Okay, let’s see if I’ve got this straight. Both air conditioners and dehumidifiers reduce relative humidity within a room. So if humidity is an issue, doesn’t it make more sense in summer to run an air conditioner and get the benefits of dehumidification AND cooling, rather than just getting dehumidification from a dehumidifier?
I have two dehumidifiers in my basement. Both run non$top and constantly blow warm air, requiring the air conditioner to work extra hard to compensate for the heat. What’s more, the dehumidifiers cost me about $300 each, making me wonder whether, for purposes of dehumidification/cooling, the net cost of operating an air conditioner is less than a dehumidifer.
I question how well an air conditioner really reduces humidity. I know that, all things being equal, simply turning on the air conditioner should raise the relative humidity, since colder air holds less moisture. Also, my window air conditioner really doesn’t seem to drip that much water-- I know some models do, but it is absolutely undetectable in mine (and no stains or drips on the porch floor after hours of non-stop running.) However, I know that a dedicated dehumidifier will pull out buckets and buckets of water from the air in just one day of running. I have an indoor humidity meter (hygrometer?), and after hours of running my air conditioner with all windows closed, the humidity certainly isn’t going down. I look forward to finding out more about this.
You’re right that merely reducing the air temperature raises the relative humidity. This is why cold fronts make it rain. But your air conditioner is also sucking a lot of water out of the air by condensation on the cold coils. (In other words, the coils are so cold, they raise the relative humidity to 100%, causing rain inside your air conditioner.)
Most air conditioners these days run fine with a little bit of water sloshing around in there and may not start leaking until it gets deep (a half inch or so.) Mine does this on super-humid days, for example, but doesn’t noticeably leak on mere annoyingly-humid days, even though I can hear some water in there.
A dehumidifer really is the same thing as an air conditioner, but probably not as powerful. It has a compressor and collects condensation on cold coils, just like an AC. But when you’ve got cold coils you also have to have hot coils on the other side, due to those pesky laws of thermodynamics. An air conditioner puts those outside, but a dehumidifer doesn’t.
NYC metro area resident here. We’ve been having mutha humidity and high temps of late. I have one “hotel type” (floor model, under-the-window) A/C unit in the bedroom of a 1BR shotgun apt (BR/LR/kitchen), and for the past 7-10 days it’s been running pretty much nonstop. By combining the A/C with a tower fan I’ve consistently kept the temp in all 3 rooms under 82° and the RH below 50% (even when it’s in the 90°s and 60+% RH outside, according to my desktop WX station). This is important for me as I tend to hyperhydrosis (a $20 word for “sweating like a roast pig even while sound asleep”). The grille of the A/C unit has condensate on it more or less constantly, which I take to mean that it’s sucking humidity out of the air. This makes me happy.