Air/ Moisture Flashcards
Stack effect
when hot air rises and escapes through upper level openings of a building, cold air is drawn into the basement and lower floors. the taller the building the greater stack effect.
Flue effect
NAtural aspiring duel fired venting appliance (stove, fireplace, furnace, hotwater tank) burn furl and used air from inside building for combustion. this is vented outside
ex burning fireplace can remove 400-600 cubic feet per minute. always close unused vents and fireplace.
Wind effect
winds cause pressure differential to occur across building envelope. wind hitting building creates high pressure on that side and negative pressure on leeward side.
Neutral pressure plane
NPP explanes how air flows in and out of a building. is NPP is zero, in areas where pressure is lower then NPP air enters the building. in areas where pressure is Higher then NPP (zero) air leaks out of building.
Infiltration
aproxamat heat loss of building heat loss 25-30% air infiltration 25-30% basement 20-25%doors and windows 15-20%walls 7-10%ceilings
Air barrier
maintaining air barrier will reduce pressure differentials and eliminate air infiltration caused by stack, flue and wind effect.
three types of ventilation systems
exhaust systems
supply systems
balances systems
Exhaust systems
draw air out of the buildings. this places building under negative pressure.
Supply systesm
blow air into the building. this places building under positive pressure.
Balanced systems
systems have fans that both supply and exhaust air at equal rates so that no pressure differential is set up across the envelope.
principal exhaust fan
all building must have mechanical ventilation to remove moisture from building. used to move moisture out of building
Makeup air
is air provided intentionally or unintentionally that replaces air being exhausted by ventilation systems.
is there is soil gas present makeup ventilation air is required for dwelling
combustion air
combustion air supply must be located near a NAFFVA to prevent backdrafting of harmful gasses (CO2) and to balance pressure
Co2 detectors
carbon monoxide detectors must be in same rooms as NAFFVA and at leave 5m from bedrooms
Direct venting
direct vented gas appliances are sealed, closed looped units that intake air and exhaust combusted gasses outside. other then providing heat they don’t change pressure.
Soil gas
soil gas is air between soil particles. it can contain radon that is a natural gas that causes cancer. negative pressure can cause radon to be drawn into dwelling through cracks in foundation walls or basement slabs.
Airtightness
air barriers are installed to prevent movement of air through the building envelope. it prevents warm moist air from entering and condensing in envelope.
true or false, airtightness has greater effect on thermal efficiency then the amount of insulation?
TRUE
Air Barrier Leakage rating
air barrier materials are rated by the amount of air in liters that will pass through 1m(square) of material in 1 second at a pressure of 75 Pa.
typical air barrier leakage rating are between 0.024 and 0.1L/(sxm(square)
two types of air barriers
membrane or ridged
types membrane air barriers
either 6mill poly, self adhering membrane (SAM) or house wraps sucha s tyveck and typar.
SAM’s and Poly vapour barrier true or false?
true
house wraps vapour barrier true or false
False
why does poly not perform as well as ridged air barriers in windy climates
because negative pressure on leeward side of building caused poly to get sucked into the stud or ceiling compressing insulation and ripping at staples.
Panel type air barrier
panel type air barrier include drywall, plywood, OSB and ridgid foam insulation. edges must be sealed with tape or caulking.
concrete foundation and walls are good air barriers true or false
true
Gasket materials
gasket materials are used to seal cracks and joints against air leakage. must remain flexible to maintain airtight seal.
examples, foam sill gasket, weather strip and neoprene tape
caulking
used to seal air barrier and further reduce the movement of air through building envelope.
caulking is used to seal …
- around doors and windows
- under sole plates of walls
- around electrical outlet boxes
- around plumbing pipes and vents
- any ceiling penetrations
- at sill plates
- perimeter joist connections
- at cracks in foundations
installation of caulking
should be installed to form a filet or curved bead at right angle joints.
hourglass shape at level joint.
*use backer rod for joints that are bigger then 1/8th
joint tape
used to seal joints in air barriers as well as holes
Electrical boxes and air barriers
plastic “boots” (boxes) are made to surround and connect electrical boxes. these boxes must be sealed to air barrier
- when used with drywall air barrier boxes around electrical units have foam that seals them
weather stripping
weather stripping is used to maintain airtightness around windows and doors.
in sliding units friction strip is used
what happens to weather stripping in hinged units
it is compressed between door or sash and frame
Spray foam
urethane spray foam makes excellent sealant around windows, door and pipes and other penetrations.
expanding and non expanding. expanding can cause deflection in doors and window frames
Testing for airtightness
federal government established the “super energy efficient home program. builders were provided with training and incentives to construct energy efficient homes.
Blower door test
blower door test tests your houses air tightness. a fan, pressure gauge, and computer are put in door frame. all other windows doors and vents are shut. the fan starts pulling all air out of building and instrumentation in blower calculates how much air leaks back into house through building envelope.
ELA equivalent leakage area
Equivalent leakage area is the total area of all the leaks in the building envelope at a depressurization of 10Pa
NLA Normalized leakage
Normalized leakage are is calculated by dividing the ELA by the exterior surface area of the house. gives the size f leakage area in cm square, m scuare OR in square of feet square
R-2000 technical standard calls for 0.7 cm (square)/m(Square)
Or 1 “(square)/ 100 ft (square)
ACH50
is a blower door machine that measures the air leaving the building at an envelope depressurization of 50 Pa. in meters cubed/ hour or feet cubed/hr. when divided by the buildings volume, the number of air changes within 1 hour is calculated.
Older homes have ACH50’s of 10-15 while newer homes have ACH50’s of 4-10.
Sweden requires housed to have ACH50 or 3 while r-2000 requires ACH50 of 1.5
Three phases of moisture
Solid, Liquid, vapour
solid
water is solid state is ice, water expands when it freezes. it expands approximately 10% when freezes. ace force can break concrete.
Liquid
force of gravity caused water to travel to ground. water can be lifted against force of gravity by capillary action. water of any depth will cause hydrostatic pressure. hydrostatic pressure on foundation walls can cause water to be forced into tiny cracks.
Vapour
water vapour is created when liquid water evaporates. it if the temperature is high and the air is dry water will evaporate quickly. heating water to its boiling point will create water vapour regardless of humidity of surrounding air. water vapour molecules are very small and can pass through any permial barrier.
relativity humidity
is the amount of water vapour in the air relative to the total amount it could hold at a given temperature.
there is more water vapour in air at 30% humidity at 35°C
then at 30% humidity at 5°C
what hold more moisture, warm or cold air?
warm air.
Condensation
as air containing water vapour cools, the relative humidity increases. the total volume of water vapour hasn’t changed but the cooler air cannot hold as much. as the temperature decreases the air cannot hold onto the water and it is transformed into water droplets or dew bells.
dewpoint
the dewpoint is the temperature at which water vapour condenses into liquid water.
vapour diffusion.
is the movement of water vapour through substances.
vapour will move from areas of high vapour concentration to low vapour concentration. and will also move from high temperature areas to low temperature areas. (vapour drive)
Airflow
moisture carried into envelope is still in the form of vapour, but traveling around objects not through them. eliminating airflow will shrink flow of moisture in building.
Gravity flow
weight of water causes it to flow to ground. it will take the most direct pathway. flashing and drip edges direct flow away from building.
wind pressure
wind driving rain can find its way into building through the best cladding. wind creates a pressure differential across cladding. front end of cladding will be under high pressure while the back end will be under low pressure.
Capillary action
surface tension of water causes it to be drawn into narrow pores. the force of capillary action is strong enough to cause water to travel significant distances against gravity.
vapour barrier and moisture barriers describe
must be placed on the warm side of the insulation and is intended to reduce water vapour diffusion through the interior finish into the building envelope.