I have a window AC that has a dehumidifer. What cost more, to run AC or dehumidifer? When I run the D-H it seems to stay cooler than running the AC. What is the difference?
With a dehumidifier, the evaporator coil and condenser coil are both in the room. So while it does remove water from the air, the unit also acts as a heater (i.e. it heats up your room).
With an air conditioner, the evaporator coil is in the room and the condenser coil is outside. Like the dehumidifier, it also removes water from the air, but it also removes heat from the room.
I believe an AC would cost more to run.
Wait, is it all one unit, with the option to run as a dehumidifier or an air conditioner? Although air conditioners also act as dehumidifiers, there are standalone units as well, but I don’t know why one would mount in a window.
I’m also curious…I haven’t seen a window AC unit that has a separate dehumidifier. I recently shopped for (and bought) a window unit; most can be run with the fan separately but I don’t recall seeing any that had a dedicated dehumidifier function.
Once, during a horribly humid stretch of weather that made the house sticky despite central AC, I brought my basement dehumidifier upstairs and set it in the kitchen. It put out so much heat that I quickly abandoned that idea and put it back in the basement.
As to cost, I think running AC is most expensive. I live in SE Michigan where it can get seriously cold in winter; but my highest bills have been during very hot, humid summer months when I run the AC a lot. (I leave it on during the day for the dogs even when I’m at work, so it tends to run a lot in July-August.)
Yeah, kind of weird. An AC is in essence a dehumidifier combined with heat transfer.
Both the window units I own (one samsung, one LG, both probably manufactured within the past five years) have a dedicated “dry” function. The Samsung’s manual says it’s for use on humid-but-milder days when running the A/C would result in a chilly, clammy room.
I have no idea on when it’s really sensible to use it or whether it works. In Chicago, heat and humidity are usually hand-in-hand.
Makes no sense. Air conditioning doesn’t make things clammy. Chilly, yes, but that’s because not only is the temp dropping, but moisture is being removed through recirculation. I could see perhaps wanting to dehumidify without cooling during rainy season, when relative humidity is high and there could be mold/mildew problems.
I can think of two reasons AC would have a clammy (humid) quality:
- A significant source of water vapor is entering the room (water leak, etc.)
- The AC has too many BTUs and thus “short-cycles”.
An example of #2… my father installed central AC in his house that had too many BTUs. (The calculations called for a 2.5 ton unit, and he installed a 4 ton unit.) It cools the house very quickly. *Too *quickly, in fact; it only comes on for 4 minutes at a time, which is not enough time to remove the moisture. Feels cool and clammy in his house during the summer as a result.
True enough, although it seems odd that the general instructions with an AC would include the cold & clammy comments. Also, if it’s cool outdoors, why would one wish to turn on an air conditioner in the first place?
I’m having honest problems imagining how the dry function would work, though. Does it bring in outside air that it cools, rather than recirculating? Google only came up with a very unhelpful Yahoo! Answer, and I’ve got to get to bed.
what is the make and model?
Cold and clammy = A/C unit too big (too many BTU) for the given space it needs to cool.
Cold and clammy with A/C = unit too big. A/C won’t run long enough to dehumidify, but cools things off very fast. This is a classic case of oversized A/C.
Calculate room size and get a unit that matches it, and the unit will run long enough to cool and dehumidify.
An A/C system is a dehumidifier by nature.
An A/C system sees, and is engineered to handle, two “loads”; latent heat (humidity) and sensible heat (temperature).
In both a window system and a central system the latent load is handled by condensation; the humid air passes over a cold A/C coil and the water vapor (humidity) condenses to water. The water you hear draining, or dripping out of the back of your window unit, is water that moments ago was water vapor/ humidity.
The sensible load is carried to the condenser coil where a fan “rejects” the heat out into the environment. Thats why you have a unit in the back yard, or why a window unit needs to sit in the window. In both types of units the A/C needs to have access to the outside to reject the heat from your house. A/C, at it’s core, is not about making cool, but removing/ moving heat.
A dehumidifier is designed to handle only latent heat. Humid air passes over the cold coil and condenses to water; just like an A/C system. However it has no "access’ to the outside so whatever sensible heat is in the room, remains in the room. The condensing coil blows the sensible heat out the back of the unit----right back into the room.
In fact, there is the “heat of compression” and the heat that the compressor/fan generate so a dehumidifier will actually pit a small of extra heat into the room.
The reason you see dehumidifiers in basements----for example-----is that there is little sensible load, as the basement is underground. However there is often a high latent load so a dehumidifier is used to simply remover humidity/ latent heat/ water vapor.
Clear as mud? I thought so.
“Cooler” is often subjective. You may feel cooler simply because you are drier. For example, you may feel cooler at 75° @ 50% RH, than 73° at 60% RH.
Both temperature and humidity are forms of heat that you experience/ feel. If you feel cooler using the DH function, use it.
As to the cost, I suspect it is incrementally more expensive to use the DH setting, although I doubt you’d see a big difference in your bill.
In both settings the unit is doing the same thing—the compressor and fan are in service. (and the compressor is by far the biggest energy user)
I’m betting the DH setting slows down the fan to force the compressor to run longer in order to capture more humidity; to “dry out” the room.
ETA
I can see one scenario where maybe the A/C setting is more expensive that the DH setting:
If the compressor is 2 speed, maybe a DH setting uses a lower compressor speed to simply remove latent heat. I kind of doubt it though, given the cheap prices of window units.
It seems more likely that they’re simply slowing down the fan. If that’s so, I’d bet the DH setting is incrementally more expensive to run.
Eta to the Eta
In an A/C system the total load is about 70% sensible and 30% latent.
But the system is controlled by temperature/sensible (via a thermostat) and not by humidity/ latent (via a humidistat). (Thats why it is critical not to oversize a system; an oversized system can’t control humidity)
So…if the questions is “which is more expensive to operate, a dedicated DH or an A/C system?”, I’d say the A/C system because it is designed to remover both sensible heat and latent heat, while a dedicated DH system is a smaller system because it is designed to remover latent heat only.
But…if the question is “which is more expensive to operate, an A/C system with a DH setting operating in the DH mode, or an A/C system in the normal A/C mode?”, I’d guess the DH setting. (for reasons listed above)
Thats my SWAG and I’m sticking to it.
Assuming the difference between DH and AC is that hot air from the condenser side coil is ducted back into the room for DH (ie not cooling the room but just removing the humidity) then it depends upon the temperature of the condenser coil. I am assuming that when the AC is on it is hot outside say above room temp, then the unit is having to reject heat to a hotter environment which causes higher pressure in the refrigerant system ie more work on the compressor and more electricity. In this case it would cheaper to run DH.
But, if the unit uses the condensate (water from the air) to cool the condenser coil in AC mode but can’t do so in DH mode because it would go back into the room, it may actually be more efficient in AC mode. Kind of depends how the unit works!
Could buy one of those $35 power meters and test it…
OP may have rotted due to excessive humidity…
Well in reading all the comments it’s no wonder the OP got glazed over. Many didn’t notice that the dehumidifier exhausted outside since it’s a WNDOW UNIT! Well I have a pirtable AC that has a dehumidifier setting both which vent out the window via a vent hose. So I pose the question again on a one that raindog may have answered…which is more economical to run? The AC function or dehumidifier function. Ironically, the DH setting makes the room cooler and my unit has no way to control that function. Only on the AC setting can I control the temp. I have an edge star ap8000w if that helps. So in conclusion…DH setting freezing at night…AC setting can adjust temp…if it’s cheaper to run DH, I’ll just use a blanket. If it’s cheaper to use AC, I’ll forego the blanket.
The entire room gets colder quicker in dehumidify mode or just the exit air temp is colder? These two are not necessarily the same thing. A lower speed fan setting would result in maximum moisture pulled out of the air, and a cooler exit temp, but will not result in maximum room cooling performance.