Minisplit is not dehumidifying. White lineset. Possible issues?

109A_5

jchester404 said:

We have 4 Mitsubishi heads, 1 per room. Been having a non-condensing/non-cooling issue in 1 bedroom.

With a branch box, wouldn't the whole system charge be low not just one IDU ?

As far as the humidity problem in the 1 bedroom, is the condensate drain plugged or restricted so the moisture in that room just gets blown back into the room and not drained away ? And if part of the evaporator fins are in the flooded drip tray the efficiency of that IDU will be poor.

Do all the condensate drains drip equally if all the doors, etc. are open between all the zones and all the IDU are set the same ?

Do all the line sets sweat equally or is the one to the humid bedroom worse ?

jchester404

Addressing the last 2 posters - the more I read about relative humidity and dew point, I might be doing ok. My dew points have been ranging from 43-57ish. I went and bought a couple cheap humidity gauges to check. All drains have been dripping.

109A_5 - Yeah I was thinking the same about the branch box. The unit in question has the longest line. Would that not matter in a branch box? If I'm under-charged wouldn't the furthest away receive less, or is that fundamentally wrong?

ALL lines sweat. I'm starting to think that the exterior jacket on the insulation is naturally colder than my crawlspace air...

ChrisJ

pecmsg said:

Any refrigeration supply house will carry it. 

If that crawl space is that bad 1/2” wall thickness may be required. 

Be prepared for sticker shock, insulation is more expensive then copper!

I used a Mueller lineset with 3/4" wall insulation on it in my attic. I think I did 1/2" insulation on the liquid line.

Yeah.........it hurt buying it but it's well worth it. Lather on some latex paint where it's exposed to sun and it should last the life of the unit.

The other pain with it, just like steam piping is that tiny little 7/8 line becomes 2 3/8" OD.

ChrisJ

jchester404 said:

Addressing the last 2 posters - the more I read about relative humidity and dew point, I might be doing ok. My dew points have been ranging from 43-57ish. I went and bought a couple cheap humidity gauges to check. All drains have been dripping.

109A_5 - Yeah I was thinking the same about the branch box. The unit in question has the longest line. Would that not matter in a branch box? If I'm under-charged wouldn't the furthest away receive less, or is that fundamentally wrong?

ALL lines sweat. I'm starting to think that the exterior jacket on the insulation is naturally colder than my crawlspace air...

Those linesets if memory serves should both be cold, they aren't like a normal split unit where the liquid line is warm-ish.


So one of your lines should be cold (50s), and the other should be damn cold (30s-40s).


That sweating isn't just annoying, it's also literally costing you money. Think of it like this, you know it costs you quite a bit to run a dehumidifier. Those lines are literally acting as dehumidifiers and it's using a fair amount of energy to do it. And yet, you don't want it doing it.

jchester404

Yeah the only way to stop it is to control the environment in my crawlspace I suppose. Going to fully encapsulate soon

pedmec

if your linesets are sweating then its most likely that your run cycle is too long. the temperature of your insulation has finally reached the temperature of your suction line. and from what you have written previously that you are getting the room temperature down to 51 degrees then it should be no surprise that your line sets are sweating as it is going to take hours to get that cold. eventually the temperature of the insulation is going to get below the dew point of the ambient air.

jchester404

They sweat regardless if its in dry mode. My crawlspace is very humid.

pedmec

but your refrigeration cycle is still running. your air flow is very low . so this means the temperature of the refrigerant is just above freezing to max out the humidity removal process.

jchester404

How do you suggest I run them? I typically never use dry mode. I was using it to test that particular unit

ChrisJ

@jchester404 You're not pulling the room temperature the system is cooling down into the 50s, are you!?

jchester404

It only ever went to the 50's when I had ran it on dry mode. Usually all units are set for 69 and all rooms are typically +-1 of 69

ChrisJ

jchester404 said:

It only ever went to the 50's when I had ran it on dry mode. Usually all units are set for 69 and all rooms are typically +-1 of 69

Ok.

I may have missed it, but what temperature is the crawl space?

pedmec

you can run it anyway you want. you have to understand that you have to run it within certain parameters. which is not 51 degree space temp. there is a limit to what any air conditioning system can do. i can't believe you were able to get it down to 51, to be honest.
air conditioning systems are designed at a 75 degree space temperature with a 95 degree outdoor temperature. now your never running at exactly those temperatures but that is the standard. that's were they start and everything is based on that. so 51 degrees is out range.
my feeling is that your looking at numbers on a scale and might not be understanding them correctly, which is absolutely understandable. its not that easy or everybody would be doing it. lets just say that you took that 51 degree air with the 75% rh and heated that air up to 75 degrees with no change in the moisture content. then your rh will decrease down to roughly 30-40%. so its not that the system is not working. this is kind of how we try maintain rh commercial buildings. reheat the air after cooling (simplified version).

i would run in cooling mode in low fan. this will allow more humidity removal (latent heat) and less sensible heat removal. trial and error approach

jchester404

My crawlspace is usually in the 60-65 range.

pedmec - yeah the only time it ever got to the 50s was when I ran the one until on dry mode. Typically my units are always on 69 med/high. Changing it to auto or low and keeping all doors open my humidity level has dropped to OK levels. For example, 80 outside, room set to 69, temp in room is 66 with 63% humidity. So dew point 53. Not the best, but still comfortable.

I believe once I encapsulate my crawlspace I should see better results.

That all said, I'm getting a tech out next week to check pressure and for leaks

ChrisJ

Most air conditioners I've worked on give specs for multiple room temperatures and roughly what you should see. 70 degrees is often listed as well as 75 and 80.

I've seen my own split system do 66F with 46% RH and 41F supply temps. But that's really pushing it as I have my thermostat setup to shut down and warn me if the supply hits 40F.

a TXV as well as an EEV will allow the system to keep good RH across a wide range of temperatures because the evaporator pressure will drop as necessary to maintain the same load on the system. Technically it's controlling super heat..... but ultimately it causes the system to be able to operate at full capacity over a wide range.

I assume your minisplit is using multiple EEV's outside, so it should be able to run good at 68-70F in my opinion.

A decent system should be able to maintain a respectable humidity at 68-70F assuming the system is running enough.

jchester404

I'm ignorant on most of this stuff. Isn't that what the branch box does - regulates the refridgerant indendently from each other?

ChrisJ

jchester404 said:

I'm ignorant on most of this stuff. Isn't that what the branch box does - regulates the refridgerant indendently from each other?

No idea.
I've only worked on 2 minisplits and they were single head units.

mattmia2

Run the fan at the lowest speed and make sure it stops when the outdoor unit stops so it doesn't reevaporated the condensate from the evaporator.

EBEBRATT-Ed

Refrigeration copper tubing is "L" copper tubing that has been cleaned and dehydrated......no difference in sizes or wall thickness

3/8 od refrig is 1/4" L
1/2" " 3/8"L
5/8" " 1/2" L
3/4" " no equivalent This was Carriers dream
7/8" 3/4"L

pecmsg

EBEBRATT-Ed said:

Refrigeration copper tubing is "L" copper tubing that has been cleaned and dehydrated......no difference in sizes or wall thickness 3/8 od refrig is 1/4" L 1/2" " 3/8"L 5/8" " 1/2" L 3/4" " no equivalent This was Carriers dream 7/8" 3/4"L

Actually 
the ID is .032 of the OD. 

Over time it became standard wall thickness with dehydration to label it ACR. 

jchester404

So if I have 1/4 liquid line and 3/8 line, do I want to size up or get 1/4 and 3/8 insulation. What's proper?

ChrisJ

jchester404 said:

So if I have 1/4 liquid line and 3/8 line, do I want to size up or get 1/4 and 3/8 insulation. What's proper?

Get the correct size so it fits snug against the copper.  If there's a gap it's bad.

McMaster Carr carries many options and their premium stuff seals really good.  But....id be concerned about how badly corroded that lineset is before you spend a fortune on insulation 

jchester404

Yeah going to see what the tech says. If no leak I'll just insulate the exposed pipe by the branch box along with the flare nuts

109A_5

jchester404 said:

Yeah the only way to stop it is to control the environment in my crawlspace I suppose. Going to fully encapsulate soon

Be careful with this, you don't want to trap the moisture in the crawlspace area and create a mold problem.

Larry Weingarten

Hi, Here is some info on how to seal a crawl space effectively. https://www.buildingscience.com/documents/information-sheets/crawlspace-insulation and https://www.energyvanguard.com/knowledge/crawl-space-encapsulation/ Once this is done, the crawl effectively becomes part of the conditioned space, so if you go over 60% RH indoors for any length of time, it's time for dehumidification.

Yours, Larry