Trial / Demo
Congratulations to Zero Envy, who were the winners of VE User of the Year for the North America region. Zero Envy’s submission stood out for their deep understanding of decarbonization, including a comprehensive decarbonization roadmap that covered ASHRAE Guideline 14 Calibration and Trim & Respond control. The custom scripting and central plant heat recovery analysis was exceptional.
CalPERS “Lincoln Plaza North” is an existing government office building in Sacramento, California. Zero Envy, an award-winning engineering team with international experience in Passivhaus construction, was hired as part of a team to develop a decarbonization strategy to reach net zero carbon emissions (scope 1 and 2) by 2035. This included an ASHRAE Level II Energy Audit, a Digital Twin calibrated energy model of the existing building and decarbonization analysis.
Digital Twin Calibrated Energy Model
Zero Envy developed a Digital Twin energy model and calibrated it to match actual building energy use over a year in order to provide meaningful decarbonization strategies. They conducted a rigorous ASHRAE Level II energy audit to gather key inputs for the energy model, including a site visit, existing design document/specs review, and energy usage analysis. They also performed an in-depth analysis of Building Management System (BMS) trend data to accurately model the building system controls.
Figure 1: Building aerial photographs and Energy Model Geometry
The mechanical system primarily consists of a variable volume primary air system and several smaller Air Handling Units (AHU’s) serving dedicated spaces. Constant volume fan terminal units, Variable Air Volume (VAV) terminals, fan-powered mixing boxes, and a combination of those are located on each floor to provide cooling and heating options.
Figure 2: Energy Model HVAC Systems
The energy model was calibrated to match monthly electricity and natural gas data with utility bills, following ASHRAE Guideline 14 using CVRMSE (Coefficient of the Variation of the Root Mean Square Error) and NMBE (Normalized Mean Bias Error) metrics. The calculated CVRMSE values were 3.1% for electricity and 12.3% for natural gas, and the NMBE values were 2.1% and 1.5%, respectively - both within required limits.
Figure 3: Comparison of calibrated results and actual building energy usage
Decarbonization Analysis
The calibrated model was used to evaluate decarbonization and energy conservation measures. In total, 15 measures were analyzed and eight were included in the recommended strategy. The measures covered lighting systems, HVAC systems, domestic hot water systems and miscellaneous loads such as the kitchen equipment. A few examples of the recommended strategies are described below:
Supply fan static pressure reset optimization: As part of the calibration exercise, accurate fan curves were implemented in the energy model based on Building Automation System (BAS) trend data. By applying regression analysis, Zero Envy established the correlation between fan flow and power, enabling them to explore fan static pressure reset control by implementing more efficient fan curves in ApacheHVAC. The images below illustrate the fan curve fitting process and the updated performance curve, which reflects the impact of static pressure reset control. Based on the results, a “Trim & Respond” reset control strategy was recommended to the client.
Figure 4: Fan curve comparison and curve fitting
Reduce supply fan minimum turndown: This measure reduces the minimum turndown from 30% (100,000 CFM based on 400,000 CFM at full flow) down to 10% (40,000 CFM) to allow greater fan energy savings – especially since fan affinity laws exponentially increase savings at low flow conditions. Two actionable solutions were recommended: installing backdraft dampers to supply fans or replacing the fan entirely, allowing for more tailored selections.
Plant analysis/gas boiler replacement: Zero Envy conducted a detailed plant analysis such as chiller staging optimization and heat recovery potential analysis. One key recommendation towards decarbonization was replacing the hot water plant with large-scale air-source heat pumps to supply heating hot water to the building. The highlight of this analysis was the utilization of the Python script using IESVE’s Python API, which analyzed central plant heat recovery potential. It extracts hourly results from VistaPro, conducting a thorough analysis and generating a comprehensive report that summarises the project's feasibility for utilizing heat recovery chillers. Below are several examples of the generated plots for enhanced data visualization:
Figure 5: Central plant and heat recovery potential analysis using Python
Excellent results
The graph below illustrates a clear roadmap to achieve the project's carbon-neutral goal by 2035, year by year, highlighting the eight measures and their respective implementation timelines:
Figure 6: Path to net carbon
In Summary
Zero Envy played a key role in formulating a robust decarbonization strategy aimed at achieving net zero carbon emissions by 2035. Leveraging the capabilities of IESVE software, including ModelIT, ApacheHVAC and the VEScripts Python API, the team developed eight targeted solutions, which collectively provided a well-defined roadmap for the project to successfully meet its ambitious carbon-neutral goals.
"Zero Envy's strategic approach and IESVE’s advanced capabilities enabled a clear and achievable pathway to meet ambitious 2035 net zero carbon targets. The eight solutions provided a robust framework for Lincoln Plaza North’s decarbonization journey."
Yiyu Chen, Zero Envy
