HVAC
MECHANICAL VENTILATION SYSTEMS: WHERE NOT TO CUT COSTS Prior to a revision of Building Regulations in 2010, ventilation was not high on the list of priorities in the housebuilding sector. A fan in the bathroom and cooker hood in the kitchen, plus ventilation blocks in the walls, were the default setting. Then, gradually, ventilation began to make it on to the agenda, largely driven by the now-defunct Code for Sustainable Homes, writes Paul Williams, Domus Ventilation’s Product Manager. DOMUS VENTILATION
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he code required homes to be better insulated and more airtight to stop the heat leaking out of them and wasting energy. Of course, the more airtight a property is made, the greater the requirement for ventilation to ensure good quality indoor air. At the time the code was in use, the focus was on preventing/ removing condensation. More recently, fears over pollution and over-heating have taken over as the imminent threat to the health of residents. Changes to Building Regulations Part F announced this year acknowledges these issues and the important role ventilation has to play in maintaining good indoor air quality. It lays out more stringent ventilation requirements for new builds, plus proof of effectiveness, so ventilation can no longer be ignored or side-lined. To ensure adequate, Building Regulations-compliant ventilation in a property and for it to be signed off by building control, then a mechanical ventilation system, such as a mechanical extract ventilation (MEV) or mechanical ventilation with heat recovery (MVHR), is required. FC&A – NOVEMBER – 2020
One of the key issues identified when reviewing existing Building Regulations has been the fact that a large number of homes – including those using mechanical ventilation – are not compliant with Part F (ventilation). Why is this? Is it deliberate; cutting corners to save money? Or is it a lack of understanding of how mechanical ventilation systems work and how a whole system approach is required? In our experience – which is considerable – it is a mixture of both. All too frequently, key elements of a mechanical ventilation system are skimped on to save time and money and also because they are seen as unnecessary. Here, we identify the five most frequent corners cut and why they matter, plus some tips for where you genuinely can make savings.
System design Designing a whole house mechanical ventilation system, especially an MVHR, requires a level of skill. Whilst the location of the air handling unit is normally straightforward, the duct runs, the number of bends and the angle of those bends, plus the temperature of 24
the areas the ducting runs through, all affect the airflow. The airflow needs to be maintained at a set level if the system is to perform to its best ability. To avoid the cost of employing the services of a qualified system designer, we have frequently seen builders and contractors taking an ‘educated guess’ at where to locate the ducting. This rarely ends well, especially when it’s done more as an afterthought when options for duct runs have become limited. However, there’s actually no need to cut costs here as most manufacturers will provide a system drawing free of charge, along with duct take-offs and estimations. The good manufacturers will provide ongoing support, so if you do run into any unforeseen difficulty, you can call upon them to help you out of the problem. They want the system to work, and they want your repeat business, so be sure to use their free support.
The ventilation unit The most obvious place to try and reduce costs is to buy a cheaper MVHR/ MEV unit. It’s true, you don’t always need the ‘Rolls-Royce’ model, but going for the lowest cost option could actually cost you more in the long run. That’s because, when it comes to a whole house mechanical ventilation system, a large amount of the cost is in labour. Better quality units may come at a higher price, but they are often designed with ease of installation in mind. Look out for units that are compact and lightweight so can be handled by a single person (as well as giving you more options on where to install them); that
