P1 – Describe the basic factors in simple scientific terms that influence human comfort in the internal environment.
Human comfort in the internal environment is affected in several different ways but they can be categorised to personal, visual, audible and thermal factors, all playing a part in the quality and quantity of human comfort. Each physical factor can be measured and by doing these calculations, we can design and build an environment with human comfort at the forefront of our mind.
Personal factors include age, gender, level of physical activity, the clothing being worn and the individuals state of health. Starting with gender, males on average give off 15% more heat than females do, meaning that a female individual in the same environment may feel considerably colder than the opposing sex in the same environment. Age is another factor to take into consideration, a 25 year old would have much better blood circulation and a higher metabolic rate than a 75 year old. Meaning that an elderly person is likely to feel colder than a young person in the same environment, also an older individual could be more sensitive to the sound and lighting conditions around them. An individual’s quality of health can have an impact on their comfort, some conditions such as a dysfunctional liver or auto immune disease can make you produce more heat than normal. Furthermore, conditions such as an underactive thyroid or anaemia, can make you feel considerably colder. When someone has an illness, they can feel especially susceptible to direct light, loud noises and stuffy humid environments. Another factor is an individual’s level of physical activity, humans give off approximately 70 watts while sleeping, between 120-160 watts while carrying out light working activities and between 400-700 watts when carrying out heavy exercise. The level of physical activity plays a big part on an individual’s comfort levels, too much physical activity without our thermoregulatory system could result in serious injury or even a fatality. The final personal factor is an individual’s clothing value, and this must be proportionate to the environment. It would not be comfortable for an individual to wear a heavy goose down jacket in 25 degree heat and additionally it would not be comfortable for an individual to wear shorts and a vest in 5 degree heat.
Air temperature – the temperature inside a building can be dependent on the external temperature of the building and the U-vales of the materials used to construct the building, meaning the lower the U-vale the more effective the material is at retaining heat. This can dramatically affect human comfort as the higher the U-values used, the quicker the room will lose heat through convection. By using the U-values of materials we can calculate the total heat resistivity of a building and then create a comfortable environment in which to live.
Air velocity – another crucial factor affecting human comfort, this is the movement of air through a building. Warm air will enter a room and force the cold air downwards creating a draught, in a cold environment this draught can make a person feel even colder if the draught is colder than room temperature. In a warm environment this draught can increase heat loss through convection and help to cool someone down by increasing the rate that their sweat evaporates.
Humidity – This is the water vapour content in the air. Humans cool down mainly by sweating but in an environment with 100% humidity it is not possible for the sweat to evaporate, this is called absolute humidity. Anything below 30% humidity can feel uncomfortably dry and anything above 60% can feel uncomfortably wet or damp. Relative humidity is the ration between the amount of water vapor in the air and the amount of water vapor that can be held in the air.
Sound – Made up of longitudinal pressure waves, sound is a form of energy that will have a crucial impact on human comfort. Two different types of sound are present in the built environment, one being air born and the other one structural. Air born sound will travel through the air and is usually generated by talking, music, motors and machines. Structural sounds will travel through an object or material by vibrating the particles and almost using it as an amplifier, these sounds are generated by impacts like walking or running even vibrations from machinery. We must consider the absorption coefficient of the materials used, to ensure that sound does not decay to quick meaning people cannot hear you and to ensure that sound does not take to long to decay, resulting in an echo.