HRV + humidifier vs. ERV in a mostly dry climate Passive House
I’m looking at using a Messana system with radiant ceiling panels which has an HRV+dehumidifier to manage the dew point and an optional humidifier. I want to compare that to a Zehnder ERV/HRV swappable core.
Here’s my assessment:
Constraints:
– Location: Colorado, 7,000′ elevation
– will need to help maintain humidity during cold winter days
– will need to remove humidity on a half dozen warm humid days in the summer
ERV/HRV swappable core:
Pros:
– simpler system for managing humidity
– more efficient at humidifying than an integrated humidifier? (not sure about this)
Cons:
– Doesn’t have fine grain control of humidity
– may require manually changing cores seasonally.
– ERVs are not as efficient as HRVs for heat exchanging.
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Replies
Mike,
An ERV is an appliance used for ventilation. It shouldn't be depended on to maintain indoor humidity levels.
A Passive House shouldn't need a humidifier. By reducing random air leaks through the building envelope, you should have adequate indoor humidity levels during the winter.
Thanks, that’s was what I was wondering.
Martin is probably right, but it depends on the size of the house, the ventilation rate chosen, and the habits and number of inhabitants.
If you start with a Zehnder system, and you guess wrong about which core to use, you can swap cores.
If you start with a Messanna HRV with optional humidifier, and you decide you want to start humidifying, that energy cost will be higher than you would have had using an ERV.
So I vote for Zehnder. You will most likely find a ventilation rate and core that lets you set and forget.
> humidifier?
+1 on "it depends". One person in a largish house in a cold dry climate with a HRV probably will need a humidifier to be comfortable. They don't generate enough moisture without it.
Do not use experience from older, leaky homes and apply it to tight new homes.
yea, I'm wondering too. I spoke with Messana and we can integrate a humidifier after the fact if we find we need it, so we try it out and see.
I looked into this for my remodel, near Denver. Dryness here, esp. in the winter, IS an issue.
I'm not that knowledgeable on the topic, but did investigate quite a bit to find Denver a very unclear geography, climatewise, depending on what mfg I spoke with. Ultimately, I ended up going with the Lunos spot HRVs, and one attractive factor was that they retained around 20-30% of the moisture, so it was a little more in the middle. My remodel is huge and moving slowly, so I can't speak to how well they work yet.
I'm unclear of any climate where an ERV is at a distinct disadvantage compared to an HRV, unless the concern is a few % lower efficiency?
Both ERVs and HRVs will dehumidify a home during cold/dry winters, and will humidify a home in hot/humid summers. The difference is, an ERV will do so less than an HRV since it transfers moisture between the incoming and outgoing airstreams (assuming the home is air conditioned in the summer). More specifically, an ERV will have less of a detrimental effect on your home's interior humidity than an HRV will for a given level of ventilation.
ERVs vary greatly in their ability to transfer moisture, with some being rather poor and others being very efficient. One that I'm familiar with is Panasonic's IntelliBalance 100, which has a Net Moisture Transfer rating of between 70-80% depending on conditions and ventilation rate. This means up to 80% of the moisture in the outgoing airstream can be added to the incoming airstream, significantly reducing the drying effect of running the ventilation system in winter months. It's also very efficient at up to 81% Sensible Recovery Efficiency, which is better than most affordable HRVs which use cross flow cores (Panasonic uses a more efficient counter-flow core).
Remembering a previous thread discussing the Zehnder Comfoair 200 (and deep-diving their PH certification vs. the actual performance specifications), it performs nearly identical to the Panasonic which is to say, very well (it also uses a counter-flow core). It costs a SIGNIFICANT premium, though it offers nice accessories like a ground-loop pre-heating system and their proprietary ductwork if your budget allows.
> an ERV will have less of a detrimental effect on your home's interior humidity
Unless your home is too humid in the Winter (a common problem in tight homes). Then the ERV will have less of a *beneficial* effect.
True, but studies have shown that in average (read: code) construction an ERV is very beneficial in winter time compared to an HRV.
If we're talking tight custom builds then yes, the smaller the home and the larger the family (or the more moisture generated) the more dehumidification is necessary from the ventilation system in winter.
Studies have also shown a reduction of 12% in energy consumption for AC with an ERV in hot humid weather compared to an HRV. This was done at the twin house research center in Ottawa, and researchers guess that it's from the less humid air entering the house through the ventilation system keeping humidity lower and allowing the AC to spend more energy cooling and less pulling moisture from the air (more favorable sensible/latent split).
Makes sense but I’m in Colorado and hot humid nights is the minority. Most of the time it’s dry. So those savings wouldn’t apply to me. Not using a humidifier in winter would be the savings that applies to me.
With the uncertainty of humidity levels in winter, I think the best solution is an HRV with humidifier set to activate at a specific set-point.
Possibly, but humidifiers take a lot of energy to evaporate water. If an ERV could work in a certain home environment all of that energy could be saved.
If we use the Messana HRV and controller, the honest truth is that Messana can adjust radiant cooling even in humid hot nights when we sometimes get a lot of rain in the summer. And they only have an HRV. I figure I’m better off throwing up another solar panel if I need to and guarantee that I’ll have adequate cooling no matter what and have adequate accurately set humidity too.
If someone can assure me that I do not need dehumidification ever in the summer and ERV humification is enough, then I would go with an ERV over Messana’s HRV.