Setting the Standard - September 2013

This article appeared in HABM, September 2013

As local authorities and housing associations look to build properties to ever higher levels of efficiency, specifying Mechanical Ventilation with Heat Recovery (MVHR) systems that maximise energy performance is essential. Titon’s Operations Manager, Paul Rainbird, identifies what to look out for to ensure these standards are met.

With Part F of the UK Building Regulations offering guidance on improving levels of airtightness in an effort to meet enhanced energy efficiency targets, maintaining adequate ventilation and recovering heat from exhausted air is only going to grow in importance – especially with further revisions on the way.

Additionally, Part L, the document covering fuel and power, also contains information about the energy efficiency of ventilation. This document has improved the energy efficiency targets for buildings by 25%, in accordance with Level Three of the Code for Sustainable Homes. Ventilation also enables energy targets to be achieved via SAP (the Standard Assessment Procedure) Appendix Q – the method by which energy efficient ventilation systems can be selected and the energy benefit be added back into the SAP calculation. Combining these changes in legislation as standard should see MVHR increasingly become a more common route to energy efficiency throughout housing developments in the UK.

Already a core part of many low energy building designs, modern MVHR systems can deliver heat recovery efficiencies of over 90%, and are essential in ensuring good indoor air quality and reducing energy demands. Poor ventilation can result in invisible threats to the health of occupants, such as the build up of harmful chemicals and mould spores, as well as condensation forming on colder surfaces, which are all threats to householders’ health and a well known cause of many occupant complaints to housing providers.

In order for air to be circulated around a property’s system, MVHR units rely on continuously running fans which ensure the air flow rates determined by the attributes of the dwelling are met. Noise can be an issue if an appropriate product is not chosen or not installed properly and so it makes perfect sense to ensure acceptable noise levels are achieved.

Units offer best performance when installed in a location that allows the most efficient ducting layout, with least resistance to air movement minimising the effort required from the fans. This should be an area that’s accessible, insulated and large enough to allow plenty of room for ducting in and out of the unit. Previously, it was common for units to be placed in the loft space but, since modern homes have become more insulated and airtight, lofts tend to be one of the colder areas – which can adversely affect the performance and efficiencies of the system! Therefore, we recommend placing the unit within the heated space of the building, such as the airing cupboard or a dedicated service cupboard and this also removes the need to provide safe, permanent access routes within the loft to enable servicing.

Noise and efficiency issues can also be avoided if the main unit has been correctly sized at the design stage. A trick of the unscrupulous supplier is to use cheaper undersized units that are then forced to work too hard, making them loud and inefficient. Furthermore, lower quality units will produce more noise than their better constructed counterparts – so it is worth consulting manufacturers early on regarding any potential acoustic issues and comparing the manufacturers’ test data. To ensure optimum levels of performance and efficiency, units should also be incorporated into building designs as early as possible, taking into account considerations such as location (as referred to earlier), ducting design and the valves and terminals being used. Larger ducting and terminals allow more air to pass through at a slow rate, minimising any noise, thus the second trick of the unscrupulous supplier is to use smaller, cheaper ducting that increases the resistance and greatly increases the risk of noise. One or both of these shortcuts often mean that the correct airflows are often not achieved as reduced airflows are used to offset the noise. Then, to compound these issues, poor installation in addition to poor design exacerbates the issues.

If MVHR has not been designed, installed and commissioned correctly in line with the issues identified, not only will its efficiency be compromised, expect complaints and servicer complications during its lifespan. However, these issues can be avoided if local authorities and housing associations demand a declaration from the installer, which includes the installed performance as set out in the Domestic Ventilation Compliance Guide (DVCG) 2010 that accompanies Part F of the Building Regulations. They should also insist on installers who are able to provide all the necessary documentation required, enabling any ventilation projects they undertake to be suitably policed.

In support of this, manufacturers are encouraging installers to undertake the relevant training. Courses such as the BPEC Domestic Ventilation Systems 2010 training course are designed to meet the requirements of the DVCG, teaching installers about topics including system design, installation and commissioning, as well as the required theory and practical applications. Completion of the course also provides training evidence for suitably qualified individuals to include when applying for registration on a Competent Persons Scheme in ventilation.

So, with MVHR becoming increasingly specified, it’s important for local authorities and housing associations to ensure systems are specified appropriately, ‘designed in’ and installed correctly. Not only will this enable MHVR units to function efficiently, it will also keep indoor air clean, and the occupants fit and healthy – as well as less likely to complain. It’s also essential to plan for the future maintenance of the units, which is much easier and cheaper to deliver when properly designed and installed in the first place!

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