Science and materials in construction and the built environment
Human Comfort Thermal and air quality 3 – 4 Sound 5 – 6 Light 6 – 7
Images 9 – 12
There are several basic factors that will affect human comfort in an internal environment, these include, heat, air quality, light and sound. Each variable has certain levels at which they are acceptable and comfortable in an enclosure and must be controlled in order to maintain these conditions.
Thermal and air quality
Heat is a form of energy, which is measured in Joules (J), thermal energy is the result of the atoms and molecules that make up matter bumping into each other or vibrating back and forth. This transforms kinetic energy into thermal energy. For practical reasons we measure 'heat' using a degrees Celsius temperature scale, and in practice the thermodynamic temperature scale (fig. 1.), which is measured in Kelvin (K). The freezing point of water as 0°C (at standard atmospheric pressure – 101.32kN/m²), is equal to 273.15K and the boiling point at 100°C s equal to 373.15K, this shows the intervals between Celsius and Kelvin are equal. Absolute zero is measured at 0K where all particle movement has stopped, it is very difficult for matter to reach this temperature as the cosmic microwave background radiation is measured at approximately 2.73 Kelvin (temperatures at a billionth of a kelvin can be produced by laser cooling). Heat can be transferred from one mass to another in three ways (fig. 2.). The passage of heat through molecules in a body is known as conduction, for example, hot water travelling through pipes. Heat can also be transferred through convection – the bodily movement of a fluid, gas or liquid, for example, a radiator heats air which expands and rises, becoming less dense and is replaced by cooler air below. Heat can also be transferred through radiation – the rays of heat travelling across a space as either energetic waves of particles, with or without matter being present, such as the heat from the suns rays. Humans have an average body temperature of around 37°C, if the external temperature is much below this we start to feel cold. Clothing is worn by humans to trap layers of warm air, the amount of clothing is normally dependant on the season and even the use of the room. The Chartered Institute of Building Services Engineers (CIBSE) has categorised clothing in a scale of clo values. One clo – a business suit – represents 0.155m² K/W of insulation to the body, and typically range from 0 – 4 (fig. 3.). A person gives off more heat with increased level of activity, this varies with different people depending on their age, gender and surface area. A seated person doing small work has a heat output of around 100-120W, whereas a person doing heavy lifting and athletics may have an output of 430W – for an average male adult, females have approximately 85% of a males heat output . Average room temperature is recommended at 21°C, with 24°C being the top range of comfort and much below 20°C the death risk increases. The temperature of a room is maintained through heating, it must be provided with what heat is lost through ventilation and the conduction of materials. The optimum temperature will depend on the use of the room whereas ventilation will vary with the number of people present. The structural loss of a building depends on the type of…