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Some googling of experts shows it can be quite a concern. https://www.eng-tips.com/viewthread.cfm?qid=188008 https://www.eng-tips.com/viewthread.cfm?qid=188008

Scoundreller 4y ago
I can only barely understand what’s going on in that link, but I think it really depends on target indoor environment. While I don’t want the walls sweating, I could imagine there are industrial or commercial environments where moisture level matters a lot. Electronics plant: dry is always bad! Want some moisture to dissipate static. A library wants low, but not zero moisture. A manufacturing plant wants it to be very consistent. A fruit market wants its humidity high. In a residential environment, it’s a toss up: some stuff wants to be dryer while other stuff doesn’t.
- amluto 4y ago
  I don’t think you’re likely to make the walls sweat by running an economizer or, for that matter, opening a window while it’s cooler outside than inside. You may end up with more humidity inside than you like, though, depending on the weather. That link seems to be discussing a situation where there is too much humidity coming in relative to the amount of heat the A/C needs to remove, and that hits my pet peeve about air conditioning design. Air conditioners generally run at a roughly constant coil temperature, which means that there is no independent control over dehumidification versus cooling. If you happen to be at the design conditions, great. Otherwise you don’t end up with the humidity you want. I know of one system (“dynamic humidity control” by Chiltrix) that adjusts the coil temperature to control humidity. As far as I know, any hydronic system can do this with minimal modification, but I don’t think it’s popular.
  - Scoundreller 4y ago
    I have a similar issue with thermostats in general: set points without a humidity coefficient is a constant battle. 26C and dry is comfortable: Stay off. 26C and humid is sweltering: Power up. My "smart" thermostat has a settings for this, but I seem to be at its algorithm's mercy instead of specifying: "50% RH or less, no change, 50-70%, -2C to the set points, 70%+, -3C to the set points". Let alone being able to do dehumidification only.
    - amluto 4y ago
      This isn’t entirely a problem with your thermostat. If it’s 26C and humid, all your thermostat can do is to call for cooling. (Maybe it can call for stage 1 or stage 2. You are unlikely to have anything that can do stand-alone dehumification.) So it can’t actually achieve a comfortable and efficient target.
      - Scoundreller 4y ago
        Would still be more comfortable and efficient if could aim for what I'd be equally happy with: 23C + humid or 26C + dry

Scoundreller 4y ago

I can only barely understand what’s going on in that link, but I think it really depends on target indoor environment. While I don’t want the walls sweating, I could imagine there are industrial or commercial environments where moisture level matters a lot. Electronics plant: dry is always bad! Want some moisture to dissipate static. A library wants low, but not zero moisture. A manufacturing plant wants it to be very consistent. A fruit market wants its humidity high. In a residential environment, it’s a toss up: some stuff wants to be dryer while other stuff doesn’t.

amluto 4y ago
I don’t think you’re likely to make the walls sweat by running an economizer or, for that matter, opening a window while it’s cooler outside than inside. You may end up with more humidity inside than you like, though, depending on the weather. That link seems to be discussing a situation where there is too much humidity coming in relative to the amount of heat the A/C needs to remove, and that hits my pet peeve about air conditioning design. Air conditioners generally run at a roughly constant coil temperature, which means that there is no independent control over dehumidification versus cooling. If you happen to be at the design conditions, great. Otherwise you don’t end up with the humidity you want. I know of one system (“dynamic humidity control” by Chiltrix) that adjusts the coil temperature to control humidity. As far as I know, any hydronic system can do this with minimal modification, but I don’t think it’s popular.
- Scoundreller 4y ago
  I have a similar issue with thermostats in general: set points without a humidity coefficient is a constant battle. 26C and dry is comfortable: Stay off. 26C and humid is sweltering: Power up. My "smart" thermostat has a settings for this, but I seem to be at its algorithm's mercy instead of specifying: "50% RH or less, no change, 50-70%, -2C to the set points, 70%+, -3C to the set points". Let alone being able to do dehumidification only.
  - amluto 4y ago
    This isn’t entirely a problem with your thermostat. If it’s 26C and humid, all your thermostat can do is to call for cooling. (Maybe it can call for stage 1 or stage 2. You are unlikely to have anything that can do stand-alone dehumification.) So it can’t actually achieve a comfortable and efficient target.
    - Scoundreller 4y ago
      Would still be more comfortable and efficient if could aim for what I'd be equally happy with: 23C + humid or 26C + dry