Passive cooling techniques to reduce heat gains

Passive cooling techniques to reduce heat gains

In our previous discussions,the physics of heat gain and components of building envelope have already been discussed. It is beyond any reasonable doubt that heat gains,especially in the context of rising global temperatures, is an unavoidable fact. We require effective strategies to counter the heat build up in these spaces. Active cooling technologies like air conditioning is by far the most effective,but on the flip side , it comes with challenges of high initial costs, access to electricity and questions of environmental sustainability.


Under such circumstances,passive cooling techniques must be resorted to, keeping in mind the sustainability of the adopted measures. These techniques are not fraught with the challenges of energy access,high incurring electricity costs or being environmentally damning.These mainly rely on building dynamics, external application of products, geo engineering methods to counter heat build up.However,passive cooling is not meant to dethrone active cooling methods,it is at best , complementary to active cooling paraphernalia.


Among the most popular passive cooling methods, green roofs, white roofs with high SRI paints, window shading, fenestration, plantation drives are the most common.


  • Green roofs: as the name suggests, green roofs comprise of vegetative growth which partially or fully cover the roof tops. They are functional, nature based solutions.

 

  • White SRI roof coats: a pu based paint used to cover surfaces exposed to heat,reflecting more than 85-90% of the incoming solar radiation.

 

  • Window shading: shaded films with adhesive is used to prevent the incoming radiation( both infrared and UV)  through glass structures of buildings.

 

  • Fenestration: refers to changes made in doors, windows, ventilation to regulate the entry of external factors like wind, sunlight etc in the interior of building spaces.

 

  • Plantation drives: among the most popular. It seeks to restore greenery and fight heat through natural vegetation.


All of the above techniques are implemented sometimes in conjunction to achieve the best results. 

Passive cooling technologies like cool roofs and window films stand out as the most effective among other methods.Reports from organisations like US Department of Energy( DOE), Lawrence Berkeley National Laboratory ( LBNL) and various peer reviewed studies highlight their strong preference in real world and modelled solutions.


Cool roofs using high SRI paint: key insights from reports

Minimise heat absorption by reflecting sunlight through high solar reflectance and thermal emission.Department of Energy emphasises it’s use in tropical climates to prevent heat transfers indoors.Although it’s typically applied on roof surfaces( because roof occupy approximately 30% of exposed surfaces in urban areas), it can also be applied on external walls facing the sun for increased thermal comfort.

  • Energy performance: in hot climates, cool roofs reduce energy demand by upto 30%. Lawrence Berkeley Laboratory studies on commercial buildings report peak demand reductions of 25-30% in air conditioning structures.This decrease in cooling load also has multifarious significance in building dynamics of design and construction.

 

  • Broader impact: they mitigate the phenomenon of urban heat islands, lowers peak demands,provide quick paybacks( often within 3 years in tropical urban settings).Advanced versions like reflective sheets offer even greater sub ambient cooling.Environment sustainability of this product is also a serious consideration: helps reducing fossil fuel emissions through energy optimisation.

 

  • Long term view: over 20-30 years, cool roofs often shows the lowest life cycle costs among other options. It also has a bearing on increasing the shelf life of roofs.


Window films 

Applied as retrofits to existing glazing, to reduce solar heat gain by rejecting incoming infrared and UV while maintaining visible light transmission.Studies from DOE and LBNL and Shanghai commercial buildings show films reduce heat gains through windows by upto 35%. Total Solar energy rejected is often in the range of 40-45% depending on type( ceramic or reflective) 

  • Energy performance : reducing cooling loads of 30% is common,with some Shanghai case studies achieving 45-50% in controlled environments.DOE notes that reflective films block upto 99% UV and provide glare/ heat rejection without full replacement.

 

  • Broader impact : improve comfort near windows,prevents fading and offer quick installations.Payback periods are shorter than other alternatives.

 

  • Long term: it’s durable, lasts almost a decade requiring almost zero maintainence.They also provide upgraded glazing at lower upfront cost,with energy modeling from LBNL showing 30%+ HVAC savings in summers.


Cool roofs and window films excel as low barrier,high impact passive measures. They  deliver  strong cooling,affordability,ease of retrofit and favourable economics.They are more suitable in a wide range of buildings,especially where rapid deployment and price sensitivity matters most.