CREJ

November 2019 \ BUILDING DIALOGUE \ 23 houses (not refrigerated), offices (excluding high-rise), retail buildings and schools. • Whole-buildingenergymodelingisacrit- ical first step to achieve ZNE. Whole-building energy modeling (BEM) is a versatile, mul- tipurpose tool that is used in new building and retrofit design, code compliance, green certification, qualification for tax credits and utility incentives, and real-time building con- trol. By “energy modeling,” we mean using computer-based tools to simulate the energy useof abuilding throughout anentireyearof operation. This also is commonly referred to as annual energy use simulation or building performance simulation. We use the energy model to calculate a building’s pEUI (predicted EUI) – the only re- liableway to do so. For thiswe need to have knowledge of the building’s real-world operation (i.e., howwill it be used). Understanding how a building uses energy allows us to tar- get the areas that have the most impact to get the maximum bang for the buck. For example, not every building type will benefit from exceeding code-required envelope insulation values – one of the first things we consider when thinking “high-performance.” Thishelpsusdirect theproject’s resources wisely to the areas thatmove the needle. Steps to Approach Net Zero To achieve NZE, we suggest the following order of opera- tions: 1. Reduceenergydemandthroughaggressive loadreduction. 2. Use free energy resources and passive engineering. 3. Use themost efficient technology possible. 4. Recoverwaste energy. 5. Incorporate renewable resources/energy (on- and off-site). In our experience, success is achieved only if each step is ex- hausted beforemoving to the next step. Strategies for EUI Minimization There are many pathways to achieve a ZNE building with more becoming available as new technologies are developed, as existing technologies improve, and as renewable energy technologies rapidly advance. Here is a list of areas and strat- egies that projects pursuing ZNE will need to address and op- timize to be successful within the framework of the five steps listed above: climate analysis; building massing; window-to- wall ratio; solar controls and passive solar design; building en- velope and infiltration; user behavior, educating and engaging building occupants; daylighting and lighting; equipment, re- ceptacle schedules and loads; HVAC and service water heating systems; and renewable energy systems. Conclusion Eachprojectwill forge its ownpath to achieve ZNE.Wehave seen average projects achieve ZNE because the project was able to fund a large enough on-site solar PV array to offset all its energy use, while several high-performance and even ul- tra-low energy projects not reach ZNE status because they did not have that extra capital to fund on-site renewables or did not have the roof or the site area available. ZNEmay be a concept and a choice today but it will be base- line building energy code for new construction sooner than later in Colorado, especially with signing into law the recent House Bill 19-1261 – Climate Action Plan to Reduce Pollution. This law sets the state on a path to reduce 90% of statewide greenhouse gas emissions by 2050. With that said, there are numerous tangible and intangible benefits of ZNE buildings. Total cost of ownership is potential- ly lower. These buildings are thoughtfully designed and con- structed and are better insulated with tighter envelopes that lead to quieter, more thermally comfortable spaces and have longer lifespans with increased durability. Theymaximize the use of daylighting thus connecting the occupants to the out- side/nature. \\ It’s All About the Carbon Relationship between EUI reduction and increase in on-site renewable energy. Source: Jamy Bacchus (ME Engineers). Key Takeaways To recap, the central takeaways from the first column in the series were: 1. Atmospheric CO 2 levels are rising year after year and corre- sponding to warmer global surface temperatures. 2. The building industry is the leading cause of CO 2 emissions. 3. Merely designing to energy code compliance and green build- ing certifications such as LEED are not enough; thus, state and local governments have committed to adopting net zero building energy codes and source 100% fossil fuel-free energy. And from this column: 1. Energy codes in Colorado and especially cities along the Front Range are moving toward developing ZNE building codes. 2. Begin every project with a whole-building energy model to assess pEUI and energy by end-use (how and where the building uses energy). 3. Exhaust all measures and strategies to reduce your project’s EUI. 4. Consider renewable energy offsets: on-site plus approved off- site options.