We’ve established that the new root cellar does a good job holding its temperature and humidity relatively stable when the outside temp fluctuates. That’s great once we get it to the right temp, but at the moment it’s far too warm (~20° F so).
Even though it was near 90° F just 48 hours earlier, the overnight temps Saturday were predicted to be in the low 40s. Around 5pm, I propped the door to the cellar open and put a fan in the doorway blowing in, hoping to bring some of that cold night air in to the cellar. The fan was removed and the door closed again around 7am, so we wouldn’t blow in any of the warmer daytime air.
You can see the effect, but it was very moderate. We lost nearly 7° in the cellar overnight, but regained 5° during the next day. Perhaps the ground packed around the cellar is still too warm? We also lost a lot of humidity while the fan was going, but that’s sort of expected, and recovered quickly once the door was closed.
So in short, this didn’t work very well. One shortcoming of this cooling approach is that the cellar door opens into the back of the shed, so the air we’re pulling in at night is shed air, not outside air. The shed doors were wide open, but there’s still probably a meaningful insulating effect.
Next, we can try running some PVC across the shed floor to make a sort of intake pipe that would pull from the outside air. If that works, it might be possible to make it permanent with a valved intake duct in the cellar. This would need some digging, as the ground level outside is flush with the cellar ceiling (where the exhaust duct is currently), but should be doable.