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A Question of Ventilation
air is drawn towards the rooms where the air is
Here, Chris Marriott, Managing Director of ADM Systems,
being extracted.
Once specified MEV systems are relatively
takes a look at the alternative ventilation systems available,
easy to install in both new and refurbished
and assesses how the correct ventilation can result in both
buildings and there are units available which are
suitable for everything from small flats to large
healthier and more energy efficient homes.
houses. In addition, MEV systems have only
uestionable indoor air quality is first glance appear to contradict each other one external terminal and one electrical
Q
something that we hear about because, for instance, the latest update to AD’L connection and discreet ceiling-mounted
regularly, particularly with the requires a 20% improvement in thermal internal grilles which mean that its overall
increasing incidence of allergies performance over the previous regulations. appearance is more aesthetically pleasing than
and hay fever. It is a fact that the This means that many developers are now individual extractor fans.
air quality inside a property can looking for methods of ventilation that provides
have a significant affect on the health and the adequate internal air quality (AD’E) but also Passive Stack Ventilation (PSV)
comfort of its occupants. The indoor air quality retain thermal efficiency (AD’L). The days of PSV systems work by extracting the warm
can be altered by a range of factors including simply providing ventilation through passive contaminated air through ceiling or wall
microbial contaminants, such as bacteria and systems such as windows is arguably not the mounted terminals that are connected to
mould, along with chemicals such as carbon best solution. ducting before being expelled through the roof.
monoxide and radons. It can also be affected Providing adequate ventilation can be done Replacement fresh air is introduced by
by allergens such as pollen and fumes. in several ways. window/wall mounted inlets into other rooms.
Ventilation is an excellent way of filtering and Many of the extract terminals and inlets on PSV
diluting this spoiled air, however systems that Central (Mechanical) Extract Ventilation (MEV) systems are humidity controlled, so that the air
simply transfer air from the inside of the dwelling Spoiled air is simultaneously extracted from the flows will vary according to demand.
to the outside can often make the property very ‘wet rooms’ through a centrally-located extract Movement of air within the building is created
thermally inefficient. Building Regulations fan. Ducting connects the fan to the extract by the natural stack effect, which results from
obviously play a large part in the type of system terminals in each room whilst introducing fresh air the difference in temperature between indoors
chosen and the two approved documents into the other rooms via trickle ventilators which and outdoors, together with the effect of wind
that determine this are AD’F - ventilation then permeate throughout the home. passing over the roof of the building.
and AD’L, thermal performance. This creates a clean and fresh Many specifiers and clients prefer PSV
These two approved environment within the systems because their operating principle is very
documents at building as the pressure simple, with no mechanical fan. In addition,
difference ensures because the system relies on the natural stack
the supply of effect it consumes no energy and therefore
doesn’t need any electrical connections.
Positive Input Ventilation (PIV)
The process of PIV ventilation involves
tempered fresh air being gently introduced from
the loft by a single fan unit through a ceiling
diffuser mounted over the landing (or hallway, in
a single storey dwelling). This filtered air
creates a slight positive pressure, reversing the
normal airflow. This results in air being now
forced out of the building taking with it
unwanted moisture, smells and pollutants.
The incoming air collects solar gain from the
loft and redistributes heat that naturally
accumulates at the top of the stairs.
Many clients prefer PIV systems because
most of the products on the market have an
automatically controlled fan unit to optimise
condensation control and minimise running
costs. This method of ventilation can be
adapted to reduce Radon gas levels within the
building and also maintains a constant flow of
filtered tempered air.
Mechanical Heat Recovery Ventilation (MVHR)
A Mechanical heat recovery ventilation system
works by a series of ducts that collects stale
moist air from inside the house from areas
such as the kitchen, laundry and bathrooms.
This stale contaminated air passes through the
HRV unit and is exhausted to the outside.
Typical Heat Recovery System
Clean fresh air is then drawn from the outside
and, as the two air streams pass each other,
4 See inside back cover for Reader Enquiry Card or go online: www.atdonline.eu
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