Specifications

2008 Residential Appendices RA3-14
Appendix RA3 – Residential Field Verification and Diagnostic Test Protocols
Actual Superheat = Tsuction, – Tevaporator, sat.
2. Determine the Target Superheat using Table RA3.2-2 using the return air wet-bulb temperature (T
return,
wb
) and condenser air dry-bulb temperature (Tcondenser, db).
3. If a dash mark is read from Table RA3.2-2, the target superheat is l
ess than 5°F. Note that a valid
refrigerant charge verification test cannot be performed under these conditions. The usual
reason for a target superheat determination of less than 5°F is that outdoor conditions are too hot and
dry. One of the following is needed so a target superheat value can be obtained from Table RA3.2-2
either 1
) turn on the space heating system and/or open the windows to warm up indoor temperature; or
2) retest at another time when conditions are different. Repeat the measurement procedure as
necessary to establish the target superheat. Allow system to stabilize for 15 minutes before the final
measurements are taken.
4. Calculate the difference between actual superheat and target superheat (Actual Superheat - Target
Superheat).
5. In order to allow for inevitable differences in measurements, the Pass/Fail criteria are different for the
Installer and the HERS Rater.
For the Installer, if the difference is between minus 5°F and plus 5°F, then the system passes the
required refrigerant charge criterion.
For the HERS Rater inspecting the system, if the difference is between minus 6°F and plus 6°F, then
the system passes the required refrigerant charge criterion.
6. For the Installer, if the difference is greater than plus 5°F, then the system does not pass the required
refrigerant charge criterion and the Installer shall add refrigerant. Adjust refrigerant charge and check
the measurements as many times as necessary to pass the test. After the final adjustment has been
made, allow the system to run 15 minutes before completing the final measurement procedure.
7. For the Installer, if the difference is between minus 5°F and minus100°F, then the system does not pass
the required refrigerant charge criterion, the Installer shall remove refrigerant. Adjust refrigerant charge
and check the measurements as many times as necessary to pass the test. After the final adjustment
has been made, allow the system to run 15 minutes before completing the final measurement
procedure.
RA3.2.2.6.2 Variable Me
tering Device Calculations
The Subcooling Charging Method is used only for systems equipped with variable metering devices. These
include Thermostatic Expansion Valves (TXV) and Electronic Expansion Valves (EXV). Since variable metering
devices are constant superheat valves, measuring the superheat determines whether they are working
properly.
1. Calculate Actual Subcooling as the condenser saturation temperature minus the liquid line
temperature. Actual Subcooling = T
condenser, sat – Tliquid.
2. Determine the Target Subcooling specified by the manufacturer.
3. Calculate the difference between actual subcooling and target subcooling (Actual Subcooling - Target
Subcooling
4. In order to allow for inevitable differences in measurements, the Pass/Fail criteria are different for the
Installer and the HERS Rater.
For the Installer, If the difference is between minus 3°F and plus 3°F, then the system passes the
required refrigerant charge criterion.
For the HERS Rater inspecting the system, if the difference is between minus 4°F and plus 4°F, then
the system passes the required refrigerant charge criterion
5. For the Installer, if the difference is greater than plus 3°F, then the system does not pass the required
refrigerant charge criterion and the Installer shall remove refrigerant. Adjust refrigerant charge and