Letters: March/April 2008
A version of this article appears in the March/April 2008 issue of Home Energy Magazine.
I am an energy auditor, and have been using the Princeton House Doctor approach to instrumented auditing since 1981. We employ blower doors, infrared scanners, and combustion analyzers among other tools, to figure out where to improve a house for best comfort increase, best bill decrease, and best payback. By 1982 we had realized that it is not your windows and not your receptacles causing your bills and your comfort to go awry. The Building Performance Institute (BPI) standards have been great validation of what we have learned over the years.
Every five years or so there is a resurgence of interest in fixing houses, and there has been an endless parade of “improve your house” articles and news stories. Invariably I end up throwing a book at the television or writing a letter to an editor. I realize that there is limited time on TV or radio, and limited space in a newspaper, but we have to get across the message that all houses are different and virtually all houses have a couple of big problems that, if properly repaired, will truly pay back and truly increase comfort—you just have to find them.
On December 16, 2007, NBC did a short story that, after showing a picture of a blower door, talked about the added attic insulation without mentioning the air sealing that should have gone on first. It ended up by saying we should all caulk our windows and doors.
This current interest in energy improvements may well be the real deal, and if so, we will see many new faces in the business. We all need the exposure that all of us can provide. My wish would be that none of us allows anyone to film smoke going through a receptacle or around a window sash. Rather, we need to use the diagnostics tools to their potential and in the 30 seconds allotted, show that open kitchen soffit from the attic, that party wall gap that goes from the attic to the basement, that front-porch ceiling open to the interior through the missing band, that ventilated crawlspace allowing outside air straight into the return through the missing end cap. Come on, people—we have a responsibility here.
Energy Services Group
Solar No Solution
I live in rural Alaska, where the cost of fuel is close to $5 per gallon for stove oil. I am thinking of switching to electric heaters. Our house has a great southern exposure. Is there any small solar-power equipment that could power a 1,350W heater?
Staying Warm in Alaska
Technical Editor Steve Greenberg replies:
The short answer is no.
Here’s some detail and food for thought. Solar energy is diffuse (about 1,000 watts per square meter—a bit under 11 square feet—of area when that area is pointed directly at the sun in clear conditions), and the equipment to capture it is not very efficient—on the order of 10%-20%. So you’d need roughly 100 square feet just to power the heater when the sun is bright. You need lots of area and an expensive technology and are stuck with a poor match between solar availability and heating load. That is, there typically isn’t much sunshine when you need the most heat. When you think about it, that’s not a coincidence; it’s cold because there isn’t much sun. Given the last point, it may still be cost-effective to take advantage of the available sun. The most cost-effective way to use solar energy for heating is with passive design (ample areas of high solar gain, low heat-loss windows, south facing, with thermal mass inside to absorb the solar energy when it’s available for use later, when it’s not).
At $5 per gallon, that’s 28,000 Btu of heat per dollar; if your heating equipment is 80% efficient, that becomes about 22,000 useful Btu per dollar. That’s equivalent to $0.16/kWh of electricity, so if your electricity (are you on the grid?) is cheaper than that, you’d be better off with the electric heater. Another option is wind. There are folks who use wind turbines directly tied to electric heaters; the more the wind blows, the more heat you get.
Obviously, with high heating-fuel prices, weatherizing your home is a very smart thing to do. For ideas, contact your local utility or weatherization agency or see the Home Energy Saver Web site at http://hes.lbl.gov.
Programmable Thermostats and Moisture
Some thoughts came to me after I read “Saving Energy Star Thermostats” (Jan/Feb ’08, p. 17).
I agree with your statement “the easiest-to-use thermostat is worthless in the hands of someone who doesn’t care to use it to save energy.” In addition, the easiest-to-use thermostats also require an operator with the smarts to program them and an operator with visual acuity and decent illumination to calibrate them—so much for a thermostat programmer job description.
I submit the attached Humidity Table (see Table) to indicate that in cold weather heating climates using zoned heating (with or without programmable thermostats) or manually lowering the temperature in a building or a section of a building can cause water activity, condensation, and subsequent mold development in the coolest areas of the building. “Contrary to popular belief, surface condensation is not necessary for fungal defacement. Water activity above a threshold value suffices for mold growth” (Hens, H.L.S.C.P.D. “Mold in Dwellings—A Building Physics Related Approach,” 9th International Conference on Indoor Quality and Climate. 2002. Monterey, California).
When relative humidity is high, temperature fluctuations may cause water activity, condensation, or mold growth. Water activity and condensation occur because air is holding all the water vapor it can in these cooler areas of the building where the temperature has been lowered. This water activity is a significant problem in North America where mold and asthma are major public health issues. The question arises as to the potential cost benefit ratio of energy savings versus medical costs using programmable thermostats. Water activity also raises the point about the value of these thermostats for heating versus cooling purposes.
Energy Star certification to endorse programmable thermostats for heating energy savings may be dubious at best. But in any case, review for certification of thermostats should consider the whole story, including heating, cooling, socio-economic, and public health factors. On the other hand, as a public health issue and in light of the possibility of mold developing in cool areas of buildings, there could be an argument made for having zoned heating with thermostats in various areas of a building synchronized at the same temperature to ensure minimizing temperature differences while decreasing the possibility of water activity.
When I consider the use of programmable thermostats in cold climates I think, Mold? Of course! I do not know if there is a big problem but if there is, part of it is easy to fix. An increase in the lower set point to above the dew point solves the water activity problem. On the other hand, a change in the occupants’ attitude, after spending money for the thermostat and expecting great returns on the investment, may be difficult to accomplish. From my experience change involves discussion, education, and often an explanation of the Humidity Table. And home performance professionals need to recognize that programmable thermostats are one of many factors that may be the cause for condensation.
Kevin M. Kelly
New Hartford, New York
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