2019-07-01 Homebuilding & Renovating

(Joyce) #1
homebuilding.co.uk 163

byDavidHilton


Ventilationis keyto a healthyhome,andwhile
mechanicalventilationwith heatrecoveryhasbecome
a buzzword,theremaybemoreoptions availablethan
self-buildersthink,saysenergy expertDavidHilton

DAVIDHILTON
is anexpertin
sustainable
buildingandenergy
efficiency,and
is a directorofHeat
andEnergyLtd

The Build VENTILATION


VENTILATION:


K now your options


W


e all need fresh air to survive and as
such, in our drive towards energy
efficiency in our homes, we are
continually looking for better, and more
efficient, ways to ventilate them and keep
them healthy.
For many homes, including most of the
existing housing stock, airbricks and trickle
vents have been the solution of choice.
They are cheap to install, comply with
regulations and are understood by most
contractors. These measures can keep the
home ventilated but with some important
caveats. If there is no wind then the home
may not be ventilated at all, and conversely
if the wind is blowing hard then the home
could end up over-ventilated. External
influences such as dirt and debris, plants or
garden features, or internal features such
as curtains or furniture can block airbricks.
Internal doors must also be open to allow
the passage of air to move through the
home to allow for cross ventilation.
It is this unpredictability that has led us
to explore active ventilation options more
closely, and solutions such as mechanical
ventilation with heat recovery (MVHR)
systems have largely become the ventilation
‘must have’ for the discerning self-builder.
This does make sense on paper as the
system extracts warm, humid and stale air
from certain rooms, such as the kitchen
and bathrooms, and then delivers fresh air
to habitable rooms such as the bedrooms
and lounge. Fresh air is also drawn in from
outside. The air passes through a heat
exchanger and the heat in the stale air is
extracted and transferred into the cool
incoming fresh air to preheat it.
Manufacturers claim efficiencies of up
to around 92% but in real world situations,
where the airtightness is not absolutely
optimised, lower figures of about 75%
can be expected. This means that if the
room temperature is around 20°C you
could expect the fresh incoming air to
be preheated to around 15°C. So, in
order to achieve worthwhile levels of heat
recovery efficiency it is important to have
manageable airtightness levels.

Earth Save Products’
Ecocent system, shown
installed in a self-build,
combines mechanical
extract ventilation with
a heat pump to provide
hot water to the house.
Free download pdf