net zero passivhaus office remodel
1619 Phillippi St. is an adaptive reuse project in Boise, ID. The project transformed a derelict auto repair shop into the regional headquarters for McCall-based EnergySeal Air Barrier Systems LLC, Idaho’s leading high-performance insulation contractor. A portion of the original building was demolished making space for a new parking area while the remaining building was renovated into a new 2,000 square foot office space. The program consists of a reception area, conference room, office space, storage garage and support spaces.
The goal of the project was to revitalize the existing structure into a modern, ultra-energy efficient building. Through a combination of an extremely high-performing building envelope with efficient mechanical equipment and a photovoltaic system, the project will be Idaho’s first certified commercial Passivhaus building as well as the first net-zero energy retrofit. Energy modeling, mechanical design, and enclosure design was provided by Energy Systems Consultants LLC.
1619 is one of the most energy-efficient buildings in North America, with a predicted energy use intensity (EUI) of 10.6 kBTU/sf/yr. This low EUI is achieved primarily through load reduction and “passive” strategies and does not account for the electricity generated by the roof mounted 4.56 kW solar PV array. This building also meets the 80% 2030 Challenge site EUI target and performs better than the most stringent 90% target when PV is accounted for. The roof mounted solar PV system will generate more electricity than the building consumes on an annual basis.
The project team achieved aggressive levels of energy efficiency by focusing on designing and executing a high- performance building enclosure which relies on super-insulation, high levels of air-tightness, and thermal bridge free design. 1619 is insulated with assemblies and components that are 3-4 times better than code minimum. As a result, the project reduces heating and cooling loads by more than 90% compared to a conventional “active” building. All structural components were carefully modeled and designed to ensure that thermal bridging was minimized and accounted for in the energy modeling. The high-performance wall and roof systems utilized 5 tons of ultra-low embodied energy plant based cellulose insulation composed of 85% paper fiber. 1619 was selected as a pilot project for a newly developed fourth generation polyurethane foam utilizing an ultra-low global warming potential (GWP) blowing agent that has 99.9% lower equivalent life-cycle carbon emissions than previous generation foams utilizing HFC blowing agents.
The high-performance R-8 windows utilize R-11 triple-pane glass with low conductivity frames. Each winter the windows will received more solar gain than they lose and are net-positive from an energy perspective. Motorized external venetian window blinds control solar gain and glare to minimize the cooling load and maximize indoor environmental quality for occupants year-round.
The HVAC System at 1619 is one of the simplest components of the project. The ultra-low heating and cooling loads are easily satisfied with two ductless wall mounted mini-split heat pumps. The space is ventilated using a 92% efficient heat recovery ventilator (HRV), controlled by an indoor environmental sensor that modulates the ventilation rate based on real time occupancy and indoor air quality. The HRV also is able to function as an economizer to take advantage of night flushing while bypassing the heat recovery core. Before fresh outdoor air passes through the high efficiency HRV, it is pre- conditioned by a closed loop earth-to-air heat exchanger. This simple system consists of a small pump that pumps glycol through a 600’ ground loop (installed in existing utility trenches already needed for construction). This fluid then passes through a small heat exchanger that pre-cool incoming ventilation air in the summer and pre-warms it from the earths energy in the winter.
This project achieved an ultra-low lighting power density of 0.25 W/SF utilizing high efficacy led lighting. Lighting energy is further reduced occupancy sensors and auto-dimming daylighting controls. Plug loads, lighting, and mechanical systems are monitored with a circuit level energy monitoring system. In addition to comprehensive building enclosure testing and mechanical commissioning, all systems will be monitored for continued performance during occupancy to ensure optimal energy performance and indoor environmental quality.
Ultimately the owner and designers of this project hope other building owners and developers can build upon the success and lessons of 1619. By committing to an aggressive energy target early in the planning stages, even a challenging retrofit project can result in an ultra-low energy building that is capable of cost-effectively reaching net-zero without overly complex and expensive mechanical and renewable energy systems. The ‘passive’ building enclosure focused approach not only results in extreme reductions in carbon emissions and operating costs, but also drastically improves durability, comfort, and resilience.