Structural Controls for Climate Responsive Design (for Cooling Purpose)

The purpose is to ensure the best possible indoor thermal conditions by relying on structural (passive) controls, which may obviate the need for any mechanical (active) controls, but even if mechanical controls do have to be resorted to , their task will thereby reduced to a minimum.

The primary source of all heat that could be gained within a structure is through sun.Design strategies so as to have the control over the solar heat needs to be evolved:By limiting the solar incidenceIf incident limiting the conducted heatBy limiting the direct radiation of sun coming indoorsModulating the heat gain/loss through the design of openings and volumes for air movement.

By Limiting the Solar IncidenceOrientation and plan form of the building.Building orientation determines the amount of radiation it receives.

Orientation with respect to air pattern also affects the amount of natural ventilation.

Orient short side of building to east and west and avoid windows on these facades if possible. Use overhangs, balconies, and porches to shade both windows and walls. Use large overhanging roofs and porticos to shade both windows and walls.

Building formThe perimeter to area ratio of the building is an important indicator of heat gain and heat loss.Larger ratio means small area is being bound by larger perimeter, means greater gain of radiative heat during day time and more loss during night, smaller means vice versa.

Surface area to volume is a 3-D extrapolation of P/A ratio, that can determine heat gain and heat lossIn hot dry climate, as also in cold dry climate S/V ratio should be as low as possible.In warm humid climate need of airy spaces means not necessarily reducing the S/V ratio.

If Incident, Limiting the Conducted Heat

Heat conduction depends upon the type of material used for construction fro example conductivity of stone is higher (highest for granite) than brick work, and is highest for metals.But the transmittance value is comparable because of large capacitative insulative properties of stone.

By Limiting the Direct Radiation of Sun Coming IndoorsWindows are the primary means of solar entryFor the reduction of solar heat gain through the windows four variables which are within the control of the designer:Orientation and the window sizeInternal blinds, curtainsSpecial glassesExternal shading devices.

External Shading DevicesDesign of shading device is guided by the orientation or the the direction to which a particular wall may be facing.The path of sun for a given location on the globe.The understanding of shadow angles in order to optimize the performance of the shading device.

Altitude (Alt)measured in the vertical plane, between the suns direction and the horizon plane; In some texts this is referred to as elevation.

Azimuth (AZI)the direction of the sun measured in the horizontal plane from north in a clockwise direction (thus east = 90, south = 180, west 270, whilst north can be 00 or 360).

For the design of vertical shading device

For the design of horizontal shading device

Modulating the Heat Gain/loss Through the Design of Openings and Volumes for Air Movement.

VentilationDistinct different functions:Supply of fresh air Convective coolingPhysiological cooling

Convective coolingExchange of indoor air with fresh out-door air can provide cooling if latter is at lower temperature than the indoor air.

The motive force can be thermal or dynamic (wind)

Stack effect (thermal motive)The stack effect relies on thermal forces, set rip by density difference (caused by temperature differences) between the indoor and out-door air.

It can occur Through an open window (when the air is still): the warmer and lighter indoor air will flow out at the top and the cooler, denser out-door air will flow in at the bottom.

Ventilation duct arrangement based on the stack effect (vertical)Single duct Dual duct

(Horizontal) single duct and dual duct.

Stack effect for air circulation in town houses

Physiological CoolingIncreases convection heat lossAccelerates evaporationDepends upon:OrientationExternal featuresCross-ventilationPosition of openingsSize of the openingsControl of the openings

Effect of opening positions

Control of OpeningsSashes, canopies, Iouvres and other elements controlling the openings, also influence the indoor air flow pattern.Sashes can divert the air flow upwards. Only a casement or reversible pivot will channel it downwards into the living zone

Effect of sashes

Position of openings

Effect of CanopiesEffect of canopiesCanopies can eliminate the effect of pressure build-up above the window,the pressure below the window will direct the air flow upwards. A gap left between the building face and the canopy would ensure a downward pressure, thus can be directed into the living zone