Energy in green building and the carbon imperative

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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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


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?


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


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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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


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


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.


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 gain from natural gas via hydronic floor


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