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SEER Ratings; Declassified so that I can understand them

By
Home Inspector with Safety First Home Inspections

SEER Ratings are not as elusive as the "Loch Ness Monster" Rread on.

To start with SEER ratings are a good thing for homeowners! But I have to follow this statement with a caution or warning. SEER ratings should be good for homeowners and the intent for establishing the method of SEER ratings to evaluate energy efficiency was well intended. Let's start with two very important definitions;

1)     EER - Energy Efficiency Ratio is a method used to measure the energy efficiency of AC systems. It is quite simple to understand and determineEER = the total cooling capacity (work) / the total KW (Energy) input, this is for a single instantaneous point of measurement.

  • Example: a system uses 3.5 KW to produce 36,000 BTUH of cooling
  • = 36,000 BTUH /3500 Watts = EER of 10.3

2)     SEER - Seasonal Energy Efficiency Ratio is also a method used to measure the energy efficiency of AC systems. It is a little bit more complicated to understand and to measure.

  • SEER = the total cooling capacity (work in BTUH) in a cooling season / the total KW (Energy) input used during the same cooling season.

To measure and calculate the SEER rating of a system would mean that the total amount of cooling energy produced would have to be measured (very difficult except in a Lab condition). The electrical energy KWH used during the entire cooling season would have to be metered. The KWH is not so hard to get. There are several recording meters available that will measure and totalize the KWH. The more difficult item is the cooling output or work done in an entire cooling season.

So what does this mean to the average homeowner? The SEER rating for any AC system is impacted by the amount of start and stop cycles the unit experiences during the cooling season. It does require more energy to start and stop an AC system than it would to limit the start and stop cycles. AC systems that cycle on and off to often will consume more energy during a cooling season compared to a system that cycles normally. But the problem is not only with the energy side but also with the comfort side as well. Each time a system is started it takes several minutes for the system to stabilize the refrigerant pressures and temperatures and reach a point where the system is operating somewhat in the design condition or range. So each time the system is started the time the unit is operating will not be at the SEER value the unit was rated at. In the laboratory environment where the units are tested they are operating in a steady state condition and controlled temperatures.

Summary

It is critical that AC systems be sized properly for any home for any SEER rating. The energy efficiency of the very expensive top of the line system you buy for you home will suffer greatly and your home will not be comfortable if the unit short cycles. If your unit is sized properly it may run for long periods of time. This is not a problem as long as the unit is able to maintain the inside temperature of your home. A properly sized AC system should cycle between 3-5 times in an hour anything more than that may create problems with humidity control and will lower the SEER rating for your AC system.

Hope this helps.

Good Luck!

Ricky Ellis is the Senior Inspector for Safety First Home Inspections, www.safetyfirsthome.com located in McKinney Texas. Offering Home Inspections including Builders Warranty, New Home Phase Inspections all all types of Engineering services.

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