Measured vs. Modeled Performance of a Senior Living Passive Building

James Ortega, PHIUS’ project certification manager and a licensed architect, presented this week at the Passive House Accelerator’s Happy Hour, talking about measured versus modeled performance, and how to understand and explain gaps between the two. Ortega reviews all projects, conducts feasibility studies, and consults on dynamic energy modeling. He is also a member of the tech committee that shapes PHIUS+ standards. Ortega dug into the details of performance comparisons using the example of Gilford Village Knolls 2, a two-story, 26-unit senior living facility where two dwelling units were monitored for more than a year. He had access to granular data on the energy usage of all of the various appliances involved, including energy recovery ventilators, ductless split heat pumps, electric tank water heaters, as well as the unit’s refrigerator, range, lights, and other miscellaneous electricity usage. This recorded data was then compared to the predicted energy modeling to see how close the two were. 

Overall, the modelled and actual uses were quite close, particularly for the first unit, which had a predicted total yearly average energy usage that was 99% accurate as compared to the actual measured data. The second unit was further off, but still was within 10% of its energy model. Indoor air quality was also measured, with relative humidity, CO2, and volatile organic compounds (VOCs) being the three elements involved. These factors also proved to be accurately predicted, as their original estimates were not far off. The electric hot water tanks brought the first surprise. The amount of hot water used was significantly lower than predicted, leading to a need for “energy sleuthing” in order to determine the reasons behind the model being so off the mark. It turned out that the modeled indoor temperature setpoints were much higher than the average monitored temperature was. Ventilation was another aspect where the modeling was inaccurate, although looking at that in detail seemed to bring more questions than answers. As Ortega concluded in his presentation, “You can’t predict everything, and just have to do your best.”

Get the chat transcript here.


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