Wednesday, March 11, 2015

Humidity simplified

Today, I talked to Jay, a chemistry teacher in my building, about humidity. I explained what I was up to, growing vegetable and flower starts in my greenhouse. I learned a couple of basic points from him:

  1. Generally, I won't want my greenhouse to be more than 70 percent humidity.
  2. If it is too humid, a fan is best for exchanging the air.
  3. If a fan is not enough, or if I find it is raining endlessly, I should get a dehumidifier.
  4. If it's raining outside, humidity outside is 100 percent, so it won't do me any good to use the fan to exchange inside air for outside air.
  5. There are charts that will tell me relative humidity if I know the temperature and humidity. Update: I can only find charts where you know the temperature and the difference between the wet bulb and dry bulb temp. I don't think I'll be using a chart because I don't have such measurements.
  6. Regardless of temperature, the humidity will be within 10 degrees of the relative humidity.
  7. Only meteorologists are concerned with relative humidity. I will be just fine knowing the absolute humidity.
  8. I just need to get a feel for what my greenhouse feels like when the humidity is too high. Not only will I feel it, but I'll be able to see a good deal of condensation, not only on the glazing, but all surfaces.

It's raining right now, and it has been on and off since last night. Temperatures are warm--48 this morning and in the 50s today. One hundred percent humidity!

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