Efficiency ratings are useful, but they describe a lab test run under conditions chosen for comparison. Your house is not that lab. The attic runs hotter than the outdoor thermometer suggests, the ducts leak or they don't, and the thermostat setpoint changes every time someone opens the door. That gap is why a side-by-side measurement beats a brochure.
ACHR News covers a cooling project built around that idea. In its ACHR News story on the Transaera system, the installation "will operate alongside a conventional system in the same building," and its performance data will be published for owners weighing all-electric heating and cooling. What the report lays out is the setup itself: two systems, one building, one comparison.
Why the Same-Time Idea Matters
Two systems running in one building answer a question a single before-and-after cannot. The weather, the occupants, and the hours are shared. A homeowner usually gets one unit at a time, so the fair version is a sequence test. Log the old system through the early weeks of cooling season, replace it, then log the new one on days with similar outdoor highs. Weather is the variable that ruins most comparisons, so write it down rather than pretend it away.
What to Record Each Day
Start with the thermostat. Record the setpoint, the hours the system runs, and the indoor high and low if the thermostat logs them. Get outdoor temperature from a nearby weather station or a cheap logger in the shade on a north wall, not from a forecast for the next town over.
For runtime and current, a clamp meter is the right tool. Clamp one conductor of the compressor feed at the outdoor disconnect, keep the cover on, and limit yourself to a non-contact reading. Note the amp draw at the start of a run and again an hour in. Multiplying amps by line voltage gives a rough power figure, multiplied again by runtime gives a rough energy figure. Treat it as an estimate. Voltage sags under load, and the air handler fan adds draw that a clamp on the compressor leg never sees, so label the reading as compressor circuit only.
Check the Air Reaching the Rooms
A cooling number means little if the air never reaches the rooms. On a steady run, hold a hand over each supply register and note the strength of the flow. On a hot afternoon, feel the duct runs in the attic and note which ones are warm to the touch. If the attic is the problem, the fix may sit in the roof rather than the equipment. A roofing contractor such as Keys Roofing can check whether ventilation or the roof deck is driving attic heat, and that finding changes what your test is really measuring.
Where Home Tests Go Wrong
Most homeowner tests fail in predictable ways. The setpoint drifts a degree because someone bumped the thermostat, a filter gets swapped halfway through, or the house goes from two occupants to five for a long weekend. Each change looks small, and each one moves the runtime. Log those changes as events in the same notebook so you can explain a spike later. A test that records a bad week honestly is more useful than a clean-looking chart that hides one.
Keep the Claim Honest
When a vendor shows you a savings figure, ask which conditions produced it, which house it came from, and whether the comparison ran at the same time. The ACHR News story is worth reading for exactly that reason. It describes an installation that runs beside a conventional system, which is the structure a homeowner can approximate with a sequence test. Nothing in that summary substitutes for your own logs, and nothing here predicts what your house will do.
Bring the log to the installer. A written record of runtime, setpoint, and outdoor conditions gives the crew something real to size against, and it gives you a baseline the next time someone quotes a savings number.
Further reading: a roofing contractor such as Keys Roofing.