One of the most common mistakes made when installing a central air conditioner is assuming that the higher the SEER (Seasonal Energy Efficiency Ratio), the higher the efficiency of the system. Not so fast. Yes, the higher the higher the efficiency of the air conditioner, the better. However, a factor of primary importance is the indoor evaporator coil (the indoor coil). These coils have huge efficiency differences between them and the SEER of your air conditioning system needs to be calculated in terms of the air conditioning system as a whole. The outdoor unit is only one piece in the system
Consider the following performance measurements.
A Lennox 14 SEER air conditioner combined with a C33-48+ indoor coil operates at a combined system efficiency of 13.0 SEER. Yet that same Lennox 14 SEER air conditioner combined with a C(A,C,D,E)36C34+ operates at 13.5 SEER. Again, that same 14 SEER unit will only reach 14 SEER with a A(A,B)W364+ indoor coil or something similar. SEER ratings as high as 14.5 and 15.0 can be achieved if this air conditioner is used in combination with a variable speed DC blower motor.
This variation in real efficiency holds true throughout all makes, models and brands, The Lennox 14 SEER was used solely for illustrative purposes - I could have chosen any unit from Carrier, Amana, York, etc., and had the same differences in efficiency. The effects on efficiency due to coil type are even more pronounced in heat pump systems than on air conditioners.
So why would an air conditioning installer use a lower efficiency coil? There are a few factors, the main one of which is that the higher the rating of the indoor coil, the larger it is. A bulkier unit can be more cumbersome to install and is often not used because of this. Should this be happening? In my opinion, no, However, considering that the chances of a consumer knowing this information is next to zero, it occurs quite regularly.
If you're considering installing a new air conditioning system or replacing an old one, ask for a high-efficiency coil. They only cost about $45.00 more. You'll save your money back in the first few months.
Two other ways to increase the SEER of your air conditioning system are to have a TXV and TDR installed. A TXV, or thermostatic expansion valve, modulates the flow of refrigerant gas inside the cooling system. A TDR, or time delay relay, controls the timing of the indoor blower fan to maximize cooling and efficiency. Many manufacturers build TDRs into their furnaces, while good quality thermostats also have them included. Just make sure that your ac installer turns them on.
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