[Greenbuilding] message

[Sacie Lambertson]

---------- Forwarded message ----------
From: "John Straube" <john at buildingscience.com>
To: "elitalking" <elitalking at rockbridge.net>,
greenbuilding-bounces at lists.bioenergylists.org, "John O'Brien" <
john at boardom.ca>
Date: Mon, 25 Oct 2010 12:54:56 +0000
Subject: Re: [Greenbuilding] ERV strategy
Short answer again.
ERVs do not dehumidify. The reduce the load on the dehumidifier when and
only when it is lower RH indoors than a outdoors.

John Straube
519 741 7920
Sent via BlackBerry


-----Original Message-----
From: "elitalking" <elitalking at rockbridge.net>
Sender: greenbuilding-bounces at lists.bioenergylists.org
Date: Mon, 25 Oct 2010 08:41:47
To: John O'Brien<john at boardom.ca>
Cc: <satjiwan at alumni.brandeis.edu>; listserv Green Building new<
greenbuilding at lists.bioenergylists.org>
Subject: Re: [Greenbuilding] ERV strategy

John, thanks for responding to my question.



Using your example, you must have another process to lower the humidity
indoors in order to preserve that dryness with ERV.  Night flushing during
fair weather summer days here in Virginia Mountains, brings in cool humid
air.  When it is 95F outside, 75F inside still feels much better, even if at
70% humidity.  Less humidity would be better.  The outdoor air later in day
is just as humid in absolute terms (#vapor/unit volume).  Please correct me
if I am wrong, however, in your example of the same temp but with the same
relative humidity, the ERV has no dehumidifying ability. The indoor air must
be dryer in order to preserve that dryness.


John O'Brien writes:
You seem to be making the issue more complex than it needs to be I
think. Assume both inside and outside temperatures are the same. You
have nicely dehumidified all your nice inside air to lets say a bone
chilling dry 20%, while outside it's raging ontario swamp heat wave at
100%.

With an HRV you're exchanging 20C air with 20C air... Check. HRV is
done. You've just replaced X amount of dry air with X amount of 100%
humidity air.

With your ERV, you've exchanged 20C air with 20C air again, but you've
also transferred your 20% in_humid with your 100% out_humid, which I
will assume will give you a new entering humidity of something in the
middle.. Let's say 60%. You now have 40% less humidity to remove.

Numbers don't make sense, but the concept is correct if not very
simplistic. I think what Steve was talking about was with regards to
exhausting 100% humid bathroom/shower air, with the ERV you're
actually recyling some of that moisture back into the house. I imagine
the next SUPER_RV will have humidity sensors to disable exchange
depending on interior and exterior flow conditions.

j





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