Jeff House, Applications Manager for Baxi Commercial Division, considers the range of measures that need to be taken into account by designers and installers when consideration is being given to the inclusion of solar thermal solutions in heating systems.
The measures necessary to achieve government targets regarding the reduction of carbon emissions are not to be found in one convenient compendium. Designers and installers will be familiar with the complexities involved in achieving compliance, involving the requirements of a range of regulations, codes, standards, policies and consents. These requirements are often a primary driver in the decision making process when appraising the application of renewable energy sources, for example solar thermal solutions.
Perhaps the most significant statutory requirements are found in the Building Regulations, with Part L being central to the delivery of the Government commitment to increase building energy efficiency. Part L1&2 set out minimum efficiency requirements, with the calculation of overall building CO₂ emissions, using SAP or SBEM methodology respectively, being a key compliance requirement.
The 2010 revisions to Part L are part of the on-going process of improving carbon saving levels in buildings. This has led to advances in building insulation and thermal efficiency, with the noticeable effect that hot water has overtaken space heating as the predominant load in many applications. The resulting move towards decentralised systems has increased interest in the integration of solar thermal low carbon technology.
Setting an example
Although not embodied in detailed statutory provisions like the Building Regulations, the powers of local planning authorities to make policies on the provision of low carbon and renewable sources of energy in new buildings are of great importance. The Government’s Planning Policy Statement 22 (PPS) requires the planning system to contribute to reducing emissions and stabilising climate change. Consequently, planning authorities can require new buildings to draw a percentage of their calculated energy demand from renewable sources. In the absence of a percentage level prescribed in statute, planning authorities are free to set their own standard and levels of 10% or more are not uncommon. Solar thermal technology is attracting increasing interest as this switch to renewable energy sources gains momentum.
The independently governed BREEAM certification scheme also plays an important role, as this is frequently used to assess building performance and can be undertaken at the design stage or at the post-construction stage of the project. Energy is included in the ten categories of environmental impact that are assessed, based on a score of credits achieved compared with a given number of credits available. The specification of solar thermal renewable energy technology in an integrated low carbon hot water and heating solution cannot only gain substantial credits within its own category but can also beneficially influence the overall rating level attained by the building.
Making light work
The need for compliance with statutory requirements and planning policies, together with the widespread use of authorised Certification and Assessment, is giving an increasingly high profile to solar thermal technology as a renewable energy source that delivers low carbon solutions.
The fact that it is based on the apparently simple concept of utilising the enduring energy of the sun, should not give the impression that the application of this technology is itself straightforward. Each intended application will be unique, involving the accurate assessment of domestic hot water demand, the stored water requirement, the correct calculation of the number of solar collectors and their position in the collector array area. Inaccurate calculations can result in an incorrectly sized system that, for example, produces more heat than is required, causing problems regarding excess heat and even stagnation in the collector panels.
In many instances the documentation supporting regulatory or policy requirements do not prescribe or refer to robust design criteria for renewable technologies. System manufacturers are the best placed to provide full and detailed information regarding all aspects of design, installation and maintenance.
One leading industry player operates an Academy open to industry professionals needing information, advice and practical experience of the application of solar thermal technology. Industry representative bodies are also active and CIBSE (Chartered Institution of Building Services Engineers) provides a range of Guides in its CIBSE Knowledge Series; In particular the CIBSE Solar Heating Design & Installation Guide provides a comprehensive overview of all aspects of solar system solutions, providing information on regulations and costs, highlighting design and installation issues and identifying commissioning and maintenance requirements.
Phasing out, phasing in
Every building services engineer will be concerned to ensure that heating systems incorporating solar thermal solutions are designed to eliminate the risk of legionella. This can arise during the winter when the solar system is providing about 10 or 20% of the total system demand and the water held in the storage tank may be between 20-45°C.
This is a temperature range that Legionella bacteria thrive in, therefore it is important that the storage cylinder and secondary return circuit are pasteurised at an elevated temperature at least once a week. Full information and explanation is provided in CIBSE TM13, which is a further example of how industry bodies are responding to the need of practitioners for practical information and advice.
It is evident that the present range of energy efficiency measures that apply in the design of new buildings is driving the specification of solar thermal as the low carbon component of integrated hot water and heating systems. However, the energy efficiency savings in such an installation apply equally in a refurbishment application.
With correct application, solar thermal technology can be designed into an existing system and deliver up to 40% of a building’s annual hot water demand from solar energy. This represents a significant reduction in energy costs and CO₂ emissions, so it was no surprise that solar thermal has been included in Phase 1 of RHI (Renewable Heat Incentive). This Phase came into effect on 28 November 2011, a little later than expected as implementation was delayed whilst the Department of Energy & Climate Change (DECC) resolved the scheme’s compatibility with EU requirements. Non-domestic users who qualify can apply to Ofgem E-Serve and receive payments on a quarterly basis for heat generated over a tariff lifetime of 20 years. In the case of solar thermal installations of less than 200kW peak output, the payment will be 8.5 pence per kWh of metered renewable heat produced.
In the round
The implementation of the Government’s commitment to reducing UK carbon emissions, in particular from energy consumed by buildings, is continuing apace, based on a mixture of statutory requirements, policies, codes and practices. These measures are supported by advice and guidance from industry representative bodies and taken together they provide designers and installers with obligation, direction and sometimes incentive to incorporate renewable energy sources into building energy solutions.
The practical application of all the relevant measures is showing that solar thermal technology is playing a prominent role as part of integrated hot water and heating systems. The efficacy of a solar thermal solution can be shown in both new build and retrofit applications, with correctly designed and installed systems being able to provide 40% of a building’s hot water demand from solar energy.