Thermal comfort in non-uniform environments: real-time coupled CFD and human thermal regulation modelling

2018-05-04T11:33:22Z (GMT) by Francesco Babich
Energy consumption in buildings contributes more greenhouse gas emissions than either the industrial or transportation sectors, primarily due to space cooling and heating energy use, driven by the basic human need for thermal comfort and good indoor air quality. In recent years, there has been a proliferation of air conditioning in both residential and commercial buildings especially in the developing economic areas of the world, and, due to the warming climate and the growing disposable income in several densely populated developing countries, the energy demand for space cooling is dramatically increasing. Although several previous studies focused on thermal comfort, there are only a few works on asymmetrical environments or transient conditions, such as those expected when mixed mode ventilation or other low energy techniques such as elevated air movement generated by ceiling fans are adopted in the residential sector. Moreover, even fewer studies addressed the accuracy of computer predictions of human thermal comfort in non-uniform environmental conditions. However, focusing on non-uniform thermal environments is important because the space conditioning systems that generate them are often likely to be less energy consuming than those which provide more homogeneous conditions. This is due to the fact that these less energy-intensive space conditioning systems tend to condition the occupants, and not the entire room. The aim of this research was to investigate human thermal comfort in non-uniform transient environmental conditions, focusing in particular on the capability of predicting human thermal comfort in such conditions in residential buildings. Furthermore, this research investigated the energy savings that can be achieved in residential buildings when the same level of thermal comfort is delivered using less conventional, but lower-energy, approaches. In this research, a combination of computer based modelling, experimental work in controlled environments, and data from field studies was used. Computer modelling comprised CFD coupled with a model of human thermal physiology and human thermal comfort, and dynamic thermal modelling. In the experimental work, environmental chambers were used to collect data to validate the coupled CFD model. The data from field studies on real domestic buildings in India and in the UK was used to identify the most relevant configurations to be modelled using the coupled system. This research led to three main conclusions concerning thermal comfort in non-uniform environments: (i) the coupled model is able to predict human thermal comfort in complex non-uniform indoor configurations, as long as the environment around the human body is accurately modelled in CFD, and is superior to the traditional PMV model as both temporal and spatial variation and non-uniform conditions can be taken into account; (ii) dynamic thermal simulation completed using a dynamic cooling set-point showed that the energy demand for space cooling can be reduced by as much as 90% in mixed mode buildings by using ceiling fans, without jeopardising occupants' thermal comfort; and (iii) the accurate and validated transient three-dimensional CFD model of a typical Indian ceiling fan developed in this research can be used for any study that requires the air flow generated by a ceiling fan to be modelled in CFD.