re: infiltation measurements?
18 dec 2000
>how does one measure infiltration and are there any measurement devices?
the most popular way is a blower door test. someone attaches a blower
and calibrated venturi and sensitive manometer to measure airflow in cfm
while the blower creates a particular indoor-outdoor pressure difference,
eg 50 pascals. natural infiltration is about 20x less in the winter, and
there may be no airflow on a still spring or fall day with equal indoor
and outdoor temperatures. one approach to providing adequate ventilation
on those days is to make the house airtight and use and use an exhaust
fan in series with a humidistat. airtight houses tend to build humidity
one example: if a house that leaks 300 cfm at 50 pa has a natural air
infiltration rate of about 15 cfm. the ashrae standard for ventilation
is 15 cfm per occupant. infiltration is often reported in air changes
per hour (ach), ie house air volumes per hour. for instance, a 1 story
2000 ft^2 house with 0.2 ach has 0.2x8'x2000 = 3200 ft^3 per hour (53 cfm)
of air leaks. it's hard to make a house much tighter than 0.2 ach.