Air conditioner working, room cold, but can't get humidity down...???
666666
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#31
27th June 2010
Old 27th June 2010
  #31
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Originally Posted by slymo View Post
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.....
Yes, have the same problem here too, especially in the basement rooms. And this one new above ground room in question is acting a lot like my basement rooms. They seem to stay cool on their own... but yet the humidity will rise above desired levels... and this happens more so in the spring-time before outside temps get high. In one basement room, summer-time, even with no conditioning running, temps will stay at 70F degrees, but humidity will climb to 70%+ RH. I guess the simple answer here is, a separate dehumidifier is needed to control humidity.

So last night I stuck a dehumidifier in the above ground room and ran it along with the AC unit. Actually worked out great. Right now, it's 75F degrees and 42% RH, feels REALLY NICE in there. The dehumidifier pulled out about a gallon of water in the past 12 hours or so to get it from 60% RH to 42% (and keep it there). But when I turn off the dehumidifier, the RH starts rising pretty fast.

And, oh yeah, I'm not seeing a vapor barrier under the floor in that room, I'll surely have to add one... floor work will begin relatively soon. I hope that once the vapor barrier is in place, the room will hold the dehumidified air better so that the dehumidifier won't need to run nearly continuously.

So, having an AC and dehumidifier work together seems totally fine... set the AC to the desired temp and set the dehumidifier to the desired RH and they should run appropriately in order to condition the air as desired.

But, in my case anyway, there is one problem here... I need to now figure out a dehumidifier solution that is going to be efficient and QUIET. The ductless split AC is dead quiet... I do not know if anyone makes a dehumidifier that is designed to be quiet.

One thought is to look more into a "remote" dehumidifier that would sit in an adjacent room, with send and return ducted to the studio room, and a remote humidistat of course placed in the studio room. I did see one unit, a Santa Fe "Compact", that should work well in this way... and I do have an adjacent closet that is in a spot that will make it easy to add a water drain line to the outside. But if I try this, I'll need to deal with shock mounting the unit to kill any vibrations from the compressor, etc... also concerned about the degree of isolation I'll lose by adding two 4" or 6" holes in my multi-layered wall in order to add the in and out ducts.

Well, before I buy any special dehumidifiers, I need to fully complete the room (review the entire vapor barrier situation), and get all my gear in there and fire it up etc. It's possible that once my vapor barriers are fully in place, and the gear is in there running, the needs of the room will be a bit different.

It still puzzles me how this one room will rise to 62+% RH (whether the AC is on or not), but yet the rest of the building will stay at 50% RH or less, even when the AC is barely running or not running.
666666
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#32
27th June 2010
Old 27th June 2010
  #32
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Originally Posted by moracspace View Post
HVAC has been my day gig for 23 years and some of the answers you are getting are completley wrong.This the worst place to get info about dehumidification.Hi fan speeds???heating the coil to cause condensation???WTF!Without checking the operation of the refrigerant pressures theres no way to diagnos your problem.If it took 2 hours to bring down the temp from 86 to 77 theres a problem with the unit.Even if your unit is oversized it will still remove moisture.Try running the fan on low speed while running it in cooling.Low speed allows the coils to ring out the air more effectively.
One thing I can tell you, now after doing more testing, when I do crank the AC hard, it does cool the room pretty fast (considering the room is about 8,000 cubic feet in size) and water WILL start streaming out of the drain tube... and the humidity DOES drop down to a desirable level. I think my "problem" earlier on here was that I wasn't cranking it hard enough. But... the problem with cranking the AC hard... the room gets too cold! While I have not checked the refrigerant pressures, I have noted, FWIW, that the refrigerant lines do get ICE cold. I know that this isn't a true "test" of anything, but... the refrigerant system can't be too far off if the lines get ice cold.

I did try running the AC at slower fan speeds, and also ran it in "dry mode" (which is basically a slow fan speed mode), but interesting this didn't seem to make much a change in the RH. But, as I've mentioned in my past few posts, it appears there is no vapor barrier in the floor... so maybe when I am running the AC in slow fan speed mode, and considering the size of the room, the outside humidity is seeping into the room faster than the AC is taking it out... remember, the fan is running VERY slow here.

Now when I run my temporary dehumidifier in there, even in low fan speed mode, the fan is blowing a LOT harder and moving way more air than the AC unit in "dry" mode... but of course a dehumidifier works a bit differently than an AC. The dehumidifier was able to drop the RH over 10 points in a fairly short amount of time.

In sum, it does still seem that my unit may be a bit "oversized" for the current conditions. But again, once I have audio equipment in there producing heat, and make sure the room is fully surrounded by vapor barriers, hopefully things will improve a bit beyond where they are now.

But as also discussed, there are indeed times (in the spring, etc) when dehumidification is needed or desired, but yet it's not "hot" enough to make it practical to call on an AC... in which case a dehumidifier is what is needed. So one way or another, I probably can't go too far wrong adding a dehumidifier, it'll cover me in the spring, and it'll help keep RH low in the summer too when my "oversized" AC isn't able to.

But, more testing and observing to be done.
666666
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#33
27th June 2010
Old 27th June 2010
  #33
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Originally Posted by Rod Gervais View Post
As far as your existing exhaust fans go - don't worry about it - you don't need make up air for them..... I could not disagree more about your thoughts on allowing native air into the home without tempering it... Rod
Thanks Rod, excellent info!

So, in sum, it would appear that I could probably use one HRV in my building, and then continue to use my assorted vent fans (that move air from one room to another) to make sure that all rooms receive fresh air.

I suppose I could attempt to add an HRV within my one above ground "sealed" room, but the way the room is configured, and considering that I'm trying to achieve some degree of sound isolation in there, I'd rather locate the HRV elsewhere in the building where I have a more convenient space for it and need not worry about isolation. And again, I'll have a vent fan pushing air into this sealed room from an adjacent room, and an exhaust port back to another adjacent room or to the basement. For this sealed room, I'd rather not have any holes on outside walls.
#34
27th June 2010
Old 27th June 2010
  #34
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Quote:
Originally Posted by moracspace View Post
heating the coil to cause condensation???
Sorry I phrased that wrong....cool the air to create condensation and then reheat the air. My apologies.

Glad to hear the dehumidifier worked.
#35
27th June 2010
Old 27th June 2010
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Quote:
Originally Posted by 666666 View Post
I suppose I could attempt to add an HRV within my one above ground "sealed" room, but the way the room is configured, and considering that I'm trying to achieve some degree of sound isolation in there, I'd rather locate the HRV elsewhere in the building where I have a more convenient space for it and need not worry about isolation. And again, I'll have a vent fan pushing air into this sealed room from an adjacent room, and an exhaust port back to another adjacent room or to the basement. For this sealed room, I'd rather not have any holes on outside walls.
I am not suggesting that you locate the HRV in the room itself - in fact further away from the room is preferable - BUT - one way or another you are going to provide fresh air for that room - and are going to have to make penetrations in order to do so - at which time making the penetrations to supply the air directly makes more sense than screwing around with trying to pull it from other rooms......

Not to mention the fact that pulling it from other rooms is a Code Violation ...... thought I mentioned that earlier... if I didn't I would be happy to elaborate further if you wish.

ROD
#36
27th June 2010
Old 27th June 2010
  #36
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Quote:
Originally Posted by moracspace View Post
.Even if your unit is oversized it will still remove moisture.Try running the fan on low speed while running it in cooling.Low speed allows the coils to ring out the air more effectively.
I don't believe anyone here ever said that an oversized unit will not dehumidify - what was said was that an oversized unit will not dehumidify a space properly due to short run cycles - in addition, oversized systems are not anywhere near energy efficient (which is an issue the OP has been very VERY focused on) due to the fact that energy efficiency requires long run times for the compressor, short cycles mean more start ups which consume the greatest amount of energy...... running the compressor requires no where near the energy of starting the compressor.

It would not surprise me to know that a room that has been sitting for a day would take a long time to come to temperature with a unit running in low or dry fan mode. The fact that he put it in high fan mode and cranked it up - and that it dehumidified well (he said the condensate was really flowing) says that the system is operating properly. I would be very surprised to find that the charge for the lines was too far out of spec with that being the case.......

HOWEVER - once it reaches temperature and all it has to do is maintain that temperature - the coil needs to have long run times in order to over come the humidity - yet the room is super insulated - with no solar gain to speak of - no windows and air tight door assemblies....... he said he has little gear in the space right now - which means the single largest source of heat would be coming from his body - which is being mixed into 6,000 cf of cool air. Not expecting this to call for cooling very quickly once it reaches temperature.

Running the fan constantly isn't doing anything for him if he isn't in a cooling mode - just recycling the air will not dehumidify.

The run time cycles for the compressor are going to be short - the cooling coils will not be dehumidifying because of the short cycles - and in the dry mode the air flow is apparently so low that the air exchange is too low to keep up with the vapor entering the space.

There is no real mystery here.

The fact is that control rooms - once completely filled with gear are generally easy to handle - the sensible load provided by the lighting and gear generally require long run cycles to maintain the temperature......

It is generally required that additional dehumidification be provided for tracking rooms due to the fact that this is not the case in those spaces.

In some cases both humidification AND dehumidification systems are required in both spaces in order to maintain relatively flat humidity levels due to diverse humidity conditions during the heating and cooling seasons (or - even more importantly the fringe seasons between those seasons....... this becomes increasingly more important as things like pianos are placed into these spaces due to the consistent humidity required (for them) so that they remain in tune (pretty much a constant 42 to 43% relative humidity). Try pulling that one off with any typical system - never mind an over sized one........

I too have been doing this for a little while (about 30 years) both designing and overseeing the construction of these systems (recording studios, movie studios, commercial buildings, hotels, apartment buildings, industrial systems, museums, archive storage facilities, to name a few) - and have a wee bit of understanding about how they work (or don't as the case might be).

Rod
#37
28th June 2010
Old 28th June 2010
  #37
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Could you hook a digital thermometer with a in or out setting. The out setting is a sensor on the end of a 12 foot wire. I just put the sensor right inside my ac vents. When the compressor is on it will read 59 to 65 deg. Off maybe 75-80.
My Ac in my last studio building was strong,but neeeded freon every 4 months.
The Ac repair guys loved me. They finally found the friggin leak after 4 years.
I got a leak for themdfegad.
GT.
666666
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#38
29th June 2010
Old 29th June 2010
  #38
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My room has a "humidity memory"

When I first started this thread, I had just begun using my ductless split AC. The room had been sitting for days at about 80F degrees and say 65%+ RH. As described in the initial posts, even though I ran the AC and cooled the room, the humidity would barely drop, and then when I'd shut it off, the humidity would zip right back up to the low 60% area.

Afterward, running the AC even harder, RH would drop even more, but then again bounce back up pretty quick once the compressor would shut off.

So more recently I've been running a temporary dehumidifier at full blast all night long (with AC turned off), bringing the RH down to 40% (and temps up to around 79F degrees). Then in the morning, I shut off the dehumidifier and set the AC to fully automatic mode. The AC brings the temps down to desired levels (around 74F - 75F degrees), and the RH has remained hovering in the upper 40s / low 50s area, all day (with dehumidifier OFF). However, once night time comes, the RH does start to rise a bit into the mid 50s area.

In sum, "drying out" the room during the night is allowing the AC to keep RH at desired levels all day long... even with extreme outside RH.

This above described activity has occurred three days in a row now... and I'm measuring with two different gauges on opposite ends of the room, gauges pretty much agree all the time. And, oh yeah, it's been consistently hot and humid the past few days, 75%+ RH in the garage below the room (and no vapor barrier).

Key note... I will mention again, the room is currently covered about 85% in exposed natural wood. Bare 3/4" plywood subfloor exposed, plus lots of natural wood planking on walls and ceiling... unfinished. I am wondering if all that exposed unfinished wood is causing a "humidity momentum", after all, wood is very much like a sponge when it comes to humidity. So when the wood is fully saturated with humidity, it takes a while to fully dehumidify the room. Even when an AC dehumidifies the immediate air inside the room, the wood is still emitting stored humidity, the AC can't keep up. But when the wood is "dried out" first, the AC seems to be able to keep up with the dehumidification.

Well, just an observation for whatever it's worth. Will test this yet again today. Early this morning the RH was 40% in there, and 79F degrees (with dehumidifier running all night long). Will now go turn on the AC and see how we do again today in terms of RH while keeping the dehumidifier off.

I of course still need to complete the room and do a lot more "testing" before any true conclusions are drawn. It's possible that once the vapor barrier is in place, audio gear turned on and running, and then "pre-drying" the room before observing AC performance, maybe then the AC will prove to be able to do the job (cooling AND dehumidifying) on it's own. We'll see.
#39
4th July 2010
Old 4th July 2010
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#40
4th July 2010
Old 4th July 2010
  #40
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Drew,

How did you determine the unit size?

Rod
#41
4th July 2010
Old 4th July 2010
  #41
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Quote:
Originally Posted by Rod Gervais View Post
Drew,

How did you determine the unit size?

Rod
I told my HVAC guy (brother in law) the size and usage of the room and this is what he recommended.
#42
14th December 2012
Old 14th December 2012
  #42
Gear interested
 

Regarding HVAC Ductless Split Systems

Let me clarify one thing right away – over-sizing ANY HVAC system is a problem. I won't bore you technical details but the bottom line is that it will cause humidity problems due to what is referred to as “short-cycling.” This has been defined earlier in this thread and the assessment presented is essentially accurate.

Rather than over-sizing a system, it’s normal and a bit better to UNDER-size it a little. When a calculation is run to determine the size required, many factors are taken into account and the final number nearly never matches the available capacities of the HVAC systems. If the calc comes up with 1.7 tons, I rarely upsized it to 2 tons. Rather, I’d call for a 1.5 ton as I prefer the system to run longer to cool (thus increasing the dehumidification) for the space.

I could go into a LONG litany of things to consider here. But now that the technology has improved, my design criteria has changed. With the advent of variable speed compressors being standard in these types of systems, upsizing some is OK as the system can “slow down” to meet the varying loads of a space. This now provides a better comfort range over varying conditions. I’d caution you to not jump more than half a ton from the calculated load unless you fully expect to dramatically increase the load in the space in the foreseeable future.

Residential applications do not require ventilation air (outside air) although these systems do have a very limited ability to cope with this. Be cautious of low humidity as much as high humidity. High humidity is a comfort issue as well as a mold and mildew issue for the space. Low humidity is comfort also, but also can produce static electricity issues (bad for electronics in particular).

My advice to people considering this type of system is to have a reputable HVAC person run a load calculation for your application. This is a computer-based calc that accounts for many things that some web-based “toy” likely won’t. Not only is the insulation a factor but the various other components in the wall/roof/floor as well as the type of glazing very important. Direction of exposure, quantity of those various items, weather, geographical location, etc. etc. etc. are all components that will change one person’s needs from another’s – even in the same town.
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