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  1. #1
    Join Date
    Jun 2006
    Posts
    96

    RH Humidity Problems - Help!

    I'll try to keep this as short as possible.

    I have a 3,000 sq ft ranch style home in western Canada. We had new AC system installed 5 years ago, including ductwork in the attic of our home. 2 AC units were installed, (both 3 ton). One provides cooling for the LR/DR/Hallways and Den and the second does the bedroom wing. From day one we got extremely cold air and excessive cycling. In addition, the RH was never lower than 62%. After some discussion with the contractor, it was discovered that the manual J called for 4.2 tons (Supplier of the equipment did the manual J but didn't provide it to the contractor, just the recommendation for 6 tons) . The contractor discovered that the air handler for the LR unit was sized for a 4 Ton unit as was the duct work. The bedroom air handler was for a 3 ton and the ductwork was also sized for a 3 ton.

    After a meeting last month the contractor said the following was the fix:

    1. Remove the bedroom 3 ton unit and replace with a 1.5 ton unit and matching 1.5 ton air handler;
    2. Remove the 4 Ton air handler from the LR unit and discard. Use the 3 Ton air handler (from the bedroom unit) connecting to the 3 ton outdoor unit - existing (this set up will give 4.5 ton of cooling capacity);
    3. Balance air flow and adjust ECM air handlers to optimum speed.

    With this new setup, cooling comfort has improved. Airflow has been reduced significantly and we no longer feel blasts of cool air (the "meat locker" effect). There was some discussion during the recent installation that we might not have enough "static pressure" with the new setup given that the ductwork was 3 ton for a now 1.5 unit compressor (bedrooms) and 4 ton for 3 ton compressor (LR/DR/Den). We had no further discussion on this.

    I had asked the contractor to make sure they sized the new units correctly and asked that they upgrade me to 2 stage units. I reasoned that in off peak running times, the Rheem units running in stage 1 would dehumidify without lowering the temperature much below the set point on the thermostat. They said the cost would be excessive as their remediation plan involved using some of the same equipment, wiring, setup, etc.

    I don't know where to turn at this point for a solution. I feel the RH of 63% when the outdoor is 60%RH (+28C) is too high. Crackers in our cupboards are soft and it just feels "wet" in the house.

    Anyone have ideas as to what is wrong with out setup and what it will take to correct it?

    Thanks,

    kayjh

  2. #2
    Join Date
    Oct 2011
    Location
    NJ
    Posts
    149
    The humidity hasn't improved when the HVAC units were changed for the proper sizes? This should have allowed longer run times and better dehumidification.

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,921
    Got model #s for the indoor & outdoor units?

    What controls (thermostat) do you have on these?

    Are both air handlers variable speed? Do you run the fan constantly?

    Is the humidity high on a hot day or just in mild weather and overnight when the units don't run much?

  4. #4
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,248

    Lightbulb

    Quote Originally Posted by kayjh View Post
    I'll try to keep this as short as possible.

    I have a 3,000 sq ft ranch style home in western Canada. We had new AC system installed 5 years ago, including ductwork in the attic of our home. 2 AC units were installed, (both 3 ton).

    One provides cooling for the LR/DR/Hallways and Den and the second does the bedroom wing. From day one we got extremely cold air and excessive cycling.

    In addition, the RH was never lower than 62%. After some discussion with the contractor, it was discovered that the manual J called for 4.2 tons (Supplier of the equipment did the manual J but didn't provide it to the contractor, just the recommendation for 6 tons) . The contractor discovered that the air handler for the LR unit was sized for a 4 Ton unit as was the duct work. The bedroom air handler was for a 3 ton and the ductwork was also sized for a 3 ton.

    After a meeting last month the contractor said the following was the fix:

    1. Remove the bedroom 3 ton unit and replace with a 1.5 ton unit and matching 1.5 ton air handler;
    2. Remove the 4 Ton air handler from the LR unit and discard. Use the 3 Ton air handler (from the bedroom unit) connecting to the 3 ton outdoor unit - existing (this set up will give 4.5 ton of cooling capacity);
    3. Balance air flow and adjust ECM air handlers to optimum speed.

    With this new setup, cooling comfort has improved. Airflow has been reduced significantly and we no longer feel blasts of cool air (the "meat locker" effect). There was some discussion during the recent installation that we might not have enough "static pressure" with the new setup given that the ductwork was 3 ton for a now 1.5 unit compressor (bedrooms) and 4 ton for 3 ton compressor (LR/DR/Den). We had no further discussion on this.

    I had asked the contractor to make sure they sized the new units correctly and asked that they upgrade me to 2 stage units. I reasoned that in off peak running times, the Rheem units running in stage 1 would dehumidify without lowering the temperature much below the set point on the thermostat. They said the cost would be excessive as their remediation plan involved using some of the same equipment, wiring, setup, etc.

    I don't know where to turn at this point for a solution. I feel the RH of 63% when the outdoor is 60%RH (+28C) is too high. Crackers in our cupboards are soft and it just feels "wet" in the house.

    Anyone have ideas as to what is wrong with out setup and what it will take to correct it?

    Without knowing what the exact set-up of the 3-ton and 1.5 ton units are currently.

    One might look elsewhere : i.e. amount of air leakage from outside
    1. Duct Blaster Test.
    2. House pressurization Test - Blower Door

    A/C should definitely provide < 45% R.H. when outside temperature is > 80'F/27'C.

    Electric billing would tell one a little about your run-times.

    http://www.energyconservatory.com/ap...lications1.htm
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  5. #5
    Join Date
    Jun 2006
    Posts
    96
    Quote Originally Posted by vangoghsear View Post
    The humidity hasn't improved when the HVAC units were changed for the proper sizes? This should have allowed longer run times and better dehumidification.
    That is what I though.

  6. #6
    Join Date
    Jun 2006
    Posts
    96
    Quote Originally Posted by BaldLoonie View Post
    Got model #s for the indoor & outdoor units?

    What controls (thermostat) do you have on these?

    Are both air handlers variable speed? Do you run the fan constantly?

    Is the humidity high on a hot day or just in mild weather and overnight when the units don't run much?
    I don't have the model numbers for the inside and outside units. I can get them (when I get back to the lake), but a trip to the attic is required for the inside unit information and I believe they are now wrapped in 3 layers of insulation to help combat condensation.

    The air movers are ECM type. The 1.5T unit is matched to a Rheem air mover, while the 3 ton unit was matched to a non Rheem air handler (not sure why). THe fans do not run constantly. We find the humidity to be high even on hot days, although I think we are in the high 50's (% RH) under those conditions and 60 - 63% on cooler days when the units are running less.

    Any ideas?

  7. #7
    Join Date
    Jun 2006
    Posts
    96
    Quote Originally Posted by dan sw fl View Post
    Without knowing what the exact set-up of the 3-ton and 1.5 ton units are currently.

    One might look elsewhere : i.e. amount of air leakage from outside
    1. Duct Blaster Test.
    2. House pressurization Test - Blower Door

    A/C should definitely provide < 45% R.H. when outside temperature is > 80'F/27'C.

    Electric billing would tell one a little about your run-times.

    http://www.energyconservatory.com/ap...lications1.htm
    Thanks Dan,

    I'm not sure what he total run times are. I would have thought when it was 80F, the bedroom unit would have been running almost all day, but it doesn't, although the tech set it up to cycle 6 times/hour. I assume this is set to do this if there isn't the need to run for long periods of time due to heat load requirements. The LR unit cycles more than the bedroom unit does under high heat load.

    Overall, the cooling is very even, it is just the miserable humidity I need to get rid of. As to air infiltration, we don't have an energy sealed house, but this 1950's bungalow has older dual pane Pella windows in the bedroom wing and new Loewen triple pane windows in the LR/DR/den. We re insulated the attic 6 years ago when we installed the new AC duct work in the attic and before we insulated we had the attic spray foamed to seal all through the ceiling device boxes and the tops of the wall plates. I can't say for certain, but I don't think we have allot of leakage. The house isn't drafty in the winter.

  8. #8
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,248
    Cycles per Hour should be = 2.

    You'll never get to a firm resolution without FACTS on Infiltration and condenser Performance.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  9. #9
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,921
    The mismatch on the big one doesn't help. Also wonder if they reused the 3 ton air handler on the 1.5 ton unit. Coil too big and it the blower won't slow down enough.

    My 2 ton is oversized for my 1000 sq ft but I don't have a humidity problem despite being in a steamy climate. If it does climb into the upper 50s in cool, muggy weather, I use the dehumidify feature of my control and variable speed blower to drop it.

  10. #10
    Join Date
    Jul 2001
    Location
    Gold Coast of Connecticut
    Posts
    4,571

    need to check CFM

    Quote Originally Posted by kayjh View Post
    I'll try to keep this as short as possible.

    I have a 3,000 sq ft ranch style home in western Canada. We had new AC system installed 5 years ago, including ductwork in the attic of our home. 2 AC units were installed, (both 3 ton). One provides cooling for the LR/DR/Hallways and Den and the second does the bedroom wing. From day one we got extremely cold air and excessive cycling. In addition, the RH was never lower than 62%. After some discussion with the contractor, it was discovered that the manual J called for 4.2 tons (Supplier of the equipment did the manual J but didn't provide it to the contractor, just the recommendation for 6 tons) . The contractor discovered that the air handler for the LR unit was sized for a 4 Ton unit as was the duct work. The bedroom air handler was for a 3 ton and the ductwork was also sized for a 3 ton.

    After a meeting last month the contractor said the following was the fix:

    1. Remove the bedroom 3 ton unit and replace with a 1.5 ton unit and matching 1.5 ton air handler;
    2. Remove the 4 Ton air handler from the LR unit and discard. Use the 3 Ton air handler (from the bedroom unit) connecting to the 3 ton outdoor unit - existing (this set up will give 4.5 ton of cooling capacity);
    3. Balance air flow and adjust ECM air handlers to optimum speed.

    With this new setup, cooling comfort has improved. Airflow has been reduced significantly and we no longer feel blasts of cool air (the "meat locker" effect). There was some discussion during the recent installation that we might not have enough "static pressure" with the new setup given that the ductwork was 3 ton for a now 1.5 unit compressor (bedrooms) and 4 ton for 3 ton compressor (LR/DR/Den). We had no further discussion on this.

    I had asked the contractor to make sure they sized the new units correctly and asked that they upgrade me to 2 stage units. I reasoned that in off peak running times, the Rheem units running in stage 1 would dehumidify without lowering the temperature much below the set point on the thermostat. They said the cost would be excessive as their remediation plan involved using some of the same equipment, wiring, setup, etc.

    I don't know where to turn at this point for a solution. I feel the RH of 63% when the outdoor is 60%RH (+28C) is too high. Crackers in our cupboards are soft and it just feels "wet" in the house.

    Anyone have ideas as to what is wrong with out setup and what it will take to correct it?

    Thanks,

    kayjh
    I would check to be sure you have matched equipment (AHRI) and the blower settings are correct for a humid climate. You need a contractor that can verify CFM, subcooling to verify the current equipment if doing what it is supposed to do. We need model numbers of indoor and outdoor units on bith systems and maybe someone can look up the AHRI here.
    Aire Serv of SW Connecticut- Gas heat, dual fuel and central a/c systems installed and serviced

  11. #11
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,270
    I am posting the data of a properly setup ac supply and the effect on the space as the ac cycle. The critical issues are the air flow and the length of the cooling cycles. It takes 20-30 mins. to load the a/c coil /pan and moisture to start driping to the drain. Also at the end of the cooling cycle, the moisture on the coil re-evaporates back to the home. Longer fewer cooling cycles helps. Colder coil helps.
    Keep in mind as the cooling load declines, do not expect the a/c to maintain <50%RH. Supplemental dehumidification from a dehumidifier is required when the outside dew points are near or above the desire inside dew point and there is note enough cooling load.
    Regards TB
    Family RM AC F Dew Pnt.pdf
    Attached Images Attached Images
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  12. #12
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    3000sqft in western canada. 4.5 tons combined capacity might still be on the big side. You should have seen some improvement however. But as mentioned, a 3 ton coil with a 1.5 ton condenser will result in a dry coil unless you really, really slow that blower down. I think a 2 ton coil is about as large as you want to go. I'd start by slowing the blower, but long term
    you may need to put in a properly sized, matching air handler.

    Also, 6CPH as mentioned is way too much. 2-3CPH is better for AC.

  13. #13
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,898

    RIGHT SIZING Equipment to Control Humidity Problems

    Allow me to shock U concerning some sizing realities in your climate toward controlling humidity.

    I live in SW Wisconsin today 9/4/12 at 2-PM at Lancaster it was 90F & 54% RH; indoors it is 52% RH & 76F with good air circulation & totally comfortable.

    Lancaster, WI very close to me, at 3-PM on the hour updates, it was 91-F; 50% RH; Heat Index: 97-F. NOW at 3:26 PM it's 50% RH in here on my first floor area & 76-F; around 25-C.

    The indoor contains 45.7 gr/per/lb/air; outdoors 116 gr/per/lb/air; A/C has to remove 45.7 gr//per/lb/air to get to 52% humidity level indoors.

    This is a 1937 farm home loaded with 13 windows on 1st floor &, NO shade until very late in the afternoon; first floor area 620-sf have a Half-Ton window shaker with an adjustable floor fan positioned to move air through all the rooms & back to the A/C.

    Okay, 620-sf divided / by .5 (1/2-Ton) is 1240-sf per/ton of cooling.

    3000-sf home (however, your climate should be milder in western Canada than here in SW WI).
    3000-sf / 1240-sf per/ton of cooling is 2.4-Ton;

    Well, U would have duct losses, etc., however, your home is way, way better insulated & protected from radiant & convection heat transfer than my home!

    I have a Half-Ton on the 2nd floor which I only use in the evenings...

    These small units have kept me perfectly comfortable in 112-F Heat Index.

    How in the world could anyone 'initially' oversize equipment by that much?
    Your home's calc should not be near where they had figuring it; even now it's still oversized for effectively controlling humidity plus meeting the sensible load.

    I've never had a load calc performed on my home by me or anyone else; however, these light weight units do the job perfectly & use less wattage than most indoor blowers use!

    It is amazing how much U can effectively cool with small tonnage; my all electric home monthly bills would shock your shoes off!
    Last edited by udarrell; 09-04-2012 at 04:39 PM. Reason: Typo...

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