Location is fundamental to MVHR performance - March 2013

This article appeared in PHAM News, March 2013

With MVHR units becoming common place in new build properties, their location is an important consideration. However, as Paul Rainbird, Operations Manager at Titon, explains, some products are not as well designed as they might seem and specifiers should approach them with caution.

When you look back over the last decade to see how the house building industry - and by implication - the ventilation industry has changed, they’re almost unrecognisable. Not only have they smartened up their acts, but sustainability and green issues have come to the fore with technology transforming the design, quality and energy efficiency of new build properties. But while to the consumer, ventilation might not be a household priority, builders and developers are all too aware of the need to choose efficient and reliable products, which not only comply with the more stringent Building Regulations, but also guarantee healthy air quality for occupants.

The product which has shot to the top of many specification sheets in the house building industry is mechanical ventilation. The increasing levels of air tightness in buildings has meant that traditional ventilation is not always appropriate, so to ensure occupants have healthy air environments throughout the year, mechanical units are now a key appliance in the ventilation mix.

However, despite the improving technology and developments in house building design, the location of units in a property - particularly those with heat recovery - is fundamental to their performance. From Titon’s standpoint, this needs to be carefully considered at the design stage, and we have long been advocates of placing the unit either in the airing cupboard, specially designed service cupboard or a space in the heated envelope of the building. Doing so ensures the unit is well insulated and not affected by climatic conditions, as well as ideally positioned not to compromise ducting design. With this in mind, it’s surprising to see that manufacturers are now producing mechanical ventilation with heat recovery (MVHR) units that are designed for - what we would deem - inappropriate locations. Although these models might tick the Regulation boxes on paper, it’s highly likely that problems can crop up when the units are taken to task in a real life environment - often rendering them ineffective and inadequate for the ventilation requirements of the property.

Among the main offenders that we’ve come across which astonish our technical department, are the latest MVHR units with a plastic heat exchanger situated directly above a cooker and hob. From a design point of view, we can understand the merit of producing such a model, as there is certainly a space saving element involved, as well as a dual purpose role of replacing a dedicated extractor fan with a heat recovery unit. Yet as a manufacturer of highly efficient MVHR products, we would have serious concerns about placing such an important appliance so close to a cooker and hob.

The first obvious problem is the volume and quality of air passing through this type of combined unit. Now, as anyone with an oven extractor will know, the filters on the underneath are designed to hold onto air borne oily and fatty matter (grease to you and me). This eventually needs to be removed and cleaned to ensure continuous air filtration in the cooking environment – as well as prevent grease dripping back onto your hob! This is fine with a dedicated extractor ducted directly to the outside, which only operates intermittently and needs occasional cleaning, but for an MVHR unit that is running 24/7 to provide filtered air to the rest of the property, the filters will require constant attention - not only to maintain adequate levels of air movement but also prevent pervasive cooking odours circulating throughout the property.

In addition, the build-up of grease in an MVHR unit’s filters can also have some fairly detrimental knock-on effects to the rest of the system. Notably, the restricted air movement will force the unit to work harder, often causing efficiency levels to plummet below the unit’s published figures. And further still, the over working of the fan might cause noise levels to increase dramatically. This could potentially aggravate homeowners and may cause them to seek methods of turning the unit off altogether.

Taking these potential problems into consideration, the location of a mechanical ventilation unit is clearly an important issue. Understandably, specifiers are not always aware that choosing a product which apparently fulfils a building’s requirements on paper, can actually cause more long term problems and hassle for the occupiers. So it’s certainly worth considering all product types on the market, especially those that are appropriately and solely designed for the ventilation requirements of a building.

We believe all of these issues can be ironed out at the design stage of a project, by taking into account the location of the mechanical ventilation unit, as well as the design of the ducting system and positioning of room diffusers. Plus, this approach will ultimately guarantee higher efficiencies and improved air quality for occupants – which, after all, are the core objectives of any specified mechanical ventilation units.

So as the house building industry begins its return to growth and the investment in efficient ventilation systems gains in importance, specifiers are going to have to choose efficient ventilation systems that deliver the air movement required for a modern, well insulated property. Plus, by understanding the possible pitfalls of certain product designs, they can ensure that owners and occupiers alike enjoy their new homes, safe in the knowledge they will breathe a little more easily and without the issues associated with a badly designed system or unit.

If you’ve got any questions about good ventilation design, best practice, or Part F of the Building Regulations, why not give the experts at Titon a call on 01206 713800?

Download as PDF