As public awareness of the growing need to improve indoor air quality and the forward moving technology of extraction devices, more and more people are opting for continuous ventilation systems for their homes and businesses. But why is continuous ventilation beneficial, and what systems are available?
The main benefit of constant flow fans is the relentless movement of air through a structure. Removing stale and humid air is nothing new, intermittent extraction has been around for a while now. But by keeping a low level of extraction 24 hours a day, humid and stale air is constantly being displaced and removed from the structure. This is particularly effective when it comes to dealing with damp and mould issues as the continuous movement of air helps to dry out moisture, both on surfaces and in the air, by pulling warm dry air into the areas where damp can build up while removing the moisture from the building.
Let's look at two extraction systems and the differences between them:
MEV Systems
MEV (Mechanical Extract Ventilation) allows for continuous extraction across multiple rooms via a single ventilation unit which acts as a centralised hub. This allows for a single ventilation exit to exhaust the air out of the building rather than multiple exhaust points around the building for each room being vented. This is especially helpful when internal rooms with no external wall need venting as well.
The MEV unit runs continuously giving 24hr protection against moisture and indoor air pollutants. The majority of MEVs also have an integrated Humidity sensor in the main hub. If any of the incoming air’s humidity level rises above the set trigger point, say from a shower being run or boiling pots in the kitchen, the fan will boost to a higher extraction rate to help remove the moisture from the building faster. This will boost the extraction across all the vented rooms and the fan will drop back to the trickle extraction rate once the humidity levels drop back below the trigger point. MEVs can also be triggered via a manual switch which is usually a hard-wired connection but some units offer a wireless boost switch option.
The internal grilles in each room can be installed with extract diffuser grilles which allow the user to adjust the airflow at each individual extraction point by attenuating the airflow to tailor the needs of the room.
MEV units are usually installed in loft spaces with ducting runs to each room being ventilated and a single duct run to the outside for exhausting the extracted air. Installing as part of a new build or renovation is easiest as ducting can be run in voids between floors and ceilings as well as between interior walls to hide it from view. For existing buildings with loft access, fitting MEVs for upstairs use is less invasive as grilles can be placed in upstairs ceilings and ducting can be run to the MEV in the loft with minimal structural disruption. Reaching ground floor rooms in two or more storey buildings can be a more invasive install when retrofitting MEVs due to the need to run ducting to the loft space passed upstairs spaces.
dMEV Units
This leads us nicely on to dMEV units. dMEV (decentralised Mechanical Extract Ventilation) units work on the same principles as MEV units, continuously running on a trickle flow and boosting when needed either by humidity (if unit is spec’d with built-in humidistat) or by manual operation via a switch such as the light switch. The difference here is the decentralised part - these units, unlike the larger multiroom MEVs which are centrally placed, are designed for single room use only and are installed in the room in the same way a standard extractor fan would be.
Most dMEV units cannot deal with ducted runs and are designed for direct-to-outside through the wall mounting. There are a couple of exceptions to this such as Tornado ST100DMEV range and the Envirovent Silent Dual units which can duct up to 5m (the Tornado will in fact do up to 7m in a straight line!).
As these units are generally standard 4” fans and utilise a switched live, constant live and neutral 3-core wiring design, they are easy to use as replacements/upgrades to existing intermittent extractor fan installations, excellent for helping to protect damp and mould suffering bathrooms etc. Due to the nature of the continuous flow operation, these units will also meet current building regulations for both utility rooms and kitchens as well. Where standard intermittent kitchen fans are generally 6” installations, the Tornado ST100DMEV has another trick up its sleeve - there is an optional 6-4” installation adapter plate that allows you to retrofit the 4” dMEV unit into an existing 6” kitchen fan installation without having to make good the bored hole in the wall or ceiling!
dMEV units can allow you to cover downstairs kitchens, utility rooms or bathrooms/WCs in existing buildings where an MEV unit is installed for the upstairs areas but not capable of venting from the downstairs areas. dMEVs can also be used as an independent extraction choice without pairing with an MEV system and are a fantastic choice for bathrooms and other spaces where humid or stale air can affect the internal air quality of a building.
Both MEV and dMEV systems can help create a healthier indoor air quality either as part of a new build or as a retrofit to an existing structure, and with low energy usage, modern continuous extraction not only helps keep running costs down but also helps to protect both your home, family and the environment.