In mid-October 2010, the Alliance gathered a group of over 50 experts—leaders in the Denver-area green building industry and representatives from local architecture and engineering firms—at the Tattered Cover bookstore adjacent to the Alliance Center for a design charrette. The goal was to tap the combined expertise of these professionals to develop a “kit of parts”—a set of flexible design strategies and process solutions—for retrofitting existing buildings toward a net-zero energy balance, with a particular focus on the Alliance Center. Unlike typical design charrettes, which usually take place later in the design process, this event was staged prior to the selection of a specific design/build team, with the goal of stimulating a cloud of potential solutions in an atmosphere of brainstorming collaboration.
The charrette took place over two days, with the first day focused on orientating the participants to the Alliance Center, touring the building, presenting the pre-design information already gathered and creating “process maps”—timelines for placing different strategies along the life of the project. Following these presentations, participants broke into groups covering the major systems and design elements of the building, including space planning, the building envelope, tenant behavior, water, lighting and HVAC. On the second day of the charrette, each group presented the findings of their brainstorming and timeline exercises. Some highlights:
- Space planning—A more open floor plan and possibly a more communal work environment could improve daylighting and ventilation for building occupants. This may also reinforce the Alliance’s mission of facilitating collaboration.
- Envelope—Group participants concluded that improvement of the building’s envelope should begin with careful assessment, including analysis of the brick shell for porosity and moisture migration, a blower door test to check for leakiness, and a structural analysis to determine if the building is strong enough for additions or changes to roof structures. It was noted that the property’s status as part of the LoDo Historic District may restrict what might be done to the envelope.
- Occupant behavior—This was thought to be an opportunity-rich area for improving the building’s energy efficiency. The Alliance Center, housing about 130 people, already enjoys higher occupancy than average for the area, but the fire code might technically allow a tripling of the number of tenants. This might make a focus on an alternative metric—thousand Btu per occupant (kBtu/occupant), rather than kBtu/square foot—valuable as a measure of energy efficiency.
- Lighting—Recommendations included eliminating unused fixtures and moving to more efficient designs in the existing fixtures, but a more holistic approach was also proposed to achieve the energy savings needed for a near-net-zero outcome (at the time of the charrette, net zero was still the nominal goal). It was generally agreed that shifting away from the traditional 2X4, 3-lamp fluorescent fixtures would reduce load and, when coupled with an emphasis on task lighting, could provide meaningful savings. Cutting-edge technologies like light-emitting diode (LED) lamps as well as solar tubes would also benefit the project.
- Water conservation—In a net-zero future the energy to purify, deliver and heat water will be an important design consideration, and improvements in grey water re-use, composting toilets and on-site black water treatment may prove necessary. These improvements will require changes in policies and building codes.
- HVAC system—A full system replacement is crucial for achieving anything close to net zero. Although complex systems such as block-wide geothermal, cogeneration, biomass gasification and sewer pipe heating/cooling were discussed, more traditional and proven technologies seemed more practical from an investment perspective. These include natural ventilation and evaporative cooling, which may be able to handle a large percentage of the HVAC load.
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