Cool roofs in Spain - Health and energy efficiency in buildings

Cool roofs study for 50 cities in Spain with energy simulations (EnergyPlus)

EnergyPlus is the most accurate building energy simulation software, managed by the Department of Energy in the United States

Performed thousands of energy simulations with cool roofs using EnergyPlus to calculate heating and cooling loads to maintain the home and the office building between 20°C – 25°C during their occupation. Analyzed data to show cost-efficient solutions and the cost effectiveness of cool roofs

Reducing roof solar absorptance to compare savings in the cooling systems with penalties in the heating system using cool roofs

If ‘Total (kW·h/m2·year)‘ (penalties in the heating system minus savings in the cooling systems) is a negative number and ‘Cooling/Heating‘ (savings in the cooling system divided by the penalties in the heating system) is greater than 0, it indicates that savings in the cooling system are greater than penalties in the heating system, reducing solar absorptance and using cool roofs

Solar absorptance on the roof (0.2, 0.4, 0.6, 0.8). 0.2 would be a white cool roof and 0.8 a standard brown roof

Thermal transmittance (U) on the roof. (without insulation: 1.86 for home and 1.74 for office, and 0.67, 0.4, 0.33 W/m2·K). Technical building code (CTE) requirement in Barcelona is 0.4, most strict CTE requirement is 0.33

Scientific studies and experiments showed that the energy savings provided by by cool roofs are greater than the results in energy simulations because the software does not consider the lowest temperatures around the building, the energy savings due to ventilation and air infiltration with lower temperatures, and that the cooling systems work at higher performance. In addition, the climate files are not usually updated

In the United States, colder cities also regulate with cool roofs to mitigate the urban heat island and avoid peak consumption in summer

Simulations performed for a home and office building with a low level of air tightness, and considering an optimal level of air quality in offices, for homes and offices with a better level of air tightness and offices with heat recovery the benefits of using cool roofs are greater

Single family home

Cool roof analysis in a 100 m2 single family home

Office building

Cool roof analysis in an office building with 2 floors (800 m2 per floor)

Summary of cool roof results for 50 cities in Spain

‘Total (kW·h/m2·year)’ (penalties in the heating system (positive number) minus savings in the cooling system (negative number)) difference and ‘Cooling/Heating’ (savings in the cooling system divided by penalties in the heating system) reducing solar absorptance by 0.1 (e.g. from 0.8 to 0.7) for a single-family home (U1.86 and U0.40) and for an office building (U1.76 and U0.40). A cool roof should be used if ‘Total (kW·h/m2·year)’ is a negative number and ‘Cooling/Heating’ is greater than 0

Map of Spain with “Cooling/Heating” for a single family home U1.86

In the four cases presented, the ratio between the savings in the cooling system and penalties in the heating system “Cooling/Heating” is lower in a single family home without roof insulation (U1.86), although greater savings are obtained by reducing solar absorptance in homes without roof insulation

The map of Spain is shown with “Cooling/Heating” for a single family home without insulation U1.86 to see the suitability of using cool roofs for a different cities in Spain. For an office building the benefits of using cool roofs are greater

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