Building a wine cabinet

[Gary]

You really don't want to keep 75% humidity in your house, do you? Anything over 60% can give you mold problems. 50%RH is ideal, and going over that is not necessary.

Let's say you keep your house at 75F with 50%RH. When that air drops to 56F, it's RH will be about 95% with a dewpoint of 54F. This means that any surface in the cooler whose temperature is below 54F will form condensation.

Of course, the only surface in there which is below 54F is the cooling coil. This coil will remove humidity from the air. How much it dehumidifies the air depends upon its temperature. The colder the coil, the more it dehumidifies. But it needs to be cold enough to maintain the temperature inside the cooler.

If the coil temperature is not allowed to drop below 42F, assuming the cooler temperature is 56F, then the coil will stop removing moisture from the air when the humidity has reached 60%. A higher coil temperature will give you higher humidity. A lower coil temperature will give you lower humidity. The desired coil temperature can be maintained by using an EPR valve.

Again assuming 42F coil temperature, with 59F cooler temperature, the humidity could go as low as 55%. With a 54F cooler, the lower limit would be 65% RH. Of course, the upper limit would be the 95% RH provided by opening the door.