Identification of Retrofit Options

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Identification of Retrofit Options

After the identification of the inefficiencies, requirements and issues to be improved with the pre-retrofit survey and the energy auditing, different options appear as possible solutions with different investment costs and results. The identification of all the possible options is needed for the best choice of the suitable retrofit option according to the particular conditions.

The process for identifying the different retrofitting options has a special consideration in the cases with a stagged approach. The key of the staged upgrade approach is to complete improvements to building systems in the order that reflects the influence of one system on another.

Before addressing the replacement or re-dimensioning of the heating and cooling system as a retrofitting action, it is very important to analyse the influence of other retrofitting actuations over the heating and cooling loads and identify where the heating and cooling system can be resized to meet the demand of the optimized building.

Some measures directly reduce energy consumption such as replacement of inefficient lighting. The more efficient lights will emit less wasted energy into the building as heat, and therefore reduce the building’s cooling needs and potentially increase its heating needs. The envelope improvements may eliminate energy losses and reduce solar heat gain (through improvements in facade and windows) having a considerable impact on the building’s heating and cooling loads. By first completing retrofits to these systems, the next stage of retrofits can be optimized for the new heating and cooling demands. Figure below shows a simple workflow when analysing the retrofit options.

Retrofit option identification work flow

Building envelope

The purpose of this section is to summarize and categorize information regarding the building envelope for an easy consultation. Firstly, it starts with a review of the commercial insulating materials for walls, roofs and windows, including the innovative ones. The most promising solutions have been selected mainly on the basis of the optimal costs/performance ratio, taking into account also the pros and cons of each product.
The insulating panels with self-cleaning coatings to achieve both depolluting and self-cleaning effects in indoor environments have been included.

Insulating materials for walls/roofs

The most common materials for thermal insulation are:

  • Mineral wool, a non-metallic inorganic product manufactured from glass (fiber glass) or rock (rock wool), which combines high thermal resistance with long-term stability, good fire resistance and acoustic properties;
  • Expanded polystyrene (EPS) or extruded polystyrene (XPS), a polymer made from the monomer styrene, a liquid petrochemical. Polystyrene can be rigid or foamed;
  • Polyurethane (PUR), where during an expansion process the air is exchanged with a lower thermal conductor gas, trapped in the closed pore system. It rises serious health concerns and hazards in case of fire, due to the release of hydrogen cyanide, which is very poisonous.

Their thermal conductivity is typically around 30-40 mW m-1K-1, decreasing to 20-30 mW m-1K-1 only in PUR. These values vary with temperature, moisture content and mass density.
The more innovative thermal building insulation materials are called “super-insulator”.

  • Aerogel is a low-density solid-state material (0.2% of SiO2-chains) in which the liquid component of the gel has been replaced with gas (99.8% of air filled pores on a micro and nano size scales). Its thermal conductivity is 13-14 mW m-1K-1, but it can be decreased to 4 mW m-1K-1 using carbon black to suppress the radiative transfer.
  • Vacuum insulated panels (VIP) consist of solid material with a high porosity level and a very small pore dimension on which a technical vacuum is produced and maintained by enveloping the solid core with a plastic and/or metallic sheets. The fine porosity of the matrix is very effective in decreasing the thermal conductivity and blocking the convective transfer, while making the core material of VIPs opaque (e.g. with a dispersion of carbon powder) reduces the radiative heat transfer. The application of VIP has important drawbacks: they cannot be cut for adjustment at the building site or perforated without losing a large part of their thermal insulation performance; moreover, the initial thermal conductivity increases from 3-4 mW m-1 K-1 to typically 8 mW m-1 K-1 after 25 years ageing, due to water vapor and air diffusion through the envelope and into the open pore structure of the core material.
  • Gas-filled panel (GFP), which replaces air with a gas having a lower thermal conductivity, usually noble gases such as argon, krypton or xenon. GFP is made of two types of polymer films. Metalized films are used in a tied assembly called baffle, arranged in a three-dimensional form of multiple layers of cavities that produce a cellular structure which suppress convection and radiation. Low diffusion gas barrier foils are very thin layers of aluminum or polymer barrier resins that are used in a hermetic barrier, keeping the panels gas-tight. Thermal conductivities for prototype GFPs are quite high, e.g. 40 mW m-1 K-1, although much lower theoretical values have been calculated.

The document “Appendix 10. Insulation Materials SWOT Analysis” presents a SWOT analysis for the above mentioned materials. The data of the insulation materials has been collected through a dedicated website, that is running at On this website every user can create an account, with different privileges, that allows the user to complete a form with the required parameters for a material and create a new record in the database.

The choice of an insulation material can be made considering different parameters such as Thermal conductivity, Cost and Thickness. A higher thermal resistance can reduce the energy demand of the building, that is prescribed by the standards of the section. As construction have also strict budget limitations, the cost is a fundamental parameter. A reduced wall thickness may increase the value in the real estate, overcome legal or practical restrictions in the retrofitting of existing buildings, allow a reduction of transport costs.

The implementation of insulation solutions can be done through three different systems (external, internal and mixture), and each one is also subdivided in different categories. More information about the applicability of insulation solutions can be found in the document “Appendix 11. Applicability of insulation solution”.

Insulating products/technologies for windows

The manufacturers of windows are developing products more and more effective from the point of view of energy saving. The window is usually composed by one or more glass panes attached to a frame that covers typically less than 15% of the total area. In order to improve the insulation of the windows several strategies can be followed:

  • Increasing the number of panes (triple-pane, quadruple-pane);
  • Inserting gases with low thermal conductivity in the cavities between the panes (argon, krypton);
  • Covering the internal surface of the panes with low-emissivity coatings in order to reduce the radiative heat transfer.

The frame is usually made of wood, aluminium or plastic materials (e.g. PVC) and could be designed with thermal break in order to lower the thermal transmittance.
In the current market, triple-pane windows with low-emissivity coatings and argon in the cavities between the panes are widespread, as required by several of the current standards. Their thermal transmittance can be lower than 1 W m-2 K-1.

The most insulated product available in current market is a quadruple-pane window with krypton in cavities between the panes, that guarantees a glass thermal transmittance equal to 0.3 W m-2 K-1 and a global thermal transmittance of the window equal to 0.6 W m-2 K-1.

For the windows products, as for the insulating products for walls and roofs, a database is available in

Self-cleaning products

Environmental issues become more and more relevant year by year, and topics related to the air quality improvement through air pollutants removal have created great interest in the research world. Photocatalytic methods are known to be widespread applicable in advanced oxidation processes (AOPs). Thanks to the high reactivity of the in situ generated active species, the selectivity of the photocatalyst is very low, leading therefore to the complete mineralisation of a wide number of organic pollutants (producing CO2 and H2O as final degradation products). Inorganic pollutants such as NOx and sulphureted compounds are converted into nitrates and sulphates respectively, while ozone is converted into O2. Photocatalytic processes are also active in removing microorganism: cellular membranes are degraded thus leading to the bacteria death . A large number of papers well resumes the main characteristics of a photocatalytic process . Titanium dioxide is considered as one of the most suitable photocatalysts because of its chemical stability, non-toxicity toward environmental and living species, low cost and wide availability . self-cleaning materials currently available include glass, concrete, ceramic tiles and paint . Photocatalytic paints can be conveniently applied in a wide variety of cases. Their use can help in preventing the diffusion of infections caused by antibiotic-resistant pathogens.

For the self-cleaning materials, as for the insulating products, the database is downloadable in


This section aims at analysing the main lighting systems along with their characteristics. The diagram below shows the main lamp types for general lighting:

The development of luminous efficacies of light sources