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Avoiding ventilation complications - April 2013

This article appeared in Heating, Ventilating & Plumbing, April 2013

Mechanical ventilation with heat recovery (MVHR) systems are becoming more commonly specified in a growing number of new build properties. As a result, the manner in which they are installed has been subject to greater scrutiny. Unfortunately, poorly fitted systems not only waste energy, they also pose potential health risks. Paul Rainbird, Operations Manager at Titon, looks at the key design and installation issues to consider when designing and fitting MVHR systems.

Energy efficiency is all the rage at the moment, with 2013 initiatives such as The Green Deal encouraging homeowners to upgrade to better forms of insulation and glazing, to name just a few measures. While this sustainability drive is to be applauded, it’s important that improved levels of insulation and air tightness do not result in inadequate levels of ventilation.

Inadequate ventilation can lead to health problems and fail to deal with damp and  condensation thus leading to mould growth. Fortunately, Part F of the Building Regulations (England and Wales 2010) is centred on how ventilation systems are designed and installed, in addition to prescribing their overall performance, to ensure minimum standards of indoor air quality are maintained.

Designers have been specifying MVHR systems (System 4) into new build houses and apartments due to the benefits they offer under SAP (the Standard Assessment Procedure) Appendix Q. Of course, but if end users are to fully benefit from MVHR, the systems need to be professionally installed and commissioned to a standard that mirrors the predictions of the SAP model. But what needs to be done in order to ensure requirements are met?

To realise the benefits of reductions in building energy and improved indoor air quality, MVHR systems must be properly designed and installed; indeed, if MVHR is to perform to its maximum potential, it is important that it is included in a building’s design as early as possible. The process of ‘designing in’ to dwellings centres on three main areas: ducting design, valves and diffusers, and the location of the actual MVHR unit.

Good ducting design is essential if the MVHR unit is to operate and perform effectively – as well as comply with the Building Regulations. It is important that the route taken between ceiling or wall terminals and the central unit offers the least resistance to airflow; after all, the higher the resistance, the higher the energy consumption and the risk potential for noise.

When it comes to valves and diffusers at the end of the ducting, these should encourage air movement throughout a room, and throughout the dwelling by utilising the door undercuts, and air extract points close to the primary source of pollutant, usually moisture, will prevent stale air and excessive humidity, while ensuring compliance with Part F.

In terms of positioning the actual MVHR unit, it should be installed in a location that allows for an efficient ducting layout offering the least resistance to air movement,  minimising heat loss and be accessible for maintenance, repair and eventual replacement, ideally, within the heated space of the dwelling such as the airing cupboard or a dedicated service cupboard.

Of course, MVHR can have a textbook specification and design, yet still suffer from being installed poorly. In turn, installation errors can lead to complications and potential long-term issues – such as stale air and condensation. Unfortunately, the source of these initial errors usually lies at the feet of an inadequately trained installer. If the industry is to prevent installation issues, developers need to ensure they are only employing certified installers. Manufacturers can also do their bit by encouraging installers to enrol on schemes such as the two-day BPEC Domestic Ventilation Systems 2010 training course. This educates installers about topics such system design, installation and commissioning, in addition to the required theory and practical applications. Completing the course also provides training evidence that can be included in an application for a Competent Persons Scheme in ventilation.

A final point of note concerns financing; while the cheapest products may appeal during these austere times, such units are unlikely to offer high levels of performance and energy efficiency in the long-term. A poor quality system may not perform as anticipated – creating more noise or insufficient airflow, for example. They may also be prone to developing problems, requiring frequent maintenance and repairs; therefore, it makes sense to invest in a high quality MVHR unit that will offer reliability and longevity.

So, while MVHR systems offer significant energy efficiency improvements, it is important that air quality and occupants’ health are not jeopardised by poor design, installation or cost cutting. Contractors and installers should ensure that they keep up to date with the latest information from manufacturers regarding product development and legislative updates – so that all projects involving MVHR will operate economically and efficiently.

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