Poor dehumidification on new HVAC system
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  1. #1
    Join Date
    Mar 2005
    Posts
    14
    I have new Bryant R410 2.5 ton SEER12 HVAC system installed April 2004.

    Area being cooled is 1500 sq ft. House is Split Entry so some overflow to first floor. Living area is on second floor. Two adults. No children. One dog.

    the humidity levels in our home last summer stayed at 48 to 55 percent despite running 24/7.

    Some days we had to open the windows as the humidity was lower outside. We kept a careful log of humidity and some mornings the humidity in the house was higher than outdoors.

    Contractor and Bryant engineer drew out all refrigerant and recharged system in July 2004 upon our complaint about lack of dehumidification, but there was no change.

    I opened the door to air handler in attic in June.Very little water was coming out of the condensate pipe before and after the recharge. There is very little water dripping off the coil even on a 75 percent humidity, 90 degree day.

    I had an American Standard 2.5 ton HVAC system for 34 years. On a hot, humid day I watched the water poured off
    the coil and into the drain tube. I loved the 34 year old American Standard system but it was falling apart.

    Only measured drops come off this coil. The pan is tilted correctly. It was not so at first, but was corrected upon my complaint.

    Bryant and the contractor refuse all help.

    Today I talked to a different HVAC supplier who suggested that the superheat temp and subcool temp may be the culprit.Wouldn't the Bryant engineer have checked that routinely?

    We are fast coming into a new season here in Reading MA in beautiful New England.

    Can any one help me

    rhblake57@comcast.net

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,829
    Anybody check the blower speeds? Most installers leave on factory setting which can be well above 400 CFM per ton. For best dehumidification, run at 350 CFM per ton. Best way to set is check static pressure of ducts and look at blower performance chart.

  3. #3
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,231
    Originally posted by rhblake57
    I have new Bryant R410 2.5 ton SEER12 HVAC system installed April 2004.

    the humidity levels in our home last summer stayed at 48 to 55 percent despite running 24/7.

    I opened the door to air handler in attic in June.Very little water was coming out of the condensate pipe before and after the recharge. There is very little water dripping off the coil even on a 75 percent humidity, 90 degree day.

    Only measured drops come off this coil. The pan is tilted correctly. It was not so at first, but was corrected upon my complaint.

    Can any one help me

    rhblake57@comcast.net
    48%-55%RH is acceptable regarding mold/dust mites growth and comfort. This is good for a conventional a/c . At this indoor %RH, normal a/c with the a/c loads in NE does not have enough load to provide real humidity control. Making the coil colder with less air flow decreases the efficiency of the a/c but increases moisture removal. Without significant cooling load like 6-8 houtrs per day, you need supplemental dehumidification from a dehumidifier. No cooling equals no moisture removal. In most homes, you must remove 60-100 pints of moisture per day during +60^F outdoor points. It is important to maintain <50%RH if you want a mold free basement and no dust mites in your bedding.

  4. #4
    Join Date
    Apr 2002
    Posts
    11,808
    Originally posted by rhblake57


    the humidity levels in our home last summer stayed at 48 to 55 percent despite running 24/7.

    Sounds like it is dehumifidifying to me.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  5. #5
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,273
    Today I talked to a different HVAC supplier who suggested that the superheat temp and subcool temp may be the culprit.Wouldn't the Bryant engineer have checked that routinely?
    Others have responded that your reported humidity levels appear normal. I would agree, but you also stated your system runs 24/7. Do you mean this literally? That the system is literally locked on non-stop around the clock?

    If this is so, then I would say the only reason you're seeing the humidity levels you have is because of the unit constantly running.

    You may indeed have a superheat issue. Not as many techs check it as they should. I'll admit that I went along for a long time before truly understanding the value of superheat and subcooling readings. Once I learned differently, it made a tremendous difference in my ability to diagnose the more difficult refrigeration circuit problems in the field.

    I also agree with the airflow speed BaldLoonie mentioned. If the superheat reading was checked, the value would indicate whether the system had too much airflow or not.

    Here's my take without having the advantage of being at your house and running an analysis on your system:

    A) If airflow is too high, it is placing too high of a heat load on the evap coil. This would be indicated by a high superheat.

    B) If airflow is nominal, a slight undercharge on a fixed restrictor metering device system will underfeed the evap coil, also resulting in high superheat.

    C) If airflow is nominal, a slight overcharge on a fixed restrictor metering device system will overfeed the evap coil, resulting in low superheat.

    Any of these conditions above will diminish the dehumidification performance of your system

    Pulling the charge out and weighing virgin refrigerant back in at the same amount did nothing for the system if it was under or overcharged initially.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  6. #6
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,829
    Rereading the original post, I'm gonna add to the concensus that things are good. Keeping it 48-55% in the summer when hot & humid is about perfect. My system, a TXV evap and Comfort R turned on, will stay in the 52-55% range at best in steamy weather. I have a real steady stream of water pouring out of the drain though but obviously your water is going somewhere if it is that dry in the house.

    I'm with the hound, questioning your statement about the system running 24/7. I would believe you mean you don't turn it off but not that the compressor runs that much. When the unit is off, you aren't dehumidfying and you are building up natural moisture from people, cooking, laundry, showers. Sometimes in milder weather, the system runs so little humidity can get high.

    Today's stuff doesn't have the latent capacity of the relics with their 32 degree 5 row coils. Overall, Bryant tends to be average in their moisture sucking ability. But it can only suck when running!

  7. #7
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,923
    Humidity level is ok.

    As stated, too much air flow and constant air flow when the condenser is not operating will adversely affect the moisture in the air.

    I have decreased the amount of humidity in a home many time by lowering the fan speed.

    You are in a high humidity, low temperature load region of the country. Keeping the blower on constant will continually pick up and redistribute any moisture in the air handler. Too high of a blower speed will not allow the coil to get cold enough to condense the moisture in the air.
    Government is a disease...
    ...masquerading as its own cure…
    Ecclesiastes 10:2 NIV


  8. #8
    Join Date
    Mar 2005
    Posts
    14

    Poor dehumidification on new HVAC

    Thank you all for your questions and suggestions.

    To elaborate: I mean the thermostat is set on 74 degrees on 24/7.

    I have both a Bionaire and an Oregon hygrometer that are both properly calibrated.

    I never put just the system fan on alone. the thermostat is set on the Cool setting.

    Keep in mind I had an American Standard system that was 34 years old, that I replaced. It was set on Cool for 74 degrees all summer in those previous 34 years. I loved it.

    The hygrometer read around 38-42 percent in the house all summer with the old American Standard unit.It now never goes below 48-50 percent. Often it is 55 percent.

    If we did have an occasional cold day in the summer we would turn off the AC. But once the temp went above 75F we would put it back on to Cool setting mode.

    The Bryant people evacuated the system last July and recharged it again with supposedly the same weight of R410.

    They claim that there is no need to check sub cool at compressor if I have correct pressure reading there. They claim the pressure is right as of last June and was tested for leaks.

    Also Bryant says there is no piston in the FX4B air handler TXV valve, so there is no way or need to test superheat at the air handler.

    Re air speed, the air handler has 3 speeds. I have tried all 3 speeds re dehumidification ability. There is no difference on the amount of water coming off the coil on all 3 speeds on a 75 percent humidity 85 degree day.

    I had the unit set at the lowest of the 3 speeds to cut down on airflow noise into the rooms.

    I did say earlier, that some water(humidity) is being removed, but far less than with my old 34 year old American Standard unit, by at least 300 percent differential. A 5 gallon pail at 70 percent humidity on an 85 degree day now takes 7 or 8 hours to fill.

    On a separate note this past January and February, the cold air poured out of my ductwork so bad that I had to close the feed dampers to the rooms, and had to put a plastic bag over the filter onto the hallway return duct.

    I realize that this is a different and separate problem. The return and feed plenums were sized for a 3 ton air handler, and when it was replaced by the correct 2.5 ton air handler the contractor would not downsize the plenums. So they are both larger than the height of the box and are taped and (supposedly) sealed properly.

    By the way with the humidity at 50-55 the sheets on our beds are damp and clammy. There are no children running showers. Husband wife and one 55lb beautiful loving Lab mix.

    All thoughts are appreciated

    rhblake57@comcast.net

  9. #9
    Join Date
    Apr 2002
    Posts
    11,808
    The old systems ran a lot colder and would remove moisture but if you were measuring 38% humidity I am wondering if this was from the old hygrometer because that is an unrealstic sounding number.

    Damp sheets at 50 to 55%RH sounds like it is pyshcological to me. Similar effect with an old mercury thermostat with the temperature indicating 'needle' being out of calibration. People would complain they were too warm or too cold when all that was wrong was the temperature indicator was not calibrated. Recalibrate the needle and they are suddenly comfortable.

    You mentioned plenums are now taped properly. Is it possible some of the ducts were in unconditioned spaces. In your case, before, is it possible that some un-sealed return ducts were in an unconditioned space. These ducts would draw in humid outside air and maybe that is why you observed a 'pail' fill up quickly with water.

    You do have a proper condensate drainage system now I hope.

    Relative humidity is a confusing term, 50 degree air at 100% RH holds less moisture than your 74 degree room air at 55%.

    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  10. #10
    Join Date
    Apr 2002
    Posts
    11,808
    Actually from re-reading your posts it sounds like the air conditoning ducts are in your attic. Maybe they were leaky before, and you were drawing in a lot of humid air into the return.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  11. #11
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,597
    Go in your attic and see if you have any ducts that are not sealed right.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  12. #12
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,273
    To elaborate: I mean the thermostat is set on 74 degrees on 24/7.
    Given this, does your system cycle on and off as it maintains 74 degrees and the 48-55% range?

    Was your thermostat replaced when you replaced the system? Reason I ask is that if you have a new thermostat, 74 degrees on your new thermostat may not mean the same as 74 degrees on your old thermostat. If this is so you may be setting the new thermostat at 74 degrees, thinking your system should perform the same as the old thermostat did at 74 degrees. But the old thermostat could have been out of calibration and your house was actually running colder than 74 in order to reach the lower humidity levels you posted earlier.

    I would take a close look at the ductwork in the attic. If you have cold air pouring out of the supply registers during the winter months, you could have a leak, loose or missing insulation, or both. I'm assuming this is a cooling only system since you covered up the return air grill in the hall ceiling to keep cold air from spilling down into the house.

    They claim that there is no need to check sub cool at compressor if I have correct pressure reading there. They claim the pressure is right as of last June and was tested for leaks.
    I'm known on this board as saying to fellow technicians that "pressures tell only part of the story". For you as a homeowner it only means that if a technician is going by gauge pressure readings alone, he's half blind to what's going on with your system when it's running. For the technicians, how many of you reading this would think that if superheat and subcooling readings were taken on this homeowner's system, something would turn up as out of whack?

    Also Bryant says there is no piston in the FX4B air handler TXV valve, so there is no way or need to test superheat at the air handler.
    I disagree. Again, for you the homeowner it may not mean much. I only address it as it strikes me they're saying there's "no way" to test superheat at an air handler. Sure there is. Directly downstream of the TXV bulb on the suction line, the technician can attach a type k thermocouple probe to the line, bury it in the insulation, and read the temperature of the line, Yes, he'll likely have to get his suction pressure reading at the condenser in order to obtain the saturated vapor temperature inside the evap for comparison. That's why for residential A/C, most superheat discussion revolves around suction line superheat vs. evaporator superheat. But a tech that knows his stuff can get a superheat reading at the sensing bulb and get an idea whether the TXV is maintaining good superheat or not in the evaporator.

    Additionally, suction line superheat on a TXV system is just as useful to a tech as it is on a fixed restrictor system. A properly adjusted TXV will maintain consistent evap superheat with a normal to overcharge condition, but will show an increase in superheat if the system is undercharged or if the TXV is out of adjustment.

    For you the homeowner all that carrying on I just did probably doesn't mean a lot. I just had to address what appears to me to be bad info.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  13. #13
    Join Date
    Mar 2005
    Posts
    14

    More on dehumidification woes

    To Carnak:
    I put a 5gal pail under the condensate tube outside. It did not fill quickly. It took 7 or 8hrs on a 85 degree, 70 percent humidity day, to fill that 5gal pail.As I noted, I can count the drops of water coming out of the condensate tube or off the coil on a warm humid day.

    Also, there is only one return duct for the whole system and is in the hallway of the living area. The original American Standard system was put in after the house was built in 1971. The house was built in 1967. It is a split entry.

    To Beenthere:
    The thermostat is a new and properly calibrated Honeywell digital.
    Last July I had two young men wrap and tape the new return ductwork with 8 mil plastic. We only wrapped the return as that would be the only duct that could draw in outside air from the attic.
    This winter the cold air came through the ducts despite this. Where can it be coming in? The air handler box?

    I did tell the Bryant engineer that the box is not sitting firmly in the cradle.
    It is not dead level and is slightly wracked. He said that little bit off would be of no consequence! I thought of the old joke about the woman who told her husband that "she was only a little bit pregnant".
    I have duct taped the small openings that were drawing in air such as at the conduit opening. This is a cooling only system. We have forced hot water heat.

    To Shophound:
    Can the TXV valve on the FX4 air handler be replaced or is it permanent?
    Thanks for the suggestions about how to test superheat despite the dealer saying it can't be done.
    I don't feel that a properly operating system should be relegated to producing 50 to 55 percent humidity in a house.
    My old American Standard operated at 38 to 40 percent humidity______ the same as my car air conditioner after the car has been on for less than 15 minutes on a hot, humid day.
    I recall measuring the humidity in both my car and the house back in 2003, when I still had my old American Standard central air system and my 1993 Caddy Deville.
    I was in sales for 45 years and a car with no AC after 1965 was a non starter.

    I am hoping to get to understand the basics, so I can know if I'm being snowed when I get another contractor to look at this system.
    I appreciated your comment about all contractors not knowing how to properly test for defective operation.
    I understand how important it is for me to know when I am not being told the truth by a contractor.There is so much to know!

    I appreciate all of you hanging in there. At 76, I could tell you how to sell a set of cookware after 45 years of doing so, but as a homeowner with a poorly operating AC system, I feel almost powerless.

    Thanks rhblake57@comcast.net



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