[Greenbuilding] HRV or ERV

[Steven Tjiang]

Eli,

Your analysis seem correct for your climate.  If there is no active source
of moisture removal an ERV would only delay the inevitable equalization of
humidity between the external and the internal.

However, an ERV will ventilate and help to preserve higher humidity in an
air-tight house during cold, dry winters when there are internal sources of
moisture generation,  i.e moisture from occupants and plants, as well as
regular house hold activities such as cooking, and bathing.  An ERV probably
isn't sufficient on its own to preserve the humidity but it can help.

---- Steve (KZ6LSD)


On Tue, Oct 26, 2010 at 8:42 PM, elitalking <elitalking at rockbridge.net>wrote:

> 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
>>
>>
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>>
>
>
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