What is an HRV? A heat recovery ventilator (or any sort of air exchanger) is critical for a house like ours that is super insulated. Because of the tightness of our walls, windows, and doors, our house will not "breathe" on its own. An HRV provides mechanical lungs for the house by constantly exchanging indoor air with air from outside. This helps maintain a high quality indoor air environment. A "heat" recovery ventilator also ensures that the fresh air coming in from outside is warmed up before entry. Here is a summary of how an HRV works from Popular Mechanics:
A heat-recovery ventilator (HRV) is similar to a balanced ventilation system, except it uses the heat in the outgoing stale air to warm up the fresh air. A typical unit features two fans-one to take out household air and the other to bring in fresh air. What makes an HRV unique is the heat-exchange core. The core transfers heat from the outgoing stream to the incoming stream in the same way that the radiator in your car transfers heat from the engine's coolant to the outside air. It's composed of a series of narrow alternating passages through which incoming and outgoing airstreams flow. As the streams move through, heat is transferred from the warm side of each passage to the cold, while the airstreams never mix.
What is the difference between an HRV and an ERV? According to the experts, HRVs make sense in climates that do more heating than cooling (e.g. northern Vermont). Again, Popular Mechanics:
Although an HRV can be effective in the summer months, when it will take heat from incoming fresh air and transfer it to stale air-conditioned exhaust air, it's most popular in colder climates during the winter. HRVs are ideal for tight, moisture-prone homes because they replace the humid air with dry, fresh air. In climates with excessive outdoor humidity, an energy-recovery ventilator is more suitable. This device is similar to an HRV, but dehumidifies the incoming fresh airstream.
You can read the article from Popular Mechanics here. Another good resource is this article from Eco Home Magazine.
For those of you building super-insulated homes, are you going with an ERV or HRV?
10 comments:
We went with a Lifebreath HRV and their Turbulent Flow Precipitator (air cleaner) and have been very happy.
I'm leaning towards the ERV, but haven't completely decided on that yet. So why did you go with the HRV? Was it primarily a financial decision?
Thanks for letting us know, Ian. Glad to hear your HRV is working well!
Dan, we ultimately went with an HRV because it recaptures the warmth of the air leaving the house and transfers it to the incoming air. Since we'll be heating here in northern VT much more than cooling (well, we actually don't even have an AC so we'll only be heating!), it seemed important that the unit had that capacity. I remember the price difference being negligible...
What are your thoughts re: an HRV vs. ERV? Why are you thinking ERV?
Thanks for the comments, guys!
Susan
I'm leaning towards the ERV since it does what the HRV does plus is also capable of exchanging some of the humidity. The incoming air in the middle of winter is very dry. I'd like to be able to maintain some of the moisture already in the inside air under those circumstances. If the price difference really is neglibible, that's all the better!
We went with the Ultimate Air ERV because it not only exchanges heat, but also controls humidity. Additionally we can turn on the "econo-cool" during the summer months when we have warm days and cool nights, and as the outside air drops below a specific temperature the system begins sucking in the cooler air. No AC and our house stayed extremely comfortable all summer long. We have been in the house since August and it works fantastic for us in Montana.
I went with HRV. A main reason ventilation is necessary is to remove moisture from the inside air and keeping the indoor air's Relative Humidity in check. If you are concerned with having too dry air with the HRV then run the system less often. Less run time = less energy consumption for ventilation. Controlled ventilation is key - not neccessarily 24/7 run time unless that is how much you need to remove the moisture.
I have heard of new homes with ERV's (in VT) not being able to remove enough moisture to keep Relative Hummity levels in check ... at least in the first year when the house is wettest.
We are in MI's Upper Peninsula. We chose an ERV because it works great to remove humidity in the summer. BUT... we aren't happy at all with it for winter months. The intake vents bring in freezing air! Very uncomfortable, so we are forced to shut it off and suffer with condensation on the windows. I really wish we'd gone with HRV. Our walls are all finished, so it'd be a project to switch since HRV venting is set up differently.
Just talked to a technician... there are a few tweaks I can do to fix my problem listed above. If the exhaust vents are longer than the intakes, I need to lessen the amount of air coming in. So, maybe the ERV isn't so bad after all. While it's on, the condensation disappears from the windows, so it is very effective in that respect.
This conversation has been fascinating--thanks to everyone for sharing their perspectives! I'll post an update on how our system is working once we move in (scheduled for 12/24). We've been spending a lot of time over there recently painting, etc. and the indoor air climate always seems perfect...not too hot or dry. I'm sure we'll get a much better sense when we're there all the time. I'll keep you guys updated!
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