UNIT I CLIMATE AND HUMAN COMFORT Weather: Weather is the day-to-day atmospheric conditions of a particular place. Weather is the day-to-day state of the atmosphere, and its short-term variation in minutes to weeks. Weather keeps on changing from place to place. It may be hot and sunny in one part of the world, but freezing and snowy in another. Climate: Climate is the average weather condition of a place, measured over a long period of time. The standard averaging period is 30 years .while the weather can change in just a few hours, climate takes hundreds, thousands, even millions of years to change. 1.1 Factors affecting climate There are many different factors that affect climate around the world. It is the varying influence of these factors that lead to different parts of the Earth experiencing differing climates. The most important natural factors are: 1.distance from the sea 2.ocean currents 3.direction of prevailing winds 4.'relief' or 'topography'(shape of the land) 5.distance from the equator 6.The El Niño phenomenon. 7.It is now widely accepted that human activity is affecting climate, and that the impact is not the same everywhere. also 1. Distance from the sea The sea affects the climate of a place. Coastal areas are cooler and wetter than inland areas. Clouds form when warm air from inland areas meets cool air from the sea. The central areas of continents are subject to a large range of temperatures. In the summer, temperatures can be very hot and dry as moisture from the sea evaporates before it reaches the centre of the land mass. 2. Ocean currents Ocean currents can increase or reduce temperatures. Currents are driven by the prevailing winds passing over the surface of the ocean. Therefore winds blowing from tropical areas bring warm currents and vice versa. warm currents move away from the Equator and cold currents towards it The diagram below shows the ocean currents of the world . 3. Direction of prevailing winds Winds that blow from the sea often bring rain to the coast and dry weather to inland areas. 4.'Relief' or 'topography' Climate can be affected by topography. Mountains or high altitude areas receive more rainfall than low lying areas because as air is forced over the higher ground it cools, causing moist air to condense and fall out as rainfall. The higher the place above sea level the colder it will be. This happens because as altitude increases, air becomes thinner and is less able to absorb and retain heat. That is why you can see snow on the top of mountains all year round. 5. Distance from the equator The distance from the equator affects the climate of a place. At the poles, energy from the sun reaches the Earth's surface at lower angles and passes through a thicker layer of atmosphere than at the equator. This means the climate is cooler further from the Equator. The poles also experience the greatest difference between summer and winter day lengths: in the summer there is a period when the sun does not set at the poles; conversely the poles also experience period of total darkness during winter. In contrast, day length varies little at the equator. 6. El Niño El Niño, which affects wind and rainfall patterns, has been blamed for droughts and floods in countries around the Pacific Rim. El Niño refers to the irregular warming of surface water in the Pacific. The warmer water pumps energy and moisture into the atmosphere, altering global wind and rainfall patterns. The phenomenon has caused tornadoes in Florida, smog in Indonesia, and forest fires in Brazil. El Niño is Spanish for 'the Boy Child' because it comes about the time of the celebration of the birth of the Christ Child. 7. Human influence The factors above affect the climate naturally. influence of humans on our climate. However, we cannot forget the Early on in human history our effect on the climate would have been quite small. However, as populations increased and trees were cut down in large numbers, so our influence on the climate increased. Trees take in carbon dioxide and produce oxygen. A reduction in trees will therefore have increased the amount of carbon dioxide in the atmosphere. The Industrial Revolution, starting at the end of the 19th Century, has had a huge effect on climate. The invention of the motor engine and the increased burning of fossil fuels have increased the amount of carbon dioxide (a greenhouse gas - more on that later) in the atmosphere. The number of trees being cut down has also increased, reducing the amount of carbon dioxide that is taken up by forests. Elements of climate The most important elements of climate and weather parameters that affect human comfort and are relevant to building design are: •Temperature •Humidity •Wind •Precipitation Temperature Temperature is the measure of how hot or cold the air is. It is commonly measured in Celsius or Fahrenheit. Temperature is a very important factor in determining the weather, because it influences other elements of the weather. Temperature may be affected by: •Sunshine •Latitude •Altitude •Aspect •Sea Proximity and Temperature •Ocean Currents Humidity Humidity is the amount of watervapour contained in the air. The more water vapour in the air the higher is the humidity. If the humidity level exceeds the amount of water air can hold condensation occurs forming dew if it's warm or frost if it's cold. When air is at a high altitude and has a high humidity then clouds start to form. Humidity varies with temperature. Warmer air can hold more moisture. Humidity is measured in percentages on the scale of air's ability to hold moisture. Therefore condensation occurs at 100% humidity for a given temperature . Precipitation Precipitation is the term given to moisture that falls from the air to the ground. Precipitation can be snow, hail, sleet, drizzle, fog, mist and rain. it is measured by rain gauges expressed in millimeter per unit time.(mm/month) or mm/ day . The maximum rainfall for 24 hr period is useful guide for design of pavements, roofs, gutters 1.Convectional Rainfall This is where a water surface is heated by the sun, e.g. the sea. The air above the sea then becomes heated making the air less dense so it rises and cools. As we know cooler air can not hold as much water vapour as warm air therefore when the rising air becomes too cold to hold the moisture the condensation occurs giving us clouds. Once there is too much water in the cloud for the air to support gravity forces the water to be released in what we know as rain. 2.Frontal Rainfall When two air masses met, one is warmer than the other the warmer air is forced to rise over the colder air. As this warm air rises it cools and forms clouds just like the air in convectional rainfall. 3. Relief Rainfall Wind bringing moist air from the seashore starts to rise up a hillside. As this air rises the air passes its Dew Point, the point at which condensation occurs, and the vapour forms clouds. The water vapour then falls as precipitation on top of the hill or on the other side. Wind On the surface of the Earth, wind consists of the bulk movement of air. Wind is caused by differences in atmospheric pressure. When a difference in atmospheric pressure exists, air moves from the higher to the lower pressure area, resulting in winds of various speeds. On a rotating planet, air will also be deflected by the Coriolis effect, except exactly on the equator. Globally, the two major driving factors of large-scale winds are 1. the differential heating between the equator and the and 2. the rotation of the planet. wind vanes anemometers Measurement Wind speed is measured by cup type or propeller anemometers and direction is measured by wind vanes. An anemograph can produce continuous recording of wind velocity and directional changes. Wind velocities are normally recorded at a height of 10 m.Measued in m/s, mph or knot(nautical miles per hour) vegetation The picture of climate is incomplete with out some notes on the character of abundance of plant life. Vegetation can influence the local climate or site climate. It is an important element in design of outdoor spaces, providing sun shading and protection from glare. Sky conditions It is usually expressed in terms of presence or absence of clouds. On average two observations are made per day. It is usually expressed in percentage. Components of Climate The term "climate system" refers to the many elements that contribute to creating a climate in a particular place or region. The climate system of the earth is an interactive system consisting of five major components namely 1. atmosphere, 2. cryosphere 3. biosphere 4.Lithosphere 5. hydrosphere. Surface water Sea or ocean Climate classification systems There are three fundamental types of classifications used in climatology. 1. empirical systems 2. Genetic classification systems 3. Applied classification systems 1. empirical systems of classification that are based on observable features. The Koeppen system is an empirical system based on observations of temperature and precipitation. These are two of the easiest climate characteristics that can be measured, and probably the ones with the longest historical record. It's fairly easy to collect air temperature readings with a thermometer and precipitation with some sort of collecting device that can measure the amount of precipitation. Climates are grouped based on annual averages and seasonal extremes. 2. Genetic classification systems are those based on the cause of the climate. A genetic system relies on information about climate elements like solar radiation, air masses, pressure systems, etc. These are inherently the most difficult classifications to create and use because of the multitude of variables needed. 3. Applied classification systems are those created as an outgrowth of, a particular climate-associated problem. The Thornthwaite classification system is one based on potential evapotranspiration and thus groups climates based on water requirements. His classification system grew out of the issue of trying to predict the supply and demand for water in different climate regions. Koppen climate classification system The Koppen climate classification system one of the most widely used systems for classifying climate because it is easy to understand and data requirements are minimal. It is an empirical system largely based on annual and monthly means of temperature and precipitation. The Köppen system uses a letter coding scheme to classify climate. The five main groups of climates are designated by capital letters, all but the dry climates being thermally defined. These are: 1. A - Tropical climates (sometimes identified as "equatorial" climates) 2. B - Dry climates (sometimes identified as "arid" climates) 3. C - Warm temperate climates 4. D - Subarctic climates (sometimes identified as "snow" or "boreal" climates) 5. E - Polar climates tropical climates A tropical climate is a climate of the tropics. In the Köppen climate classification it is a non-arid climate in which all twelve months have mean temperatures above 18 °C . Unlike the extra-tropics, where there are strong variations in day length and temperature, with season, tropical temperature remains relatively constant throughout the year and seasonal variations are dominated by precipitation. A - Tropical climates B - Dry climates C - Warm temperate climates D - Subarctic climates E - Polar climates tropical climates The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at 23° N and the Tropic of Capricorn in the southern hemisphere at 23° S; these latitudes correspond to the axial tilt of the Earth. The tropics are also referred to as the tropical zone and the torrid zone . A tropical climate is the climate experienced in the tropics. In the Köppen climate classification it is a non-arid climate in which all twelve months have mean temperatures above 18 °C . Unlike the extra-tropics, where there are strong variations in day length and temperature, with season, tropical temperature remains relatively constant throughout the year and precipitation. seasonal variations are dominated by Classification of tropical climates The classifications of tropical climates are provided by G.A Atkinson in 1953. The basis of classification is given by two atmospheric factors which dominantly influence human comfort : 1. Air temperature and 2. Humidity. The extremes of these main criterions are the ones that causes discomfort. The tropical regions of earth are divided into 3 major climatic zones and 3sub groups :Within the tropical climate zone there are distinct varieties based on precipitation: 1. warm- humid equatorial climate – subgroup : Warm humid island or trade- wind climate. 2. Hot-dry desert or semi-desert climate – subgroup: hot dry maritime desert climate. 3. Composite or monsoon climate( combination of 1 and 2) subgroup : tropical upland climate. 1. warm- humid climate warm- humid climate warm- humid island climate 2.Hot-dry desert or semi-desert climate hot dry maritime desert climate. 3. Composite or monsoon climate tropical upland climate. Human body heat balance Human body heat production Heat is continuously produced by the body. Most of the biochemical process involved in the tissue- building , energy conversion and muscular work are exothermic..i.e. heat producing. All energy and material requirements of the body are supplied from the consumption and digestion of food. The process involved in conversion of foodstuff into living matter and useful form of energy are known as metabolism. The total metabolic heat production can be divided into 1. basal metabolism – heat production due to vegetative, automatic processes . 2. muscular metabolism- heat production of muscles while carrying any work or activities. Of all the energy produced in the body only about 20% is utilized, 80% is surplus heat and must be dissipated to environment. Human body heat loss The deep body temperature must remain balanced and constant around 37 degree. Like all mammals, humans “burn” food for energy and must discard the excess heat. In order to remain body temperature at this steady rate , all surplus heat must be dissipated to environment. If there is some form of simultaneous heat gain form the environment that also must be dissipated. This is accomplished by evaporation coupled with the three modes of sensible heat transfer: conduction, convection, and radiation. The body is in a state of thermal equilibrium with its environment . It loses heat exactly in the same rate as it gains heat. Mathematically, the relationship between the body’s heat production and all its other heat gains and losses is: Heat production = heat loss Convection The convection is the transfer of heat from one part of a fluid (gas or liquid) to another part at a lower temperature by mixing of fluid particles. Heat transfer by convection takes place at the surfaces of walls, floors and roofs. Because of the temperature difference between the fluid and the contact surface, there is a density variation in the fluid, resulting in buoyancy. This results in heat exchange between the fluid and the surface and is known as free convection. However, if the motion of the fluid is due to external forces (such as wind), it is known as forced convection. These two processes could occur simultaneously. The rate of heat transfer (Q convection) by convection from a surface of area A, can be written as Radiation Radiation is the heat transfer from a body by virtue of its temperature; it increases as temperature of the body increases. It does not require any material medium for propagation. When two or more bodies at different temperatures exchange heat by radiation, heat will be emitted, absorbed and reflected by each body. The radiation exchange between two large parallel plane surfaces (of equal area A) at uniform temperatures T1 and T2 respectively, can be written as Convection : The rate of convective heat loss is increased by a faster rate of air movement , by a lower air - temperature and a higher skin temperature. Radiant heat loss depends on the temperature of the body surface and the temperature of opposing surfaces. Evaporation heat loss is governed by the rate of evaporation, which in turn depends on the humidity of air ( the dryer the air, the faster the evaporation) and on the amount of moisture available for evaporation. Evaporation takes places in the lungs through breathing and on the skin as imperceptible perspiration and sweat. As soon as the sum is more than zero, vasomotor adjustments will take place, blood circulation to skin surface is increased, more heat is transported to the surface and the skin temperature is elevated- all forms of the heat loss processes are accelerated. Conversely if the sum of the above equation is less than zero, the blood circulation to the skin is reduced, skin temperature is lowered and heat loss process is slowdown. The thermal balance of body can be expressed by an equation. The heat gain and heat loss factors are : Gain : Met = metabolism (basal and muscular) Cnd = conduction (contact with warm bodies) Cnv = convection ( if air is warmer than skin Rad = radiation( from sun sky and hot bodies). Loss : Cnd = conduction (contact with cold bodies ) Cnv = convection ( if air is cooler than skin ) Rad = radiation( to night sky and cold surfaces) Evp = evaporation (of moisture and sweat) Met- Evp ± Cnd ± Cnv ± Rad = 0 Heat Exchange Of The Body With The Environment Met- Evp ± Cnd ± Cnv ± Rad = 0 CONDUCTION Regulatory mechanism Body heat exchange Thermal balance of the body Effects of climatic factors on human body heat loss Effective temperature Mahoney tables The Mahoney tables are a set of reference tables used in architecture used as a guide to climate-appropriate design. They are named after architect Carl Mahoney,. The concept developed by Mahoney (1968) in Nigeria provided the basis of the Mahoney Tables, later developed by Koenigsberger , Mahoney and Evans .) . The Mahoney Tables proposed a climate analysis sequence that starts with the basic and widely available monthly climatic data of temperature, humidity and rainfall, The tables use readily available climate data and simple calculations to give design guidelines, in a manner similar to a spreadsheet, as opposed to detailed thermal analysis or simulation. There are six tables; four are used for entering climatic data, for comparison with the requirements for thermal comfort; and two for reading off appropriate design criteria. A rough outline of the table usage is: •Air Temperatures. The max, min, and mean temperatures for each month are entered into this table. •Humidity, Precipitation, and Wind. The max, min, and mean figures for each month are entered into this table, and the conditions for each month classified into a humidity group. •Comparison of Comfort Conditions and Climate. The desired max/min temperatures are entered, and compared to the climatic values from table 1. A note is made if the conditions create heat stress or cold stress (i.e. the building will be too hot or cold). •Indicators (of humid or arid conditions). Rules are provided for combining the stress (table 3) and humidity groups (table 2) to check a box classifying the humidity and aridity for each month. Then these indicator are checked and added up, giving a yearly total. •Schematic Design Recommendations. The yearly totals in table 4 correspond to rows in this table, listing schematic design recommendations, e.g. 'buildings oriented on east-west axis to reduce sun exposure', 'medium sized openings, 20%-40% of wall area'. •Design Development Recommendations. Again the yearly totals from table 4 are used to read off recommendations, e.g. 'roofs should be high-mass and well insulated'.
