Of three available options, the team selected a 33-story office tower built in 1980 and managed by Unico Properties located in Seattle¡¯s downtown core. The property included 6 levels of subterranean parking and an at-grade plaza fronting a bus transit corridor on Seattle¡¯s Third Avenue at the southeast corner of the site. Inspired by progressive ideas and strategies for carbon reduction, we pushed the boundaries of current zoning and building codes on District Carbon.

Below, I¡¯m sharing some of the aspects of our approach¡ªsome broad, some specific¡ªthat make District Carbon a powerful and realistic case study for reaching net zero energy performance in existing buildings.

1.?Big ideas rooted in pragmatic thinking

Our team approached the competition with big conceptual drivers¡ªreduce Energy Usage Intensity (EUI) onsite to limit energy offsets, value carbon and energy equally, and promote a walkable city. These objectives guided our team from beginning to end.

But we also designed within realistic limits. We would need to address seismic deficiencies, deal with legacy mechanical, electrical, and plumbing systems beyond their useful life, leverage viable existing equipment and shafts, maintain partial occupancy throughout construction, stay on budget, and schedule and track phased investment. We did this while designing in response to current downtown zoning for livability and transit-oriented development. The result is a realistic concept that thinks big.

2. Reuse the building, efficiently

Adaptive reuse is far more friendly to embodied carbon than new construction. Our reuse of the steel-framed, high-rise building required us to design for seismic upgrades and overcome existing conditions. We chose lighter cladding¡ªlow carbon, prefabricated panels with integrated photovoltaic film. Built offsite, these panels increase thermal performance, lower thermal bridging, and refresh the existing facade. The increased air tightness from the new envelope panels improved the performance of the proposed energy-recovery system.

3. Rebalance program to reduce energy usage intensity

We analyzed maintaining a full office program versus switching to a mixed-use program of residential and office, with the goals of optimizing the building¡¯s energy use while allowing for some continued occupancy during phased construction. In either scenario, we would maintain many existing systems, which constrained the possibilities for core and shell reuse.

Looking at the data, we arrived at a mix of 80% residential and 20% office, which allowed for synergies in the building systems, reuse of existing shafts and hitting an EUI of 19.1, a significant improvement from the 53.4 EUI for a 100% office program. The mixed-use nature of the building plays up livability. The team created a design concept that reached out to engage life on Third Avenue by adding shared amenities that make downtown living attractive and practical¡ªrecreation areas, rooftop terrace, daycare, electric vehicle charging, and bike parking.

4. Update power system for control and flexibility

The building¡¯s aging power-distribution system had become difficult for the owner to maintain. Rather than extend its life or replace in-kind, we looked for a system that could grow with the building and offer additional resilience. The concept includes a system that can plug in to future renewables, initiate demand response and manage peak energy usage, layer in smart monitoring and control systems as needed, and harness the power and resiliency of emerging smart buildings technology.

These strategies will enable the property manager to operate their building like a microgrid, adjusting energy use when appropriate.

5. Update mechanicals for efficiency

We devised an active/passive hybrid mechanical solution with a new HVAC system. The design separates ventilation air from heating and cooling, so that residential units can leverage natural ventilation during the moderate weather months and utilize a modest volume of dedicated ventilation air during the more severe weather months or when air quality is poor.

A four-pipe system delivers heating and cooling, leveraging a heat-recovery chiller, which supplies radiant panels on the office floors and fan-coil units in the residential units. The temperate climate in Seattle makes this low-energy intensity approach possible.

6. Find synergies

Throughout this competition project we looked for synergies. Within the building we looked to capitalize on the mixed-use program and found heat recovery and water cycle as the largest influencers of energy saving.

The team considered district-level ideas such as recovering heat from the public sewer line or from nearby buildings, and even sharing renewable sources with other buildings. In the end, we determined the most efficacy was found in building-centric synergies. We drove down the EUI by using heat recovery in both wastewater and return air systems, grey water production from residential units, and multiple photovoltaic installations. We were able to offset 18% of the total energy usage of the building through on-site building-integrated photovoltaics on the facade and solar panels on the roof.

7. Design for energy resiliency

Today, we take the idea of personal vehicles for granted, but in 10 years we may simply pay for rides in autonomous vehicles. In the meantime, the idea of shared electric vehicles (EV) is appealing to city dwellers. So, we proposed that the garage should provide a building-owned fleet of shared EVs available to residents and office tenants for their use, as needed. In addition to a battery energy storage system, we utilized bi-directional chargers for the EV fleet, which gives the property manager the flexibility to utilize the EV fleet as a battery storage medium (even emergency power) to enhance resiliency.

Along with onsite renewables and a smart building monitoring and controls, this approach gives the property manager more capability to control peak energy usage. It drives down building utility costs and lessens dependence on the city¡¯s power grid.

Using competition ideas in the real world

In this competition entry, the Â鶹´«Ã½ team developed building system engineering solutions that target net zero, energy resiliency, and a low carbon future for downtown high-rise buildings. While we thought big on the District Carbon, we grounded our approach in a suite of strategies that are available and applicable today.

There¡¯s no reason we can¡¯t take this low-carbon approach on building conversions today and tip the needle toward net zero for our clients and communities.