Letters: July/August 2006

July/August 2006
A version of this article appears in the July/August 2006 issue of Home Energy Magazine.
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Refrigerator Habits

        I read your Jan/Feb ’06 editorial (“Milk, Melons, and Smaller Refrigerators,” p. 2) about refrigerators and agree with your sentiments that most people could probably get by with smaller refrigerators. Although people could buy smaller portions of things, in America it always seems that bigger is better, as well as cheaper.
        I have visited Europe many times and always like to visit the local grocery stores. I see the major difference between the American and European stores is the size of the portions. Pricing in America is always biased toward selling larger quantities of items.Take a stroll through any Costco, BJ’s,Wal- Mart, and other superstore and you will see frozen and refrigerated food sold in quantities unheard of in Europe. From a consumer standpoint, it is more cost-effective to purchase a large refrigerator (or multiple refrigerators) to take advantage of these quantity savings; they will vastly outweigh the incremental electricity bills.
        The key to successful energy-saving products is to give consumers what they want (that is, larger refrigerators), and use technology to deliver it.As you mention, refrigerator manufacturers have an enviable track record in delivering better energy efficiency.There are still major advances to be made using such things as variable-speed compressors, variable-speed fans, better insulation, and so on.As an example,we have pioneered the concept of a hybrid refrigerator to reduce power consumption in large refrigerators by 50% or more just by circulating cold air from outside during cold winter months.



Ceiling Fan
Choices

        In the letters section of your Mar/Apr ’06 issue (“Not a Fan of Fans During Heating Season,” p. 3), Norman Bair noted,“We had a recommendation ... for people to use their ceiling fans at home to save natural gas for heating. I challenged this and had it removed. Unfortunately, I have not found very much more than the article I mentioned above regarding the use of ceiling fans during the heating season to defend my skepticism. Can you help?”
        Providing empirical evidence for energy savings—or not—for a strategy that primarily impacts comfort and occupant interaction with its systems is difficult at best. Examining the situation on the basis of first principles—and one’s own personal experience— however, can provide valuable insight.
        I noted my personal reaction to ceiling fans back in the ’70s while sitting in an atrium restaurant in mid- December. The combination of the cold glass surfaces and the cooling capacity of moving air from overhead fans designed to bring warmth down from the ceiling provided a decidedly uncomfortable environment, despite moderate room air temperatures. The normal impact of such conditions is, of course, to drive the occupant to turn up the thermostat in order to achieve comfort conditions by compensating for the low mean radiant temperature and the wind chill effects. It may be hard to quantify, but in almost any but the most extreme conditions, the resulting increase in air temperature is more likely to exacerbate whole-house heat loss than “recovering”warmth that may have stratified at the ceiling (and thus improving the mean radiant temperature of the space).
        I doubt if I was the first to note this phenomenon, but I did raise the issue in a letter to the editor in an early issue of Energy Design Update. Coincidence or not, it was only a few years later that manufacturers began offering ceiling fans with reversible-flow switches, supposedly to direct the air flow away from building inhabitants—but still drawing cooler air upward through the central occupied spaces.
        This change in operational strategy has an additional liability. A basic assumption of ASHRAE heat loss calculations is that part of the overall R-value of a building section is the still-air surface dynamics on the interior of our homes. For this we typically ascribe an R-0.68, compared to an exterior air film R-value of 0.17, on the assumption that there is a 15 mph wind blowing on the exterior of the home but interior air is still. This may not seem like a major difference, unless one considers that for, say, a typical double-glazed window, this R-0.68 amounts to almost 35% of the overall R-value of the cross-section (R-1.95).
        If the interior air film were reduced to that of an exterior surface by matching that air flow impact, the overall R-value for the window would be reduced from 1.95 to 1.44 or over 25%. (U-value changes from 0.69 to 0.51 for a nearly 35% increase in energy loss.) Here in Wisconsin, this amounts to a seasonal energy increase of nearly 1/3 therm for each ft2 of glass exposed to the moving air.
        All of this theory notwithstanding, in a large religious sanctuary with a cathedral ceiling (as it were), filled with occupants all of whom are adding heat to the space, I might advise the building operators to try a warm-air destratification strategy—but to note carefully the impact on comfort with the fans both on and off under similar conditions. Being in tune with our own thermal comfort sensations may well be our most powerful diagnostic tool.

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