INTRODUCTION TO BUILDING CLIMATOLOGY

INTRODUCTION

Climatology is simply the scientific study of the climates. Building Climatology is therefore the scientific study of climates with regards to the built environment. Buildings do not exist in isolation; they exist within a particular geographical context. Architecture as a scientific discipline seeks to ensure that the building and the contextual geographical environment are in a symphonic unity. If this is not achieved, the building will not yield maximum user comfort and will thus not fulfill its purpose.

It is worthy to note that design mistakes of this nature are very expensive to remedy, if at all there is a remedy to it. On the other hand, the geographical characteristics of the environment can be harnessed to achieve maximum comfort and user experience.

Weather is a sum total of atmospheric conditions of a relatively small geographical area in a short period of time. Climate on the other hand, is the sum total of atmospheric conditions observed in large geographical area over a long period of time. The period of this observation could be 25 – 30 years. Hence, climate can be said to be an average of weather conditions taken over a long time.

CLIMATIC ELEMENTS AFFECTING THE BUILT ENVIRONMENT

There are five major climatic elements affecting the built environment. They are temperature, humidity, wind, atmospheric pressure and precipitation.

Temperature is the degree of hotness or coldness of the atmosphere. Of all the other climatic elements, temperature is the most important because it influences the other elements. Temperature goes a long way to influence thermal comfort of the building. Thermal comfort is the condition of the mind which expresses satisfaction with the thermal environment.

The human thermal environment is not straight forward and cannot be expressed in degrees. Nor can it be satisfactorily defined by acceptable temperature ranges. It is a personal experience dependent on a great number of criteria and can be different from one person to another within the same space. For example, a person walking up stairs in a cold environment whilst wearing a coat might feel too hot, whilst someone sat still in a shirt in the same environment might feel too cold.

The factors affecting thermal comfort in buildings could be Environmental or Personal. Environmental in the sense that such factor surrounds you and may be beyond your control, or personal in the sense that you can directly influence the factors and control them.

Environmental factors affecting thermal comfort.

·         The temperature of the air that a person is in contact with could make the person feel hot or cold.

·         The velocity of the air that a person is in contact with (measured in m/s), could make exchange of heat between the person and the air faster, thereby giving the person a cooling effect.

·         Radiant temperature is the temperature of a person’s surroundings (including surfaces, heat generating equipment, the sun and the sky). This too affects thermal comfort.

·         Relative humidity (RH) is the ratio between the actual amount of water vapour in the air and the maximum amount of water vapour that the air can hold at that air temperature. This is usually expressed as a percentage. The higher the relative humidity, the more difficult it is to lose heat through the evaporation of sweat. In such conditions, one’s body will feel moist and sticky.

Personal factors affecting thermal comfort

·         Clothing. Clothes insulate a person from exchanging heat with the surrounding air and surfaces as well as affecting the loss of heat through the evaporation of sweat. Clothing can be directly controlled by a person (ie they can take off or put on a jacket) whereas environmental factors may be beyond their control.

·         Metabolic heat. The heat we produce through physical activity. A stationary person will tend to feel cooler than a person that is exercising.

·         Well being generally and sickness, such as the common cold or flu which affect our ability to maintain body temperature, 37C at the core.

Other effects of temperature on buildings

·         Thermal expansivity. Building components such as metals expand when hot and contract when cold. The higher the temperature rise in a building, the more the expansion of building components in that building. We may not readily see the effects of this due to the small of fraction of change that occurs, but over the years, the wear and tear will be evident.

·         Economic effect. The cost of mechanical Heating, Ventilation and Air Conditioning (HVAC) will normally rise with adverse effect of temperature rise or decline. During the hot season, mechanical ventilators and air conditioners are over worked which leads to the probable damage of these systems. The operational cost too and cost of repairs and servicing will be on the increase. Conversely, during the cold season, there may be attendant need to look alternative means of heating up indoor spaces; this too is will lead to further expenses.

Humidity is the amount of water vapour in the atmosphere. It becomes Relative Humidity when a ratio is taken between the actual amount of water vapour in the air and the maximum amount of water vapour that the air can hold at that given air temperature. Like earlier said, it is usually given as a percentage. The effects of humidity can be seen as it effects thermal comfort. In a very humid environment, people will tend to sweat a lot, and clothes will not get dry easily after laundry.

Effects of Precipitation and Vapour Pressure on buildings

Precipitation is the product of a rapid condensation process (if this process is slow, it only causes cloudy skies). It may include snow, hail, sleet, drizzle and rain. In our geographical context in northern Nigeria, as well as other parts of Nigeria, rain and fog are the most common form of precipitation.

Whereas rainfall is a blessing and can be harnessed for various building services and commercial/industrial purposes, water damage from rain can have devastating effects on buildings and can quickly cause damage after even minimal rain.

Water damage can ruin building contents, and cause costly closures for repairs. Poorly sloped roofs and defective workmanship are readily observed in the event of heavy downpours. Paints and other surface finishes could peel off as result of moisture rise, flooring and floor finishes are not left out too especially for places that are prone to capillary action of underground water.

When people think of rain damage they usually assume from the roof, but keeping a properly maintained roof is only part of protecting your building from water damage. Parking lots and other open areas could collect a great deal of runoff water during rainfall. These waters are supposed to be delivered to a drainage system. However, this does not always happen. Leaf litter, debris, and garbage can clog or obstruct these drains and cause the water to collect or travel toward the building instead of away from it. Furthermore, in areas where the ground is sloped towards the building, water will run back toward the building during rainfalls causing leaks and damage.

Precipitation can take several different forms. Rain is falling drops of liquid water with diameters that are 0.5 mm (0.02 in) or greater. Drizzle is falling drops of water smaller than rain. Some raindrops are cloud droplets that grew by coalescence and fell. However, the majority of raindrops that fall over the middle and higher latitudes begin as snowflakes or graupel. As they fall, they enter warmer layers of air and melt, forming raindrops. If the falling rain evaporates before reaching the ground, it forms streaks in the sky called virga. In the cold air of winter, falling snowflakes and graupel may reach the ground without melting and accumulate as snow. Graupel that reaches the ground is called snow pellets. If rain falls into a deep, subfreezing layer of air near the ground, some of the rain may freeze into tiny ice pellets called sleet. When rain falls into a shallow, subfreezing layer of air near the ground, it may remain as a supercooled liquid and freeze upon striking a cold surface, forming freezing rain. Freezing rain can coat everything with glistening ice, the weight of which can break tree branches and snap power lines.

Hail is the largest form of precipitation, varying in size from peas to golf balls or larger. Hail forms as graupel grows in size by colliding with and sticking to supercooled liquid droplets, all while suspended in violent updrafts in a thunderstorm. When the ice particles become large and heavy enough to overcome the updrafts, they begin to fall as hailstones. Hail damage in the United States alone amounts to hundreds of millions of dollars annually.

Dew and frost are not actually forms of precipitation because they do not fall from the atmosphere. Dew consists of tiny beads of water that form as water vapor condenses onto surfaces near the ground (such as blades of grass) when the surface’s temperature drops to below the air’s dew-point temperature. When the dew-point temperature is below freezing, water vapor changes directly into ice without becoming a liquid first. The white, delicate ice crystals that form in this manner are called frost.

Pressure

Air is held to the earth by gravity. This strong invisible force pulls the air downward, giving air molecules weight. The weight of the air molecules exerts a force upon the earth and everything on it. The amount of force exerted on a unit surface area (a surface that is one unit in length and one unit in width) is called atmospheric pressure or air pressure. The air pressure at any level in the atmosphere can be expressed as the total weight of air above a unit surface area at that level in the atmosphere. Higher in the atmosphere, there are fewer air molecules pressing down from above. Consequently, air pressure always decreases with increasing height above the ground. Because air can be compressed, the density of the air (the mass of the air molecules in a given volume) normally is greatest at the ground and decreases at higher altitudes.

Whereas atmospheric pressure may not have direct effect on low-rise buildings, in the construction of very tall buildings such as sky scrapers, pressure becomes a serious part of design considerations. Alternative means (mainly mechanical) are sought to create a comfortable habitable pressure level. Except for surgical theatres where the room is to be maintained at a specific temperature, pressure and humidity, pressure is not too serious a part of design considerations for low rise buildings.

Effects of wind on buildings

Wind is air in motion. It is caused by horizontal variations in air pressure. The greater the difference in air pressure between any two places at the same altitude, the stronger the wind will be. The wind direction is the direction from which the wind is blowing. A north wind blows from the north and a south wind blows from the south. The prevailing wind is the wind direction most often observed during a given time period. Wind speed is the rate at which the air moves past a stationary object.

Wind is the major component of ventilation in buildings. The pressure between the building envelope and the external environment differ, and that is why ventilation is possible. Adequate fenestration is required to harness this. Spread of communicable diseases is faster in poorly ventilated places.

Inasmuch as wind is needed for ventilation, the adverse effect of wind on buildings can be quite detrimental. Prime of these adverse effect is that of wind-load on high-rise buildings. In the design and construction of high-rise buildings, the impact of wind-load must be taken into cognizance. Adequate provisions have to be made in the foundation design and the load-bearing framework of the buildings to ensure adequate strength and support against wind-load.

Solar Radiation and its effect on buildings

Solar Energy, radiation produced by nuclear fusion reactions deep in the Sun’s core. The Sun provides almost all the heat and light Earth receives and therefore sustains every living being.

Solar energy travels to Earth through space in discrete packets of energy called photons. On the side of Earth facing the Sun, a square kilometer at the outer edge of our atmosphere receives 1,400 megawatts of solar power every minute, which is about the capacity of the largest electric-generating plant in Nevada. Only half of that amount, however, reaches Earth’s surface. The atmosphere and clouds absorb or scatter the other half of the incoming sunlight. The amount of light that reaches any particular point on the ground depends on the time of day, the day of the year, the amount of cloud cover, and the latitude at that point. The solar intensity varies with the time of day, peaking at solar noon and declining to a minimum at sunset. The total radiation power (1.4 kilowatts per square meter, called the solar constant) varies only slightly, about 0.2 percent every 30 years. Any substantial change would alter or end life on Earth

The solar energy that falls naturally on a building can be used to heat the building without special devices to capture or collect sunlight. Passive solar heating makes use of large sun-facing windows and building materials such as brick and tile that absorb and slowly release solar heat. A designer plans the building so that the longest walls run from east to west, providing lengthy southern exposures that allow solar heat to enter the home in the winter. A well-insulated building with such construction features can trap the Sun’s energy and reduce heating bills as much as 50 percent. Passive solar designs also include natural ventilation for cooling. Shading and window overhangs also reduce summer heat while permitting winter Sun.

In direct gain, the simplest passive heating system, the Sun shines into the house and heats it up. The house’s materials store the heat and slowly release it. An indirect gain system, by contrast, captures heat between the Sun and the living space, usually in a wall that both absorbs sunlight and holds heat well. An isolated gain system isolates the heated space (a sunroom or solar greenhouse, for example) from the living space and allows the solar heat to flow into the living area via convective loops of moving air.

Active solar heating systems involve installing special equipment that uses energy from the sun to heat or cool existing structures. Passive solar energy systems involve designing the structures themselves in ways that use solar energy for heating and cooling. 

Picture showing passive solar design

WEATHER MODIFICATION

Although weather conditions may sometimes be inconvenient for people, or even dangerous, most people accept weather as an unchangeable force of nature. Some meteorologists, however, have been involved in a variety of experimental techniques designed to modify the weather.

Cloud Seeding

One method of weather modification is to seed clouds with tiny particles to try to coax more precipitation from them. There are two primary ways to seed clouds. The first method uses the coalescence process of rain formation. Small water drops or other particles are injected into the base of a cloud. As updrafts carry these particles up through the cloud, the particles grow in size by colliding and merging (coalescing) with drops in their path. Eventually, the drops grow large and heavy enough to fall. On their way down, the drops continue to grow in size and may even fragment into many new drops.

The second method of seeding clouds employs the ice-crystal (Bergeron) process of rain formation. Small particles of silver iodide (AgI) are injected into a cloud that contains both ice crystals and water droplets at below freezing temperatures. Inside the cloud, the silver iodide particles act like ice crystals. Water vapor from the surrounding liquid droplets evaporates and freezes onto the silver iodide particles, which grow larger at the expense of the surrounding liquid droplets. The growing crystals eventually become heavy enough to fall as precipitation.

The effectiveness of these methods of cloud seeding is disputed because it is difficult to determine how much precipitation would have fallen had the cloud not been seeded. Some studies indicate that seeding under optimum conditions will enhance precipitation by as much as 15 percent. On the other hand, some attempts to seed clouds have reduced the amount of precipitation. It is thought that in some cases the clouds were overseeded, which produced so many small ice particles that there was not enough water droplets and water vapor left to allow the ice crystals to grow large enough to fall.

Hail Suppression

Hail forms in thunderstorms when supercooled liquid droplets accumulate on small clumps of graupel. In an attempt to reduce the destructiveness of hail, large quantities of silver iodide are injected into the thunderstorm. The idea is to overseed the cloud so that many smaller hailstones form, preventing them from growing into large destructive hailstones. Results of hail-suppression experiments have been inconclusive.

Fog Dispersal

Fog is a cloud on the ground. Fog-clearing operations have mainly been attempted at airports to improve runway visibility. An early attempt at fog dispersal burned large quantities of fuel oil along runways, so that the air would warm enough to evaporate the fog. This expensive technique proved to be ineffective and very smoky. Another method employs helicopters that hover above the fog layer. The turbulence created by the blades mixes the drier, warmer air above the fog with the cooler, saturated air below. The mixing of the drier air into the fog evaporates the fog. This method works well when the fog is shallow, winds are light, and the air temperature is above freezing.

Fog has also been seeded in an attempt to dissipate it. The seeding usually involves salt particles or dry ice (frozen carbon dioxide). Tiny salt particles cause the fog droplets to grow in size and fall out as drizzle. Dry ice only works in fog at below freezing temperatures. As small pieces of cold dry ice descend, they freeze the liquid fog droplets into ice crystals. The ice crystals grow in size and fall to the ground. The remaining fog droplets evaporate, leaving a clear area in the fog for aircraft operations. No matter how successful the fog-clearing operation, it must be applied continuously or the fog will reform as it moves in from the surrounding area.

Hurricane Modification

Hurricanes have been seeded with silver iodide in an attempt to reduce their destructive winds. During the 1960s, project STORMFURY, a joint effort of the National Oceanic and Atmospheric Administration (NOAA) and the United States Navy, seeded several hurricanes just outside their centers so that clouds would develop farther away from the main area of severe thunderstorms and high winds. The hope was that this would reduce the air pressure locally and thereby reduce the hurricane’s winds. Although some of the results were encouraging, some uncertainty remains as to the effectiveness of seeding hurricanes. 

REFERENCES

http://www.designingbuildings.co.uk/wiki/Thermal_comfort_in_buildings

http://www.cultureofsafety.com/maintenance/property-damage-rain-water

Ahrens, C. Donald. "Meteorology." Microsoft® Encarta® 2009 [DVD]. Redmond, WA: Microsoft Corporation, 2008.

Holladay, April. "Solar Energy." Microsoft® Encarta® 2009 [DVD]. Redmond, WA: Microsoft Corporation, 2008.