Passive House Empirical Results: Measuring Real-world Energy Consumption Performance

Passive House Empirical Results: Measuring Real-world Energy Consumption Performance

Digital Pocket Psychrometer PHR2 from Fieldpiece.  Cost approx. $60.

Theory is all well and good, but ultimately the engineer in me wants real-world empirical data.  As trusted and proven as PHPP is, at the end of the day, I wanted to actually measure how our house was performing.

Most of the measurements and analysis that I have made have been without much occupancy, so I figured this would be the worst-case scenario (not benefiting from the internal heat-gains of both my wife and I as well as our four-legged companions).  I have now accumulated data over a period of about a year--including all four seasons during that time.

Before getting into some of our results, in future articles, I wanted to share with you the basic and inexpensive tools that we have utilized that made those measurements.

The first area of analysis that we focused on was interior relative humidity levels, which were initially quite elevated.

Beyond RH, I took numerous temperature measurements (and subsequent electrical consumption of active/backup heating) to maintain certain interior set-temperatures.

This last winter has been especially cold (with a good number of days being lower than our outside (heat-load) design temps). We also found this winter to be an especially overcast one (resulting in reduced solar heat-gain).  All of these external conditions, I believe, pushed our design to the limit.

Since my wife and I still live primarily in our existing home as we haven't quite yet moved into our passivhaus, I have been able to isolate specific electric consumption over discreet periods to get a very good handle on how the building is performing and the electrical energy it is consuming.

We also have found that there remains further tweaks that have to be made, particularly to our MHVR system, even though it had been commissioned once by Barry Stephens of Zehnder America, as we found one of the units have been performing below spec (more on this later).  We expect to examine this in the coming weeks.

Here are the simple (and inexpensive) tools and practices we have been using, to this point.

For temperature measurements:

  • Portable "weather stations" from Lacrosse with remote sensors. (Moderate accuracy).
  • Pocket digital psychrometer from Fieldpiece (More accurate)
  • Infrared Spot Thermometer (for surface temperature readings) (Moderate accuracy)

These devices are readily available either at an HVAC supplier or at retail building materials stores such as Home Depot or Lowes.

For electrical consumption measurements:
  • Amp clamps (120v/240v), for real-time energy consumption readings
  • Simple meter readings over discreet periods of time

We are expecting to use more thorough electric consumption monitoring tools once the energy consumption gets more complicated.

These are the tools/vendors we are considering:

Note: I would appreciate any feedback from those that have actually used these products.

With these inexpensive tools and some analysis, I have been able to calculate Btu losses over discreet periods of time, as well as estimated Btu output from our mini-splits at varying indoor set temperatures and outside temperature and relative humidity levels.  I was also able to roughly determine effective COPs/EERs of the mini-splits as well.


  1. Hi Bob

    I look forward to your future posts on this subject. This kind of information about passive house is hard to come by. Lots of info about building but not a lot about actual performance of passive house is found online.

    When do you think you will move into your passive house?

    Also, thanks for the comment on my blog regarding excavating (budget). We got off easy in that category. Excavating costs were "less" than expected. Lucky!

  2. Your blog is looking really really nice!

    Lisa and I are beginning the protracted and painful process of lugging our "stuff." If all goes well (which it never does), perhaps in 3 weeks. I am currently refinishing the hardwood floors now that the trades have been out. Some other misc buttoning up things have to be done as well.

    I will soon be making some posts of the interior designs as I have been focusing most exclusively on our design for performance.

  3. Hi there, your blog is fantastic!! well done. I am at the very early stages of planning for a passive house and was wondering after reading this blog, we live in an area of very low humidity (our current house has about 25%). So if you live in an area with very low humidity will it take as long for a house to dry out? The second question is a bit of a beast but if were at the start of the process what are the main pitfalls to avoid?

    Keep up the great work on the blog.

  4. Thanks Paul for your kind words!

    It's really tough to answer your first question as there are so many variables. Sounds like you are in AZ. But, I suspect if we can get our humidity down in about a year under conditioned interior, I suspect you should be able to accomplish that in a similar amount of time.

    Pitfalls. Another tough question. I suspect selecting the proper trades and/or foreman to run the job (assuming you are not personally). Attention to air tightness, I would proffer, is one of the very most challenging design elements of a passivhaus. If your trades are attentive to detail with respect to air-sealing, it's going to be much much harder (and more expensive) to remedy the situation after the fact.

    Also, give some serious thought to your ventilation system's design and distribution system (ie: "ducting).

    And it may sound obvious, but always keep in mind that the home is where you live. Make it liveable. What I mean by that is don't get so focused on design elements to maximize energy efficiency that you seriously sacrifice the aesthetic nature of your home.

    Make you window and door selection carefully. Look at air-tightness performance specs not just thermal performance. If you are going for PH certification, make sure the fenestration mfr can provide the thermal values needed for PHPP. Stay away from double hungs and french doors (to the exterior). Casements and/or tilt-and-turns are where you need to be. Select your windows properly with respect to reasonable SHGC values (I am assuming you live in a hot climate). If it is generally hot and sunny, you should consider low low SHGC values and bag the thermal gain trick that we in the Northeast use to heat during the cold months.

    That's all I can think of at the moment. Keep us posted on your progress!



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