– Jordan Frazin, PHIUS Certification Staff
Passive building strategies have become increasingly common throughout the green building community and there is an ever-expanding network of Passive House Institute US (PHIUS) certified builders, CPHC®s, raters, and verifiers throughout the country. Thanks to these professionals, PHIUS has a catalog of over 250 certified and pre-certified projects and hundreds more that have been submitted.
Many of these certified projects have been fully occupied for months or even years, and we now have the opportunity to dive into monitored data collection and analysis.
By gathering actual performance data – in the form of utility bills – we can improve our modeling protocols, and refine the practices used by all parties involved in the certified project, including component manufacturers. We also hope to gain insight into the intricacies of climate specific design and its financial implications for the passive building owner.
With the support and guidance of the Industry Advisory Council, this past summer, we began this data collection and analysis process in earnest. (Thanks to the project teams who’ve already volunteered to participate!) We are always seeking additional utility data—if you are willing to share your project’s utility data with us, please send a message to email@example.com to state your interest. We will reply with your next steps.
We’re excited to report that we’ve already processed some utility data and begun to analyze project performance with regard to predicted versus actual site energy use. Here’s a summary of the process, and preliminary findings:
The data analysis process began by gleaning the appropriate data from the project’s energy model and then by organizing it in spreadsheet format to account for all categories. This was broken into space conditioning, hot water, auxiliary energy, lighting, appliances, and miscellaneous loads. (see Figure 1 below).
Once we determined the estimated monthly energy use for the building from the certified energy model, we then compared these predictions with the actual utility data provided by the CPHC or project owner (see Figure 2 below).
Due to the nature of the utility data billing period (often not beginning on January 1st), it sometimes became necessary to cobble a year’s worth of data together using months from adjacent years. In the cases where this occurs below, it will be noted in the chart title.
Project 1 – Single family home
This project, a single-family home located in ASHRAE climate zone 4A, was certified under the PHIUS+ standard prior to the release of the PHIUS+ 2015 standard. It houses four occupants. The ‘modeled’ monthly estimates shown below follow PHIUS+ 2015 modeling protocols.
As seen above in figures 3 and 4, PHIUS modeling protocol slightly underestimated the actual site energy performance of this project. Specifically, it appears as though we have overestimated July loads in both cases, and slightly underestimated most other months. However, overall, the estimates still track the actual usage quite well month by month and are only off by ~10% on average.
Project 2 – Single family home
This project, a single-family home located in ASHRAE climate zone 5, was certified under the PHIUS+ standard prior to the release of the PHIUS+ 2015 standard. It houses two occupants. The ‘modeled’ monthly estimates shown below follow PHIUS+ 2015 modeling protocols.
We were very pleased with the results of this case, as it was by far our most accurate. However, we were soon informed of the occupants’ varied heating set-point preference of 65°F as opposed to the 68°F set-point embedded within our protocol. So, out of curiosity, we analyzed another energy model with the heating set-point at 65°F. The results of this exploration are shown below.
Despite the project operating at a lower heating set-point, our models still predicted site energy use with ~ 88% accuracy, with especially close predictions during the non-heating months of the year. As expected, these results shifted due to a predicted lower space heating energy use during the winter.
Project 3 – Single family home
This project, a single-family home located in ASHRAE climate zone 4C, was certified under the PHIUS+ standard prior to the release of the PHIUS+ 2015 standard. It houses four occupants. The ‘modeled’ monthly estimates shown below follow PHIUS+ 2015 modeling protocols.
In the case of project three, PHIUS modeling protocol significantly overestimated site energy use during the non-heating period . Heating months, however, were estimated with greater accuracy. Of the three projects analyzed, this was the only project with energy consumption far lower than we predicted.
We were initially stumped by this comparison, until our suspicion of unique occupant behavior was verified during this past October’s North American Passive House Conference in Seattle, Washington. Upon seeing these results during a presentation, an audience member (and friend of the home’s occupants) confirmed the occupants have extremely energy-conscious living habits.
Based upon these comparisons, the PHIUS modeling protocol appears to predict annual site energy within roughly 10% – a promising statistic moving forward. In some cases though, unique occupant behavior impacts actual performance of passive house projects in ways we cannot predict.
By continuing to analyze monitored data, we hope to increase our total sample size to the point of discovering climate-specific trends. Additionally, we believe that increased availability of monitored performance data will become a useful technical and marketing resource for passive building professionals, and lead to improved practices in the coming months and years. And lastly, this data can validate the level of savings you can achieve through PHIUS+ certification and provide a foundation of assurance that incentive programs can rely on.