Energy in green building and the carbon imperative
1. Energy in Green Building:
The Carbon Imperative and
the Ruby Slippers
Dr. Alexandra “Sascha” von Meier
Professor, Dept. of Environmental Studies & Planning
Sonoma State University
www.sonoma.edu/ensp
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3. Natural carbon cycle
≈ 50 GtC/y
CO2 emissions
≈ 7 GtC/y
1 GtC/y = 1 billion tons of carbon per year,
which may be bound in CO2 or other compounds
11. Burning fossil fuel means combustion of hydrocarbons:
CXHY + O2 → CO2 + H2O
hydrocarbon + oxygen → carbon dioxide + water
where the proportions of CO2 and H2O depend on X and Y
12. GISS analysis of global surface temperature; 2008 point is 11-month mean.
Source: Jim Hansen, 2008
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15. Five Stages of Receiving
Catastrophic News
Denial
Anger
Bargaining
Depression
Acceptance
20. Climate stabilization (at 450 ppm CO2) requires global emissions to peak by 2015
and to fall to ~80% below 2000 levels by 2050
Slide: Jim Williams
Source: Intergovernmental Panel on Climate Change, Climate Change 2007: Synthesis Report
23. Physical Meaning of Energy:
Energy = the ability to do work
Force
distance
Work = Force · distance
24. Energy = the ability to do work
Potential energy = mgh
(mass, gravitational acceleration, height)
velocity
Kinetic energy = ½ mv2
(mass, velocity)
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26. Examples of Energy
Natural gas in the pipeline (chemical)
Gas flame on my kitchen stove (chemical to thermal)
Hot water in the kettle (thermal)
Electricity in the wall outlet (electrical)
Spinning blade of the coffee grinder (mechanical kinetic)
Pancakes & maple syrup (chemical)
Vase sitting on top shelf (mechanical potential)
Vase falling down to floor (mechanical kinetic)
Radioactivity (nuclear to radiant)
Sunshine (radiant to thermal)
Wind (mechanical kinetic)
27. Because a measurable quantity of energy is conserved
during any conversion of one form to another,
it makes sense to give a single name to that quantity.
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33. Matter and Energy Resources
“High Quality” means High quality energy:
concentrated mechanical, electrical, radiant
pure
easy to use
in an orderly state
Medium quality energy:
nuclear, chemical
“Low Quality” means
dispersed
impure
more difficult to use Low quality energy:
disordered thermal (heat)
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41. 2nd Law requires:
Some of the chemical fuel energy will be degraded into heat.
The amount of mechanical work or electricity produced will be less
than the fuel input.
44. Units of energy: Units of power:
calories calories per hour
kilocalories
joules joules per second = watts
kilowatt-hours (kWh) kilowatts (kW)
British Thermal Units (BTU) BTU per hour
therms (105 BTU)
quads (1015 BTU)
Power = energy per unit time
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47. Electric usage 232 kWh $0.11/kWh
Gas usage 52 therms $0.71/therm
Conversion factors: 1 therm = 100,000 Btu = 105 Btu
1 kWh = 3,413 Btu
Questions:
• Which is my greater energy consumption – electricity or gas?
• Which is more expensive per unit energy – electricity or gas?
48. Electric usage 232 kWh $0.11/kWh
Gas usage 52 therms $0.71/therm
Conversion factors: 1 therm = 100,000 Btu = 105 Btu
1 kWh = 3,413 Btu
Convert 232 kWh into therms by multiplying
by the conversion factors (3,413 Btu / kWh) and (1 therm / 105 Btu):
232 kWh x (3,413 Btu / kWh) x (1 therm / 105 Btu) = 7.9 therms
→ I use 7.9 therms worth of electricity
49. $ 0.115 / kWh
PG&E electric rates have stayed about the same
over the past five years
50. $ 1.04 / therm
$ 0.92 / therm
PG&E gas rates have gone up from $0.70 / therm
51. Electric rate $ 0.115 / kWh
Gas rate $ 0.92 – 1.04 / therm
Which is more expensive, gas or electricity?
Conversion factors: 1 therm = 100,000 Btu = 105 Btu
1 kWh = 3,412 Btu
$0.115/kWh x (1 kWh/3,412 Btu) x (105 Btu/therm)
= $3.37/therm
→ electricity is over three times as expensive as natural gas
81. Heat flow example:
R-20 wall
U = 0.05 Btu/h-ft2-oF
Area = 100 ft2
∆T = 30oF
What is the rate of heat loss?
Q = U A ∆T
= (0.05 Btu/h-ft2-oF) × (100 ft2) × (30 oF)
= 150 Btu/h
82. Note:
U-value is weighted average of framing and area between framing.
Any air gap between insulation & framing ruins the insulating effect.
83. Ballpark value for residential building envelope:
UA = 500 Btu/h-oF
How much heating energy does it take?
Convenient characterization of heating climate:
“Degree-days” DD
actually oF-d or ∆T-days
84. 443 Degree-Days
in San Francisco for the
month of January
3001 Degree-Days
for the whole year
For example:
300 days of ∆T = 10oF
85. UA = 500 Btu/h-oF
How much heating energy does it take?
San Francisco heating climate: 3001 DD
Q = U A ∆T-days × hours/day
= (500 Btu/h-oF) × (3001 oF-d) × (24 h/d)
= 36 million Btu
= 360 therms
88. SHGC: fraction of solar gain admitted
through window
Performance trade-off with U-value
for solar heating
U-value: thermal conductance
U = 1/R
0.35 Btu/hr-ft2-oF ≈ R-3
90. Passive Solar Design Principle #1:
Think about where the sun is going to be.
#2
Remember conduction, convection and radiative heat transfer.
#3
Store warmth or coolth in thermal mass.
#4
Insulate well.
#5
Be smart about windows.
91. Heat loss by conduction,
convection and
infrared radiation
Heat gain by
solar radiation
Building envelope
92. Heat gain by conduction,
convection and
infrared radiation
Heat gain by
solar radiation
93. Heat loss by conduction,
convection and
infrared radiation
Heat gain from natural
gas via hydronic floor
94. Question: Should I turn the heater off Heat loss by conduction,
while I’m gone? convection and
infrared radiation
YES!
Driven by temperature difference
between inside and outside
Replaces heat lost through envelope
Heat gain from natural
gas via hydronic floor
95. Basic principle for smart energy use in any building:
Think of heat flow through the envelope.
110. Drastic reductions of carbon emissions
Three investment strategies:
Energy efficiency
plus
• carbon capture
All three are expensive, so cost
• nuclear energy alone is not a decisive factor.
• renewables
114. CCS: Carbon Capture and Storage or
Carbon Capture and Sequestration
Problematic issues:
• sheer quantity of carbon
• no inherent performance incentive
• verification
• permanence of disposal
115. Nuclear energy
Problematic issues:
• “vulnerability to human frailty, incl. stupidity and malice”
(John Holdren)
• slow, committing infrastructure investment
• ethical concerns
116. Portfolio of renewable energy resources
Problematic issues:
• spatial and temporal constraints on energy availability
• requires sophisticated, integrated planning
In my opinion, these are the most readily solvable problems.
118. Exclusion zone radius 18 km, area 109 m2
Incident solar radiation 1000 W/m2
at conversion efficiency 0.1
could generate 108 kW or 100 GW of solar power
at capacity factor 0.2 would produce 5% of U.S. electric energy
