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Greg KeeffeHead of DesignManchester School of Architecture, Manchester [email protected]
The Passive House: Issues of Cooling: Form, shading,ventilation.
Living (bioclimatic) architecture
Climate derives form
Uruguay Climate: Hot Humid
Uruguay Climate: Hot Humid
Passive Design
Building and equipment is system to provideoccupant comfort
Key issuesForm OrientationMass (inside and out)Façade design – fenestration / shading in particularFabric Solar GainVentilation controlIncidental and ambient gainsBuilding and equipment a single system
Resource/Material loop
Passive Design
Form - The Passive zone.
It is crucial all rooms are within the passive zone
The passive zone is typically 7metres from the building edge
Sometimes this can be extended
Passive Design
Form - Surface area to volume ratio
Compact versus rambling
Passive Design
Form - Self shading
Passive Design
Form - the Courtyard
Offers self shading with microclimate
Fathy Houses Tunis
Alberto Campo Baeza, Caspar House
Passive Design
Form - Minimise West façade
The West façade is the most difficult to shade
Passive Design
Form - Layering
Passive Design
Orientation
Re sun and wind
Glenn Murcutt
Passive Design
Issues of thermal Mass
Heavy or light??
Tropical light, arid heavy.
Bedouin tent - Alhrambra
Passive Design
Façade design
Nouvel
Corderch
Passive Design
Fabric design
Mass, Insulation, fenestration
Passive Design
Ventilation Control
Passive Design
Incidental and ambient gain
Passive Design
Building and equipment as single system
Rogers MVRDV Future Systems
IN WARM WEATHER
1. MINIMIZE HEAT GAINS.
2. AVOID OVERHEATING.
3. OPTIMISE COOL AIR VENTILATION AND OTHERNATURAL COOLING METHODS.
Shigeru Ban
Givoni’s bioclimatic chart
THE NEED FOR COOLING
1. SOLAR CONTROL
• To prevent the sun’s rays from reaching andentering the building.
COOLING STRATEGIES
2. EXTERNAL GAINS
• To prevent increases in heat due toconduction through the building skin or by theinfiltration of external hot air.
COOLING STRATEGIES
3. INTERNAL GAINS
• To prevent unwanted heat from occupantsand equipment raising internal temperatures.
COOLING STRATEGIES
4. VENTILATION
• Unwanted hot air may be expelled andreplaced by fresh external air at a suitabletemperature.
COOLING STRATEGIES
5. NATURAL COOLING
• To transfer excess heat from the building toambient heat sinks.
COOLING STRATEGIES
SOLAR CONTROL
• External essential.
• examples are overhangs, awnings, movableblinds/louvres and planted screens.
COOLING STRATEGIES
SOLAR CONTROL (SHADING)
• The degree and type of shade necessary dependson the position of the sun and the position andgeometry of the part of the building being shaded.
COOLING STRATEGIES
Solar Geometry and shading
Orientation
• Long axis East-West
• Shading of North fenestration simple• East and West facing windows, are more difficult
to shade
COOLING STRATEGIES
COOLING STRATEGIES
Hostel for Youth Education Institute, Windberg, Thomas Herzog
SOLAR CONTROL (FIXED SHADING)
• South facing windows can be shaded by anfixed overhang above the glazed element.
• The depth of the overhang should take intoaccount not only its distance above thewindow but also the aperture height.
• The length of the overhang is determined bythe window width.
COOLING STRATEGIES
SOLAR CONTROL (ADJUSTABLE SHADING)
• The effectiveness of fixed screens varies according tothe seasonal changes in the position of the sun.
COOLING STRATEGIES
Discarded music cassettes, Pavilion of Christ, Volkenroda.Transparent Insulation Material (extruded honeycomb).
House, Amsterdam, Heren 5
Administration Building, Wiesbaden, Herzog + Partners
Curved sunscreen and light-deflecting elements in south facingIntelligent façade allow differentiated natural lighting on overcast andclear days.
Overcast day Clear sky
Foliage used as solar filter at Tokyo-Nara tower,Japan, Exhibition Tower, Ken Yeang
Bioclimatic Skyscraper proposed forKuala Lumpur, Malaysia
Learning Resource Centre, Jubilee campus, Nottingham, Hopkins Architects
Audi Mobile Museum, Ingolstadt, Munich, Germany,Design-Agency KMS
Heliotropic solar shading, Siemens Pavilion, Expo’92 Seville, by Siemens Architecture Dept.
Albert Camus School, Frejus, FranceFoster+Partners
Single family House,Wohnhaus, Vaise, FranceJourda & Perraudin
SOLAR CONTROL (ADJUSTABLE SHADING)
• Outside the building envelope
• Daylighting important too
COOLING STRATEGIES
SOLAR CONTROL (Double Skins)
• Consists of outer single glazing - shading - doubleglazing
• Interstitial space acts as solar chimney to increaseventilation.
COOLING STRATEGIES
Business Promotion Centre, Duisberg, Germany,Foster & Partners
SOLAR CONTROL The roof
Extending the eaves offers shading potential
COOLING STRATEGIES
SOLAR CONTROL (SPECIAL GLAZING)
For windows which are difficult to shade,• Absorbing glass• Reflecting glass
COOLING STRATEGIES
Reflecting glass & clear glass Absorbing glass & clear glass
SOLAR CONTROL (SPECIAL GLAZING)
• Photochromic, thermochromic, and electrochromicglasses modify the incoming rays of the sun so thatthe optical properties of the glass change i.e. the glassdarkens.
COOLING STRATEGIES
Schematic diagram of a five-layer electrochromic coating system.A reversible low voltage charge forces ions to migrate between anactive electrochromic layer and a passive counterelectrode layercausing the active layer to darken. When the voltage is reversed andthe ions are removed, the electrochromic layer returns to its clear state.
High-transmission State (Clear) Low-transmission State (Coloured)
SOLAR CONTROL (PLANTING )
• Shading can also be provided by vegetation.
• If deciduous, the branches are bare in winter allowingsolar penetration, from spring onwards as the leavesgrow shade increases.
COOLING STRATEGIES
Minimise EXTERNAL GAINS
• Walls and roofs heated by the sun and by thewarm outside air produce uncomfortableconditions inside.
• INSULATION• THERMAL INERTIA• REFLECTION.
COOLING STRATEGIES
EXTERNAL GAINS (INSULATION)
Can be used to prevent overheating byconduction in summer.
COOLING STRATEGIES
EXTERNAL GAINS (THERMAL INERTIA)there is a time delay due to the thermal inertia ofthe walls and roof, etc., in the flow of heatthrough the building envelope which can beexploited in a heavyweight building for coolingpurposes.
COOLING STRATEGIES
COOLING STRATEGIES
EXTERNAL GAINS (THERMAL INERTIA)
Turf roofs offer transpiration coolingAnd insulation
EXTERNAL GAINS (THERMAL INERTIA)
• When solar radiation strikes an opaque surfacesuch as a wall or a roof the exterior surfaceabsorbs part of the radiation and converts it toheat.
• Part of the heat is directly re-emitted to theoutside.
• The remainder is conducted through the wall orroof at a rate which depends on the thermalproperties of the material.
COOLING STRATEGIES
Concrete has a delay of 20mins per 10mm
STORAGE OF COLD (REMOTE MASS)
• Rock beds located away from the occupied spacecan be used to increase the amount of heat andcold that can be effectively stored.
COOLING STRATEGIES
Princeton Professional Park, Princeton, New Jersey, Harrison Fraker
Summer Cooling strategy Day/Night
EXTERNAL GAINS (REFLECTION)
• Light colours
• In an air-filled cavity wall or roof space radiation iskey thermal transport, so add foil.
COOLING STRATEGIES
Minimise INTERNAL GAINS
Artificial lighting, appliances andthe tasks of occupants all lead tointernal heat gains.
This can be reduced by naturaldaylighting and by:
• Accurate control.• Choosing efficient appliances.• Expelling the heat generated.
COOLING STRATEGIES
VENTILATION
• Usually buildings are warmer inside than out.
• Thus increasing ventilation using cooler fresh airgives relief
COOLING STRATEGIES
Stack effect
Solar chimneys use the sun to warm-up the internal surface ofthe chimney. Buoyancy forces due to temperature differencehelp induce an upward flow along the plate.
Osuna Housing SevilleSotomayer, Dominguez Lopez
VENTILATION (STACK EFFECT)
• The same effect can be used to create cross ventilation.
COOLING STRATEGIES
Summer operation – Ventilation and air circulation
Am Lindenwaldle, Freiburg, GermanyDominic Michaelis Associates
La Salut, Barcelona, SpainC. Parant
Cooling mode:
Cool air is drawn up from thenorth face of the house to beexhausted through the skylights.
Office Building, Dresden, LOG ID
1. Cavity between concrete and steel roof promotes cooling of concrete.2. Stale air exits the classrooms at the highest point, preventing the formation of a
warm static air layer.3. Cross ventilation through classrooms.4. Entry of fresh air at a low height enhances air circulation in the classrooms.5. Perforated steel louvres shade from direct sunlight.6. Stale, warm air exits through the open louvres.7. Ventilation enhanced by Stack/chimney effect.
VENTILATION (WIND PRESSURE EFFECT)
• When wind strikes a building a high pressure on theexposed side and a low pressure on the opposite,sheltered face results.
COOLING STRATEGIES
VENTILATION (WIND PRESSURE EFFECT)
• The movement of air across a site is from highpressure zones to low pressure zones, throughopenings in the building envelope.
• The best distribution of fresh air throughout thebuilding is achieved when the openings arediagonally opposite each other and air flow is nothindered excessively by partitions and furniture,etc.
COOLING STRATEGIES
VENTILATION (WIND PRESSURE EFFECT)
• Maximum ventilation should be provided duringthe day in occupied areas of the building athead height.
• In addition, there should always be a good flowof fresh air along the building’s most massiveelements so that as much heat as possible isdissipated from them.
COOLING STRATEGIES
VENTILATION (THE VENTURI EFFECT)
• Used to induce circulation of air in a particulardirection.
• The air is encouraged to flow through a constrictedpart of the building. At this position, its speedincreases and the pressure decreases accordingly.
• The reduced pressure creates an air flow which canbe used to drive hot air from the building and thuscause ventilation.
COOLING STRATEGIES
The Venturi tube illustrates the ‘Bernoulli effect’: as theVelocity of air increases its static pressure decreases.
A Venturi tube used as a roof ventilator
Kanak Centre, New Calendonia, Renzo Piano
Passive ventilation: light breezes Strong Winds
Cyclone Reverse Winds
Kanak Centre, New Calendonia, Renzo Piano
Night cooling using (CROSSVENTILATION)
It is a necessary complement to heatstorage.
NIGHT-TIME VENTILATION air ispreferentially circulated pasthigh thermal inertia masses toremove the heat they haveaccumulated during the day.
COOLING STRATEGIES
COOLING STRATEGIES - Night purging
NIGHT-TIME VENTILATION AIR
COOLING STRATEGIES
Room temperaturesdependant on outsidetemperature (Summer day)
Operation of Night Cooling:06:00 to 19:00hrs.
VENTILATION (WIND TOWERS)
• Wind towers draw upon the force of the wind togenerate air movement within the building.
• The inlet of a Wind Scoop are oriented toward thewindward side to capture the wind and drive airdown a chimney.
• Alternatively, a chimney cap is designed to create alow pressure region at the top of the tower, and theresultant drop in air pressure causes air to flow upthe chimney.
COOLING STRATEGIES
SCOOP
Ventilation using Wind Towers
CAP
Windcatchers - vernacular
Iran Hydrabad
WIND TOWERS - modern• Both these principles may be combined in a
single tower providing both admittance andexhaust of air.
• A self-contained system is thus created.
COOLING STRATEGIES
View of wind cowl, Jubilee Campus, Nottingham University, Michael Hopkins
NATURAL COOLING
• EVAPORATION.
• GROUND COOLING.
• RADIATIVE HEAT LOSS tothe sky and by CROSSVENTILATION.
COOLING STRATEGIES
COOLING OF INFILTRATION AIR(EVAPORATIVE COOLING)
• To change its state from liquid to vapour, waterrequires a certain amount of heat known as the LATENTHEAT OF VAPORIZATION.
• When this heat is supplied by hot air there is a drop inair temperature.
COOLING STRATEGIES
Passively cooled house, Arizona
Stanford University CA, Ecology CentreEsherick Homsey Dodge & Davis
GROUND COOLING3 methods
Ground couplingAir systemsWater systems
COOLING STRATEGIES Future Systems
Hope House, Bill Dunster
RADIATIVE HEAT LOSS TO THE SKY
• Radiative transfer of heat always occurs between twoadjacent masses at different temperatures.
• clear night skies are (even in the warm season) cold soexposed surfaces cool appreciatively
COOLING STRATEGIES
Indirect direct direct
Skytherm House 1973
In roof ponds the heat accumulated in a building during the dayis trapped and stored in the roof pond, which is protected on the outside by movable insulation.
•At night, the insulation is removed to allow •the stored heat to be radiated to the sky.
REFERENCES
Brown, G.Z. and Dekay, M. Sun, Wind and Light: Architectural DesignStrategies (John Wiley & Sons Inc. 2000).
Santamouris, M. Advances in Passive Cooling (Buildings, Energy and SolarTechnology) (EarthScan books 2007).
Herzog, Thomas. Solar energy in architecture and urban planning (Munich:Prestel 1996).
Givoni, Baruch The Passive Cooling of Buildings (Architecture) (Wiley 1994).
Goulding, J.R., Lewis, J.O., and Steemers, T.C. Energy in Architecture: TheEuropean Passive Solar Handbook (Batsford Ltd. 1993).
Goulding, J.R., Lewis, J.O., and Steemers, T.C. (eds.) Energy ConsciousDesign: A Primer for Architects.
Melet, Ed. Sustainable Architecture: Towards A Diverse Built Environment(Rotterdam: NAI Publishers 1999).