Passive House thermal monitor

Here’s some results from a Particle Photon energy monitor I built for my Passive House.

The main elements are:

  1. The photon and firmware
  2. An RHT03 combined temperature and humidity sensor
  3. An InfluxDB timeseries database and Grafana ( u:guest, p:kingswood) dashboard running on a DigitalOcean virtual machine
  4. An InfluxDB library I wrote (
  5. OpenUV for UV Index info
  6. for external temperature, humidity, and cloud cover

It obtains external temperature, humidity, cloud cover, and UV Index from APIs triggered by webooks. It combines those with the internal sensor data and sends them to InfluxDB. It’s been running continuously for 60 days and seems to be stable.

Here’s a heat map generated from the data - date is left to right, top to bottom is one full 24 hour cycle.

Because the house is so insulated, it warms up 2 degrees around noon, and loses about .1 degree an hour to the environment, so keeps in thermal balance.

The next stage is to hook it into the house Heat Recovery Ventilation system to further optimise energy use based on forecasted external temperature and sunshine. Although the house only uses 15% of the energy of a conventional home, it still uses some and I can reduce that further by getting the Photon to deactivate the MVHR system when sun is forecast.

All very interesting.


Very cool project with the Photon. I will someday hope to replicate your project; I just need to start building a passive house. In addition to the passive house architecture and the thermal storage systems, did you also use non-traditional materials for the building exterior shell?

Thanks cyclin_al. Actually, the project is probably more relevant to conventional housing. Adaptive control of domestic energy use based on a forecast of weather is essentially what the Leaf/Tado/etc. do. In a Passive House, there aren’t many levers to pull - in my case, I can alter the flow of air in the house to reduce the temperature variation between the lower and upper floor created by air density variation. I can also open and close the heat reject bypass to smooth out temperature variations. But I’m really dealing with an excess heat rejection problem - the money saver is dealing with excess heat creation problem, which is a challenge for conventional housing.

I did consider some alternatives and non-traditional materials, including the use of a novel sawdust process for insulation. But I was pushing the thermal envelope for complying with the Passive House certification requirements due the relatively large amount of glass in the design (hence the heat rejection problem). Most alternatives involve some tradeoff in performance and I didn’t have the margin, unfortunately.

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@richlyon, very cool. It is clear you have given it some good thought. Yep, I do understand the difference between adaptive control and a passive house. I have been working on some adaptive control for a dog kennel (using a Photon), which has very different parameters and constraints than a house.

I have an interest in alternative materials, but I have not heard of the sawdust process. I will be looking into it. So far, my dream project is a passive house using straw-bale construction for the external shell. I have seen some great designs, but usually have more glass than I would like.

I agree that there are tradeoffs; it’s just a matter of choosing the tradeoff you can live with.