Choosing Between an HRV and ERV
I’ve been pondering and probably over thinking the decision between ERV and HRV. Locally I have available some decent HRV options but would need to order an ERV. HRVs seem to do a bit better in the winter versus an ERV. The main reason I’m considering an ERV is to reduce my the latent load associated with ventilation in the summer which is my homes biggest comfort challenge. With a busy household with lots of cooking and showers it doesn’t seem like I need the ERV’s wintertime humidity recovery (pretty easy to stay at 30% or higher in the winter).
I’m trying to figure out if the latent load delta (between ERV/HRV) is a significant load. I have a dehumidifier 40-50pint that doesn’t have to work too hard to keep my humidity below 60rh% (duty cycle is less than 50%). But I’m not mechanically ventilating at all, and my inside CO2 levels are sometimes higher than 1200ppm. So if it’s nice out, I try and crack a window, but if it’s hot or cold I like to install a balanced ventilation system.
Using this formula (4.5 x CFM x grains removed) / 7000 I get a peak load of just under 3 lbs/hr. This is with an assumed 70cfm ventilation rate and a dehumidification delta of 60grains (120 OA to 60 Indoor grains of moisture per pound of air). Most of the time I would think the load would be 1/3-2/3 of that.
I’m trying to figure out if the dehumidifier could easily handle the extra latent load from ventilation, or if it would be overwhelmed. Also, would an HRV significantly add to the energy consumption because of added dehumidification (versus an ERV)?
I also like that the core of an HRV is a lifetime (of the equipment) part, versus an ERV core that may degrade and require replacement after somewhere between 5-10years.
I live in the Waterloo Region, Ontario, Canada (see attached dew point profile).
My hunch is that if you have a dehumidifier, there probably isn’t a big energy difference annually between an ERV and HRV where I live, even if ERVs might have the edge. But I would love to hear if someone has thought this out, or if there are some online calculators that let you plug in your location and ventilation rates to get some annualized or month by month load data.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Hey, I'm also in Waterloo.
If you have no ventilation now, adding an HRV is going to end up losing you more water in those really cold winter days then I think you suspect. -30C air holds very little moisture. I'd you're holding 30% now, running an HRV or ERV is gonna make it dryer for sure.
We did extensive modeling and found that the ERV was worth it for reduced AC load in the summer months, since it does get humid here near the great lakes.
Thanks, your comment helps me hold out for the ERV. I think the HRV may offer slightly lower total annual energy since we are heating dominated, but the ERV will offer better summer comfort. Dealing with summer time humidity is tougher nut to crack than winter heating. Plus we have a wood stove that does the heavy lifting during the cold months.
Hi Josh,
This would have been an excellent question to ask a few weeks ago on
this episode of the BS* + Beer show, featuring Enrico Bonilauri, co-founder and chief product officer of EMU, and Cramer Silkworth, a licensed engineer and Passive House consultant. They discuss HRVs and ERVs—their differences, mechanics, and applications. I encourage you to listen to it; it may help inform your decision.
> have a dehumidifier 40-50pint ... I get a peak load of just under 3 lbs/hr.
3 lbs/hr = 3 pints/hr = 72 pints/day. So a 40-50 pint dehumidifier isn't enough, even with no other load. Note that on windy, rainy days, latent load due to infiltration can be quite high - so some extra capacity is a good idea.
It would be nice to see more publicly available models for yearly dehumidification cost.