Right so here we are with system three as I said we've skipped system two we're going
to move onto system three. System three is known as what we call as Mechanical Extract
Ventilation, this is a continuous running system now there's two ways this system can
be done. One is what we call a centralised unit which will be a centralised fan, this
is our MEV Spider and you'd run ducting from that fan to each wet room normally what we'd
do is run a series of ducts into individual ports on here we can run up to maybe two into
one port like this picture shows but if we had another utility on there and an ensuite
we'd run them into separate ports on the unit. So this unit is running all the time at a
very low rate, it's drawing air up through the series of ducting, through the unit and
then off to atmosphere again this could be for a gable-end wall or through a roof tile
vent but it's running at a very low rate all the time it's always doing it, it's sniffing
for the air and creating that little bit of background ventilation. This particular unit
is what we call a humidity tracker in it so as the air is going through it, it will sense
for the humidity so if somebody starts having a shower or a bath it'll actually increase
it's speed according to the relative humidity in the room, so if the humidity goes higher
the fan works harder, so that way it's extracting the moisture faster and off to outside, you
can also have manual overrides were you can boost it for odour reasons if you wanted to
or say if you've got a party going on in the kitchen and you may wish to extract a bit
more air. So as I said this is extracting off into atmosphere if we didn't want to use
a centralised system like that we could use some individual room fans again i'll get my
esteemed colleague to pass me one, so we've got one like this, this is our Eco dMEV, the
D stands for decentralised so what we mean by that is we have individual room fans so
rather than a centralised unit we'd have a decentralised fan, individual room fans, one
in the kitchen, one in the bathroom and because these are running all the time they run on
what we call a trickle rate, approved document f or the technical handbook would call it
a whole-dwelling ventilation rate but for ease we'll call it a trickle rate, that's
a low rate all the time so it's just doing enough, it's a very low rate, doesn't use
a lot of energy doesn't create a lot of noise but it's just drawing the air out gently all
the time and as it's doing that if we've got a humidity sensor on there they're sensing
for the humidity but it's creating a low-level of ventilation within the dwelling because
we're taking air out we're drawing air in through natural leakage or if it's a particularly
air-tight property we may have a couple of trickle vents in there, nowhere near as much
as we use with system one, when it comes to the background ventilation the requirements
are a lot less because we've got that more controlled ventilation and what they'll do
is when required if somebody is cooking, showering or even preparing fish for odour reasons we
can send these to a higher rate to get rid of that the smells or the odours and the moisture
quite quickly. Again off to atmosphere through the wall or through the ceiling and ducted
outside but the idea is we'll get rid of the moisture and any contaminants as quickly as
possible. The flow rates on these, so they do a trickle rate they then go to a higher
rate, which is what we call a boost rate and again within the approved document and building
regulations, they call that the whole-dwelling extract ventilation rate so it gets a little
bit confusing but for ease of things trickle and boost, trickle is the low rate and boost
is the higher rate that they will go to, it's a much more (thank you very much) it's a much
more beneficial and energy efficient way of ventilating a lot of people will have concerns
because it's running all the time you've got high energy consumption, you're loosing a
lot of heat out of the dwelling but it's more controlled than your standard intermittent
fans, so and because you've got something running at a low rate it's using less power
so they actually use less electricity, less power and they don't extract as much heat
because when they're on the low rate it's a very low rate, it's a lot less than what
the natural leakage would be in an old house, so it's more controlled and it's better for
ventilation hence again why when we look at this for new-builds the energy saving trust
recognise it as best practice and good practice it's an energy efficient way of ventilating
a dwelling a lot better than the traditional intermittent system one fans especially when
it comes to background ventilation you've not got all that air coming in, it's more
controlled. So that's it for system three really, obviously understand, obviously remembering
we've got centralised systems or you can have decentralised ones, so i'll finish off there
and move onto the next system which will be system four mechanical ventilation with heat
recovery.