Refrigeration Charge Verification

[ecworks]

Starting on August 1, 2009, California's new Title-24 energy requires that the refrigerant charge be verified by an independent, third party HERS rater using one of (3) methods, the "intrusive approach" requires the HERS rater to attach gauges to the HVAC and verify the proper amount of refrigerant. The "non-intrusive" approach requires the HERS rater to take a number of temperature measurements to calculate the correct refrigerant charge. The "non-intrusive" approach however requires that HVAC installer to provide temperature measurement access holes and saturation temperature measurement sensors. This allows the HERS rater to verify the system performance and refrigerant charge without attaching gauges to the system. The temperature measurement access holes are 5/16″ holes that the contractor drills, one in the supply plenum and one in the return plenum. Exact locations are specified in the standards. HVAC installers can attend training seminars sponsored by the state to become familiar with the details of this process. I attended one recently and became fairly proficient with the process in about 2 hours of hands on training.

The Saturation temperature measurement sensors are Type K thermocouplesthat are permanently attached to the evaporator coil and the condenser coil. The plug on the end of the thermocouple is plugged into a handheld digital thermometer to read the temperature which is then converted into pressure. The Type K thermocouple must be precisely attached to the indoor coil and the outdoor unit. Sens-A-Coil is one solution for this requirement.

The most common question we get from HVAC contractors is where exactly should you install the temperature sensors on the evap and condenser coil?

Do HVAC manufacturers provide a diagram to show you?

thanks in advance for your help,

[desA]

... the "intrusive approach" requires the HERS rater to attach gauges to the HVAC and verify the proper amount of refrigerant.

Sounds reasonable. What theoretical approach do they use to 'verify' the appropriate amount of refrigerant charge?

The "non-intrusive" approach requires the HERS rater to take a number of temperature measurements to calculate the correct refrigerant charge.

Sounds interesting. What theoretical approach do they use to 'calculate' the appropriate amount of refrigerant charge?

[Gary]

The temperature measurement access holes are 5/16″ holes that the contractor drills, one in the supply plenum and one in the return plenum. Exact locations are specified in the standards.

The most common question we get from HVAC contractors is where exactly should you install the temperature sensors on the evap and condenser coil?

The exact locations are specified for the duct sensors, but not for the coil sensors?

[Buckrider]

I would recommend measuring coil temperatures in at least 2 or 3 locations on an exposed tube bend near the middle of the coils. The temperature measured here (if close to properly charged) is the Saturation temperature. You do not need to convert the Temeprature back to Pressure (the only reason you measure pressure is to approximate the Saturation Temeprature).

Techs will also measure line set temperatures and then be able to calculate Subcooling and Superheat directly - just as the installing tech should be able to using the "intrusive" method. These will be compared to the OEM required Subcooling (or Superheat chart for fixed orifice).

Measuring "Air" temps in the ducts combined with actual airflow measurements allow techs to calculate absorbed capacity: Qt = 4.45 x CFM x dH (change in enthalpy). This should be very close to OEM performance tables.

[Gary]

I know how I would do it.

I'm wondering how the State of California will do it?

[Yuri B.]

I just wandered, whether tomorrow's controllers, parallel to their main function, will be taught to constantly calculate charge on the basis of all inputs measurements.