Maintaining <50%RH with low no cooling loads
I am posting a few days in SW FL with moderate temps and outdoor dew points. Low/no cooling load 3 ton a/c, Ultra-Aire 90 dehumidifier maintains 50%RH when the doors are closed. When the indoor dew point is above the outdoor dew point, the home is occupied and dehu is not operating. When the indoor dew point is below outdoor dew point, the dehu and a/c are removing moisture. Windy weather this week with 60-90 cfm of fresh air.
The 3 ton a/c is slightly oversized deals well with t-stat setup when the home is not occupied. With 10+ mph wind, the home gets and air change in 4-5 hours. During clam winds, the house needs make-up ventilation.
The main point here is that adding a dehumidifier to a home make Maintaining <50%RH for comfort and health.
Click the PDF to view.
The amount of moisture to humidify or dehumidify for comfort.
Only if you interested in the concept of how the amount of the moisture that needs to be added or removed from a home to maintain a specific %RH. It is complicated but contains specifics. Will answer any question from interested parties.
The concept is that you can estimate the amount of air infiltration during the normal different weather conditions. Also you can size a humidifier, a dehumidifier, or determined the amount of air tightening you should target.
Also in the case of high winter moisture inside a home, you can determine the amount of fresh air ventilation you need to reduce the %RH in the home.
Take a shot at the chart, it may clarify the critical indoor moisture/fresh air relationship.
Most occupied spaces need an air change in 4-5 hours to purge indoor pollutants and renew oxygen. Most spaces need X amount of humidification when outdoor dew point are <30^F. The amount is determined by the dew point, the air leakage/ventilation cfm and occupant number.
When the outdoor dew points are +55^F, a specific amount of dehumidification is required depending on the specific outdoor dew points, the air leakage/ventilation cfm, and occupant number.
A/cs remove a specific amount of moisture depending on the coil temp, size, and run time. The moisture left on the coil re-evaporates back to the home at the end of the cooiling cycle.
Providing real humidity control usually requires a properly sized humidifier and dehumidifier. Click on the attachment. After opening enlarge the pdf to make it easier to read. Try to figure out the effect of adding or removing 2 lbs. of moisture per hour.