Specifications

2008 Residential Appendices RA3-20
Appendix RA3 – Residential Field Verification and Diagnostic Test Protocols
RA3.3 Field Verification and Diagnostic Testing of Forced Air System Fan Flow and Air
Handler Fan Watt Draw
RA3.3 contains procedures for verifying airflow in split system and packaged air conditioning systems
serving low-rise residential buildings. The procedure is also used to verify reduced fan watts achieved
through improved air distribution design, including more efficient motors and air distribution systems with
less resistance to airflow.
The refrigerant charge test described in Section RA3.2 requires verification of airflow sufficient for the
refrigerant charge test. Table RA3.3-1 Summarizes the diagnostic measurement procedures in RA3.3
and shows their relationship to the equipment efficiency algorithms in RACM chapter 3.
Table RA3.3-1 – Summary of Diagnostic Measurements
Features
that require
verification
Variables
and
Equation
Reference
Description Standard Design Value
Proposed Design
Default Value Procedure
Fan Watts FanW/cfm
RACM Eq.
R3-20
The term FanW/cfm is
the ratio of fan power in
Watts to the cooling coil
airflow.
FanW/cfm = 0.58
FanW/cfm = 0.80
RA3.3.3.3
Diagnostic
Air Handler
Watt Draw
Cooling Coil
Airflow
FanCfm/ton
RACM Eqs.
R3-20
The term FanCfm/ton is
the ratio of the Cooling
coil airflow to the nominal
cooling capacity in tons.
FanCfm/ton = 350 FanCfm/ton = 300 RA3.3.3.1
Diagnostic
Fan Flow
Refrigerant
Charge
Prerequisite
n. a.
The unit must pass the
temperature split test or
an airflow of at least 300
cfm/ton must be obtained
for a valid refrigerant
charge test
n. a. n. a. RA3.2.2.7
Temperatur
e Split
Method
or
RA3.3.3 .1
Diagnostic
Fan Flow
RA3.3.1 Instrumentation Specifications
The instrumentation for the diagnostic measurements shall conform to the following specifications:
RA3.3.1.1 Pressure Measurements
All pressu
re measurements shall be measured with measurement systems (i.e., sensor plus data
acquisition system) having an accuracy of plus or minus
0.2 Pa. All pressure measurements within the duct system shall be made with static pressure probes
Dwyer A303 or equivalent.
When supply plenum pressure measurements are used for plenum pressure matching or flow grid
measurements, the supply plenum pressure shall be taken at the following location.