2018 ASHRAE LowDown Showdown
AEI participated in the 2018 ASHRAE LowDown Showdown modeling competition with our architectural partners at Lord, Aeck, Sargent. Held in conjunction with the 2018 Building Performance Analysis Conference and SimBuild, the ASHRAE LowDown Showdown modeling competition showcased the work of eight teams who focused on adopting new techniques and workflows to advance modeling and simulation to meet the growing challenges faced by today’s designers and modelers.
Our team’s mission was to design and model a net-zero or near net-zero building. The model building was a 60,000 sq ft museum (new construction) located in Denver, Colorado, that included retail space and a full-service restaurant. Teams were evaluated in six categories: energy use, teamwork, innovative approach, creativity, workflow, and presentation.
Our team’s approach was to reduce heat gain and loss through the building’s envelope as much as possible since the internal loads were fixed for the competition. The building was modeled using the EnergyPlus simulation engine. Denver’s predominant climate is cool and dry, with HDD65 of 6,020 and CDD 50 of 2,732. Tight temperature and humidity tolerances within the museum space, as well as the dry and heating-dominant climate, were the primary challenges to overcome to achieve a net-zero building.
The architectural response accommodated the program in a way that used passive measures first, followed by energy efficiency and ultimately onsite renewable energy. In fact, the entire approach to energy design on the project was based on the site’s solar budget of 25 kBtu/sf/yr provided by a 10,000 square foot photovoltaic array. While the median/average of existing building stock performed at an EUI of 86 kBtu/sf/yr, an ASHRAE 90.-2013 prescriptive baseline performed at an EUI of 61 kBtu/sf/yr. The project’s design EUI was 10 kBtu/sf/yr before on-site PV generation. Passive measures included: orientation with longer faces toward the south and north; windows to south only; passive solar gain with thermal mass; stepped below-grade walls minimizing conduction losses; clerestories for museum daylighting; and, external shading devices. Daylighting analysis was performed to ensure sufficient amounts of daylight was available while reducing glare.
Once the building’s mass had been optimized, active strategies were incorporated. The predominant energy load was due to heating and humidification of the required ventilation. Efforts were focused on reducing this energy by utilizing high efficiency total enthalpy wheels to pre-condition the ventilation air. Then, atomizing humidification was incorporated to be able to humidify by “fogging” the air vs. the traditional method of creating steam. Further efforts to reduce energy as well as increase occupant comfort included radiant heating/cooling slab with a DOAS unit to condition ventilation air. A 6-pipe geo-exchange modular heat pump system, consisting of an 8x8 array of 250’ vertical boreholes, maximized heating and cooling efficiency. The 6-pipe system allowed flexibility since the modular heat pumps incorporated a virtual end cap, essentially right-sizing the amount of heating or cooling at any time. In addition, the system was used to heat domestic hot water.
With the aforementioned strategies, the model design EUI was 12 kBtu/sf/yr. One final strategy implemented was a rooftop mounted transpiring solar collector to preheat outside air. Utilizing the technology reduced the final design EUI to 10 kBtu/sf/yr, well below the 25 kBtu/sf/yr solar energy budget.
From the field of fourteen teams that initially entered the competition, eight submitted final designs. Our team advanced from the first round of judging as the field was narrowed to five. Conference attendees then voted electronically for the fan favorite. The results were announced at a reception held Thursday, September 27, 2018. Although we did not win the top prize, the experience only served to enhance and validate our consulting capabilities amongst our peers.