13 SEER Equipment: Buyer Beware

Aug. 1, 2005
There has been a lot of talk about the coming 13 SEER (seasonal energy efficiency ratio) minimum equipment standard, and the expected impact it will have

There has been a lot of talk about the coming 13 SEER (seasonal energy efficiency ratio) minimum equipment standard, and the expected impact it will have on our industry. Yet few of us have taken the time to check out the new equipment’s engineering data. According to the preliminary engineering data I’ve received from the industry over the last two weeks, we have a problem.

The government has chosen to regulate our industry beyond consumer demands by imposing minimum equipment efficiency requirements with the intent to save energy. As a direct result, if you’ll take time to review some of the new equipment you’ll find it meets the 13 SEER requirement, but that’s about all it has to offer.

Don’t get me wrong, there is and always has been good equipment out there. The better manufacturers have taken the high road, and have used 13 SEER as a springboard to build even better equipment. But some manufacturers have produced equipment barely worthy of the recycle bin — especially their builder models. If you’ll take the time to review the engineering data, you’ll get an unexpected peek into the integrity (or lack thereof) of your favorite manufacturer.

Let’s take a look at a simple way to evaluate the new equipment that will be shipped our way soon. It’s obvious that all the new equipment will be 13 SEER minimum. However, the new equipment has to be selected with great care or the system will never work in the field when it’s attached to a duct system. This is a change from the past, when most the equipment would function pretty well under difficult conditions.

Let’s take a look at one way to evaluate what we’re going to buy, install in our customers buildings, and then be on the warranty hook for for the next 5 to 10 years.

Efficiency Formulas

I know most of us aren’t big math fans, but this one is easy. First, let’s look at the basic Equipment Efficiency Ratio (EER) formula. I call it real efficiency. You take the rated Btu output of the equipment. Let’s take a three ton unit and, in round numbers, say 36,000. Then you divide it by the Watts it takes to produce those BTUs under ideal conditions in the laboratory. Let’s say in this case, the unit uses 3,600 Watts. 36,000 Btu divided by 3,600 Watts equals an equipment EER of 10.

To make the formula work so they can stay in business, some poor quality manufacturers have made some unsavory changes in their equipment. Their response to government pressure was to reduce the number of Watts used by 12 SEER equipment, and it magically makes a false jump to number 13.

The fastest way to do this — and to immediately increase profits on a furnace or air handler — is to reduce the size of the blower motor. Smaller blower motors mean more profit per unit, although the fan is inadequate. This has slipped through the system because one equipment efficiency rating standard only requires some fans to have a 0.2-in. w.c. total external static pressure rating.

In an attempt to justify smaller blower motors, one manufacturer is now declaring required airflow to be only 350 cfm per ton. Be on the lookout for air handlers rated at less than 400 cfm per ton at 0.50-in. total external static pressure.

The next slick way to increase efficiency is to expand indoor coil surface area and increase the fins per inch count. This is another questionable move that some manufacturers have employed. Once again, this increases the coil’s resistance to airflow. The result is coils that have a pressure drop from 0.30-in. to 0.50-in.

13 SEER Rubbish

Here’s a picture of the systems you’ll get from the manufacturers that chose the shortcuts.
The fan capacity is rated at 0.30-in. total external static pressure. It’s legal. But it means the fan can only move 400 cfm per ton as long as the system air pressure remains below 0.30-in.

The ARI rated matched cooling coil required to get 13 SEER has a rated wet pressure drop of 0.30-in. Believe it or not, you’ll see some as high as 0.50-in. Do you see what happened here? But hey, it’s legal!

Here’s what system performance will look like. We’ll have a 13 SEER system, but the fan will only be rated for 0.30-in. of pressure. The coil will be rated to have a pressure drop of 0.30-in. also. Subtract the coil pressure drop of 0.30-in. from the fan capacity of 0.30-in., and you’re left with 0.00-in. (in other words, zero, zip, none) pressure to drive the filter, ducts, wyes, elbows, dampers, and grilles. Some of the preliminary engineering data is indicating that some 13 SEER equipment will only deliver 220 cfm per ton if it’s installed on a typical duct system with a typical filter.

A Quick Equipment Evaluation

Request full manufacturer’s data from your distributor before you order you new inventory. Ask for the fan performance tables, the pressure drop data for the cooling coil, and the pressure drop chart for the filter you’ll be installing with the system.

Plot the available total external static pressure of the air handler at 400 cfm/ton. Plot the static pressure drop of the wet coil at 400 cfm/ton. Then, identify the pressure drop of the proposed filter at 400 cfm/ton.

Do the math:

Rated fan static pressure - wet coil pressure drop - filter pressure drop = remaining static pressure.

Remaining static pressure should exceed 0.20-in. for a typical residential system and 0.40-in. for a two-story home or light commercial building. If less pressure is available, the fan will be unable to move the airflow that’s required to cause the heat transfer that allows the system to operate. System efficiency will plummet.

You’ll find in many cases, the remaining static pressure will be a negative value. Unless you’re installing that equipment without a duct system, you need to look for better equipment that will allow your system to operate as you said it would.

Remember, it’s our responsibility to intelligently select equipment that will match the needs of our customers and actually function in the field. The best move would be to skip the 13 SEER builder’s models and go straight to the high quality, better-built high SEER equipment with variable speed fans. Then, renovate the customer’s sickly duct system. Finally, rate and verify the installed efficiency of the new system to prove you delivered what you promised.

Bottom Line

We have conducted thousands of field tests to rate installed system performance. We then coupled those findings with the poorer quality 13 SEER builder’s models’ engineering data. We anticipate that this equipment in a replacement scenario may only produce CSER (Cooling System Efficiency Ratings) ratings between 40% and 50% of laboratory rated capacity.

In simpler terms the 36,000 BTU rated systems may only deliver 15,000 BTU and the 13 SEER systems will operate like a 6.5 SEER.

Can you imagine the huge warranty expense and the excessive energy consumption that will be imposed on the U.S. consumer? Please take time to do a little research before you place your upcoming equipment purchase orders.

Rob “Doc” Falke serves the industry as president of National Comfort Institute a training company specializing in measuring and improving HVAC system performance. If you're an HVAC contractor or technician interested in a no cost one page test report and procedure on how to measure duct loss, contact Doc at [email protected] or call him at 800-633-7058.