Pictures of ducts and systems attached...
Your duct system is a hack and slap flex job. There is no way, no how, that it is capable of moving 3 tons of air (1200 cfm), much less 4 or 5 tons of air (1600 and 2000 crfm respectively).
Your old blower motor was incapable of delivering the required airflow and hit the static pressure ceiling quickly.
The new one, being variable speed, is a completely different animal.
It will spin up to the set parameters and attempt to deliver the set CFM. Unlike the old fan motor, this one will pull more amps to spin up the RPM's.
However, it too will hit a static pressure ceiling and airflow will drop off.
What is the installed TESP (Total External Static Pressure)? Most residential furnaces are rated for 0.5" of water column. Once the TESP goes above that, airflow actually goes down. I see (1) media type air filter with what looks like a 4" filter (the 20x25 General Filter 6" thick accordion style media is far better), and that alone will bust your TESP ceiling.
Does the contractor know what TESP is?
Note that you need (2) filters (2 sides or one side+bottom) for "5 ton" airflow (2000 cfm). Says so right in the instructions for the furnace.
Your system is likely moving more air than the old one simply due to how a variable speed fan works, so it is also sucking in more hot attic air at the unsealed flex connections and register boot openings. This kills system efficiency- the AC isn't designed to cool 130*F attic air.
But it isn't moving enough air for the requirements of the system.
With some airflow and wet bulb/enthalpy readings at the equipment, total capacity can be determined.
If your return air temperature at the unit is higher than the return air temperature at the register(s), then you have duct leakage and poor insulation. Same goes for the supply ducts. What is the temperature near the evaporator coil and the temperature at the registers? You really shouldn't use a non-contact IR temperature probe for this- digital air probe.
I could almost guarantee you that if you go to a 5 ton system, performance will be worse if the ductwork is not addressed.
Yes, there are different size/capacity evaporator coils that are generically called "X ton coils". You really have to get into the specs for that. One manufacturer has model numbers with xxx60xxx for the standard "5 ton" coil and xxx61xxx for the bigger one.
So-called high efficiency equipment must be installed 100% properly to get the claimed efficiency and for it to work properly. The crowd shouting "the old one worked" obviously do not understand the new stuff. The old equipment still had the same general ratio of sensible to latent capacity and same general overall capacity as the new stuff. An "old" "5 ton" coil didn't deliver 60k btu of sensible capacity either.
With a variable speed drive fan attached to restrictive ductwork and filters, you are spending more. The amp draw tells all. High VS motor amp draw also leads to early (and expensive) failure.
Update:
1) I have quotes from insulation (~$5,600) to insulate the attic. Not sure that I understand that quote because they are talking about insulating ~3300 square feet. Attempting to clarify. In addition, they are suggesting attic vents to be installed by a roofer. They "do not believe in any kind of radiant barrier."
2) Quotes from Window World to upgrade all windows in the house to double pane. I have verified that all current windows are single pane. I am told that current building codes require at least double pane in Houston. However, my house was built in 1994-5, under previous building codes. This would cost approximately $21,000 for the entire house ($8,000 for the upstairs and $13,000 for the downstairs). The solar heat gain coefficient on the windows is 0.19-0.21 (depending on the grid pattern, if any) and the u value is 0.28.
Although they are very expensive, I am leaning toward the window replacement plan as they offer additional benefits (e.g., quieter, less UV-related fade on furniture, etc.).
3) The contractor found a 5 ton configuration that would provide a sensible load capacity of 41,000 which he tells me is likely higher than my old 4 ton. His analysis:
- From the Load requirements, and the pre-existing disconnect box the whole home was intended to have 3 system.
- No two systems are capable of satisfying the demand of the whole home as is.
- My understanding is that you've been able to have "livable" 76ish degree 2nd floor air for 10+ years.
- Since installing our system my understanding is that your hope has been to reach closer to 72 degrees.
- 75 degrees at 50% relative humidity is the set point for average human comfort.
- Current Sensible Capacity on your current 4 ton XV is 35,200
- The highest sensible capacity available on any 4 ton within Trane's current line across all efficiencies is 38,000. Likely at or higher than the capacity of your previous system.
- The highest sensible available on an XV20 5 ton is around 41,000
- This is a higher capacity than your previous 4 ton was capable.
- Still, we are short of the design conditions to satisfy fully by about ~1,400 CFM
- I am willing to replace the 4 ton with a 5 ton XV which will be better than the previous system but still short of ideal without modifying the load via, improved windows, insulation etc.
Should I accept the swap of the 4 ton for a higher-capacity 5 ton?
If you are adding powered attic ventilation, that will make your problem much, much worse.
Fancy windows are mostly a sham. You will see the biggest benefit on South and West exposures due to solar gain if energy savings are the goal. Otherwise, you are throwing good money after bad. I'd price out UV tinting of your existing S and W windows if they are in otherwise good shape.
There is a big difference between 76 degrees and 72 degrees. AC systems are rated at 77*F indoor temps. If you really want to hit 72, then you may really need a 3rd system, or foam the attic.
I'd revamp the ductwork before spending a penny on windows or foam.
Yes, I saw the Manual J numbers earlier in the thread. Yes, your rated system capacity is under the design load... but it was short before. That hasn't changed. You would need to provide model numbers for the old equipment and find someone bored enough to research the condenser, evaporator and blower engineering data to determine the *rated* (not actual) capacity that you had with the old equipment. Having the old TESP number and blower setting would also be interesting.
I would make doubly+ sure that the condensers are wired properly (low voltage wiring) and the correct switch/jumper settings are on the furnace board if you have two stage or other fancy compressors. This also includes thermostat settings/wiring. I am not intimately familiar with Trane equipment, especially the high end stuff. That said, it may need Trane thermostats to function properly. I have seen more than one high end system that was not set up properly. All of the details are in the installation and operation manuals.
Manual J also has a fudge factor built-in. A 1400 btu shortfall should not be an issue.
WTF is up with the VigLinks? I didn't add spam links to my post.
You're cooling that attic basically. You NEED ductwork improvements (ie upsizing) along with leak sealing and better insulation on duct trunks. Other GJ advice to spend money on ductwork (before windows) is spot on. That wimpy "foil insulation" is simply not adequate in your hot/humid environment. Good luck.