[Greenbuilding] HRV or ERV

[elitalking]

Nobody has endorsed my conclusion.  This list is my best access to 
knowledgeable nuance analysis.



If there is not another process to condense the vapor out of the air such as 
air conditioner, dehumidifier, or desiccants, then there is no benefit to 
latent heat transfer of ERV.



I am wanting to live without ac or heat pump refrigerant evaporative 
condensing cycle equipment.  They sometimes leak their refrigerant.  They 
also require replacing every 15 years+-.  Also, if the company goes out of 
business, service can become an issue. They also consume electricity with 
all those issues.



Last summer here in the mountains of Western Virginia; we lived without the 
use of our heat pump. It was the hottest summer we have experienced.  For 
the most part night time flushing keeps our interior comfortably cooler than 
outside during the day.  After completing the new ceiling thermal barrier 
before starting on walls, I read 103F outside, 78.7F inside on the floor 
below the roof.  That was the highest outside temperature I have ever read 
in this location, although, the interior air was humid.  My assertion is 
that the amount of vapor in #/unit volume on a fair weather day (no 
precipitation) is relatively constant.  Only the relative humidity changes 
with the temperature.  The interior daytime air has a higher relative 
humidity during the day only because air temp is lower.  As John Straub 
says, "ERVs do not dehumidify."



Therefore, if no process has been employed to dry the air out, the ERV will 
not do so either.  The disadvantage of ERV is that there is some air leakage 
from the latent transfer mechanism that reduces the effectiveness of heat 
transfer mechanism.



I grew up in Central Florida before air conditioners were common.  Last 
summer, most the time I was able to stay comfortable without our heat pump. 
During the worst days, light clothing and personal fan was able to achieve 
comfort.  However, the times where that was needed were relatively brief. 
The days where the low was in the 70's were the worst.  They daytime low was 
more a factor during night time flushing than the daytime high when the 
house was closed up.



I make the contention that living without compression-expansion refrigerant 
is a more healthy sustainable lifestyle.  So the only reason I can come up 
with for installing an ERV instead of HRV is because I might change my mind 
and go for dehumidification.  A small high efficiency mini-split could 
easily do the job.



I am intrigued by the possibility of using desiccants for dehumidification 
in a tight house.  This might provide the alternative to 
compression-expansion refrigerant equipment.  Preserving that possibility 
might be a reason to install ERV instead of HRV.



Eli


----- Original Message ----- 
From: "elitalking" <elitalking at rockbridge.net>
To: <john at buildingscience.com>; 
<greenbuilding-bounces at lists.bioenergylists.org>; "John O'Brien" 
<john at boardom.ca>
Cc: <satjiwan at alumni.brandeis.edu>; "listserv Green Building new" 
<greenbuilding at lists.bioenergylists.org>
Sent: Monday, October 25, 2010 9:48 PM
Subject: Re: [Greenbuilding] ERV strategy


> ----- Original Message ----- 
> From: "John Straube"
>
>> 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.
>
> Yes.  Then if there is not another process to condense the vapor out of 
> the air such as air conditioner, dehumidifier, or desicants, then there is 
> no benifit to latent heat transfer.  However, when you mechanically dry 
> the interior air, the ERV will preserve the value of that 
> dehumidification. Right?  Strategies of night flushing cooler high 
> relative humidity at night does not qualify.
>
> Eli
>
>
> _______________________________________________
> Greenbuilding mailing list
> to Send a Message to the list, use the email address
> Greenbuilding at bioenergylists.org
>
> to UNSUBSCRIBE or Change your List Settings use the web page
> http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org
>
>
>