AC power usage

Hello everybody, I’m trying to find out if anyone has this home AC unit. American Standard 3 ton Platinum 18 SEER with variable speed compressor system.
I have a 15+ y/o 2.5 ton trane and trying to get cost savings numbers I live in costal South Carolina with High humidity and Summer temps. Thanks in advance!

when we switched from old AC to Variable Speed Seer 23 systems we cut our electricity use in half or more of total AC use

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What does Sense say your AC usage is? My 1.5ton (?) 12 SEER heat pump uses about 2.2kW when it runs…(I know, it needs replaced)

It’s pretty straightforward to do the math if you have the specs for the units in question. @danderson has the likely ballpark answer for you but if you want to go deeper :

Typically if you want to dehumidify as much as possible (so you can set the thermostat higher and still be comfortable) you don’t want to oversize your system and you absolutely want variable speed everything: compressors & fans.

If you are replacing a ducted system I would take a serious look at replacing it with a mini-split. You get significantly better efficiencies from zoning the air and better targeted capacity. The downfall of many ducted systems is dodgy installation (bad supply and return ducts). Mini-split air handlers usually present the outdoor compressor with a more stable/known load because the intake/outflow is more controllable.

Ultimately that decision is probably going to be based on whether you also use it for heating as well because that’s when you can really save.

it depends as all of mine are mini-split, but it shouldnt matter, my old mini-split previously pulled 1.5 - 2kw for a 12k BTU, and the new one (also 12k BTU) pulls 1kw when fully loaded down to 400-600w just temp keeping. Sense has never identified any of my ACs

Yes we use it for heating as well and we have flexible ducts off the main trunk

See my other reply to Dan For more details

Trane Xl14i 2.5T single stage unit with variable speed air handler cooling a 1800sqft main floor, the 700 sqft (FROG) finished room over garage that has a dead ptac. we also have “professional club lighting equipment that we run up there that puts out a lot of heat, in addition We use a glycol based fog machine. I have no idea how the fog might effect the air handler if the FROG was a zone off the new system. It has been brought up we could also put in a 2 zone mini split for the FROG and 2 car garage. BUT code says a garage can’t be connected to the living area which the FROG is part of connected to the living area. A mini split would be fine for us but would be illegal for someone who actually wants to use the garage as a garage.
Additionally, We have aquariums in our home and 2 car garage directly under the FROG for growing coral. In the garage we have a 1 yo Amana Thru the wall ptac, It pulls 1kw when running, a dehumidifier 632watts I’m pulling 4,000w on startup and 2,100w to 2700w while running on the main home AC. I have about 6-7 inches of blown in insulation in the attic which I’m guessing is 25yo. Was considering putting Attic Foil on top of existing or any new attic insulation (anyone have any thoughts on or have used attic foil? Did it work?

A lot to consider to come up with the optimum heat pump system for our needs. Any advice would be greatly appreciated.

About the same 2.1kw

For those with an 18 SEER or above variable speed system what’s your average power usage during peak cooling times?

I live in Williamsburg Va and we also get those hot humid days as well. The first summer i was in my house i was seeing temperatures in my attic that exceeded 155F and my house is a single story and 1800sqft . I have been trying to make my house more efficient and two of the ways is by adding attic foil radiant barrier and slowly replacing the crappy blown in insulation with RockWool. So far this summer the hottest temp i recorded in my attic was 121F and that was with an outside temp of 102F while my brother was seeing a temp of 148F with an outside temp of 102F on the same day and his house is three stories and his attic is 1/3 the size of mine. I’ve only completed 75% of my radiant barrier and 1/4 of the RockWool project so far and I’ve seen significant improvements.




Ouch. What kind of roof covering do you have?

One thing I know about physics (especially thermodynamics) problems is that it’s always good to attack them at the source. Once things become turbulent (non-laminar) your chances of an efficient fix are reduced.

Meaning: light colored roofs work!

I’m in an apartment 2 floors below the roof and have a small section of roof in the back of my place (<100sqft) that for years was covered in black asphalt and acted as a toaster. It started leaking so I covered it with white Gaco silicone with an SRI (Solar Reflective Index) of something like 90 and the surface temperature dropped precipitously.

A post was split to a new topic: Attic Temperature vs. Ambient (Outside) Temperature