CFM Override / Static Pressure Tutorial

Total Performance Diagnostics utilizes the STATIC PRESSURE field as “information only” data. Static Pressure information is not used in any calculations.

CFM Override / Static Pressure Tutorial
Click to watch the video tutorial

The STATIC PRESSURE fields can be very useful in documenting and explaining static pressure related problems.

The CFM OVERRIDE field, however does affect COOLING calculations when used.

The COOLING CFM ACTUAL field initially defaults to the MAXIMUM COOLING CFM reading and uses this number to initially calculate COOLING BTU’S and COOLING PERFORMANCE.

CFM Over-ride was revised in early 2013 to auto calculate low indoor air flow.  By allowing the program to recalculate low air flow events, TPD can more accurately estimate (and communicate to clients) the actual capacity and SEER losses  associated with reduced indoor air flow.

Total Performance Diagnostic uses the CFM OVERRIDE field to CHANGE the ACTUAL default COOLING CFM when better CFM information is available.

To more accurately determine ACTUAL COOLING CFM: Use the COOLING CFM calculation procedures available in Total Performance Diagnostics HEATING WORKSHEETS.

OR – if the client is on a SCHEDULED MAINTENANCE program, technicians can find the calculated COOLING CFM by pulling up the CLIENTS’ winter CLIENT REPORT using Total Performance Diagnostics’ REPORT LOOKUP tool.

Even if Psychrometrics and experience dictates that use of a standard CFM model is sufficient in most circumstances, technicians should always strive for the most accurate information available.

Therefore, specific knowledge about a manufacturer’s CFM fan speed settings should be utilized whenever available.

The following  feature may disabled by the system administrator.  When turned off, TPD will automatically estimate low CFM conditions and enter the estimated CFM in the “CFM Override” field of the report.

There is an additional practical use for the CFM OVERRIDE feature…

Since Total Performance Diagnostics employs a temperature correcting algorithm that represents cooling BTUs at RATED capacity, any capacity reading that exceeds 100% of Nominal Tons is, in reality, an impossible REAL WORLD condition.

Total Performance Diagnostics allows this this IMPOSSIBLE READING to alert the technician to a particular problem: Low indoor air flow. It is up to the technician to determine the severity of the air flow problem. This is where the CFM OVERRIDE feature becomes very useful.

By reducing the air flow number in the CFM OVERRIDE field and re-calculating the RESULTS until the system shows approximately 93% of system capacity, technicians can quickly estimate the system’s actual CFM to determine if it is still within an acceptable operating range.

The CFM OVERRIDE is designed to be used whenever the program shows calculated BTUs exceeding the total system BTU capacity.

Any Attempt to produce a CLIENT REPORT that shows a COOLING PERFORMANCE of 100% or greater will produce a DISCLAIMER BOX on the Client Report that indicates…

  • High Cooling BTUs = This is an impossible “real world” condition. The programed calculation in this field is conditionally based on other data.
  • High cooling BTUs normally (but not exclusively) indicates:
  • Low indoor air flow…
  • Dirty filters…
  • Dirty evaporator coils…
  • High duct static pressures…
  • Dirty blower wheel…
  • Bad blower motor and/or capacitor…
  • Incorrect fan speed setting…

NOTE: To determine the actual CFM, run a TPD heating diagnostics.

NOTE: To estimate the existing CFM use the CFM ADJUST feature to bring the Cooling BTUs within 93% of expected.