[Greenbuilding] [BULK] ERV's

[Ward Edwards]

Lawrence Lile wrote:
> Ward sez: 
> 
>> I am assuming you mean an HRV, as ERV's are used mostly in a cooling 
> climate (which unfortunately, Canada definitely is not).  
> 
> The ERV, I'm thinking, recovers and conserves moisture, whereas the HRV
> does not, right?  Seems like you'd want to conserve moisture in the
> winter.  Help me understand why one is used in cooling climates and one
> is not?  
> 
The difference between an HRV and ERV is that the ERV will transfer the 
moisture from the moist air stream to the dry air stream.

In a heating climate you need the HRV in a tight house to remove the 
moisture in the air, whereas in a cooling climate you want to transfer 
the moisture from humid incoming air to the dry exhaust air in order to 
keep the humidity down in an air conditioned building.

> 
>> I have mine on a cycle that runs 20 minutes of every hour on low 
> speed and I find that keeps the humidity in check. 
> 
> You mean keeps humidity low in the summer, or keeps it high in the
> winter?  
> 
Since my house is so tight, all the moisture from cooking, showering, 
breathing, etc stays in the house.  Before I had the HRV installed, in 
the winter the windows would almost have a stream of water coming off 
them.  With the HRV the moist hot air from inside has the heat moved to 
the cold dry air from outside and lowers the humidity in the house to a 
manageable level (about 35% relative humidity) and the windows only have 
a small bit of condensation at the bottom edge and only when it is quite 
cold.

With the insulation I have, as well as the overhangs, the house rarely 
heats up to an uncomfortable level during the summer, so I don't have 
air conditioning. In the summer I turn the HRV off, as the windows are 
open during the night, so the house has a chance to air out and the air 
exchange is not needed.

There is some more detailed info on HRV vs ERV on Lifebreath's site at

http://www.lifebreath.com/en_tfaq/FAQ-ERV.pdf

Hope this clarifies things,
Ward Edwards
ward at buildgreen.ca