J-2 Heat and Sound Flashcards
Conduction
- heat moves through solid materials by conduction
- cast iron example, burner heats molecules in pan pan heats food
Heat capacity
the ability to store heat in a material.
* a piece of steel feels cold because it is more dense and can hold more heat. wood is not as dense
Convection
moves in fluids by convection. can be both liquids or gasses.
- holding your hand 10” beside a candle you will feel warm but not hot. 10’ above candle it will get hot fast.
- heat causes molecules to move rapidly then they bump not each other and spread further apart
- as hot air rises cool air flows towards the candle to replace the moving air. this is called the convection current.
Radiation
Sun heats the earth using infrared radiation
- when these waves strike na object it causes these molecules to vibrate and heat up.
- if you stand by a fire only your face gets warm not the air in between.
- radiant heat an be deflected. Low E windows reflect hat back out during winter and reflect heat back in the house from heaters.
Combination of convection, conduction and radiation
electric baseboard heaters. elements are covered with aluminum fins. heats fins with conduction, fins heat air around them through conduction, heated air rises and cooler air fills the space creating convection current.
Sound conductors
Materials that transfer sounds efficiently
Sound insulators
materials that no not transmit sounds efficiently
Absorption and reflection
sound waves reflect from solid surfaces and are absorbed into soft surfaces.
Auditorium seats
bodies or people in an audience are good sound absorbers. auditorium seats should be apolstered with materials that have close to the same absorption rating as a human body. hall will sound same full or empty
Vibration
energy in sound cam moves objects, sound waves move our ear drums.
- Sound can be transmitted from one room to another through a stud wall.
- sound vibrates drywall, drywall vibrates studs, studs vibrate drywall on other side of wall.
Reverberation
if a hammer strikes a solid surface in a room. the sound will bounce around a room.
- depending on shape and type of wall the sound wil l either die out or linger ( time to die out is reverberation time)
- rooms with short reverberation time are lecture halls, rooms with larger reverberation time is concert hall.
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Acoustics
is the study of sound quality in rooms and buildings. have a big concern in lecture theters and concert halls.
Sound transmission class
Building materials are rated for their resistance to transferring airborne sound. (STC)
- walls at doctors office have STC of 45 + two walls in a movie theater have a 50+
most materials that are used for insulating heat are also good for noise.
decibles (dB)
used to measure the relative loudness of a sound. increase of 3 dB’s doubles sound. meaning 23 dB’s is twice as loud as 20 dB’s.
Sound Transmission
materials chosen to reduce sound transmission have high absorption qualities. these materials absorbe sound . (plexiglass insulation)
Acoustical sealants
sound waves travel through air. any components of a sound barrier will leak sound. examples
- gaps around ductwork
- electrical conduit wires.
- plumbing pipes
- joints between walls and floors, intersecting walls,ceiling
- gaps around light fixtures.
Double wall construction
a wall system that incorporates two separate plates. the studs are staggered in each wall to allow insulation to be woven throughout.
Staggered stud wall
incorporates two sets of studs on one plate. the stud layout is staggered to separate the wall surfaces and to allow insulation to be woven between the studs.
Resilient channels
used to dampen sound waves. the channel (often called sound bar or Zbar) had double or single bend that absorbs the vibration of the sound.
- attach to framing using screws and spaces 8” oc on ceilings and 16-24” on walls
- causes 1/2” space between drywall and framing.
fiberglass batts
placed in the double wall system significantly increase the sound absorption of wall.
Woven fibreglass
fibreglass batts can be woven between the studs in a double wall if it is not used as a fire separation.
R / RSI values
all building materials are rated based on their ability to resist heat. this is in RSI (metric) this can be converted to imperial ( r value) by multiplying by 5.7
ex RSI1= R5.7
RSI3.5 = R20
Air film
the thin film of air that surrounds objects insulates them from heat loss. the insulating value attributed to air films is small but should be concretes
- air films in dry still conditions (inside) are 4x better then outside.
thermal bridging
is heat loss by conduction through materials that are poor insulators
true R- value
less then what it says of package. every stud is a thermal bridge so this must be taken into account when finding r value
whole wall R value calculation
8’ high
- building perimeter 168’ (rectangle)
- 2x6 wall studs (r7.5)
- fibreglass batt insulation between studs single bottom double top plate and wood siding (r19)
- 10 windows each 5’x5’ (r4)
- 2 doors, each 3’x68” r6
totall wall square feet is 1344 8’ 168’
framing: studs cripples corners 11 x 168 = 168 square feet
plates 1.5 /12 x 168= 63 square feet
Window ares 10 x 5’x5’ = 250 square feet (19 of total wall area) 250/1344
door area : 2 x 3’ x 6.667’ = 40 ft square 3% total wall area 40 / 1344
subtracting area of framing, windows, and doors results in 823 square feet. which is 61% of total 823/ 1344
multiply the percentage of the total wall area by each r -value then summing total will give you whole wall R value
(.61 x R19) + (.17 x R7.5) + (.19 x R4) + (.03 + R6) = R13.8
wind washing
wind washing is air moment through insulation it decreases the insulation value.
Air barriers.
very important in maintaining the thermal efficiency of a building. air barriers prevent movement of air due to differences in air pressure. one of the biggest heat loss in building is occupants moving and cooking etc creating positive pressure. this pressure along with leaks causes heat to leave building more quickly
Heating Degree-days
is a measure of how warm or cold a location is. the higher the number of degree days, the colder the location. this is based on the number of days of the year that the mean outdoor temperature is less then 18°C. for each day under 18°C the days mean temp is subtracted from 18°C. all of these means are then added to arrive at the number of celsius degree days per year.
Batts
most common form of insulation used in residential buildings. made from inorganic glass and mineral fibre. prone to wind washing because of air pockets.
Loose fill insulation
made of fibreglass, mineral wool, or cellulose insulation chopped into small pieces and blown onto place. this is most effective ay to insulate attic space. prove to wind washing and convection problems.
rigid panels
comes in several forms
- rigid minereal wool
- rigid fibreglass
- rigid foam
Rigid mineral wool
panels that are slightly denser then mineral wool batts. they are designed to be applied on the outside of the sheathing.the panels are fireproof and vapour permeable.
Rigid Fibreglass
a dense sheet of fibreglass insulation. the 4x8 panels come in various thicknesses and finishes. vapour permeable and prone to wind washing. faced with sheathing paper on one side.
Rigid foam
three types - expanded polystyrene -extruded polystyrene - polyisocanurate are not prone to wind washing is seams are taped. they are highly combustable.
Expanded polystyrene
lightweight foam board that is not resistant to moisture and must be protected is used below grade.
Extruded polystyrene
medium density foam board that is excellent use for damp locations. used to insulate under concrete slabs.
Polyisocyanurate
has highest insulation value per inch of thickness out of any foam boards. often used as roof insulation. exterior doors are often filled it this.
Sprayed-in-place foam
open cell polyurethane is vapour permeable and can be used as air barrier.
closed cell is vapour impermeable and can qualify as a vapour barrier.
Radiant barriers
a sheet of reflective materials. some types of insulating panels will have a foil cover on one face this should be placed in wall with foil against heated side. in hot climates foil is placed toward outside. needs air between foil and material can reflect 90%of radiant energy.
foil faced rigid insulation
some rigid insulations come with thin film of polished aluminum on one or both surfaces. very expensive. using this on inside of building with foil against drywall will stop thermal bridging of studs and provide effective vapour barrier.
Foild-surfaced bubble sheets
flexible sheets of this are used in attics and crawl spaces. similar to bubble wrap. air bubbles insulate against heat loss by reducing conduction while foil reflects radiant heat energy
