New system not dehumidifying

[cjs226]

New system installed 7/10/20 (specs below). One of the main concerns I had prior to purchase was indoor humidity and was told this system would work be great.

Thus far that hasn't been our experience. The installer has been back twice to investigate. They agree the humidity should never reach the levels it is (+70% when set at 56%) and that it and the temperature should remain relatively static given the variable speed. During the 2nd trip the installer felt the answer was to use the Ecobbe thermostat's "overcool" feature where it allows the system to run up to 3 degrees lower than the desired temperature IF the system hasn't reached the desired humidity level. Well, we're just cold now. :-(

My assumption is either:
- The dehumidification isn't working and/or working as well as it should
- The system isn't running at a low enough fan speed to allow the system to run longer to dehumidify but not freeze us out

Here's what's been installed:
- Carrier® Performance™ - 3.5 Ton 16 SEER Air Conditioning Condenser
- Model: 24apb642a003
- Product: 24apb642a0030010
- 24 = AC / Product Series
- A = RES AC / Product Family
- P = Performance Series / Tier
- B = Puron / Major Series
- 6 = 16 SEER / SEER
- 42 = 3.5 Ton / Cooling Capacity
- A = Standard / Grille Variations
- 0 = Not Defined / Open
- 0 = Not Defined / Open
- 3 = 208/230-1 / Voltage
- Carrier 3.5 Ton Evaporator N Coil Cased Horizontal Painted 21" Width (Aluminum)
- Model CNPHP4321ALAEAAA
- C = Coil Product
- N = N Coil Type
- P = Puron® Refrigerant TXV Refrigerant Type
- H = Horizontal Coil Configuration
- P = Painted Cabinet Finish
- 43 = 3.5 Ton Unit Capacity
- 21 = 21" in (533 mm) Cabinet Width
- A = 1st Revision Level
- L = Aluminum Tubing Design
- A = Basic Variations
- Carrier Carrier® Performance™ - 80% AFUE 90000 Btuh 4-Way Multipoise Induced-Combustion Gas Furnace, 2-Stage, Variable-Speed
- Model: 58TP0A090V211120


Here's a graph showing humidity quickly decreasing when the system is running...and then quickly increasing when it's not:
- Blue rectangles: when the system is running
- White line: indoor humidity level
- Green: outdoor humidity


Here's a graph showing the system consistently "overcooling" past the desired temperature:
- Blue rectangles: when the system is running
- Blue line: desired (cool) temp
- White line: indoor temperature
- Green: outdoor temperature

[dan sw fl]

New system installed 7/10/20 (specs below). One of the main concerns I had prior to purchase was indoor humidity and was told this system would work be great.

Thus far that hasn't been our experience. The installer has been back twice to investigate. They agree the humidity should never reach the levels it is (+70% when set at 56%) and that it and the temperature should remain relatively static given the variable speed.

During the 2nd trip the installer felt the answer was to
use the Ecobbe thermostat's "overcool" feature
where it allows the system to run up to 3 degrees lower than the desired temperature
IF the system hasn't reached the desired humidity level.

Well, we're just cold now. :-(

My assumption is either:
- The dehumidification isn't working and/or working as well as it should
- The system isn't running at a low enough fan speed to allow the system to run longer to dehumidify but not freeze us out

- Carrier Carrier® Performance™ - 80% AFUE 90000 Btuh 4-Way Multipoise Induced-Combustion Gas Furnace, 2-Stage, Variable-Speed
- Model: 58TP0A090V211120


Here's a graph showing humidity quickly decreasing when the system is running...and then quickly increasing when it's not:
- Blue rectangles: when the system is running
- White line: indoor humidity level
- Green: outdoor humidity

Set the thermostat to 76'F

+ Report back in 3 days

What is the SUPPLY AIR Temperature?

[teddy bear]

Fan, auto or on?

Need Supply temp/%RH is critical in commenting on the a/c's function!!!s

During the design outdoor load conditions, like 92^F, 50%RH, a 70^F dew point, cooling load, a properly functioning and setup a/c should be able to maintain 75^F, <50%RH, a 55^F dew point.

During the hottest part of the day, you are in a part load condition at 88^F, 40%RH, a 60^F dew point outside. Even at this part load condition, the a/c should run enough to maintain 50% without over-cooling.

During the evenings, the a/c will not run enough maintain 50%RH even with over-cooling.

Here is how to start, Get the a/c checked for function. The amount of refrigerant and function what the tech checks. Next adjust the air flow through the cooling coil to improve the moisture removed by the cooling coil. We need cold air supply with <50^F DEW point at the supply of the a/c for a minimum of 50% of the time, 40-40 mins. per hour to remove +2 lbs.per ton per hour of cooling. This is critical. The supply should be like 55^F, 80%RH, a 50^F dew point.

Do not expect any dehumidification from your a/c during low/no sensible cooling load conditions. you will get dehumidification only during significant sensible cooling loads. With your current setup, you need over-drying during high sensible cooling to carry you through the evenings and rainy days be comfortable.

Many living in green grass regions are adding a small whole house dehumidifier to remove moisture during evenings/rainy days and high outdoor dew point plus the moisture from the occupants.

You must get your a/c setup ideally before considering adding a dehumidifier. Adding a dehumidifier to a defective a/c is not a solution. The a/c must be able do its part during peak sensible/latent cooling loads.

Your thoughts. My comments are intended to help your a/c tech guide lines on setting up the a/c function properly. Supply the temp/%RH at the supply for more feed back from me.

Regards Teddy Bear

[cjs226]

Need Supply temp/%RH is critical in commenting on the a/c's function!!!s

Where should I measure supply temp and relative humidity? While I don't know much HVAC, I am a home automation geek and can setup a sensor or 3 to monitor such things.

[pecmsg]

RH gets measured at the return.
Delta T closet supply and return

With a set point near the outside air temp how much run time do you expect?

[teddy bear]

Where should I measure supply temp and relative humidity? While I don't know much HVAC, I am a home automation geek and can setup a sensor or 3 to monitor such things.

Measure temp/%RH at the closest supply to the a/c. Would be nice to measure temp/%RH any return grill.

Regards Teddy Bear

[dan sw fl]

RH gets measured at the return.
Delta T closest supply and return

With a set point near the outside air temp how much run time do you expect?

Supply Air AT the air handler Outlet.

Relative Humidity would likely be 84% to 93%