[jeff5may]

If dehumidifying your indoor air is a major priority, the add-on to the existing air conditioning system can address this priority. Most air conditioning units are made to provide some dehumidification (latent) and lots of air cooling (sensible). To cool lots of air, you need lots of airflow. Not so true with dehumidifying.

The moisture in a humid room has to be removed at constant temperature by the heat exchanger, so the first few minutes of every run cycle, the unit is not actually cooling the room at all. Once enough water is removed to lower the dew point, the room temperature starts to drop. As more and more water is removed, the air conditioner becomes much more effective at lowering the air temperature, because it takes a lot less energy to cool dry air than to dehumidify.

To dehumidify, you need a colder heat exchanger and not as much airflow. The water cooling mister outdoors will help keep the indoor coil cold, so it will help the unit gather more water. It is common for dehumidifying units to operate below freezing, collect frost and/or ice, and then run a lengthy defrost cycle to drain all the moisture they just collected. As long as there is still ice on the indoor HX, it is cold enough to keep grabbing moisture while the ice melts. Needless to say, you don't want your minisplit to freeze its indoor coil, so it can only do so much.

Other members have been down that road, and it doesn't take a lot of added capacity to get rid of lots of water. Jake (Memphis), Randy (Randen) and Gary (Xringer) have chronicled their experiments in this realm. They have found that their heat pump water heaters have another purpose: they make effective dehumidifiers. Unlike stand-alone portable dehumidifiers, they don't add heat to the interior space: the heat goes into the water tank.

Another add-on idea that is much less wacky than it sounds is wet desiccant dehumidification. Big dogs, such as FEMA, the Army, the Navy, and others call these rigs atmospheric water generators. They build the units on trailers for huge portable sources of emergency drinking water. A cooling tower collects moisture from the air by pumping a saltwater solution and outdoor air through the tower. The saltwater is then heated, and the water vapor produced is collected for distribution. The remaining saltwater is then pumped back up the tower. Common figures for these systems are 5 gallons of water produced for every gallon of gas consumed and up to 1200 gallons of water output per day per unit. Many a university has won an award by including this type of system to boost energy efficiency of their design home. No longer do the zombie apocalypse shelters need a massive fresh water store: these things work equally well off of solar energy.