My wife and I finally have plans for our ICF home.  Slab on grade,  wood stove heated(inside), somewhat passive solar home.  Located in south central Wisconsin.  Currently looking for HVAC subcontractors.
We have met with two different contractors.  One said "You want an HRV.  ERV's are for down south."  Another said "you want an ERV, HRV's are for down south."  Our ICF builder said "yes, you want one either will do, I go for the cheaper." Can anyone help?  What is the real difference, what is best for southern WI?

Thanks,
Crawfish

The difference is the ERV transfers water vapor from the more humid air stream to the less humid one along with the heat. Down south humidity is a problem in the summer. There is a fair amount of load on the a/c system just from the dehumidification part of the a/c process. Its referred to as the latent heat load. By transferring the humidity in the incoming air stream to the exhaust air stream less energy is consumed by the a/c system. That's why it's called an ERV and not just an HRV. In northern climates humidity in the incoming air is generally low and the humidity in the exhaust air, from the living space, is higher. In an ICF home the humidity can climb uncomfortably high because it's so air tight, so an HRV may be the better choice. It'll send the humidity outside. On the other hand, if you have a fair amount of air change, and are not generating a lot of humidity in the house, an ERV might be better because you would keep the air in the house more humid. 40 to 60% is about the most comfortable range, especially during the heating season. Generally though, in the northern climate the HRV is the preferred unit.

But in my now almost ready to move in ICF house I have an ERV. The only reason is because the unit I installed, an Ultimate Air 200DX, only comes in an ERV version. The 200DX is the only ERV/HRV on the market that I could find that offers an economizer mode. When its Econo Cool mode is turned on, if the outdoor temp is less than something like 65°, the heat exchange wheel stops and cool air is brought into the house. I will be using this feature to help cool the house at night, reducing the load on the a/c. A year from now I'll be able to tell you better how my system works, and if an ERV in a northern climate is good or not!

I was always under the impression the difference was based on what heating zone you are in. Wisconsin is BRRR so I would think HRV is the way to go, I'm in Napa which is AHHH and I see ERV's go in here.

I guess heating zone would be the better way to define the areas where an HRV or ERV would normally be used. The OP, and my response, use northern and southern to mean cold zone and hot zone!!

This explains it well. It sounds like in our neck-of-the-woods an ERV would not hurt, just cost more. 

ERV would add moisture to the incoming air in the winter, but winter air is so dry anyway I don't think it would matter. Moisture in the winter can cause condensation and frost on windows.

We are using a Renewaire ERV for air exchange and humidity control, but the climate here in western washington is much milder. Its amazing just how air-tight an icf building can be, so plan on having controls for air exchange every hour year round.

Buildyourcastle,
You said "HRV is definitely for cold climate and cost a little more but is more efficient and durable." Do you mean ERV? If not what is HRV more expensive, efficient and durable than?

Thanks ICFconstruction, yes that was a confusing sentence. HRV is only for cold weather climate and maybe outdated in most regions.
ERVs are superior because of the humidity removal they have the ability to work year round, therefore supplying semi-constant fresh air which you need in an icf home anyways because of the tight envelope. You will not need a condensation drain either.
Durablity is less of a factor, HRV aluminum cores are more durable but that would not matter much as long as you mounted your ERV in a space that was above freezing and maintain the fiiter.

ERVs ADD humidity to the incoming air in winter- not necessarily a good thing in a house tight enough to NEED active ventilation in winter, since for tight houses in the heating season you're trying to REMOVE rather the preserve the humidity of the indoor air. (In leaky houses the air will normally be drier in winter, with cooking/bathing/exhaling humidity will build up indoors no matter what the outdoor relative-humidity is.)

ERVs REMOVE humidity from the incoming air in summer- generally a good thing any humid climate zone with a significant air-conditioning load since the humidity represents a latent load, impacting comfort level (and mold-growth potential.)

Generally the ERV differentiation is only significant in a humid-climates (in the US, generally the eastern-half), where there are significant air-condtioning loads (measured in annual cooling degree-days or CDD.) If you're in a humid climate with ~1000CDD or more, go for the ERV. The rest will do just fine with HRVs.

In dry climates (hot or cold) going with an ERV instead of an HRV would make an indistinguishable difference on creature-comfort (or AC load.)

A quick & dirty algorithm to get a handle on what YOU might need, find your nearest city here:

http://ggweather.com/ccd/nrmcdd.htm

Under annual ~1000CDD?
HRV- there's little value-added for going ERV.

Over 1000CDD?
Find yourself on this map:

http://www.wrcc.dri.edu/pcpn/us_precip.gif

If you're in any shade of green/blue/purple (or maybe the palest of yellow) with 1000CDD of cooling load, definitely go with an ERV.

Otherwise, HRV is probably gonna be just fine...

If the nearest city on the list is more than 1000' of altitude different from your actual location you'll have to finesse it a bit- higher will be definitely cooler. (But if you live in the mountains you probably already know this.) Similarly, if you live someplace where most of the precipation happens in winter you can probably skip the ERV, or in someplace susceptible to weeks of hot-summer monsoon events despite generally dry climate (eg Tucson) you may want to at least consider an ERV for those 2 weeks/year of utter hell from daily 100F downpours (even if an HRV is fine the other 50 weeks of the year.)

IMHO ERVs have been somewhat oversold- they're not necessarily a superior product to HRVs for much of the US. (But in the Gulf Coast states or just about anywhere in SC/GA, or the Atlantic seaboard from NYC on down, they're a better way to go.)

My understanding is that ERVs add or remove humidity from the incoming air.

This is important for one or two reasons.

In the winter (if applicable) if you draw in dry air all the humidifying that you have done will go out the window (or out the pipe). Many people with HRV complain the house becomes too dry in the winter.

In the summer (always applicable for the majority of the continent) if you draw in warm moist air you’re A/C will need to work harder to dehumidify the fresh air. Most people turn off the HRV in the summer… what’s the point of having one if you don’t use it?


In a polystyrene ICF home, the humidity regulation is even more important since the house is so vapour tight (and air tight).

Really?  If so, sounds like they're either over-ventilating, or live in climate zones colder than found anywhere the lower 48.

Vapor-tight houses in heating dominated climates in the US usually become humidity traps, and complaints tend to center more about condensation/frost/mold on the windows than ultra-dryness.  HRVs are a means of dumping some humidity with a minimum loss of sensible-heat.  If operating the ventilation at the minimum necessary air changes/hour, the amount of humidity recovered by an ERV just isn't very much, making it hard to rationalize the additional expense for those climates. The purchased energy saved is close to nil- when higher humidity is desirable it can be introduced cheaply & efficiently by other methods.  Controlling the HRV with a de-humidistat can be a wintertime solution to weeping-windows in humidity-trap homes without over-ventilating to the point of discomfort.

ERVs make most sense (and save more energy) when applied to reducing latent loads from the incoming air in hot-humid regions.  Lowering the load on the de-humidifiers or AC has real payback, even if ERVs can't be counted on to de-humidify sufficiently to be the sole method of dehumidification for the entire season.  (In less-muggy climates summer ventilation via open windows renders the ERV/HRV question  moot.)

Correct - the dry winter air complaining is a function of colder climates. This with the HRV.

I also agree with your comment regarding vapour tight houses causing condensation issues. This is without HRV or ERV. This is from the 50% RH air cooling at the window surface and condensing

I am sure you know this, but I thought I would elaborate so others know and so that you know that I know.

In the winter, as the HRV transfers heat from moist inside air to the dry outside air, The inside air cools (without losing the moisture) and RH goes up and can cause condensation issue in the outgoing flow pipe. The incoming cold/dry air heats up (without gaining moisture) and the RH goes down creating "dryer" air. This what I assume you mean by dumping humidity (i.e heating the air without adding moisture). That why we turn on the humidifier in the winter and the dehumidifier in the summer. I guess the people that complain about dry air in winter with an HRV were not informed properly that they need separate humidity control.

Your comment regarding potential overventilation is interesting. Do you have any idea why would they be overventlaiting to the point of discomfort? They like the fresher air in a tight home? I am curious because either they "overventilating" because they don't know how to operate the HRV, or they like it, but don't like the resulting lack of humidity. There may be some comfort issue here that comes into play that is not related to just cost and energy savings. Is there a set of circumstances that make ERV more desirable - because it creates a more comfortable space, requires less human ajustment and allows the people to live comfortably in their homes and not think about heating, cooling, humidty control, opening windows, etc...all perhaps making it worth the extra money. Just curious if there is a convenience factor to the ERV.