Would a Mini Split be a good dehumidifier in a basement?

DJDrew

Does anyone know or have experience if a mini split would be a good dehumidifier for the basement? It seems like it would be significantly quieter than the portable unit we use currently.

There are other issues with our basement such as fresh air, so we started looking at an HRV, but to do something wholistic and tackle fresh air and humidity at the same time might be more logical.

We are not too worried about heat, as there is a zone off the boiler with panel radiators (probably short cycling until we replace with a mod con, but it works.)

Would a ducted mini split work? Or would it make the basement even colder? I am assuming there is no all-in-one solution to tackle fresh air and humidity, so an HRV would be a separate system to run in tandem. Thoughts?

Hot_water_fan

It’s not really designed for this, but yes a heat pump/ AC would work. Carrier makes some models with reheat, which cools then heats the air so the temperature doesn’t fall as it runs. 

pecmsg

The smallest heat pump will work. 

You’ll be surprised it will operate in heat mode while A/C is on upstairs. 

Add a whole house dehumidifier for total comfort. 

HVACNUT

Some manufacturers have a "dry" setting on the remote, but it's not a dehumidifier. 

pecmsg

HVACNUT said:

Some manufacturers have a "dry" setting on the remote, but it's not a dehumidifier. 

That’s for a little extra. Even a small mini at 6,000 is oversized for an average basement 

Big Ed_4

Some times all that is needed is a good whole house dehumidifier for a basement ..Figure the basement receives the leakage from the first floor...

jumper

A separate dehumidifier saves $$$. For one thing it enables running A/C at higher temperature.

ChrisJ

jumper said:

A separate dehumidifier saves $$$. For one thing it enables running A/C at higher temperature.

How would this save money?
You're paying to run the dehumidifier and if the AC needed to be set lower it wasn't running much to begin with.

I think a whole house dehumidifier can certainly increase comfort under some conditions but I'm not so sure it saves money.  I've got a feeling it would never even pay for it self.

HVACNUT

jumper said:

A separate dehumidifier saves $$$. For one thing it enables running A/C at higher temperature.

I think you might feel more comfortable with less humidity, but a dehumidifier can discharge some pretty high temperatures that the AC now has to compensate for. 

pecmsg

Basements are cool and humid by nature. You’re below ground. If anything they need Heat 80 - 90% of the year and dehumidification. 

ChrisJ

pecmsg said:

Basements are cool and humid by nature. You’re below ground. If anything they need Heat 80 - 90% of the year and dehumidification. 

My basement is 82F and 42% right now from the dehumidifier running 24/7.

kenjohnson

I have a small Mitsubishi mini-split in my walk out basement of my condo. When set to dehumidify mode, it makes the basement quite cool. I don't use the mini-split as an alternative to a normal $300 dehumidifier.

ratio

From my perusal of the manual of a Mitsubishi I installed a few weeks ago, dry mode just cranks the coil temp down as low as it can get it for like a half-hour or so. IIRC the manual even said that it shouldn't be run more than one cycle in a row.

DJDrew

From what it sounds like (above), there are certain mini-splits might do this constant dehumidification better than others, with the advantage being that most of the latent heat is transferred outside. We have Mitsubishi on the first and second level and I have not found a way to dial in a humidity % with them. It's either AC (sometimes wet-feeling AC) or full on dry mode that turns the room into an icebox after awhile. I'll have to look into Carrier version to see if it operates differently. My thinking with a mini-split is it is more efficient than any standalone or whole house dehumidifier.

Right now we have a portable dehumidifier that is running in the basement and raising the temperature to the low 70's (at least with low humidity.) That heat is then probably traveling upstairs for the mini split system upstairs to remove.

It seems that most (85-90%) of the moisture in the basement is from condensation on the colder floor and walls (1938 construction), so perhaps the latent heat from the portable dehumidifier is helping. The whole house dehumidifiers that offer a fresh air port look enticing, but then the house would be operating under positive air pressure with the hook up the fresh air intake. Logically I'd assume that with fresh air entering, it's best to have an equal amount of stale air leaving.

Googling this issue seems to confirm that dehumidifying a basement is not so simple, but it's easy to find ways to drive up the electric bill solving.

HVACNUT

DJDrew said:

From what it sounds like (above), there are certain mini-splits might do this constant dehumidification better than others, with the advantage being that most of the latent heat is transferred outside. We have Mitsubishi on the first and second level and I have not found a way to dial in a humidity % with them. It's either AC (sometimes wet-feeling AC) or full on dry mode that turns the room into an icebox after awhile. I'll have to look into Carrier version to see if it operates differently. My thinking with a mini-split is it is more efficient than any standalone or whole house dehumidifier. Right now we have a portable dehumidifier that is running in the basement and raising the temperature to the low 70's (at least with low humidity.) That heat is then probably traveling upstairs for the mini split system upstairs to remove. It seems that most (85-90%) of the moisture in the basement is from condensation on the colder floor and walls (1938 construction), so perhaps the latent heat from the portable dehumidifier is helping. The whole house dehumidifiers that offer a fresh air port look enticing, but then the house would be operating under positive air pressure with the hook up the fresh air intake. Logically I'd assume that with fresh air entering, it's best to have an equal amount of stale air leaving. Googling this issue seems to confirm that dehumidifying a basement is not so simple, but it's easy to find ways to drive up the electric bill solving.

Look at the Aprilaire E100. Pipe it to a drain or condensate pump, plug it in, done.

mattmia2

Look in to desiccant wheel type dehumidifiers if you want to dump some of the heat from the dehumidification process outside.

If your basement is heating significantly, are you sure the dehumidifier is still running on a full charge? It definitely will warm the room some, but it will warm it a lot more if it has leaked some of its refrigerant out.

ChrisJ

mattmia2 said:

Look in to desiccant wheel type dehumidifiers if you want to dump some of the heat from the demystification process outside. If your basement is heating significantly, are you sure the dehumidifier is still running on a full charge? It definitely will warm the room some, but it will warm it a lot more if it has leaked some of its refrigerant out.

Why is that?
And how is that?


I would expect it to heat less if it was low on gas?

mattmia2

ChrisJ said:

Why is that?
And how is that?


I would expect it to heat less if it was low on gas?

The compressor runs but it doesn't dehumidify or dehumidifies very little so the humidistat is never satisfied so the compressor runs constantly or almost constantly. The heat comes from the compressor motor. If it is fully charged it uses a little more power but it also runs a lot less.

Big Ed_4

Like mentioned the Aprilaire whole house humidifier ,I found they work well . Duct the supply to the separate basement areas and duct the return into the living space .

Set up a drain. Set it and forget it . Once it brings the humidity down it will shut down . It would check the level now and then and turn on as needed .

Hot_water_fan

My thinking with a mini-split is it is more efficient than any standalone or whole house dehumidifier.

I don’t think there’s any reason to think that: a heat pump and a dehumidifier both use refrigerant to create a cold enough coil to condense water in the air. Ductless heat pumps can sometimes have high SEER ratings, but that’s usually because they use a higher temperature coil that hardly removes any moisture. The ductless heat pumps that remove substantial moisture are necessarily less efficient. 

ChrisJ

mattmia2 said:

Why is that?
And how is that?


I would expect it to heat less if it was low on gas?

The compressor runs but it doesn't dehumidify or dehumidifies very little so the humidistat is never satisfied so the compressor runs constantly or almost constantly. The heat comes from the compressor motor. If it is fully charged it uses a little more power but it also runs a lot less.

True
But undercharged would cause less and less load on the motor. Less load means less heat.

Sounds like a good myth busters episode.

mattmia2

I do know the sign of the 3 that lost their charge was it was warm in the basement and they were running whenever i went in to the basement.

pecmsg

ChrisJ said:

mattmia2 said:

Why is that?
And how is that?


I would expect it to heat less if it was low on gas?

The compressor runs but it doesn't dehumidify or dehumidifies very little so the humidistat is never satisfied so the compressor runs constantly or almost constantly. The heat comes from the compressor motor. If it is fully charged it uses a little more power but it also runs a lot less.

True
But undercharged would cause less and less load on the motor. Less load means less heat.

Sounds like a good myth busters episode.

The refrigerant cools the motor. Low charge = more heat!

mattmia2

pecmsg said:

The refrigerant cools the motor. Low charge = more heat!

But it dumps it in the condenser which is in the same space with a dehumidifier so it ends up in the conditioned space either way. It is the more run time and that the motor consumes most of its rated power even without a load on it that causes more heat if there is a low charge.

jumper

ratio said:

From my perusal of the manual of a Mitsubishi I installed a few weeks ago, dry mode just cranks the coil temp down as low as it can get it for like a half-hour or so. IIRC the manual even said that it shouldn't be run more than one cycle in a row.

Efficient dehumidifier recovers some "cooling" with downstream
condenser. A/C cannot be as efficient. Some A/C use a downstream coil to subcool refrigerant and reheat air.

Big Ed_4

The dehumidifier cools its evaporator to remove humidity . Not much heat load entering a normal cellar ? Very few window and exposed walls . Humidity is what needs to be adjusted . Cooling without removing humidity will give you the cold damp uncomfortable condition . The mini split is not designed to be a good dehumidifier ... Just beware of how you sell it..

ChrisJ

Big Ed_4 said:

The dehumidifier cools its evaporator to remove humidity . Not much heat load entering a normal cellar ? Very few window and exposed walls . Humidity is what needs to be adjusted . Cooling without removing humidity will give you the cold damp uncomfortable condition . The mini split is not designed to be a good dehumidifier ... Just beware of how you sell it..

What about if you put the outdoor unit inside with the evaporator?

Big Ed_4

A dehumidifier is a different from an AC system , AC system moves energy ,while a dehumidifier is designed to remove moisture not cool or heat. The air flow in a dehumidifier first cools the condenser and then condenses across the evaporator . Heat it up and cool it down... What works is a good efficient unit ... Those cheap potables are just that.

ChrisJ

Big Ed_4 said:

A dehumidifier is a different from an AC system , AC system moves energy ,while a dehumidifier is designed to remove moisture not cool or heat. The air flow in a dehumidifier first cools the condenser and then condenses across the evaporator . Heat it up and cool it down... What works is a good efficient unit ... Those cheap potables are just that.

Wouldn't you run it through the evaporator first to drop the dew point and then run it through the condenser to reheat?  Just like hot gas reheat setups?

Heating it first seems like it would be counter productive.

My comment about putting the outdoor unit inside was a joke but would most certainly work overall.

ratio

100% of the energy used by a packaged consumer-grade dehumidifier ends up as heat in the space it's in. If the unit is working, it'll be taking water out of the air & possibly satisfying from time to time. If not, it's just an electric heater. To actually dehum without raising the temp at all, you'll need to reject at least some of the heat outside. If you want to keep that heat inside, like during the winter, you'll need to modulate that outdoor coil.

I've always thought it would be neat to have a refrigeration rack to operate things like ACs, dehumidifiers, refrigerators, & heating coils. Kinda like a build-up VRF system, but cheaper. Maybe.

jumper

>> need to reject at least some of the heat outside.<<

If that was a big deal one can also reject heat to condensed water before it is disposed. The liquid refrigerant can be subcooled by that water. From experience I can state that dehumidifier are a good investment. As I already explained.

ratio

jumper said:

If that was a big deal one can also reject heat to condensed water before it is disposed. The liquid refrigerant can be subcooled by that water.

Possibly, I don't have much experience with water condensers, so I can't judge how much heat the water would carry out of the house. I do know that an outdoor coil would work.

From experience I can state that dehumidifier are a good investment. As I already explained.

I never believed they were anything else than a good idea if you've got high humidity. I just believe that they add heat to the space as well as remove humidity. Whether or not that heat is a significant amount is something that I haven't thought about, due to a lack of necessity.

pecmsg

ratio said:

jumper said:

If that was a big deal one can also reject heat to condensed water before it is disposed. The liquid refrigerant can be subcooled by that water.

Possibly, I don't have much experience with water condensers, so I can't judge how much heat the water would carry out of the house. I do know that an outdoor coil would work.

From experience I can state that dehumidifier are a good investment. As I already explained.

I never believed they were anything else than a good idea if you've got high humidity. I just believe that they add heat to the space as well as remove humidity. Whether or not that heat is a significant amount is something that I haven't thought about, due to a lack of necessity.



Heat pump water heaters do exactly that.

jumper

Easy to calculate heat produced by dehumidifier: hours times power.
Those heat pump water heaters with inside evaporators can cool your basement somewhat. But dehumidify?
BTW if condensation is an issue in basement a cheap fan might help.
>>

add heat to the space as well as remove humidity. Whether or not that heat is a significant amount is something that I haven't thought about, due to a lack of necessity.
Heat pump water heaters do exactly that

. <<

ethicalpaul

pecmsg said:

Heat pump water heaters do exactly that.

Well actually they do the opposite, they remove humidity and cool the space

Edit: on re-re-reading I'm not exactly sure what pecmsg meant by "that" (there is a lot being said in this thread) so maybe we're saying the same thing.

mattmia2

jumper said:

Easy to calculate heat produced by dehumidifier: hours times power.

easy to calculate but very difficult to measure unless you hook it up to a data logger since the power consumption depends on exactly what conditions it is operating in at any particular moment

Rich_49

Santa Fe ventilating dehumidifier . That's all ya need to do what you describe

ChrisJ

Rich_49 said:

Santa Fe ventilating dehumidifier . That's all ya need to do what you describe

Wow,

https://www.sylvane.com/santa-fe-dehumidifier.html

I guess that's a real, good quality version of a standalone dehumidifier.

Well, there you go @mattmia2 Tired of them dumping their charge, pay for one that's made to last.

mattmia2

I bought an aprilaire about 2 years ago, so far so good. A friend had a cheap Chinese dehumidifier catch fire over the weekend, looks like it did a lot of smoke damage to the whole house.

jumper

I'm surprised that nobody comments about my suggestion to try a fan.

ChrisJ

jumper said:

I'm surprised that nobody comments about my suggestion to try a fan.

How will a fan help with condensation issues in a damp basement?