HEATING TECHNOLOGY


Time to reconsider solar


thermal


Solar thermal systems are gaining traction in the commercial sector, offering a cost-effective and sustainable solution for water heating – so says Bill Sinclair from Adveco


Bill Sinclair www.adveco.co


A


Technical director Adveco


systems that have fallen into disrepair. This is especially true of office spaces where rental trends are increasingly based on multi-occupancy driving demand for more dispersed, sustainable cloakroom and canteen facilities within a building.


well-understood and proven technology, solar thermal is currently experiencing a renaissance as organisations


seeking to meet new sustainability goals for their buildings are recognising the technology’s value as a true renewa ble capable of offsetting increasing energy costs. Well-designed commercial solar thermal systems are capable of offsetting on average a minimum of 30% of the energy demands for water heating, making it potentially ideal for organisations that rely on large amounts of domestic hot water (DHW). For existing buildings, 80% of which


are still expected to be in use by 2050, the application of solar thermal pre- heat is a well-established means of reducing demands on prevalent gas- fired water heating, not only offsetting operational costs but also actively cutting carbon emissions from the buildings. Commercial new builds or


refurbishments, however, are either mandated or opting to shift to direct electricity. They are finding that the move comes with a new financial burden as electricity remains substantially more expensive to operate than gas – currently by a factor of 3.8. This transitional process, as well as organisations coming to the end of fixed energy tariffs, has driven a clear upswing in interest for new solar thermal systems where a ten-year return on investment is very achievable. The latest commercial EPC regulations have also instigated interest in revitalising old solar


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Daily and peak demands A correctly designed and sized system will consider the daily usage and peak demands. It aims to serve all peaks from storage, with the size of the peak determining the size of pre-heat. The recovery time for peaks is what ultimately determines the number of solar collectors a building requires. The design process also sizes usage with available space. A south-facing and unobstructed roof with an inclination of 30° from the horizontal is optimal, though by no means essential as modern solar collectors can be installed in a variety of permutations. Unsurprisingly, solar thermal collectors do suffer if the building is significantly shaded, in which case a commercial air


source heat pump may be a preferred option to produce low-carbon pre-heat. Modular, high-


performance flat plate collectors can be situated on


or integrated into flat or sloped roofs, as well as mounted on a building’s façade. By far the most efficient way to heat water with solar energy, flat plate collectors offer a smaller footprint compared to equivalent solar photovoltaics (PV) for DHW. A typical 4 kW PV system requires approximately 16 panels covering 25m² of roof to match just three flat plate collectors covering just 6.6m² roof area. This makes solar thermal a prime choice for DHW when roof or facade space is limited.


Drain back design Solar thermal collectors work by absorbing solar energy into a fluid (glycol) which transfers heat from the panel to the building’s water system via an indirect cylinder. To correctly manage solar fluid, Adveco is a proponent of drain back technology to protect the fluid from overheating. Failure to do so can ‘cook’ the fluid


High performance flat plate collectors can be situated onto both flat and sloped roofs


to a tar-like consistency causing permanent damage to the collector. As the name implies the solar fluid drains from the collector to a reservoir when not in use. Flat plate collectors with an integrated drain back module offer a more cost-effective (as there is no requirement for large solar storage) and more efficient (as there is no call to dump unused heat) approach. The technology has proven itself in the field with fluid changes required perhaps once in eight years.


Hybrid method For new build properties with electrical connection, the gas water heater is replaced with an electric boiler and cylinder to supply the afterheat which raises system temperatures to a necessary 60°C. This hybrid approach maximises the solar thermal input, typically offsetting 30% of the electrical demand, although it could be more depending on location. This hybrid approach can be simplified by integrating a packaged electric water heating system. This also gives the option of adding an electric immersion to the system as a backup for enhanced resiliency when assured water heating is a business-critical service. The all-electric solar thermal approach further reduces carbon associated with grid electric systems and aids in lowering operating costs. The hybrid approach can be


further extended with the inclusion of air source heat pumps to provide the initial pre-heat for the system. Operating at lower temperatures with the cold feed maximises the efficiency of the heat pump, reducing electrical operating costs and raising working flow temperatures from 10°C to 40°C. This is not hot enough for commercial applications, so the pre-heated water is then passed to the mid-solar thermal system. Essentially free to operate, the


A solar thermal preheat and gas afterheat system combines solar thermal energy and an electric boiler to efficiently raise water temperatures


solar thermal system boosts the working flow temperatures from 40°C to at least 50°C. Although not operating at maximum potential, there is enough advantage gained from solar thermal to warrant the additional system complexity and capital investment. During summer months the solar thermal system can deliver the necessary 60°C working flow for safe provision of commercial hot water, but to ensure safe, consistent, and necessary high operational temperatures, the water is passed to the electric boiler. Here final consistent water temperatures of up to 65°C are assured year round. ■


EIBI | SEPTEMBER 2024


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