All the forums seem to go directly to the complicated, (heat pumps, HRU, HRV, HVAC, etc). Can't I simply use cool air in the large crawl space for the few days I might need some cooling in N. Ca. ? Anticipating a very tight house. 4,000 sq ft home is new construction w/ TF System. Thanks, K52

Not sure how your climate would affect this situation, but here in the upper south, the humidity levels in most crawlspaces would make your suggestion a bad idea. In addition to increased humidity, the air in most crawls tends to stagnate, even with the 'crawlspace vents' fully open. This increases the chance of mold spores being present and being drawn into your living space. I certainly would not recommend this plan.

I'm not an expert on these systems but I do remember many years back reading an article on a house that was built in Lake Tahoe (if I remember correctly) that incorporated the crawlspace as a temperature regulator.  I believe it was built in the side of a hill so they had a larger amount of air available with more earth to moderate the temperature.  With the normally drier air in the mountains of California this might be a viable approach.  I think the article was in Sunset magazine.  If you did some research you might be able to track it down.  Have you talked to any builders or HVAC people in your neck of the woods about this idea?  Looking at Wes's comments that's a good point about the stagnant air.  Maybe if you pursued this option a crawlspace that has been sealed with plastic or other vapor barrier might be something to consider although if it's in a dry environment to begin with that might not be so critical.

Thanks for the help thus far. No I havent talked to a HVAC installer yet, Not sure they think of anything but the the more complicated. Perhaps I'll look for one who will think of horses before zebras..! ICF is fairly "new" out here so most HVAC's won't accurately calculate the loads. Moisture isn't a problem in the SF Bay area. Yes the crawl space will be fully vented according to the codes. K52

conditioned crawlspaces have been done for years,  in hot and cold climates. You need to insulate the walls and at least install 2 layers of 6 mil vapor barrier over the earth and no open vents, the walls need to be tightly sealed

I guess I'm not making the question clear. I DON'T want to condition the crawl space as it "automatically" remains cool. (thats assuming that conditioning means heating or cooling the space and insulating it so that it is "conditioned"). I simply want to know if there is a fan or distribution system that is efficient amd makes sence for moving existing air from below to the conditioned first floor spaces. The additional concern is that this system will allow conditioned room temps to escape and will not, in the long run, be a good and/or energy savings idea? k52

K52;

not a good idea, since the air quality in a crawl space can contain dampness, critters  and mold, you would be pushing that air into your living space.
 You want to always draw supply air from a known good source

How about instead of using the crawlspace air directly, run uninsulated sheet metal ductwork in the crawlspace and draw fresh air from outside the foundation and let the crawlspace air cool the ductwork which will condition/cool your fresh ducted air. A simple inline blower fan would make the air move.

Thinking more on the subject, isolating the crawlspace air in some fashion whether with the sheet metal ducting as mentioned above or by some other manner is going to important for the reasons enumerated above (possible mold, critters, etc.).  I think if you do isolate it, and probably even if you don't, you're going to find the amount of cool air that will be required to make a difference in the house is going to be greater than the amount that will be able to be generated in the proposed fashion.  Even if you would just bring in the cooler air directly from the crawlspace, as first suggested, once that air had been brought in the air to replace it would be at the temperature of the air from outside the crawlspace.  One thing I've noticed from reading on the ground source heat pumps is how many feet of the pipe that brings the fluid back to the desired base temperature is required in order for the system to work.

It's easy for us to forget that there are actually a few places in the world where conditioned air isn't really necessary, for example some spots in California. Having said that, I would think the worst air you could use would be from your crawl space (when I lived in San Diego skunks used to find their way under the house!).

Are you in the design stage k52? Are you oriented and shaded properly enough for simple cross ventilation of your windows to be enough?

past design stage except for perhaps pushing air from crawsl space into floor or wall vents. I guess if air is really of inferior quallity I'll forget the idea, I know, from my present house, that a lot of nice cool air is just behind the lower floors wall and the lower floor is much cooler than the main/upper floor. I anticipate a lot of cool air just siitting under the new home waiting to be used. (without skunks of course) thanks K52

I'Il reply to my own forum. I think the best idea so far is to use an uninsulated duct that snakes around under the house. This duct takes air from outside and distributes that air through vents to the interior. As the warmer air snakes through the ducts under the house it is cooled because the ducts are cooled by the air existing under the house.

The problem is ?........If a lot of air is pulled from outside that air will probably heat the ducts faster than they can be cooled by the cold air around them. Oh well it was a nice idea I thought. K52

Have you looked into earth tubes for pre-conditioning your incoming air?

Not that I am a professional, but it would seem to me that an air to air heat (or cool) exchanger would be the ticket.  They are efficient, can dehumidify the warm air being cooled.