Wang, Hong
(2017)
Study of Chinese household cooking practices: energy and cooking fumes.
PhD thesis, University of Nottingham.
Abstract
First, this research has attempted to identify the underlying reasons for high Chinese family cooking energy consumption. Second, this research has tried to identify ways of reducing Chinese kitchen cooking fume pollution.
The literature review indicated that, although cooking energy takes one of the largest proportions of residential building energy consumption, previous studies in this area have not been enough. The published knowledge found indicates that urban residential buildings takes 1/4 of the national building energy consumption (excluding heating). This portion has grown continuously since 2001 in terms of energy consumption intensity (kgce/m2). Among household energy (excluding heating), cooking, home appliances and lighting are the three largest energy end users. Although the increase in cooking energy is low, partially attributed to wide adaptation to gas cooking fuel instead of coal fuel in China, it still takes the largest household energy consumption: 31% in 2011.
Many research papers report different results based on field measurements of household energy end users, some of which show conflicting results. However, the literature review has confirmed that in China cooking energy consumes the second-largest amount of household energy after space heating. The literature review also pointed out that, although compared with Western counterparts, Chinese residential buildings consume less national energy, cooking takes a large percentage of household energy.
A further literature review showed little valuable information underpinning the reasons for high cooking energy use in Chinese households. Some overseas research papers give hints regarding cooking energy and cooking techniques, cookware, and occupant behaviour. However, the difference in food culture traditions has led to a greater difference between Western and Chinese cooking techniques. Compared with Western countries, Chinese hot dishes require a greater number of cooking techniques.
In order to find out more details of cooking energy and fume generation in real Chinese home kitchen conditions, the author used a series of research methodologies to measure and test home energy and cooking fume concentration. The results reconfirm that cooking energy is the second-largest home energy end user after space heating, along with other findings. These other findings include:
• The four largest energy end users in northern Chinese households are space heating, cooking, hot water and entertainment.
• Hot water, lighting and entertainment energy consumption have clear seasonal characteristics i.e., daily consumption is low in summer and high in winter. This is because of the colder weather in winter (demanding more energy to heat water) and longer nights in winter (with a longer indoor entertainment time and a greater requirement for lighting in the evening).
• Daily cooking energy consumption in a given family is almost fixed, although the difference between different families is large. This could lead to further study on the underlying reasons for the difference between families.
The most important finding in the research is the discovery of the relationship between home cooking energy and family life cycle. A strong relation was observed between these two factors. This was confirmed by the measurement of the test families as well as the survey of 70 random selected families. The relation is, therefore, denoted as the CookEUI (cooking energy use intensity) of the different family life cycles. Following the data analysis and survey, it was also found that the cooking energy for a certain family life cycle was constant, i.e., locked in an FLC stage until the stage changed. Finally, a database was built into the IES energy simulation using figures found in the research. This represents significant progress in home energy study. Before discovering cooking EUI, cooking energy in most pieces of energy simulation software was treated as a process load with a constant figure.
A literature review of a large number of research papers concluded that cooking fumes have an adverse impact on people’s health. In China, a typical housewife spends about 4 hours in the kitchen every day, preparing and cooking meals. A comfortable and healthy cooking environment is critical for cooks’ health. It was also found that COF emissions in Western and Chinese kitchens differed largely in mass concentration. Cooking method, cooking oil and cooking temperature all contribute to the difference.
Many other researchers have investigated the details of hood systems and their construction features in order to understand their efficiency in removing cooking fumes. However, most of the research has been based on commercial kitchen application. There is very little research on home kitchen hood efficiency. Research also points out that natural ventilation in the kitchen space has a certain amount of influence on the capture efficiency of an exhaust system. For example, opening the door is more efficient than opening a window.
In this research, the measurements of kitchen PM2.5 and PM10 were carried out in real home kitchen cooking conditions. The relation between PM2.5 and PM10 emissions and different Chinese cooking methods was measured. It was found that deep frying and stir frying discharged the most PM2.5, while boiling emitted the least. A typical PM2.5 discharging pattern in Chinese cooking was observed. The pattern showed a sharp increase in PM2.5 concentration in the beginning at breath level with a drop afterwards because of the using up of cooking oil or the rising of water steam to a higher level. A small sub-surge was observed after the first selection because the downward flow of cold air brought high-level PM2.5 down to breath level.
A very interesting finding observed when using tracer gas to measure kitchen cooking hood efficiency was the large difference between the airflow rate listed on the kitchen fume hood nameplate and the airflow rate measured in real kitchen conditions. On the nameplate of the cooking hood, airflow was rated as 800 m3/h at medium speed, while in the tracer gas testing the flow rate was a maximum of 175 m3/h when all the kitchen windows and the door were open. This finding reinforces the experiment conclusion by the Lawrence Berkeley National Laboratory for the seven representative devices they tested, whereby, according to Chen (2012), the capture efficiency varied from less than 15% to more than 98%.
Identifying the airborne moving characteristics of PM2.5 can be used to help redesign ventilation systems for Chinese home kitchens. The traditional way of enhancing cooking fume removal efficiency is to increase the fan discharge pressure head. This leads to increased energy consumption. It also has less effect on removing PM2.5 particles, since, unlike PM10, PM2.5 is affected by airflow rate more significantly than air velocity. The proposed new ventilation system is intended to treat PM2.5 and PM10 separately. PM10 will be removed by the filter in recirculation devices and PM2.5 will be exhausted by a direct venting fan with replacement air. In this way, less energy is used and the system is more efficient at removing kitchen PM2.5.
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