Letters: January/February 2007

January/February 2007
A version of this article appears in the January/February 2007 issue of Home Energy Magazine.
Click here to read more letters.

Inside and Outside SEER?

I have a home warranty policy and I purchased a rider to “upgrade my AC unit to a SEER-13 rated to comply with new Federal Guidelines.” The inside coil is defective, or so I have been informed by my home warranty company. They say that by replacing the coil, they can achieve the SEER-13 rating without replacing the 17-year-old outside unit. My impression of the federal mandate is that due to the age of the unit installed, they cannot. So I contend that they should replace both outside and inside components to achieve both the electrical and environmental standards. Am I mistaken?  

Tommy Bowden

via e-mail

Technical Editor Steve Greenberg responds: The SEER is a rating that includes a specific outdoor unit and a specific indoor coil. A SEER rating based on a new indoor coil and an old outdoor unit could in theory be obtained, and in theory a SEER-13 result is possible. Though the SEER is a strong function of the indoor coil, it is difficult to get a high-performance system (even in theory) with an older outdoor unit. An old outdoor unit is likely to have significant compressor and coil degradation as well, making the possibility of actually achieving a high SEER rather remote. Also, with new refrigerants (typically R410a) replacing R22, not only should the indoor coil be replaced along with the outdoor unit, but the refrigerant lines should be replaced as well, due to chemical compatibility issues.

Remember that while high-efficiency units have been around for a while, SEER-13 was only recently required, so there are relatively few of them out there. If someone claims that they can give you a SEER-13 unit by replacing the indoor coil only, make them prove it by showing you the documentation that shows the specific combination and performance, and/or by field-testing the unit’s performance.

Ceiling Fans

I recently purchased a Windward III ceiling fan and it is a great fan.  I have read some complaints online about trying to contact Gossamer Wind, Hampton Bay, and Home Depot about these fans, and I have been trying to find another one for myself, to no avail.  Hampton Bay has no Web site, Home Depot is a merry-go-round with no fan available, and Gossamer Wind is a one-pager-that-goes-nowhere Web site.

It really is a shame that the people who came up with this great fan can’t find anybody to sell it or sell parts for it. If you have any ideas about sales or service of these fans, it would be greatly appreciated!

Mark Harkrader
via e-mail

Danny Parker, one of the people who came up with the great fan, and a principal research scientist at the Florida Solar Energy Center, responds: First, thanks for your interest in the Gossamer Wind series of fans.

While I agree that Hampton Bay is not all that helpful, the Windward III is readily available from Home Depot as an online order. You can go to www.homedepot.com/prel80/HDUS/EN_US/jsearch/product.jsp?pn=100317614 to order it. I do understand that stocking policies are not uniform around the United States, so that might be the source of the problem you are experiencing.

We also have a Web site on the fans. May not be the best Web site on the planet, but we make an effort to produce something that is informational: www.gossamerwind.com.
Hope this helps.

Ceiling Fans II

I have been trying to find an answer to a simple question about ceiling fans and have been unable to do so.  I was hoping you could help.  What is the most efficient speed at which to run a typical ceiling fan?

At first blush, this would seem obvious—the lowest speed.  However, since I cannot find the method by which the fan speed is altered, it may be that the total power consumption is equivalent for low, medium, or high speed, even though the motor’s power requirement is reduced by the reduction in air flow.  For instance, if the speed is reduced through the use of an impedance, it may be that the energy used is simply shifted from conversion to air flow to a combination of conversion to air flow by the motor and heat by the impedance but is not (or not substantially) reduced.

Your site got close to answering this question with this article: www.homeenergy.org/consumerinfo/fans/index.php.  But even the graph provided at the bottom may be based, by the manufacturers, on motor power consumption.
If you can help, I would be most appreciative.

High Desert Fan

Home Energy’s ceiling fan expert Chris Calwell responds: Regarding your ceiling fan efficiency question, the answer is definitely the lowest speed.  The graph you mentioned from the article that is linked on the Do-It-Yourself section of the Home Energy Web site, “Getting the Most from Your Fan,” shows the input watts to the fan and fan controls (see Figure). You can see from the graph that for the fans listed, the lower speeds do use significantly less energy than the higher speeds.

The Home Energy article gives information that is a few years old. To see current lists of fan energy use at various speeds, go to the CFM per watt data posted on the Energy Star product list for ceiling fans:
www.energystar.gov/ia/products/prod_lists/ceiling_fans_only_prod_list.xls. The test procedure includes all AC power use of the products (motor and controls), and so accounts for any losses in the speed switch. The Energy Star data consistently show higher CFM per watt values for models operating at low speed than at any of the other speeds.

Danny Parker chimes in:
I agree with Chris. Low speed is definitely most efficient, and the advanced ceiling fans’ designs also show large differences in efficiency at these speeds. Given that the fans move more air at the lower speeds, my assumption has always been that they will typically operate at a lower speed than a conventional fan to produce equivalent air flow.

Is Insulating a Cool Roof Cool?

It is hard to know how the various elements in a roof/attic assembly will react with one another and the effect those interactions will have on home energy use. For example, I understand that when you insulate the roof deck of an unvented attic, it doesn’t make sense, from an energy efficiency and comfort standpoint, to invest in a cool roof. Since the benefit of a cool roof is reduced heat transfer to ducts in attics, the extra benefit of a cool roof is minimal with insulation in place at the roof deck. Is this correct?
Un-cool in Florida

Danny Parker responds: No, it is just the opposite. Cool roofs make the most difference with attic deck insulation and unvented attics. The delta T across the insulation is much increased with an unvented attic (185ºF vs. 85ºF to interior of attic = 100ºF delta T). With a vented attic, (140ºF attic to 75ºF interior) delta T = 65ºF. So cool roofs actually will have the greatest impact when the battle is all to be fought right under the roof.

Duct heat transfer is important, but it is affected by sizing and a host of factors (getting the attic heat balance correct). Simulating heat transfer in attics is complex. Our residential simulation, EnergyGauge USA, does a good job. Here is more than you want to know, but that’s what it takes to get it right: www.fsec.ucf.edu/bldg/pubs/techsupport_cec/indexhtm. The software can be downloaded for a 15-day free trial at: http://energygauge.com/usares/default.htm.

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