energy in green building and the carbon imperative
TRANSCRIPT
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
CO2 emissions ≈ 7 GtC/y
Natural carbon cycle ≈ 50 GtC/y
1 GtC/y = 1 billion tons of carbon per year, which may be bound in CO2 or other compounds
CO2 emissions ≈ 7 GtC/y
CO2 removal from atmosphere ≈ 3 GtC/y
7 800
3
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
GISS analysis of global surface temperature; 2008 point is 11-month mean.
Source: Jim Hansen, 2008
Five Stages of Receiving Catastrophic News Denial Anger Bargaining Depression Acceptance
Source: Arctic Council and International Arctic Science Committee, www.acia.uaf.edu
Slide: John Holdren
Source: Intergovernmental Panel on Climate Change, Climate Change 2007: Synthesis Report
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
California’s Big Step Forward:
Assembly Bill 32
2050 Target (EO 03-05)
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Emissions
Inventory
Electricity
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Industry
Slide: Snuller Price
American Heritage Dictionary, 10th ed.
Physical Meaning of Energy:
Energy = the ability to do work
Force
distance
Work = Force · distance
Energy = the ability to do work
Potential energy = mgh
(mass, gravitational acceleration, height)
Kinetic energy = ½ mv2
(mass, velocity)
velocity
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)
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.
Matter and Energy Resources
“High Quality” means
concentrated
pure
easy to use
in an orderly state
“Low Quality” means
dispersed
impure
more difficult to use
disordered
High quality energy:
mechanical, electrical, radiant
Medium quality energy:
nuclear, chemical
Low quality energy:
thermal (heat)
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.
Basic lesson:
Use energy sources matched in quality with end use needs.
Units of energy:
calories
kilocalories
joules
kilowatt-hours (kWh)
British Thermal Units (BTU)
therms (105 BTU)
quads (1015 BTU)
Units of power:
calories per hour
joules per second = watts
kilowatts (kW)
BTU per hour
Power = energy per unit time
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?
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
$ 0.115 / kWh
PG&E electric rates have stayed about the same over the past five years
$ 1.04 / therm
$ 0.92 / therm
PG&E gas rates have gone up from $0.70 / therm
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
Time for a break, maybe?
Basic Passive Solar Design Problem:
Get solar heat when you want it, not when you don’t.
Careful:
Windows can be net gain or loss.
The Environmental Technology Center at Sonoma State University
Passive Solar Design Principle #1:
Think about where the sun is going to be.
from Miller, Living in the Environment
Note different scales for power radiated!
Thermal IR
Passive Solar Design Principle #2:
Remember conduction, convection and radiative heat transfer.
Q = m c ∆T Q is amount of heat stored m is mass c is specific heat ∆T is temperature difference before/after
Outside and Inside Temperatures
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Passive Solar Design Principle #3:
Store warmth or coolth in thermal mass.
R-value: thermal resistance
U-value: thermal conductance, R = 1/U
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
Note: U-value is weighted average of framing and area between framing. Any air gap between insulation & framing ruins the insulating effect.
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
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
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
Passive Solar Design Principle #4:
Insulate well.
U-value: thermal conductance U = 1/R 0.35 Btu/hr-ft2-oF ≈ R-3
SHGC: fraction of solar gain admitted through window Performance trade-off with U-value for solar heating
Passive Solar Design Principle #5:
Be smart about windows.
#4
Insulate well.
#5
Be smart about windows.
#3
Store warmth or coolth in thermal mass.
#2
Remember conduction, convection and radiative heat transfer.
Passive Solar Design Principle #1:
Think about where the sun is going to be.
Heat gain by solar radiation
Heat loss by conduction, convection and infrared radiation
Building envelope
Heat gain by solar radiation
Heat gain by conduction, convection and infrared radiation
Heat gain from natural gas via hydronic floor
Heat loss by conduction, convection and infrared radiation
Heat gain from natural gas via hydronic floor
Heat loss by conduction, convection and infrared radiation
Question: Should I turn the heater off while I’m gone?
Driven by temperature difference between inside and outside
YES!
Replaces heat lost through envelope
Basic principle for smart energy use in any building:
Think of heat flow through the envelope.
Solar collectors for domestic hot water
Focusing with a parabolic mirror
If you use solar energy, your children will be well-groomed, polite and gladly help with chores.
Solar Thermal Power at Kramer Junction, CA Photo: PG&E
Photo: Pacific Gas & Electric
www.tva.gov Vestas 1.8 MW 260’ height, 135’ radius
Interesting constraints: Transmission infrastructure Resource location, cooling water Energy storage capacity Temporal coordination
Drastic reductions of carbon emissions
Three investment strategies:
Energy efficiency plus
• carbon capture • nuclear energy • renewables
All three are expensive, so cost alone is not a decisive factor.
Image: IPCC
South Texas Project, Photo: www.nielsen-wurster.com
CCS: Carbon Capture and Storage or
Carbon Capture and Sequestration Problematic issues: • sheer quantity of carbon • no inherent performance incentive • verification • permanence of disposal
Nuclear energy Problematic issues: • “vulnerability to human frailty, incl. stupidity and malice” (John Holdren)
• slow, committing infrastructure investment
• ethical concerns
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.
Pacific Gas & Electric, 1989
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