erv vs hrv in Alaska

[anrl@uaa]

We are in the process of building a tight, energy efficient house in Palmer, AK (40 mi N of Anchorage) and are trying to decide on ventilation systems. We have gotten 2 bids for systems, both from recommended local outfits, one recommending a Honeywell HR200 HRV and the other a Venmar Duo 1.9 ERV. I have heard different opinions on ERV's in cold climates, with many comments on discussion groups saying that ERV's are less desirable and are vulnerable to icing and consequent damage to the exchange element (more fragile than the HRV plate); others say that problem has been addressed and that they are more efficient than HRV's and that their ability to transfer humidity as well as heat is a plus in dry winter air. Does anyone there have experience with ERV's in general and how effective they would be in cold climates? Does anyone have experience with these two units in particular? Thanks-

[Dancing Dan]

We're in the middle of trying to figure the same thing out. Our climate is not as brutal as yours but we have the same questions. I know the guy with the best reputation locally uses ERV's, and his logic is that you're recapturing the moisture in the exhaust air. I think he uses an American Standard.

[anrl@uaa]

The Venmar guy said the same thing. Sounds like it might not be a problem unless you are getting prolonged periods of cold (say -40 for several weeks), as in Fairbanks. We get the occasional bout of -40, but rarely for more than a day or two at a time. Of more concern was the comment someone made that they may not filter out contaminants and odors as well as an HRV.

[Riversong]

In a tight house, the primary indoor environment problem is excess humidity. Other than the marginal advantage of reclaiming part of the latent heat of vaporization, why would you want to recapture the moisture, particulary if there were any ancillary problems such as freezing associated with it?

[ThingOfBeauty]

I don't live in a climate like any of y'all, but my 2 cents it it depends on whether you want to keep your indoor level of humidity.
An ERV will get the outside air that's coming in closer to whatever humidity level you have inside already.
Around here our old-fashioned leaky houses are very dry in winter, and we spend effort to humidify the air. So, we would want the dry air coming in to be humidified by the moist exhaust air stream--we would pick an ERV. (For us in humid summertime, we also want the reverse to happen, so ERV works good for a leaky, mixed climate house.)
But, if you build a tight house, you will have excess humidity during the winter, so using an HRV and just getting rid of the excess humidity makes more sense.
It's definitely a change from the typical house that gets so dry inside during the winter season.

[Stacey]

HRV's are very common in Anchorage and the Valley and the Kenai Penn., especially when you have infloor heat. You need to get rid of the moisture sometimes or sometimes add moisture. The HRV will take care of that. Also the HRV will take the dust out, and Palmer is about the dustiest place on earth. So if you are on infloor heat, go for the HRV, then you can set your moisture level. Make sure to clean the outside intake screens. Sometimes bugs can fill up the screens every couple of days. Make sure you get rid of the moisture coming out of the system into your drainfield. It's a no brainer for me. Just make sure you run your ducts correctly if you are doing it yourself.

[Riversong]

So if you are on infloor heat, go for the HRV, then you can set your moisture level.

What does an HRV have to do with infloor radiant heat? The need for indoor air exchange is independent of the heat source. And you can't "set your moisture level" with an HRV, only the air-change rate. Any change in humidity is a secondary consequence.

Make sure to clean the outside intake screens. Sometimes bugs can fill up the screens every couple of days.

And what's the point of installing a mechanical system that requires maintenance every two days?

Just make sure you run your ducts correctly if you are doing it yourself.

What is the "correct" way to install ducts?

[frenchie]

You're really knowledgeable, and clever, and I really hope you stick around. But ease up on folks a bit, willya?

What does an HRV have to do with infloor radiant heat? The need for indoor air exchange is independent of the heat source.

When the usual alternative is forced air & an inline humidifier? Think about it.

Any change in humidity is a secondary consequence.

Last week, I had to spend a few hours in my shop, and my heaters are on the jobsite, so I turned on all my halogen worklamps. The heat was a secondary consequence, but it still felt pretty nice.

[Riversong]

You're really knowledgeable, and clever, and I really hope you stick around. But ease up on folks a bit, willya?

If by "ease up", you mean stop asking questions to get people to clarify what they're saying, or to stop challenging ill-informed building practices - then that ain't gonna happen.

If this is a professional forum, then we should all welcome hard-headed questions and well-justified answers.

[frenchie]

If by "ease up", you mean stop asking questions to get people to clarify what they're saying, or to stop challenging ill-informed building practices - then that ain't gonna happen.

No, that's not what I meant...

[BillHartmann]

[q]When the usual alternative is forced air & an inline humidifier? Think about it.[/q]

Force air heating system does not require any more or any less humidification than hot water heating systems, either radiant or baseboard or radiator.

Any differences are do to construction details of the envelope.

[frenchie]

Typical forced air setup, with an inline humidifier, offers you a means to control the humidity.

A radiant floor, doesn't.

An air-exchange setup, whether HRV or ERV, with all the attendant ducting, would create a means to condition the air, in the absense of any other means...

That's what I understood Stacey to mean, anyways.



Then again, I though her meaning was fairly obvious - and I'm starting to realize that isn't so, it was only obvious to me.

[Riversong]

Typical forced air setup, with an inline humidifier, offers you a means to control the humidity.

No, it offers a means to increase humidity, but not to decrease it - which is the need in a tight house with a well-sealed and well-balanced FHA system or any other type of heat.

[frenchie]

typical = tight house? well-sealed and well-balanced FHA?

...since when?

[BillHartmann]

typical = tight house? well-sealed and well-balanced FHA?

...since when?

Since always.

Lets start with a build a large room with steel panels welded together so that the room his hermetically sealed.

Then put an opening in each the left side and the right side, say 12 sq in, to represent leaks in the envelope.

And in that room we will had people, pets and plants. All 3 release moisture into the air. Then you have the people cooking and bathing which also adds moisture in the air.

The only way that the moisture level is reduced is by outside air coming in at a lower absolutle moisture level.

So far we have not given any way to heat this space.

In one we will but not water pipes under the floor. But nothing inside the space.

In the other we will put a flame on one of the walls. How one might thing claim that be an other form of radiant heat. So lets build a wall in front of it with some vents. And a small fan to circulate the air. Now this is force warm air heating with the wall being the heat exchanger.

That system won't have any more or less opening in the wall or pressure diferential to drive air in or out of the leaks than the version with hot water pipes under the floor.

how lets convert the last case to a more conventional FWA system by cutting two holes in the steel walls and making steel ducts connected to a heat excahnger and fan. With everthing welded and hermtically sealed.

Again no changes.

BUT replace that sealed duct work with the more common sections of sheet metal and flexable ducts with leaking joints. Then instead of continuous ducts to the cold air return just pan the joists and cut hole in the subfloor at the stud bays for the returns.

So now the blower is not only pulling air out of the room, but also from the unconditioned space. But blowing all of it back into the room. So the room is pressurized and the extra pressure is forcing more air out of the room. And that air is being replaced by the drying air being sucked into the leaky ducts.

So the moisture level in the room is reduced.

But that is because of leaking construction in the HVAC system not, because it is FWA rather than radiant.