Impact of Home Energy Use Actions (Box 1)

 

Avoided CO2 emissions for Box 1 Challenge

AVOIDED CO2 EMISSIONS FROM UNPLUGGING DEVICES TESTED IN THE BOX 1 CHALLENGE

One giga-Watt hour (GWh, 1,000,000 kWh) of electricity usage reduction in California leads to 540 metric tons (540 Mg, 1,190,000 lb) of avoided CO2 emissions (1), or 1.19 lb per kWh. Each Watt of electricity usage for a year is 8.76 kWh, and therefore each watt of continuous use avoided leads to 10.4 lb of CO2 emissions avoided.

Even though some cities have committed to using 100% carbon-free energy, only 29% of electricity in California as a whole comes from renewable sources (2). Because the supply of electricity from renewable sources is limited, reducing electricity use has an impact on overall CO2 emissions, even when that reduction takes place in cities that use carbon-free energy sources. This is because reducing use leaves more of the renewable supply available for other regions in California.

 

Avoided CO2 emissions for Box 1 Code Words

UNPLUG

THERMOSTAT (winter Bootcampers only)

DUCK (summer Bootcampers only)

COLD WATER

AIR DRY

SHOWER

Putting it all together

 

UNPLUG - ELIMINATE ENERGY USE BY DEVICES IDENTIFIED IN THE BOX 1 CHALLENGE

To calculate the avoided CO2 emissions from unplugging devices that were continuously using electricity, multiply their electricity use while turned off in watts by 10.4 lb of CO2 emissions avoided per watt per year, as described in the Box 1 Challenge section above. As a rule of thumb, think of it as 100 lb of CO2 for every 10 watts of phantom load.

THERMOSTAT - TURN DOWN THE THERMOSTAT WHEN YOU HEAD OUT FOR THE DAY OR TURN IN FOR THE NIGHT

 

69% of Bay Area household heat by natural gas (3). For simplicity, we have therefore assumed heating by natural gas in the following calculation. CO2 emissions from natural gas consumption in Bay Area households are 1.97 metric tons per year (3). Home heating and water heating use approximately the same amount of energy in California (ratio of 27:25) (4), for an estimate of 1.02 metric tons of emissions attributable to home heating. You can save about 10% of energy use by turning down your thermostat by 7°-10°F for 8 hours a day from its normal setting (5), or 0.102 metric tons per year, which is 225 lb per year or 0.62 lb per day. We have rounded this to 1 lb for each use of the THERMOSTAT code word.

DUCK - MINIMIZE ELECTRICITY USE BETWEEN 6PM AND 9PM

 

29% of electricity in California as a whole comes from renewable sources (2), but that doesn't mean that every hour of the day is created equal! According to the California Independent System Operator, which manages the flow of electricity across the high-voltage, long-distance power lines that make up 80 percent of California's grid, hourly average CO2 emissions rates in 2018 ranged from 0.32 lb CO2 per KWh to 0.48 lb CO2 per kWh around noon (depending on season), but ranged from 0.65 lb CO2 per kWh to 0.73 lb CO2 per kWh around 8pm (depending on season) (6). This means that emission rates are much high in the evening relative to the middle of the day! Meanwhile, electricity demand stays high during the evening hours, which means that the largest amount of electricity comes from non-renewable sources during that time, leading to the famous duck curve of energy from non-renewables (7). Switching some of your high-electricity-demand activities (e.g., washer, dishwasher, dryer, EV-charging, even air conditioning) to the daytime hours can save tons of CO2! We have rounded the numbers above to a 40% reduction in emissions for each use of the DUCK code word!

COLD WATER - USE THE COLD WATER SETTING FOR A LOAD OF LAUNDRY

 

As noted above, 69% of Bay Area households heat by natural gas (3), so we have based the calculation on natural gas water heaters. A typical newer washer uses about 20 gallons of water per load (8). The amount of energy required to heat water is 1 BTU per lb per ºF. Heating 20 gallons of water from 55ºF to 90ºF (a typical warm cycle temperature) therefore takes 5840 BTU, which is 0.0583 therms.  Current regulations (9) require anywhere from 34% efficiency for the smallest natural gas water heaters to 81% for the largest, so we have assumed the midpoint of 58% efficiency here. This means that you need 0.101 therms per load of laundry for the warm cycle. One therm of energy produced from natural gas emits 0.0053 metric tons of CO2 (10), such that one load of laundry leads to 1.2 lb of CO2 from heating water for the warm setting. These are the emissions avoided by using the cold water setting. We have rounded this to 1 lb for each use of the COLDWATER code word.

 

AIR DRY - AIR DRY A LOAD OF LAUNDRY

75% of clothes dryers in the United States are electric (11). For simplicity, we have therefore assumed electric dryers in the following calculation. Typical electric dryers use 1,800 to 5,000 watts, or 1.8 to 5 kWh per one hour cycle (12). Taking the average of 3.4 kWh per load, and the fact that one giga-Watt hour (GWh, 1,000,000 kWh) of electricity usage reduction in California leads to 540 metric tons (540 Mg, 1,190,000 lb) of avoided CO2 emissions (1) as discussed above, this results in approximately 4.1 lb CO2 emissions avoided for each load that is not dried in the dryer. We have rounded this to 4 lb for each use of the AIRDRY code word.

SHOWER - TAKE A 5 MINUTE SHOWER

 

A typical shower head uses 2.5 gallons per minute (13), leading to 25 gallons of water use for a 10 minute shower. The amount of energy required to heat water is 1 BTU per lb per ºF. Heating 25 gallons of water from 55ºF to 110ºF therefore takes 11,470 BTU, which is 0.115 therms.  Current regulations (9) require anywhere from 34% efficiency for the smallest natural gas water heaters to 81% for the largest, so we have assumed the midpoint of 58% efficiency here. This means that we need 0.198 therms per 10 minute shower. One therm of energy produced from natural gas emits 0.0053 metric tons of CO2 (10), such that heating water for one 10 minute shower leads to 2.3 lb of CO2. Cutting the shower down to 5 minutes reduces this by half, or 1.2 lb of CO2 saved. We have rounded this to 1 lb for each use of the SHOWER code word.

PUTTING IT ALL TOGETHER

 

Households in the Bay Area emit 44.3 metric tons of CO2 equivalent per year on average (3). Of that, 5.8 tons comes from housing (3), which is 35 pounds per day. By taking the actions associated with the THERMOSTAT code word twice a day, and the COLDWATER, AIRDRY, and SHOWER code words once a day, you are reducing your footprint by 8 pounds a day, or over 20% of your emissions from household energy use!  That’s pretty incredible!

 

References

© 2019 by CrownTheCrowd

© 2019 by CrownTheCrowd