Re: OT : Plumbing help as well

["Simon Coates" <ecolume@xxxxxxx>]

Bruno,

Thanks for your comments - I agree with the advice you have been given.
That's why I want to make the ventilation system myself.
The problem with a lot of commercial heat recovery systems is that they
are
designed to be 'always on' providing a certain number of air changes
per
hour in certain rooms.  What I want to do is recover some of the heat
that
is extracted from our bathroom and en-suite, and the system to only
work
when necessary.  Instead of just having bathroom fans which will cause
cold
air to be drawn into the house from wherever it can get in, I'd like to
have
a controllable ventilation system which also has a heat exchanger.
The system I am thinking about is as follows:

Loft mounted heat exchanger
Powerful fans inline with the ducting - extract and input in each
ventilated
room
Fans controlled via AD10/LD11 modules
Automatic control of fans via HomeVision
DS18S20 temperature sensors in each room (and outside)

The above will allow extract only, input only (positively pressurise
house)
or extract and input with heat recovery.  Since HomeVision will be
controlling the system it will be easy to program the system to behave as
I
want it.

The most difficult part is getting the right size heat exchange unit to
maximise efficiency since there will be varying flow rates.

Regards

Simon

BTW - your proposed ventilation system sounds interesting.  What
source are
you going to use for your heat pump?

----- Original Message -----
From: Bruno Prior <bruno@xxxxxxx>
To: <ukha_d@xxxxxxx>
Sent: 28 December 2002 16:32
Subject: Re: [ukha_d] OT : Plumbing help as well


> We are currently living in a house with a BAXI ventilation/heat
recovery
> system. We were also planning to install a BAXI system in the house
we
> are currently converting. However, we just got caught by the new
> Building Regs. and the project was so complex that we had to employ
an
> environmental consultant for the Part Ls. Surprisingly, he advised
us
> that there was little if any environmental or cost benefit to a
> BAXI-style ventilation system.
>
> The reasoning goes something like this. Heat exchange depends on
> temperature gradient. Heat exchange over a small temperature
difference
> is inefficient. We live in a temperate climate, where the number of
days
> when there is a large temperature difference between inside and out
are
> limited. The number of days where a ventilation system offers
> significant energy recovery is also therefore limited. Against this,
you
> must set the fact that heat exchange ventilation systems require 2
fans,
> whereas normal ventilation systems require only one fan. The balance
in
> our temperate climate is normally that the energy saved by heat
exchange
> is less than the energy used by the extra fan.
>
> Of course, this is simply one expert's opinion (although our
heatpump
> supplier also held this opinion). And it is not hard to imagine how
one
> might design systems to get round it (allow the system to route
round
> the heat exchanger and input fan on warmer days). But you should
be
> careful with standard designs, as they are not usually this
flexible.
> And if not, not only are you wasting energy and money, but you are
also
> returning the heat to already hot rooms in summer, when you really
don't
> want it.
>
> One other observation on the BAXI system we are currently living
with.
> It is designed for trickle ventilation - slowly refreshing the air
in
> buildings that are intended to be air tight. But trickle ventilation
is
> useless in bathrooms - you want strong, intermittent extraction,
not
> slow, steady extraction. BAXI is wholly inadequate for humid rooms.
But
> I guess the efficiency of the heat exchanger depends on the flow
rate
> across the plates. There may not be a happy medium where you can
exhaust
> the air from the bathroom as quickly as possible and still recover
a
> significant proportion of the energy.
>
> I had hoped to do exactly what you want to do, but I am now
persuaded
> that it is a better idea in theory than practice. Instead, we are
going
> for a (Unico) high pressure/velocity ventilation system without
heat
> recovery but with fan coils connected to our heatpump, so we can run
the
> heatpump in reverse-cycle in summer to provide cold water to the
fan
> coils to blow cold air into the building, provide neither hot nor
cold
> on the moderate days to provide simple ventilation, and take a hot
water
> feed from the heat pump to the fan coils on cold days to provide
blown
> warm air for a more immediate heating effect than is provided by
the
> underfloor heating. Hopefully, this should be
environmentally-friendly,
> cost-effective and provide a comfortable climate year-round in the
house.
>
> Cheers,
>
> Bruno Prior
>
>
> Simon Coates wrote:
> > I'm going to install a 'home brew' heat recovery system for
the
> > ventillation.  I like heat recovery systems :o)  They
are up to 70%
> > efficient - and work well when extracting warm steamy air from
bathrooms
and
> > showers etc...  The extract air passes through a heat
recovery chamber
(size
> > dependant upon flow rate and air speed) which heats up the
replacement
> > incoming air.
>
>
>
> http://www.automatedhome.co.uk
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