Unlocking the potential of MVHR systems - November 2012
This article appeared in PHAM News, November/December 2012
With levels of air tightness in new build properties increasing, mechanical whole house ventilation systems are being specified more and more. Well-installed mechanical ventilation with heat recovery (MVHR) systems will perform as designed, providing clean and healthy air for occupants, while reducing the risk of condensation and mould growth. However, if poorly installed, they will not work as intended, often using too much energy and unable to deliver the benefits of adequate ventilation. Tyson Anderson, Sales & Marketing Director at Titon, explains what needs to be done to ensure ventilation systems perform to their full potential.
The revisions to Part F of the Building Regulations (England and Wales 2010), focused on the strict levels of control with which ventilation systems are designed and installed, as well as their overall performance to ensure adequate indoor air quality. This legislation, coupled with increasing levels of air tightness, has seen designers increasingly specifying MVHR systems (System 4) in new build houses and apartments because of their benefits in SAP (the Standard Assessment Procedure) Appendix Q.
However, for occupants to benefit from these savings, systems must be professionally installed and commissioned to produce a level of performance that matches the predictions of the SAP model. In order to achieve such a level, there are a series of barriers that need to be overcome:
‘Designing in’ to dwellings
To ensure optimum performance from an MVHR system, it should be incorporated into building designs as early as possible. When ‘designing in’ to dwellings, there are three important considerations that need to be taken into account. The first is the ducting design, which is essential for the effective performance of an MVHR unit. The most economical route should be taken between the ceiling or wall terminals and the central unit. If a duct run is too long or tortuous, the system becomes inefficient as it forces the mechanical unit to work at higher speeds and use more energy to compensate for the convoluted route. This can then lead to increased noise levels and additional running costs for the homeowner, while running the risk of compromising compliance with the Building Regulations.
The next important aspect of design concerns valves and diffusers, which should be positioned to encourage the movement of air throughout the room, as well as filter out any airborne dust and debris, ensuring a good level of indoor air quality. This latter point is significant, as recent BRE figures indicate that people in Europe spend at least 90% of their time indoors, so it’s important the air they breathe is kept clean .
Finally, the location of the MVHR unit itself needs to be considered carefully. Units offer best performance when installed in a location that allows the most efficient ducting layout, with least resistance to air movement and minimal heat loss. 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 air tight, lofts tend to retain colder temperatures – which in turn may affect the performance of the system! As a result, we recommend placing the unit within the fabric of the building – such as the airing cupboard or a dedicated service cupboard.
Now, it can be particularly frustrating when MVHR has been specified and ‘designed in’ as detailed above but then inadequately installed. More often than not, installation errors lead to complications, which the contractor blames on either the product and/or the manufacturer – when, in actual fact, it’s a lack of installer training that is usually the source of the problem. Indeed, on the rare occasions we receive a report about an issue with one of our systems, 99% of the time the fault lies with the installation and not with the product.
In order to prevent these situations, developers need to insist on only using certified installers, while manufacturers should encourage installers to undertake the relevant training, especially as we move towards creating zero-carbon homes.
The first step for installers should be to complete the two-day BPEC Domestic Ventilation Systems 2010 training course. This has been designed to meet the requirements of the Domestic Ventilation Compliance Guide 2010 and requires installers to have a minimum of NVQ Level 3 in plumbing, heating or electrical engineering. Successful completion of the BPEC course (which is run by manufacturers including Titon) will allow installers to learn about topics including system design, installation and commissioning, as well as the required theory and practical applications. In addition, it allows installers to acquaint themselves with the equipment used on site and the potential issues they could encounter. Completion of the BPEC course also provides training evidence for suitably qualified individuals to include in their application for registration on a Competent Persons Scheme in ventilation.
As with all industries, the ventilation sector is well aware that the current financial climate has led some contractors to look at projects in terms of affordability – i.e. selecting the cheapest options – rather than ‘Best Value’ levels of performance and energy efficiency. It may be easier on the bank balance in the short term to spend less on a system, but over time, a poor quality system is highly likely to develop problems and require frequent maintenance and repairs. Consequently, it makes financial sense in the long term to invest in a quality, reliable and energy efficient system that will stand the test of time and offer reduced running costs throughout its lifecycle.
From a house builder’s perspective, any contractors used need to be financially stable, to ensure that the supply chain is not disrupted. After all, if a contractor fits an MVHR system and then goes out of business, a replacement contractor will be required, who is often unfamiliar with the system and other aspects of the installation – resulting in more time and money being wasted.
So, there you have it – plenty of food for thought. In order for ventilation systems to function at optimum levels of performance and efficiency, they need to have been specified, ‘designed in’ and installed correctly, with a secure supply chain. To help specifiers and installers achieve this, manufacturers need to be on hand to supply up to date information on the latest regulations and product developments. Doing so will then enable MHVR systems to function efficiently, keeping indoor air clean, and ensuring building occupants are happy and healthy.