SOLAR TODAY - May 2010

Heating Emissions in Cold Climate
Based on different design strategies, including passive

FIgurE 2.

Cooling Emissions in Hot and Dry Climate
Based on different design strategies, including passive

TAblE 2.

EffECt of ClimatE on Emissions from BuilDing opEration
(Construction, waste and water factors are constant)

Emissions source Climate

Cold 69 ( 13,310 lb) 12 12 7

Operation
Construction
Waste
Water
percent of total emissions
Temperate Hot & Dry
59 68
( 8,486 lb) ( 12,776 lb)
16 12
16 12
9 8

Hot & Humid 65 ( 11,115 lb) 14 13 8

46 May 2010 SOLAR TODAY solartoday.org

Different GHGs have different warming potential. To express the impact of these gases in one standard unit, we converted emissions of GHGs into CO2 equivalent (CO2e) based on their 100-year global warming potential. One unit of CO2e is equal to one unit of CO2. GHGs include CO2, nitrous oxide (N2O), methane (CH4) and some fluorinated gases such as hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride. To normalize results, CO2e is used as the standard unit throughout this article, even when CO2 is the only output.

estimated by the various carbon-counting tools, we find that a family of four living in the model house would generate 19,230 lb ( 8. 72 metric tons) of CO2e per year in the cold climate, 14,383 lb ( 6. 52 metric tons) in the temperate climate, 18,788 lb ( 8. 52 metric tons) in the hot and dry climate and 17,100 lb ( 7. 76 metric tons) in the hot and humid climate. as detailed in Table 2 (below), operations are the single-largest source of emissions, and heating and cooling are usually the most important contributors of operation emissions.

Analyzing Emissions
by Climate

To determine the effect of different design strategies on emissions in different climates, we analyzed emissions in a model single-family dwelling located in four climates. The house was two stories high with 2,300 square feet (214 square meters) of gross building floor area, close to the 2005 U.S. average. The four climates we chose were the classical types classified according to their effect on human thermal comfort: (a) hot and dry, represented by California climate zone 15 (El Centro); (b) hot and humid, represented by Miami; (c) temperate, represented by California climate zone 6 (Los angeles); and (d) cold, represented by California climate zone 16 (Bishop). although most of the climate files are from California, we selected each to represent a general U.S. climate.

In the cold climate, this building’s average emissions from operational energy are 13,310 lb ( 6.04 metric tons) of CO2e per year, or 69 percent of total emissions. To determine the effect of the different sources of operational energy, we performed a more detailed analysis that included heating, cooling, fans and blowers, appliances, water heaters and lighting. This analysis indicates that, in the cold climate, most emissions from operational energy are from heating — 36 percent, plus an additional 6 percent for fans and blowers in the HVaC system.

In the temperate climate, emissions from operations are a smaller proportion of all emissions, averaging 8,486 lb ( 3.85 metric tons) of CO2e, or 59 percent of the total. Heating and cooling are a smaller portion of the total, and water heating and lighting become more important factors.

To calculate emissions in these climates, we made some assumptions for each type of building carbon emissions: operational energy, construction, waste, water and transportation. These calculation decisions are detailed at solartoday. org/laroche. California’s energy code, Title 24, was used to design the initial building envelope for all climate zones using package D for homes with a gas furnace rated at an annual fuel utilization efficiency (aFUE) of 80 percent. The same building envelope was used in the hot and humid and hot and dry climate zones.

Operational energy in the hot and dry climate accounts for 12,776 lbs ( 5. 8 metric tons) of CO2e per year, a large portion of total emissions ( 68 percent). Most of these emissions ( 41 percent) are from cooling, plus 8 percent for fans and blowers.

In the hot and humid climate, operational energy accounts for 11,115 lb ( 5.04 metric tons) of CO2e per year, or 65 percent of the total building emissions. Most of these emissions are from cooling ( 40 percent), plus 7 percent for fans and blowers.