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Energy Estimation
This page provides a detailed reference for the Energy Estimation tool, including its inputs, outputs, and calculation methods.
Purpose
The Energy Estimation tool calculates the annual energy consumption of a building based on its geometry, climate data, and construction specifications. It is designed for early-stage design when detailed engineering models are not yet available.
Geometry inputs are derived automatically from the active massing.
Inputs
Building Geometry
| Input | Unit | Description |
|---|---|---|
| Facade areas by orientation band | m² | Facade areas grouped into eight direction bands: N, NE, E, SE, S, SW, W, NW. Each band includes facades with maximum deviation of 22.5° from that direction. |
| Roof areas | m² | Sum of all roof areas derived from the massing. |
| Floor areas / GBA | m² | Sum of all floor areas derived from the massing. Gross Building Area (GBA) is derived from the same floor-area total across all storeys. |
These building-geometry inputs are not entered manually in the tool.
Climate Data
| Input | Unit | Description |
|---|---|---|
| EPW file | — | EnergyPlus Weather file containing hourly weather data. |
| Outdoor temperature | °C | Hourly dry-bulb temperature. |
| Solar radiation | Wh/m² | Hourly global, direct, and diffuse radiation. |
Construction Specifications
| Input | Unit | Description |
|---|---|---|
| Wall U-value | W/m²K | Thermal transmittance of walls. |
| Roof U-value | W/m²K | Thermal transmittance of the roof. |
| Window U-value | W/m²K | Thermal transmittance of windows. |
| Floor U-value | W/m²K | Thermal transmittance of floors. |
| Window-to-Wall Ratio (WWR) | % | Percentage of facade area that is glazed. |
| Shading coefficient | — | Fraction of solar energy transmitted through windows. |
Occupancy and HVAC
| Input | Unit | Description |
|---|---|---|
| Occupants per m² | p/m² | Occupant density. |
| Heating setpoint | °C | Minimum indoor temperature. |
| Cooling setpoint | °C | Maximum indoor temperature. |
| Ventilation rate | L/s/p | Fresh air supply per person. |
| Heat recovery efficiency | % | Percentage of heat recovered from exhaust air. |
Outputs
| Output | Unit | Description |
|---|---|---|
| Energy Use Intensity (EUI) | kWh/m²·year | Annual energy consumption per square metre. |
| Heating energy | kWh/year | Annual energy for heating. |
| Cooling energy | kWh/year | Annual energy for cooling. |
| Lighting energy | kWh/year | Annual energy for lighting. |
| Equipment energy | kWh/year | Annual energy for equipment. |
| Fan energy | kWh/year | Annual energy for ventilation fans. |
| Domestic Hot Water (DHW) energy | kWh/year | Annual energy for hot water. |
Calculation Methods
The tool uses a simplified steady-state hourly method:
- Pre-computation: Calculate UA coefficients, internal gains, and solar gains.
- Hourly loop: Compute drift temperature, heating/cooling loads, and energy use for each hour.
- Aggregation: Sum hourly values into monthly and annual totals.
Limitations
- Assumes a single thermal zone.
- Does not model thermal mass effects.
- Simplifies infiltration and ventilation rates.
For detailed formulas, see the calculation flow.