K-12 School Library humidity control

[ssn61]

What is the recommended temperature and RH for Libraries in K-12 schools.
ASHRAE HVAC Application handbook- 2011, chapter 7 says:
" To avoid growth of mold and mildew, a dew point above –1°C (33.8 F) and maximum of 55% rh are recommended.
Does this mean we can not have a temperature of 72 F and 20% Rh, since we are lower than 33.8 F dew point temperature?
Can someone explain this relative to psychometric chart?
How long would it take for books to start getting damaged in conditions outside this envelope.

 

[ChasBean1]

Your ASHRAE reference is talking about a summer condition and not a winter condition.

I’ve recently been on a project that forfeited a substantial amount of capital to a consultant that determined that the ideal conditions to prolong the life of an archive are 60°F and 35% relative humidity, as constant as possible.

This particular project went through extremes to maintain these conditions, which meant precise humidification and dehumidification based on ambient dew point. In their archives were books and transcripts from as early as the 1100s. Putting a dollar value on priceless works is almost inconsequential; maintaining these conditions became imperative.

For archives that are NOT worth as much as my, your, and your mother’s lives combined, keep it cool and consistent (60-70°F), with a non-cyclical temperature and humidity between 55% max in summer and 30% min in winter.

For this, supply 50°F air when the outdoor air dew point is above 50°F (and reheat it to maintain the space conditions); humidify to 35% in the space when outdoor air dew point is below 40°F.

One note: humidifiers (esp. electric ones) that have cold water makeup can tend to deliver the necessary humidification, then the makeup water fills the pot thereby quenching the cycle, and after some time the cycle repeats after the water heats again. Result is horribly cyclical control, which is exactly what these systems don’t want! You’d be better off not trying to humidify…

Best of luck, CB