Re: [mh] Venting the house automagically

[Jim S. <js...@sy...>]

Hi Jim,

Well one would think that given their name (HRV). And I was all set to make
a summer bypass core for the machine - but first I did some tests and it
turns out they don't do that much heat recovery at full speed (boast) when
the temperature differential is small (like 15 or 20 degrees F). At normal
speed and with the winter outside / inside temperature differential they do
recovery a lot of heat.

And again because the algorithm is basically temperature bound - e.g. don't
consider outside air cooling unless the temperature is lower outside than
room temp, and only do so when it is cooling season - e.g. outside air is
probably greater than 50 Degrees C. Relative Humidity works out just fine
and can be done with a really simple threshold test.

Engineering wise - not precise, but really simple and easy to implement if
you have a HRV and can bring it under the home automations control.

Jim

-----Original Message-----
From: JimMH [mailto:jsk...@sb...] 
Sent: August 29, 2011 8:46 AM
To: mis...@li...
Subject: Re: [mh] Venting the house automagically


The problem I see with heat recovery ventilators (other than cost) is that
they do a heat transfer between the outgoing and incoming air.  This is not
something you want to do when the air outside gives free cooling or free
heating.  It actually slows or reduces the effectiveness of ventilation
considerably.  

They are great when you want fresh air and you are trying to retain as much
heat or cooling in the house as possible.

Dew point is a much better measure of comfort and availability of free
cooling than relative humidity.  If the air is 55F and a very high humidity
it is still suitable for free cooling.  Relative humidity is a very poor
indicator of how much moisture is in the air because warm air holds much
more moisture than cool air.  Dew point measures how much moisture is in the
air independent of temperature. 


Jim Serack wrote:
> 
> Some ideas for those interested in reducing AC.
> 
> I live in Canada in Eastern Ontario - so we have a supply of cool air
> outside for some of the evenings even after 80 Degree days in the summer.
> I
> just drive the heat recovery ventilator
> (http://www.venmar.ca/AfficherProduit.aspx?id=2&langue=en) on boost and
> the
> central air / furnace fan on low speed circulate. This only is used as a
> stage one cool and only if the outside humidity is less than 45%. The
> other
> thing I have done with my newer Furnace and the Omnistat 2 is implement
> dehumification control and set the AC temperature much higher - so 76
> degrees as the cool point but with the humidity under 45% is very
> comfortable - and a reduced cost / energy demand during the peak rate
> period. (One can use the cheap electricity at night to dehumidify).
> 
> -----Original Message-----
> From: JimMH [mailto:jsk...@sb...] 
> Sent: August 28, 2011 10:58 PM
> To: mis...@li...
> Subject: [mh] Venting the house automagically
> 
> 
> I have a duct to outside with a damper on the inlet side of the furnace. 
> My
> plan was to close off the house returns and pull in outside air with the
> furnace blower.  I planned to automate a couple windows somehow to vent
> air
> to the outside and haven't completely figured out that part.  I have
> casement windows so a few gear motors would do the trip (but might look
> ugly).  Have been wanting to do this for a long time.
> -- 
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