Gas consumption based on occupancy levels

The number of occupants in each of the dwelling types and experimental conditions may account for some of the higher values of gas consumption within each group. Figure 4.9 shows the difference in gas consumption scores between experimental conditions for the different occupancy levels across the two property types. The results show that those in flatted accommodation with an Ewgeco IHD on display have considerably lower gas consumption than the controls. The results are similar for the housing group. There is no clear trend from the data explaining how occupancy levels affect the gas consumption scores.

Figure 4.9: Percentage difference gas consumption for flats and houses based on occupancy levels

The three or more person group can be separated into three and four person households. For the three person houses, the intervention group had a 2% higher gas consumption score than the controls and the four person intervention group

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had a score 7% lower than the control group. However, due to participant withdrawal, this group had only one control property in it, which arguably is not enough data to draw a conclusion. Therefore the three person and four person dwelling sizes were grouped together. During the qualitative data capture, the occupants in the three and four person households commented on the difficulties they faced when trying to persuade or enforce energy saving habits relating to gas usage (heating). This is further explored in Chapter 6.

Gas consumption over time: A longitudinal study

Due to the available resources and to participant drop out, only 20 of the original 31 participants in the flatted accommodation were available for the 2013 data capture. The analysis of the difference in gas consumption between the experimental conditions (n=20) was isolated for the monitoring period Sept 2010 to Feb 2011 (Phase 1) and then calculated for Phase 2. The results are plotted in Figure 4.10. Similar to the findings for all 31 available flats, the average (mean) gas consumption scores for Phase 1 for the 10 intervention flats (M=0.93, SE=0.12) available in 2013 was 25% lower than for the 10 flats in the control group (M=1.24, SE=0.10). A one-tailed independent t-test showed that this difference was statistically significant (t(18)=1.97, p < .05) and that it represents a medium–sized effect (r=0.42).

When the average (mean) gas consumption scores were compared for the monitoring period Phase 2, the same 10 properties in the intervention group (M=0.84, SE=0.15) had a gas consumption score that was 26% lower than the score for the control group (M=1.13, SE=0.14). A one-tailed independent t-test showed that this difference was not statistically significant (t(18)=1.44, p=.08) and that it represents a medium–sized effect (r=0.32)

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Figure 4.10: Mean gas consumption scores for 20 flats within the experimental condition across phase 1 and phase 2

During Phase 2, the control group (M=1.13, SE=0.14) reduced their mean (average) gas consumption score by 9% compared to the mean (average) consumption for the Phase 1 monitoring period (M=1.24, SE=0.10). A two-tailed dependent paired samples t-test showed that this finding was not significant (t(9)=1.06, p> .05). This was a large-sized effect (r=0.68). The mean gas consumption score calculated for Phase 2 for the intervention group (M=0.84, SE=0.15) showed that they reduced their consumption by 10% compared to their average (mean) gas consumption score for Phase 1 (M=0.93, SE=0.12). This was not statistically significant (t(9)=2.11, p=.06), but it was measured as having a very large-sized effect (r=0.96).

The decrease in gas consumption score between the two periods is of a similar magnitude. Assuming that the internal temperatures of the dwellings and the consumption of hot water have not changed significantly, then the drop in gas consumption score may be a result of less extreme cold weather during the winters of 2011-12 and 2012-13. The temperature margin between the SAP and local temperatures is much closer for the monitoring period Phase 2. Working

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with the assumptions made by the SAP based on research carried out by the Energy Savings Trust (2013) on the linear relationship between the number of occupants and hot water use, it is likely, because the number of occupants living in each property has not changed over time, that their hot water consumption has not changed a great deal. As the boilers are less than five years old, it is conceivable that the boiler efficiency has not dropped to levels that would impact on water heating.

The change in gas consumption over time is likely to be a result of differences in year on year winter temperatures. The HDD plotted in Figure 4.10 gives an indication of one reason why the gas consumption score in Phase 2 is lower than that of Phase 1, which is arguably the most influential reason for the change. Other reasons include the increase of the average UK domestic gas bill, which increased by 10% from 2011 to 2012 and by 7% from 2012 to 2013 (DECC 2014c).

Overall, for the entire 37 month monitoring period, on average the intervention group of 10 flats (M=0.84, SE=0.14) reduced their average gas consumption score by 27% compared to the control group (M=1.15, SE=0.13). This difference was statistically significant (t(18)=1.71, p=.05), and the result represented a medium-sized effect (r=0.37).

Conclusion

The results from the normalised gas consumption data for the first six month Phase 1 monitoring period show that the intervention group had on average (mean) significantly lower gas consumption than the control group. This was also the finding when the groups were divided by property type. The intervention group for those living in flats and houses had a significantly lower gas consumption score than the respective control groups for December 2010, which was the coldest December for 100 years.

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When the property types were further divided by number of occupants, a large difference in energy savings was observed between the lower occupancy (one and two person) homes and the larger occupancy (three and four person) homes. The three and four person properties where typically occupied by two adults and a person below the age of 18. In contrast, the two person houses and flats where typically occupied by 1 adult and a child below the age of 18. The interviewees who lived in houses with households of three or four people and an Ewgeco IHD commented on the increased difficulty of trying to regulate the use of gas that resulted from the number of people, specifically adults who had access to the heating controls. The person in the three and four person homes who professed to be the more energy efficient and therefore the more likely to obverse the IHD was not always the person responsible for paying the utility bills. Often the person who paid the bills had little time for changing their existing energy saving habits.

This type of conflicting dynamic between the two adults appeared to be commonplace across the group, where energy saving or energy efficiency was subconsciously seen as another household chore that was then allocated to or voluntarily done by one of the adults. Furthermore, energy saving actions or accomplishments made by one adult were often undermined by the other. Both adults would criticise each other for their role in ‘wasting’ or saving gas (heating). These actions did not seem to be any more than a trivial annoyance. This finding suggests a weakness in the ability of the IHD alone to both implement and maintain long term energy savings for homes with multiple adult occupancy and for households with more than two people.

This type of energy use dynamic within the home suggests that the likely reason for the smaller savings in gas consumption score made by the intervention group who lived in four person rather than two person homes. However, the self- professed energy champions of the three and four person intervention homes praised the gas display portion of the device, describing how they could for the first time see the benefits of turning down the thermostats.

According to the UK census data collected in 2011, the ONS and National Records of Scotland estimate that the average household size in the UK is 2.3

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people (ONS 2013) and the average household size in Scotland is 2.2 people (National Records of Scotland 2013). Two person households accounted for the largest single household group (34% UK, 34% Scotland), followed by one person households (31% UK, 35% Scotland). The average household size (number of occupants) has shown a downward trend over the past 50 years. However, this means that households with three or more persons collectively account for the largest group in the UK (35%) and are still a substantial proportion of the dwelling population in Scotland (31%).

The census data does not differentiate between two person households with two adults or one adult and one child (under the age of 18). While the IHD appears to provide saving in gas usage for the two single largest household size types in the UK, it may not be as effective in homes with more occupants, which may also have a higher demand for gas fuel.

The additional 31 months of data collected for the 20 participating flats shows that on average those with the Ewgeco IHD had a significantly lower gas consumption score than the control group for the full 37 months of data. This is a significant finding and demonstrates that occupants with the coloured dual fuel Ewgeco IHD not only had a significantly lower gas consumption score than those properties with no IHD, but also maintained that same level of lower gas consumption score for the three years after they had begun to interact with the device.

Many authors in the field of domestic energy use change have reported that the participants in their trials become detached from the energy monitor after six months and that the energy consumption of the intervention group either rose or become higher than the control group’s. As discussed in Chapter 2, many other studies have only focused on electricity use, and many used only monochrome or numerical style energy monitors.

Effect of selecting a normalisation condition

As discussed in Chapter 4.2, the normalisation condition applied to the raw gas consumption data for each property was chosen from a list of well recognised

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normalisation conditions. Dividing the gas energy by the SAP-predicted energy requirement for space and water heating overcame a plethora of variables, such as fabric and ventilation heat loss, heat gains and floor area, which are applicable but in this case different for each property. The SAP gas requirement normalisation condition was selected because it had consistently lower coefficient of variation (score).

The difference in gas consumption, as calculated through the use of the other normalisation conditions, has been summarised in Table 5.2. These differences are listed for the intervention group and for the control group; the normalisation condition used to calculate the results in this chapter is highlighted in grey.

If the raw gas consumption data was used to provide the results, then the overall energy difference result would be the same – a 20% reduction over the control group. However, the magnitude of gas savings would be different between the property types. The occupants living in houses would have saved 6% more gas over their control group than those living in flats.

If the gas consumption data were normalised by total floor area, the percentage difference in gas consumption would be considerable lower for the flatted properties, but the same for the housing sample. If the data were normalised by the number of occupants or dwelling volume, the percentage difference made by the flatted sample would have been significantly lower.

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Intervention group mean (average) consumption value was less than the control groups mean (average consumption by: Normalisation

condition

for the entire sample (n=52):

For sample grouped to flatted

accommodation (n=31)

For sample grouped to housing accommodation (n=21) gas recorded (unconditioned) 20% 17% 23% gas/Area (m^2) 14% 11% 17% gas/Volume (m^3) 10% 2% 17% gas/# ppl 14% 2% 29%

gas / SAP gas req 20% 22% 17%

gas / SAP gas primary energy

20% 23% 17%

Table 4.2: Gas consumption differences by normalisation condition for data collection during Phase 1

This chapter has analysed the gas consumption data collected from the 52 social housing tenants for six months and the 20 social housing tenants for 37 months. The analysis shows that those in the intervention group with a new generation of coloured real-time IHD consumed significantly less gas than a group of similar control properties. The longer term study shows that the intervention group with the IHD continued to consume less gas than the control group.

The next chapter presents and discusses the effects on domestic electricity consumption of the occupants having visual access to the coloured real-time electricity consumption IHD.

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