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Re: GSBN:HRVs and SB


I would have a good look at the HRV but then taking the following into

A good HRV unit will recover at least 85% of the exhaust heat in a well
insulated house this can build up to rapidly. Commercial balanced units here
95% are about $1500 the air coming in is about 1-2 C below inside air temp
during winter. You easily save the energy required for the ventilator.

ie 250m^3/h at delta T 28C=1.2*28*250/3.6=2333W if you recover 85% means the
HRV saves 2333*.85=1983W not bad

In a properly designed system the ventilator should not require more then
400W leaving you a saving of 1583W

If you design carefully you don't need much ducting besides this also saves
on resistance and noise. In summer you can switch off and just open the
windows. To keep noise and losses down keep the flow rate below 2.5m/s in
the ducting. I used to work at a HVAC engineering buro and before this I did
an apprenticship at an alternative energy consultancy buro. Besides
fluorescent lighting the next best energy saving measure is balanced
ventilation with a HRV unit. If you want you can keep it running on energy
collected with solar panels. But then again this costs more money then you
save by not using the grid. It is much better to limit the amount of energy
required for moving the air. If the system is designed well 150W would
already move enough air. An efficient system also cuts back on noise.

I must confess I live in a house that is so leaky that we don't need a
ventilation system. But I should do something about it. HRV is a good thing
if done properly. Maybe running a ventilator doesn't seem right but it is
very sensible energy saving measure.


----- Original Message -----
From: "Chris Magwood" TLSEditor@...
To: "GSBN" GSBN@...
Sent: Wednesday, January 22, 2003 8:18 PM
Subject: GSBN:HRVs and SB

> Hello All,
> In the past month, I've had numerous enquiries like the following:
> >> Has anyone with a strawbale home NOT installed a heat recovery
> >sytem (HRV) and if so do you have a problem with condensation? I'm trying
> >decide whether to install one before my interior walls are closed in.
> Now that HRVs are part of our building code, it seems inspectors are not
> giving owners any options other than installing the full systems ($3-6000
> and require constant fan noise and energy, plus ductwork everywhere). Does
> anybody know of an indoor air quality expert who might have
> options/opinions other than the installation of full HRVs? My own home was
> built without one, and we don't have any moisture problems, which I
> attribute to the amount of porous, unsealed natural materials in the house
> (barn board, beams, unpainted gypsum plaster, etc) which are capable of a
> lot of storage when conditions are humid, and release when conditions are
> dry.
> Thanks!
> Chris
> ***************************
> Chris Magwood / Camel's Back Straw Bale Construction
> http://www.strawhomes.ca
> Interested in bale building? Have you subscribed to
> The Last Straw Journal?
> You should!
>  http://www.strawhomes.com