Amortización de los Bonos

The role of behaviour in domestic energy use is often the subject of research focusing on different appliances. Verhallen and Raaij (1981) presented a study of the energy used for home heating, showing that occupant behaviours explain 26% of the variance of energy use. They demonstrated that levels of awareness, commitment to energy saving measures and personal preferences vary enormously from one person to another (Verhallen, Raaij 1981). One study on washing up methods showed that people behave in diverse ways, and on average use more detergent, water, energy and time than a regular dishwasher, and the plates are usually less clean when people do the dishes by hand (Berkholz, Stamminger et al. 2010). But when a set of ‘best practice tips’ were given to consumers as instructions, they “used around 60% less water, 70% less energy and 30% less detergent compared with the average everyday behaviour the other subjects used. Additionally, they achieved a slightly better cleaning result” (Fuss, Bornkessel et al. 2011). Cultural differences showed to be an important factor on user behaviours for dish washing, influencing water and detergent usage (Elizondo, Lofthouse et al. 2011, Elizondo, Lofthouse 2010). Laundry and dish washing energy use was reported to be highly influenced by lifestyles, and “results show a variation of a factor of five between a more sustainable and a

Chapter 2: Literature review – 2.5: Domestic energy use and behaviours

platform for the study of human behaviours. Video evidence shows that families have particular ways of storing and retrieving food from the fridge, and the frequency and length of interactions with the appliance can affect the energy consumption (Tang, Bhamra 2009, Tang, Bhamra 2012). One user observation study demonstrated that people perform their daily activities with a high level of interaction with kitchen appliances, sometimes causing unnecessary energy usage (Elias, Dekoninck et al. 2008).

One thorough case study performed by Gill and colleagues (2010) involved evaluations of the energy performance of low-energy houses together with behavioural survey, interviews and measurements of satisfaction and comfort of occupants. Their results showed significant variation of electricity use, with the highest consumer using 2.8 times the amount used by the most efficient residence. The conclusion is that behaviour accounts for around 37% of electricity consumption, even between neighbours living in similar houses with similar appliances. Remarkable variations in energy use were also observed during a study of flats with the same number of residents, comparable built infrastructure and fixed appliances, occupied by students of roughly the same age, similar study and work schedule: some units used almost three times the electricity of other similar apartments. They conclude that “the way occupants inhabit their apartments is a significant source of variation” (Morley, Hazas 2011). To sum up, numerous studies can be found demonstrating the role of behaviours in electricity, gas and water consumption, even people using the same appliances, performing the same tasks or using the same infrastructure (Gill, Tierney et al. 2010).

2.5.2.1 Cookers

A recent survey of 251 households in England reports that cooking activity accounts for 13.8% of the overall domestic electrical power demand (DEFRA 2012). One French investigation found similar figures: combined cooking related energy consumption accounted for 14% of the total electricity usage from the 100 households surveyed (Sidler, Waide et al. 2000).

The energy consumption of all hobs in the UK is estimated at 4.8TWh/year from gas and 3.2 TWh/year from electric devices, and it is believed that the energy consumption will gradually rise due to increases in number of households (DEFRA 2009). Approximately 55% of households have a gas hob, and 45% use electric (DEFRA 2009), and the stock of electric cookers is estimated in 12 million units (EC 2011).

Energy use monitoring demonstrates that cooking activity can contribute to the concentration of electrical load during specific periods of the day (Newborough, Augood 1999). Generally, the aggregate electricity demand associated across the use of hobs, grills, ovens and

Chapter 2: Literature review – 2.5: Domestic energy use and behaviours

kettle last for about 5 minutes on average. However, “[e]lectric cooking creates the greatest peak demands of any single domestic activity” (Newborough, Augood 1999). These peaks happen during the time of the day when there is already coincident demand of electricity (DEFRA 2012). Figure 3 below illustrate how concentrated cooking activities at 5:00 pm lead the way through the evening peak electricity demand, which put tension on the generation and distribution grid.

Figure 3 - Electricity consumption - Hourly load curve (DEFRA 2012)

The energy effectiveness of cooking appliances attracts little attention, and developments in cooker design have been concerned mainly with making the appliances easier to use and clean, improving their appearances and reducing cooking time, which generally increases the electricity load (Probert, Newborough 1985). Since modern cookers can use even more electricity than old models of same technology, their replacement is not included in recommendations by government campaigns due to the lack of potential savings (DEFRA 2012). In addition, historical data of cooking appliances shows that “limited improvements in efficiency have been offset by an increasing number of households” (Wade, Hinnells et al. 1995).

Different studies report that conventional electric resistance cookers use more energy than induction and ceramic hobs (Sidler, Waide et al. 2000, Newborough, Probert et al. 1990). These

Chapter 2: Literature review – 2.5: Domestic energy use and behaviours

hobs take more time to heat and also present more thermal hazards than halogen or induction hobs (Newborough, Probert et al. 1990). For example, a coil hob (or radiant ring) is “capable of more precise temperature control and, being of smaller mass, heats up more rapidly than the comparable size hot-plate” (Probert, Newborough 1985). However, considering only the financial aspect, updating to modern technology such as induction hobs is not a worthwhile option compared to resistance hobs. One study shows that taking in consideration the prices of induction cookers, the average usage and the stand-by energy consumption, the payback time might be as long as 282 years (Sidler, Waide et al. 2000). This indicates that households have low motivation to own more efficient cookers, since better technology comes with higher costs. Buyers rarely take into account energy consumed during products lifecycle, and installations are often chosen on the basis of the lowest quote (EC 2011). Furthermore, the replacement of cooking appliances occurs rather slowly, given that the average life for a free-standing cooker is about 15 years (Probert, Newborough 1985) or even 20 years according to various sources (EC 2011). Those might be the explanations for the modest market penetration of induction hobs: a report from the European Commission estimates that they represent less than 1% of the stock of domestic hobs in the UK (EC 2011).

2.5.2.2 The cooking activity

The cooking activity demands several interactions between users and appliances. As described by Wood and Newborough (2007), the user is next to the appliance during energy consumption, and the consumption is highly influenced by this interaction (as opposed to boilers or fridges which use energy in the background). Furthermore, there are numerous energy saving behaviours that can be performed during the cooking activity. Consequently, people’s behaviours play an important role in energy consumption.

Caraher et al. (1999) performed extensive studies on the relationship between cooking and skills among the English population. They established that there are considerable variations in knowledge about how to cook. Their results point towards “a population unsure of specific cooking techniques and lacking in confidence to apply techniques and cook certain foods”. DeMerchant (1997) observed how people cook one specific menu and concluded that participants’ behaviours partially explained energy usage. She noticed subjects pre-heating the cookware, using high heat, leaving the heat source on after cooking was completed and not controlling the temperature adequately.

Previous research on cooking methods presents a few examples on how to prepare food more efficiently. When it involves boiling, there are several techniques that can be performed and reduce significantly the energy use, time to prepare and even water needed (Das,

Chapter 2: Literature review – 2.5: Domestic energy use and behaviours

Subramanian et al. 2006). These involve, for example, pre-soaking grains, fine-controlling the temperature and using a pressure cooker. Heat is needed in order to cook food, make it soft, taste better and be safe for consumption. However, the water can be below 100º C (consequently requiring less energy) and still cook most foods such as vegetables, grains and beans (Potter, Ruhlman 2010, McGee 2004). Experiments performed by Oberascher et al. (2011) indicate that it is possible to improve the efficiency of cooking if people switch between stove, kettle, microwave and other appliances according to the quantity of food that is being prepared. The possible savings from these techniques indicate that “[p]roviding information to users on ways to cook efficiently is thought to be worthwhile and to have a greater impact on energy consumption than improvements in design” (EC 2011).

This section presented diverse issues related to energy use for cooking activity. These comprise the lack of efficiency improvements of traditional cookers in recent years, slow replacement of old appliances, prohibitive prices of more efficient technologies, problems related to peak electricity consumption, role of people’s behaviours in consumption, people’s lack of cooking skills, and the amount of energy that can be saved by performing a number of techniques targeting energy saving. These issues indicate that there is room for improvement and also suggest an avenue for further investigation on ways to reduce energy consumption in the kitchen. By selecting cooking behaviours as the object, this research is targeting an area with high potential for environmental improvement.