Heat recovery ventalators
Does anyone have any experience with heat recovery ventilators. I am looking for a unit to change the air in a basement and at the same time make the incoming air either hot or cool depending on the season?
I have been looking at Fantech’s unit. They seem to be fairly compact and easy to install. I am not sure if they are standalone units or they need to be on some kind of HVAC system. Any users out there that can give me some tips.
We are required to use them on every new house we build. They are required by energy code primarily to control indoor humidity in the winter. We have used Fantech and Venmar. I'd suggest visiting their websites, reading the instructions, etc. Lots of information about them out there.
I do not think a HRV will help in the summer. You need an Energy Recovery Ventilator. But then I live in a place that bills itself as the "air conditioned city" (We had our first flirtation with temps approaching 80 degrees F this week)so I am a bit ignorant about the subject.
In the winter, the incoming air is still cooler than the indoor temperature. Even if a HRV is 100% efficient (which they are not) the intake air and the exhaust air will be the same temperature, which will be an average of the heat content of the inside and outside air. So don't locate a supply over your favorite rocking chair. And realize that you are pumping heat out. They can be run on intermittent timers so that you don't have to continually be pumping heat out if you don't need it.
They can operate as stand alone units (in a house with hydronic heat and no AC, for example). They of course require duct work of their own in that case. In houses with AC or forced air heat, we use the existing ductwork for supplying fresh air, and locate stale air exhausts in the bathrooms, laundry room, kitchen, etc.
"In the winter, the incoming air is still cooler than the indoor temperature. Even if a HRV is 100% efficient (which they are not) the intake air and the exhaust air will be the same temperature, which will be an average of the heat content of the inside and outside air."
If I remember correctly from when I researched these, if you have a counter current HRV the temperatures of the two streams are not an average of the two, which is why they can be more than 90% efficient.
I just installed one of these systems in my house. My plan is to run the system when temperatures are moderate, say 35 to 85 degrees. When temperatures are out of this range just turn it off. I figure in my area July,August ,January, and February it will be off.
A heat recovery ventilator can work summer and winter. Not sure about the humid southeast. 80 degF exhaust air will cool 90 degF air in the summer.
If memory serves me right ... I thought the effectiveness (not efficiency) of these units is more in the range of 50-70%, not 90% ...
Manufacturers seem to claim efficiencies in the high 70's and 80's. That's with new, clean exchanger cores in laboratory conditions.
I wonder whether they maintain their efficiency as they age?