It is getting hot here in Atlanta.  I can no longer just leave the windows open to stay cool; I must rely on my air conditioning units.  We've been in our town home for over 2 years now so I figured it was time to have an AC service technician come out and do some routine maintenance on our AC units.  I also wanted to get a better understanding of how my AC unit consumes electricity and how I can make it more efficient.  You would think because I wrote the blog post "How much electricity does my AC consume?" I'd be an expert....but you know what they say about believing what you read on the internet....I realize now that I made a small mistake in my earlier post (more on that to come later).

First, a little about our AC units:  Since our town home is 3 stories we have 2 AC units:  One, 2-ton unit for upstairs, and one, 2.5-ton unit for the basement and mid-level.  Our AC system is a split-system.  I like Goodman's description and diagram of a split-system: "The typical central air conditioning system is a split system, with an outdoor air conditioning, or "compressor bearing unit" and an indoor coil, which is usually installed on top of the furnace in the home."  The illustration of this is below:

Example of a Split-System

Further improving the efficiency of our system, the AC unit that controls the basement and mid-level has an automatic damper system on it.  This means that by using the thermostat on each level we can turn just the basement on, or just mid-level on, or both.  If you don't have a damper system then your unit is either on or off, and you end up cooling/heating areas that you don't need conditioned.  I only wish we had an automatic damper for upstairs so we didn't have to cool our empty office and guest bedroom at night, when we only need our bedroom cooled.

Of my two AC units, my upstairs unit is the only one that is connected to the Ecobee internet programmable thermostat.

Here are some things I learned from the AC technician's visit:

• Cleaning off the condenser coils (the metal fins on the outside of your unit) with water from your hose can help it run more efficiently (dirts and debris inhibit heat transfer - number 1 in the diagram above)
• There was a manual damper on our upstairs unit that was partially blocking the flow of air into our bedroom.  This means that the AC was staying on a little bit longer than necessary to bring the room to the desired temperature.
• When the warm air from your home hits the evaporator coils in your furnace (number 3 in the diagram at the top of the post), moisture in your home's air condenses on the metal coils (this is why an air conditioner acts as a dehumidifier).  If you live in a humid environment (like Atlanta or in the tropics) you know that air that has a higher moisture content makes you feel hotter.  This is because drier air helps your body evaporate moisture better, which is how our bodies cool.  As this article from EnergyStar titled Right-sized Air Conditioners points out, an Air Conditioner that is sized too big for your home will "short-cycle"; which means that it doesn't stay on long enough to reach the optimal operating point where moisture in the air condenses and drains away.  Make sure your AC unit is sized properly so your AC unit can de-humidify the air!
• The water that does condense on your evaporator coils has to drain somewhere.  I have two indoor furnaces, one in the garage that services the basement and mid-level, and one in my attic that services our upstairs.  The unit upstairs just uses a pipe and gravity to get the water to drain from my attic to outside.  But the unit in the garage needs a pump to do the work of gravity because there is no height differential between my garage and the outside.  The important thing here is to always make sure the pipe in your attic is not clogged!  If it get's clogged, the water has nowhere to go and it ends up in your attic...and then your attic ends up in your bedroom.  Always make sure your condensate drain remains open!
• The AC technician pointed out that a lot of units have a float switch on their condensate drain line.  If the line gets clogged, the water that is backing up causes the switch to activate which shuts off the unit.  Mine doesn't have this, so I have to be extra careful ensuring the line remains clear
• The technician told me a great water saving trick.  Just use an old bottle to collect the water coming out of the condensate drain and use it on your garden or flowers!  Just make sure to empty it regularly so it doesn't get clogged.
• The technician said that often times, when an AC unit fails it is because the compressor (number 4 in the image at the top) fails.  Some people actually opt to pay upwards of $2,000 for a new compressor even though they could spend around the same amount to buy a new AC unit.  Why would anyone want to get a new AC unit?  Because it could qualify for a 30% (up to $1,500) tax credit!  Not only are you getting a new, more efficient AC unit, but after the tax credit chances are you are paying less for it.  If your compressor fails, don't waste the money replacing it, take the time to upgrade!

So I learned a lot from my AC preventative maintenance and I'm glad I had it done.  It did cost $130 for the two units, but the technician was here for an hour and a half and he had to deal with me huddling over him asking annoying questions the whole time.  If you live in a hot environment, chances are that you spend more electricity and money on air conditioning than any other energy hog.  Luckily my units were already fairly efficient and in good working order, but who knows how yours are performing?