Amogh N P
✦ In loving memory of Amogh N P — Architect · Designer · Visionary ✦
A laptop on a desk showing a building-energy simulation interface with a 3D model and weather-data charts, beside a notebook, the start of a performance analysis.
Unit IBuilding Performance Analysis

Performance & Data Files

The weather file that drives every simulation.

≈ 45 min + studio task

A simulation is only as good as the weather you feed it. Learn how performance analysis grows from a BIM model; the weather data files every simulation needs — the EPW file, the Typical Meteorological Year (TMY) it is built from, and IMD data for Indian sites; and the pipeline from a model plus a weather file, through an analysis engine, to a result. Get the weather file right, and everything downstream becomes possible.

Learning objectives

By the end of this lesson, you will be able to — mapped to the course outcomes for Building Performance Analysis:

1
CO1 · Understand

Explain building performance analysis and how it grows from a BIM model.

2
CO1 · Understand

Describe the EPW, TMY and IMD weather data files.

3
CO1 · Apply

Trace the simulation pipeline from model and weather file to result.

4
CO1 · Analyse

Explain why the weather file is the foundation of every simulation.

EPW, TMY, IMD

Analysis & the weather file

Performance analysis simulates a design's behaviour and grows from a BIM model; every simulation begins with a weather file (EPW), built from a Typical Meteorological Year — and the file must match the site's climate.[1, 2]

The weather file drives everything years of recordsdecades of weather IMD data (India)+ international TMY TMYa 'typical' year EPW file8,760 hours · one site The EPW holds a full year of hourly temperature, humidity, sun and wind for the site. 'Any weather file will do' is a myth — a Chennai design on a Delhi file gives confident, useless numbers.
DiagramWeather data files — the EPW file of 8760 hours, built from a typical meteorological year, and IMD data for Indian sites

Simulate, don't guess

BUILDING PERFORMANCE ANALYSIS asks how a design will actually behave — its daylight, energy, comfort and airflow — by SIMULATING it before it is built, rather than guessing. It grows naturally out of a BUILDING INFORMATION MODEL: the geometry, orientation, materials and openings already in the model become the inputs to an analysis, so the same model can be OPTIMISED and its performance VISUALISED. MISCONCEPTION→correct: 'simulation is for engineers, after design' — early simulation is for the ARCHITECT, because the cheap, high-impact decisions (form, orientation, glazing) are made early.[1]

From the model to the analysis BIM model geometry · orientation materials · openings ANALYSIS daylight · energy comfort · airflow the same model, optimised & visualised The geometry already in the model becomes the input to the analysis. 'Simulation is for engineers, after design' is a myth — early simulation is the architect's tool.
DiagramA BIM model's geometry, orientation and materials become the inputs to a performance analysis
Model + weather → result

The simulation pipeline

Every analysis follows the same pipeline — model + weather + assumptions → engine → results → design change; the engine is rigorous, but the inputs are where error enters.[1, 3]

The simulation pipeline model weather assumptions ENGINEsolves the physics results design change The engine is rigorous; the INPUTS are where error enters and where the judgment lives. Garbage in, garbage out — a precise result can still be wrong. Precision is not accuracy.
DiagramThe simulation pipeline — model and weather and assumptions into an engine, out to results and a design change

Model + weather → result

Every analysis follows the same PIPELINE: a MODEL (geometry, materials, openings, often from BIM) + a WEATHER FILE + assumptions (schedules, loads, system) → an ANALYSIS ENGINE (which solves the physics) → RESULTS (illuminance, energy use, airflow) → interpretation and a design change. Understanding the pipeline tells you where error enters — a wrong weather file, a careless material, an unrealistic schedule — and where the leverage is. The engine is reliable; the inputs are where judgment lives.[1, 3]

The foundation

At a glance

AspectDetailNote
ApproachGuess the performanceSimulate it (analysis)
Weather fileEPW (8,760 hours)Built from a TMY
Indian dataIMD + international TMYMatch the site's climate
PipelineModel + weather → engine→ results → design change
ReliabilityEngine: rigorousInputs: where error enters
Vocabulary

Key terms

Building performance analysis

Simulating a design's daylight, energy, comfort and airflow before it is built.

EPW file

EnergyPlus Weather — 8,760 hours of climate data for one location.

TMY

Typical Meteorological Year — a synthetic 'typical' year from many years of records.

IMD

India Meteorological Department — the source of Indian weather data.

Simulation pipeline

Model + weather + assumptions → engine → results → design change.

Garbage in, garbage out

An engine computes precise nonsense from bad inputs — precision ≠ accuracy.

Apply it

Studio task

Find the EPW weather file for your city (or the nearest one) and note what it contains and where the data comes from. Then sketch the simulation pipeline for a daylight study of a classroom, labelling each input — and write one sentence on what would go wrong if you used a weather file from a different climate zone.

Check your understanding

Self-assessment

1. An EPW weather file contains —

2. A Typical Meteorological Year (TMY) is —

3. 'Garbage in, garbage out' in simulation means —

In a nutshell

Recap

Performance analysis simulates a design's behaviour before it is built — and grows naturally from a BIM model.
Every simulation begins with a weather file (EPW), usually built from a Typical Meteorological Year (TMY).
Indian weather data comes from the IMD and international TMY datasets — the file must match the site's climate.
The pipeline is model + weather + assumptions → engine → results → design change; the inputs are where error enters.
Garbage in, garbage out — a precise simulation result is only as accurate as its inputs and its validation.
The evidence

References & further reading

  1. [1]Autodesk / building-performance-analysis guides — BPA from BIM, design optimisation and visualisation.
  2. [2]EnergyPlus weather-data documentation + the EPW/TMY format; IMD / ISHRAE Indian weather data.
  3. [3]ASHRAE / IBPSA building-simulation guidance — the simulation workflow and input reliability.

Further reading

  • Hensen & Lamberts (eds.) — Building Performance Simulation for Design and Operation.
  • EnergyPlus Documentation — Auxiliary Programs / Weather (EPW).
  • Autodesk — Building Performance Analysis material.

Sources gathered and fact-checked June 2026. Published values vary by source, sample and method — treat as indicative and confirm against the cited standard before structural use.