Ventilation is the most underrated system in any building. Get it right and occupants stay alert, healthy and comfortable while energy bills stay low. Get it wrong and you get stuffy rooms, condensation, mould, sick-building complaints — or an HVAC plant burning electricity around the clock to fix a problem that a well-placed window could have solved for free. This guide compares natural ventilation and mechanical ventilation in buildings in depth: the physics that drives each, what ASHRAE Standard 62.1 requires, energy implications, HRV and ERV heat recovery, hybrid mixed-mode design, and how CFD is used to prove a design works before it is built. Figure 1. Two ways to deliver fresh air. Natural ventilation uses wind pressure and buoyancy through openings; mechanical ventilation uses fans, ducts and filters to deliver a controlled airflow regardless of weather. Table of Contents Why Ventilation Matters Natural Ventilation: How It Works Types of Nat...
You can build a beautiful mesh, choose a respected turbulence model, run for three days on a cluster — and still get drag wrong by 30%. Very often the culprit is a single number that beginners overlook and experts obsess over: y⁺ . It decides whether your turbulence model is even being used correctly, and it is set before you ever press "solve". This guide covers the full theory of y⁺, gives you a free first-cell-height calculator (validated against published data), and shows exactly how to choose, achieve, and verify the right value for your simulation. Figure 1. The turbulent boundary layer is not uniform. y⁺ tells you which of these zones your first cell centre lands in — and that determines which near-wall model is valid. Table of Contents The y⁺ / First Cell Height Calculator What Is y⁺? (Theory) Structure of the Boundary Layer Why y⁺ Matters So Much The Formula, Step by Step Target y⁺ for Each Turbulence Model The ...