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:

• Powerhouse Dynamics (eMonitor)
• The energy detective TED
• Faronics Powersave

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.