An Unglazed Transpired Solar Collector consists of a micro-perforated pre-finished steel collector installed as an additional skin onto a southerly facing wall of a structurally sound building and sealed at the perimeter. Colorcoat Prisma® pre-finished steel by Tata Steel is used for the solar collector, which can be easily incorporated into the steel building envelope at initial construction phase or retrospectively.

The outer perforated skin creates an air transfer cavity or plenum with the supporting wall and pre-finished steel skin. Transition ductwork, installed in a penetration within the supporting wall substructure, transfers heated air from the cavity into the building interior. A fan unit within the building space or within the air handling unit creates negative pressure within the transfer cavity.

The pre-finished steel solar collector absorbs solar radiation, developing a boundary layer of solar heated air on the surface of the micro-perforated collector. The renewable, solar heated air layer is drawn through the perforations into and upwards through the cavity into the building and can be distributed directly into the building as ventilation air or ducted into the main heating system to reduce the energy load.

Benefits of an Unglazed Transpired Solar Collector

• Provides fresh, warm air for mechanical ventilation and space heating.
• Fast capital payback of approximately 3-7 years for low initial investment.
• Sized to meet individual building requirements and specification.
• High conversion efficiency of ≤75% of solar energy to usable heat energy.
• Designed to complement primary heating systems, reducing energy demand.
• Savings in overall heating energy costs of up to 50% on annual heating bills.
• Simple damper control mechanisms to regulate air flow and temperature.
• Ideal for commercial and industrial buildings.
• Utilises freely available, sustainable solar radiation to pre-heat fresh air-feed to a warm air space-heating system.
• Typically, 1m² of collector area delivers approx 200-250kWh/year.
• Typically supplies 30-40% of daytime heating demand of suitable buildings.
• Solar collector guaranteed up to 25 years.
• Quick and easy installation.
• Minimal maintenance.
• Blends or contrasts with the building envelope to meet required aesthetics and planning requirements.

The Unglazed Transpired Solar Collector system requires a micro-perforated collector and a fan unit for operation. The most straightforward and cost-effective integration is to install the solar collector as a pre-heater, using the fan of an integrated HVAC air-handling unit to draw the warmed air through the cavity into the HVAC system.

The system is designed to blend seamlessly with your building envelope to provide you with a renewable energy solution that will please both the local community and planners alike. It is sized to suit your specific building requirements through assessment of the following considerations:

• Level of ventilation (m³/s) or air changes required per hour.
• Heat demand of the building.
• Temperature set point of the building.
• Geometry, aspect and location of the building.

An Unglazed Transpired Solar Collector uses freely available renewable solar radiation and provides fresh ventilation air that can be easily controlled, in terms of airflow rate and temperature, to maximise occupant comfort in the most sustainable way possible.

Suitable building types
Suitable buildings have open, unrestricted internal spaces, for which heating of air is the most efficient and economic medium for occupant comfort, and which benefit from medium to high mechanical air-change or ventilation rates. Suitable building types include factories, workshops, showrooms, offices, schools, hospitals and leisure centres.

General design factors
A number of factors will need to be evaluated for an individual building, to determine the optimum collector type and size and airflow requirements. 

The following are important considerations:

• Gross internal dimensions of the space to be heated.
• Thermal efficiency of the building envelope fabric.
• Actual building space heat demand (affected by solar heat gain through windows or roof lights).
• Ventilation requirements.
• Orientation of the building and environmental shading effects.
• Available wall space for installation of the collector.

Solar collector orientation
Ideal orientation is south-facing wall elevation. A collector will also provide excellent results on a variation of up to 20° from south, and quite acceptable levels of performance will be achievable with orientations 45° from due south. A collector facing due east would benefit from early morning solar radiation and a westerly orientation would benefit from the later afternoon solar radiation.

Colour selection and influence on performance
An Unglazed Transpired Solar Collector utilises Tata Steel’s high performance 3 layer Colorcoat Prisma® pre-finished steel. The superior solar absorption characteristics, durability and corrosion resistance of Colorcoat Prisma® are key attributes for achieving maximum collector efficiency and longevity.

For Unglazed Transpired Solar Collector applications we would recommend dark colours with a high or preferably very high solar thermal performance. In some instances, however, this may not always be possible as the colour choice may be dictated by other aesthetic requirements and building design. 

Solarthermal performance Based on SSST data Colorcoat Prisma® 3 layer

Metal hand samples are available for all colours. Our hand samples give a true representation on colour and can assist in colour selection and finalising product specification. 

Order samples online for Colorcoat Prisma®
Please select your chosen Colorcoat Prisma® colour to request samples. Or order samples by contacting the Colorcoat Connection® helpline +44 (0) 1244 892434.

Solar collector angle tilt
For maximum solar radiation benefit during the heating season, we recommend wall collectors as the most practical and cost-effective to install. A vertical wall is more efficient whilst the sun is lowest in the sky during the winter months, a period when heating demand is likely to be at the maximum.

Solar collector shading
Shading of the system should be avoided. Consideration should be given early in the design process to any potential shading from elements such as trees, pylons, chimneys, stacks, surrounding buildings and other landscaping features. Potential shading from any of the above should be taken into account when carrying out a feasibility study or site visit.

Looking for help and advice with your collector design and sizing?

The Colorcoat Connection® helpline can offer support and more detailed information on unglazed Transpired Solar Collectors +44 (0) 1244 892434 or E: colorcoat.connection@tatasteeleurope.com

Tata Steel have published and Environmental Product Declaration (EPD) for Colorcoat Prisma® that complies with EN 15804 and ISO 14025. 

Furthermore EN15804 compliant Environmental Product Declarations for Supply Chain Partner cladding systems using Colorcoat Prisma® and independent third party performance accreditation fully supports your building certification schemes such as LEED and BREEAM.

Unglazed Transpired Solar Collectors using Colorcoat Prisma® or Colorcoat HPS200 Ultra® are readily available through CA Group Limited in various profile shapes and depths. The choice of design allows for integration of the system within the envelope, and will also present various solar absorber plate surface areas to the sun that will influence the development of the boundary solar heat layer. Profile design will also have an impact on heated air movement within the plenum.

For further advice contact Tata Steel or CA Group Limited.

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