air conditioning (thing)

A couple of clarifications and corrections to Dman's writeup:

• Mr. Carrier's major contribution to the field of air conditioning was the development of the psychrometric chart, rather than the air conditioner per se.
• The psychrometric chart allows an individual to determine the properties of moist air and to plot various air conditioning processes. Until the development of psychrometrics, air conditioning was mostly voodoo and proper air conditioning was usually just good luck.
• A basic air conditioning system consists of a cooling coil and a heating coil in that order (this will become clear in a moment). You also need a fan and motor to blow the air (or draw the air) over the coils.
• A mixing box or mixing plenum is the correct term (not mixing chamber).
• Proportions of fresh air and recirculated air are controlled by dampers not valves.
• Filters can remove both particulate and gaseous contaminants (which is useful if you are talking about recirculated air). Particulate filters can range from 20% to 99.99% HEPA while gaseous filters usually consist of charcoal or activated carbon but can get more exotic.
• Air is never preheated when you are air conditioning (i.e. cooling and dehumidifying). Warm air can indeed absorb more water vapor, but you don't heat up the air just to cool it back down. Here's the basic process:
  1. Fresh air at a given temperature and humidity enters the air handling unit and is cooled until it reaches saturation (it's dewpoint).
  2. It is then further cooled to between (50 & 55 Deg.F depending on the desired supply air temperature) until most of the moisture condenses out of the air stream.
  3. This overcooled air is then reheated to the desired supply air temperature.
• Finely atomized droplets of water will cool the air via the latent heat of vaporization. But unless you live in Arizona, you've just spent a lot of money trying to remove moisture from your air. Reintroducing it at this point can cause problems with repect to indoor air quality. Besides if you've properly designed your system this type of kludge won't be neccesary.