Theme 3: Other difficulties when comparing consumption . 92

Participants mentioned other ways in which judging energy consumption is dif-ficult, and demonstrated how they tried to overcome the difficulties. Difficulties included comparing the energy consumption of appliances that used different types of fuel; using unfamiliar units of energy; comparing appliances that are typically used within different periods of time.

3.3.4.1 Different fuel types

Participants found it difficult to compare the energy consumption of appliances that used different types of fuel: “it’s difficult cos trying to get my head round comparing petrol to electricity” (PC03); “It’s hard to put it into the same category

as the other things I suppose. Just because it’s a different sort of power that it’s using. Fact it’s using the petrol to make it go. . . instead of electricity. It is using electricity but it’s generated by the petrol” (PC07).

To simplify the problem, some participants attempted to mentally convert one of the appliances to using the same fuel as the other so that they could then make a like-for-like comparison of the two appliances. PC03 attempted to consider the relative rates of energy consumption of a car and electric heater if both were powered by petrol (using a petrol-fuelled electricity generator for the heater):

the function’s so different, the energy is so different. If I had for ex-ample a generator, I might be able to think about and compare how much does a generator run something. . . . Probably an electric heater would drain quite quickly. And if I have my car last week, I think I drive it for a couple of hours a day, so maybe quite similar actually in how they would drain. That’s how my brain works: . . . if you were to power a generator with petrol or whatever you use, how quickly an electric heater would drain it. Probably if you were using it for two hours a day, quite quickly actually. (PC03).

PC07 tried a similar approach to considering the relative rates of energy con-sumption of a smoke alarm and an electric shower if they were both powered by batteries: “when I had batteries in the smoke alarms it lasts for ages and if I was to put batteries in my shower I don’t think I would get an awful [large] amount of showers out of it” (PC07).

Although comparing across different fuel types was seen as problematic, some participants took advantage of the situation to help them infer the energy con-sumption of certain appliances. Most appliances are electrical and only the cen-tral heating and hot water (and the hob in some households) use the gas supply.

This means that the gas bill represents the use of only 2-3 appliances compared with the 50 appliances in the average household that are represented by the elec-tricity bill (BEIS, 2017a). Participants attempted to infer the proportion of energy consumed by central heating and water heating (gas) versus appliances (electric-ity): “I sort-of know how much my gas heating because I get a bill” (PC05) but she was still not able to distinguish between water heating and room heating: “I don’t really know what that split is. If my water was heated by electric and my heating by gas, I’d have a clear split but . . . I wouldn’t even know what the split is for heating water and heating the radiators” (PC05). PC08 went a step further

and worked out how to roughly separate the central heating energy consumption from the water heating energy consumption. While the energy consumption of heating hot water was perceived to be similar all year round, variation in the gas bill in the winter months could be used to infer the relative increase in energy consumption due to the central heating:

the heating must be by far the biggest element because if you think about the gas bills throughout the year. So the gas is basically used for the heating, the hot water, and the hob, okay? It’s the only places it’s used for. The hob is a low constant use, the hot water is a constant use, whereas the heating is a seasonal use, okay? And I don’t know the figures but I know that approximately my winter usage for the winter bill is probably in the order of four or five times my summer usage, okay? The only difference can be heating (PC08).

Participants found it difficult to compare the energy consumption of appli-ances across fuel types. Some attempted to mentally convert one of the appliappli-ances to use the same fuel as the other to make the comparison easier. Some were able to use the separation of appliances by fuel types to help them infer the energy consumption of some of the appliances.

3.3.4.2 Unfamiliar units of measurement

Participants tended not to use scientific units to quantify energy consumption, even though some mentioned them. Instead, when referring to units at all, they tended to use financial units: “I pay £36 for a gas bottle, where if I kept the cen-tral heating going, it would cost me in the region of £50, £60.” (PC10). PC08 used money as a common unit across different fuels but accounted for the high amount of tax he perceived to be included in the cost of petrol versus gas (which he perceived not to include any tax). By accounting for the proportion of tax, he perceived that he could estimate the proportion of energy that the money was paying for for each appliance: “I probably spend as much on fuel for my car as I do for heating for the house, and I’m guessing a large proportion of that will be tax, which is why I’m saying energy is gonna be less” (PC08).

PC09 agreed that a common unit would be useful:

it’s just a thought that occurred to me: if the man on the omnibus thought of energy as a unit and it didn’t matter what form it came in,

he may be a bit more conscious what he uses. He thinks of gallons of fuel. He [gets] gas bills and electric bills but he doesn’t ever compare them. They’re separate entities. (PC09).

However, PC10 captures the problem with relying on cost to inform how much energy has been consumed: “my bills are telling me I use more only be-cause the price has gone up more” (PC10). She complained that she could not infer whether changes she made in using household appliances actually made a difference to how much energy she consumed because she used the cost as a unit of measurement: “one minute they’re up, prices are up, one minute they’re down.

. . . So even though I have cut down and cut down and, you know, it doesn’t to seem to have really made that much of an impact” (PC10).

The most used unit of measurement when making judgements about energy consumption was money. This might have been partly because financial units are common across fuel sources, including electricity, gas, and car fuel, and make comparisons easier (Kempton & Montgomery, 1982). It is likely to be also because money is more familiar and easier to understand; most people, though aware of the scientific unit kWh, don’t really understand it (Wood & Newborough, 2007).

3.3.4.3 Different usage periods

The typical duration of using an appliance varies greatly depending on the ap-pliance. For example, a kettle boils water in approximately three minutes while a washing machine cycle can typically vary between 30 minutes and 90 minutes, depending on the wash settings used. Similarly, the typical frequency of use of a kettle might be daily or multiple times a day, while a washing machine might be used three times a week, a lawnmower just once a month in the summer, and the central heating daily but only the winter. Making comparisons of energy consumption between appliances that have different typical usage periods is dif-ficult.

To simplify the problem, some participants tried to use a common usage pe-riod that was applicable to both appliances in the comparison. For appliances that are used only a few times a year or appliances that are used only at certain times during a year, participants tended to judge their energy consumption for the year: “It depends what period you take it over but say over 12 months that one’s [heating] going to be much bigger.” (PC09); “in my head I was annualising

it as well, so the gas barbecue will get used maybe four or five times a year. What I’m guessing, when it does get used it uses up quite a lot of propane” (PC08).

Judging energy consumption for a full year was a useful strategy for PC01 when comparing his weekly use of the car with his infrequent use of the train: “So if I use the car once a week, what’s that? About 52 times a year. How many times do I use a train? Five times? . . . say a car journey’s a 25th of a train journey . . . then I’d say relatively it’s twice [as much energy as the car]” (PC01).

Another way to simplify the comparison was to consider the hypothetical con-sumption of the appliances if they were both used for the same period of time, even if that period of time was not actually realistic for both appliances: “If they were both on for the same amount of time, every day then . . . I would say prob-ably lighting the house would be twice as much as the TV, for the same period of time” (PC06); “I would say when they were both on that the oven uses about four times more than the lights” (PC07); “I know it only lasts for a very short time but if I was to run it the same amount as my iron which is a good hour, yeah the kettle would use a lot more” (PC10).

Different appliances have different typical usage periods. When comparing appliances with different usage periods, participants either found a common us-age period that made sense for both appliances, or they tried to imagine con-sumption over the same period of time, even if it was not realistic.

3.3.4.4 Summary and implications of Theme 3

In addition to the complexities discussed in Theme 2, participants demonstrated other difficulties experienced when judging energy consumption. These other difficulties were mainly around making comparisons between appliances that differed in significant ways: comparing across different fuel types and compar-ing across different typical usage periods. Participants also suggested difficul-ties with using unfamiliar units of measurement. In each case, some partici-pants attempted to simplify the problem by looking for common factors that both appliances in the comparison shared. It would be necessary for more system-atic research to explore whether all householders perceive these difficulties and whether all householders are then able to simplify the problems by identifying common factors across both appliances.

3.4 Discussion

Three themes were constructed using thematic analysis to capture how partici-pants inferred and compared the energy consumption of appliances and the com-plexities they faced in making the judgements.