HRV/ERV systems for fresh air during the winter

[mixedpuppy]

I'm curious if anyone has considered an HRV/ERV system in an Airstream. I'm finding we're tightening things up for the winter to keep warm, and though we always have a fanstastic fan vent cracked about an inch, today I ran one of the fans for an hour to cycle/freshen the air. In our old hot water heated condo we used to keep windows open except on the coldest days, we're missing that fresh air a bit.

http://www.ecohome.net/guide/choosing-between-hrv-erv

[cameront120]

We use these in Passivhaus construction where the building envelope is very tight (less than 0.6 air changes per hour under 50Pa. By comparison, and Airstream is not nearly tight enough to warrant the expense of an HRV. These units are also pretty large, so you would need to figure out where it would go and what you'd be willing to give up (space-wise). When I was living in my Airstream during the winter months, I found that cracking a front and rear vent with the fan going did a pretty good job of expelling condensation while providing fresh air.

[AnnArborBob]

Look at the size of the holes in the floor for the plumbing penetrations and you will quickly realize that Airstreams provide plenty of passive fresh air!

[Protagonist]

Originally Posted by AnnArborBob

Look at the size of the holes in the floor for the plumbing penetrations and you will quickly realize that Airstreams provide plenty of passive fresh air!

Not really, because "passive" ventilation through floor penetrations doesn't actually move air, it only allows equalization of air pressure between inside and outside. With that kind of passive ventilation you don't really get airflow through your floor penetrations; most of your air exchange actually comes from opening and closing your door as you go in or out.

There is one exception— you will get good passive ventilation if you have one window open upwind when there's a good breeze blowing, and another window open downwind so that the wind takes the place of a fan.

But for proper ventilation all the time regardless of wind speed, there's no substitute for an exhaust fan and a cracked-open window.

[Ted S.]

My window is calibrated to ASHRAE 62.2.

[cameront120]

Originally Posted by Ted S.

My window is calibrated to ASHRAE 62.2.

You mean it opens?

[Protagonist]

Originally Posted by Ted S.

My window is calibrated to ASHRAE 62.2.

ASHRAE 62.2 calls for
CFM of continuous forced ventilation = .01×Floor area + 7.5×(#bedrooms+1) for the trailer as a whole;
plus 50 CFM on demand for the bathroom (but ASHRAE 62.2 doesn't make a distinction with regard to the split baths found in some Airstreams so do they count as one or two baths?);
plus 100 CFM on demand for the kitchen.
Open windows count as a 20 CFM credit (reducing required forced ventilation by 20 CFM each) but only one window per exhaust fan can be counted. However, if memory serves ASHRAE 62.2 is non-specific as to the opening size in square inches of an open window, so a cracked-open window theoretically counts the same as a wide-open window with regard to the formulas.

[mixedpuppy]

ASHRAE 62.2 lol

I have found these:

EKO 1.5 HRV Air Exchanger | Venmar
https://foursevenfive.com/product/lunos-e%C2%B2/

The Lunos looks very interesting, sized about right that they could be used inside one of the overhead cabinets, perhaps right above the stove exhaust [in that convenient empty wasted space at either end], maybe a second above the fridge, taking advantage of the fridge vents (probably a bad idea due to propane use?) and avoiding additional exterior modifications.

The eko is larger, but at 10” x 10” x 14.25” it's not out of the question if one was willing to loose some storage under the couch.

[cameront120]

Lunos through wall hrv's are a great little unit but expensive. You already have roof vents available that will likely provide you with more fresh air than the Lunos at far lesser cost.

[mixedpuppy]

Originally Posted by cameront120

Lunos through wall hrv's are a great little unit but expensive. You already have roof vents available that will likely provide you with more fresh air than the Lunos at far lesser cost.

I'm sitting in Capilano right now in the airstream. Other than fresh air, we're keeping pretty confortable, but at -1c turning on the roof vents at this temperature would freeze us out pretty quickly. Thus the consideration for something like Lunos. We can tighten down even the roof vents and still have ventilation that looses much less heat.

[cameront120]

I spent a winter in my Tradewind and found that interior temperatures didn't change a great deal with vents open a crack and a fan going due to the entire trailer being a poor insulator against cold. The entire trailer is 1.5" of fibreglass insulation encased in metal punctured at regular intervals with glass. That insulation offers an insulating value of R5.14 which is effectively reduced to much less than that due to the thermal bridging created by each of the aluminum ribs and the window and vent penetrations. There is nothing in it's manufacture that would be recommended for construction in a cold climate. Even with an HRV, I suspect the trailer will still be cold without relying on the furnace turned up to maximum. You would simply be throwing good money after bad.

[Ted S.]

Originally Posted by Protagonist

ASHRAE 62.2 calls for
CFM of continuous forced ventilation = .01×Floor area + 7.5×(#bedrooms+1) for the trailer as a whole;
plus 50 CFM on demand for the bathroom (but ASHRAE 62.2 doesn't make a distinction with regard to the split baths found in some Airstreams so do they count as one or two baths?);
plus 100 CFM on demand for the kitchen.
Open windows count as a 20 CFM credit (reducing required forced ventilation by 20 CFM each) but only one window per exhaust fan can be counted. However, if memory serves ASHRAE 62.2 is non-specific as to the opening size in square inches of an open window, so a cracked-open window theoretically counts the same as a wide-open window with regard to the formulas.

Wow, that's pretty good. My post was actually a joke, I am a HERS Rater and deal with this standard often. We also build houses but typically install continuous Panasonic bath fans.

I guess I just feel if we start talking HRVs/ERVs were about as far from sleeping under the open sky as possible....

[Protagonist]

Originally Posted by Ted S.

Wow, that's pretty good. My post was actually a joke, I am a HERS Rater and deal with this standard often.

Even as a joke, citing a standard to an engineer is like playing Russian Roulette with a machinegun— you'll get what's coming to you, and how!

[Ted S.]

Originally Posted by Protagonist

Even as a joke, citing a standard to an engineer is like playing Russian Roulette with a machinegun— you'll get what's coming to you, and how!

I take it you are a mechanical engineer?

[Protagonist]

Originally Posted by Ted S.

I take it you are a mechanical engineer?

Used to be. Retired now.