So why does my HRV work so well?
I installed a Venmar HE1.3 HRV in our new house a couple weeks ago. When it was purchased, I seemed to get fuzzy answers on how the efficiency is measured, so I was skeptical as to how well it would work. But I have been pleasantly surprised- to the point that I need an explanation because it seems to defy the laws of thermodynamics in my mind!
On a day with an outside temp of about 10F and inside temp of 58F, the fresh air was measured at about 53F after passing through the HRV (I did not measure the exhaust temp, as it was too cold and snowy to allow for climbing on ladders outside).
Intuitively, I would’ve expected that the two airtreams would ‘normalize’ at the same temperature after passing through the heat exchanger- in other words, (inside temp – outside temp)/2= temp of both fresh supply air and stale exhaust air. Obviously, I am wrong, so can anyone shed some light on how the HRV can be so efficient??
Replies
It's a "countrflow" heat exchanger -- the outgoing air flows one direction and the incoming air flows the opposite direction, so that the coolest outgoing air just barely warms the cold incoming air, and the warmest outgoing air warms the already-sorta-warm incoming air.
Ahhh, now I get it, thanks!Shawn
Thanks Dan. I need to install one in my house and I've delayed untill I could find some real value information regarding them.. Do you know if there are any superior brands?
No. Know nothing about them, other than what I've read.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
and to add to what Dan said....the highest efficiency units will have the outgoing air and the incoming air close to the same temperature, since most of the heat or cold has been held and exchanged.
Your intuition is correct, sort of. What is happening is that the warm inside air that is being expelled, has a higher humidity than the cold outside air. The higher humidity air has a higher heat energy content and this allows the incoming air temperature to be heated to a temperature approaching the inside air temp.
does mold ever form in these units?