How a House Works
How a House Works in 773 Words
There is science behind why things are sometimes warm, sometimes cold and sometimes wet.
Most of us don’t spend a lot of time thinking about how our houses work. This section is designed to give you some insight into how your house functions as an interactive system. To you, your house is more than four walls and a roof— it’s the place where you and your family go to relax, feel safe, and make memories. The building scientists at Home Green Home appreciate your home in a different way— as a complex and interactive system made up of many components where each component influences the performance of the entire system.
Basic Principles
Buildings perform in a very predictable fashion. These performance characteristics are based on four simple principles of physics.
•Moisture movement
•Dew point temperatures
•Pressures
•Heat flow
Moisture movement
Moisture levels in a home depend on a variety of different factors such as lifestyle (showering and cooking), number of occupants, leaks, and ground/atmospheric moisture. Moisture wants to move from areas of high vapor pressure to areas of low vapor pressure. Vapor pressure is the pressure exerted by water molecules in a mixture of air. An example: when the home is being heated, moisture wants to move to the outside, and when it is being air conditioned, moisture wants to move from the outside to the inside of our homes.
One of the most common ways we discuss moisture in homes is relative humidity (RH) levels. RH is a percentage that indicates the amount of moisture in the air relative to the maximum amount the air can hold at that temperature. Warm air can hold more moisture than cool air, so the RH of a sample of air will change as the temperature changes, even though the actual amount of moisture in the sample does not. If we raise the temperatures, we lower the RH and if we lower the temperature, we raise the RH.
Dew point temperatures
Dew point is the temperature where water vapor will change to liquid water. This is a function of both temperature and the amount of moisture in the air. If we have a dew point of 40 degrees, any surface in the home that reaches this temperature will have liquid water condensation on it. To prevent this condensation, we can either raise the surface temperature or lower the relative humidity.
Pressures
Pressure moves from areas of high pressure to areas of low pressure.
Pressure imbalances are big concerns in residential construction, and they are tied into much of what we need to understand about how our homes function. Pressures can be caused by external conditions (wind and temperature) and internal conditions (exhaust fans, air handlers, chimneys and vents, a
