That Orion fan looks really nice--only downside is the higher price. Factors I'd use in deciding would be to estimate the value of the electricity saved based on expected hours of operation, or to also factor in my confidence that the design using that fan is the final design vs. wanting to change it after a year of experience.

Another option to consider would be a fan with speed control capability. The Orion catalog indicates that that capability is available but it might be a special order; I don't see it in the digikey catalog. If you look at the power vs. CFM for the different models in that size, the CFM/W is MUCH better for the lower speed models. Similarly, if you ran the 550 CFM rated model at 275 CFM, it would require less than half the power. So you'd use less energy running it for 8 hour at 275 CFM than running it at 550 CFM cycling on and off, on half the time and off half the time. The variable speed option might also let you increase the CFM is you decide the 550 isn't enough. So it's a way to hedge your bets if you aren't 100% sure of the design.

To take full advantage of the variable speed operation, you'd want automatic control of fan speed based on temperatures. But even if you use a simple on/off control, you might find it valuable to be able to adjust it in the intial set-up and tuning of the system to leave fixed for the rest of the life of the system, or perhaps to make noise/power/performance adjustments on a seasonal or even daily basis (e.g. sunny day when you are not home = high speed to harvest heat without caring about noise).

These are great thoughts...I hadn't thought much about the variable speed capability, but what you say has me thinking.  I think in the whole scheme of things the price difference isn't all the great...I think the Orion makes sense to try.