Page 61 - Green Builder Nov-Dec 2021 Issue

KEY
BUILDING PERSPECTIVE: 2019 60% 160%
Hour Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
1
2
3
4
If you want the short summary for 6 5
California: 7
The extraordinary efficiency of electric 8
■ 9
heat pumps trumps the inefficiency of 10 11
electricity production and transmission. 12
As the grid gets cleaner, the case for 13
14
heat pumps grows even stronger. 15
Hot water is used year-round, including 16
■ 17
when the grid is cleanest in California, 18
19
which makes heat pump water heaters 20
21
an easy win. 22
Heat pump space heaters are a win in 23
■ 24
well-insulated homes, and even more SOURCE: CALIFORNIA ENERGY COMMISSION, “BUILDING DECARBONIZATION,” 2018
so when the heat is turned down for a
few hours when the grid is dirtiest (e.g.,
evenings). For other homes, it may be BUILDING PERSPECTIVE: 2030
best to improve the building envelope Hour Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
first. 1
The California analysis has some 2 3
gaps, and work on this is ongoing. The 4
analysis will be quite different for states 6 5
with different grid mixes and heating 7 8
needs. For example, a state that relies 9
more on wind energy and less on solar 10 11
would have relatively more clean energy 12
available during colder times, further 13
14
strengthening the case for heat pumps. 15
16
17
18
GETTING ENERGY TO THE BUILDING: 19
GAS VS. ELECTRICITY EMISSIONS 20
21
How much pollution is generated, just to 22
transfer energy to a building? The chart 23
24
at the top right compares electricity SOURCE: CALIFORNIA ENERGY COMMISSION, “BUILDING DECARBONIZATION,” 2018
emissions to gas emissions, as delivered
to the building. No appliance is using the
energy yet; the chart reflects emissions are red. On average, gas emissions are It is important to note that fugitive
just from generating and delivering the lower than electricity emissions. Yes, emissions (methane leaks from
energy. The chart has one square for you read that right. And, in particular, transmission and distribution) are not
each hour of the year. Months go across you can see that the comparison is poor included in the calculations behind
the x-axis (from January on the left to for electricity during times when you this diagram, while the corresponding
December on the right), and hours go are likely to be heating a building the adjustments for electricity (transmission
along the y-axis (from early morning at most (e.g., fall and winter mornings and and distribution losses to the home) are
the top to late night at the bottom). A green evenings). included. Methane leaks can be significant,
square indicates that electricity has lower If you look to 2030 (above), when we so incorporating those leaks would make
emissions intensity than gas, measured will have more renewables (60 percent these pictures greener.
in emissions per unit of energy, while red compared to 31 percent in 2019), the
means electricity has higher emissions. picture is better, with 70 percent of the HEATER EFFICIENCY
You can see that 40 percent of the squares favorable for electricity, though Given the above, we know that heater
squares here are green, and 60 percent it has a similar overall pattern. efficiency is critical if we want to reduce

www.greenbuildermedia.com November/December 2021 GREEN BUILDER 59