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re: air changes per hour
10 jan 2004
 wrote:

>how can i estimate the rate of air exchange between an apartment
>and the outside ? 

a couple of weeks ago, i accidentally tried a tracer gas method, altho i
can't recommend it. i scooped a few pounds of what turned out to be mostly
live ashes out of a woodstove and put them into a galvanized bucket next to
the stove, then went to bed, and woke up at 2 am wondering what was on fire,
and noticed my $40 nighthawk co monitor said "22" (parts per million.)

i emptied the smouldering bucket outdoors and opened some windows, and the
reading decreased to 10, then eventually zero. osha says the max allowable
co concentration is 50 ppm over 8 hours, so a healthy adult with more
patience and fortitude might use an indoor charcoal fire to crank up the co
level to 50, then remove the fire and watch what happens over a few hours
with all the windows and doors closed. if it drops to 25 in 1 hour, that's
1 ach, and so on. with a few more calcs and measurements, we might do the
same with water vapor--raise the rh, then watch it fall. airtight houses
don't need humidifiers in wintertime.
 
>i understand that there is a blower door test that can provide some data

sure. low-income houses are often blower-door-tested when new or as a part
of weatherization programs. the house is pressurized and depressurized to
50 pascals with a blower and frame that fits into a doorway, and the flow
is measured with a calibrated venturi and pressure gauge. the natural air
leakage rate is about 1/20th of the 50 pa flow rate.

>i am willing to pay for such a test but the hvac company that the landlord
>contracts with seems rather unresponsive (the person they sent out to fix 
>the furnace and airconditioner did not seem to know what i was talking 
>about, or perhaps such work was not interesting to the company)

typical.

>the apartment (a townhouse with 3 exterior walls) seems very well 
>insulated and weatherstripped. it also seams well sealed against the
>next townhouse beside it

you might turn off the heat and run a window exhaust fan on a cold day
and use a cigarette or a damp hand to feel for air leaking in around
baseboards, window trim, holes in the walls for pipes and wires, electrical
outlets, and so on.

>i understand that dwellings in the usa average one air change an hour. 

sounds about right, with 0.2 or 0.3 for new "energy star" homes, vs 0.025
for new swedish houses. each cfm of air leakage adds about 1 to the house
conductance in btu/h-f, like a square foot of single-glazed window. ashrae
recommends 15 cfm per occupant, but most us houses are a lot leakier.

>is it possible to verify that indeed this apartment will average 
>one air change an hour with all windows and doors closed?

yes, altho reducing the overall heat loss might be more interesting. you 
ight estimate the overall heat loss (including air leaks) by maintaining
the house at a constant temp with an electric heater and measuring the
electrical energy needed to do this, along with the outdoor temp. 

>how can i locate a company that might do such work ?

you might look for low-income programs...

>as an aside: i have read these two newsgroups for two or three years
>and i just want to thank (most) of the posters here for many
>insights into the complexities of hvac

billing, politics, and so on :-)

>i know now 
>
>0)installation is everything
>1)so that means: pay for a professional
>
>its just the bit about finding a professional that i have trouble with

diogenes had similar problems.

nick




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