Second + Delaware, MO

On a project of this scale, it becomes quickly clear that integrated design is not optional. Weekly meetings of the entire design and construction team have kept us on the same page and allowed all team members to understand challenges and offer solutions. Keeping the CPHC® involved at every step of the process ensured the design didn’t diverge from target performance criteria.  

This project was started prior to PHIUS+ 2015 criteria going into effect and the preliminary passive house energy model and recommendations based on the German Passivhaus criteria. Once the project transitioned to the PHIUS+ 2015 criteria, we experienced a rather large wake-up call with respect to internal gains. Utilizing the recommended Passivhaus default modeling entries for plug loads and small appliances and the auto calculation provided for lighting, caused modeled internal gains to be understated by 214%. This skewed the simulation results to understate cooling load, site energy and primary energy and overstate annual heat demand by more than double. We came to understand that had we continued to rely solely on the German Passivhaus criteria targets for optimizing the project, we would have been led to provide performance recommendations to meet the Passivhaus annual heat demand criteria of 4.75 kBtu/sf/yr that resulted in overheating and a potentially undersized cooling system.

We came to see firsthand just how critical it is to accurately account for internal gains and to harmonize static passive house certification models and dynamic HVAC and comfort models so that inputs, and as much as possible, outputs are aligned. We learned that this alignment of energy models ensures that utility and operational cost projections are realistic and that the passive house certification model results are not just a pie-in-the-sky set of numbers.

In piloting PHIUS+ criteria and protocols on a large scale project, we started with the occupancy and diversity patterns we all agreed upon for our dynamic HVAC model and confirmed that PHIUS+ miscellaneous electric loads and lighting calculations, based on RESNET data, aligned quite well with what the realistic projections used. In comparison the PHPP recommended default entries for plug loads and small applications led us to a kWh/yr result for those end uses that was 1/5 of what we agreed was realistic. PHPP 100% high efficacy lighting (11W), amounted to only 11% of the annual lighting kWh usage we calculated using our actual lighting schedule.

Though it can certainly be said that Passive House is about certifying buildings and not people, we came to the conclusion that it is unwise to discount the impact that occupant related internal gains have on multi-family building energy balance, and that frequent checks between static and dynamic simulations ensure that the passive house model has a grounding in reality.

Dynamic thermal + hygrothermal analysis of the worst case summer unit performed with WUFI Passive®’s WUFI Plus calculation engine shed light on hourly temperature and relative humidity fluctuations, as well as surface, operative and dew point temperatures. We were able verify the amount of dehumidification required for comfort in the unit, and ideal times during the cooling season for natural ventilation. Additionally, we benefited from more accurate simulation of thermal inertia associated with the structure’s massive enclosure than is available with static passive house certification energy balance calculations or with our IES VE HVAC models.