House as a System
There is a continuous interaction among the occupants, structure, mechanicals, environment, pollutants and energy sources in your home. As one changes the other items must adjust.
1st Law of Thermodynamics
- Energy is neither created nor destroyed. It can change form and move from place to place.
2nd Law of Thermodynamics
- Energy flows naturally from high concentrations to low concentrations in an attempt to equalize.
- Heat goes to cold
- Wet moves to dry
- High air pressure moves to low air pressure
Heat is a form of energy. Heat loss or gain occurs three ways:
- Transfer of heat through solid materials between objects in contact.
- The flow of heat through a fluid substance, such as air or water.
- Transfer of heat from warm object that are in sight of one another but not in contact. Heat energy via invisible light rays.
- Trapped air. Various materials are used to create, or attempt to create, tiny pockets of air slowing heat transfer through a space or material.
- Water is one of the biggest enemies to homes when left unchecked. Most effective is to control bulk moisture at its source. Prevent or reduce rain water from pooling and entering foundation. Regulating indoor humidity levels is key and must be adjusted with seasonal changes.
- The amount of water in a sample of air. Warm air can hold more moisture than cold air. Condensation occurs when warm air that is saturated comes in contact with a surface that is cool enough to meet dew point and the water in vapor form returns to its liquid state.
- Dehumidify damp spaces. Use vent fans that exhaust to the exterior of the building at the source of humidity in bathrooms and kitchens.
Importance of Air Sealing
- Over the course of one year, a 100 square foot wall can allow just one cup of water to diffuse through drywall with no vapor barrier. But if only a half inch hole is present, fifty cups of water can pass through by convection.
Thermal Envelope/Thermal Boundary
- Refers to location of insulation in the building shell. Should be continuous and preferably aligned with pressure boundary.
- The air barrier that separates indoor air from outdoor air. Should be continuous and airtight and preferably aligned with thermal boundary.
- How well a material resists heat transfer. Measured in a laboratory at 75 degrees once material has reached steady state. Inverse of U. R = 1/U
- How fast heat moves through a material. Inverse of R. U = 1/R
- Whole wall R-value concept.
- The natural effect when a building is heated, and the warm air inside the building is less dense than the colder air outside. The warm air rises up and out of any holes in the upper portions of the envelope. The escaping air is replaced with outside air that enters through holes in the lower portions. Air sealing helps minimize loss.