COOLING COILS AND HOW COOLING TAKES PLACE:

			

Your cooling coil may look something like this or it may look quite
differently.  Some are slabs of fins and tubes that lay flat and others
lay diagonally, but this makes no difference here. Air passes through it on
its way to the duct distribution system.

From the factory, this coil will induce some restriction to the airflow.
Any more restriction than this amount will reduce the efficiency and increase
the system repair costs.  It is extremely important that it be kept in 
really clean condition.

The filter system and the prevention of unfiltered air
is THE MOST MAJOR PREVENTION that keeps this coil clean.

As a filter loads with contaminates there will be gradually less and less
space for circulated air to pass through.  That means your furnace or air 
conditioner will have to run longer to produce the temperature set on your 
thermostat.  And that means higher electric (and fuel) bills.  The chart
below shows estimated increases in heating/cooling costs caused by 
too-dirty air filters: (These figures will vary for various types of filters)

Days Filter           Heating/cooling
 is in use:           costs increases:
    20                    1.0%
    40                    2.5%
    60                    4.0%
    80                    6.5%
   100                    11%

(Chart information credited to Precisionaire, Inc., 2399 26th 
Ave. N., St. Petersburg, FL 33734-7568)

			
HOW COOLING TAKES PLACE:

The reduction of the temperature of a space is a very easy and very quick
act for an air conditioning system -- IF it only had to reduce the temperature
of the "air". 

Air, the floating-around-us kind, in a technical term is called the 
SENSIBLE HEAT that an air conditioner adjusts for us.  The air conditioner
is designed to remove heat. Right? Well, kind of. Since a home air unit
may circulate ALL of the air in a space (the home) up to eight times an hour,
then it would change the temperature of that total volume in only the first
pass through the system, so to speak.  But in reality, it would change back
almost instantly to nearly the original condition before we could get a chance
to feel its comfort.  Why?

The answer lies in the fact that air is not air alone in the real sense.
Air is many things.  It is dust, it is ozone, it is smoke, it is chemicals of
many forms, and it is laden with MOISTURE. Here is the culprit of our problems!
AIR CONTAINS A LOT OF MOISTURE. A bit of this moisture is airborne but most of
it hides in the bricks, books, wooden furniture, carpet, walls, food and the 
concrete we walk on, etc. This moisture is LATENT.

(It is a very difficult, and different, problem in the winter  and you 
should read that section The Diagnostics Chain/Heating/Gas Heat/
Moisture on windows, etc..)

The LATENT HEAT is more difficult to remove.  The air conditioner may 
remove six to eight gallons or more of this moisture from our home every day
in the process of trying to cool the environment of our space. Latent heat is
in the moisture everywhere and it may even be in the liquid form.

Think of a drinking glass filled with ice water.  Immediately, the outer
sides of it form droplets and will run onto our table. The water on the glass 
didn't come from the ice.  It came from the air that is around the cold glass.  
There was enough moisture in the passing air to collect as water droplets and 
run off the drinking glass.

This is exactly the thing that the air conditioner does for us.  The cooling
coil becomes cold enough for the passing air to condense droplets out of the 
air.  So much is captured that we must provide a drainage system around the
coil to collect it and direct it to run off to the sewer or other place. While
this is taking place, our now reduced moisture content air is being blown past
the books and things and it is "pulling" some of that moisture out of them and
back into the air. 

This process continues until a stabilized point is reached
in the entire building.  The air conditioner may shut off many times in the
process, but it will continue to pull that moisture out of the surroundings
for days and even weeks before it reaches a point of equalization at the 
desired temperature and relative humidity. Note: When Latent moisture is 
"pulled" from things it turns into Sensible heat as it becomes part of the air
again and this process will RAISE the temperature of that air and the 
thermostat will want to run or continue to run to reduce it again.  Typically, 
it will reach our chosen temperature and a relative humidity of about 20% 
by design. Remember, the concrete floor or walls will have to reach a 20% 
level for this to become stable. It takes a lot of time to develop.


		Think back to the first few warm days of spring when you turned on the
		air conditioner.  Remember that you worried that the system ran so very much?
		The air outside was almost as cool as inside, yet, the system ran a lot.
		MOISTURE latent in the mass of the home!  After a few weeks as the temperature
		outside became really hot and yet the system started running better. Less frequently.
		It has removed and stabilized the relative humidity inside. For humidity problems 
		similar to this in the winter time during heating, see the section thermostats.

		So the air conditioner works 90% of the time to remove moisture and only 
		about 10% to lower the temperature.