With the UK government aiming for a zero-carbon economy by 2050, the knock-on effects to social housing are already in effect. One of the main focuses of the decarbonisation of Social Housing is to reduce energy costs for residents. Decarbonisation is the term given to the move to minimise the use of carbon-based fossil fuel energy to achieve lower emissions and minimise energy use, lowering living costs in the process. With the main focus on properly insulating homes to reduce heating bills this will have a negative effect on the indoor air quality, where natural ventilation will cease to be effective if not addressed. This is not necessarily a bad situation to be in as naturally allowing free air movement through buildings comes with its own drawbacks, but it is one where a suitable alternative needs to be put in place.
By stopping free air movement heat will be retained in the building and external pollutants such as particulate matter from traffic pollution will be kept from entering the structure. However, this will also trap stale air, indoor pollutants and humidity in the building - all of which have their own negative impact on the health of the occupants and the building structure itself. It is therefore necessary to introduce a suitable mechanical ventilation solution to combat these issues that also addresses the total carbon footprint of the home by effectively ventilating the property whilst also being highly energy efficient.
There are various ventilation solutions available for both existing residential properties as well as for new planned developments that can dramatically improve IAQ (Indoor Air Quality). With all of these solutions there are also some simple steps that occupants can undertake to maximise the effectiveness of ventilation systems whilst minimising the cost of energy bills. Let’s start by looking at some different mechanical ventilation systems available:
If you are in the building development stage, there are systems that can be incorporated into the design and structure of the building to create an integrated ventilation system. These can be installed easily as part of the build, allowing for ducting to be routed within the building structure to all areas of the home before internal walls and ceilings are finished to hide them from view. There are two systems that this applies to, MVHR and MEV systems. MVHR units are the most effective in terms of energy saving as they not only remove stale air from the building but also introduce fresh air back into the home which is not only filtered but also warmed passively through the use of heat exchangers. The heat exchangers glean warmth from the exiting air so that the energy already used to warm the home isn’t lost. This is then applied to the incoming filtered air so that it is introduced into the building already warmed. If the air was not warmed before entering the home, the introduced cold air would constantly drop the internal temperature meaning more energy would be needed to keep the internal temperature constant. By capturing the heat from the exiting air and applying it to the incoming air, heat recovery units help to limit the energy expenditure for reheating the home. The other crucial benefit to MVHR systems is the controlled cyclical flow of air through the building. By extracting and introducing air at a balanced volume and rate, the internal air quality can be kept to a high standard without the use of any passive ventilation, making a new build home highly efficient at minimising heat loss and moisture build-up, preventing damp and mould issues.
MEV systems are essentially half of an MVHR system. They are designed as a multi-room constant flow extraction unit. Predominantly used to extract from potential problem areas such as bathrooms, utility rooms and kitchens, MEV systems allow for a single integrated unit to cover all the spaces in a building that require ventilation in line with Part F(1) of the current Building Regulations. Similar to MVHR systems, MEVs are best utilised during the planning stage of a build to incorporate ducting into the building structure. Unlike MVHRs, MEVs only extract and do not supply air back into a building. This is notable because there will need to be an allowance for free air movement back into the property to keep a balanced atmosphere. This can be achieved through passive ventilation, however, if the building is designed to have a high threshold for minimising heat loss, passive ventilation can scupper chances of meeting these needs and an MVHR would be the optimal choice of system in these cases.
Where MEV systems can really excel is as a retro-fitted system in an existing building. It can be a more involved install to introduce ducting runs from the loft to the ground floor areas in existing properties with more than one floor unless you are undertaking major renovations. However, for buildings with loft spaces, MEVs can be easily installed to service multiple spaces on the floor directly below them, for example bathrooms, en suites and toilets and ideal for bungalows where access can be gained to all rooms from the loft space.
But what if your dwelling doesn’t have a loft space? Well, in these cases, such as flats, apartments and downstairs maisonettes, there are options to improve ventilation where ducting options can be minimised in existing buildings. Single room Heat Recovery systems can be implemented here. These systems work under the same principle as their big sibling MVHR units, implementing a heat exchanger to warm the incoming air. They are often designed with a single in/out ducting position, usually mounted through an external wall or in some cases can be ceiling void or loft mounted with separate intake and extract ducting points. These are useful in balancing both the incoming and outgoing air volume but do not offer much in the way of protection or ventilation beyond the room they are mounted in.
dMEV fans are essentially single room versions of MEV systems and are installed similarly to standard intermittent bathroom or kitchen fans. Working continuously with the function to boost when spaces are in use, dMEV units are a fantastic option to control humidity, damp and mould problems as well as allowing for continuous controlled venting of stale air from the home. In properties where the return supply of air may be compromised by the structural design, pairing dMEV units with a PIV or Positive Input Ventilation device designed for non-loft domiciles can create a minimal ducting extract and supply system with a similar outcome to that of an MVHR installation and improving whole-house circulation beyond that which single room heat recovery units are able to provide. PIV systems introduce fresh, filtered air into a dwelling which in many cases incorporates a heating element. Unlike an MVHR the unit does not recover existing internal heat but does ensure that the clean air being brought into the home is pre-warmed to again minimise central heating expense, however, it is worth noting that the heating element in the unit will draw more power when in use so it may be necessary to work out the additional energy cost to offset against the savings of the central heating bill. The PIV unit will need a supply of air from the outside and is ideally located centrally in the dwelling, so a duct run will be needed to supply the air to the unit. This can be hidden by concealing the duct in a ceiling void if possible or conduit run to an external wall.
It goes without saying that, in some cases, the most cost effective option for an existing building is going to be an intermittent fan. If you are looking to install fans to meet building regulations for social or privately rented housing in a building with no previous problems with humidity, damp and mould or any other problem needing specific or specialised ventilation, then a standard intermittent fan may well end up as the best box-ticking option in terms of both extraction and energy efficiency. The drawback with intermittent extraction comes in the shape of possible backdraught and heat loss when the unit is not in use. Most intermittent fans generally come with built-in backdraught protection or shutters can be added either inline on as part of the external grille, but it is important to understand that these will help to minimise backdraughts but are not 100% effective.
Occupants can also help to minimise energy costs in relation to internal air quality by following some simple steps. During winter months, keeping windows closed to maintain both the warmth in the building and to eliminate a cold air entry point will help to keep heating bills low. However, in summer months it may be beneficial to utilise passive ventilation by opening windows and turning off continuous ventilation systems - for example setting dMEV fans in bathrooms to only run when the room is in use rather than continuously will minimise energy usage. It is important however to remember that if your home is situated in an urban environment or in an area with heightened external pollutants, opening windows for passive venting will allow these pollutants to enter your home, including not just air borne particles but also noise pollution.
It is also important that occupants understand the need for free air movement within the dwelling. This not only allows for effective extraction and supply throughout all of the internal spaces, but also ensures ventilation systems are not starved of airflow which will inevitably add pressure to the unit which can cause a higher energy use if the unit is not working to its optimal performance. Making sure airflow between internal spaces is not blocked or hindered and that external vents, either for extract or supply, and ducting are kept clear will help to maintain a system running at its full potential and efficiency.