RE: Air Con vs. Heat Exchangers

[Mark Harrison <Mark.Harrison@xxxxxxx>]

Ian wrote:

>> Seems mad that it doesn't! I've got various brochures at home from
other
>> companies who provide similar stuff... let me know if you want me
to dig
out
>> some other names...

> Yes please!

OK - will do so!

>> Alternatively, for the price of a four valves

> Can't it be done with just one?  Open a bypass past the exchanger for
incoming
> and it should take the least resistance path. And there's never any
need
to
> divert outgoing air that I can see.

That's a good question...

Please bear in mind that half of what I know comes from working with HVAC
engineers designing things like the Jubilee Line Extension ventilation
systems, so I may well have over-engineered for a house ;-)

I guess that I'd been assuming that you didn't want to pass hot air through
a heat exchanger without a coolant flowing the other side, because the heat
sinking capacity _within_ the exchanger might not be adequate.

However, for a domestic installation, the "hot" air ins't really
"hot"
unless you're extracting from a kitchen and need a solution that won't melt
in cases of "frying pan" fires immediately below the extract. So,
if you are
_not_ extracting from the kitchen, you can almost certainly make do with
two
valves (but see below). If you _are_ extracting from the kitchen, then it
depends on the quality of your heat exchanger - I've seen some very flimsy
lattices that I believe _would_ melt if you were extracting "pan
fire" air
through them without a balancing airflow to take away the heat.

Assuming, therefore, that we are now down to a single bypass of the
"extract" side. I'd be concerned about actual performance with
only a single
valve. I would say that, for the price of a second valve, you may as well
shunt the wrong path shut on the "down" side of the airflow.
Again, I may be
more concerned about turbulence than is required with domestic
volumes/speeds!





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