With design and installation of ventilation systems increasingly essential for both new builds and renovations, Richard Poole of Siegenia looks at how decentralised systems can offer an important way around trickle vents.
As we produce more tightly insulated buildings, window ventilation alone is no longer sufficient to ensure adequate air exchange and thus protect living spaces from moisture and pollutants.Â
On 15 June 2022, following several years of consultation, revisions to Part L, F & O of the Building Regulations finally came into force. This was the first update to these regulations in nearly a decade, and the next step on the road to a more sustainable future. The Future Homes Standard ensures that all new homes built from 2025 produce around 75% fewer carbon emissions than those constructed under current regulations, with a final goal of net zero in 2050.Â
The regulation changes set improved targets for air movement and notably the requirement for enhanced trickle vents in windows. Under this change, all new and replacement windows should be fitted with trickle vents. For two storey properties, habitable rooms and kitchens require window vent performance to 8000 mm2 EA, and bathrooms (with or without a toilet) to 4000 mm2 EA. There is however an important caveat within the new regulations that could ignite the uptake of heat recovery ventilation for those who do not wish to disturb the sealing and integrity of their windows by drilling holes through them. For homes with a balanced ventilation system i.e., whole-house decentralised or whole-house centralised, trickle ventilators are not required.Â
Centralised whole-house heat recovery systems have been around for some time and so are well accepted and understood. However, the installation of these systems does require careful design and planning due to the ‘spaghetti’-like ducting network required to interconnect all rooms. For this reason, they are normally only considered for new build projects. But even for the new build sector, such an undertaking can be off-putting.
Decentralised whole-house heat recovery ventilation is less understood but offers some meaningful benefits over its centralised cousin. Decentralised heat recovery ventilation is a great alternative, not only being quite possibly the only viable solution for refurbishment projects, but also offering a less labour-intensive and costly option for the new build market. So, let’s look at this system in a little more detail, and the potential installer and consumer benefits.Â
HOW DO DECENTRALISED HRV SYSTEMS WORK IN HOMES?
Decentralised heat recovery ventilation consists of a wall mounted control panel, duct with an integrated ceramic heat exchanger or accumulator, bi-directional fan, external grille, and filter. Like an MVHR system, the purpose is to reclaim heat, provide fresh air and to extract damp and stale air to prevent condensation and mould.
These units run continuously and automatically switch between air extract and supply in approximately 1 minute intervals. When running in extract, warmed stale air from the room is extracted and heat is collected in the heat exchanger. The cycle then changes and the unit switches to air supply drawing in fresh air from outside and transferring the captured heat to the incoming clean air supply to raise the fresh air temperature before entering the room.Â
Using heat recovery units as opposed to conventional fans therefore reduces heat losses significantly, with some units able to recover as much as 90% of the heat. Single-room ventilation units also provide a constant supply of fresh air to help maintain a healthy home environment. Â
INSTALLER BENEFITS
Decentralised ventilation systems are a flexible solution in which compact individual devices are inserted into the outer wall, which when configured in pairs guide the airflow through the living space. By installing units on a room-by-room basis, the designer can create a highly efficient decentralised whole-house HRV system with airflow rates tailored much more precisely to suit the occupant’s needs.Â
In addition, as each unit is self-contained, there is no need to specify a loft-mounted centrally managed ventilation device – and the associated costly and time-consuming ducting – presenting a further benefit both for renovation work and new build projects. Once the wall opening is prepared, the installation of each ventilation unit is completed in less than one hour.Â
END USER BENEFITS
In a world of rising fuel and energy costs, the focus on energy conservation has never been greater. A study carried out by the open university in 2018 concluded that 30% of the heat lost in our homes is through conventional ventilation. To put that into context, 30p in every pound we spend on heating is being wasted. Decentralised units have an integrated heat recovery unit manufactured from ceramic to limit moisture build-up and to provide heat recovery efficiency of up to 90%, thereby dramatically reducing these heat losses to as low as just 3p per pound.Â
Heat recovery ventilators can also be very economical to run, with the most energy efficient units consuming less than 4 Watts of electricity on the maximum setting and costing around £5 to run continuously for 365 days (based on typical energy costs as of June 22). Furthermore, unlike centralised systems, maintenance contracts are not necessary with decentralised ventilation; any cleaning requirements can simply
be carried out by the homeowner.
With so many cost and efficiency benefits for installers and end users alike, it is sensible for developers to consider decentralised HRV systems as a credible alternative to both centralised systems and trickle vents.
Richard Poole is head of ventilation sales at Siegenia