Understanding consumers’ behaviour for a more sustainable product design and reduced energy consumption in automatic dishwashing – an Australian household investigation and learning from a comparison with European ecodesign

Understanding consumer usage to design new products and the right recommendations of use need to be based on a profound understanding of how such a product is actually used.

Shove (Shove, 2004), for example, describes the modern washing machine cycle programme design as a result of an interplay between clothing fashion designers, synthetic fabrics, environmental concerns, cleanliness standards of excellence and technology limitations. Thus, it can be described as a socio-technical system with an interplay between a variety of factors and participants, including manufacturers, technology, regulators, consumer practices, cultural norms and infrastructure (Elzen et al., 2004). Changes in socio-technical systems are difficult because of the need to change not only the technology but also the behaviour of all the stakeholders (Chmutina et al., 2021).

This is especially true for dishwashing at home, which has the task to provide clean and dry dishes to the household members; not only an aesthetic task but also with hygienic requirements. To perform the dishwashing task, the householder has the choice between doing it manually or using an automatic dishwasher if the household owns one. Doing the dishes needs resources (water, thermal or electric energy), investments (mainly if an automatic dishwasher is used), supporting chemical compounds, and the time and efforts of the user (Stamminger, 2011). Behind all of this, an infrastructure is required providing the resources, manufacturers producing the dishwashers and the chemistry and regulators ensuring that only safe and efficient products are utilised. The most uncontrolled and uneducated factor in this interplay is the consumer/user. Without ever being educated and trained in automatic or manual dishwashing, he/she is deciding how to wash and dry the dishes either manually or automatically based on the resource use of their household and the economic consequences (Stamminger, 2020). Studies have shown that this user behaviour is rather pre-assigned and not easy to change (Gillessen et al., 2013).

Although efficiency comparisons between manual and automatic dishwashing were already carried out in the last century (e.g. (Weaver et al., 1956), studies on dishwashing techniques used in private households and their efficiency were scarce for a long time. It has only been in the last 20 years that more studies on dishwashing behaviour have been conducted. The initial aim was to record the current behaviour in different countries (Belke et al., 2018; Berkholz et al., 2013; Stamminger, Elschenbroich, et al., 2007). Nowadays, the private household sector accounts for a large share of global water and energy consumption, thus, the focus has changed towards increasing energy and water efficiency (Belke et al., 2018; Maitra et al., 2017). This immediately raises the question of which of the two basic ways of washing dishes, by hand or machine, provides the more efficient way of cleaning dishes, with consistently good cleaning results. Various studies have addressed this issue (Berkholz et al., 2013; Vivian et al., 2011), showing that regarding water, energy and time consumption, automatic dishwashing is clearly superior to manual dishwashing. Furthermore, automatic dishwashers lead to hygienic cleaning results. Vivian et al. (Vivian et al., 2011) confirmed these findings with an analysis of data from six European countries (United Kingdom, Germany, Italy, Spain, Portugal and Poland). They stated that the shift from manual to mechanical dishwashing was beneficial for energy consumption, CO₂ emissions and cost-savings. On average, relative reductions of between 50 and 60 % could be achieved regarding all three parameters.

Regardless of the type of washing-up, both methods show large differences in the amount of resources used for the same work (Belke et al., 2018; Berkholz et al., 2013; Maitra et al., 2017; Stamminger, Rummler, et al., 2007). In the case of automatic dishwashing, these differences are only partly due to the efficiency of the dishwasher itself, but mainly to the way in which the machine is used by the consumer (Alt et al., 2023b; Richter, 2010). Alt et al. (Alt et al., 2023b) have shown for Europe that simple changes in consumer behaviour can save more than an average of 20 % of energy consumption. This type of study reveals many details about how consumers use their dishwashers, such as the cleaning programme selected for different soiling levels. Consequently, recommendations can be made to ensure that the consumer’s wants and needs are met, while still saving resources. It is interesting to see whether this concept also works on the opposite side of the world, down under, in Australia.

Automatic dishwashing and its regulation by energy efficiency programmes has had a long tradition in Australia (Harrington & Wilkenfeld, 1997). However, consumer behaviour studies and real-life investigations into the usage of dishwashers are not reported in the literature.

The specific task, therefore, is to estimate the distribution of total energy and water consumption of the automatic dishwashing machines installed in private homes and data from a representative survey of consumer usage in Australia. Those values are for specific programmes of individual models of dishwashers available on the Australian market, thus, it is also necessary to consider the market share of the manufacturer and the representative consumer choice of individual programmes. Using this information, which recommendation of changes in the consumer behaviour may be proposed to achieve a saving of resources, while still fulfilling the basic requirements for a good cleaning of the dish items will be modelled. This will also provide some understanding of consumer usage to design new products and the right recommendations of use. Comparing this learning for Australia with other countries may also let a deeper understanding of the socio-technical system in which the dishwasher is operated be gained. This may allow solutions to be found for optimising the system beyond Australia.

This model allows the calculation of representative average household energy and water consumption for the dishwasher programmes selected during normal use in Australian households. Due to the high use of the modifier ‘express/speed/quick/time-saving’ by consumers, it is relevant to consider the use of the “pure” seven programmes plus those programmes with the modifier 'express/speed/quick/time-saving’. This model allows the calculation of the average consumption for each of the programmes defined with and without the use of the modifier (Table 6).

It is possible to calculate the average of the consumption per cycle by adding the information from the representative consumer survey of the frequency of programme use by the consumer (Table 6).

The average consumption of 1.02 kWh of energy and 13.0 L of water is considered the base case for this study as these figures describe the average resource use of dishwashers in Australian households today in the most representative way. The data for the ‘eco’ programme are well in-line with what is known from the official report on the energy efficiency trends of whitegoods in Australia from 1993 to 2014 (Whitegoods Efficiency Trends 1993–2014, 2016). Here, an average energy use of 0.76 kWh and water use of 12.4 L for all dishwashers sold is described for 2014, the last year reported. As the disclosed trend of lowering those values has probably continued up to 2020, an average of the installed base of dishwashers in 2020 of 0.71 kWh and 11.8 L is quite realistic. Data on other programmes are unfortunately not found in the literature published.

It is known from the consumer survey how the consumers assess the soil level of the dishes cleaned in the programmes selected¹. This allows the average energy consumption of the programmes used for the soil levels the user has to be depicted (coding: lightly soiled = 1, normal = 2, heavy = 3). This qualitative approach based on the self-assessment of the participating consumer reveals (Fig. 2), on the one hand, the clear differentiation the consumer makes when selecting a programme and, on the other hand, that there are a variety of programmes available for almost the same level of soiling.

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The base case of the scenario simulation is the situation of the dishwasher as installed in Australian homes and the consumer behaviour as assessed by the consumer questionnaire (representative consumer survey). Both data sources combined give an average consumption of 1.02 kWh of energy and 13.0 L of water per cycle as the base case.

Based on this, a scenario has been developed where only those programmes which use the lowest amount of energy have been selected and modelled for each soil level (Fig. 2). This would mean the usage of the ‘IntS’ programmes should be shifted to the ‘Int’ programme. Similarly, the usage of the Quick high temperature programme ‘Quh’ and the Gentle ‘Gen’ programme should and could be shifted to the Quick low temperature programme ‘Qul’ as the soil levels used by the consumers are quite similar.

The situation is not as obvious for those programmes used for the medium level of soiling, as here, two programmes using low energy are somehow competing with each other: the programme called ‘Normal/regular/everyday’ and that called ‘Eco’. One needs to consider the legal requirements in Australia as defined in the “Greenhouse and Energy Minimum Standards Act 2012”, referring to the national standards AS/NZS2007.1 (Australian/New Zealand Standard, 2005a) and AS/NZS2007.2 (Australian/New Zealand Standard, 2005b) to understand the possible differences. The programme for energy efficiency labelling is defined here as “The program to be used for energy efficiency labelling is the program, including all associated specific settings, nominated by the supplier that is recommended to wash a normally soiled load at rated capacity and which meets the performance criteria specified in Section 3” (AS/NZS 2007.2:2005 chapter 1.5.6). In Section 3.3 it is defined that “The dishwasher shall meet the requirements for washing index set out in Section 4 of AS/NZS 2007.1:2005 when connected to the primary water connection mode.” ((Australian/New Zealand Standard, 2005a)). In Section 4 it is specified that “[…] the washing index of a dishwasher shall be not less than 0.9”. Furthermore, “… the drying performance index of a dishwasher shall be not less than 0.5 (50 %)”. Both indices are calculated as the ratio of the test machine to the performance in a special reference programme for AUS/NZ in a reference dishwasher. This programme heats up to a nominal temperature of 45 °C.

If there is more than one program recommended to wash a normally soiled load at rated capacity e.g. ‘Normal’, ‘Normal eco’ and/or ‘Normal plus’, then the washing index performance criteria of Section 3 shall be met by each of these programs” (AS/NZS 2007.2 chapter 2.2.1).

This means that all programmes nominated for cleaning normally soiled loads have to fulfil the minimum performance requirements of cleaning a normally soiled load. In many cases, these are called ‘Eco’ or ‘Normal Eco’. Thus, the strategy must be to use this ‘Eco’ programme for all normally soiled dishes (Fig. 3).

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Only three programmes remain when this is done: Eco, Intensive and Quick (low temperature), and the modifier ‘express/speed/quick/time-saving’ is no longer used. This delivers (Fig. 4) an average energy consumption of 0.78 kWh and water consumption of 11.8 L per cycle, corresponding to a saving of 24 % in energy and 9 % in water consumption. This is at an expense of just 4 min prolongation of the programme duration (from 102 min to 106 min on average).

This is the most energy-saving scenario achieved by matching the programme performance level with the consumer soil level, while avoiding an unacceptable prolongation of the average programme duration.

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Implementing this learning in consumer communication would require that the following messages are conveyed:

“Do not use the programme modifier ‘express/speed/quick/time-saving’ as it may take significant additional resources (energy, water).

Use the ECO programme for all normally soiled dish loads and accept the slightly longer programme duration as this will provide a good cleaning performance with the lowest use of resources (energy, water).

Use the Quick/fast (45 °C, Jet, 30', express, …) programme for lightly soiled dishes.”

The task of this study was to understand Australian consumers’ behaviour regarding automatic dishwashing and to learn about a more sustainable product design and use. It was possible to identify relatively simple recommendations by using publicly available data on the installed base of dishwashers in Australian home and performing a representative consumer usage study of the dishwashers that, when followed, would allow a considerable reduction of energy and water consumption in automatic dishwashing. Furthermore, a comparison of the results of the Australian model of resource use with a similar model of European resource use allowed one to identify important differences in the regulatory approach.

The calculations depicted above show that by applying some simple rules, consumers in Australia would easily save an average of more than 20 % on energy without reducing the performance of their dishwasher. However, it may be even of more interest comparing those results with results from other parts of the world, especially with Europe, as socio-demographics and political systems are comparable. Alt et al. (Alt et al., 2023a, 2023b) performed a similar analysis in six European countries and also found a possible saving of about 20 % on energy by applying the same three rules for the programme choice by the consumer. However, while in Australia the actual value of the average consumer programme choice is modelled to be at 1.02 kWh of energy, the values for European countries are between 1.16 and 1.25 kWh, a difference of again about 20 %. It is of interest to see where this difference comes from and learn what has possibly influenced this difference. A comparison between the technical data and consumer behaviour may help us to understand whether this difference comes from different dishwashing machine characteristics (programme, market representation) or consumer behaviour (programme choice, soil level)?

When comparing the use of the different programmes offered by a dishwasher (Fig. 5), it can be seen that Australian consumers use the “Normal/Regular/Everyday” programme and the “Eco” programme to a high degree, which is similar to British users, but generally higher than other European countries examined. Additionally, Australian consumers select the modifier ‘express/speed/quick/time-saving’ quite often, especially for those two programmes (Fig. 6), which increases the energy and water use of these programmes.

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Comparing the soil level associated with each of the seven programmes (when used) shows no deviation to the soil level associated in the other countries (Fig. 7). The same is true with the praxis to pre-rinse the dishes before loading them in the dishwasher, although Australian consumers seem to do it a bit more frequently (Fig. 8) than consumers in any of the other countries investigated. Australian consumers do not use their dishwashers very much differently from European consumers, at least to the extent that this would explain the lower energy use per average programme which resulted from the model calculation.

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With more than half of dishwashers coming from manufacturers in Europe, the difference in dishwashers in Australian households must lie in the dishwashers themselves (Table 3). The dishwashers for the Australian market will probably be specially adapted to meet regulatory requirements, in particular the lower requirements for cleaning performance, while, at the same time, fulfilling higher energy efficiency requirements. The difference is not only remarkable in the energy use, but also in the programme duration, which is also quite short (Fig. 9). No difference is evident regarding the water usage. Comparing the energy use for the three most relevant programmes (Int, Nor and Eco) (Fig. 10) clearly shows the advantage of the Australian average installed dishwasher, especially in the programmes Nor and Eco.

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In contrast to the Australian regulation presented in Chapter ‘Simulation’, the European regulation on ecodesign requirements for household dishwashers requested since 2011 ‘for all household dishwashers, the Cleaning Efficiency Index (I_C) shall be greater than 1,12’ (European Commission, 2010), meaning 12 % better than cleaning in the EN50242/EN60436 reference programme of the reference dishwasher. This programme works at a maximum of 50 °C. Furthermore, “the drying efficiency index (ID) shall be greater than 1.08” (European Commission, 2010). The programme tested on a household dishwasher is the ‘Eco’ programme. No requirement exists in Europe for other programmes.

Comparing the two minimum requirements of cleaning performance is not easy, because the test conditions (e.g. soils, detergent, ambient conditions) are different. Brueckner et al. made a comparison of typical dishwashers from both markets tested using the same test methodology (Brueckner et al., 2010). The European machines (called EU high and EU low) are reported with a cleanliness value of 71.8 % and 60.8 %, respectively, versus 44.2 % for the Australian dishwasher. This shows that the requirement on the cleanliness of the Eco programme in Europe is considerably higher than an Eco or Normal programme in Australia. Consequently, the programme in Australia will be able to perform the task to comply with the Australian performance requirement at a lower maximum cleaning temperature and shorter programme duration, both reducing the energy demand. Additionally, the reference programme used in Europe heats up at least 5 K more than the reference programme used for Australia and, thus, will use considerably more energy. This is a plausible explanation why the Eco and Normal programme in Australia take at least 20 % less energy. No counteraction of the Australian consumers, such as using more intensive programmes, is visible from the data. The small increase in the frequency of manual pre-wash of the dishes (Fig. 8) is probably the only minor indication of a counteraction of consumers. The latter behaviour of the consumer needs to be studied more intensively, as it may try to compensate for the inadequate performance in one area by a shift to another behaviour with even higher resource use.

The exercise as presented is an attempt to determine the real-life average energy/water consumption and programme duration of the dishwashers in Australian households as accurately as possible. However, there is little current national data on the use of dishwashers, so a degree of uncertainty is unavoidable. Assuming a dishwasher is used 338 times per year (as recorded from the consumer survey) and 55 % of Australian households own a dishwasher (https://www.statista.com/forecasts/1004158/household-appliances-ownership-in-australia – assessed 16.9.2024), the total use of electrical energy for automatic dishwashers can be estimated to be at 1.9 TWh per year. Similarly, the water use is 24 million m³ per year. The simulation of a modified consumer behaviour shows the potential of saving 24 % of energy and 9 % of water without counterproductive programme prolongations and the risk of unsatisfactory cleaning performance. This would save an 0.45 TWh on electrical energy and 2.2 million m³ of drinking water for Australia per year. In addition, it must be kept in mind that manual dishwashing takes probably much more water and energy and can be optimised as well (Schencking & Stamminger, 2022). This fact is especially worth noting in the light of a relatively high (manual) pre-rising rate in Australia.

This analysis also revealed some surprising results when comparing Australian dishwasher energy with estimates from a range of European countries. This comparison showed that the energy use for automatic dishwashers in Europe is about 20 % higher per average cycle than it is in Australia. The most plausible explanation turns out to be the setting of the legal requirement for a minimum cleaning (and drying) performance an automatic dishwasher has to fulfil before being allowed to enter the market. The European legal requirement asks for a cleaning programme (Eco) which takes at least 20 % more on energy than that requested in the Australian regulation. No negative consequences for consumers were detected from the Australian setting, so there is a potential saving effect of 20 % on energy in Europe by adapting the Australian requirement. This is in addition to the 20 % energy saving that could be achieved by applying the same recommendations on consumer behaviour regarding applying the same recommendations as found for Australian dishwashers

This example is also a good exercise to learn about the socio-technical system behind the use of a dishwasher with its interplay between a variety of factors and participants, including manufacturers, technology, regulators, consumer practices, cultural norms and infrastructure.

Understanding consumer usage to design new products and the right recommendations of use need to be based on a profound understanding of how such a product is actually used and what limiting boundary conditions are set. Overcoming those limits may be not easy but necessary to reach overarching targets, such as the reduction of energy consumption that is driving climate change.

As usual, it is necessary to state that the research results in this study are based on the reliability of the data used and needs to be verified by further studies. In particular, consumers' self-assessment of how they use their dishwasher is a source of uncertainty. Especially the assumption that the European legal requirement for a cleaning programme (Eco) may be reduced without negative consequences needs to be further proven. A compensatory behaviour of the consumers may be envisaged as a negative consequence of a reduced cleaning performance of the standard programme, such as an increase of the pretreatment of dishes before being placed in the dishwasher, more manual cleaning operations or a change to higher temperature programmes. All of these changes of the behaviour would increase the resource use, diminish the savings or even turn them into an additional resource use.