About Physics of Buildings
Physics of Buildings explains how the systems inside homes and commercial buildings work, through their physics: pumps, tanks, boilers, heat pumps, ducts and wires. It is written for two readers at once: the homeowner with a question, and the technician, apprentice, student or engineer who wants the mechanism and the numbers.
This page on the refrigeration cycle is made by an AI-assisted production system: an AI agent researched the sources, wrote the text, and built the simulations and the calculator, and a separate, independent verification step checks every claim and every model against the cited sources before the page is published. There are no ads and no sign-up. The first Physics of Buildings piece, on well pressure tanks, was made the same way.
How the physics is checked§
The refrigerant properties come from published equations of state: Lemmon’s 2003 equation for R-410A and Tillner-Roth and Yokozeki’s 1997 equation for R-32, evaluated with the open-source CoolProp library and tabulated for the page [1][2][3]. The tables are tested against the equations at points between the table entries, against the check values printed in Lemmon’s paper, against the NIST Chemistry WebBook, and against pressure–temperature values used in the trade. Every model behind a figure is also tested by an independent suite written from the model specification and the sources alone, without reading the model’s 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 refrigerant circuits, energized electrical equipment or gas appliances. In the United States, only technicians certified under Section 608 of the Clean Air Act may service equipment that contains refrigerant [4].
- Readings such as superheat and subcooling point to common causes, not a diagnosis. A licensed HVAC technician confirms the cause before anything is changed.
- Codes and licensing vary by state, province and county. Nothing here is a statement of code compliance, and no calculator result is a charging target or a sizing guarantee.
- Simulations illustrate mechanisms with representative numbers. They are not measurements of any particular installation.
- Manufacturers’ documents are cited because they publish the numbers technicians use; citing one is not an endorsement.
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.
Sources
- (2003). Pseudo-Pure Fluid Equations of State for the Refrigerant Blends R-410A, R-404A, R-507A, and R-407C. International Journal of Thermophysics 24(4): 991–1006 (copy hosted by NIST). journal article R-410A = 50% R-32 / 50% R-125 by mass; Helmholtz-energy equation fitted to the full mixture model (densities within 0.1% except near the critical point; heat capacities 0.1% average, 0.5% max); dew and bubble pressures from ancillary Eq. 13 (Table VI), within 0.02–0.05% of the mixture model; valid 200–450 K; Table V check values (300 K: bubble 1.7404 MPa, dew 1.7351 MPa); dew and bubble curves of R-410A nearly coincident.
- (1997). An International Standard Equation of State for Difluoromethane (R-32) for Temperatures from the Triple Point at 136.34 K to 435 K and Pressures up to 70 MPa. Journal of Physical and Chemical Reference Data 26(6): 1273–1328. doi:10.1063/1.556002. journal article Read via the NIST Chemistry WebBook fluid page for R-32, which uses this equation and states its estimated uncertainties: 0.05% for density, 0.02% for vapor pressure, 0.5–1% for liquid heat capacity and speed of sound.
- (2014). Pure and Pseudo-pure Fluid Thermophysical Property Evaluation and the Open-Source Thermophysical Property Library CoolProp. Industrial & Engineering Chemistry Research 53(6): 2498–2508. doi:10.1021/ie4033999. software CoolProp (MIT licence), version 8.0.0, implements the Lemmon (2003) R-410A and Tillner-Roth & Yokozeki (1997) R-32 equations used to build this site's property tables.
- (2020). EPA’s Refrigerant Management Requirements: What Technicians Need to Know (Section 608 fact sheet). U.S. EPA. government guidance Section 608 prohibits knowingly releasing refrigerant during maintenance, service, repair or disposal; requirements cover HCFCs and non-exempt substitutes such as HFCs and HFOs; only certified technicians can use non-exempt refrigerants to service AC and refrigeration equipment; refrigerant sales restricted to certified technicians; technicians must pass an approved certification exam.