2019-07-01 Homebuilding & Renovating

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.