Sep 1, 2022
RACT manual co-author Eugene Silberstein joins the podcast to talk about the titular topic of his book, Pressure Enthalpy Without Tears.
Pressure Enthalpy Without Tears is a book that introduces engineering concepts to HVAC technicians in a way they can understand and apply in the field. Enthalpy is a fancy way of saying “heat,” and we use it to refer to the total heat content (BTUs).
The pressure-enthalpy chart shows the relationship between the refrigerant pressure and enthalpy in a system; it’s like a P-T chart that shows the relationship between heat content instead of temperature.
Each refrigerant has its own pressure-enthalpy chart, but the points and lines on the chart usually form a right trapezoid. Dirty air filters and other less-than-ideal conditions can distort the trapezoid or shift it on the chart. Each side of the trapezoid represents the refrigerant inside a major component of the HVAC system: evaporator, compressor, condenser, and metering device. The pressure-enthalpy diagram allows you to get a look at individual components while keeping the entire system in mind.
To plot points on a pressure-enthalpy chart, you need the high side pressure, low side pressure, condenser outlet temperature, evaporator outlet temperature, and compressor inlet temperature. Pressure is usually measured in absolute units (rather than gauge units), but ballpark estimates are typically sufficient.
Entropy is another concept we need to consider. Compression theoretically leaves no additional entropy and is reversible. Crossing a line of entropy means that a process is no longer reversible.
Eugene and Bryan also discuss:
You can visit https://www.escogroup.org/ to purchase Pressure Enthalpy Without Tears and access all of ESCO Group’s resources. You can also use the code HVACSchool22 for a discount on ESCO Group’s eLearning services.
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