Specifications

2008 Residential Appendices RA3-9
Appendix RA3 – Residential Field Verification and Diagnostic Test Protocols
RA3.2 Procedures for Determining Refrigerant Charge for Split System Space Cooling
Systems Without a Charge Indicator Display
RA3.2.1 Purpose and Scope
The pu
rpose of this procedure is to determine and verify that residential split system space cooling systems
and heat pumps have the required refrigerant charge and that the metering device is working as designed. The
procedures only apply to ducted split system central air conditioners and ducted split system central heat
pumps. The procedures do not apply to packaged systems. For dwelling units with multiple split systems or
heat pumps, the procedure shall be applied to each system separately.
The procedures detailed in Section
RA3.2 are to be used after the HVAC installer has installed and charged the air conditioner or heat pump
system in accordance with the manufacturer's instructions and specifications. The installer shall certify to the
builder, building official and HERS rater that he/she has followed the manufacturer’s instructions and
specifications prior to proceeding with the procedures in this appendix.
Appendix RA3.2 defines two procedures, the Standard Charge Measurement Procedure in Section RA3.2.2
and the Alternate Charge Measurement Procedure in Section RA3.2.3. The standard procedure shall be used
when the outdoor air temperature is 55°F or above and shall always be used for HERS rater verification. HVAC
installers who must complete system installation when the outdoor temperature is below 55°F shall use the
alternate procedure.
The following sections document the instrumentation needed, the required instrumentation calibration, the
measurement procedure, and the calculations required for each procedure.
The reference method algorithms adjust (improve) the efficiency of split system air conditioners and heat
pumps when they are diagnostically tested to have the correct refrigerant charge and the metering device is
operating properly. Table RA3.2-1 summarizes the algorithms that are affecte
d by refrigerant charge testing.
Table RA3.2-1 – Summary of Diagnostic Measurements
Input to the Algorithms Description Standard Design Value Proposed Design
Default Value Procedure
Cooling System
Refrigerant Charge and
Metering
F
CID
takes on a value of 0.96 when the
system has been diagnostically tested
for the correct refrigerant charge, or a
charge Indicator Display is field verified.
Otherwise, F
CID
has a value of 0.90.
Split systems are assumed
to have refrigerant charge
testing or a Charge
Indicator Display when
required by Package D.
No refrigerant
charge testing or
Charge Indicator
Display.
RA3.2.2 or
RA3.2.3
Note that diagnostically testing the refrigerant charge requires a minimum level of airflow across the evaporator
coil, as defined in RA3.2.2.7.
RA3.2.2 Standard Charge Measurement Procedure
This
section specifies the Standard charge measurement procedure. Under this procedure, required refrigerant
charge is calculated using the Superheat Charging Method for Fixed Metering Devices and the Subcooling
Charging Method for Thermostatic Expansion Valves (TXV) and Electronic Expansion Valves (EXV). The
method also checks airflow across the evaporator coil to determine whether the charge test is valid using the
Temperature Split Method. The measurement methods in RA3.3 may be substituted for the Temperature Split
Method; however the Temperature Split Method may not be substituted for the measurement methods in
RA3.3.
The standard procedure detailed in this section shall be completed when the outdoor temperature is 55°F or
higher after the HVAC installer has installed and charged the system in accordance with the manufacturer’s
specifications. If the outdoor temperature is between 55°F and 65°F the return dry bulb temperature shall be
maintained above 70°F during the test. All HERS rater verifications are required to use this standard
procedure.