actually even the passive house guys started to pull back earth tempering of ventilation air due to costs mainly as you can see in this interview with Dr. Feist:

http://www.passivehouse.us/passiveHouse/Articles_files/EDU%20Jan%2008.PDF

and when those guys say that something is too expensive.....well.....

for a house which is already equiped with an ERV/HRV the benefits are minimal and I'm sure there are better ways to spend those money.

there are fully engineered solution out there like this one from REHAU if anyone really wants to try it:
http://na.rehau.com/files/REHAU_ECOAIR_Brochure_05.10.pdf

adi

If the cost/benefit of earth tube tempering has now been demonstrated unfavorable even in a PassiveHouse, you can bet it's not there for YOUR house.

Some already argue that building to PassiveHouse spec on under-slab insulation is more expensive than making up the difference using photovoltaics on the roof.

Earth tubes may make sense in some applications, but on this particular house getting the infiltration down and R-values up are a far more important place to spend the next round of cash than any of the ventilation system stuff. Taking it with a "What's the next-most-cost-effective project?" approach to staged upgrades usually works out better in both comfort & dollar terms than getting enamored with one technology or another.

one way of making air tempering via earth tubes work (financially speaking) in an efficient house would be to skip the instalation of an HRV/ERV and use an exhaust only ventilation system with bath fans. instead of using exterior passive air inlets for the make up air, one can actually duct the underground intake to supply fresh air. such intakes could be ducted to serve as a source of fresh air as well as a source of make-up air for a clothes dryer or range hood.

during the winter it will heat the air and during the summer it should cool and dehumidify. some of the cost can be recuperated by avoiding the HRV purchase and reduced ducting (only supply ducts). bath fans like panasonic or delta are more efficient than HRV/ERV so ....some additional svings from there.

such a system may work as a passive ventilation system during the summer assuming there is an exit for the air in the upper part of the house (clerestory windows or similar). the hot air should rise and assuming no other windows are open air should be drawn passively thru the underground tubes which would cool and dehumidify it to the point that in some climates there would be no need for AC. by not having to use active ventilation or AC during the summer we can add some more in the savings column. bacterial growth shouldn't be an issue with proper precautions for condensate drainage even less so with speciality piping with antibacterial coating from REHAU.

I have no base for this scenario, I've never seen such system in operation so please don't blame me if it doesn't work as described. I think it should work and taking into consideration that it would probably last the life of the building (which I'm sure is not the case for any HRV/ERV) it may actually prove financially feasable.

am I dreaming with my eyes open? what do you think?

adi

I you add up your trenching & buried plumbing & exhaust ventilator/solar-stack costs and compared it to the cost of an HRV/ERV you may be dissappointed.

At bsmith1051's outdoor dew points and subsoil temp there is ZERO dehumidification going on, but in southern Ontario summer dew points & subsoil temps there would be some.

To do it as exhaust only, what guarantees that the earth tube is the lowest impedance path for incoming air? It would be if the house was built PassiveHouse tight (or maybe even R-2000 tight), but most existing homes depressurizing the house with a solar stack or active ventilation the incoming air would come from numerous alternate (and un-tempered) paths.

HRV/ERV are balanced systems, and do not drive infiltration whether house tests at 20 ACH/50 or 0.20 ACH/50.

Wow, thanks for debating my project for me! :-)

Actually, what I had long considered doing for the intake (did I discuss this yet?) was to have a large concrete or brick structure/wall on the north-side of the house. Ideally I could bury the bottom part so that the whole thing acted like a passive 'cooling' fin, then have all my intake windows pull air from/through it. At the initial/simplest review this should do wonders for cooling my house. Of course, on further reflection I don't know how much 'capacity' this would actually have, e.g. on a hot Santa Ana day where the outside temp hits 90F by 7am and 100F by 8am, and stays around 80F during the night, how much would this passive radiator really be able to cool the air before it's drawn into the house?

P.S. I have never had a problem with excess humidity. There's maybe a week of 60-70 pct humidity here, and the rest of the year it's in the 40-50 pct range, with maybe a month or two of 20-30. (I have a squadron of humidifiers I bring out of storage when it's painfully dry!)

Earth tube systems simply are not adequate if the house is a POS house. Assuming the house is designed to be passive, you can replace the HRV with an earth tube system. The costs are similar. You can have over all energy savings if you have 40 feet of thermal siphon designed into the system. This allows for natural convection so you do not have to mechanically ventilate. The system must be set up as a counter flow system if you have any amount of heating and cooling days to deal with.

Brian

Posted By bsmith1051 on 30 Jun 2011 07:53 PM
Wow, thanks for debating my project for me! :-)

Actually, what I had long considered doing for the intake (did I discuss this yet?) was to have a large concrete or brick structure/wall on the north-side of the house. Ideally I could bury the bottom part so that the whole thing acted like a passive 'cooling' fin, then have all my intake windows pull air from/through it. At the initial/simplest review this should do wonders for cooling my house. Of course, on further reflection I don't know how much 'capacity' this would actually have, e.g. on a hot Santa Ana day where the outside temp hits 90F by 7am and 100F by 8am, and stays around 80F during the night, how much would this passive radiator really be able to cool the air before it's drawn into the house?

P.S. I have never had a problem with excess humidity. There's maybe a week of 60-70 pct humidity here, and the rest of the year it's in the 40-50 pct range, with maybe a month or two of 20-30. (I have a squadron of humidifiers I bring out of storage when it's painfully dry!)

The "percent humidity" is only a relative humidity number, so the outdoor %RH is meaningless without knowing the temperature.  The same air mass will have a different %RH if you heat it up or cool it down.  The absolute humidity of the outdoor air is measured by it's dew-point, which is the temperature at which it's %RH = 100.

This is relevent since to be totally comfortable & healthy at ~75F indoor temps, it's 75F RH needs to be ~60% or less, which is air that has a dew point of ~ 60F.  If the outdoor temp is 90F, with an RH of 45%, which has a dew point of ~ 66F.  Bringing that air down to 75F indoor temps would raise the indoor RH to ~73%, a temp & humidity where mold grows exponentially, and fungal infection risk to humans increases dramatically (not to mention it's damned uncomfortable- sticky.)

According the the Weatherspark data sets the mean summertime dew points in San Diego are in the low 60s F.  S ince your subsoil temps are well above 60F in San Diego an earth tube provides ZERO dehumidification, since it's above the dew point of the outdoors air, thus a very modest amount of mechanical dehumidification would be a good idea in an air-tight high-R house (but it's not a huge load.)  For an average house at average insulation, even the small amount of sensible air-conditioning would keep indoor humidity at comfortable and healthy levels.

See: http://weatherspark.com/#!dashboard;a=USA/CA/San_Diego 

(Set it up to display monthly data- be sure both the dew point and temperature graphs are checked.)

You can't really cool the house with it either, since if you're drawing very large volumes of air through it, it heats the surrounding soil. To be effective as a cooling system  in anything other than a super-insulated house it needs to be on the order 100x bigger than something designed just for tempering the ventilation air.

And until you get the ACH/50 blower-door test number down to at least under 3, odds are a large fraction of the ventilation air would be drawn from somewhere other than the earth-tube- it could be actively HEATING the place in summer by drawing in warmer outdoor.

Things like HRV or earth tube/solar chimney ventilation schemes aren't even the frosting on the cake- they're the sprinkles on the frosting on the cake.  In a leaky uninsulated building you need to bake the cake first- air seal & insulate.  If you can't get the ACH/50 under some very low number (like <<1.5ACH/50), an HRV is going to buy you a lot more than any sort passive or active earth tempered ventilation scheme of literally ANY size. (An uninsulated timber frame house is likely to be over 10 ACH/50 even when the dead-obvious air leaks are treated.) Bake the cake first, figure out what to do for frosting & sprinkles only after you know how it turned out.

@Dana1, you realize that I'm not the one discussing the earth tube? I think that's a very different project from my original 'solar chimney' or other form of passive ventilation. As you alluded to in your response ("since you're drawing very large volumes of air, it heats the surrounding soil") I suspect that my idea of a concrete 'radiator' next to my intake windows would have limited effect. But it might be sufficient on typical summer days, e.g. where the day-time high is 80 F and the overnight low is 65 F.

re humidity, I understand the difference between absolute and relative humidity. And I am not concerned about dehumidification for 99% of the San Diego weather-days.
_________

I've spoken to some local insulation contractors and the basic blown-in for attic and roof are very affordable (maybe $4000 for both, i.e., R-38 attic and R-13 walls). I asked about 'advanced performance' wraps for increasing the walls but none of them had any experience with that.

Yeah, I got that- sorry if I'm in perpetual verbose-mode these days.. ;-)


BTW: In a tight house you'd never need active humidfication in your ZIP code unless you were intentionally over-ventilating the place. Dew points are only rarely below 20F, and with 3+ people in the house breathing & bathing it would keep up if ventilation rates were throttled back to a minimum. (Our January mean dew points are in the low teens, and it only rarely drops below 30% RH indoors, and we're by no means the tightest house on the block.)

If there's room for more than R38 in the attic (which there may not be), there's a long-term economic rationale for up to R50 (3.5" more than what was quoted.) Higher density cellulose will outperform low-density fiberglass at equivalent-R in walls, but even more so in open-blown attics. Air-retardency is as important as the (75F rated) R-value, particularly in retrofits. Low density goods lose significant R performance at the temperature extremes due to convection currents within the fiber layers, whereas high density goods to not. Going with a high-density fiberglass give you a higher center-cavity R, but above R12-13 the thermal bridging of the framing dominates the whole-wall-R and the increased performance of the center-cavity R is largely undercut. "Dense packing" the walls comes at a price premium but cuts the air infiltration measurably more than a low-density "2- hole method" blow, and will never settle or sag.

I think that's a very different project from my original 'solar chimney' or other form of passive ventilation.

Without having put pencil to paper, I think your idea has merit.

In my mind, it would take the form of glazing a vertical channel from top to bottom on the South side of your home. Of course, the "power" of your collector would be limited to the collected area, so you might want to consider how wide you need it to be. Structural issues aside, you could either open up a stud wall or simply remove siding and frame out an additional "chimney" on the side. The bottom opening would be at floor level in the house (or, better yet, the basement) and the top would either vent into the house (for heating) or outside (for cooling). The key is getting the vertical draw long enough and making sure the chimney isn't too restrictive.

Pretty simple. You could just add the glazing to your home as windows, but then you couldn't control the heat gain in Summer by venting it out immediately and you would lose the power of the long vertical draw.

I would abandon the notions of trying to utilize the ground for additional cooling on this.