Where SEER Goes Wrong?
We use a Seasonal Energy Efficiency Ratio to get a vague idea of how well a system performs, but what if the test is rigged? A few years ago, word came out that several major manufacturers had been cheating on their emissions testing. What if the same problem goes on in the HVAC world?
An Old Standard
In the United States, there was no legislation on SEER until the late 1980s. It didn’t take effect until the 90s. That’s a good thirty years or so for the world to change. The testing for SEER is done at 80 Degrees indoor temperature, against a variety of outdoor temperatures up to 105 degrees. That sounds like a balanced test, but it has its flaws.
The test results are weighted, giving more value to a milder summer, with a focus to highs in the 80s and lower humidity. We don’t necessarily experience such results today. We might hit highs in the 90s in much of the US, have higher humidity, and often want our thermostats set in the 70s.
These testing conditions are even more out of line for places like Arizona, where the 105 degree day is the standard experience. The SEER gives you a great comparison between machines, but it doesn’t give you a true picture of what to expect on your bill.
Loss of Performance
There are also concerns that the testing doesn’t truly cover how the changes in temperature impact the system. It’s easy enough for a system to hit 80 degrees output temperature in a 90 degree environment, but as the temperature climbs, power draw increases dramatically.
Consider that a car can go 5 miles an hour while basically idling. It’s easy enough to get to 50 miles per hour. Going 60 or 70 though, starts to produce a strain. You have to give it significantly more gas to go from 50 to 60 than you did to go from 5 to 10. There is some of the same logic applied to an air conditioner.
The compressor and the various fans and blowers have to work harder to achieve the same cooling in a hotter environment. The increased power draw can be exponential as motors spin faster and faster, potentially operating outside their ideal running points.
There are further flaws where a manufacturer can improve the results. The standard doesn’t specify what filters must be used for the test. There are ways to increase or decrease air flow in the system as tested versus how it’s actually used in the real world.
What Does This Mean?
The standards testing we do isn’t rigged, but it is really optimistic. We are more efficient today than we were last year. You can compare the efficiency of two units and the comparison will generally be correct. The energy consumption however, is probably unrealistically low. The sticker may say $500 for the entire summer or even $1000, but most localities won’t match the testing conditions. Most installed systems won’t have a chance to reach the peaks seen by the test systems due to variances in ducting, filter choices, and climate.
The SEER is useful for comparison shopping, but its’ not the be-all and end-all of what system you should actually install. The minimum value for SEER is increased frequently, with manufacturers and legislatures bumping it up every few years as technology improves. You just have to remember to take it with a grain of salt. In the real world, your numbers probably won’t match the paperwork.