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

Big Ed_4

Aprilaire , I used them for years . They work .....

jumper

ChrisJ said:

jumper said:

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

If there are openable windows simple ventilation. Even without windows moving air reduces temperature difference between walls and air?

realliveplumber

I put a 2 head Fujitsu (2x7000) in my basement 2 years ago, for a gym area and a laundry room. Works excellent. Dry and 74 degrees feels great down there.

mikeg2015

Wont work very well. There wont be enough sensible heat gain, so it will just quickly make it cold. So while it will remove moisture, It will jus be cold and damp instead of warm and damp, which really isn't that much better unless it's a completely unfinished space.

Specifically, the minisplit might be able to get the sensible to latent ratio up around 50%, but removing 1lb of water takes 970 BTUs. SO at a 50% S/L ratio, you would need to add 970 BTU. so to remove roughly 20 gallons of water in a day, you would need 6000BTU of heat removed from the space.

A standard AC unit might run at 20-30% S/L ratio. SO minisplit is better, but you will still just ride the RH slope down.

mikeg2015

In a previous career, I was a facilities engineer and we had a brand new, super insulated, tight commercial building with a overly compilated heat recovery chiller. They had placed the hot water coils before the chilled water ,typical in a cold climate and per standard ASHRAE codes. On typical cool damp, cloudy midwest days, there was minimal sensible gain. I set chiller water to 45F and reprogrammed the AHU drives to run down to 10HZ but still couldn't get humidity out.

I pointed this out to the engineers and asked why the how water coils weren't configured for reheat. They pointed to ward the energy codes. I nicely pointed out that ASHRAE has a exception to this design, when you had a heat recovery chiller. Some spaces did have VAV's so I could force reheat there. But most of the building was always damp.

We had a host of other control and design issues. Left that job since my boss wouldn't support me and wasn't sure if I was FOS or really smart. The fact that she couldn't tell the difference pretty much summed up her intelligence. We once spent 30 minutes explaining was a chilled water coil as to her.

winnie

ChrisJ said:

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?

If you put the outdoor unit inside with the evaporator, then you've just built a dehumidifier.

It would have a great chance of being more efficient than a small box unit, but no guarantee.

Daikin has their 'Quaternity' system which splits the coil on the indoor unit with a solenoid valve. In some operating modes it closes that valve and allows hot gas to condense in half of the coil, while it evaporates in the other half of the coil. This turns the indoor unit into a reheating evaporator, allowing dehumidification without overcooling.

Different companies implement 'dry mode' in different ways. Some systems simply ignore the room temperature and will turn the room into an icebox in Dry Mode; others will stop drying if the room gets too cold.

I have to wonder why no minisplits implement dry mode by actually flipping the 4-way valve to _heat_ the room if it gets too cold, but by guess is that this would require wider temperature swings.

-Jon

ethicalpaul

This thread is now swallowing its own tail

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

If you put the outdoor unit inside with the evaporator, then you've just built a dehumidifier.