# Buildings Energy Efficiency: Interventions Analysis under a Smart Cities Approach

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## Abstract

**:**

## 1. Introduction

## 2. Methodology

- The solar absorbance of walls, roofs and other external surfaces was considered through different dyes;
- Thermal transmittance variation was considered, taking into account vertical and horizontal surfaces;
- Thermal transmittance and the solar gain factor (g-value) of some window categories were considered, taking into account that the first and the second parameters are mutually influenced.

- (1)
- The standard configuration model: characterized by specific values of solar absorbance, vertical and horizontal surface transmittance, window thermal transmittance and the solar gain factor;
- (2)
- The solar absorbance variation model: characterized by the same parameters values assumed in the standard configuration model, except for the solar absorbance, which is characterized by five different values, from 0.100 to 0.600;
- (3)
- The vertical opaque surface’s transmittance variation model: characterized by the same parameter values assumed in the standard configuration model, except for the vertical wall thermal transmittance, which is characterized by five different values, from 0.650 to 2.341 W/m
^{2}K; - (4)
- The horizontal opaque surface’s transmittance variation model: characterized by the same parameter values assumed in the standard configuration model, except for the roof thermal transmittance, which is characterized by five different values, from 0.628 to 2.080 W/m
^{2}K; - (5)
- The window g-value variation model: characterized by the same parameters values assumed in the standard configuration model, with five different values for the solar gain factor, from 0.855 to 0.910;

α (-) | U_{vs} (W/m ^{2}K) | U_{hs} (W/m ^{2}K) | U_{w} (W/m ^{2}K) | g-value (-) | |
---|---|---|---|---|---|

Standard configuration model | 0.600 | 0.650 | 0.628 | 5.680 | 0.855 |

Solar absorbance variation model | from 0.100 to 0.600 | 0.650 | 0.628 | 5.680 | 0.855 |

Vertical opaque surface’s transmittance variation model | 0.600 | from 0.650 to 2.341 | 0.628 | 5.680 | 0.855 |

Horizontal opaque surface’s transmittance variation model | 0.600 | 0.650 | from 0.628 to 2.080 | 5.680 | 0.855 |

Window g-value variation model | 0.600 | 0.650 | 0.628 | 5.680 | from 0.855 to 0.910 |

#### 2.1. Building Model

^{2}, and each floor is 3 m high. The building is characterized by large windows, as shown in Figure 1. This has an important impact on the building’s energy demand, because of the climatic conditions of Rio de Janeiro in terms of solar radiation.

Materials | Thermal Conductivity (W/m K) | Specific Heat Capacity (kJ/kg K) | Mass Density (kg/m^{3}) |
---|---|---|---|

Plasterboard | 0.70 | 1 | 1,400 |

Concrete | 0.33 | 1 | 1,200 |

Reinforced concrete | 1.91 | 1 | 2,400 |

Brick | 0.24 | 1 | 600 |

Mortar | 1.40 | 0.67 | 2,000 |

Perforated brick | 0.40 | 1 | 800 |

Full brick | 0.72 | 1 | 1,800 |

Polystyrene | 0.05 | 1.22 | 15 |

Tile | 1.47 | 0.71 | 1,700 |

Bitumen | 0.17 | 1 | 1,200 |

Gravel | 1.20 | 1 | 1,700 |

Windows | Characteristics | Transmittance (W/m^{2}K) | g-value |

Frame | 2.27 | - | |

Single | Single glazing 4mm | 5.68 | 0.855 |

#### 2.2. Modeling via TRNSYS

^{2}, also scheduled by the USE function.

## 3. Results and Discussion

^{2}K to 2.341 W/m

^{2}K, and the subsequent energy demand variations, for both heating and cooling, are shown in Figure 6.

^{2}K to 2.080 W/m

^{2}K, and the energy demand variations, both for heating and cooling, are shown in Figure 7.

Window | Transmittance (W/m^{2}K) | g-value |
---|---|---|

Single (standard configuration) | 5.68 | 0.855 |

Float 5 mm | 5.61 | 0.827 |

Float 10 mm | 5.46 | 0.774 |

Float 19 mm | 5.16 | 0.682 |

Optiwhite 4 mm | 5.68 | 0.910 |

Optiwhite 5 mm | 5.64 | 0.907 |

- ▪
- A variation of the dyes’ solar absorbance coefficient approximately equal to 84% can lead to an energy demand variation equal to ±10%;
- ▪
- A variation of the g-value equal to 20% can bring an energy demand variation equal to ±15%;
- ▪
- A variation of the vertical wall thermal transmittance approximately equal to 260% can result in a heating energy demand variation equal to +27% and a cooling one equal to −1.5%;
- ▪
- A variation of the horizontal surfaces thermal transmittance approximately equal to 230% can result in a heating energy demand variation equal to +40% and a cooling one equal to +4%.

## 4. Conclusions

## Author Contributions

## Nomenclature

α | Solar absorbance |

U_{vs} | Transmittance of vertical opaque surfaces (W/m ^{2}K) |

U_{hs} | Transmittance of horizontal opaque surfaces (W/m ^{2}K) |

U_{w} | Window transmittance (W/m ^{2}K) |

g-value | Window solar gain factor |

## Conflicts of Interest

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**MDPI and ACS Style**

Battista, G.; Evangelisti, L.; Guattari, C.; Basilicata, C.; De Lieto Vollaro, R.
Buildings Energy Efficiency: Interventions Analysis under a Smart Cities Approach. *Sustainability* **2014**, *6*, 4694-4705.
https://doi.org/10.3390/su6084694

**AMA Style**

Battista G, Evangelisti L, Guattari C, Basilicata C, De Lieto Vollaro R.
Buildings Energy Efficiency: Interventions Analysis under a Smart Cities Approach. *Sustainability*. 2014; 6(8):4694-4705.
https://doi.org/10.3390/su6084694

**Chicago/Turabian Style**

Battista, Gabriele, Luca Evangelisti, Claudia Guattari, Carmine Basilicata, and Roberto De Lieto Vollaro.
2014. "Buildings Energy Efficiency: Interventions Analysis under a Smart Cities Approach" *Sustainability* 6, no. 8: 4694-4705.
https://doi.org/10.3390/su6084694