ASHRAE Journal - February 2021 - 29

TECHNICAL FEATURE

FIGURE 5 HPWH electrical load shapes by occupancy schedule.

FIGURE 6 HPWH electrical load shapes for COVID-19 versus pre-COVID-19.

400

350

300

300
Average Power (W)

Average Power (W)

400

250
200
150
100

0
1

" Yes " -Adult Home

11 13 15
Hour of Day
" No " -Away

All Water Heaters

2020 COVID-19 Stay-at-Home Load Shape
During 2020, 49 sites in the Portland, Ore., area were
still active in the ﬁeld study during a regional stay-athome order. Figure 6 shows the Spring 2020 (COVID-19
stay-at-home) aggregated HPWH electrical load shape
for the 49 sites and a load shape for the same ﬁeld sites
from Spring 2018 (pre-COVID-19) in which 43 of the 49
sites were active. For the Spring 2020 proﬁle, it is likely
that most ﬁeld sites had an adult at home throughout
the day due to the regional stay-at-home order. During
Spring 2018, the occupancy schedule would be expected
to generally align with the mix established in Table 1.
Pre-COVID-19 (Spring 2018) and stay-at-home (Spring
2020) HPWH load shapes demonstrate a signiﬁcant shift
in daily use (Figure 6). The pre-COVID-19 load proﬁle
was dual peaking (a.m. and p.m.), while the stay-athome proﬁle demonstrated a plateau load shape with
more consistent HPWH electrical demand throughout
the morning, afternoon and evening for the aggregated
population. For the COVID-19 load shapes, the resulting
HPWH energy use was 2,766 Wh for the pre-COVID-19
(Spring 2018) proﬁle, while the HPWH energy use was
3,692 Wh for the stay-at-home (Spring 2020) proﬁle.

Conclusion
Based on the 147 HPWHs included in the ﬁeld study,
the following trends were observed through the segmentation analysis of HPWH electrical load shapes:
* Occupancy schedule and occupancy count are primary drivers impacting the HPWH electrical load shape.
* Occupancy count and seasonal changes (inlet air
and water conditions) are primary factors inﬂuencing

11 13 15
Hour of Day

Spring 2020 N = 49

19 21

Spring 2018 N = 43

HPWH energy consumption. The condition of the air
entering a HPWH is impacted by its location in the home
and the climate. Inlet water temperature, which varies
over the year, impacts performance.
* Occupancy schedule, occupancy count and seasonal
conditions (entering air and water conditions) are primary drivers for establishing the aggregate peak power
demand of HPWHs.
* The regional COVID-19 stay-at-home period had a
signiﬁcant impact on the HPWH electrical load shape.
The pre-COVID-19 load proﬁle was dual peaking (a.m.
and p.m.), while the COVID-19 stay-at-home proﬁle
demonstrated a plateau load shape with more consistent
electrical demand throughout the day for the aggregated
population.

References

1. NEEA. 2014. " Residential Building Stock Assessment:
Metering Study. " Northwest Energy Efﬁciency Alliance.
https://tinyurl.com/y7jjhbxr
2. Pratt, R.G., et al. 1989. " Description of Electric Energy Use in
Single-Family Residences in the Paciﬁc Northwest-End-Use Load
and Consumer Assessment Program. " DOE/BP-13795-21. Paciﬁc
Northwest National Laboratory.
3. EIA. 2020. " Residential Energy Consumption Survey. " Energy
Information Administration. https://tinyurl.com/y2dfoo9d
4. Mayhorn, E.T. 2015. " Evaluation of the Demand Response
Performance of Electric Water Heater. " Paciﬁc Northwest National
Laboratory. https://tinyurl.com/ybjr8o92
5. CTA. 2018. " CTA-2045-A: Modular
Communications Interface for Energy
Management. " Consumer Technology
Association. https://tinyurl.com/yaxw4mam
6. State of Oregon. 2020. " Stay Home, Save
https://bit.ly/3aC5wVH
Lives. " Oregon Executive Order No. 20-12.
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ASHRAE Journal - February 2021

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