In 2016 nine architects, engineers, building physics proffessionals and students who use EnergyPlus and OpenStudio were put together in a team to compete in the Lowdown Showdown, an annual competition held at the ASHRAE and IBPSA Energy Modelling Conference. The aim is to compete against other teams to design a net zero building using simulation to show the energy savings. The 2016 competition required the teams to model a healthcare facility in Omaha Nebraska. I was assigned team captain and our team managed to design our building to be energy positive and were voted most creative! Below is the presentation on our design.
The proposed design has a circular form with easy access to critical areas and 30% window-to-wall ratio. An efficient dedicated outdoor air system (DOAS) equipped with a desiccant heat recovery wheel and an evaporative cooler provides fresh air to all the zones. Chilled water (CW) and hot water (HW) coils were selected for the DOAS unit. Four-pipe chilled and heated beams provide zone conditioning. A few high load zones were equipped with supplemental CW fan-coil units to satisfy thermal comfort. A 200 kW PV array, and 65 kW combined heating cooling and power (CHCP) plant, fed by local bio-gas from a landfill, provide the entire building electricity demand with 26% surplus energy fed back to the grid annually.
Energy Saving Strategies:  The compact circular building form provides ample daylight while minimizing the exterior exposure.  A very tight envelope (0.1 CFM/ft2 infiltration) with R-40 roof, R-40 wall and triple pane windows (U-0.18 Btu/hr.ft2.F, SHGC-0.2, VT-0.7) combined with medium thermal mass reduces the HVAC loads.  LED lighting for the entire building and daylight sensors for all the perimeter spaces.  Thorough research was performed on internal loads and key strategies targeted elevator, medical equipment and office computer loads.  DOAS has a desiccant heat wheel and evaporative cooler to minimize heating and cooling energy.  Both DOAS and four-pipe beams’ CW/HW coils take advantage of a central water plant heat recovery with a micro-turbine and an absorption chiller.
Net Zero Design Workflow: The analysis of baseline model and climate condition made it clear that the internal loads and the cooling load associated with humidity control are the biggest energy consumers. As the first key step in design, the design team reduced the envelope loads via a large optimization run including 8 different building forms and a range of design variables containing infiltration rates, insulation values, orientation-dependent window-to-wall ratios and glazing properties. The given outpatient facility programming areas were fitted into the optimized circular shape and optimal thermal properties were used for the rest of the analysis. Extensive research was done to reduce (34% total) the internal load associated with the operation of elevators, MRI machines and office computers by employing efficient regenerative drive elevators, state-of-the-art MRI machines and virtual servers/thin clients instead of personal computers. LED lighting was used throughout the building to reduce the average LPD to 0.6 W/ft2 as compared to the baseline average of about 1.1W/ft2. Daylighting sensors in the perimeter zones complemented the already low design LPD for further lighting load reduction. Multiple variations of DOAS coils (DX, CW/HW and evaporative cooling), heat recovery strategies (Heat wheel, run-around pipes) and supply air temperature (SAT) setpoints were examined to find the optimal DOAS performance for the climatic conditions of the site. The high internal load nature of the building warranted the use of zone conditioning equipment that is capable of load sharing either on the zone or plant level. Air-cooled VRF, water-cooled VRF, chilled ceilings and four-pipe beams were chosen as zone equipment alternatives to compare. Although the air-cooled VRF system showed better performance than the four-pipe beams, the beams proved more effective in their capability to connect the CW/HW coils to a plant loop that could take advantage of higher water loop efficiencies. A local bio-gas fed micro-turbine generator combined with an absorption chiller for heat recovery proved to be a reasonable generation pathway to complete the efficiency and production cycle. The team identified a local source of landfill generated bio-gas which was used to feed a 65 kW micro-turbine generator capable of recovering 120 kW thermal energy. The optimal placement of PV panels was obtained from an optimization study to be at 35° south facing angle. The design team decided to use a south-facing sloped surface to install the PV panels to avoid self-shading loses as well as provide shading to the south windows. Our strategies outperform a net zero building by 10 kBtu/ ft2.