Letters: September/October 2006

September/October 2006
A version of this article appears in the September/October 2006 issue of Home Energy Magazine.
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Defending the Big Fridge

        I am writing in response to the recent “Milk, Melons, and Smaller Refrigerators” editorial (Jan/Feb ’06, p. 2). I am not technically oriented, although I’m learning. I do try to keep my refrigeration, as well as other energy use, down. I try not to needlessly keep the refrigerator door open and have gotten a low-energy-use refrigerator. The interior space is less than I had before.There are real practical problems, however. I ended up keeping my old one and using it also most of the year.
        I only have a household of two, but my spouse and I like to cook, especially holiday dinners; those dinners require a much bigger storage space than my smaller refrigerator could hold—both before and after, for keeping leftovers. Although I have only two people in my household, fresh vegetables, salad greens, fruit, dairy products, and bread take most of the space, and previously opened containers of beverages like juice and soda as well as milk take up a good deal more space. Previously cooked foods, and other small jars of jams, mustards, and medicines take up the rest.The freezer, which is also inadequate on the new refrigerator, is needed for previously cooked or salepriced larger-quantity purchases.
        Smaller melons are no solution (especially if one needs to have a larger one). Milk storage is just one pretty minor item if you consider everything else that goes into the average refrigerator. If one needs more food on hand for guests, for oncoming bad weather, for budgetary reasons, or to take advantage of seasonal produce, sorry, but my experience indicates techno solutions just don’t hack it if they don’t consider real space needs.


Technical Editor Steve Greenberg replies:

        One should carefully assess what one’s requirements are for any appliance before seeking to replace it. Was the old refrigerator big enough by itself? In any case, the new refrigerator should have been selected to meet the size requirement. Other variables include number of doors, freezer location, and so on. Remember that there is a range of efficiency available in every size range, so one need not choose between efficiency and size. Of course, all other things being equal, a smaller refrigerator will use less energy, but other things are frequently not equal, with the result that there’s a big overlap in energy use between sizes. For example, refrigerator freezers in the 16.5–18.4 ft3 size category that meet Energy Star efficiency requirements range from 335 to 522 kWh per year, and units in the 20.5–22.4 ft3 category (two size categories larger) range from 417 to 584 kWh per year. Thus you could easily find a smaller new unit that uses more energy than a larger one. Note also that these are just units that meet the Energy Star requirements; there is an even larger range of efficiencies available for purchase. See www.energystar.gov/ index.cfm?c=refrig.pr_refrigerators for details on how this works.
        If one has special intermittent refrigeration needs, two units might make sense to minimize energy use, if they are carefully selected and used. So what are the options for minimizing refrigeration energy use, given the stated situation? The right decision would depend on how much space you need for how much of the year, and how willing you are to invest in another unit:
        Use the old (second) refrigerator as little as possible, unplugging it and propping the door open when it is empty. If you use the old unit just a few weeks per year, this may meet your temporary storage needs with minimal energy use.
        If, as you say in your letter, you use the old unit most of the year, the most energy-saving strategy is probably to sell the new refrigerator and buy a single new one sufficiently large to meet your requirements; recycle the old refrigerator.
        If there is a well-defined period of a few weeks a year when you need excess capacity, you might buy a new refrigerator sized to meet your requirements the rest of the year. The existing new unit could be used as the buffer, and the old refrigerator could be recycled.
        Hope this helps!

Applying Ventilation Standards

        Your article “Ventilating Small Chicago Homes” (Jan/Feb ’06, p. 24) was interesting, but I noticed a problem related to the project’s attempt to apply the new ASHRAE residential ventilation Standard 62.2–2004. It’s important to realize that the new standard assumes a significant portion of the recommended minimum ventilation rate of 0.35 ACH is provided by infiltration. Specifically, Standard 62.2 assumes that homes receive 2 CFM of infiltration for every 100 ft2 of floor space. Regardless of house size, that amounts to about 0.15 ACH, or 40% of 0.35 ACH.
         This assumption regarding airtightness might be valid for typical new construction (on an annual basis), but the homes in this project measured 300- 350 CFM50, which is extremely tight. I’m concerned that conscientious builders who “do the right thing” by making homes as tight as possible and installing a ventilation fan sized according to Standard 62.2 will end up producing homes that are significantly underventilated with respect to 0.35 ACH.If, as the subtitle says, the builders are “especially concerned with providing adequate ventilation and good indoor air quality,” a better way to size ventilation fans in such tight homes would be to size the ventilation fan(s) to deliver 0.35 ACH (a very simple calculation); verify the air flow at installation; and operate the fan continuously. That way the house always receives at least 0.35 ACH and any infiltration is supplemental. On this project, simply operating the 80 CFM fan(s) continuously instead of 75% of the time would ensure a minimum ventilation rate of about 0.35 ACH (given 1,700 ft2 of conditioned floor area).


Lawrence Berkeley National Laboratory Building Scientist Max Sherman replies:

        ASHRAE Standard 62.2 does not set any requirements for the total ventilation rate. It sets minimum requirements for the mechanical ventilation rate.
        Under some circumstances, that value can be lowered if the infiltration is above the default rate, but that is not the same as saying the standard requires that the total be the sum of the mechanical requirement and the default infiltration.
        The total ventilation rate is a combination of the infiltration and the mechanical system, but it depends strongly on whether the mechanical system is balanced (for example, a heat recovery ventilator) or unbalanced (for example, an exhaust fan). The latter results in a total ventilation rate that is less than the sum of the infiltration and the mechanical ventilation rates.
        So one meets 62.2 without upsizing the mechanical ventilation in tight houses, but a conservative design might recognize that there will be less infiltration and might compensate for that fact. On the other hand, there are a variety of other things to consider and compensate for. Does the house have more or fewer sources than the typical house? Does it have better or worse air distribution than the typical house? Does the house have balanced or unbalanced mechanical ventilation?
        Consideration of all these issues could lead to the conclusion that the ventilation rate should actually be lowered. I would not recommend lowering it below 62.2 because of uncertainties in infiltration rates, for example, and concerns about liability for inadequate ventilation, but the mere fact that the envelope is higher performance should not automatically lead to the conclusion that more air is needed.

Author Robb Hammond puts in a word:
        I agree with Mr. Sherman that the proper mechanical ventilation rate depends on many variables, and I would submit that this proper rate is quite subjective. The goal of the study described in this article was to evaluate three homes with three systems complying with ASHRAE 62.2 minimum requirements. I believe 62.2 offers a much-needed baseline for builders and designers; certainly designers, builders, and homeowners are able to increase (or even decrease) ventilation as desired. It’s ideal for ventilation systems to have adjustable flow rates or schedules to accommodate such building and occupant variables.

More on Ventilation

        In the article “Quiet and Efficient Vent Fans” (Mar/Apr ’06, p. 14), the first paragraph states, “While HVI [Home Ventilating Institute] recommends that bathroom exhaust fans run for 20 minutes after each bathroom use, these fans are often not used as intended...” Here in western Pennsylvania, in winter my average indoor humidity level is 27% if I don’t add humidity to the air.That is too low to be comfortable or to be any good for my furniture and hardwood floors.We always run the exhaust fan in the bathroom during bathing, and in the summer we leave it on a good bit longer to get out as much humidity as possible. However, in the winter I like to turn the fan off when we leave the bathroom in the morning to allow whatever humidity is left from showering to waft out into the hallway.
        I had just gotten my husband winter trained when this article turned up. Now he wants to do what he does all summer in the winter and leave the fool thing on for half an hour or more till he’s done with breakfast. In the winter I think that is a waste of electricity and humidity both.
        I’m sure that the HVI’s recommendation is quite valid for summer or in the southeastern part of the country, but I doubt that it is appropriate to the Northeast in winter.There’s not going to be much peace in this household till we get some clarification here.


Author David Shiller replies:
        HVI recommends that the fan be left on for 20 minutes after use of the bathroom. Energy Star does not recommend reducing necessary ventilation as a means of saving energy even in winter. Rather, we recommend using Energy Star-qualified vent fans to achieve recommended ventilation using less energy.
        HVI describes the risks associated with insufficient ventilation. “According to research, proper ventilation produces greater IAQ—Indoor Air Quality—to protect people from unhealthy indoor pollutants and buildings from excess moisture and heat, ultimately aiding in the control of all contaminants including moisture and mold.”

Steve Greenberg offers another opinion:

        A reasonable interpretation of the reasoning behind the HVI recommendation is to reduce the amount of unwanted moisture in the home. When the moisture is wanted (indeed, where it would need to be added by a humidifier in order to get the humidity up to a reasonable level), then less fan operation would be appropriate.
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