Does running a dehumidifier with an AC unit save money?

Question

I've done as much research as i can an every site i hit seems to have a different story on my question: "Will a dehumidifier save energy while running your AC through the summer"?

The ones that say "yes" pretty much reason that you usually can raise your thermostat a few degrees because of the lower humidity it will "feel" more comfortable. While they reason that yes AC do dehumidify also but it will put less of a load on your AC system.

The ones that say "no" say AC units doesn't run optimally when a dehumidifier is running (they don't go into details). Also, by design, dehumidifiers heat the air. How much of a difference that makes, i don't know.

That being said dehumidifiers do pull quite a bit of energy (i'm sure not NEARLY the amount of an AC unit though).

I live in zone 5 (central IL). Hot/humid summers and cold/dry winters. I don't need a dehumidifier for the winter (we actually need a humidifier then).

Also, as a lot of you probably already know, current dehumidifiers are some of the most unreliable appliances you can buy. Its one of the few things i know make sure i get an extended warranty for. I'm on my 3rd unit and, one of the reasons i'm here, is to find out if i need to budget for another one. Sure i'm sure there will be days when i could not run the AC and just run the dehumidifier but i don't think there will be enough of those days to warrant a dehumidifier if i really don't need one.

Answer 1

A dehumidifier is about the same as a window AC unit with both parts in the house, for most purposes. They draw just as much power as an A/C unit of similar size (or more if they happen to be old and inefficient.)

Given that the required energy labeling on A/C units tends to promote a degree of of paying attention to that, and it's much less clear on dehumidifiers, I suspect that in many cases the A/C of similar size will actually use less power - and it doesn't make your house hot.

Sure, comparing a room dehumidifier to a whole house A/C, the whole house uses more energy - but it also removes more water from the air, and cools the house. It would only be ANY savings if the whole house was LESS efficient (power in to water out) than the dehumidifier. If you are running the A/C as well, you are also ADDING the heat from the dehumidifier to the A/C load.

In short, run the A/C, don't bother with a dehumidifier unless you have a job that a dehumidifier (alone) is suited for; Which it sounds like you probably don't.

If you want to get "something like that" without the downsides, when your water heater wears out, consider a heat pump water heater - free hot water with a little A/C, or free A/C with your hot water. Still rather expensive, but sometimes with large rebates available too.

Answer 2

I would say a dehumidifier would not be a more efficient choice for summer comfort than turning down the thermostat on an A/C. Sure, the delta-T across exterior walls would drop, so somewhat less heat would seep in from outside, but as was already mentioned, the A/C then has to remove the dehumidifier's additional heat from the home (100% of the input power plus the heat imparted from condensation). However, they can be useful in certain home scenarios, like a mold/mildew-prone basement that is typically cold and humid. Colder air can hold less moisture than warmer air (check out a psychrometic chart for proof), so cooling raises the relative humidity of the supply air, and in areas that are very humid, targeting a certain relative humidity using a split (condenser outside) A/C system can lead to runaway cooling. Indeed, the simplest and cheapest dehumidifier is a space heater (resistive heating strips are used in some commercial applications in combination with an A/C), but that's not much good for efficient comfort in the summer.

In the summer, we need to operate a dehumidifier in our basement to keep it below 60% RH despite (and likely due in part to) setting a relatively low (70-72F) A/C setpoint for comfort on the main level. An added benefit is that the heat from the dehum keeps the basement less chilly, which also indirectly helps to lower the RH.

Answer 3

I live in the Florida Panhandle, before I got married I had a small 1400 square foot block house that was built in the 50's. Since it was a rental the owners never wanted to spend money to make improvements. That being said the ac would never shut off in the heat of summer. I put 2 roof vents in with my own money to try and make a difference.

I deal with construction contractors every day and I talked to an ac friend one day and told him what was going on with my issues and the ac. He told me to go and buy a dehumidifier on my way home and put it in the hallway of my house. Reluctantly I did on Friday afternoon the week before the 4th of July. The next day was the first time my ac shut off in the middle of the day. Up to that point I could not tell you that it ever shut off during the day. My power bill went from the low 300's to about 190 average in the summer.

I don't have a degree in, nor do I profess to really understand all the theories, but I can tell you if you live down here and you need immediate relief you will definitely notice a difference. I've been all over the country and nothing compares to the humidity on a regular basis as we have on the gulf coast. We have about 3 months of winter if we are lucky and the rest of it is summer.

Answer 4

I just had an AC technician advise me to get an AC unit with included dehumidifier to address a problem of dripping vents and mold on the upstairs units. I live in New Orleans, so the humidity is high. He says that the combo should eliminate the mold and the AC would be more efficient, thus cost saving. Another option is to get just the humidifier unit to go up with the AC unit, although our AC units are already 12 years old, so perhaps a new unit is a better choice.

Answer 5

My personal experience: our AC wasn't running well in humid weather so we bought a dehumidifier to help it out. It made the room warmer and removed the humidity from the rooms, which according to the technician, the AC actually needed. The AC stopped working at all and the house became warmer. I can't say for certain all things are related but the evidence is there.

Answer 6

I have been running a dehumidifier all summer, WITH the AC. My July Bill was EIGHTY SEVEN DOLLARS here in central Delaware for my 1700 SF house,....normally it is $200.....Dehumidifying and running an AC unit both use evaporative cooling....Knowledge of the laws of Thermodynamics is very useful, and not for just disproving ridiculous "Global Warming" alarmists!!!!

I have been manually cycling my ac unit on for 25 minute intervals and allowing it to rest for 18 minutes all day. It's The RH in my house is now very low, and it feels great at 80 degrees. It's 97 outside with a RH of 75%

A psychrometric chart and a graph of compressor efficiency Vs. cycle length is a dangerous thing (TO THE POWER COMPANIES) if it falls into the wrong hands!!! Most folks have their AC units running for no more than 10 minutes at a time, with only ten to 15% of the time running at optimum efficiency.

I may break out the wet bulb thermometer and due a RH calculation, but I bet it's close to 35% in here!!