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Imtiaz Ali Khan
Imtiaz Ali Khan

Passive cooling is a design approach that focuses on controlling heat gain and dissipating heat without energy usage. It involves preventing heat entry, storing heat in thermal mass, and releasing heat at night. Key techniques include site design for climate/wind, solar shading, insulation, natural ventilation like cross/stack ventilation, night flushing to release stored heat, radiative cooling of roofs at night, evaporative cooling using water, and coupling buildings to cooler earth temperatures underground.

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PASSIVE COOLING
Passive cooling is a building design approach that focuses on heat gain control and heat dissipation in a building in order to improve the indoor thermal comfort with low or no energy consumption.
Approach 1. Heat Prevention 2. Modulation and Heat Dissipation
Heat Prevention To provide protection and/or prevention of external and internal heat gains. Techniques Microclimate and site design Solar control Building form and layout Thermal Insulation
1. Microclimate and Site Design The passive design depends very much on local climate and site characteristics. Factors Local climate (sun, wind) Site characteristics (type of terrain and landscape ie., plain, hilly, plateau) These two factors influence selection of suitable cooling strategy, building design and location.
2. Solar Control (Shading) A properly designed shading system can effectively contribute to minimizing the solar heat gains. Shading both transparent and opaque surfaces of the building envelope will minimize the amount of solar radiation that induces overheating in both indoor spaces and buildings structure. By shading the building structure, the heat gain captured through the windows and envelope will be reduced.
Over hangs Awnings Light colored building material and paints Deciduous trees
(passive cooling of a building to ).pptx
(passive cooling of a building to ).pptx
3.Building Form and Layout/Orientation The form refers to surface/volume ratio of the building.
The orientation is the positioning of building in relation to sun.
4. Thermal Insulation Insulation in the buildings envelope will decrease the amount of heat transferred by radiation through the facades. This principle applies both to the opaque (walls and roof) and transparent surfaces (windows) of the envelope. Since roofs could be a larger contributor to the interior heat load, especially in lighter constructions (e.g. building and workshops with roof made out of metal structures), providing thermal insulation can effectively decrease heat transfer from the roof.
(passive cooling of a building to ).pptx
Modulation and Heat Dissipation This technique makes use of heat sinks which store and remove internal heat gain. Examples Night sky, Earth soil, Building mass There are two types of modulation and heat dissipation. Thermal Mass Natural cooling
1. Thermal Mass These materials store the heat during day and re- radiate it to space at night. Concrete, brick is a good example of thermal mass. In summer, the re-radiated heat can be removed through ventilation at night and vice versa for winter.
(passive cooling of a building to ).pptx
2. Natural cooling Natural cooling refers to the use of ventilation or natural heat sinks for heat dissipation from indoor spaces. Natural cooling can be separated into five categories different categories: Ventilation Night flushing Radiative cooling Evaporative cooling Earth coupling
Ventilation Ventilation as a natural cooling strategy uses physical properties of air to remove heat or provide cooling to occupants. Types Cross ventilation Stack ventilation
Cross Ventilation It relies on wind to pass through the building for the purpose of cooling the occupants. Cross ventilation requires openings on two sides of the space, called the inlet and outlet. The sizing and placement of the ventilation inlets and outlets will determine the direction and velocity of cross ventilation through the building. Generally, an equal (or greater) area of outlet openings must also be provided to provide adequate cross ventilation.
(passive cooling of a building to ).pptx
Stack Ventilation It is the upward movement of air through openings in a building fabric due to thermal buoyancy and/or negative pressure generated by the wind over the roof.
Night Flushing The building thermal mass (concrete, brick) absorbs solar heat during day and re-radiate the same at night. The ventilation (winds) removes the heat and make building cool. The technique is mostly suitable in areas where there is large difference in daily max and min temperature.
(passive cooling of a building to ).pptx
Radiative Cooling All objects constantly emit and absorb radiant energy. An object will cool by radiation if the net flow is outward, which is the case during the night. At night, there is a net flow to the sky. Since the roof provides the greatest surface visible to the night sky, designing the roof to act as a radiator is an effective strategy.
(passive cooling of a building to ).pptx
Evaporative Cooling It is the evaporative process of water to cool the incoming air while simultaneously increasing the relative humidity. A saturated filter is placed at the supply inlet so the natural process of evaporation can cool the supply air. Apart from the energy to drive the fans, water is the only other resource required to provide conditioning to indoor spaces. The effectiveness of evaporative cooling is largely dependent on the humidity of the outside air; dryer air produces more cooling. A study found that evaporative cooling reduced inside air temperature by 9.6 属C compared to outdoor temperature. An innovative passive system uses evaporating water to cool the roof so that major portion of solar heat does not come inside
(passive cooling of a building to ).pptx
Earth Coupling Earth coupling uses the moderate and consistent temperature of the soil to act as a heat sink to cool a building through conduction. This passive cooling strategy is most effective when earth temperatures are cooler than ambient air temperature, such as in hot climates. Direct coupling Indirect coupling
Direct coupling or earth sheltering occurs when a building uses earth as a buffer for the walls. The earth acts as a heat sink and can effectively mitigate temperature extremes. Earth sheltering improves the performance of building envelopes by reducing heat losses and also reduces heat gains by limiting infiltration.
(passive cooling of a building to ).pptx
Indirect coupling means that a building is coupled with the earth by means of earth ducts. An earth duct is a buried tube that acts as avenue for supply air to travel through before entering the building. The supply air is cooled by conductive heat transfer between the tubes and surrounding soil. Therefore, earth ducts will not perform well as a source of cooling unless the soil temperature is lower than the desired room air temperature.
(passive cooling of a building to ).pptx

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(passive cooling of a building to ).pptx

  • 2. Passive cooling is a building design approach that focuses on heat gain control and heat dissipation in a building in order to improve the indoor thermal comfort with low or no energy consumption.
  • 3. Approach 1. Heat Prevention 2. Modulation and Heat Dissipation
  • 4. Heat Prevention To provide protection and/or prevention of external and internal heat gains. Techniques Microclimate and site design Solar control Building form and layout Thermal Insulation
  • 5. 1. Microclimate and Site Design The passive design depends very much on local climate and site characteristics. Factors Local climate (sun, wind) Site characteristics (type of terrain and landscape ie., plain, hilly, plateau) These two factors influence selection of suitable cooling strategy, building design and location.
  • 6. 2. Solar Control (Shading) A properly designed shading system can effectively contribute to minimizing the solar heat gains. Shading both transparent and opaque surfaces of the building envelope will minimize the amount of solar radiation that induces overheating in both indoor spaces and buildings structure. By shading the building structure, the heat gain captured through the windows and envelope will be reduced.
  • 7. Over hangs Awnings Light colored building material and paints Deciduous trees
  • 10. 3.Building Form and Layout/Orientation The form refers to surface/volume ratio of the building.
  • 11. The orientation is the positioning of building in relation to sun.
  • 12. 4. Thermal Insulation Insulation in the buildings envelope will decrease the amount of heat transferred by radiation through the facades. This principle applies both to the opaque (walls and roof) and transparent surfaces (windows) of the envelope. Since roofs could be a larger contributor to the interior heat load, especially in lighter constructions (e.g. building and workshops with roof made out of metal structures), providing thermal insulation can effectively decrease heat transfer from the roof.
  • 14. Modulation and Heat Dissipation This technique makes use of heat sinks which store and remove internal heat gain. Examples Night sky, Earth soil, Building mass There are two types of modulation and heat dissipation. Thermal Mass Natural cooling
  • 15. 1. Thermal Mass These materials store the heat during day and re- radiate it to space at night. Concrete, brick is a good example of thermal mass. In summer, the re-radiated heat can be removed through ventilation at night and vice versa for winter.
  • 17. 2. Natural cooling Natural cooling refers to the use of ventilation or natural heat sinks for heat dissipation from indoor spaces. Natural cooling can be separated into five categories different categories: Ventilation Night flushing Radiative cooling Evaporative cooling Earth coupling
  • 18. Ventilation Ventilation as a natural cooling strategy uses physical properties of air to remove heat or provide cooling to occupants. Types Cross ventilation Stack ventilation
  • 19. Cross Ventilation It relies on wind to pass through the building for the purpose of cooling the occupants. Cross ventilation requires openings on two sides of the space, called the inlet and outlet. The sizing and placement of the ventilation inlets and outlets will determine the direction and velocity of cross ventilation through the building. Generally, an equal (or greater) area of outlet openings must also be provided to provide adequate cross ventilation.
  • 21. Stack Ventilation It is the upward movement of air through openings in a building fabric due to thermal buoyancy and/or negative pressure generated by the wind over the roof.
  • 22. Night Flushing The building thermal mass (concrete, brick) absorbs solar heat during day and re-radiate the same at night. The ventilation (winds) removes the heat and make building cool. The technique is mostly suitable in areas where there is large difference in daily max and min temperature.
  • 24. Radiative Cooling All objects constantly emit and absorb radiant energy. An object will cool by radiation if the net flow is outward, which is the case during the night. At night, there is a net flow to the sky. Since the roof provides the greatest surface visible to the night sky, designing the roof to act as a radiator is an effective strategy.
  • 26. Evaporative Cooling It is the evaporative process of water to cool the incoming air while simultaneously increasing the relative humidity. A saturated filter is placed at the supply inlet so the natural process of evaporation can cool the supply air. Apart from the energy to drive the fans, water is the only other resource required to provide conditioning to indoor spaces. The effectiveness of evaporative cooling is largely dependent on the humidity of the outside air; dryer air produces more cooling. A study found that evaporative cooling reduced inside air temperature by 9.6 属C compared to outdoor temperature. An innovative passive system uses evaporating water to cool the roof so that major portion of solar heat does not come inside
  • 28. Earth Coupling Earth coupling uses the moderate and consistent temperature of the soil to act as a heat sink to cool a building through conduction. This passive cooling strategy is most effective when earth temperatures are cooler than ambient air temperature, such as in hot climates. Direct coupling Indirect coupling
  • 29. Direct coupling or earth sheltering occurs when a building uses earth as a buffer for the walls. The earth acts as a heat sink and can effectively mitigate temperature extremes. Earth sheltering improves the performance of building envelopes by reducing heat losses and also reduces heat gains by limiting infiltration.
  • 31. Indirect coupling means that a building is coupled with the earth by means of earth ducts. An earth duct is a buried tube that acts as avenue for supply air to travel through before entering the building. The supply air is cooled by conductive heat transfer between the tubes and surrounding soil. Therefore, earth ducts will not perform well as a source of cooling unless the soil temperature is lower than the desired room air temperature.