NetZeroCities

Building Integrated Solar Thermal (BIST) can be considered a typology of solar thermal collectors, which are directly integrated to the building and used to convert solar radiation into useful heat that can be used in different applications.

BIST typologies can be classified using different criteria, most commonly by the heat transfer fluid used in the solar thermal system which can be air, water or refrigerant. BIST using air as heat transfer fluid can be used for example to pre-heat the air passing through a heat recovery ventilator or an air coil of a heat pump [2]. The air-based BIST consists of an air gap between a glazed or opaque cover (or also PV panels) and the building fabric. Air-based BIST has the main advantage of avoiding freezing problems and corrosion, low cost, and simple structure. Water-based BIST can be employed in a building to produce domestic hot water or space heating. In this case, flat plate collectors are the main technology used but evacuated tubes can also be employed due to the higher efficiency but with the disadvantage of fragility.

Refrigerant as heat transfer fluid can be used in systems coupled with heat pumps and PV/thermal systems. In this case, the BIST can operate as the evaporator of the heat pump increasing the efficiency using the rejection heat from the PV/thermal systems.

BIST can be made in different designs to be integrated as architectural element that can be integrated in roofs, façades, windows, or used as shading element or to substitute frames and balustrades [3].

Source: https://siko.at/

The integration of BIST has a strong influence on the building aesthetics, therefore colour and the shape, and support elements have a fundamental role. Moreover, the integration of solar thermal elements must offer structural integrity, protection from wind, rain and moisture [3].

MATURITY:

BIST systems are based on solar thermal technology which is already mature and available in the market (TRL 9). BIST can be used for domestic applications, to produce domestic hot water, space heating/cooling, air ventilation, and they are able to operate in different range of temperatures. Different examples of BIST systems installed in buildings are available in the database published and created in the framework of IEA-SHC Task 39.

Climate and geography: There are no specific constraints for the installation of BIST systems. Nevertheless, the cost-benefits are higher in locations with high solar radiation and high incidence angles. Another factor that should be taken into account is the wind exposure that can highly affect the heat losses of the BIST system.

Technical aspects/infrastructure: Constraints in the building architecture and also in existing heating systems (in refurbishment cases) can be the main barrier for the BIST integration. The potential of energy generated by the BIST is proportional to the? surface available that can have different perspective in the case of new construction or refurbishment. The presence of obstacles (e.g., windows, chimneys, and stairwells) causes a reduction of useful spaces for BIST. Shading should be also taken into account that could decrease the system performance. BIST should offer mechanical and structural integrity and protections with all weather conditions. BIST that integrates thermal energy storage should also have enough space for the installation.

Aesthetics aspects: In order to be architecturally and social accepted, BIST must be integrated naturally and be consistent to the context of the building. The design should be architecturally pleasing with a good composition of colours and materials. The size should fit the harmony and combination of the building components [7].

Policy and regulatory/legal framework: Generally, the integration solar systems is supported by different direct policies [8]. These include targets such as the aim to reach the share of renewables that nowadays in Europe is proposed to be increased to 45% under the Fit for 55 package including as well a solar rooftop initiative [9]. Moreover, the installation of BIST must comply with building codes and standards, which in most cases were developed for conventional envelope elements.

Projects

SUREFIT project (Grant agreement ID: 894511) aims to demonstrate fast-track renovation of existing domestic buildings by integrating innovative, cost-effective, and environmentally conscious prefabricated technologies. This is to reach the target of near zero energy through reducing heat losses through building envelope, and energy consumption by heating, cooling, ventilation and lighting, while increasing the share of renewable energy in buildings.

The project EnergyMatching (Grant agreement ID: 768766) aims to maximize the RES harvesting in the built environment by developing and demonstrating cost-effective active building skin solutions as part of an optimised building energy system, being connected into local energy grid and managed by a district energy hub implementing optimised control strategies within a comprehensive economic rationale balancing objectives and performance targets of both private and public stakeholders.

BRESAER is a EU-funded project (Grant agreement ID: 637186) with the aim to design, develop, and demonstrate an innovative, cost-effective, adaptable, and industrialized envelope system for buildings refurbishment including combined active and passive pre-fabricated solutions including BIST.

The EU project SOLABS (Grant agreement ID: ENK6-CT-2002-00679) developed novel unglazed BIST for building façades to server as multifunctional construction element and ease the architectural integration (both in new buildings and in renovations).

MULTISOLAR project (Grant agreement ID: 508439) developed a new generation of solar panels that can serve as structural element of the building, forming part of the structure and covering walls and roof, giving it a good aesthetic impression together with the glass surfaces that form the panels and capable of replacing the energy demands, be it electric power, hot water, or hot air for heating.

IEA-SCH Task 39 “Polymeric Materials for Solar Thermal Applications” has a building database with successfully integrated solar thermal energy systems.

IEA-SCH Task 41 “Solar Energy and Architecture” has the aim of helping in achieving high quality architecture for buildings integrating solar energy systems, as well as improving the qualifications of the architects, their communications and interactions with engineers, manufactures and clients. Publications contain different examples of BIST.

COST Action TU1205 aimed to foster and accelerate long-term development in solar thermal systems through critical review, experimentation, simulation and demonstration of viable systems for full incorporation and integration into the traditional building envelope.

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