Local HVAC ERV Install
Today a local HVAC company (northern Michigan) came to finish up a towel radiator install and what I thought would be ERV (Renewair EV Premium L) commissioning.
When I asked about the ERV they said something like “they don’t balance them, they don’t need it and they probably don’t even have the tools to do it.”
I bought a manometer for setup/maintenance and realistically knowing they were not as excited as me in dialing in the perfect CFM to each room — lol. However, I thought they would at least check to make sure it was balanced!
So a few questions out of curiosity…
Is balancing more of a fine-tuning thing? Or out of the box can they be so out of balance as to cause damage (ex. excessive positive pressure in northern Michigan winter)? It seems to me you would be at the mercy of your duct layout. But is it normal to have the ducting so off-balanced that it causes real issues?
I know they are super busy too so maybe they’re just saying forget it because they can still pass their inspection without it?
Overall I was surprised. Maybe this is a somewhat common experience since ERVs are somewhat new?
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Replies
I would guarantee almost all residential ERVs/HRVs are out of balance and have never been balanced. About the only thing an HVAC tech do is connect the ducting to the unit and make sure it turns on.
Building envelopes tend to be pretty robust, an ERV out of balance won't cause major issues except for higher energy consumption.
The only precision tool I've seen HVAC tech use is an adjustable wrench. One time when doing an line evac, I had to insist the tech get a micron gauge, he had to go out and buy new batteries for it, so you can guess when that was ever used.
Autobalance ERVs tend to be be in the ballpark but even those still need balancing to get the flow spot on. The RenewAir is not an autobalance unit so it definitely needs to be commissioned properly.
If you are going to do the job yourself, make sure to get a decent manometer. Lot of the on-line ones have a 3PSI (83" WG!!!) range, so they won't be much good at measure 0.4" WG with any accuracy. 1PSI range is better but those tend to be pricey.
An ERV out of balance can significantly reduce the overall efficiency of ventilation, it doesn't take a lot of unbalance on an 80% ERV to be 50% efficient, as all out of balance flow is essentially pulling unconditioned outside air into the house through the leaks.
In cold climates, being out of balance can cause premature icing, and will affect efficiency.
Air flow of fresh vs stale on most HRV cores is quite asymmetric (out of the box, unbalanced), not so much on some of the newer ERV cores. Auto balancing ERVs are using current at the EC motor vs flow maps to match fresh and stale air flows…however I have no real data on how effective that is…probably close enough as 10% is what most manufacturers are stating for balance tolerance.
Aside from the obvious issue of a house being pulled negative or positive vs outside pressure, there is a real impact of balancing on efficiency. Think of it simply as balancing energy input vs output at the core. Speed up your stale air fan, efficiency will jump (you are adding more energy at the core), but the house will be pulled negative. Speed up the fresh air intake, efficiency will drop, and the house pressure will be positive. The problem here is that you will be cooling the core faster than heating it (and likely adding more moisture at the same time)..and the manufacturer has designed defrost cycles based on a balanced core. If ambient outdoor temps never get below freezing, not an issue.
In tests, I was able to skew sensible efficiency from about 55% to 90% by using unbalanced profiles in the HRV programming I’ve been working on (200CFM HRV core). Extreme example, but easy to replicate.
I’d also want to make sure that the unit was flowing the correct CFM target based on your calculations.