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Letters: November/December 2010

November/December 2010
This article originally appeared in the November/December 2010 issue of Home Energy Magazine.
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Factor 9 Home Not a Lab Experiment

My family and I built and live in the Factor 9 home you covered in your last issue (see “Monitoring Results for the Factor 9 Home,” HE Sept/Oct ’10, p. 40).

The author, Rob Dumont, points out that we’ve done some things differently, such as using more expensive materials. We chose shingles that are rated to last for 45 years rather than the standard 15- or 20-year shingles that most builders use because I only want to do this once. I would have bought shingles good for the lifetime of the house but they were not available at the time. I chose to use deep piles when I designed the home to keep the house from shifting in our clay soils, but I also wanted to use them for cooling—against the recommendations of the Saskatchewan Research Council (SRC). The deep piles proved to provide several tons of cooling. 

The initial cost of the house may be slightly more than if we had used cheaper alternates, but in the long run the house is actually cheaper if you factor in that many five-year-old homes in the neighborhood now need to have $40,000 plus of remedial work done due to the homes shifting. One of our neighbors could not close several doors because the frames in their home had shifted by well over an inch after two years. 

If you consider quality, the old saying still holds true: “You get what you pay for.” I chose to use structural insulated panels (SIPs) over other options since using SIPs was the most cost-effective way for me to build walls with high R-value without the walls appearing to have high R-value. If you believe in being energy efficient I can likely sell you a home that looks different. But if I want to reach the masses, it needs to look “normal” or attractive to those who are not so inclined. I believe a research home does not need to look like a lab experiment!  

Rolf Holzkaemper
Regina, Saskatchewan, Canada

Attic Fans and Insulation

I live in Florida. The house was built in 1958 but has a four-year-old light-gray-colored asphalt shingle roof with a ridge vent and soffit vents. My central air ducts are older but insulated and run inside of the attic. There are about 3–4 inches of blown-in attic insulation. Would an electric or solar-powered attic fan be very effective to help reduce cooling costs?

Phil Beck
Tampa, Florida

Danny Parker, senior scientist at the Florida Solar Energy Center, replies:

The bad news: Adding an AC-powered attic vent fan will use more electricity than it will save (they draw 300–400 watts, which is much higher than what will be saved in air conditioning). So as popular is this is, it is a losing proposition from an energy standpoint.


On the other hand, a couple of solar-powered attic vent fans will probably reduce your cooling energy use by about 5% to 6%. See the experiment we did on precisely this question at www.fsec.ucf.edu/en/publications/html/FSEC-GP-171-00/.

Two PV fans will likely cost about $1,200, and more to have them installed.

A better option is this: Only 3 or 4 inches of insulation is a substandard R-11 in your attic. Blow in another 6 inches of insulation in the attic to bring the ceiling insulation level up to R-30. The cost to do this should be about $600 or less, depending on house size, and some of the ducts may end up being partially buried—a good thing.


Simulating this with EnergyGauge USA for Tampa with a heat pump showed the following results for a typical existing home (Table 1):
 

Energy Savings from Insulation

That’s an 11% reduction in heating and cooling (941 kWh), worth $122 at $0.13/kWh. Twice the savings of solar attic vent fans at half the price!
Hope that helps!

 

 

Tankless Hot-Water Question

I use a Rinnai tankless water heater (model V2532FFU), which works well most of the time, but I have a couple of problems. We keep the temperature set at 116°F to 120°F, which provides the hot water we need except when filling a bathtub.

The tub faucet will accommodate 6 gallons per minute (gpm) flow but works fine with 3 gpm flow. When running hot water from the Rinnai water heater, the flow drops to a trickle. Our plumber measured the flow at about 1.3 gpm. By reducing the water temperature, the flow increases as it should according to Rinnai specifications, and the tub fills fine except the temperature is too cool.

The second problem is the so-called sandwich effect, characteristic of tankless heaters, wherein hot water is followed by cold if the hot water is turned off for a minute or so. Rinnai says the best way to eliminate the sandwich effect is to put a small water heater (electric) in series with the tankless heater that will serve as a buffer. My plumber says that won’t work, but hasn’t given me a reason.

I wonder if the small water heater might not solve both problems. If the Rinnai water temperature is set between 96°F and 100°F, the flow is fine. If the small heater is set for 118°F to 120°F, we would get the temperature desired. This should also eliminate the sandwich effect. It seems that if the small electric heater is being fed water at 100°F, it shouldn’t have to work too hard to boost it to 120°F. If use exceeded the storage of the small tank, the hot water should still be at 100°F. Is there something I am missing? 

Bill Rupp
Asheville, North Carolina

Here is a response from one of our water heater experts, Jim Lutz, scientist at Lawrence Berkeley National Laboratory:

Many of the tankless water heaters, Rinnai included, can modulate the water flow through them. They will turn down the water flow if they can’t provide enough heat to deliver water at the set temperature. That’s what’s happening when you try to fill the tub.

It takes nearly 150 watts to heat 1 gpm of water 1°F. Three gpm of water raised 20°F will take nearly 9 kW. That might be why your plumber doesn’t think it would work. If he installs a small electric tank heater, then he’ll have the standby losses on that heater. That sort of defeats the benefit of the tankless heater.

Evap Cooler Help

I just read the article “Installing and Maintaining Evaporative Coolers” (HE May/June ’96, p. 23) online, and it completely saved my sanity! This year, up until I read the article, my evaporative cooler, in Las Vegas, Nevada, was keeping my house at 83°F to 84°F, which was a bit unpleasant, since it had been keeping it at a nice 74°F without problems before! This is only its second season. I Googled “evap cooler problems” and your article came up. I read the whole thing and set to work on taking mine apart to look for problems. I found quite a bit of mineral deposits at the bottom catchment pan and on the top of the pads. I spent maybe one and a half to two hours detailing the inside and the pads so that now they look almost brand new! I also cleaned out the sump pump and around the water intake. After I put the unit back together and turned it on, discharged air into the house is reading 70.6°F.

Figure 1.

Thank you for this wonderful article! Now I don’t have to sweat inside and I didn’t have to pay someone to come out to fix it! I’m so happy I could cry! I’ll just enjoy my 75°F with a cold brew instead.

Mary Cristina Berta
Las Vegas, Nevada

 

Errata

The author of the “New and Notable” item on p. 62 of the HE Sept/Oct issue, “DOE Program Takes on Market for Highly Efficient Windows,” is Walter Zalis, not Walter Zalas.

The page numbers of two articles on the “Table of Contents” page of the HE July/Aug issue, “The Case for Accreditation” and “Time-of-Sale Energy Labeling of Homes: A Concept,” were inadvertently reversed. Also, the author of the article “The Case for Accreditation,” Matt Golden, is a member of the BPI board of directors. Since BPI was a focus of the article, Golden’s affiliation should have been mentioned.

The editors regret the errors. They also made sure that a letter praising the magazine immediately preceded the “Errata” section.

 
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