ERV or HRV?

Paul Pollets

Jed, I'm told that code in Canada requires either an HRV or ERV, depending upon location, for new construction.

Here's a quote from the US Energy website:

"The core the heat exchanger in an HRV or ERV is usually made of aluminum, resin-impregnated paper, plastic, or a combination of these materials. Plastic and aluminum cores are relatively good conductors of heat and prevent the transfer of water vapor and contaminants in the exhaust air into the incoming air. They are also more durable relative to other materials.

Transferring a little water vapor across the core is often desirable because in extremely cold weather [consistently below 20°F (-7°C)], the water vapor from the exhaust air of an HRV can freeze the core and the exhaust vent to the outdoors. If this should happen, the ventilation rate is severely reduced. HRVs are also known for drying the house air to uncomfortable levels in climates where winter can last months.

Since an ERV transfers some of the moisture from the exhaust air to the usually less humid incoming winter air, the humidity of the house air stays more constant. This also keeps the heat exchanger core warmer, and so helps minimize problems with freezing. Some systems also have an electric heating element for defrosting the exterior vent to minimize freezing in that location..."



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Steven_4

Which is better and why?

New construction in central Vermont with long winters and a tight house. We are trying to figure out which system would work better in our climate and why? Can we use either of these to replace the fans in the bathrooms or would this clog the system? Any companies to look into?

Constantin

Conventional wisdom says...

... that an HRV is more appropriate in your climate. However, when you start talking to experts like Jerry Scharf, it becomes apparent that there is more to the whole question than simple climate.

For example, the Stirling ERVs made by Ultimateair.com are probably the highest efficiency ERVs that one can buy. The owner of the company thinks that the performance of his energy recovery wheel works just as well during the heating as well as the cooling season.

For a more conventional approach, look into using a Lifebreath DCS unit or a TRV. I see no reason that they cannot be used to exhaust bathrooms - I am running mine out of my bathrooms. If you use a occupancy sensor like the ones from Leviton (+ a powerpack), you can ensure that the HRV kicks into high gear whenever the room is occupied. KISS...

Steven_4

difference?

What will I get out of the stirling ERV that I won't with the Lifebreath HRV? Stirling recommends that you still use a separate fan in the bathroom. Why is that?

Weezbo

Think about it.....you got time...

Constantin

It is my understanding...

... that HRV/ERV manufacturers consider bathroom and kitchen air to be more contaminated than the air found in the rest of the house. It is certainly true that a bathroom will be among the most dusty of places, since it's where we lose most of our dead skin. That said, it is precisely because of these attributes that I exhaust my fan out of the bathroom.

Kitchen hoods are a no-no, naturally, unless you find a way to degrease the air 100%.

Another possible ding in the bathroom department is the humidity of the air being exhusted. Perhaps this will lead to long term reliability issues. FWIW, I've elected to have the fans running on slow speed 100% of the time and only have them kick into high gear during bathroom occupancy. As such, I'd like to think that the HRV/ERV I use will "dry out", particularly when 3 bathrooms feed into the HRV/ERV and typically only one will be occupied.

don_133

My thoughts

is the reason for the extra exhaust fan and the bath is strictly has Constantin mention..to be able to have control
and remove the air back to the erv/hrv at a faster rate.

Most the ones I have seen comes with only one selector switch..so which bathroom do you put it in? Also you have to
keep in mind,that you want and hope to exhaust the same amount of air as you put in,not easy to do with a psc motor.

Personally I like what erv/hrv can do for the home,however untill they make a variable speed airhandler that can be
interlock to all exhaust fans and equipment and could ramp the motor up or down has needed,it still a guessing game as to rather you have the home in a negative or a positive pressure.

Constantin

Oh, it can be done...

... I took the KISS route where a single Leviton ceiling occupancy sensor in every bathroom is powered by a Leviton Power-Pack (these units usually switch on lights). Up to three occupancy sensors can be powered by a power-pack, and the power-pack has a built-in 120VAC-rated relay with which to play with. In my case, I'm using it to create a dry contact.

Once any bathroom is occupied, the Powerpack makes a dry-contact at the HRV high-speed terminal, kicking it into high gear. As every occupancy sensor has a user-selectable delay, I can "program" them to keep the HRVs going for up to 20 minutes after the sensor last detected movement in the room. Kudos to Nutech tech support for suggesting I go down this route...

A slightly more sophisticated approach can be had via the Conservation Technology occupant sensing ventilation system. Same idea, except that the inlets have louvres so that the exhausting is maximized in the rooms that are presently occupied. As humidity as well as occupancy trigger the high-speed response, this is pretty ideal for bathrooms and HRV's as best as I can tell. Unfortunately, I only became aware of this system long after the drywall in the rooms was up, so no go there!

A simple ladder-logic and the like would allow you to program different response speeds (and combinations) into the HRV based on which sensor is calling for flow. IIRC, the Lifebreath TRV/DCS series has 5 different wire terminals to select different fan speeds, so the logic would have to interface with them to achieve the desired speed. However, I would argue that the conservation technology system is probably your best bet, allowing quick dehumidification and then a return to loafing / IAQ maintenance.

Paul Pollets

HRV's & Bath exhausts

I always put a return from the HRV in baths + the required exhaust fan. The low CFM of the HRV will constantly remove humidity, and the exhaust fan will quickly remove odors. Since fans are on 10 min or less, it makes good design sense to duct in a return from the HRV.

ERV's are generally used in colder climates. See product specs for use in your climate. I've had excellent results using the LifeBreth products over the past 12 years. Their product line is comprehensive and support is tops.

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Jed_2

fUNNY

I always thought it was the other way around, Paul. ERV's have enthalpic cores, wheareas HRV's usually have aluminum cores. Isn't it the enthalpic cores which handle humidity!!? Generally accepted "rule Of thumb": If the heating requirements are more than the cooling requirements;HRV is called for. Of course, there is always the possibility of exceptions.

While not the highest rated units for effeciveness, Greentek(Imperial) makes units with optional controls which provide up to 8 or nine series capable add-ons for "timer overides" for specific areas when boost is required. Fans are all variable speed.

Jed

Jed_2

Paul

I need to explore this more. Most HRV's include freeze protection(basically, fan speed. They do need condensate drains). Filters need to be changed regularly anyway. Untits are typically located in a conditioned environment(they are with the Canadian Homes shipped to the Northeast). There are increasingly more homes requiring air exhange around here. I thought I had had it pinned down, but you bring up some good points for discussion. Maybe this could be continued with further Professional input. Looking at weather data for the northeast, I find some rather high RH #'s. Of course, air temp will affect that. ERV's, as I understand, will transfer the higher latent load to the lower. A bit confusing.

Jed

rb_6

HRV/ERV Listing

You might find both these links interesting

Oregon Department of Energy - Conservation Division HRV/ERV Listing



HRV or ERV?


RB

jerry scharf_3

late to this thread

I really like the Stirling ERV, as I've said before. I own one, but haven't gotten any data collection off it yet to see if it lives up to it's billing.

Lot's of comments:

In a tight house, the general problems are increased volitile organic polution, odors and moisture. Unlike the houses of old, the problem with tight houses is too much moisture.

There are a bunch of ways to tackle each problem, depending on the specifics (including medical sensitivities) of the people and house.

For volitile organics, you can use dilution (HRV/ERV), adsorption (carbon filers) or photochemical reactions (UV light, catalyzed UV reactions) among others. For the general situaion, dilution is effective and the simplest approach.

For odors, you can use most of the same techniques as for volitile organics, but the effectiveness is different. Plants can be suprisingly effective in people's reactions to odors, though I've never seen any mechanism to explain this.

Moisture is more dynamic, and requires careful ventilation. Whenever you read about mold problems, you're really talking about moisture problems.

You asked why you don't want an ERV for the bathroom. The reason is simple, you want to get rid of the moisture, and the ERV will feed the moisture back. Almost as bad as those ads for "saving he heat" from the dryer. Kitchens have the oil problem plus they make lots of moisture that also needs to be gotten rid of.

Thn there is the map that Robert posted a link to from Fantech. There is a fundamental assumption behind these that I no longer consider to be true. That is that the trasfer of sensible heat is always better in an HRV than ERV. With that "truth", the map makes complete sense. In places where there is maximum indoor/outdoor air temp difference, the maximum sensible heat transfer is wanted. The ERV section is based on the idea that humidity reduction is a key part of air conditioning, and without an ERV this is lost.

The Stirling unit breaks those rules, having higher sensible heat transfer than the better crossing laminar flow HRVs. It's not smoke and mirrors.

One minor downside to HRVs is that it's easy for them to have condensation. They have to have drains plumbed in, and this is another opportunity for mold to grow. Since ERVs are exchanging the moisture, the heat and humidity move at the same time and condensation is not a problem.

I think I've added my $.02 to several things. If there is anything else that I can help with, please ask more.

jerry

Craig Bergman

We always...

tie all bath fans to simple SPST relays mounted in a box
by the unit. When the bath light goes on it kicks the unit into high speed.

Craig

Paul Pollets

Good Stuff!!

A good approach to be sure. See you at Wetstock...Paul

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Cliff Brady

Conserv ERV

I haven't heard any talk about the Conserv ERV line here. It looks to have the best ratings I have seen summer and winter humidity control. The web site has some interesting articles and residential and commercial ERVs as well.

http://www.daisanalytic.com/conserv.htm

jerry scharf_3

not much meat there

Cliff,

I had not heard of them, they say the heat exchanger is their own special sauce. But there is no information about them at all.

Their numbers aren't up their with the stirling/ultimateair product, mid 70s for the core vs low 90s for the system.

The thing that I don't like about all these cores compared to the stirling is that the core is not designed for replacement. One has to assume that they have a finite life due to particulates sticking to the surface. They have longer life than the enthalpy wheels, but it's still finite. The nice thing about the stirling product is that they address it head on, the fabric is replacable for a modest cost with few tools, and the ECM motors adjust torque to provide constant air flow as the media loads up.

sorry to sound like an ad, but I just haven't seen anything out there that comes close to the stirling unit. The only down side is that the cost is higher.

jerry