Specifications

2008 Residential Appendices RA3-23
Appendix RA3 – Residential Field Verification and Diagnostic Test Protocols
Diagnostic fan flows shall be converted to Fan Cfm/ton by dividing the measured fan flow (Qah) by the
nominal tons of the air conditioner. The measured airflow shall be expressed in cubic feet per minute of
standard air (standard air has a density of 0.075 lb/ft3). When the airflow measurement is made at
altitudes significantly different from sea level or at temperatures significantly different from 70°F, the
airflow indicated on the device gauge may differ from the standard CFM by as much as 15 percent.
Corrections from indicated to standard CFM shall be made using the procedure specified by the flow
measurement device manufacturer.
RA3.3.3.1.1 Diagno
stic Fan Flow Using Plenum Pressure Matching
This fan flow measurement shall be performed using the following procedures:
1. If the fan flowmeter is to be connected to the air handler outside the conditioned space, then the door
or access panel between the conditioned space and the air handler location shall be opened.
2. With the system fan on at the maximum speed used in the installation (the cooling speed when air
conditioning is present), measure the pressure difference (in Pa) between the supply plenum and the
conditioned space (Psp). Psp is the target pressure to be maintained during the fan flow tests. Place
the pressure probe in the Supply Pressure Measurement Location described in Section 3.3.1.1.
Adjust the probe to achieve the highest pressure and then firmly attach the probe to ensure that it
does not move during the fan flow test.
3. If the fan flowmeter is to be connected to the air handler at the access, block the return duct system
from the plenum upstream of the air handler fan and the fan flowmeter. Filters are often located in an
ideal location for this blockage.
4. Attach the fan flowmeter to the duct system at the air handler or alternatively at the inlet to the return
from the conditioned space with the grille and filter removed.
5. Turn on the system fan and the fan flowmeter, adjust the fan flowmeter until the pressure between
supply plenum and conditioned space matches Psp.
6. Record the flow through the flowmeter (Qah, cfm) - this is the diagnostic fan flow. In some systems,
system fan and fan flowmeter combinations may not be able to produce enough flow to reach Psp. In
this case record the maximum flow (Qmax, cfm) and pressure (Pmax) between the supply plenum
and the conditioned space. The following equation shall be used to correct measured system flow
and pressure (Qmax and Pmax) to operating condition at operating pressure (Psp).
Equation RA3.3-1 Air Handler Flow Qah = Qmax x (Psp/Pmax) ^0.5
RA3.3.3.1.2 Diagno
stic Fan Flow Using Flow Grid Measurement
The fan flow measurement shall be performed using the following procedures:
1. With the system fan on at the maximum speed used in the installation (the cooling speed when air
conditioning is present), measure the pressure difference (in Pascal) between the supply plenum and
the conditioned space (Psp). Place the pressure probe in the Supply Pressure Measurement Location
described in Section 3.3.1.1. Adjust the probe to achieve the highest pressure and then firmly attach
the probe to ensure that it does not move during the fan flow test.
2. The flow grid shall be attached at a point where all the fan air flows through the flow grid.
3. Re-measure the system operating pressure with the flow grid in place.
4. Measure the airflow through the flow grid (Qgrid) and the test pressure (Ptest).
5. The following equation for air handler flow shall be used to correct flow through the flow grid and
pressure (Qgrid and Ptest) to operating condition at operating pressure (Psp).
Equation RA3.3-2 Qah = Qmax x (Psp/Ptest) ^0.5
RA3.3.3.1.3 Diagno
stic Fan Flow Using Flow Capture Hood