How much worse is running HRV air through central air handler ducting vs. dedicated HRV ducting?
I’ve been quoted an additional $4500 to run stand-alone HRV ducting to/from individual rooms in my 2350 sqft single story home — on top of an already fairly pricey unified/central air handler based heat pump installation. I’m trying to understand the pros/cons of integrating the HRV supply/returns into the central air ducting vs. stand-alone ducting, and wonder if anyone has a thoughts, experience, or a linked article that might help me better decide if it’s worth the $$$. I’m also a little confused about the best way to integrate into the central air ducts if we go that way, so any good resources or suggestions experiences on that would be much appreciated (I have read a 5-year old article on the subject, but seems like it could be it dated). Thanks!
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First, why are you installing an HRV instead of an ERV?
Second, dedicated is definitely the way to go mainly because the static pressure rating of your HRV is not going to be high enough to move significant air through the air handler ductwork, so you will probably have to “lock” the air handler blower to kick on whenever you want the HRV to run. That is a huge energy penalty. If you don’t do that you won’t be grabbing stale air from all rooms, but rather just the rooms closest to the air handler. Similar problem on the supply side where the HRV will not be strong enough to evenly spread the air to the last rooms in the duct run. You can do a hybrid where you have dedicated HRV ductwork for just the return (exhaust) air, but still use the air handler ductwork for the supply (fresh air).
Thanks! HRV because I’m in Seattle, where ERVs appear to me (via literature and discussions) to be unnecessary. I’m open to your thoughts if you think otherwise.
Thanks for your thoughts on static pressure! Got any good resources with examples of hybrid runs? I’d love read more about this technique. Thanks!
Did a Google search to try to find a concise article and this is the first one that I found that resonates my opinion that ERV’s are better in nearly every climate, especially in new construction:
https://marketscale.com/industries/building-management/maximize-ventilation-potential-with-ervs-as-compared-to-hrvs/#:~:text=As%20Marks%20outlined%20in%20the,you%20have%20a%20controlled%20space
What it comes down to is basically this: especially in new construction, you are going to have mechanical systems installed to sustain your desired indoor setpoint (both sensible and latent, with dehumidifier, etc). So, why in the world would you purposely take a more significant energy penalty by letting in raw outdoor humid fresh air when you could use an ERV to “temper” the humidity closer to your steady state indoor setpoint. Once you factor in the latent heat efficiency of the ERV, the total system efficiency is better than an HRV, even if the HRV’s tend to be better when looking only at sensible heat exchange.
If you aren't installing a dehumidifier, you might want an HRV to help reduce indoor humidity during the spring and fall. (This is specific to your location.) There's frustratingly little information on this topic though.
Since the OP is in Seattle my concerns would be more about reducing humidity coming from outside, rather than removing humidity buildup from indoor sources (showers, etc). I’m in Houston so I can relate. If you are in cold/dry climate I could see a slight case for HRV over ERV but then you run the risk of potentially making the house too dry when retaining a little RH might be desirable. A new house in a humid climate should really have a dedicated dehumidifier though. And if it does, then ERV > HRV all day.
I live in nearby Vancouver BC, and for most of the year the outdoor absolute humidity is lower than what we accept indoors - so ventilation will reduce indoor humidity most of the year.
I'll add a qualifier here... if I had a dehumidifier my indoor absolute humidity would be lower and I would definitely want an ERV.
The issue with sharing air handler ducting is the blower unbalancing the ERV/HRV.
You can avoid this problem by using an auto-balance unit (ie Pansonic IB100/200, Broan AI, Zehnder Q series). These automatically adjust the blowers to maintain the correct airflow. They are also simpler to set up so less chance of a bad install.
The other thing to watch is air handler fan power consumption. Older capacitor start motors use almost the same amount of power regardless of air flow, so running it 24/7 can cost some real dollars. This is typically not an issue with newer ECM blowers especially at the low speed you need for circulation.