As a student of this work, rather than a teacher, I am going to take information directly from two articles that can better explain the need for both dehumidification and air conditioning in areas of high humidity.
From Fine Homebuilding Magazine, “Excess humidity can encourage the growth of mold and even damage a house’s structure and furnishings over time. Many homes control indoor humidity with a dehumidifier. A liquid refrigerant passes through evaporator coils, which contact incoming air. Moisture from the air condenses on the cool coils and drains into a tray. While passing through the coils, the low-pressure liquid absorbs heat from the air and evaporates into a gas. The compressor squeezes it into a high-pressure, high-temperature gas before it flows into the condenser coils. There the refrigerant gives up its heat to the outgoing air and condenses back to a liquid.” The liquid is expelled from the structure.
From the Journal of Light Construction, “In the commercial market, vendors have started to provide equipment that can cool air down enough to dry it out, then reheat the delivered air stream to return it to design temperatures for people in the space. But on the residential side, no single company today makes both the cooling equipment and the dehumidification gear to solve the shoulder-season humidity problem in houses.
That means designers and contractors need to custom-craft solutions that mix and match equipment from different companies, and devise control systems that can effectively manage the whole system. A fairly widespread approach is to choose an air conditioner for cooling—either a central system or one or more mini-split heat pumps—and team up that cooling equipment with a dehumidifier for air drying and an energy recovery ventilator (ERV) for fresh air.
On some days during the hottest part of the year, the air conditioner alone may adequately control humidity as well as temperature. The ERV will also help, in any season, by passing moisture from the incoming air stream to the exhaust stream. But for many hours out of the year (especially in spring and fall), the dehumidifier will shoulder a load that the home’s other equipment can’t handle.
One house was cooled with a ducted mini-split, but the owner knew that hot, humid air would tend to accumulate at the open-plan building’s peak in the upstairs living room. So when he built the house, his HVAC contractor lined one stud bay in the home’s elevator shaft with metal duct material and installed a fan to pull air from the home’s peak down to the entry stairwell at ground level.
Later, the owner tied a dehumidifier into the air-mixing system, with a dehumidistat at the upper story’s peak. A simple meter on his desk tells him the relative humidity in the living space. ‘We’ve had some really foggy cool mornings this spring,’ Dugan told JLC in April. ‘It’s sitting right at 100% dew point and it’s 60°F outside, and right now my indoor humidity is 45%. I say, OK. I like that.'”
The next step is to investigate companies that make whole-house dehumidifiers that will work with a (proposed) Mitsubishi Mini-split system. One company, Ultra-Aire, has dehumidifiers have been used with a Mitsubishi Mini-split system. Another issue is “are there local contractors who are familiar with whole-house dehumidifiers and how they work with air conditioning systems?”