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

Heat Balance: Human daily activities are done in cycles. After long working hours we need to rest, sleep and refresh to be able to work again. If any human came under thermal stress for long period, he may become seriously ill or die. This can be from Very high cold (Hypothermia) or very high heat (heat Stroke). Thermal loads on humans have two main components: 1.Heat from food digestion (metabolism). 2.Heat exchange between the climate and our bodies. We need energy to perform our activities and for our bodies to perform their internal activities. ( tissue repair, growth, etc…). Since our bodies are not efficient in utilising the energy it produce, we use only 20% of the energy we produce and the other 80% will be transferred to heat and passed to the environment. Humans managed to live in hot climates of deserts and cold climates like the Eskimos. Despite all these Very hot and very cold conditions humans were able to keep their Heat Balance and do their activities and their bodies to do their internal processes and keep the internal tissue temperatures at about 37.2º.

-Our bodies regulate it’s heat balance through its Thermo- regulatory system. Thermo – regulation: -For humans to stay alive, they need to keep their internal tissues temperature around 37.2º. -To do this they need a special system to exchange the heat with the surrounding weather and climate. -This system is very well capable of maintaining the temperature within the range required. (i.e., even in the very difficult conditions of the weather). -We know very little about this system only by the reactions of it to different climatic conditions, but not exactly what is happening. -This system is based in our brain and control all the important processes. (i.e., like eating, keeping the right amount of water in our body, keeping or losing heat. -When there is an imbalance in the thermal balance, the system send more blood to the skin and try to cool the skin by evaporating sweet until the temperature is balanced.

When looking at the relation between the effective temperatures of the weather and that of the human internal tissues figure blow, we can see that: -The regulatory system can keep the internal tissues in their right temperature, regardless of the external weather conditions. This proves it’s high efficiency. -We can see that the change in internal tissues temperatures can happen only according to the nature of the activities of the person in the climate. -With increased rate of physical activities, the need for energy is increased and the mount of heat he need’s to lose will also increases. -We lose heat to the environment by: 1. Long wave radiation Air convection Evaporation.

1. Heat exchange by radiation: We have two types of radiation: 1.1 Solar Radiation or Short wave Radiation: mainly coming directly from the sun, can be 800 Watts/m 2 or more. Compared to heat from metabolic process around 60W/m 2. Short wave radiations are absorbed more by dark colours, (i.e., black colour can absorb 20% more Than White colour). 2.2 Long wave Radiation: short wave radiation after reflection from surfaces becomes Long wave Radiation. It is not affected by colours. -Humans can receive heat from sun’s short wave radiation, but can either receive or lose heat by Long Wave radiation. - Humans can receive heat from Long Wave radiation only when the temperature of surroundings surfaces is greater than his temperature or his external cloths temperature. (And the reverse is true.)

2. Convection Heat Exchange: - Heat exchange between humans body/external Cloths by convection currents. -When air temperature is higher than human body/cloths temperature the body/cloths gain heat from the air. -When air temperature is lower than human body/cloths temperature the body/cloth loose heat to the air. We have two types of convection heat exchange: 2.1 Natural convection Heat Exchange: -When air temperature is lower than body/cloth temperature, the air is heated and its particles depart from each other and therefore becomes lighter. Light air rises up taking the heat with it. This create natural currents to cool the body. 2.2 Forced Convection Heat Exchange: -If the air currents around the body is driven by a mechanical means (i.e., Fan) it is called Forced Convection. Heat Exchange with both natural and forced convection is normally very small compared to Radiation Heat Exchange.

3. Evaporative heat loss: When the climate is moderate, the body thermal balance is kept by convective heat exchange and long wave radiations. If the human body is subjected to high thermal stress and failed to maintain thermal balance, Then it losses heat by evaporation: We have two evaporation types: 3.1 Sweat Evaporation: Sweat is formed as an ejection of water and salts from the blood to the skin surface. When sweat is evaporated it takes ( latent heat of evaporation from the human body) and therefore cools it surface and the surface cool the blood in the skin. The blood then cools the inner tissue of the body. Important : cooling is experienced by the rate of evaporation not the rate of sweating. cooling is decreased if the rate of sweating is higher than the rate of evaporation. Sweat falling of human body does not affect the cooling process. Sweat on cloths cools them first and the cloths cools our bodies. 3.2 Respiration Heat Loss: Heat loss through breathing is an evaporative cooling process, but it is less efficient than sweat.

3.2 Respiration Heat Loss: Heat loss through breathing is an evaporative cooling process, but it is less efficient than sweat. With air coming into the lungs it becomes saturated with water and its temperature similar to body temperature. With air going out of the lungs it evaporates water therefore cools the inner tissues of the lungs. Thermal equilibrium is reach when the heat lost to the environment is equal to the heat gained from it. Thermal imbalance: Thermal imbalance happens if the internal tissues temperatures are either higher or lower than 37.2º. A heat struck ( complete collapse) happens when inner tissues are 46.5 º. Hypothermia ( complete collapse) happens when inner tissues are 35º. Up to 18° (10 hours comma). Heat Strokes are more dangerous than Hypothermia, Why? Heat Stroke takes short time to happen and hypothermia takes long time to happen. Our bodies can resist hypothermia far better than heat stroke.

3.2 Human Sensation to heat: There has been considerable research and studies into human responses to the thermal environment aiming at establishing scientific basis describing human sensation of heat. As an outcome of these studies they laid some indicators helping to understand this matter, namely: 1.The Equivalent Temperature index. معاير درجة الحرارة الفعالة 2.Corrected effective temperature index معاير درجة الحرارة الفعالة المصححة 3.Resultant Temperature محصلة درجة الحرارة 4.Standard Effective temperature index. معيار درجة الحرارة الفعالة القياسية 5.The equivalent temperature index. معيار درجة الحرارة المتكافئة 1.The Equivalent Temperature index. معاير درجة الحرارة الفعالة -Made by ASHRAE 1919, to study the effect of air temperature and air humidity to find the condition of comfort. -Measure temperatures from zero to 69°.

2. Corrected effective temperature index معاير درجة الحرارة الفعالة المصححة -this is a further development to the first index by adding other factors such as air speed and Clothing's to the main factors of Dry temperature and wet temperature. They also added the globe thermometer instead of the dry bulb thermometer. The result can be shown in the following figure: 3. Resultant Temperature Index: Relates to dry temperature, wet temperature and long wave radiation. 4.Standard effective temperature index: Depends on the coverage of the skin with sweat and the temperature of the skin. The standard experiment was made with people sitting in comfortable position with light cloth on. When the relative humidity was 50%, Dry bulb temperature is 24°C then the (standard Effective Temp SET is 24°C). When we change clothing then the SET change because the feeling of the people will change. It’s a comprehensive approach to measure human sensation for the thermal environment, taking into account the effect of clothing and level of activity with, air temperature, humidity, long wave radiation.

5. Equivalent temperature index معيار درجة الحرارة المتكافئة A practical experiment was made specifically for measuring thermal responses for workers in factories and can be applied mainly in similar situations. Thermal comfort: It is the state of total content of the Environment.( a person feels with His full senses with comfort) Or it is the state when you don’t feel It is a bit hot or a bit cold. So it is neutral Hot or cold feeling. Fanger Equation : معادلة الراحة الحرارية