Rich wrote:

A properly controlled exhaust fan can dehumidify with 100X less energy
than a dehumidifier.

Do you have any links to information about these units being 100X more
efficient? That would be interesting reading for me!

I measured a new efficient dehumidifier, which produced 1.6 kWh of heat
for every kWh consumed, ie 1 kWh from motors plus 0.6 kWh to condense
about 2 pints of water, ie it consumed 0.5 kWh per pound of water, ie
5 cents/pint at 10 cents/kWh.

A 70 F basement with 60% RH has humidity ratio w = 0.00947 pounds of water
per pound of dry air. NREL says w = 0.008 for outdoor air on an average May
day in Phila with a 62.9 F 24-hour average temp and 52.7 and 73.1 daily min
and max. On an _average_ (vs dry) May day, we might run Lasko's 16" 2470 cfm
90 watt 2155A window fan ($53 from Ace Hardware) for an hour and remove
60x2470x0.075(0.00947-0.008) = 16.34 pounds of water at 90/16.34 = 5.5 Wh/pint,
ie $0.1x90/1000/16.33 = 0.055 cents/pint, 91X less than the dehumidifier.

But some days are drier than average. Running the fan longer on dry days
vs running it every day would be more efficient. We might invent a nice
adaptive algorithm with the help of a simulation using TMY2 weather data.

And the outdoor humidity ratio (vs the RH) doesn't change much over a day,
so we might as well run the fan when it's warmer outdoors if the house needs
heat or when it's cooler outdoors if the house needs cooling.

Nick