Envelope Flashcards
Radon action levels
200 Bq/m3
How do you calculate total R value when there are some in series and some in parallel?
Each section of materials in parallel should be treated as a layer, and its overall R-value calculated. Then all layers can be summed for the total R-value.
Air has a high resistance to this, and a little resistance to this
High resistance to heat conduction
Low resistance to heat convection
When conduction, convection and radiation occur at the same time, the overall thermal resistance of air spaces becomes this
Virtually independent of gap with when it is greater than 1 inch
It is most effective when adding layers of insulation in
Series, not in parallel. Because in parallel the materials used to divide air spaces might cause what are called thermal bridges.
The density of material is, the better it will
Conduct heat
Metals and glass have little resistance to
Convection
Describe convection
Transfer of heat between objects that are not touching each other. Transferred by means of a fluid such as water or air movement is called convective current.
Difference between permeance and permeability
Moisture transmission rate of a material is permeability. (Perm inches)
Permeance is dependent on thickness
Divide permeability of material by its thickness gives materials permeance in perms
Metric measurement for insulation
RSI
The three effects of air movement in homes
Wind affect
Stack affect
Combustion and ventilation
Will hot or cold water, lower viscosity
Heating material lowers viscosity. They permeate faster than cool liquids.
Fungal growth range
19- growth continues but can’t start
26- saturation point/growth
Describe framing factor
The extent to which wall roof or floor framing reduces R-value
Wall R-20
Framing factor 25%
=R-15
More framing= higher framing factor
Two types of building insulation
Bulk
Reflective
Permeance
The degree to which material transmits another substance
Radon
Radioactive gas formed by decay of radium
First way heat is transferred
Radiation. It can occur in a vacuum unlike convection.
What kind of heat flow does radiant heat barriers reflect
Reduce downward heat flow because upward he flew tends to be dominated by convection. (better used in hot climates for roofs.)
Radon can be breathed into the lungs with a break down further and emit
Alpha particles
How to calculate, parallel R-value
U1= 1/R x area fraction = x
U2= 1/R x area fraction = x
U3= 1/R x area fraction = x
U4= 1/R x area fraction = x
Add them together for total U
R= 1/U
Describe R-value
Ratio of temperature difference across an insulator and the heat flux (heat transfer per unit area per unit time)
Low emissivity windows will transmit these waves, and reflect these waves
Transmit light and short wave infrared in
Reflect long, wave infrared radiation
Four laws of thermodynamics
- Heat can either be created or destroyed.
- Entropy.
- 100% efficiency is impossible
- No heat flows between objects at the same temperature.
