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Directly Controlling the Winter Peak

Learning lessons from PSE’s residential demand response pilot.

Fortnightly Magazine - August 2012

evaluations like the PSE program analysis. Fixed effects make it possible to control for the fact that individuals can have very different levels of electricity consumption that don’t change over time; a participant with a very large house, for example, will consume much more electricity than one with a small house, just as one whose home is poorly insulated will consume more than one whose home is well insulated. Using fixed effects, it’s possible to control for all those differences between individuals that don’t change over time without collecting detailed information about each participant.

The estimated average demand impacts of the various devices on winter morning and afternoon events called by PSE are shown in Figure 2. As noted previously, there were only two afternoon events compared with seven morning events.

The estimated impacts of water heater curtailment weren’t particularly surprising, and are in fact very close to those estimated for PJM in a study by RLW Analytics in 2007 (see endnote 1). Specifically, that study found that the average water heater curtailment load impact between 6 a.m. and 9 a.m. totaled 0.73 kW, and that the average impact between 4 p.m. and 7 p.m. was 0.49 kW. Likewise, there was nothing particularly surprising about the impacts estimated for electric furnaces—outdoor temperatures in morning tend to be colder than the in the afternoon, leading to higher use in the mornings and therefore higher demand reductions during morning events.

The most surprising results are the very high estimated impact resulting from heat pump curtailment in the morning and the very low estimated impact for baseboard heating curtailment in the morning, along with the fact that no statistically significant impacts at all could be estimated for afternoon baseboard curtailment. Interestingly, according to the survey conducted by EMI, while more than half of participants with heat pumps needed to take extra steps to stay warm— e.g., put on a sweater—a large majority of participants whose water heaters, baseboard heating, or electric furnaces were controlled remained comfortable and undisturbed throughout the event. Indeed, many water heater participants were unaware that a curtailment event had taken place.

Heat Pumps

The morning heat pump impacts are even more striking when plotted (see Figure 3) . The left vertical axis shows the average hourly demand observed among pilot participants with heat pumps on the two days in which there was both a morning and an afternoon event, the average hourly demand observed on days in which the temperature was comparable to that of event days, and what the analysis implies the average hourly demand would have been on the event days if no event had been called. The right vertical axis shows the average temperature at each hour of the day for the event days under consideration, and the average temperature at each hour of days with comparable temperature.

Particularly striking is the difference between the magnitude of the impact of morning and afternoon curtailments. While it’s clearly warmer during the afternoon curtailments, the degree to which the impact appears to be sensitive to that difference in temperature suggests