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The basic factors that effect human comfort

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Introduction

THE BASIC FACTORS THAT EFFECT HUMAN COMFORT As a species, we human beings are warm-blooded creatures; that is we are biologically able to maintain a constant body temperature of 37? centigrade, regardless of the temperature of the air around us (within reason). However, for us to be truly comfortable in our environment, it is desirable that the temperature of the air around us is maintained at around 10? - 20? centigrade, depending upon whether we are active or at rest. When planning and constructing buildings for human habitation, it is very important that we bear this fact in mind; a satisfactory thermal environment is an essential purpose of good building design. Summary of comfort measurements - temperature. 100�C BOILING POINT OF WATER 25�C FINE SUMMERS' DAY COMFORT POINT 10�C WINTERS' DAY 0�C FREEZING POINT OF WATER To achieve an acceptable thermal environment we need to consider the comfort of people using the building as well as the requirements of objects stored in them. Humans and buildings interact with the heat that surrounds them; the amount of excess heat generated by a human body is directly proportional to the level of activity in which the body is engaged. Consequently; the temperature of a room may limit the level of human activity that occurs within. For example, a room temperature of 19C may be comfortable for a person who is quietly reading a book, but somebody using an exercise machine in that room would soon become overheated. Typical heat output of human body Activity Example Typical heat emission of adult male Immobile Sleeping 70 Watts Seated Watching TV 115 Watts Light work Office 140 Watts Medium work Factory, dancing 265 Watts Heavy work Lifting 440 Watts Sound Sound is a sensation produced in the ear and brain by variations in the pressure of air. ...read more.

Middle

and Kelvin (K). Celsius scale Freezing point of water = 0? C Boiling point of water = 100? C Kelvin scale 0? K is the point at which all heat energy has been extracted from a body. This point is known as absolute zero and occurs at -273? C. Heat transfer. Heat energy will always travel from a region of high temperature to one of lower temperature. If several bodies of varying temperature are placed close together, then heat will be exchanged between them until they are all of equal temperature. This equalising of temperature can occur by three basic processes of heat transfer: - Conduction - Convection - Radiation Conduction can occur in solids, liquids and gases, although the speed at which it occurs will vary. If a material is heated in one area only, the molecules in that area will acquire energy and become hot. These molecules will then transfer some of their energy to neighbouring molecules, which will in turn become hot themselves. In this way the whole of the material will eventually become hot. This process is most effective in solid materials; particularly metals. This is why we say that metal is a good conductor of heat, as opposed to most gases and liquids, which are known as insulators. Convection can occur in fluids (liquids and gases) but never in solids. It is the transfer of heat energy through a material by the bodily movement of heated particles. Natural convection occurs when a sample of fluid, such as air, is heated and so expands. The expanded air is less dense than the surrounding air and so it rises, to be displaced by cooler air. ...read more.

Conclusion

As well as being a comfort consideration the rate of ventilation has a great effect on the heat loss from buildings and on condensation in buildings. Heat gains. A building gains heat energy as well as loses heat energy, and both processes usually occur at the same time. In a location with a temperature climate such as the British Isles, the overall gains are less than the overall losses, but the heat gains may still provide useful energy savings. Factors which affect heat gains in a typical home: - Solar heat gains from the sun - Electrical appliances in the home - Water heating and cooking - Light fittings - The occupants of the building themselves - The position of windows around the building Typical heat gains in a building. These types of heat gain may be beneficial when it comes to maintaining a comfortable temperature in the home. Solar heating in particular is a great factor to be considered when calculating heat gains in a building. In cold climates it is desirable to design buildings with windows that are south facing. However, it is possible to gain too much solar heat energy and we may want to consider this in our designs. Heavy blinds may be required to shut out the suns rays when a building becomes uncomfortably hot. Heat balance. The thermal comfort of human beings requires that the inside temperature of a building is kept constant at a specified level. In order to maintain constant temperature the building will generally require heating or cooling, and both of these processes involve the consumption of energy. By being aware of the nature of heat and how good building design can effect losses and gains of it, we can ensure that we maintain a comfortable temperature for habitation in a cost-effective way. 1 ...read more.

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