You have three estimates for central air conditioning in your house? Each estimate quotes you a different size unit. What do you do? Buy the middle one because they are between the other two? You may be happy and maybe not. Let me explain how this works and what the results are of not getting it right.
Air conditioning is not an exact science. There are many variables that can affect the way an air conditioning system performs. Also there are many factors that can affect the size of the air conditioner that you need. What I want to get into next is the problems that can show up from an air conditioning system being either too big or too small.
If your central air conditioning system is too big for the space being cooled you are actually worse off than if it was too small. Yes too large of a system creates some major problems! If your system has too much capacity and cools your house off too quickly, you will not get he secondary effect of that an air conditioner is designed to give you. The second benefit of your system is to dehumidify the air. If your system can cool the air very rapidly before it has time to take the water out of the air, you will not have a comfortable house. This also goes for any other building. Have you ever entered a store and it felt like you just walked into a refrigerator? That is because the equipment is so large that it is cooling the air, but not removing the water out of the air. The effect is a very uncomfortable cool. This can happen in homes, but usually to a lesser degree. The discomfort may not be that pronounced, but it will not be as comfortable as it could be.
If the air conditioning unit is undersized, this is actually the lesser of the two evils. If your system is too small the worst that can happen is not nearly as bad. An air conditioning system that is too small will just not quite keep up on a very hot day. This usually is not that noticeable because as long as there is a difference between the inside and the outside temperatures you will still be happy. If the house is 80 degrees on a 95 degree day, you still feel rather cool in the house. The other advantages to the under sized air conditioning system is that you still get very good dehumidification on a mild rainy day when you still want some cooling and everyday that you are running the air conditioner you are saving money. Yes, even if the air conditioner is running longer, you are still saving money because it is using less power. The efficiency of the slightly undersized system will be much higher than the oversized system.
So, as you can see size really does matter when it comes to air conditioning. The oversized system will give you an uncomfortable cool and waste energy at the same time. Neither of these things are something that you want. The undersized system may allow the temperature to creep up a bit on a very hot day, but will save energy and give great comfort most of the time. The ideal sizing is for the unit to be running constantly on the hottest day of the year and barely be able to keep up. When you are shopping for central air conditioning make sure that you tell the salesperson what you want and insist on seeing their heat loss/gain calculations for your building. No one can guess at what you need and do it correctly. Making sure you have the right central air conditioning for your house or building will make you comfortable and happy for many years to come!