Air conditioner working, room cold, but can't get humidity down...???
Old 22nd June 2010
  #1
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Air conditioner working, room cold, but can't get humidity down...???

In one new 600 sq/ft above ground room, I'm running a ductless split AC. Room is still under construction, but mostly done.

Past few days it was hot and humid and the AC in that room had not been running. I went into the room yesterday and it was about 84F degrees and about 66% RH. Felt very hot, sticky and uncomfortable.

Side note: room has a lot of wood planking and exposed, unfinished wood in general.

I turned on the ductless split yesterday, within a few hours it brought the temperature down to 78F degrees, but RH barely moved, still around 63%. Temp kept dropping.

Then last night for the heck of it I cranked the AC to 70 and in a relatively short period of time, the room did get down to about 70F degrees. And it's been around 70F all day in there, feels nice and frosty. BUT... the RH is still hovering in the 61% - 63% zone! ???

Few notes... I believe it's about 82F degrees outside and likely pretty high humidity.... I didn't check it, but I'd guess at least 65% outside if not more.

Other rooms in this building (being cooled by a central system) are 77F degrees (as set), and RH at a SOLID 50% or LESS.

I also put a second humidigauge in that room to make sure I was looking at a correct reading... both gauges agree... 61% - 63% humidity... yet 70F degrees.

So I go outside and check the drain hose on the ductless split, it's dry...?????? The outdoor compressor unit seems to be running fine, the refrigerant lines are ice cold and sweating. The drain line IS very long, once the unit starts making water, it usually takes a pretty long time for the water to start dripping out of the hose outlet. But... the unit's been running for almost 24 hours now, I think I should see some water coming out, considering it's still 60%+ RH in the room. UPDATE: just checked again, there IS a very small bit of water exiting the drain hose, but VERY little... like maybe one droplet every few minutes.

This is a mystery... the room is humid, the AC is clearly working (cooling the room), but yet somehow it's not pulling the humidity out...?

One thought... because the room has so much exposed unfinished wood in it, perhaps the wood is holding the humidity like a sponge, and it may take a day or two running the AC at full blast to dry out the room and bring the RH down...? But this doesn't explain why I don't see water dripping from the drain hose... yet.

In the past when it's gotten very humid in that room, I HAVE seen water dripping from the drain hose.... but not now. (I will also follow the entire drain hose run and make sure there are no kinks, leaks, etc, but no evidence of that thus far)

It feels quite comfortable in the room anyway, it's clearly nice and "cold", but I can still sense the "high" humidity (I'm very sensitive to this stuff). I have a few basement rooms with dehumidifiers running, have the RH at about 45%, those rooms feel NICE.

So it'll be interesting to see how this plays out. I hope there is no inherent issue with the ductless split, or maybe mine is experiencing a problem...? But how could it COOL the room without pulling out humidity??? Doesn't make sense.

I realize that if an AC is over-rated for a room, it may not reduce humidity efficiently because it would not need to run much to cool the room etc... well, I don't believe I have that problem, I even tried running the AC on "dry" mode which forces the unit to run continuously at a very slow fan speed... tried this for quite a few hours... still didn't seem to make a difference in the RH. I can't get the RH below 60% no matter what I try, whether I run the AC hard with fast fan speed, or run it very slow on dry mode, etc.

Am I overlooking something here? With every other room I've dealt with, utilizing a typical AC system, once the room would get cooled down, the RH would almost always drop down to at least 50%. An RH of 60% seems unusually high for a room that has been cooled from 85F to 70F.

One thought... as a test, I could put a dehumidifier in there, see what happens... if it starts wicking humidity out of the air like crazy, then it shows that the AC is simply not performing this function for whatever odd reason (even though it IS cooling). If the dehumidifier seems to not want to run much, then perhaps it's just not as humid in there in general as I think... maybe BOTH my humidigauges are inaccurate???

Well, I have more testing and observing to do.

Another thought comes to mind... I should stick a humidigauge right in FRONT of the cold air output ducts on the AC and get a reading.... I'd like to think that the air coming OUT of the unit is very cold and very dry. UPDATE: I tried this and the "cheap" humidigauges I have seem to go bananas and yield seemingly exaggerated, inconsistent readings... they're obviously not designed for this type of measuring.

I should also stick the gauges outside for a while and get an idea what's going on out there. UPDATE: did this too, it's about 80F degrees, 72% RH outside, partly cloudy.

Final comment as I wipe some sweat off my brow... I HATE humidity!

Extra credit: I realize there are many factors involved when sizing an AC system for a room. I worked with a pro HVAC team and their recommendation seemed to make good sense to me. In sum, the room is 600 sq/ft, 12 ft ceiling height, only two well insulated windows total, one inside door only (no outside door), and overall very heavy insulation in the roof, walls and flooring. That given, would anyone like to take a stab at what might be a good BTU unit for this room? Just a rough idea? Would like to see how your ideas compare with those of the HVAC guys I use.
Old 22nd June 2010
  #2
jdg
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the dry drain line is your huge clue.
something is not right there.

how long is "long" for your line?

i had a long line, (50 feet) and it still pushed out water like crazy
Old 22nd June 2010
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Quote:
Originally Posted by jdg View Post
the dry drain line is your huge clue.
something is not right there.
how long is "long" for your line?
i had a long line, (50 feet) and it still pushed out water like crazy
Thanks. Makes good sense.

I just updated my above first post. I am NOW seeing some water at the drain line, but very little... maybe one small drop every few minutes. But, with my other ductless splits in the basement, when the humidity is very high, water literately pours out of the drain hose.

The drain hose on the unit in question... just a rough estimate (will go climb up in the attic later to fully inspect it, haven't been up there in a while)... maybe 20 feet... but that's 20 feet horizontally, with a minimum degree of pitch (we pitched it the best we could but there were some limitations, but have no fear, it IS adequately pitched)... so one thought comes to mind, I wonder if there is a possibility of a small bit of water sitting inside the unit (because it cannot escape quickly due to a less than idea drain pitch), and that small "puddle" in there is in effect acting like a humidifier. I have not taken this unit apart so I'm not exactly sure of the inner workings, or possible issues. One person once told me that their drain hose got clogged and water started pouring down the wall of the room causing massive destruction (they were away and this went on for days).

In my situation, if water started leaking anywhere, I'd likely see it pretty soon, just due to where the unit and drain hose is, etc... so I'm not too worried... but I'll go inspect it first-hand soon anyway.

Thanks for the input... will report back.
Old 22nd June 2010
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Isn't this generally a sign that the unit is oversized for the space?
Old 22nd June 2010
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Quote:
Originally Posted by dykstraster@gmai View Post
Isn't this generally a sign that the unit is oversized for the space?

Yes. It usually means that the cycles aren't long enough to condense water (ie. Unit is too large and cools too fast in the infancy of its own cycles). If you're running your unit non-stop though, there's something else amiss...

Neil
Old 22nd June 2010
  #6
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Quote:
Originally Posted by dykstraster@gmai View Post
Isn't this generally a sign that the unit is oversized for the space?
Yes, and I did make reference to this point in my first post. But I believe this is not my problem. To dehumidify well you need to be moving a lot of air over the coils almost continuously. If the AC is oversized, it will cool quickly and only cycle on for short periods, not allowing the air to spend enough time moving over the coils, etc. That's how I understand it anyway. And if you run an oversized unit continuously you'll freeze your butt off... and also waste a lot of electricity.

The ductless split I have (Fujitsu) has a "dry mode" as well as cool mode. In dry mode, the unit runs with a very slow fan speed to continuously move air over the cold coils in order to pull moisture out while not over-cooling the room. I did try running the unit in dry mode for several hours but there was no difference in the room RH.

I would find it very interesting to hear what BTU people would recommend for my room (as described in the last paragraph of my first post)... just to get an idea if I'm somehow far off. But I don't think so. If anything, per my own observations and studies, my unit might be slightly under-rated if anything... just slightly. But, on a not-so-severely hot day, my unit will cool the room pretty well in just a few hours. I don't have enough experience with it yet to report how it does is ALL situations... I have yet to fill the room with gear, but I've ditched a lot of my "hot" gear anyway.... so far I've been able to make it nice and cold in there.

Quote:
Originally Posted by amishsixstringe View Post
Yes. It usually means that the cycles aren't long enough to condense water (ie. Unit is too large and cools too fast in the infancy of its own cycles). If you're running your unit non-stop though, there's something else amiss...Neil
Just saw this post now, thanks for the clarification.
Old 23rd June 2010
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Quote:
Originally Posted by 666666 View Post
Yes, To dehumidify well you need to be moving a lot of air over the coils almost continuously. If the AC is oversized, it will cool quickly and only cycle on for short periods, not allowing the air to spend enough time moving over the coils, etc. That's how I understand it anyway. And if you run an oversized unit continuously you'll freeze your butt off... and also waste a lot of electricity.

The ductless split I have (Fujitsu) has a "dry mode" as well as cool mode. In dry mode, the unit runs with a very slow fan speed to continuously move air over the cold coils in order to pull moisture out while not over-cooling the room. I did try running the unit in dry mode for several hours but there was no difference in the room RH.
Sorry - but the unit only dehumidifies if the compressor is running constantly - when the compressor turns off the unit does not dehumidify even though the the fan may be blowing air through the coil - a fan can run 24 hours a day and never over cool the room - because the fan is not doing the cooling............

however - if your drain line is clogged which means your drip pan is filled with water - the air blowing over the water will put moisture back into the air - I think I would start with blowing out the drain line using a compressor to make certain it is draining properly (another thing to do would be to check the drip pan and see if it was filled with water).

Rod
Old 23rd June 2010
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Thanks Rod.

Quote:
Originally Posted by Rod Gervais View Post
Sorry - but the unit only dehumidifies if the compressor is running constantly.... - when the compressor turns off the unit does not dehumidify...
Yes, I do know this, I probably didn't explain myself clearly.

Quote:
however - if your drain line is clogged which means your drip pan is filled with water - the air blowing over the water will put moisture back into the air...
Yes, this is what I'm thinking. I don't think there are any clogs etc, but I'm wondering if, due to a less than ideal pitch on the drain hose, the water just might not be exiting the drip pan as fast as it could, and I may have a little bit of standing water in the pan at all times.

I don't think I can easily get to the drip pan... so this may be hard to impossible to truly figure out. And the drain hose of course is connected to the unit... and the unit is "permanently" attached to the wall (held in by it's refrigerant lines), I can't unhook the drain hose or get behind the unit without undoing the refrigerant lines... which I'm of course not going to do. Though, now thinking about it, I wonder if there may be a way to somehow see or access the drip pan from the front, after removing the decorative plastic cover... it would be sweet if they had a little drain cock under the drip pan accessible from the front... if so I could undo it and see if a lot of water pours out... if so, then that's my problem.

Will look into it. Thanks for the feedback!
Old 23rd June 2010
  #9
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Most definitely sounds like an obstructed drain line. I had the same issue a few years back on a central system and it turned out to be an insect that had crawled up the drain line and "expired" creating a blockage.
Old 25th June 2010
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If the unit is over sized for the room than you will likley have moisture issues.

What happens is the ACunit is cooling the space quickly enough that it has no chance to remove condense the moisture in the air.

I've seen this get real ugly when a public school library had an oversized unit for the application and within 8 months they realized that books were growing mold due to the RH being so high. Can you say law suit.

Could you perhaps give us the CFM of the unit, and the SF + ceiling height of the space?

If its a done deal you could run a dehumidifier but thats not optimum.

Good luck
Old 25th June 2010
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Thanks for the replies.

First I'll mention that I traced the entire drain system, the hose that exits the unit (and passes through the wall) was perhaps not pitched downward as well as it could have been, but it WAS pitched. So, using my Dremel Multi-Max plunge cut tool, from the back side of the wall, I made the hole in the wall larger (had to cut through several layers of sheetrock, OSB, etc) so that I could achieve a greater pitch on the drain hose.

I then tested the drain piping (PVC) (that the drain hose fits into), good pitch, I didn't have an air compressor handy, so as a test I poured a lot of water into it at a very rapid rate and the drain piping took all the water I could put in with ease. No restrictions, no blockages.

In sum, I did not find any serious issues with the drain system, it's in a tip-top state of being at this point.

After spending some more time with the unit now, doing more testing, etc, it seems that the unit is indeed "oversized", at least per the current conditions.

One test I did after fine tuning the drain system... it was maybe 76F degrees in there and 60% RH... I then set the unit to 64F degrees and medium fan. Within about 15 minutes I had water exiting the drain system quite rapidly and the RH when down to the low 50% area... but of course the room started to get pretty cold. (Indication of being oversized)

So it seems that the unit IS working and is able to pull out the water when it's cranked.

With these split systems, you can't hear the compressor, can't tell if it's running or not. So, per my initial observations, I was never really sure when the compressor was on or not, even though the fan was always running. BUT, it SEEMED like there was always cold air coming out which made me think that the compressor was always running.

So far it's only been me in the room, and ZERO audio gear. When the room is finally in use, there could be two or three people in there, plus a good amount of analog audio gear. Maybe once the gear is in there etc, the unit will then be properly sized for the situation.

The room is about 650 square feet, with an average ceiling height of about 12 feet. The room is on a second story (over an uninsulated garage). Part of the ceiling is vaulted (no attic), and no shade, sun beats directly on this room. Room has only two, tight windows, and only one door that opens into the interior of the building.

The unit is a Fujitsu ductless split, 30,000 BTU.

When we sized the unit, we did factor in that there would be computers, amplifiers, a decent amount of audio gear and possibly even video lighting in there.

I think what the problem may be though... I very heavily insulated the roof system and walls too... my HVAC guys maybe did not consider how well insulated the room is. When you look at this room, high vaulted ceiling, no shade, over a garage etc, it certainly seems like a room that going to need a LOT of cooling. But, before getting the AC, one the first super hot day of the summer, the rest of the building would be sweltering (poor insulation), and this one room in question would actually stay cool almost all day (before finally warming up a few days later if we had a constant heat wave). It's possible that the unit will need to work harder as the summer commences... we haven't yet had any continuous, lengthy ultra heat waves yet, just a few hot days here and there under 90. Maybe things will work better when we finally have say a solid week of 94F+.

But also remember... this split unit has a "dry mode" and a super slow fan mode. I'd think that if the unit was oversized, it would still remove the humidity quite well in either dry mode or super slow fan speed mode. But, even in these modes, it just can't seem to get the RH below 60%.

Another thing that is puzzling. This room in question always seems to stabilize at 60% RH, whether the AC is running hard or not, whether the temperature inside is 74F or 79F. The rest of the building seems to sit at 50% RH, AC running hard or not, temperature at 74F or 79F. Seems that the room in question has in inherent humidity issue verses the rest of the structure. However, the ambient RH underneath all these rooms (garage, basement) has been constant at about 70% - 75% RH, it's not like one part of the structure is exposed to greater outside humidity than another. Similar degree of sun exposure too overall.

One other thing I need to look at though... the room in question has blow-in insulation under the flooring (as observed from underneath). I'm wondering if there is a vapor barrier against the room floor underneath. If there is no vapor barrier, then that's 650 sq/ft of area exposed to 70+% RH with nothing stopping it... I'd imagine that the outside RH would be passing into the room faster than the AC could deal with it, etc. I'll be working on the subfloor soon anyway, so I'll have a chance to look into this and correct if necessary.

In sum though, given the specs of the room, would you say the unit is grossly oversized, or...? Do you think my HVAC guys made a huge, foolish error with the sizing, or do you think the sizing is reasonable considering that they were told the room was to be used for audio gear, computers and possibly video lighting, etc?

Thanks.
Old 25th June 2010
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Regarding BTU sizing....

I just found some BTU "calculator" online and ran my numbers... just for the heck of it...

The calculation yielded a recommended BTU value of 28,512 for my room... (and my unit is 30,000 BTU)... so, perhaps I'm not TOO far off in any case.

Again, I am well aware that you cannot size an AC based on one standard calculation, there are of course a lot of things to be considered, but at least this is giving me a rough "ballpark" idea.

And the calculation I just ran does not even factor in heat producing gear that may be in the room. This would then almost suggest that I'm undersized, if anything.

For the heck of it, here's the calculation I just did:

Room area: 33ft X 20ftX 12ft ceiling height = 7920 cubic feet

Multiply by a "south facing room" factor of 18 = 142,560

Divide by a "good insulation" factor of 5 = 28,512 BTU recommended

This is just one thing I found, not sure how accurate it is... but it seems to be yielding a number that makes sense.

Another thing I remember my HVAC guy telling me, he feels that as the years go on, the EFFECTIVE BTU will drop a bit below the rating, so he likes to oversize slightly for this reason. I do also remember we had been considering the 24,000 BTU model (2 ton), and then, especially once the discussion of audio gear and video lights came up, we decided on the 30,000 BTU (2.5 ton). Who knows, maybe for how the room is being used at this moment (no audio gear etc), the 24,000 BTU would have been better... I guess the true test will occur once the room is "finished" and everything is up and running.... AND also once we enter into a heat wave, etc.

In a perfect world, for a room like this, perhaps you'd have TWO separate units... a 1 ton, and also a 1.5 ton... and you only use the 1.5 ton when the cooling needs are not that great (no gear on, etc)... then switch on the additional 1 ton when things get extra hot (once you have all your gear running, lights, etc).

Regarding the last paragraph... I know that you CAN buy dual stage compressor central air units (one unit with TWO separate compressors within)... I actually have one of these for the rest of the building at it works GREAT... at night one baby compressors runs only and keeps the house nice and cool with very little energy being wasted. When the sun comes up and is beating down on the vaulted ceilings and things really start heating up, the secondary larger compressor kicks on and delvers frosty goodness.

Old 25th June 2010
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Another quick note...

In my basement rooms, they're often nice and "cold" naturally, but yet have high humidity. Dehumidifiers are necessary here.

In this other above ground room in question, I can predict having instances where the temperature (especially at night) could stabilize at a low, comfortable number, but yet the humidity might still be "too high".

And, I"ll also mention that I am considering 60% RH "too high". I think, for most general residential uses, 60% RH would be considered fine. And indeed, 60% RH is really not TOO bad. But, like most gearslutz, I'm being overly fussy here, also concerned about the health of the gear, etc.

I think 50% RH is fine, 45% RH is even better.... 55% RH is still ok, but then once you hit 60% RH, you're really at the line. Above 60% and you really start to feel it, it's not comfortable.... and not really good for electronics, etc.

In a perfect world, the RH would remain somewhere between 45% and 50%, but to be more realistic, figure 47% to 53%... and perhaps 56% being absolute max peak. Thus, I'm not happy that I can barely keep my room below 61% RH right now. I'm thinking that I might very well need a dehumidifier for this room (in addition to the AC).

so then the next thought is, does anyone make a QUIET dehumidifer? I know there are very expensive, heavy-duty units out there, but they're not necessarily quiet. Most seem quite loud in fact.

I noticed a few units out there that can be mounted "remotely" with ducting, and even have remote humidistat kits... that's cool... but unfortunately, there are reasons why this would be hard to nearly impossible to implement into my situation. Perhaps I'll wind up with a small typical floor unit, and I can build a "sound baffle" box for it (with good venting of course)
Old 25th June 2010
  #14
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Quote:
Originally Posted by 666666 View Post
Regarding BTU sizing....

I just found some BTU "calculator" online and ran my numbers... just for the heck of it...

The calculation yielded a recommended BTU value of 28,512 for my room... (and my unit is 30,000 BTU)... so, perhaps I'm not TOO far off in any case.

Again, I am well aware that you cannot size an AC based on one standard calculation, there are of course a lot of things to be considered, but at least this is giving me a rough "ballpark" idea.

And the calculation I just ran does not even factor in heat producing gear that may be in the room. This would then almost suggest that I'm undersized, if anything.

For the heck of it, here's the calculation I just did:

Room area: 33ft X 20ftX 12ft ceiling height = 7920 cubic feet

Multiply by a "south facing room" factor of 18 = 142,560

Divide by a "good insulation" factor of 5 = 28,512 BTU recommended

This is just one thing I found, not sure how accurate it is... but it seems to be yielding a number that makes sense.

Another thing I remember my HVAC guy telling me, he feels that as the years go on, the EFFECTIVE BTU will drop a bit below the rating, so he likes to oversize slightly for this reason. I do also remember we had been considering the 24,000 BTU model (2 ton), and then, especially once the discussion of audio gear and video lights came up, we decided on the 30,000 BTU (2.5 ton). Who knows, maybe for how the room is being used at this moment (no audio gear etc), the 24,000 BTU would have been better... I guess the true test will occur once the room is "finished" and everything is up and running.... AND also once we enter into a heat wave, etc.

In a perfect world, for a room like this, perhaps you'd have TWO separate units... a 1 ton, and also a 1.5 ton... and you only use the 1.5 ton when the cooling needs are not that great (no gear on, etc)... then switch on the additional 1 ton when things get extra hot (once you have all your gear running, lights, etc).

Regarding the last paragraph... I know that you CAN buy dual stage compressor central air units (one unit with TWO separate compressors within)... I actually have one of these for the rest of the building at it works GREAT... at night one baby compressors runs only and keeps the house nice and cool with very little energy being wasted. When the sun comes up and is beating down on the vaulted ceilings and things really start heating up, the secondary larger compressor kicks on and delvers frosty goodness.

Your rooms is a super insulated area with very little passive solar gain and very little air infiltration.

Any standard calculator would yield a system that was grossly oversized. The solar gain is almost meaningless - and the insulation factor is as well - those calculations are for typical construction. Normal doors - windows - air infiltration and insulation - they cannot handle the requirements for a super insulated room with not firect openings to the outside world.

It wouldn't surprise me that a contractor talked you into the next larger unit - they do it all the time and it's bullshit........... I don't even let them do that in standard construction - they say it's good because it will handle the worse 2 weeks of the year - but that also means it is inefficient for the rest of the cooling season........

A 2 stage is a great investment........

The volume of the room is pretty much irrelevant for cooling because anything above 6 feet doesn't mean squat - you could care less what the temp is 12' in the air - all you care about is that first 6' - once the T-stat is satisfied you've done the job - and the cooling thermal layers work from the floor up in this case - not the ceiling down - a heating calculation is where i might think about that.

The other thing is this - and for this I do not know the answer - at least not for a mini split - and that is what the sensible versus latent load capacity is of the equipment.

When you work with HVAC systems you calculate latent (moisture laden) air cooling and sensible (which is gear - lighting - etc.) loads and then size the equipment to match (split systems give you the info they are designed for) and it all has to do with the size of the cooling coils - you spread the air over a greater coil area to increase dehumidification while maintaining the same total cooling capacity to handle the total BTU load......

3 tons of cooling capacity for a load that has 2 tons of latent and 1 ton of sensible is totally different than 3 tons of cooling for a load of 2 tons sensible and 1 ton of latent......

the 2 systems are not designed with the same cooling coils......

I think you end up back with a dehumidifier any way you cut it here.....

Are you using an HRV for fresh air?

Rod
Old 25th June 2010
  #15
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Thanks Rod. Interesting stuff... especially the sensible / latent differences and different coil configurations for such, etc. Wish I had known more about this in the past... this AC was installed two years ago before I was aware of a lot of these types of issues.

Before I commence much with my AC study here in this room, I will first check out the vapor barrier situation, since the more I think about it, the more I suspect there is no vapor barrier under the floor. I'd imagine that this would surely make a difference in what goes on with the RH in the room. If the room is not vapor tight, then even an appropriately sized unit will probably have trouble keeping the RH nice and low.

As for venting... at the moment, a positive venting system is not yet in place, again, the room is still not yet finished. My plans are to, like with my basement rooms, add a high CFM remote vent fan that will blow air from other parts of the building INTO this room, and then of course have an exhaust port. This will accomplish 100% positive venting, at least as long as the vent fan is running.

Also to be noted, due to the location of this room in the building, I will probably be able to even keep the door OPEN a lot of the time, isolation will not be a big concern in this particular room, at least not for a good percentage of the time.

The air in the other parts of the building will already be "conditioned", so pumping such air into the room should not cause any issues in terms of cooling / humidity. If anything, the air getting pushed into the room will likely always be more dry.

Thanks again Rod... your thoughts / comments are always educational and appreciated. Of course all this keeps reminding me how important it is to hire a professional (like yourself) for consulting etc before commencing a big project. My current rooms are a part of a somewhat "smaller, temporary" set-up that might have to be converted back into "typical living space" at some point... which is why I didn't want to go too crazy with the build up. I'll surely be giving you and perhaps some of the other helpful pros at this forum a call the day I'm ready to build up a serious pro facility... that's my goal... always working towards that. One step at a time.

Old 25th June 2010
  #16
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One thing it could be is; all HVAC have to pull a certain amount of outside air in WITH the return air, this is adjustable on most systems, anywhere from 20% to 100%...
So my point should be obvious, you will always have SOME outside air being mixed with the return air..with its moisture content..Just a thought..
And a sure way of knowing if your system is way over sized if it cools down very quickly, say 10 minutes..not enough time to remove the moisture in the air..

Had the above problem in a studio that removed the Large console..with its heat generating affect..once removed the air ran about 1/3rd the time..
Old 25th June 2010
  #17
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Quote:
Originally Posted by nosebleedaudio View Post
One thing it could be is; all HVAC have to pull a certain amount of outside air in WITH the return air
I'm running a ductless split unit which does not pull in any outside air at all. The compressor is outside, and the air handler is inside. It's a very cool set-up.

Quote:
Had the above problem in a studio that removed the Large console..with its heat generating affect..once removed the air ran about 1/3rd the time..
Wow, interesting. I will be using a good amount of rack gear, but no huge analog console. Though, my prediction is that the effect of my gear will not be overly huge in my room, considering the size of the room.

One time I had some gear in a SUPER small room with low ceiling and the temps would go over 95F degrees in the room almost immediately without the AC running. But in a big room with a high ceiling, you have a bit more leeway.
Old 25th June 2010
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Quote:
Originally Posted by 666666 View Post
I'm running a ductless split unit which does not pull in any outside air at all. The compressor is outside, and the air handler is inside. It's a very cool set-up.



Wow, interesting. I will be using a good amount of rack gear, but no huge analog console. Though, my prediction is that the effect of my gear will not be overly huge in my room, considering the size of the room.

One time I had some gear in a SUPER small room with low ceiling and the temps would go over 95F degrees in the room almost immediately without the AC running. But in a big room with a high ceiling, you have a bit more leeway.
So no fresh air at all??
Old 26th June 2010
  #19
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Originally Posted by nosebleedaudio View Post
So no fresh air at all??
Not from the AC system. But as I described in post #15, I'll be adding a separate positive vent fan system in order to keep the air fresh.

The great thing about the ductless split AC... you are not forced to compromise isolation by cutting "big" holes in your layers. The only holes you need to make in your wall are for the refrigerant lines, drain tube and electric line (all very small stuff). I believe you can drill one 2 inch hole and run all of the above through this one hole... then seal the hole.

With a wall AC unit, isolation is essentially impossible. And central systems create some degree of extra work, dealing with the ducting, baffles, etc.

In my opinion, for a smaller installation, a ductless split is the most efficient option and allows excellent isolation with minimal work. And, oh yeah, they're very quiet too.... essentially zero compressor noise, and very minimal fan noise.

But, with a sealed room and ductless split, you DO need some type of dedicated vent system... and because it will be dedicated, you have a lot of options in terms of where / how you put it together. Even now, I've been studying options for my own room, I have several good options, I will be able to choose whichever I feel is best for maximum isolation, etc.
Old 26th June 2010
  #20
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I've been following this thread with great interest as I have been using a 2 unit split system for my CR for about 15 years now.
Gotta chuckle about the insect thing. The first year I had mine we had a flood of water cascade out of the drip pan (all in one big rush, no hint of a problem until the waterfall) and onto a Dolby SR unit. The other unit did the same thing to a Lexicon control head the next year. BE CAREFUL WHERE YOU SITE THESE THINGS! At least on mine we learned that the condensation trays get filled (when drain line gets plugged) and they tend to tip slightly, releasing the water in a big way off the front right corner which is near the outlet. The first flood was caused by a cocoon in the drip outlet, the second was caused by dirt that fell into the tray during a fan cleaning. The fans can get very gummed up with dirt and have to be brushed clean every few years.
Anyway, my guess is as soon as you get a little more equipment (heat source) in that room things will stabilize on the humidity front.
Old 26th June 2010
  #21
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Originally Posted by Rick Sutton View Post
...The first year I had mine we had a flood of water cascade out of the drip pan (all in one big rush, no hint of a problem until the waterfall) and onto a Dolby SR unit. The other unit did the same thing to a Lexicon control head the next year. BE CAREFUL WHERE YOU SITE THESE THINGS!.....
Oh boy! Sorry to hear about your spill problems. Ouch!

What type of ductless split units do you have?

I located my ductless split in an area that will not be directly over gear. However, it is on a wall that is covered in nice natural wood planking. If I ever have any "leaks" from the air handler, it could destroy the planking... so I'm a little nervous about that. In my opinion, all these units should have, at the very least, an overflow alarm and safety shut off... so if the drip pan is ever about to overflow, an alarm would sound and the unit would turn itself off. I need to review the paperwork that came with my Fujitsus, but I don't think they have this.

On the central AC unit in my attic, there is a giant safety drip pan UNDER the air handler, so if the air handler ever leaked, the water would go into the safety drip pan. The safety drip pan has it's own drain tube that exits at a soffit of the building so if it was ever expelling water, it would be noticeable from the outside of the building, thus creating a "visual alarm". In addition, inside the safety drip tray, there is an accessory water sensing cut off switch, if water starts collecting in the safety drip pan, this safety switch will shut down the system. So... my central AC system is almost bullet-proof in terms of leak potential.

But yeah, ductless splits... one ultra crude idea would be to add your own "safety drip tray" right under the unit, try to disguise it as a decorative "shelf" or something... then have a small "drain tube" running from this tray back into the wall and out to an area where it is safe to expel water. But I'd imagine that most folks would not want to do this.

Another general thought... to help with the problem of having insects etc block the drain tube... run a dual drain tube. Once the drain hose exits the unit, stick it into a PVC pipe that shortly thereafter splits into two separate PVC pipe runs... this way if one leg gets clogged, you'll have a second leg. And then make it a point to test both pipes (if at all possible) each spring before season start up, make sure they both pass water easily.

In my case, the ductless split is up high on a wall in such a manner that I am able to get directly behind the wall from inside the attic. So I can easily see the drain tube from the back side as it exits the AC unit, and thus I have access to all the drain piping. I realize though that in other installations, the drain hose / pipes may be "inside" a finished wall and cannot be accessed. Not sure how to deal with this. I guess each season you could blast the drain line from the outside with compressed air, hopefully that would not damage anything. Though if there was some sort of junk in the line, it would then shoot up into the unit, might cause other issues. Not sure how easy it is (or if even possible) to access the drip pan inside these units from the front. It would surely be sweet if this WAS possible. I need to go review my unit's instruction / installation manual.

Another thought too... maybe at the open end of the drain pipe, add a small bit of screening to keep larger insects out. And just make sure to inspect / clean this screen maybe once a month, make sure nothing is building up behind the screen that could cause a blockage. You surely cannot have large insects going up your drain pipe and getting stuck in there, or creating cocoons, etc.

The end of my drain pipe goes into a roof gutter downpipe. We drilled a hole into the gutter downpipe and stuck the 3/4" PVC AC drain pipe into it, nice and tight. So, nothing can get into the AC drain pipe, unless it's already inside the gutter downpipe... and chances are, there will not be many or any creatures hanging out inside the gutter downpipe. If anything did go in there, chances are the next rain fall would wash them out before they found the AC drain pipe. Though, I'm thinking I may add a little screen at the end of the AC drain pipe anyway for extra safety.

I've heard more than one story about ductless AC units overflowing, it's definitely a bit scary. I'm really surprised that they ALL do not have a built-in "automatic safety anti-overflow kill switch" that would completely prevent the possibility of any spills. In my opinion, this should be considered a NECESSARY feature, as it would prevent the realistic possibility of major property damage.
Old 26th June 2010
  #22
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Quote:
Originally Posted by 666666 View Post
What type of ductless split units do you have?
I'd have to look tomorrow but I'm pretty sure they are Sanyo
Quote:
Originally Posted by 666666 View Post
one ultra crude idea would be to add your own "safety drip tray" right under the unit, try to disguise it as a decorative "shelf" or something...
That's similar to what I did over the Dolby unit in the machine room. I put an angled shelf under the AC that would divert the water so it would spill down the wall instead of going into gear. It would still be a mess but it wouldn't cause major gear damage.
Old 26th June 2010
  #23
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Quote:
Originally Posted by nosebleedaudio View Post
One thing it could be is; all HVAC have to pull a certain amount of outside air in WITH the return air, this is adjustable on most systems, anywhere from 20% to 100%...
So my point should be obvious, you will always have SOME outside air being mixed with the return air..with its moisture content..Just a thought..
And a sure way of knowing if your system is way over sized if it cools down very quickly, say 10 minutes..not enough time to remove the moisture in the air..

Had the above problem in a studio that removed the Large console..with its heat generating affect..once removed the air ran about 1/3rd the time..

He has a mini split - not the same conditions...........
Old 26th June 2010
  #24
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It is relatively inexpensive to add a pan sensor to the unit that will kill the power if the pan begins to fill with water.

We have to do this as a matter of course (and code) with any fan coil units that have finished areas below then in hotels, apartments buildings, offices etc.

our choice is either that - or an entire secondary drain system with a separate drip pan..... which can get real expensive real fast........ (seeing as all of the drip pans have to be connected to a primary drain system as well - no way out of that one)

Rod
Old 26th June 2010
  #25
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Originally Posted by Rod Gervais View Post
It is relatively inexpensive to add a pan sensor to the unit that will kill the power if the pan begins to fill with water.
We have to do this as a matter of course (and code) with any fan coil units that have finished areas below then in hotels, apartments buildings, offices etc.
our choice is either that - or an entire secondary drain system with a separate drip pan..... which can get real expensive real fast........ (seeing as all of the drip pans have to be connected to a primary drain system as well - no way out of that one) Rod
As I described in post #21, on my central unit (which takes care of the entire building except for the room in question), I have both a secondary drip with it's own secondary drain tube, and ALSO a safety shut-off sensor. That's what my HVAC guys apparently use in all their installations. In my case it was not difficult or expensive due to the lay-out.

But, Rod, are you suggesting that you've added safety sensor shut-offs to ductless split units? If so, please add a bit more detail. If this is possible and relatively "easy", I'll add one to my ductless split tomorrow!

So far I took a peek at my ductless split manual, and there are some microscopic diagrams that show / suggest that the main plastic housing can be taken off the unit without having to undo the refrigerant lines. I wonder if the internal drip tray can be accessed from the front...? If so, and if there's any room at all, I suppose a safety sensor kill could be added in there... but judging from the size of my sensor switch on my big central unit (which is at least a full inch or more "tall"), I'm doubting it would be an easy or even possible fit in the compact mini-split. But... I've never actually seen a drip tray in a ductless split, so this is all just speculation / assumptions at this point.

Quote:
Originally Posted by Rick Sutton View Post
That's similar to what I did over the Dolby unit in the machine room. I put an angled shelf under the AC that would divert the water so it would spill down the wall instead of going into gear. It would still be a mess but it wouldn't cause major gear damage.
Cool! You could find a rectangular tray of some type and place it ON your shelf, silicon it to the wall, then drill a hole in the shelf / tray and add some type of "drain tube", and route it to a place where you can afford to have a bit of water leak.... or even just have the tube hang into a fairly big pail on the floor. This would be pretty quick and easy to do, and would eliminate the possibility of encountering a "mess". If it's the machine room, I assume you are not overly concerned about aesthetics, so having a tray on a shelf with a little tube coming down and/or pail should not be an issue.

In my case, I AM somewhat concerned about aesthetics, I don't think I could get away with an adequately sized "drip tray shelf" without really creating an eyesore. I will, at the very least, attempt to add a secondary drain pipe, so if the main one ever gets clogged, the water will have a place to go, other than into the room itself. Though this does not protect against any future issues of having dirt etc build up INSIDE the internal drip tray (causing a blockage) or any blockages caused by insects etc that might actually get all the way up into the one drain hose that immediately exits the unit (prior to where the drain piping would split into two legs).

After taking a very quick look at my instruction manual, it suggests that TWO drain hoses could have been fitted directly to the unit (they give you the option of adding a hose on either the left side or right side)... I was not aware of this previously. If I had known better back then, I would have had the HVAC guys add TWO drain hoses on the unit, on left AND right, and then pipe them out to different places... that would have then almost completely eliminated the possibility of any spills, ever... assuming that these two drain legs were checked for blockages periodically.

Well, one idea... even with only one drain line and no safety shut off, I'd like to think that if the unit and drain line is fully inspected (and cleaned if necessary), each spring before start up, that you'd have a really good chance of never having a problem. Perhaps add a little screen at the open end of the drain line (to keep larger insects out), and then you should be good to go at least for one whole season without any catastrophes.

After at least one full year of service, I will be trying to figure out how to remove the main plastic cover from my unit and will attempt to clean it out well. Perhaps I'll be able to clean the internal drip tray and blow out the drain line from inside the unit... that would be sweet.
Old 26th June 2010
  #26
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Quote:
Originally Posted by 666666 View Post
Cool! You could find a rectangular tray of some type and place it ON your shelf, silicon it to the wall, then drill a hole in the shelf / tray and add some type of "drain tube", and route it to a place where you can afford to have a bit of water leak.... or even just have the tube hang into a fairly big pail on the floor. This would be pretty quick and easy to do, and would eliminate the possibility of encountering a "mess". If it's the machine room, I assume you are not overly concerned about aesthetics, so having a tray on a shelf with a little tube coming down and/or pail should not be an issue.
I could but I've got too many other, more pressing matters, to attend to. Anyway, the one in the machine room only dumped once in 15 years and I watch it pretty closely now. The CR one is more problematic because its drip tube is very restricted where it goes out of the unit (came that way) and is prone to plugging up. Also, I'm somewhat lazy in these type of matters. The one in the CR I watch like a hawk!
Old 26th June 2010
  #27
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Originally Posted by Rick Sutton View Post
I could but I've got too many other, more pressing matters, to attend to.....
I hear that! I have a VERY long list of these types of "projects" that will likely never get done before I die. But it's nice to think about them anyway.
Old 26th June 2010
  #28
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Originally Posted by Rod Gervais View Post

Are you using an HRV for fresh air?

Rod
Rod,

So I looked into HRVs, wow, interesting.

I see that HRVs take air in and also take air out.

Here's a question for you. In my building I have a lot of high cfm exhaust fans (in bathrooms, kitchens, etc). I've been thinking about how to add some type of filtered air inlet port to the building so that when the exhaust fans would run, there would be a place for filtered air to enter the building (as opposed to having "dirty" air yanked in through cracks and crevices around the building).

One thought I had was to add a custom HEPA filter box in the attic, with say two ports through the wall into the interior, and then add two vent trap / flaps to keep the ports blocked when no vacuum is present. I have one spot in the building that would be ideal to install such an inlet set-up, it's a hallway where humans are never hanging out, so if cold or hot air enters there, it should not be a nuisance, and it will get "conditioned" by the time it gets near humans.

The problem with the above idea... indeed very hot or very cold air will be drawn into the building when an exhaust fan is run, which is of course "inefficient"... though you could argue that this is what is happening right now anyway without any inlet system.... whatever air is being drawn in through cracks and crevices will either be humid in summer and cold in winter, etc (likely pulling air from the attic / basement). As well, for the past few years, when my wife has to run the big exhaust fan in the kitchen, i almost always wind up just opening a window anyway, letting cold air in.

Now, I understand the concept of the HRV, warm air exiting helps warm up cold air entering (and vise-versa). But in my case here, I already have exhaust fans in place that I wish to run. Unless I was to add HRV boxes at the outlet ports of my assorted exhaust fans (so that the exhaust air could help condition incoming air at each location)....? Not sure if this is practical. I've never dealt with an HRV before, all new to me.

Bottom line, I wish to be able to run my assorted exhaust fans, and I'd like to have an "official" filtered air inlet to effectively feed these exhaust fans.

I did once see some units made by Broan that would take air from outside and either cool or heat the air before blowing it into the living space. But, my argument against such a unit, it's going to use energy... and they're not cheap. May as well just have hot or cold air come into the building and let it get conditioned by the already existing conditioning systems that are in place, this may "waste" less energy, and you avoid buying some extra $1000+ unit that has to go somewhere and be serviced etc.

In a very small house, I could see the need for blowing in fresh air that is already conditioned (otherwise occupants might really be bothered by the drastic temperature changes), but in somewhat larger buildings, if a bit of cold air gets sucked in during the winter, say into a hallway area, it should not prove to be much of a nuisance to occupants. Chances are the exhaust fans are not running too long anyway, and the air would get conditioned pretty well before it reaches occupants.

Short of adding an HRV at the end of each and every exhaust fan, any other thoughts on how to add an "efficient" air inlet system to "feed" already existing exhaust fans?

I happened to find this one pic online... envision a "flapper" door as shown in this pic... then envision a custom filter box around it, so that air would have to get sucked through some large, tight, HEPA filters, then pass through the flapper(s), then into the building. It's that simple.

http://i137.photobucket.com/albums/q...g/DSC05975.jpg

Some baffling could be added "behind" the flappers so that any wind issues in the attic would not cause the flappers to open and close unnecessarily. Though, air pressure changes might cause unwanted flap opening I suppose. Hmmmmm.....
Old 26th June 2010
  #29
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As far as your existing exhaust fans go - don't worry about it - you don't need make up air for them.

It's like this - take the volume of air in the house - look at the minuscule amount of air (in proportion) that is being exhausted - that small amount of exhaust air is made up by air infiltration through the normal construction of the home.....

Unless I had a brand new home with spray insulation in the wall cavities and todays most tight construction I would not even think about bothering to install a fresh air supply.

However - in the case of a home studio I have begun using them quite often in my designs....... they work very well to provide fresh air for air tight rooms using mini split systems.

As far as operating expense goes - if they were 100% efficient there would be no cost - and we know that isn't happening - but even with air flow of 75 cfm (enough for 5 people) the unit sized for that operation is running around 85% efficiency - which means the cost is very little......

I could not disagree more about your thoughts on allowing native air into the home without tempering it.

You are going to make for one frigid hallway when you dump 15 degree winter air into it while waiting for it to acclimate and mix with the warmer air in the house......

Systems aren't designed like that for a reason - and that is that it doesn't make sense from a comfort point of view nor from an energy efficient point of view.

The house system will work a lot harder trying to make up for what you are dumping into it than it if it was already tempered.........

The entire idea of using the existing air to temper the incoming air (and to dehumidify it at the same time) is the most cost effective way you can do this without having a ducted system using an existing air handler system.......

The only cost here is the cost of operating the fans themselves......... and you don't need them running except for when you are in the studio. (them because the HRV uses 2 fans).

Rod
Old 26th June 2010
  #30
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This happened where I used to work during the spring and fall when our outside air is damp from rain and cooler than the summer months. The units just don't have a need to cool and therefore we don't have that temperature differential on the coil to create condensation even though the fans may be running non-stop. Now make that 100% return air and there is very little need to cool. Two stage systems really help in this scenario. Your condensate drain may be fine but I routinely inspect mine all the time cause overflows really suck.

A dehumidifier is going to heat the room because they typically first cool the air with one coil and then heat it create condensation so that will be an interesting mix. I actually envy you because where I live now our air is extremely dry and I have to run humidifiers all the time to keep my room at 50% for my guitars. Looking forward to hearing what solves your problem.
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