The importance of Psychrometrics
An understanding of psychrometrics is vital to HVAC and it is at the heart of Computair’s coil selection software. Psychrometrics describes the properties of moist air, which we consider as a mixture of dry air and water vapour.
The amount of water vapour in the air can vary quite a lot and has a significant effect on our perception of temperature and comfort. At a given temperature and pressure there is only so much water vapour that air can hold. The point at which water will no longer evaporate is called “saturation”. At low temperatures this happens at low humidity ratios. As temperature increases the saturation humidity ratio increases rapidly until the boiling point of water is reached and it can no longer exist as liquid.
Dry air is a mixture of several gases. It’s mostly Nitrogen and Oxygen, but also contains Argon and Carbon Dioxide. What we call ‘moist’ air also contains water vapour. Water vapour is a colourless and odourless gas, but it’s important for air conditioning. Consider some of the factors below.
A few definitions