b'PSYCHROMETRICSBACK TO BASICS: Reviewing the principles of psychrometrics By Alex McGowan, WSPIam occasionally called upon to explain arcane building science fundamentals to technical people, so I thought I might be able to save some time by writing it down in Elements magazine. This article reviews the principles of psychrometrics, as the concepts are very useful in diagnostics and design. Building science lives in the overlap between architecture, materials science, civil engineering and mechanical engineering, and a building science specialist should know about all these areas. The problem is that psychro-metrics is often only taught to mechanical engineers, and even then, only in the context of HVAC equipment design, operation and maintenance, when it is much more than that. Some readers may find this extremely basic, even to the point of being insulting; you folks can skip to the much more interesting cover story. This article is for those unfamiliar with psychrometrics or those who have forgotten the concept after they hastily finished crammingexpand and contract so the different coloursLater, Dr. Carrier creates the Carrier Corpora-for that exam. Based on my conversations withdont line up in the print process. They calltion and makes tons of money, but in 1902 industry professionals, there are a lot morethe Buffalo Forge Company, who sends theirhe is interested in the properties of humidity people in this group than will admit it! top expert, a mechanical engineer named Dr.(water vapour) in air. He carefully controls Lets start with a bit of history: its 1902, andWillis Carrier. He designs a ventilation systemand measures air temperature and humidity Sackett & Wilhelms, a Brooklyn printingusing chilled water piping that provides enoughin a test chamber (see the sidebar Psychro-company, is having trouble with the qualitydehumidification to control humidity withinmetric Measurement). He finds that at a of their multi-colour brochures. Uncontrolledacceptable tolerances, solving the printersconstant concentration of water vapour, as humidity in the air causes its paper stock toproblem (and inventing air conditioning). the air temperature is reduced, water vapour FIGURE 1: SCHEMATIC GRAPH SHOWING CARRIERS EXPERIMENTS, 1902-1905 FIGURE 2: THE CONCEPT OF RELATIVE HUMIDITY IS INTRODUCED SPRING/SUMMER 2020 13'