Overview
This lecture explains the concepts of site energy and source energy, their roles in zero energy building calculations, and presents examples of their application.
Zero Energy Building Definition
- A zero energy building is energy efficient and its delivered annual source energy is less than or equal to its on-site renewable exported energy.
- Defining the building boundary and measuring energy flows are crucial when calculating zero energy balance.
Site Energy vs. Source Energy
- Site energy refers to the energy consumed at the building site, measured at the utility meter.
- Source energy includes site energy plus the energy used in extracting, processing, transporting, and delivering the fuel, including losses in generation and transmission.
Energy Losses and Conversion Factors
- Significant energy is lost in converting fuels to usable electricity; average electric generation is just over 35% efficient.
- Conversion factors (multipliers) are used to change site energy values into source energy values, differing by fuel type.
- For natural gas, the site-to-source conversion factor is about 1.09 due to extraction and transport losses.
- For electricity, the conversion factor is typically 3.15 due to generation and transmission losses.
- For chilled water, the conversion factor is about 1.04.
Zero Energy Balance Calculation Examples
- To determine zero energy status, multiply each delivered energy amount by its source factor and subtract exported renewable energy (also multiplied).
- If the resulting balance is zero or negative, the building qualifies as zero energy.
Building Energy Types in Calculations
- When multiple energy types are delivered (electricity, natural gas, chilled water), apply each energy’s specific conversion factor in the balance formula.
Power Plant Quiz Answer
- The power plant shown likely uses coal, as indicated by smoke stacks for flue gases and cooling towers for water vapor.
Key Terms & Definitions
- Zero energy building — Building whose delivered source energy does not exceed exported on-site renewables.
- Site energy — Energy measured at the building site; metered utility input.
- Source energy — Total energy used, including site energy plus all upstream losses and conversion inefficiencies.
- Conversion factor (multiplier) — Ratio used to convert site energy to source energy for each fuel type.
Action Items / Next Steps
- Review resource page for further reading on building science and zero energy calculations.
- Practice zero energy balance calculations using provided source conversion factors.
- Reflect on the difference between site and source energy for future design work.