Most likely too much air and/or duct infiltration not dehumidifying as well as is possible. The low delta-t is a direct indicator of too much air.
Possible cures; VS blower set for 600-700 cfm of air and programmed for dehumidification, an enthalpy controlled evap coil by-pass or a volume damper in the main supply trunk closed to create enough SP to drop air volume to below 800 cfm.
I'll look into these solutions come next summer. A simple volume damper may be enough to do the trick.
Pull the specs on that compressor and id bet its a 19000kbtu.
Heat is more than enough, I didn't replace the furnace, just the AC. As much as it annoys me to have a 88,000BTU furnace that never runs more than 5 minutes at a time I couldn't justify replacing a working furnace. Even when temps dipped down to 12 degrees the last 2 nights the furnace never ran more than 5 minutes out of 15. Most of the time if runs about 5 minutes out of 30. The furnace I want would be the Thermalzone (made by Rheem/Ruud) 95% 45K 2 stage with variable sped blower. Overkill, probably so.
I'll have to look up the Compressor and see what the actual BTU rating is.
Now that temps are warmer I took another look at the system. Charge was a little low, topping it off made a bigger difference than I expected. Delta T measured 19 degrees at the air handler with a temp probe across the evap coil, the IR temp gun was off more than I expected. Temps were in the upper 80's yesturday, system ran about 1/3 of the time. System pulled 30lbs of water out of the air during the last 24hrs (collected condensate in 5 gal bucket and weighed it). It had been raining here for the past few days, so a real "torture test" for humidity removal capability. Suction line sweating like it's supposed to on a humid day, superheat back to normal.
I pulled the expanded data for the compressor, it's 23,600 @ 110F SCT with a 45F SST. Looking at the chart it's interesting to see how the SCT and SST affects compressor power and and output. EER is very sensitive to these 2 parameters, it's easy to see why manufactures are making huge outdoor condenser coils and running relatively high evap temps in order to hit those high SEER numbers..
I just dropped down to a 2 ton 15 SEER system in my 1350 square foot house, from a 3 ton 10 SEER system.
It's only been a couple of weeks, but so far I like it. The last few fairly humid 90º days, it has kept the humidity down to around 50% at my 78º set point most of the time, but has spent some time in the blowers dehumidification mode, and overcooling by 2º.
The best part, the equipment was free!
I still need to do something with my crummy 1966 vintage metal duct system though.
I should probably get on that before the 100º+ weather gets here...
If more government is the answer, then it's a really stupid question.
It's quite refreshing to see people acknowledge 500 SF/Ton is not cast in stone.
I went from a 2-1/2 ton 10 SEER to a 2 ton 14.5 SEER in my townhouse, saved about 15% of KWH and noticed a big improvement in humidity. Now if I could just get around to doing something about the daylight I see around the front door...
Did some more tests at 83F outdoor ambient and took pictues this time. Looks like pressures are right on when compared to chart. The 6.2A compressor draw is right on spec according to the compressor expanded performace data. SCT at ambient +15F is where the chart crosses which seems low, but that's how the newer high SEER units are.
What was the indoor temp at the time? 50deg evap is pretty warm. I remember you did say old unit dehumidifyed better. Have you mapped out the indoor air flow yet?
Indoor temp 75 degrees at time of test. New unit dehumidifies a lot better now that charge is correct, will fill a 3 gallon bucket in 24hrs, about what the old unit did. Digital indoor humidity gauge ranges between 48-52% most of the time, not sure how accurate it is. I do question the 50 degree indoor coil, according to the Carrier furnace spec sheet I'm running about 900CFM on the lowest blower speed. I have the 91-14 furnace. How possible is it that the extra 100CFM is what is driving the coil up to 50 degrees?
I do not own any tools to measure static pressure or a flow hood to measure airflow. I have 2 12" returns. Supplies are 2 8" and 2 10" off the plenum. All flex, should be enough for 800CFM+