Chapter 5-part 1
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Physical Properties of Building Materials
Physics of Home Insulation
Selection of Home Site
Physics of Window Design
Effects of Energy Conservation on Heating
and Cooling Costs
Energy in the News
Uses CO2 and a
Surfactant
What else is a
Surfactant?
Drawbacks:
Need high pressure
(900 psi)
Machines cost more
BUT
Only waste:CO2
+ surfactant
Less heat: Less damage
to fabric, less energy use
Less water used.
Radiation of Heat-Effect of Color
Which radiates heat faster: coffee with cream or
Coffee without cream? How does heat move in a vacuum?
Conduction of Heat
Q/t = k * A * Delta T/ delta
Q=heat flow, k = thermal conductivity, A= area
Delta T = temperature difference
New formulation:
Q/t = 1/R * A * DeltaT
R is an insulation factor that is a function of material
Properties and thickness.
R values add-this is very useful.
Changes in Insulation Requirements
After WWII, who granted large numbers of home mortages?
Differences in R value of
Common Materials
Table of R Values
What has the highest R
Value at a 1 inch thickness?
Polyurethane board =
High R sheathing
Sick Building syndrome?
Composite R Values
Preventing Convection
Infiltration of Air
Heat loss from infiltration=Cp * V * K * Delta T
Where Cp is heat capacity of the air, V is house volume
K is number of air changes per hour, T is temperature difference
Add up size of air slots
Around the edge of a
Door.
Infrared pictures of a
House on a cold day
Weather Stripping
Heating and Cooling Degree
Days
• Heating Degree Day = 65°F - T average
• Cooling Degree Day = 75°F - T average
• T average = average temperature for the
day.
Heating and
Cooling DD
in the United
States
R-Values
Transmittance/Reflectance of
Glass
Glass transmits visible
light, but is opaque to
long wavelength infrared
light.
Table of Optical Properties
Which is the best material for energy efficient windows?
Convection
in Windows
Heat can be
Transferred by
conduction,
Convection and
radiation.
Low E (emissivity)
coatings are to prevent
radiation of heat.
Optimum Air Space Thickness
Results for
A double paned
Window:
Minimum heat
loss is for a
15-20 mm
Thickness of
Air space
Between two
panes of glass
Energy Savings from Conservation
Savings and Payback Times
What sort of payback times are short enough to convince the average
person to invest in energy conservation? What is the lifetime of a house?
Radiant Slab Heat
Reducing Cooling Needs
Coober
Piedy
Passive
Cooling
Methods
Radiant Barriers
What form of heat gain or loss is being prevented?
Savings from Energy Efficient
Landscaping
Savings depend
On your location
Savings from
Planting for wind
shielding and sun
Shading.
Effects of Windbreaks
House should be
within 10 to 15
times the height
of the trees.
Trees should be
evergreens.
Don’t break with
A driveway.
No shadows on
south walls.
More on Windbreak Design
Length must be greater
Than 11 times windbreak
height.
Driveway is curved to
preserve windbreak
effectiveness.
Plant perpendicular to
Prevailing wind
direction.
Summer Shading
Use deciduous trees
Find the hottest week
Of the year
Calculate sun angle
At mid afternoon
If sun angle is 75
Degrees, trees should be
no closer than on a line
75 degrees from true
South.
Shade East and West
Walls (more important
Than South walls!!)
Winter: Let the Sun Shine In!
Plant trees outside
Of south wall of
House.
Avoids unwanted
Shade in winter.
Funneling Summer Wind
Summer Wind
Goes past moist shrubs
and cool bricks before
Entering house.
Remind you of some
Mediterranean houses?