Letters: January/February 2008

January/February 2008
A version of this article appears in the January/February 2008 issue of Home Energy Magazine.
Click here to read more letters.
Multifamily Questions

The article on pressure testing multifamily buildings (“Measuring Leakage in Multifamily Buildings,” HE Sept/Oct ’07, p. 34) is quite a fine article, but it raises some important issues for me.

Multifamily buildings fall under two U.S. Green Building Council (USGBC) Leadership in Energy and Environmental Design (LEED) programs—LEED 2.2 and LEED Homes. There are airtightness requirements in each. They are completely different in design, application, intent, and effect. LEED Homes requires air sealing and testing the thermal enclosure of the whole building; LEED 2.2 requires air sealing and testing each unit to limit tobacco smoke transfer. Oddly, in an exhaust-ventilated, greater-than-two-story multifamily building in a cold climate, sealing each unit is more important for ventilation and thermal performance than air sealing the enclosure. Unfortunately, the article does not mention either LEED program by name (except in Bud’s sidebar). I believe this is confusing. In addition, neither LEED program refers to the other nor do they separate themselves by scope (for example, ASHRAE 62.1 covers multifamily buildings greater than three stories in height, while ASHRAE 62.2 covers three stories or less). I have alerted folks at the USGBC about this issue.

A technical issue. As is drawn in a figure in the article showing pressure tests of a single floor by a guarded fan door method, no mention is made of air leaks that may bypass the guard floors through shafts, stairwells, chases, and so on (see Figure 1). Sometimes these air leaks are quite important. I realize the argument can be made that this is a conservative test—if it passes with these leaks included, then the floor is tighter than we thought. Kind of a bummer if you fail by a little and it’s the bypasses, though. This method also assumes that all floors have equal leakage characteristics, which may or may not be a good assumption.

Last, a smaller item. I have not had the pleasure of using a Retrotech door since the one I had in the early 1980s. The article mentions that the controller subtracts room pressure from flow pressure when pressurizing. This works if channel A is measuring the change in pressure across the fan and if that is equal to the change in pressure across the building. Using multiple doors in multifamily buildings, that may not be the case. In the example in the body of the article, the doors are set up so they would be depressurizing the stairwell in order to pressurize the units.  If channel A is measuring across the nozzle it may not be the same as across the enclosure—the stairwell may be depressurized by the blower doors.

Pressure testing larger buildings is not the same as pressure testing smaller buildings. There are far more ways for things to go wrong. Hopefully I’ve made them all at this point.
Terry Brennan
Camroden Associates
Westmoreland, New York

Author Colin Genge replies:
Terry raises several good points that should be of interest to readers, and I will see if I can get them all covered. I appreciate Terry’s input, since he played a large part in developing the LEED standards for multifamily buildings.

High-rise buildings must have 1.25 square inches of effective leakage area measured at 4 Pa from multipoint blower door tests under LEED 2.2. This is primarily for controlling odors, smoke, and so on from other apartments.  There is currently no requirement for exterior envelope tightness measurement as there is in the low-rise residential standard, but there is movement in that direction. We both agree that it certainly makes sense to test the envelope from the standpoint of overall energy efficiency and the control of smoke, noise, moisture, and even vermin. These are all expensive problems to correct once a building is occupied, but inexpensive to control during construction. Terry points out that some buildings are impossible to seal after or even during construction because of designs that should have been reviewed prior to construction. Careful training of those responsible for air sealing and air leakage testing of floors as they are constructed is necessary to control costs. Construction costs for a noticeably superior building may differ very little, as long as the correct techniques are implemented from the start. Just handing the task to the construction crew will not work; experience and use of the correct materials and techniques are mandatory in getting the work done correctly.

I agree that bypasses will increase the apparent leakage of an individual floor, making it appear as if the floor leaked slightly more to outdoors than it does. However, bypasses should not leak enough to make a huge difference, and if they do, they should be sealed. Measuring pressure differences between the test zones and shafts or floors outside the guarded floors can help determine whether bypass leaks are important or not.

I agree that pressures in the stairwell will make the floor appear slightly tighter. Interestingly, this effect is somewhat balanced off by the bypasses. I have discovered that many of these effects counteract each other. As a rule of thumb, an open double door will relieve the flow from one high-powered fan. The worst case would be two man doors to relieve three high-powered fans, which would cause the leakage across the stairwell wall to be undermeasured by 16%. Not impossible to live with, considering that the stairwell wall probably consists of 5% of the total wall area to outdoors on that particular floor, netting an error of about 1%.

We are still learning about the best testing techniques for multifan testing. We have tried more detailed analysis, including computer monitoring of many of the variables involved, and have discovered that the technique described in my article, though simplified, is fairly robust. Our interest is to develop a methodology that is as fast and as simple as possible, so that it can gain wide acceptance in the field while maintaining good repeatability and still represent the building shell fairly. Our method quickly identifies leaky problematic building envelopes, which is our end goal. I encourage others like Terry to interact with us.

 Sustainable Art

Miranda Bergman and Susie Lundy used a familiar building material, Tyvek House Wrap, to make a statement about the importance of art. The mural was painted on site at the Oakland Museum on the occasion of the first Oakland Youth Arts Festival in June 2007.  The creators of the house wrap made it suitable for uses such as this—beautiful and meaningful art that can withstand the California coastal weather. Good thinking all around.

—The Editors

Refrigerator Myth or Fact?

Does a full refrigerator use more energy than an almost empty one?

Chilling in Memphis

Technical Editor Steve Greenberg responds:
If the door is never opened, there will be little or no difference in energy use between an empty and a full refrigerator. A full refrigerator reduces energy use from door openings because less cold air is in the refrigerator to spill out and get replaced by warm room air that then needs to be cooled down by the compressor. Also, the greater the mass of the items, the fewer the cycles of the compressor, increasing refrigeration cycle efficiency. On the other hand, the more items in the refrigerator, the more often the door may have to be opened. Also, if the refrigerator is kept full of items
that are rotated through, and thus need to be cooled down each time they’re put in, that could add to the energy use.
But generally speaking, a fuller refrigerator will use less energy.

Thinking About Next Summer

I own a double-wide mobile home and have contracted with Sears to install a new Kenmore air conditioning unit. I understand the refrigerant Freon is being phased out and replaced by Puron. However, I was told that mobile homes are not equipped to take the Puron, and therefore the refrigerant being used is Freon. Can you tell me, please, if the mobile homes are in fact not equipped for the newer refrigerant?
 I was told that in three years the Freon will be completely phased out and that it may be necessary at that time to switch to the Furon. Can you give me any information about this so that I can make an intelligent decision? Thanks so much.

Maria Piccione
via e-mail

Steve Greenberg responds:
Freon and Puron are trademarks for refrigerants. Freon refers generically to chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerants, which are in fact being phased out (CFCs already have been). Typically, residential air conditioners and heat pumps have used HCFC-22, also known as R-22 and Freon-22. No new R-22 units will be available after 2010, but the refrigerant will still be available to service them (see www.epa.gov/ozone/title6/phaseout/22phaseout.html).

There are a variety of substitute refrigerants, including Puron, which is a Carrier trademark for R-410A. I’m not sure about the claims relative to mobile homes; I don’t know why they’d be different. Maybe the indoor units designed for R-410A aren’t readily available for mobile homes yet. If you are trying to reuse the indoor coil, there is a difference between those designed for R-22 and those designed for R-410A (and also for different efficiency ratings); perhaps this is the incompatibility being referred to.


The volume number of the Nov/Dec ’07 Home Energy at the bottom of p. 1 should be 24.6 and not 25.6. We may have wanted to begin celebrating our 25th year of publishing a little early! Thanks to the hawk-eyed librarian who told us of the mistake.
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