December's Last Word "SEER vs IAQ: Can They Co-Exist?" (CB, Dec. 2003, p 119) triggered dozens of letters and e-mails from readers. Interestingly, while the general consensus was this is a serious issue, many added that the article didn't go far enough. I agree.
As thousands of NCI-certified contractors measure delivered BTUs in the field, we're getting daily confirmation that the current SEER rating method is extremely flawed and outdated. This is due to a number of reasons, beginning with the fact that SEER ratings are measured under perfect laboratory conditions that don't begin to approach what a unit will actually "see" once it's installed in a real home.
A major deficiency of this method is it doesn't account for the effects of resistance caused by the ever-increasing array of IAQ accessories being inserted into the air stream of a typical split system. In addition, most duct systems are undersized, causing high static pressures, and also extremely leaky, bringing in hot, humid, dirty air from attics and crawl spaces. What we have is a horse that's so handicapped that it has no chance of winning the race.
Adding insult to injury, the higher the SEER rating of the unit, the more sensitive it is to outside variables, making the effect exponential. In simple terms, higher SEER equipment's efficiency can drop much faster under adverse field conditions than their lower SEER counterparts. Why? Here are two main reasons:
High efficiency units with standard blower motors often operate at or beyond allowable static pressures, resulting in insufficient airflow. Higher evaporator coil resistance (due to more fins per inch), coupled with high pressure drop over filtration systems and undersized ductwork are a sure recipe for failure.
We commonly see external static pressures of 1-in. wc or more on systems designed to produce 400 cfm/ton at 0.5 in. or less. At these high statics, fan performance is severely impaired, and efficiency goes out the window -- not to mention comfort!
Better high efficiency units with variable speed blowers help overcome some of the static issues, but also introduce two new potential efficiency penalties. First, many are set to run almost continuously at lower speeds, which can help reduce humidity issues.
The problem is, when they're installed on undersized, leaky duct systems, they actually pull in more hot, humid, dirty air from attics and crawls because of longer run times. This decreases efficiency due to the additonal sensible and latent load.
The other downside is when variable speed blowers are used to overcome extreme system static pressures, increasing torque to maintain a set volume, they draw higher amps. When used this way, they can continuously overheat and even burn out. Having said this, they still perform better than standard motors under real field conditions.
The bottom line is manufacturers and ARI (the Air-Conditioning and Refrigeration Institute) need to take a fresh look at how equipment is rated to better reflect field conditions.
How can we make this happen? The HVAC industry must take a stand and call for a reform of the current efficiency rating methods.
We also need to educate the Department of Energy, the Environmental Protection Agency, and other government agencies about the folly of increasing minimum SEER standards and the negative ramifications of such pursuits.
Using the car analogy, we need to teach these agencies to think of the equipment as the engine, the duct system as the transmission, and the registers and grilles as the wheels. Just as with a car, mileage can only be rated with all of these components working together. When's the last time someone measured a car's mileage with the engine running on a stand in a garage? Yet that's how our HVAC systems are rated today!
So why not focus on delivered BTUs through field measurement instead? This would take pressure off manufacturers to continuously try to defy the laws of physics by taking DX systems beyond their inherent limitations and point of diminishing returns. With that pressure off, they could focus on creating better equipment with more robust blowers that can handle true field conditions.
The energy penalty due to higher blower motor amp draw would be easily compensated for if we deliver correct airflow and the right amount of Btus to where they need to go. Make no mistake, this doesn't alleviate the contractor's responsibility to design and install air distribution systems properly -- it does, however, give well-installed systems a chance to actually work as intended.
By removing some of the delivered efficiency responsibility off the equipment, and sharing the burden with the delivery system, we could truly design and install systems that deliver the optimum balance of comfort, good IAQ, and real energy efficiency.
Dominick Guarino is chairman and CEO of National Comfort Institute, a national training, certification, and membership organization. He can be reached by phone at 800/633-7058, or by e-mail at [email protected]. For info on NCI, visit www.ncinstitute.com.
