SEER is what makes efficiency

In an A/C system, everything works together to create SEER, so if your present system is old and inefficient, you cant just buy a 12, 14, or 16 SEER outside unit, install it and expect to get the rated SEER for that unit without taking the system as a whole into consideration. 2 major factors that are required for rated SEER are a "matched" evaporator coil, and a properly sized copper refrigerant lineset.

Most A/C evaporator coils are "capillary tube coils" in which refrigerant is sprayed into them in an unregulated fashion to produce the gaseous form of the Freon. This is equivalent to running a car engine without a carburetor. To obtain your higher SEERs, either a thermostatic expansion valve which regulates the refrigerant is required, or a matching coil with a piston-actuated flow control check valve is needed. Even with an expansion valve, you may or may not obtain the desired SEERs due to system design considerations, and should replace the coil with a matched one. The Association of the Refrigeration Industry (ARI) publishes matching standards on a quarterly basis, and your HVAC contractor needs to consult this book anytime he considers matching evaporator coils and condensing units of different brand names. Your contractor should also be able to tell you if using an expansion valve, as opposed to replacing the evaporator coil with one that matches, will deliver the desired SEER.

The second factor in determining SEER is the size of the copper lineset used. The principle behind higher SEER products is moving a larger volume of refrigerant at a faster rate. Therefore, manufactures design these system components using more and larger tubing, and more powerful compressors. The size of your copper lineset is extremely important here. Too small a lineset will not only result in defeating the the method used to obtain higher SEERs, but will put undue stress on the compressor, and possibly shorten its life. Your contractor needs to be familiar with this issue, and have manufacturers' engineering data on hand at all times when making a bid. Bottom line - For high SEER, you cant just replace an outside unit and coil without usually having to replace the copper lineset too.

System sizing - Bigger is not necessarily better

Sizing is critical in determining, not only the efficiency of your system, but also your comfort level. A system that is too small, of course, will result in your system not delivering enough cooling, and also running all the time, which will drive up your electric bill. Too many contractors, however, fail to take into account the consequences of having too large of a system. Their philosophy - Bigger is better. The result is dissatisfied customers who no longer have faith in the high-end brand name they trusted in and paid a large sum of money for. Its not the fault of the manufacturer, however. The blame is solely the contrator's for not installing the equipment according to proper guidelines.

Properly designed and installed HVAC sytems not only cool your home, but also remove moisture. In order to remove moisture, your system must be able to run long enough to this task. A system that is too large will cool the home off so quickly that it will not remove moisture. The result is that, instead of feeling cool and comfortable, the customer feels cold and clammy, He or she, therefore sets the thermostat at a higher temperature, and this exacerbates the problem, not to mention the fact that the customer still does not feel comfortable. Eventually, indoor air quality is affected as mold and mildew begin growing in the humid environment.

Your contractor needs to follow these rules in order to do a proper installation at your home.

I.

A heat load analysis. He should take the square footage of your home, taking into account cathedral and other high ceilings, calculate heat loss from windows, especially those facing east and west, estimate heat loads based on the number of people living in the home, number of appliances, etc. The number of square feet of living space per ton of cooling is usually somewhere between 500 and 600, but that is not a hard and fast rule.  Without a load analysis, you risk undersizing or oversizing. .

II.

Since some homebuilders cut corners on HVAC installations, the size of your present system should never be a "given". If you have 2,000 square feet in your home, but only a 3 ton system, there is a good reason your electric bills are high. Your contractor should do heat load estimations on his own for all estimates.

III.

Your contractor needs to evaluate your copper lineset, along with your evaporator coil if you only wish to replace your outside unit. Your contractor's recommendation should be based on his (or her) observations.

IV.

If you feel that a contractor is using these issues in order to overprice a system, get a second opinion, or other bids.

Economics - An intelligent bottom line

Do you need a high efficiency? If the home is rental property, efficiency is not nearly as important. After all, you are not paying the utility bills. If you plan to sell your home, energy efficiency is a consideration, but not necessarily the final selling point. And if you plan to stay in your home for at least 10 years, having an energy efficient system is certainly a very important aspect.

First of all, evaluate your own situation, and what kind of HVAC system is apporpriate for it. If you feel comfortable with a 10 SEER system after thinking things out, stick with that decision, and don't give a salesman a chance to change your mind. If pushed too hard, choose another company. On the other hand, if you feel that it is logical to buy a higher SEER system, then decide how efficient you want it to be.

SEER is a complicated formula, and varies according to where you live in the country. A consending unit that wont save you much money in, say, Green Bay, Wisconsin. might save you a bundle in Houston, since SEER is a function of the number of hours per year in an "Air conditioning season". That season varies widely, depending on where you live.

However, since SEER is a "linear" function, there is a way to determine how much money you will save comparatively, based on the SEERs of existing units.

How much do you save with a 14 SEER unit over a 10 SEER unit?

% saved=1-(SEERlow / SEERhigh).

1-(10/14)=1-.714=.286 or 28.6%

A 14 SEER system will save you about 28% on your cooling bills over a 10 SEER system. A 14 SEER system installation will also have a much higher initial startup cost. This is what you must balance in considering which system to use.

When all is said and done, you will be happy with your system choice if you follow these guidelines, along with a little common sense, and choose your contractor carefully. Dont forget that comfort is a major expenditure, and plan your purchase with the goal of obtaining the result that you want, instead of succumbing to the goal of a salesman.

-DanaRhea Elliott
Manager
Cool & Heat AIRCO, Inc.