Foundation Level Exam Flashcards
HAAS
House As A System: building concept defines a house as an energy system made up of four interdependent components.
A. Environment
B. Building Envelope
C. Mechanical Systems
D. Occupant Activities
What are the HAAS principles?
Four HAAS elements work-balance, in order to:
A. provide affordable shelter (doesn’t exist)
B.Occupant Health and Safety
C.Minimize energy consumption
D. Minimize environmental impact
Thermal Comfort Factors?
A. Temperature
B. Humidity Levels
C. Air Movement
D. Surface temperature (mean radiant temperature - MRT)
Impact Occupant Behaviour
A. Moisture Added
B. Ventiliation Requirements
C. Internal heat gain
D. Increase electrical loads, water and energy use
What are the conditions that cause Heat Flow?
Conduction
Convection
Radiation
Define Conduction.
Transfer of heat across a temperature gradient: warm –> cool
In houses, conduction happens between solid objects in direct contact.
The rate of heat transfer depends on temp. difference between surfaces and R-Value of material
Define Convection.
Transfer of heat by circulation of currents from one part to another, in a gas or liquid.
In houses, convection circulates from warm side of wall to cold side of wall, resulting in heat transfer.
Mixing warm and cold air also transfers heat.
Examples: condensation on window with cold outside temp
condensation when cooking with poor ventilation
Define radiation.
Energy emitted as particles or waves that are absorbed by another body.
ie. waves of heat transmitted across an open space
Name building practices/materials that control heat flow.
- Insulation: roof, wall, foundation
- Vapour barrier: limits movement humidity/vapour into structure
- Air Barrier: Poly, Airtight Drywall, External Insulation and House Wrap
- Improve Windows/Doors to limit air infiltration
- Weather barrier (ie Tyvek)
- Building Codes: NBC requires min insulating values build assemblies
- Heating-Degree days determines level of insulation required
Data required to evaluate heatflow/conductive heat loss?
- Type of material
- Location in building assembly
- Area
- Thickness
- Spacing
- Conductivity
Effect of heat flow on thermal comfort?
- Raise or lower air temp (dry bulb effect)
- Heat or cool surfaces
- Create air movement
- Increase/decrease relative humidity
Effect of heatflow on energy consumption?
Increase the need for heating/cooling to maintain optimum temp levels
Heat loss sources?
Windows Doors Walls Chimneys Foundations Ceilings Exposed floors Infiltration
Explain thermal bridging.
Occurs when thermally conductive materials (wood framing) conduct heat through building envelope, bypassing insulation in the framing cavity.
Reduces thermal resistance wall assembly.
Any solid material that connects the warm side of the envelope to the cold side (wall studs)
Define the nominal insulation value.
Insulating value of the insulation material. Does not account for building assembly performance.
Define the effective insulation value.
Insulating value that accounts for all other building components (framing, sheathing, cladding etc), and calculated based on perfomance of building assembly. (ie. accounts for thermal bridging).
Define thermal resistance.
Measures an object, material, or building assembly’s ability to resist heat flow (RSI or R Value)
higher R Value, greater thermal resistance
How do you convert between RSI and R Value?
RSI = R-value/5.678 R-Value = RSI(5.678)
or
1R = 0.176 RSI
What materials/practices decreases effective thermal resistance?
Wall studs
Top and Bottom plates
What increases effective thermal resistance?
- Sheathing, drywall, and exterior finishes.
2. Foam boards on one side of thermal bridge (maybe this counts as exterior finish, though)
Compare R-Value and U-Factor
R-Value Measures how quickly heat flows though a material, whereas U-factor measures the ability of a material to resist heat flow.
R-Value is the #BTUs that flow through
one ft(squared) of material
per hour
for each degree temp difference
from one side of material to the other
Higher U-Factor, quicker heat flows/Higher R-Value slower heat flows
R-Value is inverse of U-Factor - R = 1/U;
U-Factor is the inverse of R-Value - U = 1?R
Describe moisture flow mechanisms.
A. Gravity (bulk water movement)
B. Capillary action
C. Air transported moisture:
- uncontrolled pressure source (wind or stack effect)
- controlled (fans/air handlers)
D. Vapour diffusion (small amounts moisture pass directly through
building envelope)
Difference capillary action and osmosis.
Osmosis: movement of molecules across a gradient
Capillary action: water travel against pull of gravity through porous material. Small holes, rather than large ones.
Describe moisture control strategies
Gravity (bulk water movement):
a. grading, drainage, gutters and downspouts
b. sealing, flashing, caulking
Capillary action:
a. capillary break via impermeable materials (plastic, metal, compounds, etc. ) or air space to large for capillarity
Air transported moisture:
a. effective sealing against infiltration
b. pressure balancing HVAC system
c. exhaust fans bathrooms/kitchens
Vapour Diffusion:
a. Installation vapour retarders with perm rating of < 1
Define Relative Humidity
The amount of water vapour present in air expressed as a percentage of the amount needed for saturation at the same temperature.
RH = (Actual VD/Saturation VD)100
So, the actual water vapour density to the saturation water vapour density, usually expressed in percent.
Effect of relative humidity on human comfort?
If relative humidity is high, skin water evaporation limited, and therefore, feel warm and stifled.
Define Absolute Humidity
The measure of the actual amount of water vapour in the air, regardless of temperature - g/m-cubed.
The maximum absolute humidity of warm air at 30 degrees C is approx. 30 g of water vapour: 30 g/m-cubed
Define the dew point.
When air cools to a certian temperature, relative humidity becomes saturated and can no longer hold more water vapour. At this temperature, the airborne water vapour condenses to form liquid (dew).
Explain a temperature gradient.
Describes direction and rate of temperature changes as it passes through an object.
warmer to cooler
higher R-value, lower the heat value
Describe Condensation
Conversion of a vapour or gas to a liquid.
- 100% relative humidity, air can’t hold any more water vapour
- Warm air contains more water vapour than cold air
- Condensation occurs as temp drops
What are the Factors that cause condensation?
A. Air Temperature - warm air holds more vapour, than cold
B. Water Vapour in the air
C. Air Circulation
Define Evaporation
A. Change of a liquid into a gaseous phase at any temperature below its boiling point.
-evaporation will cause a drop in temperature of the liquid
Causes and implication of low humidity levels?
Cause: 1) cold air leakage; 2) ventilation without humidification
Implications:
Low humidity levels promote:
- bacteria and viruses
- Respiratory infections
- Skin irritations
- structural damage (ie flooring)
- ozone production
- excessive dust
