This article was originally published in the September/October 1999 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.


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Home Energy Magazine Online September/October 1999

Guarantee Gets Attention I enjoyed your article on Tucson Power Company's Energy Cost Guarantee program (Southwest Utility Offers Energy Cost Guarantee, Mar/Apr '99, p. 24). However, I do have some questions about it. First, the article didn't specify who estimates the guaranteed energy cost for heating and cooling, and how they do it. Do they run Elite software for each house?

Also, how do you identify the energy consumption for heating and cooling? Is an extra meter necessary? Finally, how do you check the thermostat setting?

Kaoru Kawamoto
Osaka Gas Company
Osaka, Japan

Author Christina Farnsworth responds:

Tucson Electric Power (TEP) uses Elite software on each house, and it is TEP that guarantees the dollar amount of utility usage for each house.

As stated in the article, TEP uses the months of April and November, when there is little need for either heating or cooling, to determine the home's baseline energy use for operating all electric devices except those used for heating and cooling. In this way, no extra meters are needed.

TEP relies on the homeowner's honesty rather than on any meters or monitoring of thermostat settings. This seems to be working, since so far TEP has had to pay back just a few dollars on utilities for only two homes. TEP reserves the right to install meters and monitor HVAC use should it feel that such measures are necessary. So far, it hasn't been necessary.

Star Status for Blower Doors? Is there an EPA or Energy Star approval or certification for blower door tests?

Jeff Beilen

Sam Rashkin, Energy Star Homes program manager, responds:

EPA does not have an Energy Star approval or certification for blower door tests. Rather than endorsing testing procedures, Energy Star programs focus on labeling highly efficient products (such as homes, appliances, equipment, lights, and so forth). The goal for the broad range of Energy Star programs administered by the U.S. Environmental Protection Agency and the U.S. Department of Energy is to establish Energy Star as the symbol for energy efficiency for easy consumer decision making. Note that blower door testing is largely addressed by the Home Energy Rating System (HERS) industry. Effectively, every HERS rater is trained and certified to provide blower door testing by an accredited state, regional, or national HERS provider.

Time's Arrow Pricks the Rule of Thumb I read your helpful magazine from cover to cover. In an issue from last year (May/June '98), which I had forgotten under a pile, in the article Taking Control of Energy Use, p. 23, there is a 3% rule of thumb about savings with set-back thermostats. I am not a technician, but I think that you cannot obtain a said saving for every degree Fahrenheit of setback without mention of another important factor--isn't time, or duration, missing in the article? To obtain 3% savings, the setback has to last for how long--eight hours?

Congratulations for your otherwise well-documented work.

André Dupuis, Editor
Inter-mécanique du bâtiment
Montreal, Quebec, Canada

Author Lori Marsh responds:

Unfortunately, the answer is not simple. The 3% savings for every degree Fahrenheit of setback is a rough estimate that assumes that the average temperature difference (between inside and outside the house), which the heating or cooling system must overcome over the entire heating or cooling season, is about 33°F. Therefore, each degree of setback, over the entire heating/cooling season, represents a reduction of about 3% of the total load. Obviously, the 3% rule will hold better for some climate zones than for others. It works pretty well in 4,000- to 5,000-heating-degree-day climates.


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