I've decided these are a good idea, and I'd like to fit one. The trouble is
that the only suitable products I've found using google are from US
companies, designed for 110V. Does anyone know of a UK supplier for this
sort of thing?
[For anyone who doesn't know what I'm on about, a whole house fan is a
fairly powerful fan that vents hot air from the house into the attic space
(and thence outside), and draws cool air in through open windows etc. The
idea is that you run it when the house is too hot, and the outside
temperature is significantly cooler - typically to cool things down at night
after a very hot day.]
How about a number of parallel units: axial fan, 4" ducting (rigid where
possible, flexi[1] at the end for any fiddly bits?
[1] Can be got in round and rectangular form.
I'm using this method to vent an islanded bathroom to the soffit over
the front door (being a straight joist run). If you are only venting to
the loft (to exhaust via the eaves) then you'd only need short duct runs
to allow the fans to go somewhere sensible and perhaps away from being
over the bedroom to reduce noise.
You also have the option to vent via more ductwork directly outside.
I got my ductwork from BES. I'll look up the fan if you like, but they
are not uncommon. You can get fairly subtle vents in a number of
finishes (white, brown, chrome) for the bedroom ceiling end and soffit
end (if required).
It looks like I will have to bodge something (unless anyone manages to
answer my actual question!). The problem will be getting a fan (or fans)
that shift enough air - bathroom extractor type fans are orders-of-magnitude
inadequate - and yet aren't industrial ventilators!
Some of those inline fans can shift a fair volume - don't think
"bathroom" necessarily, think "inline fan" - the question is, how much
do you want? I've never been impressed with bathroom ventilation so I
got a higher rated inline fan for mine.
Ultimately, there's only so much you can shift up a 4" duct and vent
(unless you were planning to put more or larger vents in each room?).
Regarding homebrew, if you could get a bigger fan, making a distribution
box out of ply and lined with acoustic dampening with 4" spigots
wouldn't be too hard, with the fan inside to cut down noise. I wonder if
googling for 6"/150mm fans would lead to something...
Regarding readybuilt, there much be something in the 6" area. I'm
thinking offices where the loos have several 4" vents and ducts feeding
into a 6" or bigger duct with something (which I never saw) on the other
end.
Fair point. I haven't calculated how much air I need to shift yet. The US
DOE has some guidelines, which some US whole-house fan makers think are a
bit high, so I'll do some more research and some sums and then revisit
inline fans. The ones I briefly looked at didn't come close to the airflow
of the US products.
I'm rather liking another poster's idea of making a special loft hatch, with
a big fan venting directly into the loft space, at least to start with.
Ducting and multiple inlets might come later!
Thanks for your ideas.
On Sat, 29 May 2010 09:58:52 +0100, Pyriform wrote:
Some years ago I bodged up a forced-air vent from the first floor out
through an open window. I used a 15" fixed fan, some flexible metal ducting,
cardboard and duct tape. The cardboard / tape was to make a funnel over the
fan's outflow to direct air along the duct, out of a nearby window.
It did have a noticable effect on the heat in the house, but caused a lot
of vibration which resonated and was nearly as annoying as the heat.
Seconded: passive ventilation is even very effective in hot deserts. Better
would be to have a fan to pump the warm air back down from the top of the
house in the winter than the other way round. Leaving loft hatch open and a
window downstairs creates plenty of cooling draught, and a fan would have to
be going it some to even keep up.
S
I know about natural convection, thanks.
And I want to install a fan, since forced cooling will be much more
effective, on those (relatively few) occasions when I need it.
Your google-fu letting you down?
Try searching for
heat recovery ventilation
on UK sites.
Guy
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Seems most replies arent what was wanted.
Beware of venting into the loft, condensation can cause problems.
Also you need to provide trapping of dust etc that might fall down
when fan not on.
However as a cooling method it is, if used only at the right times,
very good.
NT
Do you have a loft hatch door?
1. Create a new spare door with a large Xpelair ceiling fan fitted
into it - the very big ones are actually quite cheap (about £60 or so
for 300mm or something like that).
2. Fit a 5A socket near the loft hatch off the lighting final circuit.
3. Fit a battery powered heat alarm if you wish directly above in the
loft.
4. In summer fit the "fan loft hatch door", power up, done.
The heat alarm is in case the AC fan were to stall catch fire (Xpelair
will be EBM-Papst so will have a bimetallic strip cutout but this
cycles on & off so heat can build up quickly).
Realise house humidity will be pushed into the loft, which at night
will drop in temperature significantly - perhaps below the dew point
of that humid air causing condensation. Hence remove when the hottest
days of summer are gone.
Alternatively plumb the thing in properly with aluminium (or fire
rated) ducting to an outside vent in a gable end or soffit and a
backdraught shutter (otherwise it will bleed heat out when you do not
want it to such as winter). If the fan is quiet enough to run
overnight (you can get speed controllers) it will really make a
difference dropping downstairs temperatures.
I quite like this idea - thanks. Would be a nice proof-of-concept without
making holes in any ceilings. I'll take a look at the Xpelair range to see
if they approach the sort of air flow I'm looking for (and which I haven't
actually calculated yet!)
12" extractor or even a boxed in ceilng fan.
Loft condensation can be avoided by venting outdoors rather than to
loft.
Loft can have its own fan just to cool the loft, reducing conduction
to upstairs rooms
Advantage of separate room fans is that each can be controleld
thermostatically for best effect.
Do run these things on differential stats, otherwise the overall
effect is much reduced. And arrange them to provide heat for part of
the year.
NT
On Fri, 28 May 2010 17:38:12 -0700 (PDT), NT wrote:
Wouldn't you only get condensation if the loft (either air, contents or
fabric) was cooler than the incoming air? In my house in the summer the
loft is the warmest place as the sun heats the tiles, since the insulation
is between the loft floor and the first floor ceiling. So venting from the
house into the loft will introduce cooler air into the loftspace.
It could be an issue if the night is very cold (and the loft is insulated
only at floor level). For what I have in mind, I don't envisage there being
a problem.
I don't think that would be a problem - the loft structure is hot so no
risk of condensation.
Given the OP's stated use (cooling a hot house in summer) I don't think
even the risk of introducing a little extra humidity that may condense
in the cool wee hours is worth worrying about either - it will clear the
next day. Wood rot comes from sustained condensation, not a bit once in
a while.
The only risk I see is running such a system in the winter - that would
be bad, so I suggest making provision to lock it off.
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