About Physics of Buildings

Physics of Buildings explains how the systems inside homes and commercial buildings work, through their physics: pumps, tanks, coils, ducts, windows and walls. It is written for two readers at once: the homeowner with a problem, and the technician, apprentice, student or engineer who wants the mechanism and the numbers.

This interactive psychrometric chart, its calculator and its essay on dew point and condensation are made by an AI-assisted production system: an AI agent researched the sources, wrote the text and built the chart, the calculator and the figures, and a separate verification step checks every claim and every equation against the cited sources before the page is published. There are no ads and no sign-up.

How the physics is checked§

The chart is computed, not traced. Every property comes from published equations (the Hyland–Wexler saturation pressures and the ideal-gas moist-air relations of the ASHRAE Handbook—Fundamentals, as documented in the open-source PsychroLib), and the code is tested twice: by its author against reference values (NIST’s IAPWS-95 saturation pressures, the IAPWS sublimation formula for ice, the standard atmosphere, and worked examples from EPA and university extension guides), and by an independent test suite written from the model specification and the sources alone, without reading the code. Every factual claim is recorded in a claims register with its source and checked by a reviewer who did not write it. What each figure simplifies is stated next to it and collected on the sources page.

Editorial boundaries§

• We explain mechanisms and diagnosis. We do not give step-by-step instructions for work on energized electrical equipment, gas appliances, refrigerant circuits or well-pump wiring. Air conditioners and heat pumps run on refrigerant circuits; their service is for licensed HVAC technicians.
• Codes and licensing vary by state, province and county. Nothing here is a statement of code compliance, no wall or roof assembly is prescribed, and no calculator result is an equipment sizing guarantee.
• The comfort zone of ASHRAE Standard 55 is described and cited, not reproduced: it depends on six inputs and is copyrighted. The only shaded band on the chart is the EPA’s public indoor humidity guidance.
• Figures illustrate mechanisms with representative numbers. They are not measurements of any particular building.

Found an error?§

Please open an issue on the source repository. Corrections are welcome and credited.

Reuse§

Text and figures are licensed CC BY 4.0; code is MIT. Teachers and trainers may use and adapt any of it, with attribution.