ers must learn how to quantify the carbon impact
and effect of their design decisions. Operational
energy, which includes heating and cooling, has
the most impact on emissions and should be a
priority to address. This can be accomplished
with energy-efficiency strategies and good old-fashioned passive solar. Photovoltaic and wind
systems can also reduce operational emissions
by providing clean energy. However, other strategies that affect emissions from construction,
water and waste must also be implemented.
These include strategies such as living close to
work, working at home, recycling and reducing
water consumption.
Determining the effect of all of these strat-
egies in a building’s GHG emissions is out of
the scope of this article. However, we studied
the effect on operation of implementing sev-
eral simple energy-related design strategies in
the same four climates. The strategies include
improving the insulation level of the walls and
windows and improving the efficiency of the
air conditioning and heating systems, each of
which was tested at three different levels of
performance. Some of the scenarios tested are
not allowed by code in the United States any-
more but are common practice in many parts
of the world. We also calculated the effect of
implementing two passive design strategies
(direct gain in the cold climate and night ven-
tilation in the hot and dry climate). We made
many other assumptions that are not explained
here for lack of space. The simple radar dia-
grams, figures 1 and 2 on page 46, represent
Though many carbon-counting tools are available, no single tool can be used to calculate all building-related emissions.
Furthermore, many of these tools do not provide transparency
in their calculations. This table lists free tools that can be used in
residential design projects. The results for each of these tools can
be added to determine total emissions for a project.
Carbon-Counting
TOOls
for Residential
Building Design
Greenhouse Gas
Emissions Tool
OpEra TIOnal EnErGy HEED: Home Energy Efficient Design
Provides separate results for operation sources: heating, cooling,
lights, appliances, fans and water heater, enabling the designer to
better determine the most effective strategy. Yearly energy results in
the Building Energy Performance Screen can be multiplied by a con-
version factor to obtain carbon dioxide equivalent (CO2e).
www2.aud.ucla.edu/energy-design-tools/
COns TruCTIOn Build Carbon Neutral
Provides a very rough estimate. The total must be divided by the esti-
mated life of the building to obtain CO2e per year.
buildcarbonneutral.org
Athena EcoCalculator for Assemblies provides more precision but is
not available for all areas.
athenasmi.org/tools/ecoCalculator/index.html
Wa TEr The amount of energy embedded per unit of volume of water must
be multiplied by the CO2e-conversion factors and the yearly building
water use to obtain CO2e. A CO2e factor per million
gallons (MG): 1,331 lb of CO2 per MG (0.0034 kg of CO2 per liter) is
used (Southern California Factor). The water usage can be determined using goblue.zerofootprint.net
Was TE EPA Personal Emissions Calculator (waste section) for simple analysis
permits the designer to model the effects of reducing home waste
and recycling.
epa.gov/climatechange/emissions/ind_calculator.html
TranspOr Ta TIOn To obtain emissions from transportation per family, the number of
miles traveled per family is multiplied by the CO2e factor per mile for
that mode of transportation (train, bus). For example, for automo-
biles the number of miles traveled per family is multiplied by the fuel
efficiency of the automobile(s) and the emissions factor per gallon of
fuel. Only automobile was considered here, using 19. 56 lb of CO2 per
gallon of gas and 22 mpg.
the effectiveness of the design strategies in
each climate by indicating the distribution of
the emissions.
an analysis of GHG emissions from heating
clearly demonstrates the effect of a better envelope on performance. In the cold climate, emissions from the house with the low-performance
furnace ( 72 percent aFUE), poorly insulated
with single-glazed windows, is 29,626 lb ( 13. 4
metric tons) of CO2e (upper blue corner of figure 1). When the furnace is updated to 97 percent aFUE and the house is super-insulated, the
emissions are reduced to 2,400 lb (1.1 metric
tons) of CO2e per year, or just 8.1 percent of
the previous amount (lower left green corner
of figure 1). If the windows are relocated to the
south side, reduced on the east, west and north
sides, an overhang is added on the south side
and the floors are changed to concrete slabs,
the emissions are further reduced to 640 lb (0.3
metric tons) of CO2e, which is only 2. 2 percent
of the original emissions (upper left pink corner
of figure 1). Simply adding these three additional
“passive solar” strategies (windows to the south,
overhangs and concrete slabs) reduces the emissions in all cases.
The quality of the envelope and the efficiency
of the HVaC system also affect GHG emissions
from cooling (see figure 2). In the hot and dry
climate, emissions with the low-performance air
conditioning system ( 8. 9 SEER), in the poorly
insulated house with single-glazed windows,
is 20,950 lb ( 9. 5 metric tons) CO2e (top blue
corner of figure 2). When the air conditioning
is updated to 97 aFUE and the house is super-insulated, the emissions are reduced to 4,387 lb
(1.9 metric tons) of CO2e, only 20. 9 percent of
the previous amount (lower left pink corner of
figure 2). If night ventilation is added to the best
envelope with the highest-efficiency air conditioning system, emissions are further reduced
to 1,610 lb (0.7 metric tons) of CO2e, or just 7. 7
percent of the original value (upper left pink).
Implementing night ventilation, shading of the
south windows and thermal mass reduces emissions substantially in all cases.
Implementing these design strategies — better envelope, more efficient HVaC system and
passive heating and cooling strategies — can
dramatically reduce emissions. Even with the
limited precision that these tools provide, the
relationships between these numbers clearly
demonstrate the power of energy-efficient, cli-mate-responsive design. ST
