level and the other in the attic. I started measurements around 8:45am when the sun was starting to heat up the attic. One hour later I started the fan and let it run until 12:28pm, almost 4 hours. An open window in the basement (or 1st level) allows air to flow easily and not stress the fan. Here’s a glance of the temperature data from the attic sensor, explanations below:

Just looking at it it’s obvious the fan made a big dent. I ran it at max speed which is pretty loud but this is in a closet so that helps contain the fan noise. I’ve seen more expensive similar fans  advertised as very quiet. The point here is to move as much air as possible since the fan would run during the day anyway, when nobody is upstairs to hear the fan noise. I’ve made some projections of what I think would happen if I ran the fan all day or if there was no fan at all.

I will continue to make measurements on comparable days with and without the fan and perhaps update this post, but I think the test is a success. It was a sunny day with 85° tops. If the attic normally heats up to around 140-150° at peak and the 2nd level is around 90° it is very difficult to cool it back down and the AC works very hard. If the fan can reduce the attic temperature by even 20° I assume the AC would not need to work as long and hard to cool the upstairs in the afternoons. I think this simple fan will cost much less to run for 8-10 hours, than running the AC that much harder all afternoon.

A possible improvement to this method is to install more fans in the attic, on top of the vent exhausts to help remove that hot air from the attic, more complex. Or cut a hole in the basement door to add another fan to push air, messy and not wife-friendly. Or stack another fan on the existing one at the attic hatch to increase CFM, just another $17.

To automate and remote control the fan I will need to make a SwitchMote outlet and put it in the attic. That’s for another post.



Smart meters installed in my neighborhood

About a month ago I got a notice in the mail from DTE saying they will begin installing smart meters in my area. I didn’t expect that to happen soon since the last time I talked to them on the phone they said it was not being planned at that moment. To my surprise both the electric and gas meters were replaced/updated last week. So things can happen fast. Here are the good old meters:

I was home on both occasions and the old electric meter was removed and replaced with a brand new Itron/Centron smart meter. Power went out for about 30 seconds. The gas meter was installed on a different day and I was happy to be able to snap some pictures. Continue reading

Sump pump alert with Moteino & HC-SR04

UPDATE: This project has been replaced/updated with SonarMote. See this blog post for a more rencent implementation of what you see here. The alerts are now implemented as simple events on the Moteino Gateway.

Here’s another project I wanted to do for a long time. I wanted a sump pump flood warning alert system in place, for peace of mind when I’m gone from home for prolonged periods. For whatever reason I thought this was going to be more difficult but no, it’s almost as easy as pie!

All I needed was a HC-SR04 sonar sensor and a USB 5V wall supply. The sensor only works at 5V so this method of powering the Moteino was very convenient since I already have an outlet close by for the sump pump.

The sensor has 4 pins clearly marked: VCC, GND, TRIG and ECHO. I connected VCC to VIN on Moteino, ECHO goes to D3 and TRIG to D4.


I used some of the code this instructable to get started and added my wireless code to handle packets and blink the LED and was done in no time. The setup was very simple, I estimated a good spot underneath the sump pump cover where there are no obstructions inside, cleaned it up, taped some velcro, secured the wires and that was pretty much it.

 Moteino_HC-SR04_SumpPumpAlert_cover Moteino_HC-SR04_SumpPumpAlert_installed

I added a few lines of code to my main Python script running on the RaspberryPi.
By the way, here’s how my RaspberryPi setup looks like, including the ATXRaspi power controller, the power button and the gateway Moteino (it’s an older R1 but just as good for as a gateway):


The Python script logs the data to EmonCMS and here’s a graph of how that looks like, the Moteino reports the distance to the water surface, so the spikes means the sump pump just kicked ON, and as water rises the distance decreases until the pump starts again:


It’s been a rainy spring so far here and I knew my pump kicks ON quite often, now I can see it in real time, and setup alerts if the water rises too much. Seems like the pump is always pumping water out when it rises to 32cm below basement surface. So setting an alert to something like 20cm below surface should be enough since I don’t expect the water to ever rise so much as long as the pump works. The alert code will send me a SMS message when this happens, here’s a test level, I set the live value at 20cm:


You can of course setup other types of alerts – like audio alerts or maybe a LED visual indicator (less useful when you’re not in your basement).

Fun/Scary fact: The sensor is very accurate even though there’s a variance of 1cm between some readings (resulting in a sawtooth graph) as water rises. Based on the graphs, how often the water is pumped (every ~23 minutes), and how big the reservoir is, I figured my sump pump removes roughly about 18.5 liters every cycle, or about 1158 liters (306 gal) every day, wow!

So now there’s an extra level of peace of mind when I leave on vacation. I guess being gone for even 1 day could mean disaster if the sump pump breaks down at the same time!

Time to think about how to gather/store all that water instead of throwing it away, after all, I pay something like $11 for every 1000 gallons of city water.

Source code is on GitHub:

Building the electronics lab

Recently I decided it’s time to dedicate a more professional workspace for all my electronics work where would this go better than the most remote corner of the basement?

Previously I organized my office in one of the home bedrooms but it quickly became obvious that it’s not the best place to keep heat and smoke generating equipment, mix chemicals, etch PCBs, or store parts small parts that get lost in the carpet. Plus I didn’t have outlets where I wanted them and it just didn’t feel right to solder on the office desk.

So I took a break from most of my projects and dedicated almost entirely to planning and building a workspace in my unfinished basement. Long story short, I ended up with a 120sqft room perfect for my needs. I knew I will want to watch my own progress so I captured timelapse videos of the more significant parts of this building project. This happened over several weeks, and if people want details of my planning, building and costs, I can post about that as well. Cheers!