A solar-energy success story

One of the most cost-effective and longest-established ways of harnessing solar energy is to heat large buildings. Andrew Brewster of CA Group takes up the story.

As organisations continue to develop their sustainable-building strategies, many are looking towards holistic heating solutions that enable their developments to meet the stringent requirements set by Building Regulations — without the considerable costs associated with traditional forms of heating ventilation air.

Space heating for large buildings using renewable energy.

One such technology is solar air heating. Designed for the specific purpose of heating large spaces which, according to figures published by the Department of Energy & Climate Change (DECC), accounts for about 40% of the UK’s energy demand, active solar technologies such as the transpired solar collector (TSC) have been delivering significant results around the world for more than 30 years.

TSC technology is suitable for both new-build and retrofit applications. It can be used to regenerate the visual appearance of a run-down building whilst providing a highly efficient source of renewable heating. The system delivers superior levels of ventilation, greatly improving the internal environment through the reduction of odours and airborne contaminants, whilst significantly reducing energy usage and CO2 emissions.

The world’s first TSC technology, SolarWall*, was developed by Canadian company, Conserval Engineering Inc. during the 1980s. It has been installed on more than 10 000 buildings in over 35 countries Applications range from standard space and ventilation air heating to make-up air heating and process drying. In North America and sCanada, TSC is strongly incentivised to encourage take up.

The system works by capturing the Sun’s energy and using it to pre-heat fresh, outside air before it is drawn into the building’s heating system, considerably reducing its reliance on fossil fuels. Installed as an additional skin to a building’s southerly elevation(s), the TSC technology consists of a pre-coated steel or aluminium collector with thousands of carefully engineered perforations spread across its entire surface.

As sunlight strikes the surface of the collector its energy is absorbed, heating its external surface. In turn, by means of conduction, this heat is transferred to the fine layer of air which lines the outside face of the collector, creating a film of warm air known as the thermal boundary layer.

One of the largest installation of SolarWall transpired collections on a single building in the world is this Marks & Spencer distribution building at Castle Donington.

This heated boundary layer is carefully drawn through the perforations in the surface of the collector — before the heat can escape by convection, or is lost to external wind — into a specially designed air cavity between the TSC and the building’s original elevation.

From the air cavity, the fresh, solar-heated air can be introduced directly into the building through the existing HVAC system, delivering heated ventilation, or ducted into the building’s main heating system, where it can be used as a supplementary heater.

In the UK, the solar air heating technology has been adopted by a number of major companies — including Jaguar Land Rover, Tesco and Royal Mail, to name just a few. The system was also used in the delivery of the UK’s first zero-energy cost business park, at Armstrong Point in Wigan, where its inclusion has helped the development achieve a BREEAM ‘Outstanding’ rating and an A+ ‘Zero’ rated Energy Performance Certificate.

The recent installation of a 4500 m² SolarWall for Marks & Spencer in Castle Donington, one of the largest examples on a single building in the world, has a maximum thermal capacity of over 2250 kW and is expected to reduce the structure’s heating requirement by about 30%, generating more than 1 135 000 kWh and saving over 256 t of CO2 a year.

Behind the scenes is the RETScreen solar-air-heating project model, an independent software package for analysing TSC technology. Developed by Natural Resources Canada (NRCan), in association with NASA, UNEP and the Global Environment Facility (GEF), the program can be used to assess the viability of projects worldwide.

TSC technology is easy to install, has the lowest capital cost along with the highest known efficiency (up to 80%) and the quickest return on investment of any active solar technology in the world, providing proven payback periods as low as three years.

Andrew Brewster is project development engineer with CA Group and also UK director for the Solar Air Heating World Industries Association.

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