Basement Safe Humidity: On the Rise!

With the door sealed, that tray of desiccant ran out of capacity after holding 14%RH for four months. The humidity rose to 24% at the end of this month’s record:

Basement Safe Humidity - April 2012
Basement Safe Humidity - April 2012

That’s much sooner than I expected and goes to show why one careful measurement trumps a kilo-opinion. Those characters are just about illegible (even on the original display they’re pretty small), but in round numbers the humidity is rising by about 0.3 %/day: 10 %RH in the month since the granules ran out of capacity.

The granules weighed 738 g dry and 827 g when I took them out. That’s about 89 g of water = 600 mg/day leaking into the safe over the course of five months. There’s some influence from the paper in the safe, plus the 55%RH air admitted every month when I dump the Hobo datalogger memory.

Running the desiccant through the oven produced some useful numbers:

  • Bag: 675 g → 569 g = 106 g of water
  • Loose granules: 827 g → 741 g = 86 g of water

The oven shut off (automatically) an hour or so before I woke up. The trays were still hot to the touch, but I suppose the desiccant had already gotten back to work. Or, perhaps, it’s a combination of measurement errors and aging desiccant; the stuff does wear out after a finite number of cycles.

For completeness: the tray inside the safe weighs 79 g, so the granule gross weights were 906 g and 820 g.