Homeowner’s Energy Workbook – Part 6 (Definitions)


Stack effect on a Fireplace

Infiltration and ex-filtration relate to convective air movement.  Infiltration is uncontrolled air leaking in and ex-filtration, logically, is uncontrolled air leaking out.  How and where it leaks in has a lot to do with the pressures in the house.  (Remember, high pressure moves to low pressure.)  If the pressure is higher in the house than it is outside, air will move out of the house.  Warm air is lighter than cool air so it rises, increasing the pressure at the top of the house due to the Stack Effect when it is warmer in the house than it is outside.  The top floor ceiling of a house can have an enormous amount of pressure pushing on it, pushing air through any crack or hole or gap it can find.

A wise building science guy, John Tooley, once said, “Air is like crooked rivers, crooked people, teenagers and cheap labor.  It always seeks the path of least resistance!”  He also said, “Air doesn’t care where you want it to go.  It will always move through the closest and biggest hole.”

We have to have ways to measure things like pressure and temperature and airflow.  We measure temperature with a thermometer.  In the U.S. we measure it in degrees Fahrenheit named after Daniel Gabriel Fahrenheit in 1724.  Most of the rest of the world adopted the Celsius scale (after Anders Celsius) in the mid to late 20th Century.  The Fahrenheit scale has water freezing at 32 °F and boiling at 212 °F.  On the Celsius scale, water freezes at 0 °C and boils at 100 °C.  Seems a bit more logical somehow, but there we are.  We don’t deal with change well.

The pressure in buildings is commonly measured in Pascals, because houses have gotten so tight and the pressures are so small that using the inches of water gauge or iwg or inches of water column scale was too gross.  It would be like measuring a house in fractions of a mile!  Inches of water gauge is an indication of how far a certain amount of pressure can raise a column of water.  Iwg is the most common measurement for indicating pressures in heating and cooling systems and the operation of fans.  One iwg is equal to about 250 Pascals.  The important thing to remember here is to visualize how small a Pascal is.  It’s really, really small.  If we could measure a gnat’s burp, it would be about that small.  It’s a tiny amount of pressure, but it can make an enormous difference in how a building works and the health of the occupants.  We measure pressure using a manometer.  These days it’s common to use an electronic, digital manometer, but there are analog manometers as well.  The availability of digital manometers probably has done more for the advancement of building science than any other tool.  It has allowed us to measure very small pressure differences.  It has ushered us into the world of CSI for homes.

Testo 417

Large Van Anemometer

Airflow speed is measured in feet per minute (fpm), like miles per hour.  FPM is the velocity of the airflow.  The volume of air movement is measured in cubic feet per minute (cfm).  The volume of air moving through a duct or fan is indicative of a rate of heating or cooling.  Airflow is commonly measured with anemometers which come in a wide variety of styles.  There are large vane anemometers and mini-vane anemometers and hot wire anemometers.  There is a tool called a Balometer which is commonly used to measure airflows in commercial applications.  Airflow can be measured with a garbage bag or a bathroom tissue, but the numbers are not easily repeatable with these approaches.  Airflow can be measured using a manometer as well, by using the difference in pressure across a known sized hole.

You should also be aware of some of the nasty elements that can be found in homes.  Carbon monoxide (CO), for example, can kill people.  It results from incomplete combustion.  If the flue gases don’t flow up the chimney the way they are supposed to, they can “spill” down into the house and make the occupants sick, exhibiting symptoms similar to the flu.  More about CO later.

Radon is a gas that emanates from granite in the ground.  Radon can leak into the house as a gas, and rapidly decay into particulates that can get lodged in the occupants’ lungs.  It can also be found in water.  It is much worse for smokers to breathe radon gases than non-smokers, but that is true of many things!  Certainly not every house has radon issues, and it can be tested and it can be reduced to acceptable levels.  And just because your neighbors’ house has a radon problem it doesn’t mean that yours does.

Humidity is another significant pollutant for a wide variety of reasons.  Relative Humidity (RH) is indicative of the amount of moisture a volume of air can hold at a certain temperature.  Warmer air can hold more moisture than cooler air.  As the temperature of the air rises, its RH goes down.  That’s why cold winter air drawn into a house makes the air in the house drier.  Cold air in a closet has higher relative humidity and mold grows on the cooler surfaces.  RH is not the easiest thing to visualize, but we can certainly feel it.  “It’s not the heat.  It’s the humidity!”  The dew point is the temperature of a surface that will cause moisture to condense.  As the dew point rises in warm weather, our discomfort increases.  When the dew point is only a few degrees below the outside temperature, it is almost hard to breathe.  It is interesting to note that there are microclimates all around us.  The air around a glass of ice water can be cooler and at the dew point and moisture droplets form on the sides of the glass.  This is similar to the microclimate convective loops in insulation gaps and on the surface of walls.  All this stuff is going on around you.  Right now!  And you thought things were just sitting there!

Just to be consistent, we measure relative humidity with a device called a hygrometer.  A humidistat is a control that turns something on when the humidity goes down.  A dehumidistat is a control that turns something on when the humidity goes up.

Next time: The Skeleton!

Checkout: www.HeyokaSolutions.com


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