Page 62 - Green Builder Nov-Dec 2021 Issue

BUILDING SCIENCE

Innovative solutions for high-performance homes.

2019 GHG ELEC HPWH Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
1.1
7.5
1.4
VS. GAS TANKLESS 2 1 4.9 1.6 0.9 0.5 0.4 0.2 2.5 0.5 1.3 3.2 2.6 0.4
0.3
1.3
1.2
1.1
1.8
0.4
2.9
0.6
0.1
3 3.8 2.1 0.3 3.2 0.3 2.0 1.0 0.6 8.5 4.3 0.1 1.8
4 6.1 6.3 0.6 0.5 0.7 0.3 0.3 0.3 0.5 0.4 1.3 1.1
5 0.6 0.4 0.5 0.7 0.3 0.3 0.3 0.3 0.0 0.5 0.8 1.4
emissions by switching from gas to 6 1.1 0.8 0.2 0.2 0.3 0.2 0.3 0.2 0.2 0.4 0.7 1.2
electric. An electric heater that is “just” 7 0.2 0.3 0.2 0.2 0.2 0.2 0.2 0.3 0.3 0.2 0.2 0.4
95 percent efficient, like the best modern 8 0.3 0.3 0.4 0.3 0.3 0.5 0.3 0.3 0.7 0.2 0.3 0.2
gas furnace, is not going to cut it. And that 9 0.3 0.5 0.4 0.3 0.5 0.3 0.4 0.3 0.7 0.4 0.4 0.4
is the magic of heat pumps. A modern 10 0.2 0.3 0.3 0.3 0.5 0.4 0.6 0.3 0.4 0.5 0.3 0.8
heat pump water heater produces about 11 0.5 0.6 0.2 0.4 0.4 0.3 0.3 0.6 0.3 0.6 0.4 1.1
three times as much energy (heat) as it 12 0.5 1.0 0.3 0.3 0.5 0.1 0.3 0.5 0.4 0.4 0.4 0.4
consumes. Instead of creating heat, it HOURS 13 0.4 0.3 0.3 0.2 0.3 0.1 0.2 0.3 0.2 0.3 0.5 0.3
extracts heat from the outside air, using a 14 0.2 0.2 0.2 0.2 0.2 0.2 0.1 0.1 0.1 0.1 0.5 0.2
refrigerant, and moves it into the building. 15 0.2 0.2 0.1 0.1 0.1 0.2 0.1 0.1 0.2 0.1 0.2 0.3
This is more or less how a refrigerator 16 0.3 0.2 0.1 0.3 0.3 0.2 0.2 0.2 0.2 0.2 0.2 0.1
operates, but in reverse. 17 0.3 0.4 0.1 0.5 0.1 0.2 0.1 0.2 0.1 0.1 0.2 0.2
A measure called UEF, or Uniform 18 0.9 0.2 0.2 0.3 0.2 0.1 0.1 0.2 0.2 0.3 0.2 0.3 SOURCE: REDWOOD ENERGY ZERO CARBON RETREAT, FEBRUARY 2019
Energy Factor, is used to compare heat 19 0.7 0.3 0.3 0.3 0.2 0.1 0.3 0.1 0.2 0.4 0.3 0.3
pump water heaters. It is a ratio of the 20 0.5 0.4 1.0 0.2 0.2 0.4 0.3 0.5 0.5 0.4 0.3 0.3
energy output to input, but with some 21 0.6 0.5 0.3 0.2 0.2 0.6 0.3 0.8 0.5 0.2 0.5 0.7
nuances. Per a spokesperson at the CEC, 22 0.3 0.8 0.7 0.7 0.4 0.2 0.8 0.6 0.7 0.7 0.5 0.9
the metric is pretty reliable for temperate 23 1.1 0.3 0.8 1.6 0.5 0.7 0.9 1.3 1.2 0.9 1.4 2.9
areas: UEF includes standby tank losses 24 0.7 0.3 1.9 0.7 1.3 0.4 0.9 3.0 0.7 1.1 0.7 1.4
during the test procedure, as well as
measuring the performance of the heat
pump over the whole test procedure. In
general, the UEF gets you in the ballpark
of actual performance in mild climates, but 2019 GHG ELEC HP RELATIVE TO GAS FURNACE
for colder climates or larger households, Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
there is more backup electric resistance 1 792.6 452.1 231.7 166.4 19.8 13.9 0.0 0.0 0.0 51.6 411.9 807.6
use and therefore the performance would 2 887.6 568.2 290.5 248.1 37.3 11.8 0.0 0.0 0.0 43.7 493.6 888.9
be lower. 3 969.1 649.8 352.7 315.1 59.1 13.1 0.0 0.0 0.0 58.0 585.5 975.0
The 2019 California building code 4 134.8 731.3 429.0 384.8 78.8 15.0 0.0 0.0 0.0 74.9 671.6 1040.9
requires that replacement electric water 5 30.8 239.1 477.3 387.0 90.2 15.4 0.0 0.0 0.0 92.2 55.4 116.8
heaters for consumers have a UEF of at 6 11.9 17.6 0.9 0.5 81.4 11.3 0.0 0.0 0.0 19.6 20.6 14.6
least 2 when more than 55 gallons. In 7 0.3 0.3 0.1 0.1 0.1 0.0 0.0 0.0 0.0 0.2 0.6 0.3
practice, it is easy to find heat pump water 8 0.1 0.1 0.1 0.2 0.1 0.1 0.0 0.0 0.0 0.3 0.1 0.2
heaters with much higher efficiency (i.e., 9 0.2 0.1 0.1 0.1 0.1 0.1 0.0 0.0 0.0 0.2 0.2 0.2
UEF 3 or more) for residential buildings. 10 0.2 0.1 0.1 0.1 0.1 0.1 0.0 0.0 0.0 0.2 0.1 0.2
These water heaters are a clear emissions 11 0.2 0.1 0.1 0.1 0.1 0.0 0.0 0.0 0.0 0.2 0.1 0.1
win. The chart at right shows how such a 12 0.2 0.1 0.1 0.1 0.0 0.0 0.0 0.0 0.0 0.2 0.1 0.1
heat pump water heater compares with a HOURS 13 0.2 0.1 0.2 0.2 0.0 0.0 0.0 0.0 0.0 0.2 0.1 0.1
tankless gas water heater, which is already 14 0.2 0.1 0.2 0.2 0.0 0.0 0.0 0.0 0.0 0.3 0.1 0.2
much more efficient than a gas tank water 15 0.2 0.2 0.2 0.2 0.0 0.0 0.0 0.0 0.0 0.3 0.2 0.2
heater. This chart is similar to the 2019 16 0.2 0.2 0.2 0.2 0.0 0.0 0.0 0.0 0.0 0.3 0.2 0.2
chart above, but it takes into account the 17 0.2 0.2 0.2 0.2 0.0 0.0 0.0 0.0 0.0 0.3 0.2 0.2
efficiency of the water heater. 18 0.2 0.2 0.2 0.3 0.0 0.0 0.0 0.0 0.0 0.4 0.2 0.2
Space heat pumps have a more difficult 19 0.2 0.2 0.2 0.2 0.0 0.0 0.0 0.0 0.0 0.4 0.2 0.3 SOURCE: REDWOOD ENERGY ZERO CARBON RETREAT, FEBRUARY 2019
job in some ways, because they tend to run 20 0.3 0.2 0.2 0.3 0.0 0.0 0.0 0.0 0.0 0.4 0.2 0.3
more when it is cooler. These heat pumps 21 0.3 0.2 0.3 0.3 0.0 0.0 0.0 0.0 0.0 0.4 0.3 0.3
will run nearly constantly in the relatively 22 0.4 0.2 0.3 0.2 0.0 0.0 0.0 0.0 0.0 0.4 0.3 0.3
dirty night hours, while a gas furnace 23 0.4 0.3 0.5 61.7 4.4 0.0 0.0 0.0 0.0 16.8 0.3 0.4
will run infrequently. That means the 24 703.3 332.5 163.7 101.1 10.6 2.4 0.0 0.0 0.0 19.6 349.0 685.9

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