High humidity from new mini split ductless system

[earlburnermann]

I’ve been reading and re-reading this post and decided to print out a psychrometric chart a plot all the dry bulb/relative humidity values found in this post.

So ACCA states that an ac unit should output 75 degrees dry bulb at 50% humidity. That’s what I learned anyway.

And it is sometimes hard to picture the concept of humidity and temperature. The way I see it is that there is an absolute amount of water in the air, the grains of water. As the air is cooled its volume shrinks and relative humidity rises, as it is heated the volume expands and the relative humidity falls.

The home owner experienced the lowest relative humidity when he reported the temperature at 75 degrees, the industry standard dry bulb temperature. The RH was 45 and 32. The highest relative humidity was about 58% at temperatures of 68 and again at 73 degrees. And he only went over the 50% humidity three out of about ten measurements. The temps where 68, and twice at 73.

I’m surprised by the low relative humidity for six of the readings set at under 75 degrees. Looking at this chart I really don’t see any problem with the system other than the temperature being set lower than design.

I don't think there was a manual J done to size the units. if that was done then the complaint would most likely be that he couldn't get the temperature down low enough.

What am I missing?

[jtrammel]

I'm pretty sure they're inverter minisplits so sizing shouldn't be much of an issue. My guess is MANopause.

[dan sw fl]

I’ve been reading and re-reading this post and
decided to print out a psychrometric chart a plot
all the dry bulb/relative humidity values found in this post.

So ACCA states that an ac unit should output 75 degrees dry bulb at 50% humidity.
That’s what I learned anyway.

And it is sometimes hard to picture the concept of humidity and temperature. The way I see it is that there is an absolute amount of water in the air, the grains of water. As the air is cooled its volume shrinks and relative humidity rises, as it is heated the volume expands and the relative humidity falls.

The home owner experienced the lowest relative humidity when he reported the temperature at 75 degrees, the industry standard dry bulb temperature.
The RH was 45 and 32.

The highest relative humidity was about 58% at temperatures of 68 and again at 73 degrees.
And he only went over the 50% humidity three out of about ten measurements. The temps where 68, and twice at 73.

I’m surprised by the low relative humidity for six of the readings set at under 75 degrees.

Of course, R.H. will be frequently be > 50% when indoor temperature is less than 74'F.

WHAT IS MISSING
... IS THAT IT _ _ THE WOOD IS TOO DRY_ _, RELATIVELY, OF COURSE.

+ 72'F and 45% R.H. would be Quite Uncomfortable for Many.
... TOO COLD.!

Use of a portable dehumidifier to achieve ~35% R.H. is The Issue.

75'F & 50% R.H. seems to be appropriate for both Humans and Wood.

[valar]

X2 unless he's keeping the rooms at different temps. As you know fuzzy relative humidity is just that RELATIVE. There are much better ways to guage humidity in the air.

I converted all the humidity levels to dewpoints on my spreadsheet,. it showed the same relationship. I have every room set to the same temp

There is no new air infiltration vs out central AC system and we had no humidity issues with that. The only logical explanation I can some up with is that the units are oversized for the rooms, so they cool the room to quickly, meaning they are not running long enough to dehumidify the rooms.

I tried.

I did what you said, and I used the website you pointed out. It just confirmed the numbers. The temps in the rooms are not all that different, maybe off by a degree or two.

75'F & 50% R.H. seems to be appropriate for both Humans and Wood.

75 is pretty warm for me. 70 is more comfortable.

And I moved the hygrometer to my sons room and was astounded, the humidity was 68%. I ran the dehumidifer to get it down to 40% (and the room was MUCH more comfortable), took it out, 5 minutes later is was over 60% again.

The RH was 45 and 32

That was probably with the dehumidifier running

I’m surprised by the low relative humidity for six of the readings set at under 75 degrees. Looking at this chart I really don’t see any problem with the system other than the temperature being set lower than design.

I'm sorry, but I don't believe the lowest temperature an AC unit is supposed to reach is 75. and if you don't see buckling floors, nail pops, and 68%+ humidity levels as a problem, I'm not sure what else to say.

My guess is MANopause.

So just a little constructive criticism, since this is supposed to a forum for professionals. When a customer is having major issues, that are causing him major life stress, are physically damaging his home, and are costing him 10's of thousands of dollars, making fun of them is not a good idea.

Helpful comments I am glad to hear, helpful advice I am glad to take, and data I can provide to help I will gladly provide. But don't dismiss this as "all in my head". It's a real problem having a real impact on a real person. Show some compassion.

[CraziFuzzy]

If you are keeping your home at 70°F, that is the source of your floor boards warping. As teddy bear mentioned previously, cooling the house to less than the outdoor dewpoint is risky. This causes uninsulated areas (like apparently your floorboards to the crawlspace) to form condensation, which is causing them to warp. If the home was better insulated, this likely would not be a problem, but I have a feeling it is not.

[valar]

I've uploaded my spreadsheet so you can see the numbers. I know the temp an hygrometer I am using is not lab grade or anything so I assume there is a 1-2 degree wiggle room in the numbers. It has time, date, room (each room is on a separate sheet), temp, RH, dew point (from dpcalc,org) and whether or not a dehumidifier was running. The dehumidifier is always left off overnight.

http://wikisend.com/download/386678/dpcalc.xlsx

Take a look. The Master seems to be evening out and the unit can hold it at around 48-50 RH by itself. The Master is approximately twice the size of the kids rooms. The units in my son and daughters rooms seem incapable of maintaining anything below 65% humidity on their own, even after the dehumidifier runs for hours.

I triple checked the rooms, all the windows are closed and locked, there is no new source of air infiltration, and no moisture or water leakage anywhere.

[valar]

This is upstairs, there is no crawlspace under the floor.

And with my ducted system I kept the temp at 70 for over 10 years and never had a buckled floor in my life.

[earlburnermann]

Valar,

Everyone is different when it comes to sensing comfort. You seem to be very sensitive to your environment, more than most, but not all.

When it comes time to give up on your present home I'd recommend finding the most qualified building analyst you can find to scrutinize all homes you consider purchasing.

You could end up jumping out of the frying pan and into the fire.

[CraziFuzzy]

Those numbers back up what's been saying here.. Your problem is high infiltration. Once moisture is removed from the space by the dehumidifier, it seems to come back quickly. There has to be a source to that moisture, and it is most likely outside air freely entering the home. Most your rooms are at 'acceptable' moisture levels, with dewpoints of 50-55°F. The fact that your old ducted unit didn't reveal this problem could be a few things:

1.) Low air flow from poor duct arrangement: The old system likely had poor duct-design, meaning air flow was rather restrictive, causing colder air coming off the evaporator all the time - this is analagous to the mini-split's dry mode.

2.) Duct leakage on supply ducts: The old ducts may be leaking in quite a bit of air from the attic. This may not have been as evident on the old system, if the old system was running a lot of the time (causing air to blow INTO the attic, and not be drawn in).

3.) Things change: There may be a completely unrelated introduction of moisture into the home that you have not yet found. The fact that the son and daughter's rooms are showing higher 'natural' dewpoint, I'd guess whatever the source, it is primarily entering the home in that area.

[valar]

The old unit was in the basement, not the attic.

Most your rooms are at 'acceptable' moisture levels, with dewpoints of 50-55°F.

You keep saying "acceptable", "acceptable" to me is not buckling my floors, not sticking to your skin, and not being intolerable uncomfortable. Nothing about this system is acceptable to me. Out of every HVAC system I've tried, they perform the worst, they were the most expensive, they cool the worst, the dehumidify the worst, they look the worst, and they are the most expensive to operate because of all the other equipment you need to run.

I just checked my kitchen, which has no unit it it. The humidity was 81%. The downstairs living room with a unit was over 60%.

These mini splits cannot keep a comfortable humidity, and they have zero cooling effect on rooms without units. They have almost no air flow, the house is incredibly uneven temperature wise because of that, and as for the "savings", I have to run two 9 amp compessors full time just to make the space livable! I'm probably looking at a $600-$700 electric bill this month.

I'm done with these things. For a garage or sun room, sure, they might work (but even then are way to expensive), for an entire house, mini splits absolutely suck. I'm calling the installer monday and telling him I don't even want to waste time dealing with the rep guy, I want them to tear these horrible things out and put the oil system back in and I'm done. I'll just have headaches.

That's how bad mini splits are: I would rather have constant headaches and pay out the nose for heating oil than have these things. At least with that furnace I'm the only one suffering vs everyone in the house, and the house isn't getting damaged so I can try and sell the damn thing.

I must be the only person on the planet forced out of his home by an appliance upgrade. Unbelievable.

[CraziFuzzy]

You are upset, and I understand this - but this is not a fault of 'mini-splits'. It is the fault of a poorly designed system. As far as I can tell:
- You had these installed as a knee-jerk reaction to the thought that somehow your air ducts were causing a health issue.
- You had no energy audit done prior to it being installed.
- You had no actually 'engineering' done while completely changing the method of heating and cooling the structure.

If the problem was the ducts, you should have just replaced the ducts. I don't think you actually completed any of the other threads about your problems before going out and throwing money at whoever would catch it.

[valar]

These did solve the headache problem, they just introduced a bunch of new problems.

I fail to see what an energy audit would have accomplished. It could tell me I have a lot of air infiltration? What exactly could I do about it? It's a 55 year old brick house. You can't pull down all the bricks and wrap it. Should I tear out all the drywall and sprayfoam the house? It's going to tell me my duct system isn't properly designed? So I should tear the house down to the studs to fix it? An energy audit would be a waste of money: it would tell me problems I already know I have but can't be fixed. Most "green" housing initiatives I've seen are complete rip offs to begin with, sure, spend 5 grand to save $10 a month on a heating bill, where can I sign up for that great deal.

I had thousands of dollars in AQ testing done

As for engineering, I trusted the company and installers when they sized these units and told me they would cool rooms with no units in them. What engineering do you think I should have done? I'm not an architect or an HVAC specialist. I trust the people who tell me how these things work.

I actually think I found the original problem, I think it was the insulation in the furnace. I stuffed insulation in the ducts to try and block them and a lot of the symptoms came back for a day or two after handling the insulation.

The mini splits did what I thought they would do (fix the headache problem), they are just failing to do a lot of things I was told they would do (keep the house cool, dehumidify the space). I fail to see how that is my fault. Is it wrong to trust the people who's business it is to know these things?

As for the other threads I did everything that was asked in every one of them and nothing helped.

You're right I am upset, and I feel I have a right to be. Nothing I have been sold during this whole debacle has done what I was told it would do. Nothing. I've been charged tens of thousands of dollars to render my home unlivable. Now I'm sentenced to a life of daily headaches until I can move. You would be upset too.

What exactly do you think I should do at this point? The situation is not normal, the floors are still buckling and I have a dehumidifier running non stop and a AC unit running non stop and the kitchen is too warm. So I have damaged floors, a hot kitchen, and $200+ dollars in extra electricity usage. What should my next step be?

[valar]

I'd recommend finding the most qualified building analyst

Whats a "building analyst"?

[valar]

Just checked my sons room. The dehumidifier has been out of there for a few hours. 70 degree temp, 65% humidity. These units cannot keep these size rooms properly dehumidified. Guess I'm running this thing all night, maybe I can top $1000 electric bill in a month.

[valar]

Sorry for my little rant up there, this is a very stressful situation.

I ran the dehumidifier in my sons room, got it down to 45, and the room is quite comfortable. Would that point to them being oversized for the room? If they are short cycling, woudn't that mean they were not running enough to maintain a proper humidity level?

I also tried opening the door to the hallway and turning the ceiling fan on to help airflow and see of that would help anything, it did not make any difference.

I ran an online size calculator for mini splits and it came back with around 4500 BTU needed for a room that size rooms. They currently have 9000 BTU units in them, I was told that was big for the room but it shouldn't matter due to being on inverters. Is 9000 on an inverter still too big for rooms this small? Each room is around 8x12, roughly 100 square feet, 8 foot tall ceilings so 800 cubic feet (sons room is a little smaller daughters room is a little bigger)

[jtrammel]

Sorry for my little rant up there, this is a very stressful situation.

I ran the dehumidifier in my sons room, got it down to 45, and the room is quite comfortable. Would that point to them being oversized for the room? If they are short cycling, woudn't that mean they were not running enough to maintain a proper humidity level?

I also tried opening the door to the hallway and turning the ceiling fan on to help airflow and see of that would help anything, it did not make any difference.

I ran an online size calculator for mini splits and it came back with around 4500 BTU needed for a room that size rooms. They currently have 9000 BTU units in them, I was told that was big for the room but it shouldn't matter due to being on inverters. Is 9000 on an inverter still too big for rooms this small? Each room is around 8x12, roughly 100 square feet, 8 foot tall ceilings so 800 cubic feet (sons room is a little smaller daughters room is a little bigger)

Being variable capacity systems They should be able to ramp down enough to adequately meet the load your upstairs has a high infiltration rate. A home energy audit will uncover the place/places that the humidity is coming from. A building analyst would be in the home energy auditing realm of the industry. www.comfortinstitute.org
www.bpi.org
www.resnet.us
they will use thermal imaging, blower door etc to find the source of the moisture. I don't beleive The minisplits are the problem. Something in the envelope has changed and is causing this problem or the problem always existed and the central system masked the problem. Throwing more money at the problem is not going to fix anything until you find the root cause of the problem.

[earlburnermann]

Whats a "building analyst"?

http://en.wikipedia.org/wiki/Building_performance

[hvacrmedic]

Being variable capacity systems They should be able to ramp down enough to adequately meet the load your upstairs has a high infiltration rate. A home energy audit will uncover the place/places that the humidity is coming from. A building analyst would be in the home energy auditing realm of the industry. www.comfortinstitute.org
www.bpi.org
www.resnet.us
they will use thermal imaging, blower door etc to find the source of the moisture. I don't beleive The minisplits are the problem. Something in the envelope has changed and is causing this problem or the problem always existed and the central system masked the problem. Throwing more money at the problem is not going to fix anything until you find the root cause of the problem.

Yep, I was thinking the same thing. The old system may have had a dominant return duct leak pressurizing the house. That would not only explain the change in house behavior, but also the headaches that the OP first complained about.

[valar]

Well, I'll be throwing money at them. And if they find something, I can't really do anything about it. I'm not tearing the drywall out and spray foaming the rooms, and you can't wrap the house without demoing it.

I remain convinced the mini splits are oversized for the room, so they cool the rooms to fast and then turn off, not running long enough to extract the humidity from the room. As a test I set them to dry mode, auto fan, and put the temp as low as it can go (64). That should make the units run longer, and if the humidity levels get lower, I believe it would confirm my hypothesis. It's not a solution but if it confirm them being oversized I can tell the installer to swap out the 9000's for a smaller unit

[valar]

dominant return duct leak

What is that?

Once again, I don't see the pointing hiring these energy auditors and shoving even more money in their pockets to potentially show me a problem I can do nothing about