Net Zero Feasibility Study
This exercise takes you through three key environmental analysis steps that accompany the beginning of any net zero building project: (A) Analyze the local climate, (B) quantify on-site renewable generation potential and (C) benchmark your building’s target energy use against that of existing buildings of comparable size and location. The exercise helps you to discover climatic challenges and opportunities and gain a first understanding of whether onsite net zero energy use seems realistic for your project.
Task A Climate Analysis
Go through the project brief (see Multi Unit Residential and Medium office/startup examples) and conduct an analysis of your local microclimate. The purpose of this exercise is to identify up to three climate-specific aspects that you may want to exploit in your building’s environmental concept going forward such as seasonal access to wind, sunny winter days or high diurnal temperature swings. Complement your analysis with a direct shading study of your site and provide an initial massing for your building. A “massing” is a simplified representation of the envelope of a building that should have the floor area specified in the project brief (see Figure 1). Note that for multi-story buildings the floor area is different form the building footprint, i.e. the area of the building that touches the ground. Do not worry that you “lock yourself in” any massing design. The proposed massing should just give you a sense of scale, i.e. how much space will the building take up on the site? How much exposed roof and façade area is available for photovoltaics (Task B)?
For the shading analysis, you need to a neighborhood massing model in Rhino that includes the boundaries of your site as well as key neighboring buildings and landscape that seasonally overshadow your site. Neighborhood massing models may be available from the local municipality, e.g. the Boston Planning & Development Agency, or you can build a model form scratch using GIS shapefiles and/or a combination of Google maps and Street View to determine the heights of nearby objects. Another good resource is CADMapper.
Figure 1: Example massing study
Task B Onsite PV Potential
To estimate how much electricity you can generate on your site using Photovoltaics, go through the following two steps.
B.1 PV system placement and preliminary electricity yield calculation
Add solar panels to your massing proposal. Individual panels should be 1.0m x 1.5m in size and may be placed on the rooftop, integrated in the façade and/or double-function as shading systems for a walkway or parking. Once the panels have been placed, add them as analysis surfaces to ClimateStudio and run a solar radiation analysis as shows in this video tutorial. Do not forget to assign material properties to all objects in the scene and make sure that the panels are all oriented correctly, i.e. facing the sun/sky. (Tip: The Rhino command “dir” allows you to visualize the orientation of one or multiple surfaces. The command “flip” adjusts the orientation, if necessary.) Feel free to adjust the panel location and/or orientation based on the solar radiation analysis.
B.2 PV yield
Estimate the annual electricity yield of your PV system assuming a panel efficiency of 18% and an inverter efficiency of 96%. An example solution for the PV system in Figure 2 is shown below.
Figure 2: Radiation map analysis for 500 solar panels
Example Solution
The annual electricity us of the 500 solar panels in Figure 2 is:
500 x 1.5m2 x 1699kWh/m2 x 0.18 x 0.96 = 220,190kWh
Task C Energy Benchmarking using the Building Performance Database
Use the US Department of Energy’s Building Performance Database (BPD) to create a histogram of site energy use intensities (EUI) of comparable buildings constructed between 2000 and 2020. Calculate the electricity yield per floor area that the PV system designed under Task B will provide and add it to the histogram. Pay attention to units as you convert from SI (kWh/m2) to imperial (kBtu.sq2) units. You can switch to imperial units in ClimateStudio using the “CSSettings” command. An example is shown in Figure 3.
Example Solution
The electricity yield of the PV system is 220,190kWh. Assuming a floor area of 5000m2, the PV system can support an EUI up to 220,190kWH/5000m2 = 44kWh/m2. The histogram in Figure 3 is in units of kBTU/ft2 and so PV = 44 x 0.317 kBTU/ft2 = 14kBTU/ft2
Figure 3: Histogram of EUIs of office buildings in Climate Zone 5A built between 2000 and 2021
The analysis shows that an net zero concept using on-site PV for a 5000m2 office building in ASHRAE Climate Zone 5A (for Boston) is technically feasible but requires the site EUI of the building to be in the 92nd percentile (top 6 out of 74) of comparable buildings in the BPD. If your team aims for a net zero building, you may decide to go back and forth between Task B and C and increase your PV system size. The results from this assignment are preliminary but offer a solid estimate of required energy savings and PV system size.
Optional Task: Detailed hourly PV system yield using ClimateStudio | Grasshopper | EnergyPlus
This part of the assignment is optional. Once you are satisfied with your PV system from B.2, you can model monthly or hourly electricity gains using use the Grasshopper definition Radiation Map and PV | Urban Context – PV Simulation as shown under the ClimateStudioDocs and in Figure 4, update the Input Geometry and report results in a figure similarly to Figure 5. Use the more accurate electricity yield going forward.
Related Video Tutorial/Handbook Chapter
SDL tutorial Sizing a PV System
Daylighting Handbook II Chapter 9; Climate Driven Design Chapter 2
Figure 4: Use the CS Template component to load the “PV Simulation” definition
Figure 5 Monthly electricity yield of a PV system based on ClimateStudio| EnergyPlus