1. Climate and Architecture Arch 331 Dr. Abdelrahman Elbakheit References العناصر المناخية و التصميم المعمارى, د. سعيد عبد الرحيم سعيد بن عوف.1 2. العمارة و المناخ, د. هاشم عبود الموسوى 3. Climate considerations in buildings and urban Design. Baruch Givoni

2. Thermal radiation : Thermal rays are an electro-magnetic waves emitted by the movement of the molecules of the materials. When falling on another object, then it will be absorbed and turned into heat. By this process heat transfers from one object to the other. Thermal rays are the infra- red range of the electro-magnetic waves they can be: Short waves 700 -2300 Nano meter. Long waves 2300-10,000 Nano meter.

3. Thermal radiation : Materials can be either: -Opaque : stop thermal rays from passing through them. -Transparent: allow thermal rays to pass through them. Opaque materials: The surface of opaque materials have three basic characteristics: -Ability to absorb rays = Absorbtivity. α -Ability to reflect rays = reflectivity. r -Ability to emit rays = Emissivity. ε -When solar radiation falls on an opaque surface it will be either absorbed or reflected. totally Absorbed by black surfaces and totally reflected by a reflective surface. Other materials will be between these two ends and will have both absorption and reflection. - Absorbtivity α +reflectivity r = 1 - Heat emitted by a surface = 4.9 ε ( T/100) 4. T in Kelvin.

6. Transparent materials: Transparent materials can either be of : Glass or Plastic -they can provide vision to the outside, protect from wind hot/cold, provide natural lighting. According to thermal radiation they can either: -Reflect some of the radiation. -Absorb some of the radiation. -Transmit some of the radiation.

8. Transparent materials: -The reflected component of sun radiation depends mainly on incidence angle on glass plane. With the increase of angle of incidence there would be an increase of reflection. From figure we see that with the increase of incidence angle to 50º there would be a slow increase of reflection, while when increasing the angle above 50 then there would be more reflection. We can make use of this to make full use of reflection in summer and have moderate reflection in temperate time while having the least reflection in winter, where the sun rays would be more preferred. Solar control glassing: The new advancement in glass and plastic types made it possible to control sun rays avoiding the high heat and providing good natural light or supplementing artificial light. Solar control glassing have 2 or 3 layers of glassing with air gaps between them. We have two types: -Absorptive glass -Reflective Glass.

10. Transparent materials: -Absorptive glass: have higher thermal mass, therefore can absorb heat gradually and then loss it slowly by convection and radiation. There would be some reflected radiation and some transmitted. -Reflective glass: have the majority of radiation reflected. Therefore would be some absorbed and some transmitted but is small compared to reflection. The quantity of reflected light depends on the material of the reflecting coating. Glass Shading Coefficient : is the amount of heat gained due to the heat transmitted through the glassing compared to that of a clear glass panel with 3mm thickness. Note: Normally with the above two types (reflective and Absorptive) glass to have 2 or 3 layers of glassing The air gap of between the glazing need to be 2.5cm to reduce conduction heat transfer. If it is more than this there would be convection heat transfer between the surface of the glazing.

11. Convection heat transfer: -Reason for convection: thermal changes increase/decrease or heat produce different molecule movements in liquids and gases. -Heat would increase the movement of molecules this will produce low density in the liquid/gas and therefore this part will try to rise and would be replaced by cooler and denser molecules. -If this movement is caused by fans or pumps then the convection becomes Forced convection. -Convection can be between solid surfaces and gases/liquids. As in buildings, between surfaces and air. Factors affecting convection in buildings: -Area of contact between the surface and the air. -Difference in temperatures between the surface and air. -Convection co-efficient. Depends or air viscosity and speed and nature of the surface.

13. Heat transfer in air gaps: - due to air being a good thermal barrier there is an increasing tendency to use air gaps in building constructions. -We have two type: Horizontal Air Gaps. In roofs and floors. Vertical Air Gaps. In Walls and vertical constructions. -In vertical gaps: the thickness of the gap and the emissivity of the enclosing surfaces have the say in heat exchange in the gap. -In horizontal gaps the same factors as in vertical gaps but with the addition of direction of heat transfer. If it is from down to up then there would be an additional convection in the gap in gaps of more that 2.5cm. -Gaps of 2.5cm and lower would not have convection. -