I would suggest duct outlets into the home should be placed such that they do not blow directly where people will be sitting. My personal preference is to locate them along walls to offset the heat loss or gain that occurs due to conduction or leakage through the walls, windows, and doors.

A lady I know had a heating and air duct located up in the ceiling over the couch area of the living room. When the furnace first turned on, a cold air blast would hit the back of your neck until the system heated up. She was very dissatisfied with that duct outlet location.

To bring this back on topic, or sort of...on a new construction build - where in the build would one put the fresh air inlet and stale air outlet/exhaust in the house. i.e. what part of the house?

details:

* 2 story rectangular home over a crawl space, hip roof (no gables)
* furnace room/air handler & ERV/HRV will be in the middle of the first floor - 10' from outside east wall, 22' from outside south wall
* prevailing winds can be from the west or North West, so the south and east walls are the walls that are shielded from the wind the best
* house actually orients appx 20 degrees from true N/W/E/S so the South wall is actually SW, etc...which means the only actual outside wall completely shielded from the wind, is the East wall (which is actually ESE)
* return and supply ducts will go up, out of the air handler, and trunk/branch off into the 2nd floor I-Joist area (24" deep joists) to feed both upstairs and down stairs
* vented crawl space and attic
* Coastal, Northern Calif area, heat only (no AC needed), 40-60" annual rainfall (mostly during Nov-Mar)

I presume the intake and exhaust ducts should also go into the 2nd floor joist area with the inlet and outlets breaching the rim joist, outside wall sheathing, WRB wrap and Hardi siding? Breaching the rim joist (which is even with the 2nd floor) bothers me, since the outside wall is load bearing (the entire roof truss system will load on the outside walls)

I could bring in fresh air from the crawl space but that seems like not very fresh air, even though it will be a vented space?

I could exhaust into the attic?

If I do inlets/outlets in the side of the house, what does that hardware look like? Can anyone give me an example link of what type of hardware is used? I would want to this installed before siding, so I can flex wrap it, etc.

HRV inlet/exhaust ducts are only 8" in diameter. That shouldn't be a structural problem with 24" rim joists, and it meets the holes not to exceed 1/3 joist depth rule, but, of course, your local code would trump.

I wouldn't use the crawlspace or the attic for vents. Put both intake and exhaust on the same side of the building, 6+ feet apart.

Thanks ICF and Jonr. I read through that ERV/RV document and see that it mentioned both Exhaust and Intake on the same wall, as long as it's 6' apart. Should I do this on the wall that is opposite prevailing winds? And thanks for the 8" duct comment, Fantech makes 8" hoods that would work great.

I would put them about 8' up on a wall not on the windward or leewards sides of the prevailing wind. They have high and low pressures respectively and neutral is best for minimizing air in/ex filtration. But I don't know how much difference it would make in $ terms.

The SE facing leeward side (low pressure) is only 10-12' away from where the ERV would need to be. The South West side of the home is a minimum of 22' away. And I'm not sure I can get both inlet and exhaust on that side anyway, as there is an open stairwell butt up against most of that side of the house. So there is very little floor joist space to get to that side of the house. Certainly not enough space to get both, but I could get one of the hoods to that side.

But I thought I remember reading somewhere that 22' is a bit far away and that is is a good idea to be less than 15' from ERV handler to hood? Perhaps I misread that?

FWIW the best I've found so far in an ERV is UltimateAir RecoupAerator 200DX

Claims:
•96 percent heat recovery rate
•MERV 12 filtration
•Automatically balances air flow and pressure
•Separate Exhaust and ECM Fresh Air fans

Plus they have a water-air exchanger and pump for pre-heating (no defrost needed) the incoming air (e.g. use underslab PEX as simple geo loop) and for pre-cooling \ dehumidifying in summer.

Does the UltimateAir have a damper door that closes when the unit is turned off to prevent outside air from entering or inside air from leaving?

I don't have possession of the UltimateAir yet, so I don't know. It may have an internal damper, but I doubt it. Based on the hardware pics I saw, I didn't see any external damper included which makes sense as there are just so may alternate configurations. AFAIK, the 'normal' way is to just have a spring-based flap at the air exhaust and intake because you want to keep bugs and birds out anyway.

I plan to pull outside air thru a 200' ABS earth tube. Warms cold winter air & cools summer air.

It may also grow mold in the summer. Some type of system that exposed it to several hours of highly dehumidified air every day might stop it. A water loop and an air coil is probably easier.

as jonr said, that has been an issue with a number of Passive House enthusiasts who have tried it. It is not an easy issue to resolve. Kat Klingenberg, the founder and director of PHIUS has found she needs to clean her's out annually. How you would go about cleaning a 200' underground tube is way beyond me.

Zone 5 & dry in Colorado. Don't mold also require something to eat?

One thing with the Ultimate Air is that it does NOT have a by-pass mode. I really think it is a huge benefit to have a by-pass mode. In the summer when the home interior gets hot and you have a cool (non humid) summer night. That is when you DO NOT want to condition the incoming air. The heat exchange will work against you because it will heat the incoming air, which you don't want in the aforementioned scenario.

One thing with the Ultimate Air is that it does NOT have a by-pass mode.

I believe it does. It's called EconoCool Mode.

Posted By buffalobillpatrick on 05 Nov 2013 03:01 PM
Zone 5 & dry in Colorado. Don't mold also require something to eat?

I am also interested in the earth tube tempering system. There have been a number of failures of this type of system. It seems that success has been claimed when earth tubes were covered by 4' wide foam and some type of system to keep the ground surrounding the tubes dry. Dry is good. Cleaning? Could you spray chlorine mist into the system to keep things from growing?

some type of system to keep the ground surrounding the tubes dry. Dry is good. Cleaning?

When it comes to the soil, wet is good (better thermal conductivity). You might be able to use a pull line to drag something through that would remove the accumulated dust. But I think that you would still have to dehumidify it for a few hours/day to completely stop mold.

Could you spray chlorine mist into the system to keep things from growing?

Wouldn't that put the inhabitants who breathed the air at some risk? Chlorine is toxic.

Posted By jonr on 24 Nov 2013 09:35 AM

some type of system to keep the ground surrounding the tubes dry. Dry is good. Cleaning?

When it comes to the soil, wet is good (better thermal conductivity). You might be able to use a pull line to drag something through that would remove the accumulated dust. But I think that you would still have to dehumidify it for a few hours/day to completely stop mold.

Yes thermal conductivity works better with wet soil but so does mold. A longer run or more tubes can make up for the reduced thermal conductivity A filter should be employed to reduce dust. How many people clean out their house ductwork yearly?

Posted By ICFHybrid on 24 Nov 2013 09:57 AM

Could you spray chlorine mist into the system to keep things from growing?

Wouldn't that put the inhabitants who breathed the air at some risk? Chlorine is toxic.

I was thinking once or twice a year, spring/fall to do a chlorine mist purge. I've spent many hours in public swimming pools where I have breathed chlorine laden air and bathed in chlorine pool water to excess. .