The stock of inefficient homes already built in Europe is really high, and it’s responsible for much of the total energy consumption of Countries. Important energy savings can be achieved by the renovation of these properties.
Any energy rehabilitation needs in the first place a detailed analysis of the current situation of the building. This approach will allow us to make wiser decisions on the rehabilitation and the best way to improve its thermal performance. There are certain parameters that can significantly affect the energy performance of the building, and we must emphasize one or another depending on the particular characteristics of the building and on the climate of the place where it’s located.
Improvement measures for energy refurbishment of existing buildings have to be approached from the point of view of both sustainability and the quality of the resulting building. The measures are designed to achieve the maximum reduction in energy demand in relation to the situation of the previous state of the building. The analysis should be completed including futuribles, like future energy costs.
In order to achieve a lower demand, the measures must be implemented within the logic of passive solar design, both for cold and warm periods of the year. In winter, the insulation in the thermal envelope reduces losses, retaining heat inside the building for as long as possible. Losses must be avoided. They mostly take place through the thermal envelope openings, holes in walls, and air infiltration.
The procedure for a proper use of passive solar energy goes through four stages: solar collection during the daylight hours, storage of the harvested heat in thermal mass of the building, distribution of the the heat, and conservation of the energy for as long as possible.
Among all the possible actions, the measures to take will depend on every particular case:
- Increase the level of thermal insulation at the building envelope: Insulate facades, roofs, floor slabs and walls. Preliminary assessment of the building will tell us at which part of the envelope would have higher incidence the extra insulation.
- Modification of the openings in the facade: Replacing glass panes and frames, and/or the installation of a double window. The objectives pursued are to limit night losses in winter conditions, maximizing the solar radiation that enters the building, but avoiding overheating in summer.
- Installation of shading devices: This measure is especially recommended in warm and mild climates; its aim is to reduce solar gains in summer. Some possbile devices are fixed screens, blinds (either with fixed or mobile blades), lattice frames, awnings…
- Correction of thermal bridges: The thermal protection must be as uniform as possible in the whole envelope surfaces. Thermal bridges will increase energy losses and rise the risk of condensation.
- Limitation of losses at night: Losses can be reduced by installing insulated blinds or shutters.
- Glazed galleries and greenhouses: these devices collect sunlight in a space outside the thermal envelope of the building. They can be selectively connected or disconnected to the inside of the building. In winter, for a proper use of this solution, the connection with the building must be done during the day (when solar gains happen), and disconnected from the building when energy losses take place (usually at night). In summer, it must be protected from direct sunlight, and should be opened to the outside, to prevent overheating.
- Trombe Wall: It consists in converting sunny and heavy walls (that already exist in the building to rehabilitate) into heat accumulators, by exploiting greenhouse effect. It uses a termo-circulation effect to distribute the captured heat, bringing warm air into the living space. It is suitable for day-use buildings in winter.
- Reduction of air infiltration from the outside: The aim of this is to reduce the energy demand by reducing inadvertent influx of outside air entering the building, either due to the dynamic wind pressure and/or the draft effect which is produced in high buildings.
- Changing the rendering colour on the envelope elements: The colour of the cladding influences the amount of solar radiation absorbed or reflect, and therefore its heating during daylight hours. The objective of this measure is to reduce the energy demand for cooling, especially in mild and warm climates, by reducing the solar radiation absorbed by exterior walls and roofs.
- Night ventilation, free cooling and evaporative cooling: The night ventilation allows to cool the thermal mass of the building, which has absorbed heat during the day. The free cooling involves introducing outside air, which is at a lower temperature than the inside one. Any system that takes advantage of cool air from the outside whenever possible will result in a lower demand for cooling. Evaporative cooling can also be used in dry climates to reduce air temperature, but it will require a proper renovation or air to prevent moisture.