New American Standard S9V2 Furnace Electric Usage Seems High?

[Robert Copeland]

I recently had a American Standard S9V2C100U5PSBB installed in our house. I was doing some power usage investigation at my main circuit breaker panel and found that when my furnace is running in first stage set on medium airflow (default) setting, furnace display shows 1400 CFM, I am getting a power draw between 850-900 watts on my True RMS Amp clamp (7.0-7.5amps @ 120v at panel) right at the dedicated breaker on my panel. I had the installing company out today fix some other issues and they did a total static pressure test and had 0.25" WC as the reading so its not a restriction. I pulled the Heating airflow chart from the manufacturer and on medium airflow setting 1483cfm, and a static pressure of 0.3, the chart shows I should be seeing 310 watts from the system? Am I reading this chart wrong or something because my system is pulling almost 3x what the manufacturers table is saying when I am getting 850-900 watts?

 

[Fitter30]

Did you measure before filter and before ac coil and add those two together? Im not so sure even with a true rms meter can read a accurate amp draw because of the harmonics generated by the ecm. Read this from carrier
The equipment manufacturer fits a blower wheel, and mounts the motor in their equipment. GE and the equipment manufacturer develop tabular data to relate torque and RPM to mass airflow (usually simplified to volumetric airflow). The data is stored in the ECM microcontroller, and used to control the motor to a constant airflow.
Then they develop a chart cfm to watts. Ecm is a dc motor.

 

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[Robert Copeland]

Yea, I just got a Testo 510i today and measured the Static Pressure in a many different locations to get my baseline.

In both cases my static is over the Total External Static Pressure allowed by manufacturer of 0.5" WC. When I looked at the installation manual, it looks like they should have put the furnace on a pedestal duct and opened the bottom of the cabinet up as well for airflow, it says not to use just the side as an inlet like they did here.

 

[Fitter30]

My last house had a 90%+ furnace and increased the size of the return drop and had a duct come out of the back side around the back 10wx 18h then 90 into other side 2" filter rack in drop. But also worked for a contractor with a tin shop. Raise furnace and come in the bottom have a problem with transition into trunk line being so close making the air turn.

 

[SShaw]

I am getting a power draw between 850-900 watts on my True RMS Amp clamp (7.0-7.5amps @ 120v at panel) right at the dedicated breaker on my panel. I pulled the Heating airflow chart from the manufacturer and on medium airflow setting 1483cfm, and a static pressure of 0.3, the chart shows I should be seeing 310 watts from the system? Am I reading this chart wrong or something because my system is pulling almost 3x what the manufacturers table is saying when I am getting 850-900 watts?

Your clamp meter is not measuring power--it's only measuring amperage. Your motor is an inductive load, with the voltage and current out of phase, so you need to include a power factor when calculating watts. Watts = voltage X current X power factor.

The power factor will vary with the load on the fan. To measure your power, you need a power meter, which measures both voltage and amperage simultaneously.

If I remember correctly, for my ECM blower the power factor is normally around 0.4 at low load. That would put your wattage in the correct ballpark.