Invented by Willis Haviland Carrier in 1902 (hence the famous Carrier brand of AC machines), air conditioning was a major factor in the massive increase of population in Texas, Florida and the Southwest, as well as other tropical regions worldwide. The process of turning air into a temperature more comfortable for human habitation makes life all the better, decreases frustration (it's been proven scientifically), and makes living in hot areas much more appealing. Frankly, if it wasn't for air conditioning, I would refuse to live in Shanghai.

The central feature of an air conditioning system is the air conditioning plant. Fresh air, together with a proportion of the air returned from the air-conditioned rooms (recirculated air) is drawn into a mixing chamber, the relative quantities of fresh air and recirculated air being controlled by valves. This air is cleaned by means of filters. These usually have glass-wool filter elements in which dust is retained.

After filtering, the air is preheated. This is done by means of heating pipes through which steam or hot water is passed and which are provided with fins which serve to increase their heat-exchange surface area.The air to be preheated flows along these fins and absorbs heat from them. Excess moisture is removed from a portion of the air by cooling. The warmer the air is, the more water vapor it can absorb.

This air is then mixed with the air coming straight from the preheater so as to obtain an air mixture of the desired temperature. If the moisture content of the mixture is too low, finely atomised water is added by spray nozzles. This causes some cooling of the air, and for this reason the air is passed through a reheater which is essentially similar to the preheater and which gives the air its desired final temperature.

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.
It's that time of year again in New Orleans. Though it may only be spring in other parts of the world, it is full scale summer here already. You can tell just by looking at the windows of grocery stores and Blockbusters. Already they are coated with a slick, sweaty layer of mist, indicating that businesses around the city have geared up for another long season of summer heat, humidity, and daily but short thunderstorms.

When I think of the term "air conditioning," I think more about the conditioning than the air, in that we are being conditioned to expect cool air at a time of year when cool air is not so much hard to come by as it is almost over-prevalent. To compensate for the hot temperatures we endure because we choose to live in such a maniacal weather pattern area (living between the Mississippi River and Lake Ponchartrain and being several feet below sea level never was a very smart idea, even for New Orleans' first developers), offices and all enclosed public spaces kick their A/C so far down that it's a shock to the system to go from inside to outside and back again with any regularity. Because the hot season here is so long (mostly 9 months out of a year on the average), this happens so often that I truly believe it is partly responsible for all the sinus infections and colds people seem to get all year round down here.

People think I'm nuts to wear a long sleeved jacket inside the office once I come in from outside, but I believe I am better preparing my body for the temperature change. Most of the time New Orleans has been around, there was no such thing as air conditioning and that somehow, people just tolerated it. People also think I'm nuts to not have central air (well, I would if I could, but even if I did, I could never afford to keep it on all the time), that I come home to a hot apartment and simply take time to adjust.

I am not saying that people should not be allowed to have A/C or that they should suffer because it would build character, blah blah blah. What I am saying is that as with any modern convenience that has shifted to a necessity, we should still be cautious with regard to our bodies. New Orleans is one of the top 10 fattest cities in the US, so there a fair share of people who are more sensitive to heat. But that's also not to say that every overweight person is inside sucking up the A/C. We're all equally guilty of air conditioning.

The American mentality has in no way hit an all time high in demand for convenience, but it has been on the rise for quite some time. Sweltering in the heat is seen as barbaric, something portrayed in films or books as something belonging solely to the middle and lower classes of the lower Southern states. These states themselves are states of mind, New Orleans in particular having its own all too well known eccentricities. The lush, always green foilage, in addition to the humidity and common revelry associated with the city, gives New Orleans an erotic, sultry essence, and this is something I like about living here. I see the moist shoulders and limbs of passersby as they head into the Quarter for a night of partying, and I am comforted by the fact that these people can always find shelter from the heat.

I am no saint, either. I seek out the well air-conditioned bars and coffee shops on days off in the summer. But I also willfully sweat when I exercise. To me, it's healthy to sweat when you're doing something productive, not when you're just sitting in traffic. It's ironic to me that, if sweating indeed purges the body of toxins, that we in New Orleans should and do sweat more than perhaps other places. We will always have a lot to cleanse from our systems.

For all the complaining people do about the heat, which here is so common it's taken as small talk, people never stop coming here, even in the summer months. I think we subconsciously need to sweat on occasion to bring us back into communication with our bodies, which can so often be overlooked in lieu of climate/light control used in most offices and workplaces. I think that the more detached we become from our bodies, the more anxious and unfulfilled we get, the more dangerous we become. I mean, people here will sit in bars all day (provided they don't have to be anywhere) just to avoid the heat. They stay inside and wait for the sun to go down, wait for the sidewalk to cool off. Air conditioning isn't just pleasant, it's practically necessary for business to survive in the summer. With the slow season being summer for us, people work the whole rest of the year (mainly in the restaurant/entertainment industries) just to get through the slump of summer when tourism is at its lowest. And still, we have festivals all summer long with record attendances every year. People in droves crowd on July 4th by the River to watch the fireworks.

I guess what I'm trying to say here is that I appreciate New Orleans for not letting its burdensome weather dampen its spirit. If we can do it, you can do it too. To keep people from losing their sanity in the summer's relentless heat, I guess it also helps that we have such a cornicopia of places to take your mind off it. This place has a slowness to it that, I think, helps in these situations.

So I'm buckling down for the summer, eyeing my electric bill with a savage leer, and hoping for that next storm.

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